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Genetic variance ( V G ) in fitness related traits is often unexpectedly high, evoking the question how V G can be maintained in the face of selection. Sexually antagonistic (SA) selection favouring alternative alleles in the sexes is common and predicted to maintain V G , while directional selection should erode it. Both SA and sex-limited directional selection can lead to sex-specific adaptations but how each affect V G when sexual dimorphism evolves remain experimentally untested. Using replicated artificial selection on the seed beetle Callosobruchus maculatus body size we recently demonstrated an increase in size dimorphism under SA and male-limited (ML) selection by 50% and 32%, respectively. Here we test their consequences on genetic variation . We show that SA selection maintained significantly more ancestral, autosomal additive genetic variance than ML selection, while both eroded sex-linked additive variation equally. Ancestral female-specific dominance variance was completely lost under ML, while SA selection consistently sustained it. Further, both forms of selection preserved a high genetic correlation between the sexes ( r m,f ). These results demonstrate the potential for sexual antagonism to maintain more genetic variance while fuelling sex-specific adaptation in a short evolutionary time scale, and are in line with predicted importance of sex-specific dominance reducing sexual conflict over alternative alleles.

Phytoplasmas are bacterial pathogens located in the plant’s phloem that are responsible for several plant diseases and are mainly transmitted by phloem-sucking insects. Apple proliferation (AP) is an economically important disease caused by ‘CandidatusPhytoplasma mali’ which is transmitted by two psyllid species. While Cacopsylla picta is a confirmed vector in different regions, the vector efficiency of Cacopsylla melanoneura varies between different populations. This species is considered the main AP vector in Northwestern Italy but plays a minor role in Northeastern Italy and other European regions. To investigate whether the psyllid and/or the phytoplasma subtype drive the phytoplasma acquisition in C. melanoneura, we set-up a phytoplasma acquisition experiment using single mating couples including different psyllid populations and phytoplasma subtypes. All analyzed insect populations acquired phytoplasma, but with different efficiencies and concentrations. The main factors driving the acquisition were the phytoplasma subtype and its concentration in the leaves of the infected trees together with the psyllid family. The phytoplasma concentration in the psyllids was again influenced by the phytoplasma subtype, the psyllid family and the region of origin, whereas the phytoplasma concentration in the leaves and the psyllid haplotype defined with the cytochrome oxidase I gene had only a minor impact on the phytoplasma concentration. This is the first study evaluating the roles of both the psyllid haplotype and the phytoplasma subtype on the acquisition process shedding new light on the importance of C. melanoneura as AP vector.

All too often, studies of sexual selection focus exclusively on the responses in one sex, on single traits, typically those that are exaggerated and strongly sexually dimorphic. They ignore a range of less obvious traits and behavior, in both sexes, involved in the interactions leading to mate choice. To remedy this imbalance, we analyze a textbook example of sexual selection in the stalk‐eyed fly (Diasemopsis meigenii). We studied several traits in a novel, insightful, and efficient experimental design, examining 2,400 male–female pairs in a “round‐robin” array, where each female was tested against multiple males and vice versa. In D. meigenii, females exhibit strong mate preference for males with highly exaggerated eyespan, and so we deliberately constrained variation in male eyespan to reveal the importance of other traits. Males performing more precopulatory behavior were more likely to attempt to mate with females and be accepted by them. However, behavior was not a necessary part of courtship, as it was absent from over almost half the interactions. Males with larger reproductive organs (testes and accessory glands) did not make more mating attempts, but there was a strong tendency for females to accept mating attempts from such males. How females detect differences in male reproductive organ size remains unclear. In addition, females with larger eyespan, an indicator of size and fecundity, attracted more mating attempts from males, but this trait did not alter female acceptance. Genetic variation among males had a strong influence on male mating attempts and female acceptance, both via the traits we studied and other unmeasured attributes. These findings demonstrate the importance of assaying multiple traits in males and females, rather than focusing solely on prominent and exaggerated sexually dimorphic traits. The approach allows a more complete understanding of the complex mating decisions made by both males and females.

There is considerable debate over the value of male sexual ornaments as signals of genetic quality. Studies alternately report that environmental variation enhances or diminishes the genetic signal, or leads to crossover where genotypes perform well in one environment but poorly in another. A unified understanding is lacking. We conduct the first experimental test examining the dual effects of distinct low and high genetic quality (inbred versus crossed parental lines) and low, through high, to extreme environmental stress (larval diets) on a condition-dependent male ornament. We find that differences in genetic quality signalled by the ornament (male eyespan inDiasemopsis meigeniistalk-eyed flies) become visible and are amplified under high stress but are overwhelmed in extreme stress environments. Variance among distinct genetic lines increases with environmental stress in both genetic quality classes, but at a slower rate in high quality outcrossed flies. Individual genetic lines generally maintain their ranks across environments, except among high quality lines under low stress conditions, where low genetic variance precludes differentiation between ranks. Our results provide a conceptual advance, demonstrating a unified pattern for how genetic and environmental quality interact. They show when environmental conditions lead to the amplification of differences in signals of genetic quality and thereby enhance the potential indirect genetic benefits gained by female mate choice.

Meiotic recombination is crucial for chromosomal segregation, and facilitates the spread of beneficial and removal of deleterious mutations. Recombination rates frequently vary along chromosomes andDrosophila melanogasterexhibits a remarkable pattern. Recombination rates gradually decrease towards centromeres and telomeres, with dramatic impact on levels of variation in natural populations. Two close sister species,D. simulansandD. mauritianado not only have higher recombination rates, but also exhibit a much more homogeneous recombination rate that only drops sharply close to centromeres and telomeres. Because certain sequence motifs are associated with recombination rate variation inD. melanogaster, we tested whether the difference in recombination landscape betweenD. melanogasterandD. simulanscan be explained by the genomic distribution of recombination-rate associated sequence motifs. We constructed the first high resolution recombination map forD. simulans, and searched for motifs linked with high recombination in both sister species. We identified five consensus motifs, present in either species. While the association between motif density and recombination is strong and positive inD. melanogaster, the results are equivocal inD. simulans. Despite the strong association inD. melanogaster, we do not find a decreasing density of these repeat motifs towards centromeres and telomeres. We conclude that the density of recombination-associated repeat motifs cannot explain the large-scale recombination landscape inD. melanogaster, nor the differences toD. simulans. The strong association seen for the sequence motifs inD. melanogasterlikely reflects their impact influencing local differences in recombination rates along the genome.

SummaryA classic paradox in sexual selection is how sexual traits under strong directional selection maintain underlying genetic variation. A new study has found that in Soay sheep a trade-off between reproductive success and survival maintains variation in horn size.