Intralocus sexual conflict and offspring sex ratio

Males and females frequently have different fitness optima for shared traits, and as a result, genotypes that are high fitness as males are low fitness as females, and vice versa. When this occurs, biasing of offspring sex-ratio to reduce the production of the lower-fitness sex would be advantageous, so that for example, broods produced by high-fitness females should contain fewer sons. We tested for offspring sex-ratio biasing consistent with these predictions in broad-horned flour beetles. We found that in both wild-type beetles and populations subject to artificial selection for high- and low-fitness males, offspring sex ratios were biased in the predicted direction: low-fitness females produced an excess of sons, whereas high-fitness females produced an excess of daughters. Thus, these beetles are able to adaptively bias sex ratio and recoup indirect fitness benefits of mate choice.     

Determinants of male fitness: disentangling intra- and inter-sexual selection

Both intra- and inter-sexual selection may crucially determine a male's fitness. Their interplay, which has rarely been experimentally investigated, determines a male's optimal reproductive strategy and thus is of fundamental importance to the understanding of a male's behaviour. Here we investigated the relative importance of intra- and inter-sexual selection for male fitness in the common lizard. We investigated which male traits predict a male's access to reproduction allowing for both selective pressures and comparing it with a staged mating experiment excluding all types of intra-sexual selection. We found that qualitatively better males were more likely to reproduce and that sexual selection was two times stronger when allowing for both selective pressures, suggesting that inter- and intra-sexual selection determines male fitness and confirming the existence of multi-factorial sexual selection. Consequently, to optimize fitness, males should trade their investment between the traits, which are important for inter- and intra-sexual selection.     

黑龙江省产胎生蜥蜴的染色体组型研究

本文采用骨髓细胞制片法对分布在黑龙江省孙吴县的胎生蜥蜴染色体组型进行了研究,结果表明其雄性的二倍体染色体数是36,性染色体为ZZ型,2n=34＋ZZ;雌性的二倍体染色体数是35,性染色体为W型,2n=34＋W;所以胎生蜥蜴的性别决定机制为ZZ/W型.胎生蜥蜴的染色体全部为顶端着丝点染色体（除雌性的第5号染色体为亚端着丝点染色体外）,根据其染色体的形态、大小将其配成18对,按照染色体的相对长度把它们分成3组,第Ⅰ组只有第1对染色体（相对长度＞9.0%）,第Ⅱ组包括第2、3和4对染色体（9.0%＞相对长度＞7.0%）,第Ⅲ组包括第5～18对染色体（相对长度＜7.0%）.     

Points of view: Why male cannibalism won't cause a female-biased OSR -- a comment on Smith and Wootton's paper

Reviews in Fish Biology and Fisheries -     

Points of view: Cannibalism and OSR -- a response to Kvarnemo

Reviews in Fish Biology and Fisheries -     

The kin structure of sexual interactions

The origin of sexual reproduction involved the evolution of zygotes from separate genomes and, like other social processes, should therefore be amenable to analysis using kin selection theory. I consider how kin structure affects sexual interactions in three contexts—the evolution of sexual reproduction, sex allocation and sexual conflict. Kin structure helps explain the even-handed replication of paternal and maternal genes under outbreeding. Under inbreeding, it predicts altruistic failure to replicate by one half of the diploid genome. Kin structure predicts optimal sex ratios and potential conflicts over sex ratio within social groups and individuals. Sexual conflict predictably occurs as a function of (i) the probability that current sexual partners will reproduce together in future and (ii) between-partner relatedness. I conclude that systematically analysing the kin structure of sexual interactions helps illuminate their evolution.     

Reproductive skew drives patterns of sexual dimorphism in sponge-dwelling snapping shrimps

Sexual dimorphism is typically a result of strong sexual selection on male traits used in male–male competition and subsequent female choice. However, in social species where reproduction is monopolized by one or a few individuals in a group, selection on secondary sexual characteristics may be strong in both sexes. Indeed, sexual dimorphism is reduced in many cooperatively breeding vertebrates and eusocial insects with totipotent workers, presumably because of increased selection on female traits. Here, we examined the relationship between sexual dimorphism and sociality in eight species of Synalpheus snapping shrimps that vary in social structure and degree of reproductive skew. In species where reproduction was shared more equitably, most members of both sexes were physiologically capable of breeding. However, in species where reproduction was monopolized by a single individual, a large proportion of females—but not males—were reproductively inactive, suggesting stronger reproductive suppression and conflict among females. Moreover, as skew increased across species, proportional size of the major chela—the primary antagonistic weapon in snapping shrimps—increased among females and sexual dimorphism in major chela size declined. Thus, as reproductive skew increases among Synalpheus, female–female competition over reproduction appears to increase, resulting in decreased sexual dimorphism in weapon size.     

The mismeasurement of sexual selection

Sexual selection can explain major micro‐ and macro‐evolutionary patterns. Much of current theory predicts that the strength of sexual selection (i) is driven by the relative abundance of males and females prepared to mate (i.e. the operational sex ratio, OSR) and (ii) can be generally estimated by calculating intra‐sexual variation in mating success (e.g. the opportunity for sexual selection, I_s). Here, we demonstrate the problematic nature of these predictions. The OSR and I_s only accurately predict sexual selection under a limited set of circumstances, and more specifically, only when mate monopolization is extremely strong. If mate monopolization is not strong, using OSR or I_s as proxies or measures of sexual selection is expected to produce spurious results that lead to the false conclusion that sexual selection is strong when it is actually weak. These findings call into question the validity of empirical conclusions based on these measures of sexual selection.     

Food affects the potential reproductive rates of sand goby females but not of males

The interspawning interval of female sand gobies, Pomatoschistusminutus, a batch-spawning fish with paternal care, was significantlyshorter when the fish were fed daily than when they were fedevery fourth day. The incubation time of males was not affectedby feeding, nor was the interbrood interval Males have an equalor higher potential reproductive rate than females. As femalesreproduce more slowly when food is scarce than when it is abundant,and males do not, the difference between the sexes in potentialreproductive rate increases when there is food shortage. Becauseof this difference, both male bias in operational sex ratioand intensity in male-male competition for mates are predictedto increase as food availability decreases. Furthermore, a tradeoffbetween current and future reproduction is demonstrated to operateonly when resources are limited, because the correlation betweenegg number of the first and second clutch was positive amonghigh-food females but negative among low-food females. The numberof eggs per female clutch did, however, not differ between treatmentsin first or second dutch. I conclude that operational sex ratioand sexual selection are expected to vary within and betweensand goby populations in accordance with prey availability     

Crowding, sex ratio and horn evolution in a South African beetle community

Sexually selected ornaments and weapons are exceptionally variable, even between closely related species. It has long been recognized that some of this diversity can be explained by differences in mating systems between species, but there remains substantial variation between species with similar mating systems. We investigated the roles of sex ratio (measured as operational sex ratio, OSR) and population density (measured as mean male crowding, a measure indicating the average number of conspecific males that an individual male animal will encounter) in determining horn presence in a community of South African dung beetles. Analysis of data from 14 species using a generalized least-squares model incorporating phylogenetic influences found that both OSR and mean crowding were significant predictors of horn presence, with hornless species tending to show female-biased sex ratios and high levels of crowding. The influence of mean crowding on horn diversity between species probably reflects the difficulty of guarding and monopolizing females when many competitors are present, meaning that males who adopt 'scramble' tactics tend to be favoured.