Evolution最新文献

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.

Traits subject to homeostatic regulation exhibit both active and passive phenotypic plasticity, where trait dynamics are shaped by passive effects of the environment and active physiological regulation. We present a model that decomposes the temporal dynamics of such traits into parameters that describe the passive effect of the environment, the rate at which active regulation is adjusted (i.e., rate of plasticity), and the asymptotic magnitude of active regulation (i.e., capacity for plasticity). We apply this model to a dataset comprising 653 experiments documenting time-course changes in ion concentrations and osmolality of aquatic organisms following salinity shifts. Our model captures the diversity of trait responses, and meta-analyses reveal strong phylogenetic signals in all three parameters. Ray-finned fishes had faster regulatory responses, weaker passive plasticity (i.e., diffusion), and greater magnitude of active regulation than crustaceans. Trait-specific differences were also evident. Active regulation of magnesium was faster and of larger magnitude than the other ions and osmolality, implying strong selection for precise regulation of magnesium, which may play a key role in several physiological pathways. By disentangling the passive vs. active components of homeostatic trait regulation, our approach provides new opportunities for studying novel ecological and evolutionary aspects of phenotypic plasticity.

Avian plumage maturation involves replacing feathers, via discrete molts, until reaching an iteratively-regenerated definitive plumage. In most birds, this process takes about one year. In the Neotropical lekking manakins (Pipridae), males of most species exhibit delayed plumage maturation (DPM), passing through drab predefinitive plumages for up to three years before reaching a sexually dichromatic, definitive plumage. We used a phylogenetic analysis to investigate the evolutionary history of DPM in manakins. Our unique dataset represents the developmental schedules of individual, colorful plumage patches. We found a single origin of one-year DPM, in which young males spend a year in a drab female plumage. Subsequently, there were three origins of two-year DPM, all of which featured the evolution of an intermediate plumage with colorful patches that distinguish young males from both females and older males. One species evolved three-year DPM by passing through ancestral plumage stages more slowly, and two lineages have secondarily evolved sexual monochromatism by paedomorphic retention of female plumage. By detailing this complex developmental evolutionary history, we show how the iterative regeneration of bird plumages creates multiple distinct levels of ontogenetic homologies and provides new insights into the macroevolution of social signals in young birds.

Major Histocompatibility Complex (MHC) polymorphism is maintained by balancing selection through host-pathogen interactions and mate choice. MHC-based mate choice has been investigated across a wide range of vertebrates, and an established concept is that females should choose a mate with an MHC genotype that is dissimilar to her own to ensure high MHC divergence in her offspring. Here we present evidence from a population of reed warblers, Acrocephalus scirpaceus, that social pairs with extra pair young in their nest have significantly lower MHC dissimilarity than expected by random MHC-based mate choice. Moreover, social pairs with extra pair young in their nest have lower MHC dissimilarity than the potential pairs females could form with other males surrounding the social nest. Therefore, females in pairs with low MHC dissimilarity could improve the MHC divergence of her offspring through extra-pair mating. We propose that when the MHC dissimilarity in the social pair is low, any alternative male represents a better genetic prospect for the female in terms of MHC dissimilarity. This scenario generates a pattern of MHC-disassortative extra-pair mating without requiring active MHC-based mate choice.

Evolution of novel behaviour is reflected in changes in sensory investment or integration, but the exact nature of these changes is often unclear. The Neotropical butterfly tribe, Heliconiini, offer an attractive system for studying how behavioural evolution is facilitated by changes in the neural system. Within the Heliconiini tribe, the genus Heliconius possess 4-fold larger mushroom bodies, the insect learning and memory centre, than closely related Heliconiini. Mushroom body expansion in Heliconius co-occurred with a dietary innovation, and is associated with systematic spatial foraging and extended lifespan. Heliconius' foraging relies on visual scene memories and, indeed, Heliconius have stable visual long-term memory, and evidence of visual specialisation in the mushroom bodies. Here, we explore how vision-specific neuroanatomical and behavioural enhancement in Heliconius impacts sensory pathways upstream of the mushroom bodies by assessing investment across the eyes, sensory neuropils and projection pathways. Despite evidence of refinement in visually-based behaviour, we found no increased investment in visual structures, brain areas or pathways. This suggests that the rapid expansion of the Heliconius mushroom body occurred in a context of conserved detection and processing of visual cues, and that a localised shift within integrative brain centres facilitated the evolution of Heliconius' novel behaviours.

How the brains of domestic animals evolved under domestication remains poorly understood. We quantified brain shape variation in domestic dogs (n = 203, 111 breeds) and wolves (n = 40) using endocast-based 3D geometric morphometrics. Size, shape and morphological integration were assessed on the whole brain, and in six morphofunctional subregions. Results demonstrate that domestication and artificial selection significantly restructured brain form and morphological integration patterns in dogs, reflecting mosaic evolution across brain subregions. Dogs exhibit a three-fold increase in brain shape variation relative to wolves, as well as expanded frontal lobes and areas putatively associated with social interaction behavior-these regions are also larger in cooperative versus independent breeds. Morphological integration is higher in dogs than wolves, and in modern breeds compared to ancient breeds. Thus, rather than constrain, integration appears to facilitate neuroanatomical evolvability under domestication and breeding selection. Ancient dog breeds retain more wolf-like neuroanatomy. Breed function is a poor predictor of brain shape, but brain integration restructures according to breed function, with working breeds displaying the highest integration. These findings reveal the profound impact of domestication on neuroanatomical evolution, emphasizing neuroanatomical features linked to social behavior, and challenging prevailing assumptions about the role of structural integration on evolvability.

Levels of additive genetic variation for fitness (${{V}_A}( w )$) and its components (e.g., viability, fertility) appear to be high in nature, substantially exceeding levels attributable to deleterious mutations at mutation-selection balance. Balancing selection can stably maintain genetic polymorphisms and potentially explain this "excess" fitness variation. Yet according to classical population genetics theory, balancing selection contributes nothing to ${{V}_A}( w )$ in a population at equilibrium, which has cast doubt on the potential role of balancing selection in maintaining ${{V}_A}( w )$. However, populations are only expected to be at equilibrium when there is no genetic drift and the fitness parameters of balancing selection are completely invariant over time. We explore how violations of these conditions affect the amount of additive genetic variation for fitness maintained by balancing selection. We show that drift and modest temporal fluctuations of balanced polymorphic equilibria each result in substantial ${{V}_A}( w )$, with each balanced polymorphic locus contributing as much to ${{V}_A}( w )$ as thousands of loci at mutation-selection balance. We discuss our results in reference to the surprisingly high levels of ${{V}_A}$ for fitness and life-history traits reported from lab populations of Drosophila and intensively monitored vertebrate populations in the field.

Horizontal gene transfer (HGT), the transmission of genetic material across species, is an important innovation source in prokaryotes. In contrast, its significance is unclear in many eukaryotes, including insects. Here, we used high-quality genomes of 45 termites and two cockroaches to investigate HGTs from non-metazoan organisms across blattodean genomes. We identified 289 genes and 2,494 pseudogenes classified into 168 orthologous groups originating from an estimated 281 HGT events. Wolbachia represented the primary HGT source, while termite gut bacteria and the cockroach endosymbiont Blattabacterium did not contribute meaningfully to HGTs. Most horizontally acquired genes descended from recent and species-specific HGTs, experienced frequent duplications and pseudogenizations, and accumulated substitutions faster than synonymous sites of native protein-coding genes. Genes frequently transferred horizontally to termite genomes included mobile genetic elements and genetic information processing genes. Our results indicate that termites continuously acquired genes through HGT, and that most horizontally acquired genes are specific to restricted lineages. Overall, genes acquired by HGT by termites and cockroaches seemed generally non-functional and bound to be lost.

The relationship between dominance and selection coefficients is a long-debated topic in evolutionary genetics and important for understanding evolutionary dynamics of populations. How it evolved and how it may vary across species or populations is not fully understood. Using simulations, we investigate how purifying selection and genetic drift affect the distribution of dominance coefficients for segregating deleterious variants. We find that large populations express h-s relationships shaped by efficient selection against highly deleterious and additive mutations, resulting in excess weakly deleterious and recessive mutations. This matches the classic inverse relationship between selection and dominance. Genetic drift in small populations, however, results in a wider range of dominance coefficients for any segregating deleterious variant and reduces or removes the h-s relationship. By investigating allele fixation we reveal a nuanced dependency on the strength of selection across different simulated selection and dominance distributions. We also compare the combined impact of genetic drift and repeated founder events in simulated range expansions and how these impact the segregating distribution of h, employing differences in effective population size between species core and edge. While dominance patterns in core populations resemble large, constant-size populations, edge populations lack recessive mutations relative to small, constant-size populations. Our findings emphasize the importance of genetic drift and purifying selection in shaping the observed negative relationship between dominance and selection coefficients in large populations. Small populations, however, show an h-s relationship closer to de novo mutations, without the effect of purifying selection. Therefore, it is important to consider population size, genetic drift, and the underlying distribution of dominance coefficients when studying the evolutionary dynamics of deleterious mutations.

African clawed frogs (Xenopus) have a high rate of genome duplication, which may catalyze evolution-including of sex chromosomes. To explore this, for each of four species in the subgenus Silurana, we analyzed sex-associated genetic variation, and in the diploid species X. tropicalis we explored population structure. We found that the sex-linked regions in all four species are homologous, and we infer that X. calcaratus has an unusual sex determination system with three sex chromosomes, which was previously known only in X. tropicalis. Our results evidence two independent allotetraploidization in Silurana, admixture across ploidy levels, and demonstrate that the most recent allotetraploidization that generated the X. calcaratus lineage occurred after population subdivision arose in X. tropicalis. Thus, this unusual triple sex chromosome system has been maintained independently in two different species for a protracted period, and through an allotetraploidization event. Simulations indicate that genetic drift should eliminate one of the sex chromosomes, suggesting that there may be unidentified benefits to maintaining this complex system.