Biology subjects

Castillo, D. M.

Publications and source records attributed to Castillo, D. M..

9 recordsLinked to original sources

bioRxiv2026

Sexual interactions and local selection shape reproductive gene diversity and divergence

Genes involved in genotype x genotype coevolution display unique patterns of nucleotide diversity and population divergence. In Drosophila melanogaster, Sex Peptide is a key sperm competition gene that is an outlier for both pi within populations and Fst between populations. This pattern is not predicted by current theoretical expectations of selective sweeps highlighting the need to develop predictions to identify genes experiencing balancing selection. We compared pi and FST in D. melanogaster populations to identify other genes following a co-evolutionary model that generates divergence and diversity. Multiple male and female genes that interact with Sex Peptide exhibited elevated FST x pi values. Genome-wide analyses also revealed an enrichment of genes critical for neuronal development, pointing to courtship evolution. Specifically, fruitless, its interacting genes, and a female behavior gene were identified as outliers. These parallel findings indicate that both sperm competition and mating behaviors are subject to co-evolutionary selection.

evolutionary biology↗

bioRxiv2026

Female behavioral cues control male courtship plasticity independent of female pheromones in African Drosophila melanogaster

Sexual interactions involve the exchange of information-including olfactory, auditory, and visual cues-that has been shaped by sexual selection to maximize fitness. While these courtship signals and behaviors are often characterized as stereotypical and species-specific, male courtship is plastic and can depend on the population identity of the courted female. The ability of a male to adjust his courtship behavior based on female identity has significant implications for how selection operates on courtship, potentially driving behavioral divergence between populations and the eventual emergence of new species. A major challenge is identifying the cues that males use to adjust their courtship strategy. We used Drosophila melanogaster to investigate the mechanisms facilitating courtship plasticity, focusing on male song production. Male song is often considered the paramount behavior performed by males and is stimulated by female pheromones. Previous observations have focused on cosmopolitan (non-African) genotypes, whereas the singing rate and singing plasticity is highly variable in African populations. In genotypes from Zimbabwe, females have a different major pheromone compound (5,9-HD) compared to non-African females and show strong behavioral preference for Zimbabwe males. We created a Zimbabwe genotype lacking 5,9-HD by disrupting the gene desat2 in the Zimbabwe Z53 strain. We tested the hypothesis that Zimbabwe male courtship plasticity depends on female pheromones by allowing males to court non-African, wild type Z53, and Z53 desat2 null mutant females. We found that males treated Z53 desat2 null females like wild type Z53 females, not using pheromone cues to determine singing and courtship plasticity. This suggests that other female behavioral feedback influences singing plasticity. This courtship plasticity could contribute to the asymmetrical reproductive isolation between these populations and could provide insight to the broad pattern of asymmetrical reproductive isolation across broad taxonomic groups.

evolutionary biology↗

bioRxiv2025

Reinforcement and selection against migrants maintain sperm competitive and genetic differences among populations of Drosophila pseudoobscura

Sexual interactions among closely related species can select for divergence in reproductive traits as a mechanism to avoid the costs of hybridization. This selection, termed reinforcement, produces a canonical pattern of stronger isolation in populations that are sympatric with congeners, versus in allopatric populations. While reinforcement has been observed in many systems, the resulting pattern might be transient. There must be selection against migrants between allopatry and sympatry--akin to local reproductive adaptation--for a pattern of stronger sympatric isolation to be maintained. We tested for evidence of this selection against migrants in the context of sperm competition, in Drosophila pseudoobscura. Previously we showed an advantage of sympatric genotypes in sympatric contexts, via their elevated reproductive isolation (conspecific sperm precedence) against congeneric D. persimilis. Here, using experimental crosses that simulated migration between populations that are naturally sympatric and allopatric with D. persimilis, we show that sympatric genotypes are at a sperm-competitive disadvantage against allopatric male genotypes. This selection against sympatric males in allopatry, combined with the advantage of sympatric genotypes in sympatry, produce a scenario for strong selection against migrants between these two geographic contexts. This is accompanied by population differentiation in reproductive gene expression and allele frequency variation between allopatry and sympatry, including genes with known roles in sperm competition. While some of these changes are parallel among sympatric or allopatric contexts, most are unique to individual populations and might reflect the unique ways that selection has acted on sperm competition genes in different sympatric populations.

evolutionary biology↗

bioRxiv2022

The nerodevelopmental genes alan shepard and Neuroglian are spatially structured in an admixed population and contribute to female mate preference

Mate choice is a key trait that determines fitness for most sexually reproducing organisms, with females often being the choosy sex. Female preference often results in strong selection on male traits that can drive rapid divergence of traits and preferences between lineages, leading to reproductive isolation. Despite this fundamental property of female mate choice, very few loci have been identified that contribute to mate choice and reproductive isolation. We used a combination of population genetics, quantitative complementation tests, and behavioral assays to demonstrate that alan shepard and Neuroglian contribute to female mate choice, and could contribute to partial reproductive isolation between populations of Drosophila melanogaster. Our study is among the first to identify genes that contribute to female mate preference in this historically important system, where female preference is an active premating barrier to reproduction. The identification of loci that are primarily known for their roles in neurodevelopment provides intriguing questions of how female mate preference evolves in populations via changes in sensory system and higher learning brain centers.

evolutionary biology↗

bioRxiv2022

Testing the Drosophila maternal haploid gene for functional divergence and a role in hybrid incompatibility

Crosses between D. simulans females and D. melanogaster males produce viable F1 sons and poorly viable F1 daughters. Unlike most hybrid incompatibilities, this hybrid incompatibility violates Haldanes rule, the observation that incompatibilities preferentially affect the heterogametic sex. Further, it is important to understand fully the genetic basis of this incompatibility because the causal allele in D. melanogaster is a large species-specific block of complex satellite DNA on its X chromosome known as the 359-bp satellite, rather than a protein-coding locus. The causal allele(s) in D. simulans are unknown but likely involve maternally expressed genes or factors since the F1 females die during early embryogenesis. The maternal haploid (mh) gene is an intriguing candidate because it is expressed maternally and its protein product localizes to the 359-bp repeat. We found that this gene has diverged extensively between D. melanogaster and D. simulans. This observation led to the hypothesis that D. melanogaster mh may have co-evolved with the 359-bp repeat, and that hybrid incompatibility thus results from the absence of a co-evolved mh allele in D. simulans. We tested for functional divergence of mh by creating matched transformants of D. melanogaster and D. simulans orthologs in both D. melanogaster and D. simulans strains. Surprisingly, we find that D. simulans mh fully complements the female sterile phenotype of D. melanogaster mh mutations. Contrary to our hypothesis, we find no evidence that adding a D. melanogaster mh gene to D. simulans increases hybrid viability.

evolutionary biology↗

bioRxiv2021

Population structure and introgression among recently differentiated Drosophila melanogaster populations

Despite a century of genetic analysis, the evolutionary history underlying patterns of exceptional genetic and phenotypic variation in the model organism Drosophila melanogaster remains poorly understood. How genetic and phenotypic variation is partitioned across the range of D. melanogaster, particularly in its putative ancestral range in Subtropical Africa, remains unresolved. Here, we assess patterns of population genetic structure, admixture, mate preference, and genetic incompatibility across a global sample, including 174 new accessions from remote regions within Subtropical Africa. While almost all Out of Africa genomes correspond to a single genetic ancestry, different geographic regions within Africa contain multiple ancestries, with substantial cryptic diversity in Subtropical Africa. Admixture between distinct lineages is prevalent across the range, but admixture rates vary between lineages. Female mate choice within Subtropical Africa is highly polymorphic and behavioral types are not monophyletic. The genetic architecture of mate choice is highly polygenic, including loci associated with neurological development, behavior, olfactory perception, and learning. Finally, we discovered that many segregating putative incompatibilities likely evolved during or after expansion out of Africa. This work contributes to our understanding of the evolutionary history of a key model system, and provides insight into the distribution of polymorphic reproductive barriers.

evolutionary biology↗

bioRxiv2021

Testing potential mechanisms of conspecific sperm precedence in Drosophila pseudoobscura

Drosophila pseudoobscura females that co-occur with sister species D. persimilis show elevated fertilization by conspecific sperm when they mate with both a heterospecific and a conspecific male. This phenomenon, known as conspecific sperm precedence (CSP), has evolved as a mechanism to avoid maladaptive hybridization with D. persimilis. In this study, we assessed pericopulatory (during mating) and postcopulatory (after mating) traits in crosses with sympatric or allopatric D. pseudoobscura females and conspecific or heterospecific males to evaluate potential mechanisms of CSP in this system. We observed shorter copulation duration in crosses with sympatric females, but found no difference in quantity of sperm transferred or female reproductive tract toxicity between sympatry and allopatry. Our data also support the hypothesis that parasperm, a short, sterile sperm morph, can protect fertile eusperm from the D. pseudoobscura female reproductive tract, though it is unclear how this might affect patterns of sperm use in sympatry vs. allopatry. Overall, these results suggest that copulation duration could potentially contribute to the elevated CSP observed in sympatry.

evolutionary biology↗

bioRxiv2020

Divergent selection on behavioral and chemical traits contributes to isolation between populations of Drosophila melanogaster

Speciation is driven by traits that can act to prohibit mating between nascent lineages, including male courtship and female preference for male traits. Mating barriers involving these traits evolve quickly because there is strong selection on males and females to maximize reproductive success, and the tight co-evolution of mating interactions can lead to rapid diversification of sexual behavior. Using lineages of D. melanogaster that show strong asymmetrical reproductive isolation, we ask two key questions: which specific male traits are females selecting, and are these traits under divergent sexual selection? These questions have proven extremely challenging to answer, because even in closely related lineages males often differ in multiple traits related to mating behavior. We address these questions by estimating selection gradients for male courtship and cuticular hydrocarbons for two different female genotypes. We identify specific behaviors and particular cuticular hydrocarbons that are under divergent sexual selection and likely contribute to reproductive isolation. Additionally, we discovered that a subset of these traits are plastic; males adjust these traits based on the identity of the female genotype they interact with. These results suggest that even when male courtship is not fixed between lineages, ongoing selection can contribute to reproductive isolation.

evolutionary biology↗

bioRxiv2019

Transposable elements that cause dysgenesis also contribute to postzygotic isolation in the Drosophila virilis clade

Mismatches between parental genomes in selfish elements are frequently hypothesized to underlie hybrid dysfunction and drive speciation. However, because the genetic basis of most hybrid incompatibilities is unknown, testing the contribution of selfish elements to reproductive isolation is difficult. Here we evaluated the role of transposable elements (TEs) in hybrid incompatibilities between Drosophila virilis and D. lummei by experimentally comparing hybrid incompatibility in a cross where active TEs are present in D. virilis (TE+) and absent in D. lummei, to a cross where these TEs are absent from both D. virilis (TE-) and D. lummei genotypes. Using genomic data, we confirmed copy number differences in TEs between the D. virilis (TE+) strain and both the D. virilis (TE-) strain and D. lummei. We observed F1 postzygotic reproductive isolation exclusively in the interspecific cross involving TE+ D. virilis but not in crosses involving TE- D. virilis. This mirrors intraspecies dysgenesis where atrophied testes only occur when TE+ D. virilis is the paternal parent. A series of backcross experiments, that accounted for alternative models of hybrid incompatibility, showed that both F1 hybrid incompatibility and intrastrain dysgenesis are consistent with the action of TEs rather than genic interactions. Thus, our data suggest that this TE mechanism manifests as two different incompatibility phenotypes. A further Y-autosome interaction contributes to additional, sex-specific, inviability in one direction of this cross combination. These experiments demonstrate that TEs that cause intraspecies dysgenesis can increase reproductive isolation between closely related lineages, thereby adding to the processes that consolidate speciation.

evolutionary biology↗