Journal of Evolutionary Biology最新文献

Dispersal can evolve as an adaptation to escape competition with conspecifics or kin. Locations with a low density of conspecifics, however, may also lead to reduced opportunities for mating, especially in sessile marine invertebrates with proximity-dependent mating success. Since there are few experimental investigations, we performed a series of field experiments using an experimentally tractable species (the bryozoan Bugula neritina) to test the hypothesis that the density, spatial arrangement, and genetic relatedness of neighbours differentially affect survival, growth, reproduction, paternity, and sperm dispersal. We manipulated the density and relatedness of neighbours and found that increased density reduced survival but not growth rate, and that there was no effect of relatedness on survival, growth, or fecundity, in contrast to previous studies. We also manipulated the distances to the nearest neighbour and used genetic markers to assign paternity within known mother-offspring groups to estimate how proximity affects mating success. Distance to the nearest neighbour did not affect the number of settlers produced, the paternity share, or the degree of multiple paternity. Overall, larger than expected sperm dispersal led to high multiple paternity, regardless of the distance to the nearest neighbour. Our results have important implications for understanding selection on dispersal distance: in this system, there are few disadvantages to the limited larval dispersal that does occur and limited advantages for larvae to disperse further than a few 10s of metres.

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), focussing on two streams in the NB native range that are admixed extensively with non-native Smallmouth Bass (M. dolomieu; SMB). We quantified the 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 between 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.

The dynamics of mating interactions can vary in response to a wide variety of environmental factors. Here, we investigate the potential for individuals to vary consistently in the environmental conditions under which they actively engage in courtship. Specifically, we quantify variation in how courtship activity changes with environmental temperature across levels of biological organization in Enchenopa binotata treehoppers. Male E. binotata produce vibrational courtship signals and receptive females respond with their own sex-specific vibrational courtship signal. We tested each individual twice for the production of courtship signals across a range of ecologically relevant temperatures (18-36 °C). Then, we measured repeatability and variability in the resulting thermal courtship activity curves, including the temperature of peak activity and tolerance to thermal extremes. We also looked at patterns of variation across populations and sexes. We found minimal variation across populations, but significant variation across individuals. Specifically, we found prevalent repeatability in how thermally generalized or specialized individuals are. However, repeatability was limited to females only. We also found higher variability in female traits than in male traits, although patterns of variability did not always predict patterns of repeatability. These results suggest that thermal variation could alter the dynamics of mate competition and that-due to potentially different selective optima for males and females-the sexes may respond to changes in temperature in different ways. Specifically, females show a higher potential to adapt but males show a higher potential to be more robust to changes in temperature due to overall higher courtship activity across temperatures.

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 in females of these populations and those in 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 20-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, for the evolution of MHR in females.

Character displacement theory predicts that closely-related co-occurring species should diverge in relevant traits to reduce costly interspecific interactions such as competition or hybridization. While many studies document character shifts in sympatry, few provide corresponding evidence that these shifts are driven by the costs of co-occurrence. Black-capped (Poecile atricapillus) and mountain chickadees (Poecile gambeli) are closely-related, ecologically similar, and broadly distributed songbirds with both allopatric and sympatric populations. In sympatry, both species appear to suffer costs of their co-occurrence: (a) both species are in worse body condition compared to allopatry and (b) hybridization sometimes yields sterile offspring. Here, we explored character displacement in the songs of black-capped and mountain chickadees by characterizing variation in male songs from sympatric and allopatric populations. We found that mountain chickadees sing differently in sympatry versus allopatry. Specifically, they produced more notes per song, were more likely to include an extra introductory note, and produced a smaller glissando in their first notes compared to all other populations. Combined with previous research on social dominance and maladaptive hybridization between black-capped and mountain chickadees, we posit that differences in sympatric mountain chickadee song are population-wide shifts to reduce aggression from dominant black-capped chickadees and/or prevent maladaptive hybridization.

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) or evolutionary tradeoffs (i.e., the specialist-generalist model). We tested these hypotheses by generating thermal performance curves 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 below ground at stable temperatures near 25 °C and two cultivars are farmed above ground at variable temperatures. We generated thermal performance curves using a common garden experiment confining fungal isolates to different temperatures and then used a Bayesian hierarchical modelling approach to compare competing temperature sensitivity models. Some thermal performance traits differed consistently across farming strategies, with above-ground 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 hotter is better model or specialist-generalist model were not supported as above-ground 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.

In eutherians, one of the X chromosomes in each cell of the early female embryo is rendered transcriptionally silent through X chromosome inactivation. The choice of which X chromosome to inactivate takes place independently in each cell and is stably inherited through development, leading to a roughly 50:50 ratio of cells in the adult body expressing one or the other X chromosome. However, X chromosome inactivation can be skewed, with certain X chromosomes showing a heritable tendency to avoid inactivation. Using population genetic models, we test whether genetic variation for this trait can be maintained by linked sexually antagonistic selection. In favor of this hypothesis, we find that a neutral modifier that affects the chances of its chromosome's inactivation-e.g., a variant of the X controlling element (Xce)-can spread when linked to a sexually antagonistic gene. We explore the logic of this modifier's spread, which we find to be similar in many respects to that of a modifier of dominance. We also test for the presence of a "drift barrier"-i.e., a population size below which the indirect selective force favoring the modifier becomes too weak to overcome drift. On balance, we find that sexual antagonism may encourage the spread of skewed X chromosome inactivation, but only under favorable conditions.

Recombination diversifies the genomes of offspring, influences the evolutionary dynamics of populations, and ensures that chromosomes segregate properly during meiosis. Individuals recombine at different rates but observed levels of variation in recombination rate remain mostly unexplained. Genetic dissection of differences in recombination rate within and between species provides a powerful framework for understanding how this trait evolves. In this Perspective, I amalgamate published findings from genetic studies of variation in the genome-wide number of crossovers within and between species, and I use exploratory analyses to identify preliminary patterns. The narrow-sense heritability of crossover count is consistently low, indicating limited resemblance among relatives and predicting a weak response to short-term selection. Variants associated with crossover number within populations span the range of minor allele frequency. The size of the additive effect of recombination-associated variants, along with a negative correlation between this effect and minor allele frequency, raises the prospect that mutations inducing phenotypic shifts larger than a few crossovers are deleterious, though the contributions of methodological biases to these patterns deserve investigation. Quantitative trait loci that contribute to differences between populations or species alter crossover number in both directions, a pattern inconsistent with selection toward a constant optimum for this trait. Building on this characterization of genetic variation in crossover number within and between species, I describe fruitful avenues for future research. Better integrating recombination rate into quantitative genetics will reveal the balance of evolutionary forces responsible for genetic variation in this trait that shapes inheritance.

The relationship between the evolutionary dynamics observed in contemporary populations (microevolution) and evolution on timescales of millions of years (macroevolution) has been a topic of considerable debate. Historically, this debate centers on inconsistencies between microevolutionary processes and macroevolutionary patterns. Here, we characterize a striking exception: emerging evidence indicates that standing variation in contemporary populations and macroevolutionary rates of phenotypic divergence is often positively correlated. This apparent consistency between micro- and macroevolution is paradoxical because it contradicts our previous understanding of phenotypic evolution and is so far unexplained. Here, we explore the prospects for bridging evolutionary timescales through an examination of this "paradox of predictability." We begin by explaining why the divergence-variance correlation is a paradox, followed by data analysis to show that the correlation is a general phenomenon across a broad range of temporal scales, from a few generations to tens of millions of years. Then we review complementary approaches from quantitative genetics, comparative morphology, evo-devo, and paleontology to argue that they can help to address the paradox from the shared vantage point of recent work on evolvability. In conclusion, we recommend a methodological orientation that combines different kinds of short-term and long-term data using multiple analytical frameworks in an interdisciplinary research program. Such a program will increase our general understanding of how evolution works within and across timescales.