Evolution最新文献

Evolutionary rates correlate negatively with time, which makes it complicated to compare rates across lineages that have diversified on different time intervals. The causes of this correlation are debated. Using simulations, we first show that rates of evolution estimated as a parameter in the unbiased random walk model lack a rate-time scaling when data has been generated using this model, even when time series are made incomplete and biased. This indicates that it is theoretically possible to estimate rates that are not time correlated from empirical data. We then analyze 643 empirical time series to assess whether accounting for model misspecification, sampling error, and model identifiability reduces the negative scaling, but none appear to have a significant impact. This suggests that the rate-time correlation requires an explanation grounded in evolutionary biology and that common models used in phylogenetic comparative studies and phenotypic time series analyses often fail to accurately describe trait evolution in empirical data. Making meaningful comparisons of estimated rates between clades and lineages covering different time intervals remains a challenge.

The ability of organisms to change color in response to a change in environmental conditions is widespread across taxa. Predation represents the longstanding hypothesis for the evolution of such coloration plasticity. Yet, tests of the evolutionary drivers of coloration plasticity remain rare. Here, we examine how predation shapes both baseline coloration and coloration plasticity in the Trinidadian killifish (Anablepsoides hartii). This species inhabits streams that vary in fish predator presence, creating a replicated natural experiment across three rivers. We hypothesized that fish from high-predation sites would exhibit lighter baseline coloration due to associations with open canopy and increased light, and that predators would select for stronger plasticity in background-induced color change. Our results did reveal hypothesized shifts in baseline coloration with high-predation fish generally lighter. Anablepsoides hartii also displayed strong plasticity, darkening on black backgrounds and lightening on white. However, the effect of predation on baseline color and coloration plasticity was inconsistent across rivers, suggesting that additional ecological factors also contribute to these responses. Our study provides empirical evidence that predators are not the sole driver of variation in coloration plasticity and that local ecological factors that covary with predators may also exert selection on body color.

Polyandry is prevalent, but the optimal patterns of mating for females remain poorly understood despite their importance for our understanding of sexual selection. We therefore performed a meta-analysis on the female fitness consequences of mating with multiple males. Across 166 studies spanning 127 arthropod species, we found that mating with more males generally enhanced female fecundity and reduced female lifespan. The net fitness effects of polyandry, however, were small. Moreover, fecundity benefits were not clearly detectable when females mated with more than two males. Additionally, we found first, that studies assessing partial as opposed to lifetime fitness reported greater benefits of polyandry. Second, protocols involving selection bias, where females were afforded some control over mating rates, reported lower costs of polyandry compared to studies without selection bias. Third, polyandry was reported as less beneficial in experiments that involved continuous housing of females with males. Finally, polyandry was more beneficial in species that transfer nuptial gifts. We thus suggest that future polyandry studies aim to measure lifetime fitness while also mitigating selection bias and exposure of females to excessive harassment. Doing so will help us understand how sexual selection operates in both sexes.

The evolution of tube-like floral morphologies that control pollen release via small openings (functionally poricidal flowers) represents a taxonomically and geographically widespread instance of repeated and independent evolution of a functionally similar morphology. Poricidal flowers are also often closely associated with buzz pollination by bees. Yet we lack an updated angiosperm-wide survey of their phylogenetic distribution. We identify all known angiosperm genera containing poricidal flowers via a literature survey. We determined their phylogenetic distribution and minimum number of independent gains and losses via a species-level angiosperm-wide phylogeny. We estimated if evolution of poricidal flowers is associated with changes in speciation/extinction via diversification rate analyses. Poricidal flowers occur across 87 angiosperm families and 639 genera containing > 28,000 species. At the species level, an average of 205 independent gains and 215 losses of poricidal flowers occurred. Angiosperm-wide analyses suggest an early burst in poricidal evolution, but no differences in net diversification (origination-extinction) between non-poricidal and poricidal taxa. Analyses for two focal families however indicate strong context-dependent effects of poricidal flowers on diversification. Poricidal evolution thus represents a large-scale example of convergent evolution in floral form, but effects on diversification appear to be strongly contingent on phylogenetic and ecological background.

Gamete dynamics (GD) theory for the evolutionary transition from isogamy to anisogamy relies on the biophysics of fertilization, combining the dynamics of gamete limitation and gamete competition with the provisioning requirements of gametes and zygotes. A recent development by Siljestam & Martinossi-Allibert, which incorporates competitive gamete traits (motility, target size and chemoattractants) into anisogamy evolution reaches very different conclusions from previous GD predictions, and challenges current views on sexual selection. We develop models incorporating evolution of motility and target size traits under conventional GD theory assumptions showing that (i) unless gamete limitation is strong and the trait is more efficient in the larger gamete, such traits tend to arise in the male gamete, complying with previous analyses predicting that sexually selected expenditures are most likely to arise in males, (ii) gamete trait evolution does not alter the conditions under which anisogamy evolves from isogamy, (iii) the differences between our results and those of Siljestam & Martinossi-Allibert arise from their specific function for zygote survival, which is arguably less plausible than those used in previous GD theory, and (iv) as a novel finding, we show that the coevolution of gamete size with gamete traits (here, motility) can result in the evolution of slight anisogamy.

Genetic offset models have become a popular component of the landscape genetics toolbox, with over 600 peer-reviewed publications applying these models. Genetic offset models are most frequently performed following the identification of putatively adaptive alleles from genotype-environment association analyses in natural populations of nonmodel organisms. These models allow the researcher to make predictions about the vulnerability of species populations to climate change, by estimating the extent of genetic change needed (i.e., genetic offset) to maintain "optimal" allele frequencies and population fitness under future climate change scenarios. However, several review articles have recently drawn attention to fundamental limitations of genetic offset models that compromise their reliability for interpretation. In this commentary, we consolidate and build on preview reviews by describing several key assumptions and violations of basic evolutionary principles that are often overlooked when undertaking these analyses. We use a combination of evolutionary theory and conceptual descriptions to show that current applications fail to account for critical evolutionary processes that shape the selection-fitness landscape and risk producing misleading estimates of population vulnerability. While genetic offset models could have a place in the future, our current interpretations and applications remain problematic and are likely to lead to poor conservation outcomes.

The deep sea is known for challenging abiotic and biotic conditions; yet, deep-sea fishes have been shown to have higher phenotypic diversity than shallow relatives. An open question is whether different habitats within the deep sea differentially contribute to this surprising phenotypic diversity. Here, we explore the joint effects of two major environmental dimensions, the benthic-pelagic axis and ocean depth, on body shape diversification in marine teleost fishes. We found that increasing ocean depth shifted axes of phenotypic evolution and promoted diversification for benthic, demersal, and pelagic fishes alike. However, body shape diversity and rates of body shape evolution did not scale consistently across habitats. For benthic fishes, rate increased more strongly than diversity with increasing ocean depth, while the reverse was true for pelagic fishes. Analyses of habitat transitions suggested that independent invasions may help explain the diversity of deep-pelagic fishes without invoking high evolutionary rates. Relaxed selection may also explain this diversity, as suggested by the wide range of deep-pelagic forms observed along an evolutionary axis of body elongation. Overall, our results reveal a mosaic of pathways through which body plan diversity accumulated across a vertebrate radiation, underscoring the importance of considering finer-scale habitat variation in broad-scale studies.

Phenotypic plasticity is often seen as an alternative adaptive strategy to genetic polymorphism, especially in response to rapid environmental changes. Indeed, a link between plasticity and heterozygosity, i.e., the measure of polymorphism, has previously been dismissed. Here, we compare the thermal plasticity of abdominal pigmentation in eight Drosophila species, four belonging to the melanogaster species group and four to the montium group. Despite a conserved developmental pathway for melanin synthesis, the genetic architecture of its variation has significantly evolved, being polygenic in most species (such as D. melanogaster) and Mendelian or invariable in others. By investigating the thermal plasticity of this trait in species with distinct architectures, we show that the degree of plasticity strongly associates with heterozygosity. Plasticity was resurrected in hybrids between species with no plastic responses but with contrasting melanism, and was higher in heterozygotes in species with simple Mendelian polymorphism. In plastic cases, pigmentation dominance is reversed depending on the developmental temperature. We propose simple genetic models with empirical molecular support to explain this link between phenotypic plasticity and genetic polymorphism. The relationship between these two phenomena, and the impact of each on the evolution of the other, may be more relevant than it is currently appreciated.

Replicate hybrid zones between the same taxa provide a unique opportunity to assess the repeatability of the outcome of interspecific matings by uncovering recurrent genomic and phenotypic introgression patterns. Replicates also facilitate exploration of the causes of temporal shifts in hybrid zone structure. We sampled transects along three geographically separate hybrid zones between two avian taxa -the Lemon-rumped (Ramphocelus flammigerus icteronotus) and Flame-rumped (R. f. flammigerus) Tanagers-which hybridize in low passes across the Western Andes of Colombia. We examined environmental, phenotypic and genetic variation using reflectance spectrophotometry and genotype-by-sequencing data mapped to a high-quality de novo genome assembly, aiming to assess the repeatability and progression of introgression after hybridization. We found that all hybrid zones formed independently, showed parallel phenotypic divergence along ecological gradients, low population structure across parental ranges and similar demographic histories. Replicates also exhibited asymmetric introgression of neutral markers from the yellow icteronotus into the hybrid zone. However, the age of the hybrid zones differed, resulting in differences in the extent of geographic and genomic cline displacement from environmental transitions into the red flammigerus range. Despite heterogeneity in locus-specific introgression, the only shared introgression outliers across all hybrid zones were in a genomic region linked to plumage color. Clines for these loci were consistently narrow, suggesting a role in long-term reproductive isolation. Altogether, we showed that locus-specific introgression is largely stochastic, but the magnitude and directionality of neutral introgression can be predictable when demographic conditions are similar and for traits involved in reproductive isolation.

Host heterogeneity and spatial population structure each influence parasite evolution and may interact when space structures contacts between host types. Here, we experimentally evolve granulosis virus in microcosms of its natural Plodia interpunctella (Indian meal moth) host that differ in both spatial structure and host genetic diversity. We control spatial structure by manipulating the viscosity of the food that the larvae live within and host genetic diversity by adding larvae from either one or two non-evolving inbred lines to opposite microcosm ends. We preserve spatial structure across passages and assay virus from different positions within the microcosm on both host genotypes. We find that the lower contact rates between host genotypes resulting from spatial structure can lead to the evolution of locally specialized virus, even when the host population is genetically diverse overall. We also find that spatial structure changes how viruses specialize: viruses evolved in well-mixed environments had lower exploitation rates (proportion infected x virions) on the host they evolved with, while those in spatially structured environments exhibited higher exploitation of familiar hosts. These results demonstrate that spatial structure and host heterogeneity interact to shape pathogen specialization and that the evolutionary consequences of host diversity depend on population structure.