Journal of Evolutionary Biology最新文献

Animal nests provide a beneficial environment for offspring development and as such, contribute to fitness. Gathering and transporting materials to construct nests is energetically costly, but the life history trade-offs associated with the types of nests built are largely unknown. Who contributes to building the nest could also mediate these trade-offs, as building a nest as a couple is expected to be less costly per individual than building alone. Using a comparative analysis of 227 songbird species globally, we found a fecundity cost associated with the type of nest a species builds. Species that build domed nests produce fewer broods per year than species building cups or platforms. Dome nesting species also have larger clutch sizes than open nesting species, but only when the nest is built by a couple and not when females build nests alone. This suggests that building domed nests represents a trade-off with investment in young, especially when females are solely responsible for nest building. More broadly, our results could explain macroevolutionary patterns, such as the recent finding that females, building on their own, more often build open cups rather than domed nests.

Climate change is increasing mean temperatures, and intensifying heatwaves. Natural populations may respond to stress through shorter-term acclimation via plasticity and/or longer-term inter-generational evolution. However, if the pace and/or extent of thermal change is too great, local extinctions occur; one potential cause in ectotherms is identified to be the heat-liability of male reproductive biology. Recent data from several species, including the beetle Tribolium castaneum, confirmed that male reproductive biology is vulnerable to heatwaves, which may constrain populations. However, such reproductive-damage may be overestimated, if there is potential to adapt to elevated mean temperatures associated with climate change via evolution and/or acclimation. Here, we tested this to evaluate whether pre-exposures could improve heatwave tolerance (adaptation or acclimation), by experimentally evolving Tribolium castaneum populations to divergent thermal regimes (30 °C vs. 38 °C). Findings across assays revealed that relative to 30 °C-regime males, males from the 38 °C regime, maintained constantly at 8 °C warmer for 25 generations, displayed an increase; (i) in post heatwave (42 °C) reproductive fitness by 55%, (ii) survival by 33%, and (iii) 32% larger testes volumes. Unexpectedly, in the acclimation assay, warm-adapted males' post-heatwave survival and reproduction were best if they experienced cool developmental acclimation beforehand, suggesting a cost to adapting to 38 °C. These results help progress knowledge of the potential for survival and reproduction to adapt to climate change; trait specific adaptation to divergent thermal regimes can occur over relatively few generations, but this capacity depended on the interaction of evolutionary and thermal acclimatory processes.

While senescence is a common occurrence in wild populations, not all traits decline with age simultaneously and some do not show any senescence. A lack of senescence in secondary sexual traits is thought to be due to their importance for reproductive success. However, if reproductive success senesces, why would secondary sexual traits apparently not senesce? Here, we explored this question in a wild population of red deer (Cervus elaphus) using antler form (number of points), a secondary sexual trait which shows little senescence, despite the occurrence of reproductive senescence. In line with expectations for traits that senesce, genetic variance in antler form increased with age and selection weakened with age. Therefore, there was no indication that a stronger selection on individuals that survived to older ages was countering the dilution of selection due to fewer individuals being alive. Furthermore, the effect of selective disappearance masking a slight decline in antler form in the oldest years was small. Interestingly, although genetic variance and positive selection of antler form were found, there was no evidence of a response to selection, supporting a genetic decoupling of antler senescence and reproductive senescence. Finally, a positive genetic covariance in antler form among age classes provides a possible explanation for the lack of senescence. These findings suggest that the antler form is under a genetic constraint that prevents it from senescing, providing an interesting evolutionary explanation for negligible senescence in a secondary sexual trait, and consequently, the existence of asynchrony in senescence among traits within populations.

Introgressive hybridization may lead to contrasting evolutionary outcomes that are difficult to predict, since they depend on the fitness effects of endogenous genomic interactions and environmental factors. Conservation of endemic biodiversity may be more effective with require direct measurement of introgressed ancestry and fitness in wild populations, especially for keystone taxa at risk of hybridization following species introductions. We assessed the relationship of non-native ancestry with growth and body condition in the basin-restricted Neosho Bass (Micropterus velox; NB), focusing on two streams in the NB native range that are admixed extensively with non-native Smallmouth Bass (M. dolomieu; SMB). We quantified genetic composition of 116 fish from Big Sugar Creek (N=46) and Elk River (N=70) at 14 microsatellite loci. Using back-calculated total length-at-age estimated from sagittal otoliths, we assessed whether genetic ancestry explained variation in von Bertalanffy growth model parameters, accounting for sex and stream effects. We then assessed the relationship of ancestry and body condition. We found no differences in growth parameters by sex, stream, or ancestry, suggesting phenotypic homogenization which could be mediated by selection on body size. We found a negative correlation between SMB ancestry and condition, including lower condition in Big Sugar Creek, possibly reflecting a trade-off between maximum length and condition with respect to overall fitness. We show that ongoing non-native introgression, which may be augmented by anthropogenic SMB introductions, may attenuate evolutionary differentiation between species and directly influence fitness, possibly having critical implications for long-term persistence and management of adaptive potential in a popular and ecologically important endemic sportfish.

In the last two decades, lineage-based models of diversification, where species are viewed as particles that can divide (speciate) or die (become extinct) at rates depending on some evolving trait, have been very popular tools to study macroevolutionary processes. Here, we argue that this approach cannot be used to break down the inner workings of species diversification and that "opening the species box" is necessary to understand the causes of macroevolution, but that too detailed speciation models also fail to make robust macroevolutionary predictions. We set up a general framework for parsimonious models of speciation that rely on a minimal number of mechanistic principles: (i) reproductive isolation is caused by excessive dissimilarity between genotypes; (ii) dissimilarity results from a balance between differentiation processes and homogenizing processes; and (iii) dissimilarity can feed back on these processes by decelerating homogenization. We classify such models according to the main homogenizing process : (1) clonal evolution models (ecological drift), (2) models of genetic isolation (gene flow) and (3) models of isolation by distance (spatial drift). We review these models and their specific predictions on macroscopic variables such as species abundances, speciation rates, interfertility relationships or phylogenetic tree structure. We propose new avenues of research by displaying conceptual questions remaining to be solved and new models to address them: the failure of speciation at secondary contact, the feedback of dissimilarity on homogenization, the emergence in space of breeding barriers.

Dioecious plants are frequently sexually dimorphic. Such dimorphism, which reflects responses to selection acting in opposite directions for male and female components of fitness, is commonly thought to emerge after separate sexes evolved from hermaphroditism. But associations between allocation to male and female function and traits under sexual conflict may well also develop in hermaphroditic ancestors. Here, we show that variation in sex allocation and a trait under sexual conflict inevitably generates an advantage to sexual specialisation, fueling the transition to dioecy. In the absence of constraints, this leads to the joint evolution of separate sexes and sexual dimorphism through the build-up of an association between sex allocation and the conflict trait, such that eventually the population consists of unisexuals expressing their sex-specific optima. We then investigate how such association might materialise genetically, either via recombination suppression or via sex-dependent expression, and show that the genetic architecture of sex alloca- tion and the conflict trait readily evolves to produce the association favoured by selection. Finally and in agreement with previous theory, we demonstrate that limited dispersal and self-fertilisation, which are pervasive ecological char- acteristics of flowering plants, can offset the advantage of sexual specialisation generated by sexual conflict and thus maintain hermaphroditism. Taken together, our results indicate that advantages to sexual specialisation are inevitable when there is conflict between sexual functions in hermaphrodites, but these advantages can be counterbalanced by ecological benefits of hermaphroditism.

The force of selection describes the sensitivity of population growth to changes in life history parameters, with a focus usually on the survival probabilities from one age class to the next. Importantly, according to Hamilton the force of selection generally decreases after the onset of reproduction, thereby providing a possible explanation for patterns of senescence. A second characteristic feature is that the force of selection remains constant up to the age of first re- production. This latter observation, however, rests on the assumption that offspring become independent from their parents right after birth. I show here in a minimal model that if offspring are fully reliant on their parents, either during early embryonal development or via parental care at later stages, and during this time prevent their parents from entering a new bout of repro- duction, the force of selection on offspring survival generally increases up until the age at which offspring become independent. This provides a possible explanation for the commonly observed pattern of decreasing mortality during early ontogeny. Further, genes acting during recurrent life stages are observed to experience a heightened force of selection compared to genes that act strictly age-specifically, demonstrating the need to develop a mechanistic understanding of gene activation patterns through which to consider life history evolution.

Interlocus sexual conflict is predicted to result in sexually antagonistic coevolution between male competitive traits, which are also female-detrimental, and mate harm resistance (MHR) in females. Little is known about the connection between life-history evolution and sexually antagonistic coevolution. Here, we investigated the evolution of MHR in a set of experimentally evolved populations, where mate-harming ability has been shown to have substantially reduced in males as a correlated response to the selection for faster development and early reproduction. We measured mortality and fecundity of females of these populations and those of their matched controls, under different male exposure conditions. We observed that the evolved females were more susceptible to mate harm - suffering from significantly higher mortality under continuous exposure to control males within the twenty-day assay period. Though these evolved females are known to have shorter lifespan, substantially higher mortality was not observed under virgin and single-mating conditions. We used fecundity data to show that this higher mortality in the experimentally evolved females was not due to the cost of egg production, and hence can only be attributed to reduced MHR. Further analysis indicated that this decreased MHR is unlikely to be due purely to the smaller size of these females. Instead, it is more likely to be an indirect experimentally evolved response attributable to the changed breeding ecology, and/or male trait evolution. Our results underline the implications of changes in life history traits, including lifespan, to the evolution of MHR in females.

Fungi are abundant and ecologically important at a global scale, but little is known about whether their thermal adaptations are shaped by biochemical constraints (i.e. the Hotter is Better Model, HBM) or evolutionary tradeoffs (i.e., the Specialist Generalist Model, SGM). We tested these hypotheses by generating thermal performance curves (TPCs) of fungal cultivars farmed by six species of Panamanian fungus-farming 'attine' ants. These fungi represent evolutionary transitions in farming strategies as four cultivars are farmed by ants belowground at stable temperatures near 25°C and two cultivars are farmed aboveground at variable temperatures. We generated TPCs using a common garden experiment confining fungal isolates to different temperatures and then used a Bayesian hierarchical modeling approach to compare competing temperature sensitivity models. Some thermal performance traits differed consistently across farming strategies, with aboveground cultivars having: 1) higher tolerance to low temperatures (CTLmin) and 2) higher maximum growth rate at the optimal temperature (rmax). However, two core assumptions shared by the HBM or SGM were not supported as aboveground cultivars did not show systematic increases in either their optimal temperature (Topt) or thermal tolerance breadth. These results harness ant farming systems as long-term natural experiments to decouple the effects of environmental thermal variation and innate physiological temperature sensitivity on fungal thermal evolution. The results have clear implications for predicting climate warming induced breaking points in animal-microbe mutualisms.