Evolution Letters最新文献

Our ability to predict the emergence of novel viruses relies on there being generalisable patterns in the susceptibilities of hosts to novel infections. Studies investigating variation in susceptibility among host species have consistently shown that closely related hosts share similar susceptibilities to a given virus. However, the extent to which such phylogenetic patterns of susceptibility are correlated amongst diverse sets of viruses is unclear. Here, we investigate phylogenetic correlations in susceptibility among Drosophilidae hosts to a panel of eleven different invertebrate viruses, comprising seven unique virus species, six unique families, and both RNA and DNA viruses. The susceptibility of hosts to each pair of viruses tested was either positively correlated across host species or did not show evidence of correlation. No negative correlations, indicative of evolutionary trade-offs in host susceptibility to different viruses, were detected between any virus pairs. The strength of correlations were generally higher in viruses of the same species and family, consistent with virus phylogenetic patterns in host infectivity. Our results suggest that generalised host susceptibility can result in positive correlations, even between highly diverged viruses, while specialised interactions with individual viruses cause a stepwise decrease in correlation strength between viruses from the within-species, to the within-family, to the across-family level.

Vision is a complex sensory system that requires coordination among cellular and morphological traits, and it remains unclear how functional relationships among traits interact with ecological selective pressures to shape the evolution of vision. Many species have specialized high visual acuity regions in the retina defined by patterns of ganglion cell density, which may evolve in response to ecological traits. For example, ganglion cell density can increase radially towards the center of the retina to form an area centralis, which is thought to improve acuity towards the center of the visual field in predators. Another example is the horizontal streak, where ganglion cells are dense in a horizontal pattern across the retina, which is thought to be beneficial in horizon-dominated habitats. At the morphological level, many have proposed that predation selects for high orbit convergence angles, or forward-facing eyes. We tested these hypotheses in a phylogenetic framework across eutherian mammals and found support for the association between the horizontal streak and horizon-dominated habitats. However, we did not find a significant association between orbit convergence and predation. We also tested if retinal specializations evolve in response to orbit convergence angles. We found that horizontal streaks were associated with side-facing eyes, potentially facilitating panoramic vision. Previous studies observed that some species with side-facing eyes have an area centralis shifted towards the temporal side of the retina, such that the high acuity region would project forward, but this relationship had not been tested quantitatively. We found that the temporal distance of the area centralis from the center of the retina was inversely correlated with orbit convergence, as predicted. Our work shows a strong relationship between orbit convergence and retinal specializations. We find support that both visual ecology and functional interactions among traits play important roles in the evolution of ocular traits across mammals.

Environmental stress can exacerbate inbreeding depression by amplifying differences between inbred and outbred individuals. In wild populations, where the environment is often unpredictable and stress can be highly detrimental, the interplay between inbreeding depression and environmental variation is potentially important. Here, we investigate variation in inbreeding level, fitness and strength of inbreeding depression across a fine-scale geographic area (~12 km²) in an individually monitored population of red deer (Cervus elaphus). We show that northern regions of the study area have lower birth weights, lower juvenile survival rates, and higher inbreeding coefficients. Such fine-scale differences in inbreeding coefficients could be caused by the mating system of red deer combined with female density variation. We then tested for an inbreeding depression-by-environment interaction (ID × E) in birth weight and juvenile survival, by fitting an interaction term between the inbreeding coefficient and geographic location. We find that inbreeding depression in juvenile survival is stronger in the harsher northern regions, indicating the presence of ID × E. We also highlight that the ability to infer ID × E is affected by the variation in inbreeding within each geographic region. Therefore, for future studies on ID × E in wild populations, we recommend first assessing whether inbreeding and traits vary spatially or temporally. Overall, this is one of only a handful of studies to find evidence for ID × E in a wild population-despite its prevalence in experimental systems-likely due to intense data demands or insufficient variation in environmental stress or inbreeding coefficients.

Male reproductive senescence is typically characterized by a decline in the number of sperm produced and transferred by old males, a phenomenon that may be exacerbated in polygynous species where males mate multiply. However, males also transfer seminal fluid to females, and little is known about its role in modulating male reproductive senescence. Here, we explore the contributions of sperm and seminal fluid towards male reproductive senescence in a series of sequential matings, using Drosophila melanogaster. As expected, old males produce fewer offspring than young males. However, this pattern is not driven by sperm limitation: old males have more sperm and transfer similar numbers to females, compared to young males. Instead, females storing fewer sperm of old males compared to that of young males, over a long term, drives male reproductive senescence. We are able to mitigate the age-related decline in male reproductive output by supplementing females with the seminal fluid of a young male, before she mates with an old male. Similarly, we alleviate the reduction in reproductive output across sequential matings by supplementing females with seminal fluid. Our findings highlight that seminal fluid, rather than sperm number, limits reproductive success in old or multiply mating males, highlighting its underappreciated role in reproductive aging.

Anthropogenic climate change affects wild animal populations through increasing average temperatures and more frequent extreme climatic events. Endotherms have evolved the capacity to regulate their body temperature but little is still known about how they can physiologically adapt to the pace of global warming. Adaptive responses would require that heat-tolerance mechanisms, such as the capacity to withstand high body temperatures and regulate evaporative water loss, exhibit sufficient heritable genetic variation for selection to act upon. Unfortunately, the quantitative genetics of these traits in endotherms remains poorly understood. In a recent study using infrared thermography (IRT) on semi-captive ostriches, Svensson et al., (Heritable variation in thermal profiles is associated with reproductive success in the world's largest bird. Evolution Letters, 8(2), 200-211.) sought to address this knowledge gap by measuring relative heat exchange from the head and neck and assessing the link between among-individual variation in heat dissipation and reproductive fitness. We discuss how IRT serves as a valuable tool for non-invasive data collecting, highlighting its potential for field studies of the evolutionary potential of thermal tolerance. Nevertheless, interpreting IRT data is not as straightforward as it may seem and thus must be conducted carefully. For instance, body parts from which surface temperatures are measured need to be unequivocally identified as sources of dry heat exchange in order to inform on thermoregulation-something lacking in the mentioned study. Furthermore, there is still no conclusive evidence that surface temperatures reflect core body temperatures in endotherms. Critical underlying mechanisms of the heat response, such as evaporative cooling, must also be considered. Assumptions stemming from uncertain proxies of thermoregulation can obscure our understanding of the endothermic adaptation of heat-tolerance traits to rapid global warming. These considerations emphasize that, while IRT can be a valuable tool for developing quantitative genetic approaches to estimate the evolutionary potential of heat tolerance in endotherms-particularly for species most vulnerable to warming, its application warrants careful planning.

Organism responses to environmental change require coordinated changes across correlated traits, so-called syndromes. For example, animals differ in their "pace-of-life syndrome" (POLS); suites of correlated life-history, behavioral and physiological traits. But standard "gene-centric" evolutionary theory cannot explain why POLSs exist because it assumes that the expression of phenotypic traits of animals is determined by genotype-specified reaction norms; it ignores that developmental processes can bias the direction of evolution so that phenotypes no longer match genotype-by-environment interactions. Here we apply a development-centric perspective to derive new POLS hypotheses that can resolve the conflict that current POLS predictions fail to explain which species/populations are resilient to environmental change.

Social interactions profoundly shape the dynamics and functionality of microbial populations. However, mechanisms governing the regulation of cooperative or individual traits have remained elusive. Here, we investigated the regulatory mechanisms of social behaviors by characterizing the fitness of transcriptional regulator PsdR mutants in cooperating Pseudomonas aeruginosa populations. In a canonical model described previously, PsdR was shown to solely have a nonsocial role in adaptation of these populations by controlling the intracellular uptake and processing of dipeptides. In addition to these known private traits, we found that PsdR mutants also enhanced cooperation by increasing the production of quorum sensing (QS)-regulated public goods. Although private dipeptide utilization promotes individual absolute fitness, it only partially accounts for the growth advantage of PsdR mutants. The absence of the QS master regulator LasR delayed the appearance of PsdR variants in an evolution experiment. We also demonstrated that the growth fitness of PsdR mutants is determined by a combination of the QS-mediated cooperative trait and the dipeptide metabolism-related private trait. This dual trait is co-regulated by PsdR, leading to the rapid spread of PsdR variants throughout the population. In conclusion, we identified a new social model of co-regulating cooperative and private traits in PsdR variants, uncovering the social and nonsocial roles of this transcriptional regulator in cooperating bacterial populations. Our findings advance the fundamental understanding of bacterial social interactions and provide insights into population evolution, pathogen infection control and synthetic biotechnology.

Selection often favors different trait values in males and females, leading to genetic conflicts between the sexes when traits have a shared genetic basis. Such sexual antagonism has been proposed to maintain genetic polymorphism. However, this notion is based on insights from population genetic models of single loci with fixed fitness effects. It is thus unclear how readily polymorphism emerges from sex-specific selection acting on continuous traits, where fitness effects arise from the genotype-phenotype map and the fitness landscape. Here, we model the evolution of a continuous trait that has a shared genetic basis but different optima in males and females, considering a wide variety of genetic architectures and fitness landscapes. For autosomal loci, the long-term maintenance of polymorphism requires strong conflict between males and females that generates uncharacteristic sex-specific fitness patterns. Instead, more plausible sex-specific fitness landscapes typically generate stabilizing selection leading to an evolutionarily stable state that consists of a single homozygous genotype. Except for sites tightly linked to the sex-determining region, our results indicate that genetic variation due to sexual antagonism should arise only rarely and often be transient, making these signatures challenging to detect in genomic data.

Immunocompetence evolution can involve a "resistance is futile" scenario if parasite encounter rates are so high that high investment in resistance only marginally delays infection. Here, we investigate two understudied aspects of "futility": the mode of immunocompetence and sexual selection. First, immunocompetence is usefully categorized as reducing the rate of becoming infected (resistance) or reducing the negative fitness consequences of infection once it happened (tolerance). We compare the prospects of futility for resistance, tolerance, and their joint occurrence, showing that resistance futility arises with respect to parasite encounter rates, while tolerance futility arises with respect to parasite virulence. However, if the same host trait improves pleiotropically both resistance and tolerance, futility disappears altogether and immunity investment remains profitable when increasing parasite encounter rates, virulence, or both. Second, we examine how sexual selection strength impacts these findings. If one sex (typically males) is near the faster end of a fast-slow continuum of life histories, then life history patterns reflecting futility can evolve sex-specificity. The solutions often feature sexual dimorphism in immunocompetence, but not always in the direction of strong sexual selection yielding low immunity: sexual selection can select for faster and "sicker" lives, but if sexual selection also favors traits that impact parasite encounter rates, the results are strongly dependent on whether futility (along any axis) plays a role.

[This corrects the article DOI: 10.1093/evlett/qrae056.].