Biology subjects

Parrett, J. M.

Publications and source records attributed to Parrett, J. M..

8 recordsLinked to original sources

bioRxiv2026

Population Resilience Under Environmental Deterioration in Socially Monogamous Systems with Mutual Mate Choice

Rapid environmental change and biodiversity loss make it increasingly important to identify factors influencing population extinction risk. Previous studies examining how mating systems can affect persistence of populations under environmental stress generally report higher extinction risks in monogamous than polygynous systems but have largely ignored extra-pair copulations (EPC) and paternity (EPP), despite the prevalence of genetic polyandry in socially monogamous species. Here, using an individual-based model, we study how EPP in socially monogamous systems affects population resilience under directional environmental change. We assume that in socially monogamous species, both sexes carry costly sexual ornaments, the elaboration of which depends on the strength of preference. The effect of EPPs on extinction risk depended on the strength of mate preference, population size, and the degree to which homozygosity affected fitness. Systems with EPCs are not simply intermediate in resilience between strict monogamy and polygyny: the preference strength interacts with mating system, leading to superior resilience of EPC systems compared to strictly monogamous and polygynous systems when choosiness and the negative consequences of heterozygosity loss are low, and EPP rates are high. However, this benefit was reduced in small populations due to faster loss of heterozygosity. At high choosiness, EPC systems exhibited lower resilience than socially polygynous choice systems because the higher reproductive skew of the latter system allowed them to adapt faster while not suffering from the demographic consequences of sexual signaling costs borne by females. Overall, our results suggest that EPCs can enhance population resilience when females obtain fertilizations from higher-condition extra-pair males compared to systems without EPC.

evolutionary biology↗

bioRxiv2026

Mating Systems and Evolutionary Rescue

Animal mating systems are hugely diverse, ranging from species where mating is essentially random to those exhibiting complex systems of mate choice by one or both sexes, with some species mating monogamously and others showing various degrees of promiscuity. There is now good evidence that if male signal traits are correlated with fitness, then polygynous female choice systems can show improved adaptation and persistence, but there has been little exploration of the ways that other types of mating systems modulate adaptation and evolutionary rescue. To address this, we developed an individual-based model that allows random mating, female-only choice, and mutual mate choice to be compared within both monogamous and polygynous frameworks and used it to explore how mating systems influence adaptive response, loss of heterozygosity, and extinction risk under changing environmental conditions. We find that mating system interacts with population size in determining extinction risk: because mate choice under polygyny lowers effective population size, accelerating the loss of heterozygosity, small polygynous populations with either mutual or female-only mate choice face higher extinction risks than randomly mating populations. In larger populations where inbreeding and genetic drift are less important, female-choice and mutual-choice polygynous systems show the greatest resilience to environmental change by allowing better-adapted males to dominate reproduction. Random mating populations show the lowest resilience to environmental change when populations are large and mutual-choice monogamous systems have intermediate resilience. Among polygynous systems, female-only choice leads to slower loss of heterozygosity and facilitates population resilience better than mutual mate choice. These findings demonstrate that mating systems can critically shape a populations ability to adapt to environmental change and alter extinction risks, emphasizing the need to consider mating systems in designing effective conservation strategies.

evolutionary biology↗

bioRxiv2026

Experimental evolution under biased sex ratios: phenotypic and genomic responses in the bulb mite, Rhizoglyphus robini

Sexual selection may increase population fitness by favouring high-condition individuals and accelerating the purging of deleterious alleles. However, it can also reduce population fitness through intra- and interlocus sexual conflict by promoting male-benefit traits that harm females and maintain polymorphism at sexually antagonistic loci. The balance between these opposing forces remains unresolved, yet it has major consequences for how sexual selection shapes population fitness and genome-wide variation. To explore the genomic and phenotypic effects of sexual selection and sexual conflict, we evolved replicated bulb mite (Rhizoglyphus robini) lines for 28 generations under male- versus female-biased sex ratios and combined phenotypic assays with whole-genome resequencing. Female fecundity and inbreeding depression did not differ between treatments, and genomic analyses revealed no treatment effect on the loss of rare, putatively deleterious SNPs. Contrary to expectations, males from male-biased lines were less harmful to stock females than males from female-biased lines. Genome-wide nucleotide diversity declined similarly across generations in both treatments, although synonymous exonic diversity declined more slowly in male-biased lines. While only a few SNPs diverged consistently between treatments, we identified large treatment-specific haplotype blocks indicating that multiple genomic regions were involved in response to sex-ratio manipulation. Overall, our results indicate that sex ratio manipulation drives evolution of male harm to females and widespread haplotype frequency changes without clear evidence for enhanced purging or maintenance of genetic diversity. The response thus appears to reflect adaptation to altered level of reproductive competition, but without measurable consequences for population fitness and genetic diversity. Significance statementSexual selection is often proposed to improve population fitness by removing deleterious mutations, yet it can also favour traits that harm the opposite sex; consequently, it remains unclear whether stronger reproductive competition reliably enhances population viability. By evolving bulb mite populations under strongly male- or female-biased sex ratios, we found that male-biased populations did not purge genetic load more effectively, while the genomic response to sex-ratio bias was highly polygenic. In contrast to our predictions, males from male-biased lines were less harmful to females than males from female-biased lines. Overall, our results show that sex-ratio bias can reshape male phenotypes and generate patterns of genomic divergence, but without any significant effect on population fitness. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/701246v1_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@15afcf7org.highwire.dtl.DTLVardef@95ef16org.highwire.dtl.DTLVardef@183c405org.highwire.dtl.DTLVardef@1ba3159_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2025

Stand age drives changes in the biodiversity and microclimate of oil palm plantations

Tree plantation age strongly dictates its environment. As they mature, the canopy closes and habitat complexity tends to increase, which in turn affects biodiversity. However, for oil palm, one of the most important and widespread tree plantations, we lack a detailed understanding of how this process affects microclimate and biodiversity. We therefore compiled environmental and biodiversity data of oil palm plantations that were repeatedly sampled over a 6 year period in Malaysian Borneo. Using these data, we made a chronosequence of the microclimate and biodiversity of oil palm plantations between the ages 5 and 18. We found that oil palm plantations increasingly buffer temperature and humidity over time, becoming cooler and less dry. Animal responses differed between taxa: spider and beetle abundance increased, ant abundance decreased, and mammal and dung-beetle abundances stayed constant. The diversity of beetles in general increased and family-level community composition changed, while dung-beetle and mammal diversity stayed constant. Some taxa are therefore likely limited by the harsh microclimate of young plantations, while increased habitat complexity and fruit and leaf production in older plantations could also drive increased abundances of other taxa. Our results reveal that oil palm plantations undergo considerable changes, even over a decade after establishment. Correspondingly, plantation age should be considered in studies into oil palm plantations impact on climate and biodiversity, and landscape level diversity could be increased by allowing multiple oil palm stand-ages to co-exist.

ecology↗

bioRxiv2025

Fighting to persist: Genetic rescue increases long-term fitness despite elevated genetic load

Genetic rescue (GR) can restore fitness in small genetically depauperate populations, however, long-term effectiveness, impact of rescuer quality and introduced deleterious load on population persistence remains uncertain. Using a male-dimorphic mite we tested whether a condition-dependent sexually selected trait influences GR. Genome-wide diversity and genetic load increased similarly for both morphs, while population fitness trajectories differed, suggesting that genetic quality is associated with the trait. Overall, GR sustained fitness benefits over 20 generations. The benefits persisted under thermal stress lowering extinction risk regardless of the rescuers morph and introduced load indicating their minimal importance. These results provide experimental evidence that maximising genome-wide variation via GR can yield lasting benefits, even when many deleterious mutations are introduced to populations facing environmental change.

evolutionary biology↗

bioRxiv2025

Fighting Through the Heat: How Sexual Selection Influences Demography Under Recurrent Heatwaves

Sexual selection is a potent evolutionary force with complex effects. Strong sexual selection can enhance adaptation and reduce mutational load, while simultaneously reducing survival, or causing sexual conflict that reduces fitness for one or both sexes. Many populations today face not only gradual environmental changes but also extreme, short-term stress events like droughts or heatwaves. The combined effects of sexual and environmental selection on population demography during and after such events remain poorly understood, even though such combined effects could be crucial for the persistence of small, endangered populations under climate change. In this study, we investigated how sexual selection affects survival during environmental stress by manipulating the expression of an aggressive fighter morph in small populations of the male-dimorphic soil mite Sancassania berlesei, exposing some of these populations to recurrent periods of extreme heat and monitoring survival over eight generations. We found that heat exposure reduced survival, more severely in females than in males, and survival was lower in populations with higher fighter prevalence, but there was no interaction between temperature and fighter morph prevalence. Furthermore, survival declined across generations, and the decline was steeper in populations with lower prevalence of fighters, leading to the loss of their initial survival advantage by the last generation. T265625hree populations exposed to heat became extinct during the experiment, all from the reduced fighter expression treatment. Our findings imply that despite its cost to individual survival, sexual selection does not modulate population sensitivity to heatwaves over several generations. Furthermore, we demonstrate that these mortality costs of sexual selection are gradually compensated over successive generations, which could be a result of a more effective purging of inbreeding depression. Thus, while the additive effect of sexual selection and heatwaves on survival may increase demographic risks for bottlenecked populations in the short term, sexual selection may increase resilience of populations to prolonged bottlenecks.

evolutionary biology↗

bioRxiv2024

Sex-specific recombination landscape in a species with holocentric chromosomes

The rate and chromosomal positioning of meiotic recombination significantly affects the distribution of the genetic diversity in eukaryotic genomes. Many studies have revealed sex-specific recombination patterns, with male recombination typically biased toward chromosome ends, while female recombination is more evenly distributed along chromosomes, or concentrated in pericentromeric region. It has been proposed that such patterns in females may counteract meiotic drive caused by selfish genetic elements near centromeres and should not occur in species devoid of clearly defined centromeres, but evidence for this expectation is scarce. Here, we constructed a sex-specific genetic map of a species with holocentric chromosomes, the bulb mite (Rhizoglyphus robini), a model organism for sexual selection studies with heritable alternative male reproductive phenotypes. We found a similar recombination landscape in both males and females, with a consistent pattern of increased rates towards both chromosome ends, and a higher recombination rate in females than in males. Recombination rate was positively correlated with repeat density and negatively with gene density. Our results are consistent with the meiotic drive hypothesis and suggest that the evolution of recombination patterns is closely linked to chromosome features.

genomics↗

bioRxiv2021

Morph-specific investment in testes mass in a trimorphic beetle, Proagoderus watanabei

When competition between males for mates is intense it is common to find that some males will adopt alternative tactics for acquiring fertilisations, often involving the use of sneak tactics whereby males avoid contests. These alternative tactics are sometimes associated with discrete differences in male morphology, with sneak males investing less in weaponry but more in traits such as testes which will give an advantage in sperm competition. In some cases it appears that males develop into more than two morphs, with a number of examples of tri- and even tetramorphic arthropod species being described. Here we analyse the scaling relations of the dung beetle species Proagoderus watanabei, which expresses two distinct weapon traits: paired head horns and a pronotal horn. We find that males of this species are trimorphic, with alpha males expressing long head horns and a pronotal horn, beta males with long head horns but no pronotal horn, and gamma males with short head horns only. We also find that alpha males invest less in testes than do beta or gamma males, indicating that beta and gamma males in this species probably experience higher risks of sperm competition than do alphas.

evolutionary biology↗