Biology subjects

Abbott, J. K.

Publications and source records attributed to Abbott, J. K..

7 recordsLinked to original sources

bioRxiv2022

Rapid evolution of sex role specialization in a hermaphrodite under sex-limited selection

The evolution of separate sexes from hermaphroditism is thought to have occurred independently many times, and is linked to the evolution of sex chromosomes. Even though we have a good understanding of the theoretical steps in the evolution of sex chromosomes from a hermaphrodite ancestor, the initial stages are still hard to study because many sex chromosome systems are old. We addressed this problem by experimentally selecting a hermaphrodite via sex-limited experimental evolution for several generations, simulating the early stages in the evolution of a sex chromosome. More specifically, we used a GFP (green fluorescent protein) marker as a proxy for a sex-determining locus, and selected replicate populations of the simultaneously hermaphroditic flatworm Macrostomum lignano for fitness via the male sex role, female sex role, or both (i.e. a control). After 14 generations, a fitness assay revealed clear evidence for incipient sex role specialization, presumably reflecting the release from constraints usually imposed by selection on the other sex role. Importantly, however, this was not simply explained by differential sex allocation in the different selection regimes - insofar as morphological traits reflect the underlying trade-off over resource allocation to the male and female sex functions - because testis and ovary sizes did not diverge among treatments. Our study shows that sex role specialization can occur rapidly as a result of sex-limited selection, which is consistent with genetic constraints between sex-roles, and in line with the first predicted steps towards the evolution of a new sex chromosome system.

evolutionary biology↗

bioRxiv2021

Drosophila Evolution over Space and Time (DEST) - A New Population Genomics Resource

Drosophila melanogaster is a leading model in population genetics and genomics, and a growing number of whole-genome datasets from natural populations of this species have been published over the last 20 years. A major challenge is the integration of these disparate datasets, often generated using different sequencing technologies and bioinformatic pipelines, which hampers our ability to address questions about the evolution and population structure of this species. Here we address these issues by developing a bioinformatics pipeline that maps pooled sequencing (Pool-Seq) reads from D. melanogaster to a hologenome consisting of fly and symbiont genomes and estimates allele frequencies using either a heuristic (PoolSNP) or a probabilistic variant caller (SNAPE-pooled). We use this pipeline to generate the largest data repository of genomic data available for D. melanogaster to date, encompassing 271 population samples from over 100 locations in >20 countries on four continents based on a combination of 121 unpublished and 150 previously published genomic datasets. Several of these locations have been sampled at different seasons across multiple years. This dataset, which we call Drosophila Evolution over Space and Time (DEST), is coupled with sampling and environmental meta-data. A web-based genome browser and web portal provide easy access to the SNP dataset. Our aim is to provide this scalable platform as a community resource which can be easily extended via future efforts for an even more extensive cosmopolitan dataset. Our resource will enable population geneticists to analyze spatio-temporal genetic patterns and evolutionary dynamics of D. melanogaster populations in unprecedented detail.

genomics↗

bioRxiv2020

Feminisation of complex traits in Drosophila melanogaster via female-limited X chromosome evolution

A handful of studies have investigated sexually antagonistic constraints on obtaining sex-specific fitness optima, though exclusively through male-genome-limited evolution experiments. In this paper, we established a female-limited X chromosome evolution experiment, where we used an X chromosome balancer to enforce the inheritance of the X chromosome through the matriline, thus removing exposure to male selective constraints. This approach eliminates the effects of sexually antagonistic selection on the X chromosome, permitting evolution towards a single sex-specific optimum. After multiple generations of selection, we found strong evidence that body size and development time had moved towards a female-specific optimum, whereas reproductive fitness and locomotion activity remained unchanged. The changes in body size and development time are consistent with previous results, and suggest that the X chromosome is enriched for sexually antagonistic genetic variation controlling these traits. The lack of change in reproductive fitness and locomotion activity could be due to a number of mutually non-exclusive explanations, including a lack of sexually antagonistic variance on the X chromosome or confounding effects of the use of the balancer chromosome. This study is the first to employ female-genome-limited selection and adds to the understanding of the complexity of sexually antagonistic genetic variation.

evolutionary biology↗

bioRxiv2020

The evolution of suppressed recombination between sex chromosomes by chromosomal inversions

The idea that sex-differences in selection drive the evolution of suppressed recombination between sex chromosomes is well-developed in population genetics. Yet, despite a now classic body of theory, empirical evidence that sexual antagonism drives the evolution of recombination suppression remains meagre and alternative hypotheses underdeveloped. We investigate whether the length of evolutionary strata formed by chromosomal inversions that expand the non-recombining sex determining region (SDR) on recombining sex chromosomes can offer an informative signature of whether, and how, selection influenced their fixation. We develop population genetic models that determine how the length of a chromosomal inversion that expands the SDR affects its fixation probability for three categories of inversions: (i) neutral, (ii) directly beneficial (i.e., due to breakpoint or position effects), and (iii) indirectly beneficial (especially those capturing sexually antagonistic loci). Our models predict that neutral inversions should leave behind a unique signature of large evolutionary strata, and that it will often be difficult or impossible to distinguish between smaller strata created by directly or indirectly beneficial inversions. An interesting and unexpected prediction of our models is that the physical location of the ancestral SDR on the sex chromosomes is the most important factor influencing the relation between inversion size and the probability of expanding the SDR. Our findings raise a suite of new questions about how physical as well as selective processes influence the evolution of recombination suppression between sex chromosomes.

evolutionary biology↗

bioRxiv2019

Sexually antagonistic coevolution between the sex chromosomes of Drosophila melanogaster

Antagonistic interactions between the sexes are important drivers of evolutionary divergence. Interlocus sexual conflict is generally described as a conflict between alleles at two interacting loci whose identity and genomic location are arbitrary. Here we build on previous theory and suggest that when these two loci are located on the sex chromosomes it can lead to cycles of antagonistic coevolution between them, and therefore between the sexes. We tested this hypothesis by performing experimental crosses using Drosophila melanogaster in which we reciprocally exchanged the sex chromosomes between five wild-type populations in a round-robin design. Disrupting putatively coevolved sex chromosome pairs resulted in increased male reproductive success in 16 out of 20 experimental populations (10 of which were significant), but also resulted in lower offspring egg-to-adult viability that affected both male and female fitness. After 25 generations of experimental evolution these sexually antagonistic fitness effects appeared to have been resolved. To help formalise our hypothesis, we developed population genetic models of antagonistic coevolution using fitness expressions based on our empirical results. Our models support the conclusion that antagonistic coevolution between the sex chromosomes is plausible under the fitness effects observed in our experiments. Together, our results lend both empirical and theoretical support to the idea that a cycle of antagonistic coevolution can occur between sex chromosomes and illustrates how this process may drive genetic and phenotypic divergence between populations. SignificanceSex chromosomes are not only involved in genetic sex determination - they are also important factors in sexual conflict and speciation. Here, using a combination of experiments and population genetic models, we show that the sex chromosomes in Drosophila melanogaster can coevolve antagonistically. We found that swapping sex chromosomes between five Drosophila melanogaster populations increased male fitness at the cost of reduced offspring survival. After 25 generations, the increase had disappeared, consistent with the completion of a cycle of antagonistic coevolution. Using parameter values based on these empirical data, our models show that antagonistic coevolution between the sex chromosomes is a biologically plausible explanation for the results. Thus, our results point to a potentially important path to speciation through sexual conflict.

evolutionary biology↗

bioRxiv2019

The microevolutionary response to male-limited X-chromosome evolution in Drosophila melanogaster reflects macroevolutionary patterns

Due to its hemizygous inheritance and role in sex determination, the X chromosome is expected to play an important role in the evolution of sexual dimorphism, and to be enriched for sexually antagonistic genetic variation. By forcing the X chromosome to only be expressed in males over >40 generations, we changed the selection pressures on the X to become similar to those experienced by the Y. This releases the X from any constraints arising from selection in females, and should lead to specialization for male fitness, which could occur either via direct effects of X-linked loci or trans-regulation of autosomal loci by the X. We found evidence of masculinization via upregulation of male-benefit sexually antagonistic genes, and downregulation of X-linked female benefit genes. Interestingly, we could detect evidence of microevolutionary changes consistent with previously documented macroevolutionary patterns, such as changes in expression consistent with previously established patterns of sexual dimorphism, an increase in the expression of metabolic genes related to mitonuclear conflict, and evidence that dosage compensation effects can be rapidly altered. These results confirm the importance of the X in the evolution of sexual dimorphism and as a source for sexually antagonistic genetic variation, and demonstrate that experimental evolution can be a fruitful method for testing theories of sex chromosome evolution.

evolutionary biology↗

bioRxiv2019

Genetic correlations across genetically determined and developmentally plastic alternative reproductive tactics

Alternative reproductive tactics occur when individuals of the same sex have a suite of morphological and/or behavioural traits that allow them to pursue different reproductive strategies. A common pattern is e.g. the existence of \"courter\" and \"sneaker\" tactics within males. We have previously argued that alternative reproductive tactics should be subject to genetic conflict over the phenotypic expression of traits, similar to sexual antagonism. In this process, which we called intra-locus tactical conflict, genetically determined tactics experience conflicting selection on a shared phenotypic trait, such as body size, but a positive genetic correlation between tactics in body size prevents either tactic from reaching its optimum. Recently, other authors have attempted to extend this idea to developmentally plastic alternative reproductive tactics, with mixed results. However, it is not clear whether we should expect intra-locus tactical conflict in developmentally plastic tactics or not. We have therefore run a series of simulation models investigating under what conditions we should expect to see positive estimates of the inter-tactical genetic correlation, since a positive genetic correlation is a prerequisite for the existence of intra-locus tactical conflict. We found that for autosomal, X-linked, and Y-linked genetically-determined tactics, estimated inter-tactical genetic correlations were generally high. However, for developmentally plastic tactics, the genetic correlation depends on the properties of the switching threshold between tactics. If it is fixed, then estimated genetic correlations are positive, but if there is genetic variation in the switch-point, then any sign and magnitude of estimated genetic correlation is possible, even for highly heritable traits where the true underlying correlation is perfect. This means that caution should be used when investigating genetic constraints in plastic phenotypes.

evolutionary biology↗