Evolution最新文献

Disease resistance (defined as the host capacity to limit systemic infection intensity) and disease tolerance (defined as the host capacity to limit infection-induced damage) are 2 complementary defense strategies that help the hosts maximize their survival and fitness when infected with pathogens and parasites. In addition to the underlying physiological mechanisms, the existing theory postulates that these 2 strategies differ in terms of the conditions under which each strategy evolves in the host populations, their evolutionary dynamics, and the ecological and epidemiological consequences of their evolution. Here, we explored if one or both of these strategies evolve when host populations are subjected to selection for increased postinfection survival. We experimentally evolved Drosophila melanogaster populations, selecting for the flies that survived an infection with the entomopathogen Enterococcus faecalis. We found that the host populations evolved increased disease resistance in response to selection for increased survival. This was despite the physiological costs associated with increased resistance, the expression of which varied with the phase of infection. We did not find evidence of any change in disease tolerance in the evolved host populations.

Range expansion and contraction are among the most common biotic responses to changing environmental conditions, yet much is to be learned about the mechanisms that underlie range-edge population dynamics, especially when those areas are points of secondary contact between closely related species. Here, we present field-measured parentage data that document the reproductive outcomes of changes in mate availability at a secondary contact zone between two species of woodrat in the genus Neotoma. Changes in mate availability resulted from drought-driven differential survival between the species and their hybrids. As the availability of conspecific mates declined, rates of hybridization increased, leading to the accumulation of admixed individuals in the zone of contact. Patterns of reproductive success in the wild appear to be the result of a combination of both pre-mating isolation and post-zygotic selection resulting from genomic incompatibilities between the parental lineages. Evidence of asymmetric mate preference between the parental lineages came from both skewed reproductive output in the field and laboratory preference trials. Moreover, partial genomic incompatibility was evident from the near-zero reproductive success of F1 males and because nearly all surviving hybrids had one pure parent. Nonetheless, the high reproductive success of F1 females and backcrossing in both parental directions allow for introgression between the parental species. These findings reveal how climate change may alter evolutionary outcomes for species at the edge of their ranges through an interplay of behavioral, demographic, and genetic mechanisms.

How might variations in genomic regions that impact many traits modulate fitness across different life stages? Aykanat et al. (2024) show that two large-effect loci associated with age at maturity, six6 and vgll3, impact the survival of wild Atlantic salmon (Salmo salar) through nutrient-dependent, indirect genetic effects. Specifically, the late maturation allele in parental vgll3, and the early maturation allele in maternal six6, increase survival in early life under high nutrient conditions.

In populations with separate sexes, genetic load due to deleterious mutations may be expressed differently in males and females. Evidence from insect models suggests that selection against mutations is stronger in males. This pattern will reduce deleterious allele frequencies at the expense of males, such that female mean fitness is greater than expected, preserving population persistence in the face of high mutation rates. While previous studies focus on reproductive success, mutation load depends on total selection in each sex, including selection for viability. We might expect minimal sex differences in viability effects in fruit flies, since male and female larvae behave similarly, yet many genes show sex-biased expression in larvae. We measured the sex-specific viability effects of nine "marker" mutations and 123 mutagenized chromosomes. We find that both types of mutations generally reduce viability in both sexes. Among marker mutations we detect instances of sex-biased effects in each direction; mutagenized chromosomes show little sex-specific mutational variance, but recessive lethals show a female bias, including in FlyBase records. We conclude that mutations regularly affect viability in a sex-specific manner, but that the strong pattern of male-biased mutational effects observed previously for reproductive success is not apparent at the pre-reproductive stage.

Phenotypic plasticity can alter traits that are crucial to population establishment in a new environment before adaptation can occur. How often phenotypic plasticity enables subsequent adaptive evolution is unknown, and examples of the phenomenon are limited. We investigated the hypothesis of plasticity-mediated persistence as a means of colonization of agricultural fields in one of the world's worst weeds, Raphanus raphanistrum ssp. raphanistrum. Using non-weedy native populations of the same species and subspecies as a comparison, we tested for plasticity-mediated persistence in a growth chamber reciprocal transplant experiment. We identified traits with genetic differentiation between the weedy and native ecotypes as well as phenotypic plasticity between growth chamber environments. We found that most traits were both plastic and differentiated between ecotypes, with the majority plastic and differentiated in the same direction. This suggests that phenotypic plasticity may have enabled radish populations to colonize and then adapt to novel agricultural environments.

After environmental change, the trait evolution needed to rescue a population depends on the functional form of the plastic change (reaction norm) of that trait. Nearly all previous models of plasticity evolution for continuous traits have assumed that the functional form is linear, that is, no limits on the range of plasticity. This paper examines the effect of developmental limits, modeled as a sigmoidal reaction norm, on evolutionary rescue after an abrupt environmental change and the subsequent evolution of plasticity, including genetic assimilation. We examined four different scenarios: (1) developmental limits only, (2) developmental limits plus a cost of plasticity, (3) developmental limits with developmental noise, and (4) developmental limits plus environmental variation. The probability of evolutionary rescue increased with an increase in phenotypic variation allowed by plastic development. With a smaller limit to the range of the plastic phenotype, the evolution of adaptive plasticity was limited, meaning the evolution of non-plastic genes was necessary. The addition of developmental constraints to the model did not speed up genetic assimilation, suggesting a new theory is needed to understand empirical observations. The modeling framework presented here could be extended to different ecological and evolutionary conditions, alternative reaction norm shapes, the evolution of additional reaction norm parameters such as the range or the location of the inflection point on the environmental axis, or other function-valued traits.

Endosymbiotic reproductive manipulators are widely studied as sources of post-zygotic isolation in arthropods, but their effect on pre-zygotic isolation between genetically differentiated populations has garnered less attention. We tested this using two partially isolated populations of the red and green colour forms of Tetranychus urticae, either uninfected or infected with different Wolbachia strains, one inducing cytoplasmic incompatibility and the other not. We first investigated male and female preferences, and found that, in absence of infection, females were not choosy, but all males preferred red-form females. Wolbachia effects were more subtle, with only the CI-inducing strain slightly strengthening colour-form based preferences. We then performed a double-mating experiment to test how incompatible matings affect subsequent mating behaviour and offspring production, as compared to compatible matings. Females mated with an incompatible male (infected and/or heterotypic) were more attractive and/or receptive to subsequent (compatible) matings, although analyses of offspring production revealed no clear benefit for this re-mating behaviour (i.e., apparently unaltered first male sperm precedence). Finally, by computing the relative contributions of each reproductive barrier to total isolation, we showed that pre-mating isolation matches both host-associated and Wolbachia-induced post-mating isolation, suggesting that Wolbachia could contribute to reproductive isolation in this system.

How long-lived trees escape "mutational meltdown" despite centuries of continuous growth remains puzzling. Here we integrate recent studies to show that the yearly rate of somatic mutations and epimutations (μY) scales inversely with generation time (G), and follows the same allometric power law found in mammals (μY∝G-1). Deeper insights into the scaling function may permit predictions of somatic (epi)mutation rates from life-history traits without the need for genomic data.

The study of polyandry has received increasing scientific attention with an emphasis on the fitness benefits and costs that females derive from mating with multiple males. There are still gaps in our understanding of how polyandry affects female fitness, however, as many previous studies compared the fitness outcomes of a single mating vs. two or three matings and did not separate the consequences of multiple mating from the costs of sexual harassment. We therefore conducted controlled mating trials with female fruit flies (Drosophila melanogaster) that could mate at either low (every eight days), medium (every four days), or high (every other day) rates while controlling for exposure to harassment from males. We found that female lifetime fitness was highest under the high followed by the medium mating-rate conditions. Moreover, we did not detect reductions in lifespan as a consequence of higher rates of polyandry. Our results demonstrate that even at realistically high rates, polyandry can lead to net fitness benefits for females, which can have major implications for sexual selection. Specifically, we discuss the significance of our findings as they relate to competition and the evolution of secondary sex characteristics in females, and sperm competition amongst males.

Several empirical examples and theoretical models suggest that the greenbeard effect may be an important mechanism in driving the evolution of altruism. However, previous theoretical models rely on assumptions such as spatial structure and specific sets of pleiotropic loci, the importance of which for the evolution of altruism has not been studied. Here, we develop a population-genetic model that clarifies the roles of extrinsic assortment (e.g., due to population viscosity) and pleiotropy in the maintenance of altruism through the greenbeard effect. We show that, when extrinsic assortment is too weak to promote the evolution of altruism on its own, the greenbeard effect can only promote altruism significantly if there is a pleiotropic locus controlling both altruism and signaling. Further, we show that indirect selection via genetic associations is too weak to have a noticeable impact on altruism evolution. We also highlight that, if extrinsic assortment is strong enough to promote the evolution of altruism on its own, it also favors the spread of alleles encoding the other functions of a greenbeard trait (signaling and discriminatory behavior), as well as genetic associations. This occurs despite the fact that the greenbeard effect did not favor the evolution of altruism in the first place. This calls for caution when inferring the causality between greenbeard traits and the evolution of altruism.