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Sexual conflicts and their evolutionary outcomes may be influenced by population-specific features such as mating system and ecological context; however, very few studies have investigated the link between sexual conflict and mating system. The self-compatible, mixed-mating hermaphrodite Collinsia heterophylla (Plantaginaceae) is thought to exhibit a sexual conflict over timing of stigma receptivity. This conflict involves (i) delayed stigma receptivity, which intensifies pollen competition, and (ii) early fertilization forced by pollen, which reduces seed set. We investigated the potential for the conflict to occur under field conditions and performed glasshouse crosses within eight populations to assess its consistency across populations. Flowers were visited, and produced seeds after pollination, at all developmental stages, suggesting that the conflict can be of significance under natural conditions. In the glasshouse, early pollination imposed costs in all populations. Overall, the timing of first seed set was most strongly affected by the maternal parent, denoting stronger female than male ability to influence the onset of stigma receptivity. Crosses also revealed a negative relationship between donor- and recipient-related onset of receptivity within individuals, a novel result hinting at trade-offs in sex allocation or a history of antagonistic selection. Neither timing of stigma receptivity, timing of first seed set, nor pollen competitive ability covaried with population outcrossing rate. In conclusion, these results indicate that sexually antagonistic selection may be present in varying degrees in different populations of C. heterophylla, but this variation does not appear to be directly related to mating system variation., (© 2015 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2015 European Society For Evolutionary Biology.)

A major goal of speciation research is to understand the processes involved in the earliest stages of the evolution of reproductive isolation (RI). One important challenge has been to identify systems where lineages have very recently diverged and opportunities for hybridization are present. We conducted a comprehensive examination of the components of RI across the life cycle of two subspecies of Clarkia xantiana, which diverged recently (ca. 65,000 bp). One subspecies is primarily outcrossing, but self-compatible, whereas the other is primarily selfing. The subspecies co-occur in a zone of sympatry but hybrids are rarely observed. Premating barriers resulted in nearly complete isolation in both subspecies with flowering time and pollinator preference (for the outcrosser over the selfer) as the strongest barriers. We found that the outcrosser had consistently more competitive pollen, facilitating hybridization in one direction, but no evidence for pollen-pistil interactions as an isolating barrier. Surprisingly, postzygotic isolation was detected at the stage of hybrid seed development, but in no subsequent life stages. This crossing barrier was asymmetric with crosses from the selfer to outcrosser most frequently failing. Collectively, the results provide evidence for rapid evolution of multiple premating and postzygotic barriers despite a very recent divergence time., (© 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.)

The delta smelt, an endangered fish species endemic to the San Francisco Bay-Delta, California, United States, was recently brought into captivity for species preservation. This study retrospectively evaluates the implementation of a genetic management plan for the captive delta smelt population. The captive genetic management plan entails tagging fish, molecular data collection, pedigree reconstruction, relatedness estimation, and recommending fish crosses annually in an effort to minimize the average coancestry in the population and limit inbreeding. We employed 12 microsatellite DNA markers to examine temporal genetic diversity in consecutive, discrete generations to determine the effects of intensive genetic management on the population and to quantify the amount of wild genetic diversity present within each captive generation. Wild fish are incorporated into the captive population each generation to minimize genetic drift, and 91% of the original founders are still represented in the F(3) generation. The average mean kinship in the third generation in captivity was 0.0035. There was no evidence of significant genetic divergence of the captive population from the wild population. The results of this study yield management insights into the practical application of genetic management plans for captive populations and conservation hatcheries, in an attempt to preserve the genetic integrity of endangered species.

Bean thrips, Caliothrips fasciatus, is native to western North America. Once considered a pest of several crops in its native area, its pest status has waned over recent decades. However, due to its habit of aggregating in the navel of navel oranges, bean thrips remains economically important because some countries importing oranges from California have designated it a quarantine pest. Despite continued propagule pressure, bean thrips has never established outside North America. We examined genetic variation in mitochondrial DNA among Californian populations of C. fasciatus and found that potentially two cryptic species are present (supported by Kimura 2-P distances): a common widespread form B and a rarer form A with a very limited distribution. Form B showed strong phylogeographic structure, with many haplotypes having a limited geographic distribution. Inter-population crossing experiments between three geographically isolated populations of form B resulted in the production of some female offspring, indicating a degree of compatibility between these populations of this haplodiploid species. However, substantial outbreeding depression was also detected. A low frequency of offspring production by hetero-population pairs was evidence of pre-mating isolation, while post-mating isolation was also evident in the elevated mortality of fertilized eggs in successful hetero-population crosses. One surprising finding was the total lack of offspring production by virgin females when isolated individually. However, virgin females did produce sons in the presence of other virgin females. A test for the presence of Wolbachia showed that form B was not infected, but that some populations of the rarer form A were.

Background and Aims: Since the early 1990s, research on genetic variation of phenotypic plasticity has expanded and empirical research has emphasized the role of the environment on the expression of inbreeding depression. An emerging question is how these two evolutionary ecology mechanisms interact in novel environments. Interest in this area has grown with the need to understand the establishment of populations in response to climate change, and to human-assisted transport to novel environments., Methods: We compare performance in the field of outcrossed (O) and inbred lines (S1, S2) from 20 maternal families from each of two native populations of Mimulus guttatus. The experiment was planted in California in each population's home site, in the other populations's home site, in a novel site within the native range of M. guttatus, and in a novel site within the non-native range in North America. The experiment included nearly 6500 individuals. Survival, sexual reproduction and above-ground biomass were examined in order to evaluate inbreeding depression, and stem diameter and plant height were examined in order to evaluate phenotypic plasticity., Key Results: Across all field sites, approx. 36 % of plants survived to flowering. Inbreeding depression differed among sites and outcrossed offspring generally outperformed selfed offspring. However, in the native-novel site, self-progeny performed better or equally well as outcross progeny. Significant phenotypic plasticity and genetic variation in plasticity was detected in the two architectural traits measured. The absolute value of plasticity showed the most marked difference between home and non-native novel site or non-native-novel site. Evidence was detected for an interaction between inbreeding and plasticity for stem diameter., Conclusions: The results demonstrate that during initial population establishment, both inbreeding depression and phenotypic plasticity vary among field sites, and may be an important response to environments outside a species' currently occupied range. However, the interaction between inbreeding and plasticity may be limited and environment-dependent.

According to theory, gene flow to marginal populations may stall or aid adaptation at range limits by swamping peripheral populations with maladaptive gene flow or by enhancing genetic variability and reducing inbreeding depression, respectively. We tested these contrasting predictions by manipulating patterns of gene flow of the annual plant, Mimulus laciniatus, at its warm range limit. Gene flow was experimentally applied by using crosses within warm-limit populations (selfed and outcrossed), between warm-limit populations, and between warm-limit and central range populations across two elevational transects. We measured the fitness of offspring in a common garden at the warm-edge species range limit. All sources of gene flow increased seedling emergence at the range limit, suggesting local inbreeding depression at both range limit populations; however, lifetime reproductive success only increased significantly when pollen originated from another warm-limit population. Center-to-warm-edge gene flow was maladaptive by delaying time to development at this warm, fast-drying range limit, whereas edge-to-edge gene flow hastened emergence time and time to reproduction. By empirically testing theory on the effects of gene flow on the formation of geographic range limits, we find benefits of gene flow among populations to be greatest when gene flow is between populations occupying the same range limit. Our results emphasize the overlooked importance of gene flow among populations occurring near the same range limit and highlight the potential for prescriptive gene flow as a conservation option for populations at risk from climate change.

A mapping population of 186 recombinant inbred lines developed from a cross between UC1110, an adapted California spring wheat, and PI610750, a synthetic derivative from CIMMYT's Wide Cross Program, was evaluated for its response to current California races of stripe rust (Puccinia striiformis f. sp. tritici) in replicated field trials over four seasons (2007-2010) in the northern Sacramento Valley. A genetic map was constructed consisting of 1,494 polymorphic probes (SSRs, DArTs, and ESTs) mapped to 558 unique loci, and QTL analysis revealed the presence of four stripe rust resistance QTL segregating in this population, two from UC1110 (on chromosomes 3BS and 2BS) and two from PI610750 (5AL and 2AS). The two QTL of largest effects (on 3BS and 5AL) were validated in independent populations and their intervals narrowed to 2.5 and 5.3 cM, respectively. The 3BS QTL was shown, by allelism test and genotype, to carry a gene different from the Yr30/Sr2 complex. Mapped position also suggests that the 3BS QTL is associated with a gene different from either Yrns-B1 or YrRub, two stripe rust resistance genes mapped to this region in other studies. The 5AL QTL carries a previously unreported partial stripe rust resistance gene, designated here as Yr48. This paper discusses the individual contributions to resistance of these four QTL, their epistatic interactions, and their potential in durable resistance breeding strategies based on combinations of partial resistance genes.

Genes involved in host-pathogen interactions are expected to be evolving under complex coevolutionary dynamics, including positive directional and/or frequency-dependent selection. Empirical work has largely focused on the evolution of immune genes at the level of the protein sequence. We examine components of genetic variance for transcript abundance of defense genes in Drosophila melanogaster and D. simulans using a diallel and a round robin breeding design, respectively, and infer modes of evolution from patterns of segregating genetic variation. Defense genes in D. melanogaster are overrepresented relative to nondefense genes among genes with evidence of significant additive variance for expression. Directional selection is expected to deplete additive genetic variance, whereas frequency-dependent selection is expected to maintain additive variance. However, relaxed selection (reduced or no purifying selection) is an alternative interpretation of significant additive variation. Of the three classes of defense genes, the recognition and effector classes show an excess of genes with significant additive variance; whereas signaling genes, in contrast, are overrepresented for dominance variance. Analysis of protein-coding sequences revealed no evidence for an association between additive or dominance variation in expression and directional selection. Both balancing selection driven by host-pathogen coevolution and relaxed selection for expression of uninduced defense genes are viable interpretations of these data., (© 2010 The Author(s). Evolution© 2010 The Society for the Study of Evolution.)

Understanding how genetic variation shapes species' distributions involves examining how variation is distributed across a species' range as well as how it responds to underlying environmental heterogeneity. We examined patterns of fitness variation across the local distribution of an annual composite (Lasthenia fremontii) spanning a small-scale inundation gradient in a California vernal pool wetland. Using seeds collected from the center and edge of a population, paternal half-sib families were generated and transplanted back to the center and edge of the original population. All transplants were adapted to the conditions at the center of the population. The effect of the environment on the opportunity for selection depended on the model of selection assumed. Under a model of hard selection, variance in absolute fitness was lower among transplants at the edge of the population than at the center. Under a model of soft selection, the variance in relative fitness was similar between center and edge microhabitats. Given that this population is likely well-mixed, differences in habitat quality between center and edge microhabitats will likely cause selection at the center of the population to dominate the evolutionary trajectory of this population., (© 2010 The Author(s). Evolution© 2010 The Society for the Study of Evolution.)

In the present study we screened the progeny of Vitis vinifera × V. romanetii populations segregating for resistance to powdery mildew and determined the presence of a single, dominant locus, Ren4, conferring rapid and extreme resistance to the grapevine powdery mildew fungus Erysiphe necator. In each of nine Ren4 pseudo-backcross 2 (pBC(2)) and pBC(3) populations (1,030 progeny), resistance fit a 1:1 segregation ratio and overall segregated as 543 resistant progeny to 487 susceptible. In full-sib progeny, microscopic observations revealed the reduction of penetration success rate (as indicated by the emergence of secondary hyphae) from 86% in susceptible progeny to below 10% in resistant progeny. Similarly, extreme differences were seen macroscopically. Ratings for Ren4 pBC(2) population 03-3004 screened using natural infection in a California vineyard and greenhouse and using artificial inoculation of an aggressive New York isolate were fully consistent among all three pathogen sources and environments. From 2006 to 2010, Ren4 pBC(2) and pBC(3) vines were continuously screened in California and New York (in the center of diversity for E. necator), and no sporulating colonies were observed. For population 03-3004, severity ratings on leaves, shoots, berries, and rachises were highly correlated (R(2) = 0.875 to 0.996) in the vineyard. Together, these data document a powdery mildew resistance mechanism not previously described in the Vitaceae or elsewhere, in which a dominantly inherited resistance prevents hyphal emergence and is non-race-specific and tissue-independent. In addition to its role in breeding for durable resistance, Ren4 may provide mechanistic insights into the early events that enable powdery mildew infection.

Gene flow between populations that are adapting to distinct environments may be restricted if hybrids inherit maladaptive, intermediate phenotypes. This phenomenon, called extrinsic postzygotic isolation (EPI), is thought to play a critical role in the early stages of speciation. However, despite its intuitive appeal, we know surprisingly little about the strength and prevalence of EPI in nature, and even less about the specific phenotypes that tend to cause problems for hybrids. In this study, we searched for EPI among allopatric populations of the butterfly Euphydryas editha that have specialized on alternative host plants. These populations recall a situation thought typical of the very early stages of speciation. They lack consistent host-associated genetic differentiation at random nuclear loci and show no signs of reproductive incompatibility in the laboratory. However, they do differ consistently in diverse host-related traits. For each of these traits, we first asked whether hybrids between populations that use different hosts (different-host hybrids) were intermediate to parental populations and to hybrids between populations that use the same host (same-host hybrids). We then conducted field experiments to estimate the effects of intermediacy on fitness in nature. Our results revealed strong EPI under field conditions. Different-host hybrids exhibited an array of intermediate traits that were significantly maladaptive, including four behaviors. Intermediate foraging height slowed the growth of larvae, while intermediate oviposition preference, oviposition site height, and clutch size severely reduced the growth and survival of the offspring of adult females. We used our empirical data to construct a fitness surface on which different-host hybrids can be seen to fall in an adaptive valley between two peaks occupied by same-host hybrids. These findings demonstrate how ecological selection against hybrids can create a strong barrier to gene flow at the early stages of adaptive divergence., Competing Interests: The authors have declared that no competing interests exist.

The aim of this study is to investigate the evolution of intrinsic postzygotic isolation within and between populations of Mimulus guttatus and Mimulus nasutus. We made 17 intraspecific and interspecific crosses, across a wide geographical scale. We examined the seed germination success and pollen fertility of reciprocal F(1) and F(2) hybrids and their pure-species parents, and used biometrical genetic tests to distinguish among alternative models of inheritance. Hybrid seed inviability was sporadic in both interspecific and intraspecific crosses. For several crosses, Dobzhansky-Muller incompatibilities involving nuclear genes were implicated, while two interspecific crosses revealed evidence of cytonuclear interactions. Reduced hybrid pollen fertility was found to be greatly influenced by Dobzhansky-Muller incompatibilities in five out of six intraspecific crosses and nine out of 11 interspecific crosses. Cytonuclear incompatibilities reduced hybrid fitness in only one intraspecific and one interspecific cross. This study suggests that intrinsic postzygotic isolation is common in hybrids between these Mimulus species, yet the particular hybrid incompatibilities responsible for effecting this isolation differ among the populations tested. Hence, we conclude that they evolve and spread only at the local scale.

The interaction between gene flow and environmental heterogeneity plays a key role in shaping the distribution patterns that we observe in natural populations. Although a growing body of theoretical work is exploring the effects of gene flow on the evolution of range limits and ecological specialization, explicit empirical tests of model assumptions and predictions in natural populations are almost entirely lacking. This study examines the potential for center-to-edge gene flow to occur and estimates the fitness consequences of cross-gradient gene flow in an annual plant species restricted to California vernal pool wetlands. Phenological differences and highly focused foraging patterns of pollinators reduce the potential for center-to-edge gene flow across populations within pools. Furthermore, controlled crosses simulating different patterns of gene flow across the environmental gradient reveal that center-to-edge gene flow does not reduce plant fitness at the edge but instead yields an increase in emergence rates and a trend toward overall higher fitness.

Although the ecological consequences of species invasions are well studied, the ecological impacts of genetic introgression through hybridization are less understood. This is particularly true of the impacts of hybridization on "third party" community members not genetically involved in hybridization. We also know little about how direct interactions between hybrid and parental individuals influence fitness. Here, we examined the ecological effects of hybridization between the native, threatened California Tiger Salamander (Ambystoma californiense) and the introduced Barred Tiger Salamander (Ambystoma tigrinum mavortium). Native x introduced hybrids are widespread in California, where they are top predators in seasonal ponds. We examined the impacts of early generation hybrids (first 2 generations of parental crosses) and contemporary hybrids derived from ponds where hybrids have been under selection in the wild for 20 generations. We found that most classes of hybrid tiger salamander larvae dramatically reduced survival of 2 native community members, the Pacific Chorus Frog (Pseudacris regilla) and the California Newt (Taricha torosa). We also found that native A. californiense larvae were negatively impacted by the presence of hybrid larvae: Native survival and size at metamorphosis were reduced and time to metamorphosis was extended. We also observed a large influence of Mendelian dominance on size, metamorphic timing and predation rate of hybrid tiger salamanders. These results suggest that both genetic and ecological factors are likely to influence the dynamics of admixture, and that tiger salamander hybridization might constitute a threat to additional pond-breeding species of concern in the region.

Fluorescence in situ hybridization (FISH) was used to identify the X and Y chromosomes of offspring produced by normal and "apparent" XY-female fall-run Chinook salmon (Oncorhynchus tshawytscha) from California. FISH experiments were performed using probes to 2 sex-linked loci, growth hormone pseudogene (GH-Psi), and OtY1, as well as a probe to a sex-linked microsatellite (Omy7INRA). Comparison of FISH staining patterns between the offspring produced by normal and apparent XY-females revealed that the apparent XY-female examined transmitted a "Y-like" chromosome with an attenuated OtY1 and GH-Psi signal to half of its offspring. Segregation analysis of microsatellites derived from rainbow trout (Oncorhynchus mykiss) with respect to phenotypic sex was carried out for 2 normal and 2 apparent XY-female Chinook salmon families. Inheritance patterns of Omy7INRA were consistent with this locus being closely linked to GH-Psi in males and in apparent XY-females carrying the Y-like chromosome. Another microsatellite locus (Omm1077) was closely linked to the primary sex-determining locus (SEX) in males but not to GH-Psi/OtY1 in apparent XY-females. The FISH analyses suggest that apparent XY-female fall-run Chinook salmon in California are not the product of a Y chromosome to autosome translocation. Despite the combined FISH and inheritance analyses, we were unable to differentiate between 2 alternative explanations for apparent XY-females, namely, recombination of markers between the sex chromosomes, or a Y chromosome with a dysfunctional or missing sex-determining region.

The recent observance of Fusarium fujikuroi, the causal agent of Bakanae disease of rice, in California provides a unique opportunity to assess the population diversity of an introduced pathogen in a new environment. We collected 172 isolates of this pathogen between 2000 and 2003 from California rice and two from water grass (Echinochloa spp.). Pathogenicity of F. fujikuroi was demonstrated on early water grass (E. oryzoides) and barnyard grass (E. crus-galli) indicating that weed control should be part of Bakanae management programs. Both mating types and six unique amplified fragment length polymorphism haplotypes corresponding to six identified vegetative compatibility groups were detected. The two most frequently isolated haplotypes encompassed 94% of the collected isolates, suggesting that clonal reproduction dominates. Coefficients of similarity between the unique haplotypes ranged from 0.94 to 0.98, and indicate that there is very little genotypic variation in the F. fujikuroi population in California. The near fixation of the MAT-1 idiomorph (observed ratio 170 MAT-1:4 MAT-2), is consistent with a hypothesis of predominant or exclusive asexual reproduction. The low level of introduced genotypic diversity, in conjunction with the asexual reproductive strategy of this population will slow evolutionary processes, including adaptation to the California environment.

Two different forces are thought to contribute to the rapid accumulation of hybrid male sterility that has been observed in many inter-specific crosses, namely the faster male and the dominance theories. For male heterogametic taxa, both faster male and dominance would work in the same direction to cause the rapid evolution of male sterility; however, for taxa lacking differentiated sex chromosomes only the faster male theory would explain the rapid evolution of male hybrid sterility. It is currently unknown what causes the faster evolution of male sterility, but increased sexual selection on males and the sensitivity of genes involved in male reproduction are two hypotheses that could explain the observation. Here, patterns of hybrid sterility in crosses of genetically divergent copepod populations are examined to test potential mechanisms of faster male evolution. The study species, Tigriopus californicus, lacks differentiated, hemizygous sex chromosomes and appears to have low levels of divergence caused by sexual selection acting upon males. Hybrid sterility does not accumulate more rapidly in males than females in these crosses suggesting that in this taxon male reproductive genes are not inherently more prone to disruption in hybrids.

One of the lingering paradoxes in invasion biology is how founder populations of an introduced species are able to overcome the limitations of small size and, in a "reversal of fortune," proliferate in a new habitat. The transition from colonist to invader is especially enigmatic for self-incompatible species, which must find a mate to reproduce. In small populations, the inability to find a mate can result in the Allee effect, a positive relationship between individual fitness and population size or density. Theoretically, the Allee effect should be common in founder populations of self-incompatible colonizing species and may account for the high rate of failed introductions, but little supporting evidence exists. We created a field experiment to test whether the Allee effect affects the maternal fitness of a self-incompatible invasive species, wild radish (Raphanus sativus). We created populations of varying size and relatedness. We measured maternal fitness in terms of both fruit set per flower and seed number per fruit. We found that both population size and the level of genetic relatedness among individuals influence maternal reproductive success. Our results explicitly define an ecological genetic obstacle faced by populations of an exotic species on its way to becoming invasive. Such a mechanistic understanding of the invasions of species that require a mate can and should be exploited for both controlling current outbreaks and reducing their frequency in the future.

Pitch canker, caused by Gibberella circinata, is a disease affecting pines throughout the world. Although the pathogen is capable of sexual reproduction, natural populations are often comprised of very few vegetative compatibility groups (VCGs), which implies a predominance of asexual reproduction. However, even where outcrossing occurs, a population could have limited VCG diversity due to a low level of polymorphism at the loci governing vegetative compatibility (=vic loci). To determine whether this was the case for the California population of G. circinata, inter-fertile strains were crossed under laboratory conditions. Progeny of this cross included a minimum of 29 VCGs, which was consistent with segregation of vic alleles at five loci. Only two of these VCGs were known to occur naturally in California. Three VCGs accounted for 32.4% of the progeny but 0% of the California population. Overall, the results support the conclusion that outcrossing has been rare or absent in the California population of G. circinata.

Seed and seedling traits related to germination and stand establishment are important in the production of cultivated lettuce (Lactuca sativa L.). Six seed and seedling traits segregating in a L. sativa cv. Salinas x L. serriola recombinant inbred line population consisting of 103 F8 families revealed a total of 17 significant quantitative trait loci (QTL) resulting from three seed production environments. Significant QTL were identified for germination in darkness, germination at 25 and 35 degrees C, median maximum temperature of germination, hypocotyl length at 72 h post-imbibition, and plant (seedling) quality. Some QTL for germination and early seedling growth characteristics were co-located, suggestive of pleiotropic loci regulating these traits. A single QTL (Htg6.1) described 25 and 23% of the total phenotypic variation for high temperature germination in California- and Netherlands-grown populations, respectively, and was significant between 33 and 37 degrees C. Additionally, Htg6.1 showed significant epistatic interactions with other Htg QTL and a consistent effect across all the three seed production environments. L. serriola alleles increased germination at these QTL. The estimate of narrow-sense heritability (h2) of Htg6.1 was 0.84, indicating potential for L. serriola as a source of germination thermotolerance for lettuce introgression programs.

Female Drosophila melanogaster remate more frequently than necessary to ensure fertilization. We tested whether polyandrous females gain genetic benefits for their offspring by (1) selecting secondary sires of higher genetic-quality than original partners or (2) because post-copulatory mechanisms bias fertilizations towards genetically superior males. We screened 119 hemiclones of males for lifetime fitness then selected eight hemiclones (four of extreme high fitness and four of extreme low fitness) and mated them to virgin females. Females were then given the opportunity to remate with males of benchmark-genetic quality and their propensity to remate (fidelity) and sperm displacement scored. A female's fidelity and her level of sperm displacement varied depending on which hemiclone she mated first, but not on male-genetic quality. These findings indicate that female remating and sperm displacement are strongly influenced by male genotype, but provide no evidence that these traits contribute to adaptive female choice to obtain superior genes for offspring.

Every species occupies a limited geographic area, but it remains unclear why traits that limit distribution do not evolve to allow range expansion. Hypotheses for the evolutionary stability of geographic ranges assume that species are maladapted at the range boundary and unfit beyond the current range, but this assumption has rarely been tested. To examine how fitness varies across species' ranges, we reciprocally transplanted two species of monkeyflowers, Mimulus cardinalis and M. lewisii, within and beyond their present elevation ranges. We used individuals of known parentage from populations collected across the elevation ranges of both species to examine whether populations are adapted to position within the range. For both species we found the greatest average fitness at elevations central within the range, reduced fitness at the range margin, and zero or near-zero fitness when transplanted beyond their present elevation range limits. However, the underlying causes of fitness variation differed between the species. At high elevations beyond its range, M. cardinalis displayed reduced growth and fecundity, whereas at low elevations M. lewisii experienced high mortality. Weak differences in performance were observed among populations within each species and these were not related to elevation of origin. Low fitness of both species at their range margin and weak differentiation among populations within each species suggest that adaptation to the environment at and beyond the range margin is hindered, illustrating that range margins provide an interesting system in which to study limits to adaptation.

Divergent natural selection contributes to reproductive isolation among populations adapting to different habitats or resources if hybrids between populations are intermediate in phenotype and suffer an associated, environmentally dependent reduction in fitness. This prediction was tested using two host races of Mitoura butterflies. Thirty-five F1 hybrid and parental lines were created, larvae were raised on the two host plants, and oviposition preferences were assayed in choice arenas. Larvae from both reciprocal hybrid crosses suffered a host-specific reduction in performance: when reared on incense cedar, hybrid survival was approximately 30% less than the survival of pure lines of the cedar-associated host race. The performance of hybrid larvae reared on the other host, MacNab cypress, was not reduced relative to parental genotypes. Females from both reciprocal hybrid crosses preferred to oviposit on incense cedar, the same host that resulted in the reduced survival of hybrid larvae. Thus, dominance is implicated in the inheritance of traits involved in both preference and performance, which do not appear to be genetically linked in Mitoura butterflies. Gene flow between host races may be reduced because the correlation between preference and performance that was previously described in parental populations is essentially broken by hybridization.

Recent studies suggest that chromosomal rearrangements play a significant role in speciation by preventing recombination and maintaining species persistence despite interspecies gene flow. Factors conferring adaptation or reproductive isolation are maintained in rearranged regions in the face of hybridization, while such factors are eliminated from collinear regions. As a direct test of this rearrangement model, we evaluated the genetic basis of hybrid male sterility in a sympatric species pair, Drosophila pseudoobscura pseudoobscura and D. persimilis, and an allopatric species pair, D. pseudoobscura bogotana and D. persimilis. Our results are consistent with the proposed model: virtually all of the sterility factors in the former pair are associated with three inverted regions, whereas sterility factors are present in the collinear regions in the latter pair. These findings indicate recombination and selection may have eliminated sterility factors outside the inverted regions between D. p. pseudoobscura and D. persimilis, suggesting chromosomal rearrangements may facilitate species persistence despite hybridization.

I tested whether a region of high female frequencies in the gynodioecious plant, Nemophila menziesii, may be due to hybridization between regionally distributed populations with different corolla colours. I crossed plants in the greenhouse from populations with different corolla colours and found that hybrid crosses yielded higher frequencies of females than within-colour crosses. In the field, I found that populations with high female frequencies had intermediate mean corolla colours and higher variance in corolla colour, two traits suggesting hybridization. Nemophila menziesii has nuclear-cytoplasmic sex inheritance, thus if populations with different corolla colours are fixed for different male-sterile cytoplasms and matching nuclear restorer alleles, hybridization between populations with different corolla colour should yield high frequencies of females. Two populations that are all hermaphroditic in the field segregated females in hybrid crosses suggesting that field populations may contain sex ratio distorters but appear undistorted, a prediction of genomic conflict theory., (Copyright 2004 Blackwell Publishing Ltd)

The endosymbiont Wolbachia has gained widespread notoriety over the past decade because of its high infection frequency among arthropods, and the unique heterogeneity of the host reproductive effects that it has been implicated as causing to enhance its own spread. Recently, another endosymbiotic bacterium from the Cytophaga-Flavobacterium-Bacteroides phylum has been shown to be widespread among arthropods and manipulate its hosts' reproduction to enhance its own spread. We show that infection by this Cytophaga-like organism (CLO) in the predatory mite Metaseiulus occidentalis (Acari: Phytoseiidae) is associated with a significant increase in the fecundity of infected females. This adds to the growing list of phenotypes that the CLO can induce in its hosts, which now include feminization, parthenogenesis induction, cytoplasmic incompatibility and fecundity enhancement, rivalling Wolbachia for overall diversity of host reproductive manipulations.

Before maternally inherited bacterial symbionts like Wolbachia, which cause cytoplasmic incompatibility (CI; reduced hatch rate) when infected males mate with uninfected females, can be used in a program to control vector-borne diseases it is essential to understand their dynamics of infection in natural arthropod vector populations. Our study had four goals: (1) quantify the number of Wolbachia strains circulating in the California Culex pipiens species complex, (2) investigate Wolbachia infection frequencies and distribution in natural California populations, (3) estimate the parameters that govern Wolbachia spread among Cx. pipiens under laboratory and field conditions, and (4) use these values to estimate equilibrium levels and compare predicted infection prevalence levels to those observed in nature. Strain-specific PCR, wsp gene sequencing, and crossing experiments indicated that a single Wolbachia strain infects Californian Cx. pipiens. Infection frequency was near or at fixation in all populations sampled for 2 years along a >1000-km north-south transect. The combined statewide infection frequency was 99.4%. Incompatible crosses were 100% sterile under laboratory and field conditions. Sterility decreased negligibly with male age in the laboratory. Infection had no significant effect on female fecundity under laboratory or field conditions. Vertical transmission was >99% in the laboratory and approximately 98.6% in the field. Using field data, models predicted that Wolbachia will spread to fixation if infection exceeds an unstable equilibrium point above 1.4%. Our estimates accurately predicted infection frequencies in natural populations. If certain technical hurdles can be overcome, our data indicate that Wolbachia can invade vector populations as part of an applied transgenic strategy for vector-borne disease reduction.

One objective of quantitative genetics is to identify the nucleotide variants within genes that contribute to phenotypic variation and susceptibility [1]. In an evolutionary context, this means characterizing the molecular polymorphisms that modify the penetrance and expressivity of perturbed traits. A survey of association between 267 SNPs in almost 11 kb of the D. melanogaster Egfr and the degree of eye roughening due to a gain-of-function Egfr(E1) allele crossed into 210 isogenic wild-type lines provides evidence that a handful of synonymous substitutions supply cryptic variation for photoreceptor determination. Ten sites exceed Bonferroni threshold for association in two sets of crosses to different Egfr(E1) backgrounds including a particularly significant cluster of sites in tight linkage disequilibrium toward the 3' end of the coding region. Epistatic interaction of this cluster with one other site enhances the expressivity of this haplotype. Replication of the strongest associations with an independent sample of 302 phenotypically extreme individuals derived from 1000 crosses of Egfr(E1) to freshly trapped males was achieved using modified case-control and transmission-disequilibrium tests. A tendency for the rarer alleles to have more disrupted eye development suggests that mutation-selection balance is a possible mechanism contributing to maintaining cryptic variation for Egfr.

Steinernema longicaudum Shen & Wang is redescribed based on a comparative morphological study of specimens from the type isolate from China, and two other isolates recovered from Korea and the USA. For the first and second generation female, the location of the vulva, shape of the vulval lips, and shape and length of the tail were newly observed diagnostic characters. A more detailed description of the morphology of the male spicules and gubernaculum, and the arrangement of the genital papillae is included. A description, based on scanning electron microscopy observations, of the lateral field pattern of the third-stage infective juveniles is also provided. Additionally, restriction fragment length polymorphism profiles based on the internal transcribed spacer region, and cross-breeding tests supplement the description of this species.

A fundamental goal of genetics and functional genomics is to identify and mutate every gene in model organisms such as Drosophila melanogaster. The Berkeley Drosophila Genome Project (BDGP) gene disruption project generates single P-element insertion strains that each mutate unique genomic open reading frames. Such strains strongly facilitate further genetic and molecular studies of the disrupted loci, but it has remained unclear if P elements can be used to mutate all Drosophila genes. We now report that the primary collection has grown to contain 1045 strains that disrupt more than 25% of the estimated 3600 Drosophila genes that are essential for adult viability. Of these P insertions, 67% have been verified by genetic tests to cause the associated recessive mutant phenotypes, and the validity of most of the remaining lines is predicted on statistical grounds. Sequences flanking >920 insertions have been determined to exactly position them in the genome and to identify 376 potentially affected transcripts from collections of EST sequences. Strains in the BDGP collection are available from the Bloomington Stock Center and have already assisted the research community in characterizing >250 Drosophila genes. The likely identity of 131 additional genes in the collection is reported here. Our results show that Drosophila genes have a wide range of sensitivity to inactivation by P elements, and provide a rationale for greatly expanding the BDGP primary collection based entirely on insertion site sequencing. We predict that this approach can bring >85% of all Drosophila open reading frames under experimental control.

Inferences regarding hybridization rely on genetic markers to differentiate parental taxa from one another. Intersimple sequence repeat (ISSR) markers are based on single-primer PCR reactions where the primer sequence is derived from di- and trinucleotide repeats. These markers have successfully been used to assay genetic variability among cultivated plants, but have not yet been tested in natural populations. We used genetic markers generated from eight ISSR primers to examine patterns of hybridization and purported examples of hybrid speciation in Penstemon (Scrophulariaceae) in a hybrid complex involving P. centranthifolius, P. grinnellii, P. spectabilis and P. clevelandii. This hybrid complex has previously been studied using three molecular data sets (allozymes, and restriction-site variation of nuclear rDNA and chloroplast DNA). These studies revealed patterns of introgression involving P. centranthifolius, but were unsuccessful in determining whether gene flow occurs among the other species, and support for hypotheses of diploid hybrid speciation was also lacking. In this study, we were able to fingerprint each DNA accession sampled with one to three ISSR primers and most accessions could be identified with a single primer. We found population- and species-specific markers for each taxon surveyed. Our results: (i) do not support the hybrid origin of P. spectabilis; (ii) do support the hypothesis that P. clevelandii is a diploid hybrid species derived from P. centranthifolius and P. spectabilis; and (iii) demonstrate that pollen-mediated gene flow via hummingbird vectors is prevalent in the hybrid complex.

Allelic diversity at the self-incompatibility (S-) locus in the ground cherry, Physalis crassifolia (Solanaceae), was surveyed in a natural population occurring in Deep Canyon, CA, using a molecular assay to determine the genotype of individual plants. A total of 28 different S-alleles were identified and sequenced from a sample of 22 plants. All plants examined were heterozygous, as expected under gametophytic self-incompatibility (GSI). The estimated number of alleles in this population is 43-44, comparable to allelic diversity reported for other species, as determined by the standard diallel crossing method. Allele frequencies in the sample deviated from the expectation of equal frequency under GSI; it is suggested that this deviation may result from sampling of related individuals. Molecular analysis of genotypes within single pollen donor families indicates that, for all alleles examined, segregation is consistent with predictions for single-locus GSI. The implications of a reliable and efficient molecular assay for determining the S-genotype of plants are discussed.

In Drosophila simulans, cytoplasmically transmitted Wolbachia microbes cause reduced egg hatch when infected males mate with uninfected females. A Wolbachia infection and an associated mtDNA variant have spread northward through California since 1986. PCR assays show that Wolbachia infection is prevalent throughout the continental US and Central and South America, but some lines from Florida and Ecuador that are PCR-positive for Wolbachia do not cause incompatibility. We estimate from natural populations infection frequencies and the transmission and incompatibility parameter values that affect the spread of the infection. On average, infected females from nature produce 3-4% uninfected ova. Infected females with relatively low fidelity of maternal transmission show partial incompatibility with very young infected laboratory males. Nevertheless, crosses between infected flies in nature produce egg-hatch rates indistinguishable from those produced by crosses between uninfected individuals. Incompatible crosses in nature produce hatch rates 30-70% as high as those from compatible crosses. Wild-caught infected and uninfected females are equally fecund in the laboratory. Incompatibility decreases with male age, and age-specific incompatibility levels suggest that males mating in nature may often be 2 or 3 weeks old. Our parameter estimates accurately predict the frequency of Wolbachia infection in California populations.

The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.