Evolution最新文献

Utilising whole genome sequencing and multiple species delimitation models, Gaughran et al. (2024) show support for up to 13 distinct living Galapagos giant tortoise species, in contrast to the current classification of a single species. This result highlights the potential for rapidly radiating organisms on islands to act as model systems for investigating species boundaries, helping to settle taxonomic debates.

Wolff (2024) takes a comparative phylogenetic approach to study the evolution of dragline silk in 164 species of spiders, including both araneid and non-araneid species. Many structural and mechanical properties of dragline silk showed no correlations; however, both tensile strength and toughness correlated with birefringence-an indicator for the directional ordering of protein materials in the silk fibre. These properties do not seem to differ between web-building and non-web-building spiders; many spider families were found to include species that produce super-performing silk as well as species that produce weak-performing silk.

Facultatively parthenogenetic animals could help reveal the role of sexual conflict in the evolution of sex. Although each female can reproduce both sexually (producing sons and daughters from fertilized eggs) and asexually (typically producing only daughters from unfertilized eggs), these animals often form distinct sexual and asexual populations. We hypothesized that asexual populations are maintained through female resistance as well as the decay of male traits. We tested this via experimental crosses between individuals descended from multiple natural sexual and asexual populations of the facultatively parthenogenic stick-insect Megacrania batesii. We found that male-paired females descended from asexual populations produced strongly female-biased offspring sex-ratios resulting from reduced fertilization rates. This effect was not driven by incompatibility between diverged genotypes but, rather, by both genotypic and maternal effects on fertilization rate. Furthermore, when females from asexual populations mated and produced sons, those sons had poor fertilization success when paired with resistant females, consistent with male trait decay. Our results suggest that resistance to fertilization resulting from both maternal and genotypic effects, along with male sexual trait decay, can hinder the invasion of asexual populations by males. Sexual conflict could thus play a role in the establishment and maintenance of asexual populations.

Abiotic and biotic factors interact to influence phenotypic evolution; however, identifying the causal agents of selection that drive the evolution and expression of traits remains challenging. In a field common garden, we manipulated water availability and herbivore abundance across three years, and evaluated clinal variation in functional traits and phenology, plasticity, local adaptation, and selection using diverse accessions of the perennial forb, Boechera stricta. Consistent with expectations, drought stress exacerbated damage from herbivores. Foliar traits exhibited greater plasticity than phenological traits, which displayed more consistent genetic clines. Water availability and herbivory interacted to exert selection, even on traits like flowering duration, which showed no clinal variation and limited plasticity. Furthermore, the direction of selection on specific leaf area in response to water availability mirrored the genetic cline and plasticity, suggesting that variation in water levels across the landscape influences the evolution of this trait. Finally, both herbivory and water availability likely contribute to local adaptation. This work emphasizes the additive and synergistic roles of abiotic and biotic factors in shaping phenotypic variation across environmental gradients.

Most studies investigating the genomic nature of species differences anticipate monophyletic species with genome-wide differentiation. However, this may not be the case at the earliest stages of speciation where reproductive isolation is weak and homogenising gene flow blurs species boundaries. We investigate genomic differences between species in a postglacial radiation of eyebrights (Euphrasia), a taxonomically complex plant group with variation in ploidy and mating system. We use genotyping-by-sequencing and spatially-aware clustering methods to investigate genetic structure across 378 populations from 18 British and Irish Euphrasia species. We find only northern Scottish populations of the selfing heathland specialist E. micrantha demonstrate genome-wide divergence from other species. Instead of genetic clusters corresponding to species, all other clusters align with geographic regions, such as a genetic cluster on Shetland that includes ten tetraploid species. Recent divergence and extensive gene flow between putative species is supported by a lack of species-specific SNPs or clear outlier loci. We anticipate a similar lack of association between genomic clusters and species identities may occur in other recent postglacial groups. Where new species emerge this is associated with a transition in mating system or novel ecological preferences.

Peto's paradox, which highlights the lower-than-expected cancer rates in larger and/or longer-lived species, is a cornerstone of discussions at the intersection of ecology, evolution, and cancer research. It prompts investigations into how species with traits that theoretically increase cancer risk manage to exhibit cancer resistance, with the ultimate goal of uncovering novel therapies for humans. Building on these foundational insights, we propose expanding the research focus to species that, despite possessing traits beyond size and longevity that theoretically increase their cancer risk, exhibit unexpected cancer resistance. Testing Peto's paradox without interference from transient dynamics also requires considering species that are at an equilibrium between cancer risks and defenses, which is increasingly challenging due to anthropogenic activities. Additionally, we argue that transmissible cancers could significantly help in understanding how the metastatic process might be naturally suppressed. This research perspective is timely and aims to support the continued and in-depth identification of anti-cancer adaptations retained throughout evolution in the animal kingdom.

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.

Trait diversification is often driven by underlying performance tradeoffs in the context of different selective pressures. Evolutionary changes in task specialization may influence how species respond to tradeoffs and alter diversification. We conducted this study to investigate the functional morphology, evolutionary history, and tempo and mode of evolution of the Hymenoptera stinger using Ectatomminae ants as a model clade. We hypothesized that a performance tradeoff surface underlies the diversity of stinger morphology and that shifts between predatory and omnivorous diets mediate the diversification dynamics of the trait. Shape variation was characterized by X-ray microtomography, and the correlation between shape and average values of von Mises stress, as a measure of yield failure criteria under loading conditions typical of puncture scenarios, was determined using finite element analysis. We observed that stinger elongation underlies most of the shape variation but found no evidence of biomechanical tradeoffs in the performance characteristics measured. In addition, omnivores have increased phenotypic shifts and accelerated evolution in performance metrics, suggesting the evolution of dietary flexibility releases selection pressure on a specific function, resulting in a greater phenotypic evolutionary rate. These results increase our understanding of the biomechanical basis of stinger shape, indicate that shape diversity is not the outcome of simple biomechanical optimization, and reveal connections between diet and trait diversification.

It remains unclear how variation in the intensity of sperm competition shapes phenotypic and molecular evolution across clades. Mice and rats in the subfamily Murinae are a rapid radiation exhibiting incredible diversity in sperm morphology and production. We combined phenotypic and genomic data to perform phylogenetic comparisons of male reproductive traits and genes across 78 murine species. We identified several shifts towards smaller relative testes mass (RTM), presumably reflecting reduced sperm competition. Several sperm traits were associated with RTM, suggesting that mating system evolution selects for convergent suites of traits related to sperm competitive ability. We predicted that sperm competition would also drive more rapid molecular divergence in species with large testes. Contrary to this, we found that many spermatogenesis genes evolved more rapidly in species with smaller RTM due to relaxed purifying selection. While some reproductive genes evolved rapidly under recurrent positive selection, relaxed selection played a greater role in underlying rapid evolution in small testes species. Our work demonstrates that postcopulatory sexual selection can impose strong purifying selection shaping the evolution of male reproduction and that broad patterns of molecular evolution may help identify genes that contribute to male fertility.

The iconic marine raptorial predators Ichthyosauria and Eosauropterygia co-existed in the same ecosystems throughout most of the Mesozoic Era, facing similar evolutionary pressures and environmental perturbations. Both groups seemingly went through a massive macroevolutionary bottleneck across the Triassic-Jurassic (T/J) transition that greatly reduced their morphological diversity, leaving pelagic lineages as the only survivors. However, analyses of marine reptile disparity across the T/J transition have usually employed coarse morphological and temporal data. We comprehensively compare the evolution of ichthyosaurian and eosauropterygian morphology and body size across the Middle Triassic to Early Jurassic interval and find contrasting macroevolutionary patterns. The ecomorphospace of eosauropterygians predominantly reflects a strong phylogenetic signal, resulting in the clustering of three clades with clearly distinct craniodental phenotypes, suggesting "leaps" toward novel feeding ecologies. Ichthyosaurian diversification lacks a discernible evolutionary trend, as we find evidence for a wide overlap of craniodental morphologies between Triassic and Early Jurassic forms. The temporal evolution of ecomorphological disparity, fin shape and body size of eosauropterygians and ichthyosaurians during the Late Triassic does not support the hypothesis of an abrupt macroevolutionary bottleneck near the T/J transition. Rather, an important turnover event should be sought earlier, during times of rapid sea level falls.