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Several hundred disease-causing mutations are currently known in domestic dogs. Breeding management is therefore required to minimize their spread. Recently, genetic methods such as direct-to-consumer testing have gained popularity; however, their effects on dog populations are unclear. Here, we aimed to evaluate the influence of genetic testing on the frequency of mutations responsible for canine degenerative myelopathy and assess the changes in the genetic structure of a Pembroke Welsh corgi population from Japan. Genetic testing of 5,512 dogs for the causative mutation in superoxide dismutase 1 (SOD1) (c.118G>A (p.E40K)) uncovered a recent decrease in frequency, plummeting from 14.5% (95/657) in 2019 to 2.9% (24/820) in 2022. Weir and Cockerham population differentiation (F ST) based on genome-wide single-nucleotide polymorphism (SNP) of 117 selected dogs detected the SNP with the highest F ST located in the intron of SOD1 adjacent to the c.118G>A mutation, supporting a selection signature on SOD1. Further genome-wide SNP analyses revealed no obvious changes in inbreeding levels and genetic diversity between the 2019 and 2022 populations. Our study highlights that genetic testing can help inform improved mating choices in breeding programs to reduce the frequency of risk variants and avoid inbreeding. This combined strategy could decrease the genetic risk of canine degenerative myelopathy, a fatal disease, within only a few years. [ABSTRACT FROM AUTHOR]

The Yesso scallop Mizuhopecten yessoensis is an important aquaculture species that was introduced to Western Canada from Japan to establish an economically viable scallop farming industry. This highly fecund species has been propagated in Canadian aquaculture hatcheries for the past 40 years, raising questions about genetic diversity and genetic differences among hatchery stocks. In this study, we compare cultured Canadian and wild Japanese populations of Yesso scallop using double-digest restriction site-associated DNA (ddRAD) sequencing to genotype 21,048 variants in 71 wild-caught scallops from Japan, 65 scallops from the Vancouver Island University breeding population, and 37 scallops obtained from a commercial farm off Vancouver Island, British Columbia. The wild scallops are largely comprised of equally unrelated individuals, whereas cultured scallops are comprised of multiple families of related individuals. The polymorphism rate estimated in wild scallops was 1.7%, whereas in the cultured strains, it ranged between 1.35 and 1.07%. Interestingly, heterozygosity rates were highest in the cultured populations, which is likely due to shellfish hatchery practices of crossing divergent strains to gain benefits of heterosis and to avoid inbreeding. Evidence of founder effects and drift was observed in the cultured strains, including high genetic differentiation between cultured populations and between cultured populations and the wild population. Cultured populations had effective population sizes ranging from 9 to 26 individuals whereas the wild population was estimated at 25,048-56,291 individuals. Further, a depletion of low-frequency variants was observed in the cultured populations. These results indicate significant genetic diversity losses in cultured scallops in Canadian breeding programs. [ABSTRACT FROM AUTHOR]

The evolutionary transition from outcrossing in heterostylous morphs to selfing in homostylous morphs has occurred in many plant lineages. Homostylous variants with a low degree of herkogamy may increase the reproductive advantage of autonomous self‐pollination when there is little inbreeding depression and/or low pollinator visitation. Oxalis corniculata, a self‐compatible perennial herb derived from a tristylous ancestor, is reported to have two floral morphs. Homostyled plants are broadly distributed in Japan, whereas long‐styled plants are reported to occur only in coastal areas. We examined the hypothesis that a reproductive advantage in avoiding inbreeding depression and/or frequent pollinator visits enables long‐styled plants to live in some areas. Studies on floral variation revealed that the degree of herkogamy varied widely and continuously within and among populations. Homostyled and long‐styled morphs were functionally defined based on the ability of autonomous self‐pollination. Homostyled plants were widely distributed, whereas long‐styled plants were found in and around the two coastal populations and relatively inland populations. Pollination experiments provided no evidence of inbreeding depression in either homostyled or long‐styled plants. Pollinator visitation frequency was higher in the two coastal populations than in the other populations. Thus, reproductive disadvantage in long‐styled plants lacking autonomous self‐pollination has reduced in the two coastal populations, and long‐styled plants may be maintained due to a competitive advantage of large seed size. In contrast, we recorded no comparable frequencies of pollinator visitation in other populations containing long‐styled plants, indicating that there are other factors contributing to the maintenance of long‐styled plants in these areas. [ABSTRACT FROM AUTHOR]

Captive‐breeding programs are actively engaged in conservation and resource enhancement for a variety of species around the world, yet captive‐bred individuals often experience reduced fitness in the wild due to inbreeding and adaptation to captivity. Increasing wild‐type genetic contributions has been proposed as one solution to this problem, but the demographic impacts of these contributions remain unclear. Using data from long‐term mass‐marking programs conducted by national hatcheries in Japan, we evaluated the effects of wild genes in the parental generation on the survival of captive‐bred populations. Our results indicated that increasing the percentage of wild genes improves survival of captive‐bred offspring in the wild in two salmonid species. These findings offer insights for future bioresource management efforts that use both wild and captive‐bred individuals. [ABSTRACT FROM AUTHOR]

To understand the reproductive ecology of a plant species with both selfing and outcrossing reproductive systems, it is important to know how selfed individuals contribute to the maintenance of a population. Further, examination of the magnitude of inbreeding depression after pollination is essential for the accurate measurement of reproductive success. In this study, we investigated the characteristics of viable seeds and seedlings of Rhododendron kaempferi Planch. in a region where the bumblebee pollinator Bombus ardens Smith, 1879 are abundant. In a hand-pollination experiment, the fruit set from self-pollination was 32%, significantly lower than that from outcross-pollination (81%). The number of seeds per fruit from self-pollination was one sixth the number from outcross-pollination. However, the number of seeds per fruit was negatively correlated with the mass per seed. In addition, the germination rate was low when the seed mass was light. Although selfed seeds could germinate, 89% of the seedlings died within a year. The inbreeding depression coefficient one year after sowing was very high (0.89). These results indicate that R. kaempferi shows extremely strong selection for outcrossing but maintains a slight selfing potential in a natural population in central Japan. [ABSTRACT FROM AUTHOR]

The use of genetically closely related populations as reintroduction sources is crucial in restoration programmes for endangered species because genetically distant populations may cause genetic disturbances. Aporia hippia (Lepidoptera; Pieridae) is an endangered subalpine grassland butterfly in Japan and its distribution area is restricted to the Asama, Yatsugatake and Akaishi Mountains in central Honshu Island. In the Yatsugatake Mountains, its population is probably already extinct, and reintroduction from the other sites is now under consideration. Here, we estimated the genetic diversity and spatial genetic structure of A. hippia in Japan to identify candidate source populations for reintroduction in extinct populations via multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq) and mitochondrial DNA sequencing methods. The MIG-seq method indicated the presence of very few genetic differences among the populations. The mitochondrial DNA sequencing method identified two haplotypes: haplotype A in the Asama, Yatsugatake and northern Akaishi Mountains, and haplotype B in the central and southern Akaishi Mountains. The two haplotypes exhibited only a one base pair substitution between them. Implications for insect conservation: Based on these results, we suggest the existence of two conservation units: the first group consisting of populations in the Asama, Yatsugatake, and northern Akaishi Mountains, and the second group consisting of those in the central and southern Akaishi Mountains. According to this genetic proximity, however, all populations of A. hippia in Japan can also be defined as one conservation unit group, given the risk of inbreeding depression or difficulty of adaptation in different environments. [ABSTRACT FROM AUTHOR]

Producing original knowledge is the foundation of scientific progress. Originality is associated with certain skills and practices that can be trained and socialised. This study investigates how inbreeding as a career practice influences the socialisation of originality. An analysis based on a sample of mid‐career life scientists in Japan finds that originality and associated practices are transferred to junior academics from their PhD supervisors, and that the inter‐generational transfer of the practices favourable for originality is reinforced when junior academics are inbred. Hence, if senior academics have orientation towards originality, inbred junior academics are likely to succeed the same orientation; whereas if supervisor lack orientation towards originality, inbred juniors also lack the orientation. Thus, inbreeding can be a double‐edged sword in developing originality. [ABSTRACT FROM AUTHOR]

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The Japanese golden eagle (Aquila chrysaetos japonica) is an endangered subspecies with declining reproductive success. Previous research on this subspecies reported genetic diversity in northern Japan and in captivity using neutral genetic markers, but the situation in other areas of Japan and diversity at functional genetic loci are understudied. Here, we increased wild samples from western Japan and captive samples from zoos and analyzed genetic diversity of mitochondrial DNA, nuclear microsatellite loci, and the major histocompatibility complex (MHC) DRB exon 2 region. In addition, wild Scottish samples were analyzed and literature from European subspecies and other raptor species was surveyed to compare with the Japanese golden eagle. Overall, levels of mtDNA haplotype and microsatellite diversity observed in western Japan were similar to previously studied northern regions. However, microsatellite allelic diversity was lower compared to other golden eagle subspecies. MHC diversity indices, especially in captive Japanese golden eagles, were also low relative to raptors classified as Least Concern by the IUCN. This pattern could be explained by the loss of rare alleles due to genetic drift—a consequence of a declining population—suggesting the possibility of an early population bottleneck. Moreover, genetic structure analyses suggested that the Japanese population likely consists of one gene pool, so the bottleneck may affect the entire population. From these results, we suggest maintaining gene flow between local populations to prevent inbreeding and further loss of alleles, increasing the number of breeding pairs in captivity, and releasing captive individuals to reinforce the wild population. [ABSTRACT FROM AUTHOR]

Pedigreed cats have traditionally been mated with close relatives, which increases the risks for inbreeding depression and genetic disorders. We evaluated the genome-wide population structure and the degree of inbreeding of 1022 cats, including 13 pedigreed and two random bred populations from Japan and the USA, using single nucleotide polymorphism array-based data. Ancestry structure analysis revealed Japan's American Curl, Norwegian Forest, and Siamese cat populations were genetically distinct from their American counterparts. Furthermore, we found an ancestral genetic component shared between five pedigreed and random bred Japanese cats, suggesting the breeds were admixed with Japanese cats or cats of east Asian origin. Between-country differences in inbreeding estimates based on runs of homozygosity were found for Maine Coon, Siamese, and random bred cats. To reduce the risks of inbreeding depression and genetic disorders, particularly for highly inbred breeds, such as Abyssinian cats, as well as Russian Blue and Siamese cats in the USA, appropriate breeding practices must be observed, including mating practices that increase the genetic diversity. • We evaluated the genetic structure of pedigreed and random-bred cat populations. • Some Japanese breeds were genetically distinct from their American counterparts. • Certain pedigreed breeds were admixed with cats of Japanese or East Asian origin. • We highlight the risks of inbreeding depression for highly inbred Abyssinians. [ABSTRACT FROM AUTHOR]

Rapeseed (Brassica napus L.) is one of the most economically important oilseed crops worldwide. In Japan, it has been cultivated for more than a century and has formed many feral populations. The aim of this study was to elucidate the genetic diversity of feral rapeseeds by genotyping 537 individuals (among which 130 were determined to be genetically modified) sampled from various regions in Japan. Analysis of 30 microsatellite markers amplified 334 alleles and indicated moderate genetic diversity and high inbreeding (expected heterozygosity, 0.50; observed heterozygosity, 0.16; inbreeding coefficient within individuals, 0.68) within the feral populations. The Mantel test showed only an insignificant weak positive correlation between geographic distance and genetic distance. Analysis of molecular variance showed a greater genetic diversity among individuals than between populations. These results are in accordance with population structure assessed by using principal coordinate analysis and the program STRUCTURE, which showed that the 537 individuals could be assigned to 8 genetic clusters with very large genetic differences among individuals within the same geographic population, and that among feral individuals, many are closely related to rapeseed accessions in the NARO Genebank but some have unknown origins. These unique feral rapeseeds are likely to be affected by strong selection pressure. The results for genetically modified individuals also suggest that they have two different sources and have a considerable degree of diversity, which might be explained by hybridization with nearby individuals and separation of hybrid cultivars. The information obtained in this study could help improve the management of feral rapeseed plants in Japan. [ABSTRACT FROM AUTHOR]

The impact of variation in mating system on genetic diversity is a well-debated topic in evolutionary biology. The diploid sexual race of Cyrtomium falcatum (Japanese holly fern) shows mating system variation, i.e., it displays two different types of sexual expression (gametangia formation) in gametophytes: mixed (M) type and separate (S) type. We examined whether there is variation in the selfing rate among populations of this species, and evaluated the relationship between mating system, genetic diversity and effective population size using microsatellites. In this study, we developed eight new microsatellite markers and evaluated genetic diversity and structure of seven populations (four M-type and three S-type). Past effective population sizes (Ne) were inferred using Approximate Bayesian computation (ABC). The values of fixation index (FIS), allelic richness (AR) and gene diversity (h) differed significantly between the M-type (FIS: 0.626, AR: 1.999, h: 0.152) and the S-type (FIS: 0.208, AR: 2.718, h: 0.367) populations (when admixed individuals were removed from two populations). Although evidence of past bottleneck events was detected in all populations by ABC, the current Ne of the M-type populations was about a third of that of the S-type populations. These results suggest that the M-type populations have experienced more frequent bottlenecks, which could be related to their higher colonization ability via gametophytic selfing. Although high population differentiation among populations was detected (FST = 0.581, F’ST = 0.739), there was no clear genetic differentiation between the M- and S-types. Instead, significant isolation by distance was detected among all populations. These results suggest that mating system variation in this species is generated by the selection for single spore colonization during local extinction and recolonization events and there is no genetic structure due to mating system. [ABSTRACT FROM AUTHOR]

From a framework of this study, modern society may be explained by a paradigm transformation from ascription to achievement and also from particularism to universalism. According to this hypothesis, Japanese university society has not developed successfully for more than the closed society to the opened society. This paper intends to deal with the Japanese differentiated university stratification, which has been formed among these value orientations by connection of particularism and ascription, with a focus on its effects on the academic productivity including both research and teaching productivity. For example, a closed academic structure with an inbreeding mechanism in tate-shakai (vertical society) has brought about a great deal of effect either positively or negatively on academic system throughout the country. We intend to discuss the reasons behind the declining symptom of academic productivity of the university on the basis of the given framework. [ABSTRACT FROM AUTHOR]

Viola grayi, a coastal violet, is found on sandy seashores in limited regions in Japan, but not on rocky sea cliffs or in inland areas. This stemmed violet is classified in the subsection Rostratae. Because of recent human activity on sandy seashores, this species is now recorded as endangered. The present status of this species was surveyed and its genetic diversity was analyzed using 17 newly developed simple sequence repeat markers. The results are compared with those for two commonly found inland violet species in the same subsection, V. grypoceras and V. kusanoana. The coastal violet populations showed markedly lower genetic diversity than those of the common species, V. grypoceras, whereas V. kusanoana showed intermediate genetic diversity. About a half of the total genetic variation of V. grayi is found among populations in analysis of molecular variance. In contrast, only less than 25% of the total variation is found among populations for the two common violets. These three species showed a remarkably high inbreeding coefficient, which indicates high inbreeding under natural mating conditions, although these species have both chasmogamous and cleistogamous flowers. In a population-based dendrogram, V. grayi was clustered in a single and concise group, whereas V. grypoceras and V. kusanoana were found in somewhat discrete positions. In the Bayesian analysis of genetic structure of the coastal violet, delta K was the highest at K = 7, and the seven clusters almost correspond to seven populations studied here. Implications of the conservation of this endangered coastal violet are presented. [ABSTRACT FROM AUTHOR]

Since the end of the glacial age, Picea koyamae has been sparsely distributed in Japan as a relict species and is presently threatened with extinction. We investigated the population structure and genetic structure of nine populations of P. koyamae. Population size was assessed at 9-135 individuals in habitats ranging from 0.5 to 11.5 ha, and seedlings and saplings were observed in all but one particular population, which had a Sasa-type (bamboo grass) forest floor. The effective number of alleles per locus ( N) within peripheral populations in the Yatsugatake Mountains was 1.8-2.7, much lower than that of core populations in the Akaishi Mountains (2.8-4.3) using five nuclear simple sequence repeat loci. This finding suggests that genetic variation in these populations has been reduced by isolation from other populations. The standardized genetic differentiation among populations ( G′) was 0.410 and higher than that found in other Japanese conifers, suggesting that isolation and inbreeding have progressed in this species. In two isolated populations at the Yatsugatake Mountains, the fixation index ( F) was 0.315-0.354, much higher than the values determined for the other populations (−0.188 to 0.263). This suggests that these two populations have survived several generations while increasing the degree of inbreeding. However, the highest seedling density was in a population with low genetic variation and high F. The most serious problems at present appear to be the declining number of mature trees and the deterioration of suitable environments for seedling establishment. [ABSTRACT FROM AUTHOR]

The current study was conducted to investigate the effect of short-term selection in Japanese quail for 4-wk BW and estimate genetic parameters of BW, carcass traits, and egg weight. A selected line and control line were randomly selected from a base population. In each generation, 39 sires and 78 dams were used as parents for the next generation. Data were collected over 2 consecutive hatches for 4 generations, and 1,554 records from 151 sires and 285 dams were used to estimate the genetic parameters. The genetic improvement of 4-wk BW was 9.6, 8.8, and 8.2 g in generations 2, 3, and 4, respectively. There was a significant effect of sex, generation, and line (P < 0.001). There was a significant difference for BW and carcass weights but not for carcass percentage components between sexes (P < 0.01). Females showed higher figures than males. The realized heritability for 4-wk BW was 0.55, reflecting the accuracy of selection. However the estimated heritability by using pedigree information was 0.26 ± 0.05. The genetic correlation among BW and carcass traits was relatively high (ranging from 0.85 to 0.91). Inbreeding caused a decline in the mean for all of the traits, but its effect was only significant for 4-wk BW and carcass weight (P < 0.05). Selection for 4-wk BW improved feed conversion ratio 0.16 units over the selection period. Results showed there was a strong genetic correlation between 4-wk BW and carcass traits that suggests that early 4-wk BW can be used as a selection criterion to improve carcass traits. Also, intense selection resulting in high rates of inbreeding might result in decreased response to selection due to inbreeding depression. [ABSTRACT FROM AUTHOR]

Abstract: We provide a brief review of practices and relevant studies for restoration of Nymphoides peltata (yellow floating heart, Asaza), a distylous floating-leaf clonal plant, in Lake Kasumigaura, Japan to develop a model of integrated genetic and demographic conservation for threatened plants. Several theoretically expected issues, such as sudden extinction of small populations with low genetic diversity, limited seed production in small-sized local populations, and significantly high heterozygosity in adults that have survived environmental change, were ascertained through integrated studies on demography with discrimination of genets and genetics using highly polymorphic genetic markers. Investigation of genetic properties of the remnant soil seed bank suggested that the seed bank could potentially restore genetic diversity, although the fitness reduction of seed banks caused by inbreeding could affect the success of restoration. As a result of restoration efforts, increases in the number of local populations and genets in the Lake Kasumigaura metapopulation have led to population recovery. [Copyright &y& Elsevier]

The article presents a study on characteristics of owl species covered with dense forest situated at the base of steep mountains in Hokkaido, Japan. Study shows that through observation on their breeding particularly in 1986, the original species both male and female do successfully reproduced four folds between the year of 1987 and 1991. It is noted that through observation, the birds could have been recognized by each other through the daughter for instance, returning after its dispersal in a winter, which was tolerated by the species parents.

In a long-term study of sexual behavior in Japanese macaques, we found that matrilineal inbreeding accounted for 2.9% of the copulations recorded for the Arashiyama B troop during 7 mating seasons between 1968 and 1984. Of the 906 copulatory dyads, 46 (5.1%) occurred among kin. Close matrilineal kin dyads (r = 1/2-1/8, 1.1% of the total of copulatory dyads) strongly avoided matrilineal inbreeding, but for remote kin dyads (r > 1/8, 4.0% of the total) the tendency was weaker in some years. Among the possible determinants of matrilineal inbreeding, we found that it tended to occur among younger and lower-ranking males as an effect of troop demographic changes. There is no significant association between female rank and matrilineal inbreeding. Our results are consistent with the hypothesis that different degrees of kin relatedness are discriminated by individuals with respect to mate choice. [ABSTRACT FROM AUTHOR]

Background: Swimmer puppy syndrome is a disease found in neonatal puppies mainly characterized by the inability to stand, but its direct cause is unknown. Since swimmer puppies were observed infrequently but continuously among the Labrador retriever colony at the Hokkaido Guide Dogs for the Blind Association in Japan, based on their birth record and pedigree, factors related to the onset of swimmer puppy syndrome in Labrador retrievers were examined., Results: The total number of offspring over seven years was 436, of which 16 were swimmer puppies. Most of the affected puppies except one recovered steadily. As for the swimmer puppies, the litter size was significantly lower, and the body weights on the 10th and 28th day after delivery were significantly higher than the non-symptomatic puppies. These results suggested that the onset may be related to weight gain in the neonatal stages due to a small litter size. According to the genetic analysis, 26 ancestors common to the affected individuals were confirmed, but the causative individual could not be identified with the inbreeding coefficient. The heritability of the swimmer-puppy onset trait was 0.80, and the heritability for the the 10 th -day body-weight trait was equally high at 0.78, both of which strongly suggest genetic involvement., Conclusions: In this study, the onset of swimmer puppy syndrome in the Labrador retrievers was associated with litter size and early weight gain, and result of study suggests that genetic influence might be involved., (© 2022. The Author(s).)

We constructed recombinant inbred lines (RILs) between a Japanese and a Taiwanese landrace of foxtail millet and employed next-generation sequencing, such as flexible ddRAD-seq and Nanopore sequencing to identify the candidate genes involved in the crop evolution of foxtail millet. We successfully constructed a linkage map using flexible ddRAD-seq with parents and RILs and detected major QTLs for each of three traits: leaf sheath colors, spikelet-tipped bristles (stb), and days to heading (DTH). (1) For leaf sheath colors, we identified the C gene on chromosome IV. (2) We identified a homeobox (HOX14) gene for stb on chromosome II, which shows homology with HvVrs1 in barley. (3) Finally, we identified a QTL with a large effect on DTH on chromosome II. A parent of the RILs from Taiwan and Yugu1 had a Harbinger-like TE in intron 3 of this gene. We also investigated the geographical distribution of the TE insertion type of this gene and found that the insertion type is distributed in the northern part of East Asia and intensively in South and Southeast Asia, suggesting that loss/reduction of function of this gene plays an important role in spreading into the northern part of East Asia and subtropical and tropical zones., (© 2022. The Author(s).)

An abnormal female producing only female progeny was found in Lymantria dispar in Hokkaido, Japan, in July 1996. Similarly, its progeny produced only females. Egg hatch rates were near 50% in all-female matrilines. Therefore, a certain cytoplasmic factor was thought to kill males in eggs differentially, resulting in only female hosts. In the next generation, the field population was estimated to contain 9.1% abnormal females. Severe inbreeding depression was also observed in egg hatch rates during confirmation of maternal inheritance. The cost of inbreeding was estimated at 0.395, which is one of the highest in insects. Inbreeding avoidance by their host has been cited as one of the advantages of a male-killing factor, but we suggest that this is not applicable in this moth. [ABSTRACT FROM AUTHOR]

Island populations of Campanula microdonta and mainland Honshu populations of C. punctata have several different mating systems: self-incompatible (SI) and therefore obligately outcrossing in mainland Honshu and Oshima Island; self-compatible (SC) and largely outcross- ing in the northern islands of Toshima and Niijima; and SC and predominantly inbreeding southern ones of Miyake and Hachijo. Several features possibly associated with the mating systems are described. A hypothesis is proposed that the mean and variance of pollinator availability together with inbreeding depression could explain the observed patterns of mating system as the results of evolution. [ABSTRACT FROM AUTHOR]

The article discusses the relationship the enamel defects of permanent teeth to the retention of deciduous tooth fragments. A study was conducted using 174 boys and 168 girls from families suspected of inbreeding in Nagasaki, Japan. Their teeth were tested for enamel defects such as hypoplasia or opacity. Hypoplasia was found in 56% of participants and opacity in 18%.

• Genome-wide SNPs estimated the pedigree haplotypes of citrus breeding materials in Japan. • Pedigree haplotypes revealed the genetic compositions and founder origins. • Breeding strategies can be optimized using estimated pedigree haplotypes. • A new tool to accumulate favorable alleles and prevent inbreeding depression. In fruit crops including citrus, many cultivars have been developed by cross breeding. To determine the genetic composition resulting from cross breeding, we estimated the pedigree haplotypes of Japanese citrus breeding materials. Seventy-eight accessions composed of citrus cultivars, breeding lines, and their founders, as well as 377 F 1 seedlings derived from nine parental combinations were genotyped at 285 single nucleotide polymorphism loci. The pedigree haplotypes were estimated by FlexQTL software. The most likely pedigree haplotypes were obtained for all 455 individuals. We believe that the estimated pedigree haplotypes can be useful for the optimization of breeding strategies, such as the efficient accumulation of favorable alleles and prevention of inbreeding depression. [ABSTRACT FROM AUTHOR]

An albino strain of the bitterling Tanakia signifer (Pisces, Cyprinidae, Acheilognathinae) was established through interbreeding using an albino male selected from among the offspring produced from the spawning of 18 wild-caught individuals. This is the first report of albinism in this species. Progeny tests demonstrated that inheritance of the trait follows the expected pattern for a simple autosomal recessive. A stock of 200+ individuals is currently being held at the Kannonzaki Nature History Museum, Japan. [ABSTRACT FROM AUTHOR]

This study reports findings from the pathological examination of the forestomach of an 11-month-old Japanese Black steer with severely retarded growth (41% of expected weight) and chronic ruminal tympany. The ruminal papillae were weakly formed (0.3-0.5 cm long) and unevenly distributed. The cellulae and cristae reticuli were underdeveloped; the cristae were 0.4-0.7 cm in height and milky white. The keratinized layer in the stratified squamous epithelium was thickened. Ruminal pH was 5.25, and ruminal volatile fatty acid concentration was 11.7 mM. The steer's severely retarded growth was considered to be caused by malnutrition due to developmental and functional failure of the forestomach.

The Japanese Shorthorn is a Japanese Wagyu breed maintained at a small population size. We assessed the degree of inbreeding and genetic diversity among Japanese Shorthorn cattle using pedigree analysis. We analyzed the pedigree records of registered Japanese Shorthorn born between 1980 and 2018, after evaluating the pedigree completeness. The average of the actual inbreeding coefficients increased at the same rates annually from approximately 1.5% in 1980 to 4.2% in 2018 and was higher than the expected inbreeding coefficients over time. The effective population size based on the individual coancestry rate largely decreased from 127.8 in 1980 to 82.6 in 1999, and then remained almost constant at approximately 90. Three effective numbers of ancestors decreased over time until 1995, then remained almost constant. In particular, the effective number of founder genomes (N ge ) decreased from 43.8 in 1980 to 11.9 in 2018. The index of genetic diversity based on N ge decreased from 0.99 in 1980 to 0.96 in 2018 due to genetic drift in non-founder generations. Changes in inbreeding and genetic diversity parameters were similar between Japanese Shorthorn and other Japanese Wagyu breeds, but the magnitude of the changes was lower in the Japanese Shorthorn., (© 2021 The Authors. Animal Science Journal published by John Wiley & Sons Australia, Ltd on behalf of Japanese Society of Animal Science.)

Maintaining genetic diversity and inbreeding control are important in Japanese Black cattle production, especially in remote areas such as the islands of Okinawa Prefecture. Using a single-nucleotide polymorphism (SNP) array, we evaluated the genetic diversity and genomic inbreeding in Japanese Black cows from the islands of Okinawa Prefecture and compared them to those from other locations across Japan. Linkage disequilibrium decay was slower in cows in the islands of Okinawa Prefecture. The estimated effective population size declined over time in both populations. The genomic inbreeding coefficient (F ROH ) was estimated using long stretches of consecutive homozygous SNPs (runs of homozygosity; ROH). F ROH was higher in the cows on the islands of Okinawa Prefecture than on other locations. In total, 818 ROH fragments, including those containing NCAPG and PLAG1, which are major quantitative trait loci for carcass weight in Japanese Black cattle, were present at significantly higher frequencies in cows in the islands of Okinawa Prefecture. This suggests that the ROH fragments are under strong selection and that cows in the islands of Okinawa Prefecture have low genetic diversity and high genomic inbreeding relative to those at other locations. SNP arrays are useful tools for evaluating genetic diversity and genomic inbreeding in cattle., (© 2021 Japanese Society of Animal Science.)

The domestication process of plants and animals typically involves intense inbreeding and directional selection for various traits. Here, we genotyped 370 Japanese Thoroughbred horses using the recently developed 670k SNP array and performed various genome-wide analysis also using genotype data of other horse breeds. We identified a number of regions showing interesting patterns of polymorphisms. For instance, the region containing the MC1R locus associated with chestnut coat color may have been targeted by selection for a different mutation much earlier on than the recent selection for chestnut color. We also identified regions that show signatures of selection specific to Thoroughbreds. In addition, we found that intense inbreeding early in the history of the Thoroughbred breed and also before the formation of the breed has a significant impact on the genomic architecture of modern Thoroughbreds. Our study demonstrates that the horse 670k array can be utilized to gain important insight into the domestication process of horses and to understand the genetic basis of the phenotypic diversity in horses., Competing Interests: FS is an employee of Hidaka Training and Research Center, Japan Racing Association; TT is an employee of Genetic Analysis Department, Laboratory of Racing Chemistry. This does not alter our adherence to PLOS ONE policies on sharing data and materials. All other authors declare that no competing interests exist.

Understanding the breeding ecology of a species is essential for the appropriate conservation and management of wildlife. In brown bears, females occasionally copulate with multiple males in one breeding season, which may lead to multiple paternity in a single litter. In contrast, inbreeding, a potential factor in the reduction of genetic diversity, may occur, particularly in threatened populations. However, few studies have reported the frequency of these phenomena in brown bear populations. Here, we investigated the incidence of multiple paternity and inbreeding in a high-density brown bear population on the Shiretoko Peninsula in Hokkaido, Japan. A total of 837 individuals collected from 1998 to 2017 were genotyped at 21 microsatellite loci, and parentage analysis was performed. Out of 70-82 litters with ≥2 offspring, 14.6-17.1% of litters were sired by multiple males. This was comparable to the rate reported in a Scandinavian population, although population density and litter size, factors that potentially affect the incidence of multiple paternity, differed between the 2 populations. Out of 222 mother-father mating pairs, 6 litters (2.7%) resulted from matings between fathers and daughters. Additionally, 1 (0.5%) and 4 (1.8%) cases of mating between maternal half-siblings and between paternal half-siblings, respectively, were observed; however, no cases of mating between mothers and sons or between full siblings were observed. Our results suggest that male-biased natal dispersal effectively limits mating between closely related individuals (aside from fathers and daughters) in brown bears., (© The American Genetic Association 2019. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Identifying traits that facilitate species introductions and successful invasions of ecosystems represents a key issue in ecology. Following their establishment into new environments, many non-native species exhibit phenotypic plasticity with post-introduction changes in behaviour, morphology or life history traits that allow them to overcome the presumed loss of genetic diversity resulting in inbreeding and reduced adaptive potential. Here, we present a unique strategy in the invasive ant Brachyponera chinensis (Emery), in which inbreeding tolerance is a pre-adapted trait for invasion success, allowing this ant to cope with genetic depletion following a genetic bottleneck. We report for the first time that inbreeding is not a consequence of the founder effect following introduction, but it is due to mating between sister queens and their brothers that pre-exists in native populations which may have helped it circumvent the cost of invasion. We show that a genetic bottleneck does not affect the genetic diversity or the level of heterozygosity within colonies and suggest that generations of sib-mating in native populations may have reduced inbreeding depression through purifying selection of deleterious alleles. This work highlights how a unique life history may pre-adapt some species for biological invasions., (© 2018 John Wiley & Sons Ltd.)

Premise of the Study: We posed two hypotheses for broad scenarios of postglacial recolonization of Korea by the warm-temperate vegetation: (1) that extant Korean populations are derived from a single refugium, or (2) that they are derived from multiple refugia. We chose a homosporous fern typical of East Asian warm-temperate vegetation, Selliguea hastata, to test which of the two scenarios is more likely and to check whether Japan contained putative glacial refugia., Methods: Using 16 allozyme loci, we obtained genotypes of 756 individuals from 20 populations, representative of the whole distribution area in Korea (including Jeju Island), Japan, and Taiwan. We assessed genetic variability within and among populations, Wright's F-statistics, and conducted analysis of molecular variance, model-based Bayesian clustering, and bottleneck tests., Key Results: We found no allozyme variation within populations of S. hastata in mainland Korea, whereas genetic polymorphism was detected for populations from Jeju Island, Japan (in particular a population from southeastern Shikoku), and Taiwan. The levels of inbreeding within populations were high, consistent with the potential of S. hastata for intragametophytic selfing., Conclusions: Data on allelic richness together with Bayesian clustering methods suggest a pattern of postglacial recolonization of mainland Korea from a single refugium, probably located either on Jeju Island or in Japan. Jeju Island should merit the highest priority for conservation biogeography, as it played a role as a Quaternary refugium for arctic-alpine, boreal, temperate as well as warm-temperate plants, as suggested here.

In the near future, global average temperature is expected to increase due to the accumulation of greenhouse gases, and increased temperatures will cause severe sterility in many crop species. In rice, since wild species show high genetic variation, they may have the potential to improve the flowering characters of cultivars. In this study, we investigated flowering characters under natural conditions by comparing an Asian wild rice accession of Oryza rufipogon W630 (originated from Myanmar) with a Japanese rice cultivar, O. sativa Japonica cv. Nipponbare. Further, QTL analysis for days to heading (DH) and spikelet opening time (SOT: the time of day when the spikelet opens) was carried out using BC(2)F(8) backcross population derived from the cross between them. Regarding DH, four QTLs were detected, and two of them were found to have wild alleles with strong effects leading to longer days to heading during the Japanese summer. These wild alleles may be used to produce late-heading cultivars that do not flower during the high summer temperatures anticipated in the future. As for SOT, two parameters of SOTb (beginning time when the first spikelet opens) and SOTm (median time when 50% of the spikelets open) were recorded and the time differences from Nipponbare were investigated. Two QTLs on chromosomes 5 and 10 and two QTLs on chromosomes 4 and 5 were detected for SOTb and SOTm, respectively. The wild alleles were responsible for early spikelet opening time at all loci. If the wild alleles detected in this study have the same effects in the genetic background of other cultivars, they will be very useful in producing early-flowering rice cultivars that complete fertilization in the morning before the temperature rises.

To investigate genetic diversity of a major histocompatibility complex (MHC) gene in the brown bear (Ursus arctos) population on Hokkaido Island, northern Japan, we cloned and sequenced parts of exon 2 and intron 2 of the MHC class-II DQA gene from 32 brown bears. According to strict criteria for allele identification established by mammalian MHC nomenclature committees, four DQA types (Urar-DQA*01 to Urar-DQA*04) were identified. Of the four, however, Urar-DQA*04 had a 12-bp deletion not detected in a cDNA analysis, indicating that this is a pseudogene at a distinct locus generated by gene duplication. The nucleotide sequences of the other three DQA alleles, which were expressed (because detected from cDNA), were very similar, indicating lower DQA variation In the Hokkaido brown bear population than in other mammals. We attribute this low genetic diversity to (1) some limited effect of possible balancing selection; (2) bottlenecks and inbreeding after migration and isolation of the Hokkaido brown bear population from the Eurasian Continent; (3) a much slower evolutionary rate in DQA than in other MHC genes in the Hokkaido brown bear population.

Quercus is attractive for evolutionary studies, primarily for developing the concepts of the species, speciation and adaptation; however, remarkably little is known about levels of nucleotide polymorphism in the nuclear functional genes of this genus. This article provides the first characterization of levels of nucleotide polymorphism in 11 gene fragments in natural populations of a Quercus species, Quercus crispula Blume. Results show that the level of nucleotide variation in this oak is generally higher than that in conifers, as high as that in a European oak, but lower than that in an aspen. The level of population recombination is relatively high. Within-population inbreeding is negligible and between-population differentiation is modest. The decay of linkage disequilibrium is significantly faster in the species-wide samples and the three northernmost populations than in the other populations. Statistical tests support the hypothesis of a recent bottleneck for several populations in the southern part of Japan. The amounts and patterns of nucleotide variation, recombination and linkage disequilibrium, and genetic differentiation observed among populations of this species are contradictory to our expectations, given the recent colonization history of the northern Japan populations.

Alternative breeding strategies were simulated based on the population structure of the Tajima strain of Japanese Black cattle. An analysis of the population structure revealed that some sires up to 20 years of age have been used in Tajima. In addition, 95% of newborn calves were the progeny of only 20 sires, and their mating frequencies were significantly skewed. The current average inbreeding coefficient and founder genome equivalents of the strain were estimated to be 0.199 and 2.25, respectively. Average inbreeding coefficient is expected to reach 0.394 within 27 years. Thus, different breeding strategies were assessed for their effect on the level of inbreeding and average genetic merit. We compared strategies that (1) halve the sire service period, (2) double the number of mating sires and (3) lower the skewed sire mating frequency and optimize the frequency for weighted genetic merit and diversity. Reducing the service period yielded a 7.0-12.0% reduction in the rate of inbreeding while maintaining almost the same genetic gain. Increasing the number of sires resulted in a 19.3-21.3% reduction in inbreeding with a corresponding 1.6-8.4% reduction in gain. The rates of inbreeding from the optimized strategies decreased as the weight on genetic diversity increased. However, a strategy that emphasized only genetic gain yielded lower gain than other strategies because the strategy allowed only one sire to mate, resulting in reduced genetic variance and low accuracy of genetic evaluation. In contrast, a strategy with no emphasis on genetic gain when determining mating frequency resulted in reductions of 16.0% and 63.2% in genetic gain and inbreeding, respectively. The strategies examined here are easily applicable and can be expected to reduce immediate loss of genetic diversity.

Tying-up is a condition that primarily affects the muscles of horses. In this study, the heritability of the Tying-up syndrome in the Thoroughbred racehorse was estimated by Bayesian analysis with Gibbs sampling based on the threshold model for binary traits. The data used were the clinical data in racehorses diagnosed by veterinarians of the Racehorse Clinics of Japan Racing Association from 2000 to 2003. The health status of the Tying-up was treated as a binary trait. In the genetic analysis, the effect of changing the amount of the pedigree or inbreeding information on the estimation of heritability was investigated, too. The heritability estimates with non-zero probability in the posterior densities were approximately 0.16-0.18 in minimum, suggesting that the heritability of the Tying-up is not zero at least. The posterior density distributions of the heritability estimates were generally more pointed and sharp with using inbreeding coefficients than without using it, suggesting that more stable estimations were obtained when inbreeding coefficients were used. Among the different amounts of pedigree and inbreeding information, the heritabilities obtained with three or four generations of pedigree using inbreeding coefficients seems to be preferable, i.e. heritability of 0.42 or 0.43 for Tying-up.

The Japanese rosy bitterling, Rhodeus ocellatus kurumeus, has been affected not only by the invasion of another subspecies, R. o. ocellatus, from China, but also by habitat fragmentation. In this study, the effects of habitat fragmentation on the fitness of R. o. kurumeus were investigated. Owing to exclusion by R. o. ocellatus, R. o. kurumeus in Honshu and Shikoku has disappeared entirely, except for small populations in isolated man-made ponds in Osaka and Kagawa. In Kyushu it still occupies open water systems, into which R. o. ocellatus has only recently invaded. Meristic and genetic data show that the diversity of R. o. kurumeus is significantly lower in the isolated Osaka and Kagawa populations than the non-isolated Fukuoka population. The Osaka population is inferior to the Fukuoka population in terms of viability and growth. The viability of reciprocal inter-population hybrids between the Osaka and Fukuoka populations was, however, as high as that of the Fukuoka population. In addition to the high scores of band sharing index (BSI) in RAPD-PCR analysis, acceptance of transplanted scales among individuals, irrespective of natal pond, indicates that the Osaka population forms a highly inbred line. These results suggest that low genetic variation is associated with inbreeding depression in the small isolated Osaka populations. Consequently, the management of ponds, including the free movement of individuals, in addition to measures to prevent the invasion of R. o. ocellatus, is necessary for the conservation of R. o. kurumeus.

We estimated the gene dispersal distance and the magnitude of inbreeding depression from the fine-scale genetic structure in the endangered heterostylous perennial Primula sieboldii. We indirectly estimated the neighbourhood size (Nb) and the standard deviation of gene dispersal distance (sigma(g)) from the detected genetic structure by using 10 microsatellite markers. We also estimated the fitness reduction in mating among neighbouring individuals caused by biparental inbreeding according to the genetic structure. We found clear fine-scale genetic structure (a significantly positive kinship coefficient within 42.3 m), and the indirect estimates of sigma(g) and Nb were 15.7 m and 50.9, respectively. These indirect estimates were similar to the direct estimates (18.4 m and 44.0). The slightly larger indirect estimate of Nb may reflect that inbreeding depression and genetic structure or rare long-distance dispersal that were overlooked in the direct estimate have elongated the long-term average of gene dispersal distance. P. sieboldii is also likely to suffer about 19% fitness reduction in progenies from mating among individuals 5 m apart. Our results suggest that biparental inbreeding and genetic structure can affect the range of gene dispersal and seed reproductive success in P. sieboldii.

To establish a baseline for conservation of a threatened clonal tree, Magnolia tomentosa, we investigated size distribution and genetic structure within a population, using six microsatellite markers. Within the study site, 1044 living ramets (stems) were distinguished into 175 genets (individuals). The mean number of ramets per genet was 5.97, and 76% of all genets had multiple ramets. Genets, which apparently produced new ramets through sprouting and layering, were generally composed of several large ramets and many small ramets. Spatial autocorrelation analysis of microsatellite alleles revealed positive autocorrelation over short distances for both ramets and genets. The Moran's I-value of ramets in the shortest distance class was 3.8 times larger than that of genets, reflecting the effect of clonal growth. To analyse the size-class differences in genetic structure, the 175 genets were separated into two size classes, small and large. The correlogram for the small genets exhibited positive spatial autocorrelation in the shortest distance class, but this was not the case for the correlogram for the large genets, indicating that genetic structure is weakened or lost through self-thinning as the genets grow. The FIS value over all loci for the small genets was positive and deviated significantly from zero, while the corresponding value for the large genets was close to zero. The excess homozygotes in the small genets may be the result of genetic substructuring and/or inbreeding, and the reduction in homozygote frequency from the small to large genets may be because of loss of genetic structure and/or inbreeding depression.

As in plants, fungi exhibit wide variation in reproductive strategies and mating systems. Although most sexually reproducing fungi are either predominantly outcrossing or predominantly selfing, there are some notable exceptions. The haploid, ascomycete chestnut blight pathogen, Cryphonectria parasitica, has previously been shown to have a mixed mating system in one population in USA. In this report, we show that both selfing and outcrossing occur in 10 additional populations of C. parasitica sampled from Japan, Italy, Switzerland and USA. Progeny arrays from each population were assayed for segregation at vegetative incompatibility (vic) and DNA fingerprinting loci. Outcrossing rates (t(m)) were estimated as the proportion of progeny arrays showing segregation at one or more loci, corrected by the probability of nondetection of outcrossing (alpha). Estimates of t(m) varied from 0.74 to 0.97, with the lowest rates consistently detected in USA populations (0.74-0.78). Five populations (four in USA and one in Italy) had t(m) significantly less than 1, supporting the conclusion that these populations exhibit mixed mating. The underlying causes of variation in outcrossing rates among populations of C. parasitica are not known, but we speculate that--as in plants--outcrossing is a function of ecological, demographic and genetic factors.

This is a report on an application of a new method for estimating inbreeding rates in large, semi-isolated populations over time. This study is intended to further show the versatility of the method. In a previous study, the method was shown to be useful in analysing the effect of details in a single population curve on inbreeding. In this study, the method is applied to the population curves of India, Japan, Europe and China over the past two millennia, to allow inter-comparisons of the inbreeding within those populations. Anthropologists traditionally concentrate on small isolates within a country for the estimation of inbreeding. Those isolates, however, might not be representative of the country as a whole. The method used in this study attempts to estimate inbreeding over large regions over an extended period of time. The method models the genealogical 'paradox' and yields estimates of the average inbreeding in terms of Pearl's coefficient Z, as a function of time. It is first assumed that the whole population of each country is the adult (breeding) population, corresponding to minimum inbreeding. It is found that the more complex the population curve examined, the greater the precision of the Z curves obtained. The effect of incorporating a single known value of inbreeding into the analyses is also investigated. This procedure produces a more realistic situation where the adult (breeding) population is considerably less than the entire population. It is shown, that if it is assumed that the whole population of the country is the adult (breeding) population, then a present day person from one of the four regions/countries studied is descended from between 72% and 97% of the early medieval population of the particular country. On the other hand, if a known value of inbreeding for Britain is incorporated into the analysis, these values become of the order of 1% for the older-settled regions/countries, and about 16% for Japan. However, that value for Japan is reduced to about 1% when a known value of inbreeding for this country is used. Although some uncertainty in these results remains, the versatility of the method demonstrated here will provide more accurate results, as better input-data become available.

Subterranean termites have unusual plasticity in their breeding systems. As a result of their cryptic foraging and nesting habits, detailed information on the numbers and types of reproductive individuals in colonies has been difficult to obtain. In this study, we used microsatellite markers to infer the major features of the breeding system of the Formosan subterranean termite, Coptotermes formosanus, in southern Japan, where it is believed to have been introduced from China. A total of 30 colonies was sampled from two islands (Kyushu and Fukue) located 100 km apart. Twenty workers from each colony were genotyped at six microsatellite loci. Analysis of worker genotypes within colonies indicated that 27 colonies (90%) were simple (Mendelian) families. The remaining three colonies, all from Kyushu, were consistent with being extended families having begun as simple families but being currently headed by multiple neotenic (secondary) reproductives descended from the original king and queen. Workers from simple families in both populations were significantly inbred (FIT = 0.10 for Kyushu and 0.46 for Fukue) and highly related to their nestmates (coefficient of relatedness, r = 0.59 for Kyushu and 0.77 for Fukue), suggesting that many simple-family colonies were headed by closely related reproductives, especially in the Fukue population. This conclusion is supported by the high coefficient of relatedness between nestmate reproductives in simple-family colonies (r = 0.23 for Kyushu and 0.61 for Fukue) based on genotypes inferred from their worker offspring. There was moderate genetic differentiation (FST = 0.12) between the two populations, suggesting rather restricted gene flow between them. There was no significant isolation by distance among colonies, as might be expected given the limited dispersal of reproductives, presumably because of the frequent movement of colonies by humans. Finally, there was no evidence of a recent bottleneck, a finding possibly consistent with the more than 300-year history of this species in Japan.

The objective of this research was to estimate the amount of inbreeding and effective population size of the Japanese Black breed using pedigree records from bulls and heifers registered between 1985 and 1997. Inbreeding was quantified by three F-statistics: actual inbreeding, inbreeding expected under random mating, and inbreeding due to population subdivision. During the period of 1985 to 1997, the inbreeding expected under random mating increased from 2.3% to 5.0%, whereas the increase of actual inbreeding was more gradual (from 4.7% to 5.4%). The inbreeding due to population subdivision decreased almost linearly and reached 0.5% in 1997, indicating that genetic subdivision of the Japanese Black cattle population has essentially disappeared. The effective size of the breed was estimated from the increasing rate of inbreeding expected under random mating. In the earlier half of this period (1986 to 1990), the breed maintained an effective size of approximately 30. However, after 1991 the effective size sharply decreased and the harmonic mean between 1993 and 1997 was only 17.2. The main cause of this reduction of the effective size was considered to be the intensive use of a few prominent sires. To increase the effective size, an upper limit in the use of AI semen per sire should be imposed.

To examine the effects of forest cutting on within-population genetic structure, the genetic structure and variability of two Japanese beech (Fagus crenata Blume) stands with contrasting histories in relation to cutting were investigated. Six hundred and sixty beech trees, covering two hectares in total, were mapped and genetically analysed using nine isozyme loci encoding eight enzyme systems. The proportion of polymorphic loci, the average number of alleles per locus, the effective number of alleles per locus, the expected heterozygosity and the observed heterozygosity were 78, 3.3, 1.31, 0.200 and 0.189, respectively, in a secondary stand (designated AK) cut during the 1920s. Corresponding figures were 78, 3.3, 1.33, 0.203 and 0.193, respectively, in a primary stand designated KU. The inbreeding coefficient and the grand mean of the number of alleles in common (NAC) were 0.055 and 1.684 in AK, and 0. 042 and 1.649 in KU, respectively. The genetic variability was slightly but significantly lower in AK. The genetic structure of the two stands was strikingly different. The proportions of positively significant Moran's I and SND values found in the shortest distance class were 0.86 and 0.38 for AK, and 0.14 and 0.29 for KU, respectively. Furthermore, significant linkage disequilibrium was observed in AK, but none at all in KU. To examine which, if any, differences in the genetic structure would be likely to influence succeeding generations, we simulated a self-thinning process. The simulation suggested that reduced genetic variability and linkage disequilibrium would have significant influence in the AK stand for several generations.

We compared the ability of a high-NaCl diet to produce blood pressure elevation in spontaneously hypertensive rats (SHR) from the major North American commercial suppliers (Harlan, Taconic Farms, Charles River) and SHR and stroke-prone SHR (SHRSP) from the National Institutes of Health (NIH). Animals were raised on a low-NaCl diet containing 0.30% NaCl and placed on an 8.0% NaCl diet at 37 days of age. In males, the high-NaCl diet produced large increments in blood pressure within 2-4 weeks, which were similar in magnitude for all SHR derivations. In females, increments in blood pressure occurred more slowly than in males but, in most SHR derivations, the absolute blood pressure level eventually reached was similar to that seen in males. The present findings provide no evidence of sub-line differentiation among SHR stocks from the United States regarding the blood pressure-augmenting effects of increased levels of NaCl and are consistent with the results of DNA fingerprinting studies, which have not found any genetic variation between SHR from different colonies. We speculate that the pervasive gender differences in the blood pressure response to the high-NaCl diet in SHR may reflect gender differences in food intake, and hence the dose of NaCl received, rather than intrinsic differences between males and females. On the other hand, the lack of significant gender differences in blood pressure response to the high-NaCl diet in SHRSP may reflect the genetic differences which are known to exist between this strain and the main SHR stemline.