Biology subjects

Boulton, R. A.

Publications and source records attributed to Boulton, R. A..

4 recordsLinked to original sources

bioRxiv2026

Mating allows asexual female wasps to produce offspring both sexually and asexually, but their sexual daughters have reduced fecundity

Sexual reproduction is widespread despite being less efficient than asexual reproduction. While its long-term evolutionary benefits are well recognized, it remains unclear why facultative sex, which should allow lineages to balance the advantages of both sexual and asexual reproduction, is not more common. One potential reason is that intermittent sex imposes novel costs compared to obligate sex, limiting the persistence of facultatively sexual lineages and constraining introgression. We test this possibility using the sexually polymorphic aphid parasitoid wasp Lysiphlebus fabarum. We reared offspring from females who reproduced asexually or by facultative sex for three generations (without sex after the founding generation). We genotyped F1 females to confirm facultative sex and used antennomere number, a phenotypic marker associated with reproductive mode, to test whether mixed sexual-asexual genotypes could be tracked across generations. We found multiple barriers to facultative sex. Mating did not always result in offspring with sexual-asexual genotypes, and when sex did occur, broods were usually comprised of asexually and sexually produced offspring. Additionally, lineages founded by females produced through facultative sex showed reduced fecundity compared to asexually produced broods. We saw declining frequencies of the sexual antenna phenotype in the generations after facultative sex, suggesting that genotypes generated by facultative sex are selected against. Overall, our results provide empirical support for the idea that facultative sex can impose costs that persist beyond the initial sexual event. These costs, together with low realised rates of sex, may limit long-term introgression and explain why facultative sex appears rare compared to obligate sex.

evolutionary biology↗

bioRxiv2024

Nevertheless sex persisted: facultative sex persists despite high costs in a sexually polymorphic aphid parasitoid

The prevalence of sexual reproduction has long puzzled evolutionary biologists. This is because asexual reproduction is a far more efficient way to transmit copies of ones own genome to the next generation, and, all-else-being-equal, should predominate over sex. Asexual reproduction is not without its disadvantages though, the lack of genetic recombination can render parthenogenetic lineages vulnerable to extinction under environmental change, or compromise fitness due to the buildup of deleterious recessive mutations. Facultative sex, where individuals retain the ability to reproduce sexually and asexually, has been touted as the best of both worlds, providing the long-term genetic benefits of sex without the short-term costs. In this study I tested whether sex is facultative in the aphid parasitoid Lysiphlebus fabarum, and if so whether facultative sex is the best of both worlds. I found that females from asexual populations mate with males produced by females from an obligately sexual population, and produced offspring with paternal genetic contributions, confirming facultative sex in this species. I then assayed the fitness of these facultatively sexual wasps and found, contrary to predictions that they actually had significantly lower fitness than asexual or obligately sexual females, as their daughters were up to 40% more likely to fail to reproduce entirely. In contrast, obligately sexual females were not at a disadvantage compared to asexual females in this species; they had increased fecundity compared to asexual females which compensated for the costs of sex. In L. fabarum it seems that all is not equal; the fecundity advantage that obligate sex provides, along with the costs of occasional facultative sex by asexuals may balance the scales and allow stable coexistence of the different reproductive modes in nature.

evolutionary biology↗

bioRxiv2023

Genetic differentiation at extreme latitudes in the socially plastic sweat bee Halictus rubicundus

The sweat bee Halictus rubicundus is an important pollinator with a large latitudinal range and many potential barriers to gene flow. Alongside typical physical barriers, including mountain ranges and oceans, the climate may also impose restrictions on gene flow in this species. The climate influences voltinism and sociality in H. rubicundus, which is bivoltine and can nest socially at lower latitudes but can be univoltine and solitary in the north of its range and at higher altitudes where the climate is cooler. Variation in voltinism due to the climate may result in differences in phenology between populations across this species geographical range. Differences in phenology could limit gene flow, rendering populations at extreme latitudes genetically isolated and potentially more vulnerable to environmental stressors. A previous study found that the Irish Sea restricts gene flow in this species, but there was no evidence that differences in phenology had a similar effect as there was no genetic differentiation between H. rubicundus populations on mainland Britain. Here we extend the previous study to consider populations of H. rubicundus at extreme northern and southern latitudes in the UK. Using 12 microsatellite markers for genotyping, we found that bees from a population in the far north of Scotland were genetically differentiated from bees collected in Cornwall in the south-west of England. In contrast, bees collected across the Irish Sea in Northern Ireland showed genetic overlap with both the Scottish and Cornish bees. Our results suggest that when populations at extreme latitudes are considered, phenology and the climate may act alongside physical barriers such as the Scottish Highlands and the Irish Sea to restrict gene flow in H. rubicundus. We discuss the implications of our results for local adaptation in the face of rapidly changing selection pressures which are likely under climate change.

genetics↗

bioRxiv2022

Sensory plasticity in a socially plastic bee

AO_SCPLOWBSTRACTC_SCPLOWThe social Hymenoptera have contributed much to our understanding of the evolution of sensory systems. Attention has focussed chiefly on how sociality and sensory systems have evolved together. In the Hymenoptera, the antennal sensilla are important for optimising the perception of olfactory social information. Social species have denser antennal sensilla than solitary species, which is thought to enhance social cohesion through nest-mate recognition. In the current study, we test whether sensilla numbers vary between populations of the socially plastic sweat bee Halictus rubicundus from regions that vary in climate and the degree to which sociality is expressed. We found region level differences in both olfactory and hygro/thermoreceptive sensilla numbers. We also found evidence that olfactory sensilla density is developmentally plastic: when we transplanted bees from Scotland to the south-east of England, their offspring (which developed in the south) had more olfactory hairs than the transplanted individuals themselves (which developed in Scotland). The transplanted bees displayed a mix of social (a queen plus workers) and solitary nesting, but neither individual nor nest phenotype was related to sensilla density. We suggest that this general, rather than caste-specific sensory plasticity provides a flexible means to optimise sensory perception according to the most pressing demands of the environment. Sensory plasticity may support social plasticity in H. rubicundus but does not appear to be causally related to it.

evolutionary biology↗