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Sexual selection is generally caused by female choice and male–male competition. In female choice process, female preference is favored indirectly and/or directly by sexual selection. In indirect selection, females expressing the preference might gain indirect genetic benefits. In direct selection, females expressing the preference might gain direct benefits or avoid male-imposed costs. The white-tailed zygaenid moth Elcysma westwoodii is monandrous, and males often gather around a female to mate with her, suggesting a high opportunity for sexual selection on male traits. We quantified phenotypic selection on male morphology in this species in the field. The morphological characters analyzed included body weight, antenna length, forewing length, hind wing length, hind wing tail length, genital clasper length, and the fluctuating asymmetry (FA) of these bilateral traits. In E. westwoodii, selection favored males with more symmetric genital claspers, as well as longer and more symmetrical hind wings and antennae. Negative correlations between FA and size were also detected in the clasper and the antenna. Our results suggest that FAs of male traits, in particular the genital clasper, may have indirect and direct influences on mating success. During a copulatory attempt, an E. westwoodii male will try to grasp the female’s abdominal tip with his claspers but often fail to do so because of the female’s reluctance to mate. The female abdominal tips are smooth and strongly sclerotized and could thus be difficult for males to grasp. We hypothesize that more symmetrical male claspers are more efficient in overcoming female reluctance. Key words: fluctuating asymmetry, genitalia, Lepidoptera, phenotypic selection, sexual conflict, sexual selection. [Behav Ecol]

The brachypterous grasshopper Podisma sapporensis Shiraki (Orthoptera: Acrididae) consists of two major chromosomal races with different sex chromosome systems. In the X0/XX race, the diploid number of chromosomes is 2n = 23 (X0) in males and 2n = 24 (XX) in females. In the XY/XX race, the diploid number is 2n = 22 (XY) in males and 2n = 22 (XX) in females, owing to Robertsonian fusion between an autosome and the X chromosome. The X0/XX and XY/XX races are allopatrically distributed, and each race contains geographical populations characterized by different chromosomal inversions. A previous hypothesis suggested that the XY/XX race was derived from the X0/XX race. To test this hypothesis, we examined mitochondrial DNA (mtDNA) sequence variation in two regions (cytochrome oxidase subunit II and 16S ribosomal DNA) among 29 P. sapporensis individuals representing five X0/XX and 12 XY/XX populations. The maximum parsimony tree of mtDNA indicated that neither of the two chromosomal races was monophyletic. Northern populations of XY/XX race did not join a clade consisting of more southern XY/XX populations but were included in a clade consisting of X0/XX populations. On the basis of these results, we propose two hypotheses for the differentiation between the northern and southern XY/XX populations. First, the XY/XX karyotype may have occurred more than once. Second, introgression of mtDNA may have occurred across adjacent populations possessing different karyotypes.

The sex comb on the forelegs of Drosophila males is a secondary sexual trait, and the number of teeth on these combs varies greatly within and between species. To understand the relationship between the intra- and interspecific variation, we performed quantitative trait locus (QTL) analyses of the intraspecific variation in sex-comb tooth number. We used five mapping populations derived from two inbred Drosophila simulans strains that were divergent in the number of sex-comb teeth. Although no QTLs were detected on the X chromosome, we identified four QTLs on the second chromosome and three QTLs on the third chromosome. While identification and estimated effects of the second-chromosome QTLs depend on genetic backgrounds, significant and consistent effects of the two third-chromosome QTLs were found in two genetic backgrounds. There were significant epistatic interactions between a second-chromosome QTL and a third-chromosome QTL, as well as between two second-chromosome QTLs. The third-chromosome QTLs are concordant with the locations of the QTLs responsible for the previously observed differences in sex-comb tooth number between D. simulans and D. mauritiana.

Relationships between the ommatidial structure and photoperiodic behavior of several mosquito species were investigated. Host-seeking behavioral patterns of mosquitoes were classified into 4 main groups based on previously compiled reports on field or laboratory biting activity. These groups were pattern I and I' (nocturnal), pattern II (crepuscular and nocturnal), pattern III (crepuscular and diurnal), and pattern IV (diurnal). Eye parameters (product of facet diameter and interommatidial angle) of mosquitoes that belong to the pattern I and I' group were higher (2.7 to 4.2) than those of mosquitoes that belong to the pattern IV group (0.8 to 2.3). Eye parameters of the mosquitoes categorized in the pattern II and III groups were intermediate (2.3 to 2.6). These result suggest that the crepuscular behavior of mosquitoes undergoes a transition in the course of evolution from nocturnal behavior to diurnal behavior. Large variations in the eye parameters were observed even within the same genus depending on their photoperiodic behavior. Therefore, the ommatidial structure of mosquitoes appears to be determined, not taxonomically, but evolutionarily by the photo-environment in which the mosquitoes are most active., Journal of insect physiology. 52(1), pp.67-75;2006

Previous studies have suggested that the developmental pattern of insect body parts is influenced by food conditions during the nymphal stages. In this study, we compared the developmental patterns of five body parts (body length, fore-femur length, mid-femur length, hind-femur length, and angle of claw) in the predatory insect Lethocerus deyrolli Vuillefroy fed three diets (tadpoles, Odonata nymphs, and tadpole–Odonata nymph mixture) during the nymphal stages. Significant age by sex interactions were detected in body length, fore-femur length, mid-femur length, and hind-femur length, indicating developmental patterns of these traits varied between sexes. Significant age by food interactions were detected in body length and hind-femur length and were marginally significant in mid-femur length, showing developmental patterns of these traits varied among food types. None of the interactions were significant in angle of the claw. A predation experiment was performed using double-claw nymphs as a control and one-claw nymphs (adult type) as a treatment. Double-claw nymphs successfully caught both large and small tadpoles, whereas one-claw nymphs caught small tadpoles more frequently than large tadpoles. Our results suggest that the claw development, which is very likely related to predatory function, may be less affected by nutritional conditions, and that double claws during nymphal stages may be indispensable to increased predation success.

Knowledge of the genetic basis of divergence in mating signal characters that contribute to reproductive isolation is critical to understanding speciation. Here, we describe a semi-automated system for characterizing grasshopper acoustic signals. We used this system to study the genetic basis of divergence in three male calling song components [echeme (EL), syllable (SL) and phrase (PL) lengths] between Chorthippus brunneus and C. jacobsi, two species of grasshoppers that hybridize in northern Spain. We also studied the number of pegs in the stridulatory file. For all characters, additive effects accounted for most of the genetic differentiation between species. However, the three song components also showed small but significant epistatic effects. No sex linkage was detected. Wright–Castle–Lande estimates of the minimum numbers of genetic factors underlying song and peg number divergence were low: peg number (ne ¼ 5.87 ± 5.84), SL (ne ¼ 2.37 ± 4.79) and PL (ne ¼ 0.87 ± 0.86). On the other hand, EL appeared to be controlled by many genes. These results suggest that divergence in SL and PL might be driven by sexual selection whereas EL might not be under selection. This is consistent with experimental results on female song preference in related species. However, the fact that few factors appear to underlie the differences in peg number is surprising. Peg number is not closely related to song characteristics. It often varies between closely related grasshopper species and it has been assumed to be a neutral character. The biometrical approaches used here tend to underestimate the number of factors influencing a trait but provide valuable background for subsequent quantitative trait loci analyses.

Studies of prezygotic and postzygotic isolation in Drosophila have shown in general that species in sympatry tend to evolve prezygotic barriers earlier than do species in allopatry. However, postzygotic barriers tend to evolve at the same evolutionary rate in both sympatric and allopatric species. In contrast to these observations, the grasshoppers Chorthippus parallelus parallelus and C. p. erythropus show complete hybrid male sterility but only limited prezygotic isolation after an estimated 0.5 millions years of divergence. Like their congeners, C. brunneus and C. jacobsi form a hybrid zone where their ranges meet in northern Spain. However, the hybrid zone is mosaic and bimodal and, in contrast to the high levels of postzygotic isolation between C. parallelus subspecies, these two species showed no significant reduction in hybrid fitness in F1 or backcross generations relative to the parental generations. The level of prezygotic isolation in laboratory tests was comparable to that between C. parallelus subspecies. These results suggest that endogenous postzygotic isolation does not play an important role in the reproductive isolation between C. brunneus and C. jacobsi, or in determining the structure of the hybrid zone. Exogenous postzygotic isolation may be present and should be tested in future studies. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 195–203.

Male characters that are used for male−male combat are often developed and exaggerated, whereas female equivalent characters are vestigial or vanished. In order to assess whether the characters common to both sexes share the same phenotypic variability due to common genetic architecture, we compared males and females of the stag beetle Prosopocoilus inclinatus using recently developed geometric morphometric methods. Elliptic Fourier analysis was used to compare shape variation between male characters (including exaggerated mandibles) and developmentally homologous female characters. A significant positive correlation was found between the size or between the weight of different body parts in both sexes, but a conspicuous difference was detected in the frequency distribution of the weight of all the body parts. Elliptic Fourier analysis demonstrated that there was marked discontinuous variation in mandibles in males, whereas such a discontinuity was not clear in females. The shape of a character in males exhibited some similarity with that of other characters, but this was not found in females. In a character, growth trajectory of shape was significantly affected by both size and weight in males, whereas size and shape tended to vary independently in female characters. These results support the hypothesis that a large sexual dimorphism in variation in shape is due to alleles accumulating in tight linkage with a sex-determining gene. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 219–233

This study aims to infer the proportion of queens and workers of the hornet Vespa analis parasitized by the strepsipterous parasite Xenos moutoni in overwintered females from morphological data collected for three years. It is known that both worker and queen hornets parasitized by strepsipterous insects overwinter. The parasitized queens cannot reproduce in the next season and thus the level of parasitism potentially affects the number of colonies to be established in the population. Thus, estimation of the ratio of parasitized queens to the total of parasitized females would be useful for understanding the population dynamics of the hornet. K-means cluster analysis demonstrated that 50 to 85% of individuals were workers in the total of parasitized females during the period. From 8 to 15% of total queens were thought to be sterilized by X. moutoni, a level that would not be expected to have a serious effect on the population dynamics of V. analis. Forced hibernation of workers might be considered to be a result of manipulation of the diapause system of the host by the parasite to increase its reproductive success.

A recently developed PCR-based assay, amplified fragment length polymorphism (AFLP), has been used for assessing phylogenetic relationships and the genetic structure of populations in many organisms including insects. Preliminary studies show that the procedure does not work well in acridid grasshoppers since it leads to very large numbers of indistinct bands, probably due to the large size of the genome. To overcome this drawback, we developed long primer sets with four selective nucleotides, and used these for the grasshoppers Chorthippus brunneus and C. jacobsi in northern Spain. This approach has allowed us to reduce the number of bands, so that we can compare homologous bands easily. Using the revised method, it appears that the degree of interspecific genetic differentiation of C. brunneus and C. jacobsi is relatively small.

We examined morphological variation in Kunashiri populations of P. sapporensis Shiraki and P. tyatiensis Bugrov using multivariate morphometrics to clarify their taxonomic status in comparison with Hokkaido populations of P. sapporensis. Although P. sapporensis in Kunashiri Island has a unique karyotypic characteristic, the neo-X and neo-Y system, cluster analysis indicated that the morphology is included in the range of variation seen in Hokkaido populations with the XO-male determination system. P. tyatiensis is characterized by having short-armed chromosomes compared with other Podisma species, but the morphology of this species did not differed much from P. sapporensis in Hokkaido, either. These results suggest that chromosomal changes do not contribute to phenotypic diversification. P. sapporensis in Kunashiri Island is probably reproductively isolated from P. tyatiensis on the same island because of conspicuous differences in the karyotype, whereas it is highly probable that P. tyatientsis in Kunashiri Island and P. sapporensis in Hokkaido constitute the same biological species.

Differences in the geographic patterns of genitalic and nongenitalic morphological characters in Podisma sapporensis (Podisminae) were examined using the hierarchical testing procedure in common principal component analysis. This analysis was used to evaluate the extent to which the covariance structure among characters varies geographically in both sexes. Males exhibited consistency in the covariance structure among populations both in genitalic and nongenitalic characters, whereas the covariance structures of female genitalic and nongenitalic characters were not stable geographically. We suggest that the conspicuous sexual difference in covariance structure results from different selective pressures acting on genitalia: stabilizing selection is responsible for the stability of male genitalia, whereas variability in female is the result of directional sexual selection varying among populations.

We examined sexual dimorphism and its geographical pattern in 10 morphological characters, including the genitalia, in the brachypterous grasshopper Podisma sapporensis. Conspicuous sexual dimorphism was observed in all characters. In nine characters, variance in females was significantly greater than in males. Sexual differences among populations varied more in the genitalia than in other characters. Spatial autocorrelation analysis demonstrated that there was no geographical trend in the female genitalia, whereas significant autocorrelation existed in the male genitalia. These results suggest that cryptic female choice is responsible for the autocorrelation pattern of the male genitalia, while random genetic drift or a larger effect of environment has created the geographical pattern of the female genitalia. Resume : Nous avons etudie le dimorphisme sexuel de 10 caracteres morphologiques, dont les genitalia, chez Podisma sapporensis, et en avons examine la tendance geographique. Le dimorphisme sexuel est manifeste dans tous les caracteres examines. Dans le cas de neuf de ces caracteres, la variance est significativement plus elevee chez les femelles que chez les mâles. Les caracteres sexuels relies aux genitalia varient plus d'une population a l'autre que les autres caracteres. L'analyse de l'autocorrelation spatiale a demontre qu'il n'y a pas de tendance geographique particuliere des genitalia femelles, alors qu'il existe une importante autocorrelation dans le cas des genitalia mâles. Les resultats semblent indiquer que le pattern d'autocorrelation observe dans le cas des genitalia mâles est attribuable a une preference non apparente des femelles pour certains mâles, alors que la derive genetique au hasard ou alors un effet important de l'environnement semble avoir cree le pattern geographique relie aux genitalia femelles. (Traduit par la Redaction) Tatsuta and Akimoto 1455

Using the magnetic particles method, we isolated six polymorphic microsatellite loci from an apterous grasshopper, Podisma kanoi Strozhenko, which shows conspicuous structural variation in chromosomes. The isolated loci were polymorphic, with three to 10 alleles among 20 individuals. Expected heterozygosities ranged from 0.23 to 0.90. These loci can be used to examine the history of population fragmentation and the establishment of chromosomal variation.

Understanding why some hybrid zones are bimodal and others unimodal can aid in identifying barriers to gene exchange following secondary contact. The hybrid zone between the grasshoppers Chorthippus brunneus and C. jacobsi contains a mix of allopatric parental populations and inter-mingled bimodal and unimodal sympatric populations, and provides an ideal system to examine the roles of local selection and gene flow between populations in maintaining bimodality. However, it is first necessary to confirm, over a larger spatial scale, previously identified associations between population composition and season and habitat. Here we use cline-fitting of one morphological and one song trait along two valley transects, and intervening mountains, to confirm previously identified habitat associations (mountain versus valley) and seasonal changes in population composition. As expected from previous findings of studies on a smaller spatial scale, C. jacobsi dominated mountain habitats and mixed populations dominated valleys, and C. brunneus became more prevalent in August. Controlling for habitat and incorporating into the analysis seasonal changes in cline parameters and the standard errors of parental trait values revealed wider clines than previous studies (best estimates of 6.4 to 24.5 km in our study versus 2.8 to 4.7 km in previous studies) and increased percentage of trait variance explained (52.7% and 61.5% for transects 1 and 2 respectively, versus 17.6%). Revealing such strong and consistent patterns within a complex hybrid zone will allow more focused examination of the causes of variation in bimodality in mixed populations, in particular the roles of local selection versus habitat heterogeneity and gene flow between differentiated populations.

We isolated eight polymorphic microsatellite loci from the zooplankton Moina macrocopa (Straus), which is sensitive to pollutants such as insecticides and heavy metals. The isolated loci were polymorphic, with three to seven alleles among 23 individuals. Expected heterozygosities ranged from 0.167 to 0.787. These loci can be used to examine cryptic genetic structure and to infer the connectivity among metapopulations.

The genetic structure of populations is not necessarily reflected in the geographical proximity of individuals, because environmental gradients such as those of vegetation or climate can function as cryptic barriers to gene flow. We examined polymorphisms at nine microsatellite loci to determine and discuss whether a distinctive genetic structure was detectable in a spatially continuous population of the sika deer (Cervus nippon) on the Boso Peninsula of central Japan. Spatially explicit Bayesian analysis revealed that two genetically distinctive clusters exist in the Boso population. The spatial boundary of the two clusters approximately conformed to the border defined previously from a mitochondrial DNA dataset. By combining information on the geomorphic features surrounding the boundary and that on the lineage of 1970s population, we propose a schematic scenario for characterizing the population genetic structure to the present. The current population consists of genetically different lineages, and spatially discontinuous clusters have come into contact in the vicinity of a local road running along a steep-walled ravine that could act as principal barrier to gene flow. Biological factors such as distribution of vegetation and philopatric behavior might also have helped strengthen the cryptic genetic structure of the Boso population.

Drosophila simulans strains originating from Madagascar and nearby islands in the Indian Ocean often differ from those elsewhere in the number of sex comb teeth and the degree of morphological anomaly in hybrids with D. melanogaster. Here, we report a strong segregation distortion in the F1 intercross between two D. simulans strains originating from Madagascar and the US, possibly at both the gametic and zygotic levels. Strong bias against alleles of the Madagascar strain was observed for all ten marker loci distributed over the entire second chromosome in the F1 intercross, but only a few showed a weak distortion in the isogenic backgrounds of either strains. Significant deviations of genotype frequencies from Hardy-Weinberg proportions were consistently observed for the second chromosome. By contrast, the X and third chromosomes did not show any strong segregation distortion. Crossover frequency on the second chromosome was uniformly reduced in isogenic backgrounds whereas the map lengths in the F1 intercross were comparable to or larger than that of the standard D. melanogaster map. We discuss these findings in relation to previous studies on other traits and interspecific differences between D. mauritiana, which is endemic to Mauritius Island, and D. simulans.

Fish embryo toxicology is important because embryos are considered more susceptible than adult fish to the effects of toxic chemicals. Recently, fish embryo bioassay was proposed to replace the conventional fish acute toxicity chemical test of the Organization for Economic Cooperation and Development guidelines because it offers the advantages of fewer reagents, easy handling, and efficient data production. To accelerate the establishment of a chemical toxicity database for the protection of environmental and human health, we need to determine whether the conventional toxicity test can safely be replaced by such fish embryo toxicity tests. For instance, it is unclear how the presence of the chorion moderates the toxic effects of some chemicals. If such chemical toxicities do differ between embryos and, for example, the larval stage, then different toxic effects should appear in later life. We tested the later-life effects of the neurotoxic insecticide carbaryl at sublethal concentrations (0 [control] and 5 and 10 mg/L) in embryos and posthatch larvae of the freshwater fish medaka, Oryzias latipes. Although embryos exposed until hatching showed multiple developmental malformations and reductions in subsequent survival rates over three months, no significant reduction was observed in tolerance to starvation for 7 d and in intrinsic population growth rate (r). Exposure of larvae for 96 h resulted in dose-responsive vertebral fracture, significant reduction in tolerance to starvation for 7 d, and reduced three-month survival rate; r was reduced significantly and consistently. These results suggested that posthatch larvae were more susceptible than embryos to carbaryl exposure and that the toxic cascades may differ between larvae and embryos. The influences of carbaryl exposure on population growth rate differed significantly with developmental stage.

A DNA library derived from the B chromosome of Podisma kanoi was obtained by chromosome microdissection. A total of 153 DNA clones were isolated from the microdissected DNA library. Twenty of them were sequenced. A comparison of B chromosome DNA sequences with sequences of other species from the DDBJ/GenBank/EMBL database ( http://www.ddbj.nig.ac.jp/ ) was performed. Different patterns of signals were observed after FISH with labeled cloned DNA fragments. FISH signals with cloned DNA fragments painted either whole Bs or their different regions. Some clones also gave signals in pericentromeric regions of A chromosomes. Other cloned DNA fragments gave only background-like signals on A and B chromosomes. Comparative FISH analysis of B chromosomes in Podisma kanoi and P. sapporensis with DNA probes derived from the Bs of these species revealed homologous DNA that was confined within pericentromeric and telemetric regions of the B chromosome in P. kanoi. In contrast to the B chromosomes in P. sapporensis containing large regions enriched with rDNA, only a small cluster of rDNA was detected in one of the examined B chromosomes in P. kanoi. The data strongly suggest an independent origin of B chromosomes in two closely related Podisma species.

We examined cytochrome P450 production and activity and circulating hormone concentrations in male medaka exposed to 17beta-estradiol (E2) or 17alpha-ethinylestradiol (EE2). Intraperitoneal injection of E2 at 1, 10, or 100 microg/g-fish completely suppressed CYP3A38 protein production and suppressed CYP3A40 protein levels by 89%, 52%, or 47%, respectively. CYP3A38 and CYP3A40 mRNA expression was unaltered, and CYP3A enzymatic activity initially increased and then decreased with increasing E2 dose. Males co-cultured with females were exposed to a markedly high concentration (43 ng/L) of E2 secreted by females. CYP3A protein levels in co-cultured males were suppressed. Serum testosterone (TE) and 11keto-testosterone levels in co-cultured males were downregulated to 40% of pre-exposure levels. Serum E2 levels increased in co-cultured males or males exposed to EE2. Testicular CYP19, which converts TE to E2, increased by 9.5 times in males exposed to 50 ng/L EE2 and by 21.5 times in those exposed to 100 ng/L EE2. Male medaka exposed to EE2 showed increased serum Vtg levels. Estrogenic exposure induced Vtg production, suppressed CYP3A protein production, downregulated TE metabolism, and enhanced CYP19 activity. Serum E2 endogenously induced by CYP19 could contribute to Vtg induction in male medaka.

Moths use ultrasounds as well as pheromones for sexual communication. In closely related moth species, variations in ultrasounds and pheromones are likely to profoundly affect mate recognition, reproductive isolation, and speciation. The European corn borer, Ostrinia nubilalis, and its Asian congeners, Ostrinia furnacalis and Ostrinia scapulalis, exhibit within-species and between-species variation in their pheromone communication. Recently, we reported ultrasound communication in O. furnacalis; however, variations in ultrasounds in the three congeners have not been addressed to date. Here we investigated features of ultrasound production and hearing in O. nubilalis and O. scapulalis, and compared them with those of O. furnacalis. As in O. furnacalis, males of O. nubilalis and O. scapulalis produced ultrasounds during courtship by rubbing specialized scales on the wings against scales on the thorax. The covering of these scales with nail polish muffled the sounds and significantly reduced mating success in O. nubilalis, showing the importance of ultrasound signaling in mating. The ultrasounds produced by O. nubilalis and O. scapulalis were similar, consisting of long trains of pairs of pulses with a main energy at 40 kHz, but distinctly different from the ultrasound produced by O. furnacalis, consisting of groups of pulses peaking at 50 kHz and with substantially more energy up to 80 kHz. Despite overall similarities, temporal features and patterns of amplitude modulation differed significantly among the geographic populations of O. nubilalis and O. scapulalis, which differed in pheromone type. In contrast, no significant difference in hearing was found among the three species with regard to the most sensitive frequencies and hearing threshold levels. The patterns of variations in the songs and pheromones well reflected those of the phylogenetic relationships, implying that ultrasound and pheromone communications have diverged concordantly. Our results suggest that concordant evolution in sexual signals such as courtship ultrasounds and sex pheromones occurs in moths.