Journal of Evolutionary Biology最新文献

Despite numerous lineages exhibiting ecologically and phenotypically similar species across continents, the interplay between evolutionary convergence and biogeographical dispersal in shaping continental community assembly remains largely unknown. Tropical wandering spiders (Ctenidae) are a diverse group of terrestrial predators with a pantropical distribution, exhibiting a variety of specialised morphotypes across different habitats. We used phylogenetic comparative methods to investigate the role of ecomorphological convergence through continental in situ diversification and biogeographic dispersal in assembling tropical wandering spiders (Ctenidae). We address three evolutionary questions: (1) Did independent habitat shifts result in the repeated origin of similar morphologies? (2) Is similarity in morphology across continental assemblages caused by evolutionary convergence or by biogeographic dispersal? (3) Are there differences in dispersal rates between different ecomorphs (ground and arboreal) and if so how does this affect community assembly? Ancestral habitat reconstruction suggests that ctenids were likely originally arboreal and later colonized terrestrial habitats at least six times independently. We detected morphological shifts on the phylogeny in carapace height, spine length of the first legs, and leg span that were associated with habitat transitions. Our biogeographic analyses suggest that ground-dwelling ctenids show significantly higher dispersal rates compared to arboreal ctenids. Our findings imply that ctenid ecomorphological diversity in certain continental areas originated from in situ diversification within specific biogeographical regions, driven by multiple habitat shifts closely linked to morphological changes. Furthermore, our study reveals that ctenid assembly across various regions has also been influenced by long-distance dispersal events of evolutionarily conserved ground-adapted forms.

The tendency for the genital morphology of animals to diverge more rapidly than other traits is one of the most pervasive evolutionary patterns in animal form. Current controversy regarding explanations of this pattern stems in part from the difficulty of observing the behaviour of male genitalia during copulation. This limitation is reduced in tipuloid crane flies, because most of the male's elaborate, divergent genital structures remain outside the female during copulation. Observations of genital behaviour during copulation in 45 species in 21 genera and subgenera, the most extensive sample of genital behaviour in any comparable group of animals, show a combination of trends that fits better with the stimulation version of the cryptic female choice hypothesis than with any of the other hypotheses commonly cited to explain rapid divergent genital evolution: sustained, rhythmic male genital movements such as brushing and tapping; frequent female facilitation of stimulation; lack of consistent morphological coevolution between corresponding male and female structures; lack of forceful male manipulations of females; lack of female "defenses" that impede male stimulation; and lack of direct male interference with other males' sperm. Tipuloids are atypical among Diptera in generally lacking rhythmic, forceful genital thrusting and squeezing.

Whether evolution is predictable has been tested in evolutionary biology by comparing lineages that experienced parallel evolution. For example, the repeatability of gene expression between strains was examined in the experimental evolution of bacteria. However, whether it is possible to predict the evolutionary fate of a gene (i.e., loss or retention) after an organism colonizes a new habitat and experiences a long period is not sufficiently clear. Here, we investigate a visual gene set in two species of eyeless trechine beetles (Coleoptera: Carabidae: Trechinae), which are thought to have colonized caves independently, and show that many of the lost genes and retained genes are common between them. We also estimate the pleiotropy that represents the extent to which these genes act in several tissues, using gene expression data in a model organism, and show that commonly lost genes have low pleiotropy. Our results suggest that the loss and retention of a visual gene set are relatively easy to predict in cave-dwelling trechine beetles. Furthermore, this study supports the possibility that even evolutionary fates of genes, which occur after a long period, are influenced by the functional constraints of these genes.

Sex chromosomes and mating-type chromosomes can carry large regions with suppressed recombination. As a result of a lower efficacy of selection, recessive deleterious mutations are expected to accumulate in these non-recombining regions. Multiple genomic analyses have indirectly inferred the presence of deleterious mutations in sex and mating-type chromosomes, but direct experimental evidence remains scarce. Here, we performed fitness assays in fungi with megabase-large and young non-recombining regions around the mating-type locus, using three Sordariales species, to test whether heterokaryons (diploid-like, heterozygous at the mating-type locus) exhibited a fitness advantage over homokaryons (haploid-like, with a single mating-type allele), in terms of spore germination dynamics or mycelium growth speed, under different conditions of light and temperature. We found a faster growth of heterokaryons compared to one of the homokaryons for Podospora anserina at 18 °C and for Schizothecium tetrasporum and Schizothecium tritetrasporum at 22 °C under light. These findings suggest the presence of a sheltered load, i.e., recessive deleterious mutations at the heterozygous state in or near non-recombining regions, associated to a specific mating-type allele. Genomic analyses indeed suggested that the non-recombining regions around the mating-type locus likely carry heterozygous deleterious mutations, while the rest of the genome was mostly homozygous. The difference in growth rates did not result from different numbers or densities of nuclei between homokaryons and heterokaryons. Leveraging the experimental assets of fungi, allowing cultivating separately haploid-like and diploid-like life stages, our experiments provided one of the rare direct experimental evidence of sheltered load around mating-compatibility loci.

Whilst there is a growing appreciation that mitochondrial divergence across lineages is not selectively neutral, less work has examined the functional differences that may exist in closely divergent taxa. We measured mitochondrial oxygen consumption in the blood of two subspecies of an Australian songbird-the long-tailed finch, Poephila acuticauda-before and after 10 days of heat treatment at 40 °C to explore mitochondrial metabolic plasticity in response to thermal stress. There were significant differences between subspecies in the efficiency of oxidative phosphorylation, with P. a. hecki having higher energy production efficiency than P. a. acuticauda independent of heat treatment. Mitochondrial metabolism increased significantly after the treatment in 4 out of 6 variables in both subspecies, with P. a. hecki showing higher oxygen consumption rates in acclimating to 40 °C. In the same experiment, we also measured circulating levels of corticosterone to assess the effect of the treatment on stress and to explore a possible mechanistic link with mitochondrial metabolism. The heat significantly increased baseline corticosterone, but at an individual level, corticosterone and mitochondrial metabolism were unrelated, indicating that functional plasticity in response to the thermal challenge was not mechanistically determined by corticosterone. Whilst the geographic ranges of the 2 subspecies differ in climate, the extent to which the functional divergence in mitochondrial efficiency reflects selectively neutral or adaptive divergence requires further research. Nonetheless, the reduced metabolic flexibility of P. a. acuticauda after heat suggests that future increases in the frequency and intensity of heatwaves may impose asymmetric effects on the 2 subspecies.

Defensive symbionts-organisms that confer protection to their hosts against natural enemies such as parasites, predators, or herbivores-are found throughout the natural world. Theoretical and empirical studies have shown that defensive symbionts can both interfere with ecological interactions between hosts and exploiters, as well as drive exploiter evolution. Defensive symbionts are also potential candidates for biocontrol agents to help manage infectious diseases or agricultural pests. The impact of defensive symbionts on parasite ecology and evolution has therefore recently received increased empirical and theoretical attention. In this theoretical study, we investigate the impact that a defensive symbiont which protects hosts from infection (conferred resistance) has on the evolution of parasite virulence. We also explore how the extent of protection conferred by the defensive symbiont coevolves with parasite virulence, and how symbiont and parasite evolution affect the ecology of the host population in both the short- and long-term. We show that, while costly resistance-conferring defensive symbionts always select for increased parasite virulence, the overall long-term ecological effect on the host population may still be positive due to reductions in disease prevalence. This contrasts with tolerance-conferring symbionts (which protect against virulence), where the long-term ecological effects on the host population are always negative. We also show when the defensive symbiont can successfully eliminate the parasite. Resistance-conferring defensive symbionts therefore offer more promise as evolutionarily robust biocontrols than those that only confer tolerance.

Nematode sperm contains subcellular vesicles known as membranous organelles (MOs) that fuse with the sperm cell membrane upon sperm activation to release their soluble contents into the extracellular space. The second most abundant proteins in the MOs belong to the conserved Nematode-Specific Peptide family, group F (NSPF) gene family. We hypothesize that these proteins contribute to seminal fluid and are part of postinsemination reproductive tract dynamics. We characterized the anatomical region where the NSPF proteins likely function during fertilization using dissected testes and whole-worm immunostaining of a His-tagged nspf-1 transgene. We confirmed that NSPF proteins are transferred to females during mating. NSPF proteins localize to the uterus lumen when transferred to mated females and in unmated adult hermaphrodites. These results suggest that the uterine localization of the NSPF proteins is likely a functional property of both male-derived sperm and self-sperm and not incidental to the point of transfer during mating. In males, we confirm that NSPF proteins are indeed sperm-derived. We then used experimental evolution to compete the wild-type allele against a deletion allele in 10 replicate obligate-outcrossing populations. We calculated a mean selective disadvantage of 0.1% for the deletion allele, which indicated that the NSPF genes are beneficial to male fitness. This conclusion was reinforced by qualitative trends from lower-powered, single-generation fertility assays. Together, we demonstrate that nematodes use a novel approach for contributing proteins to seminal fluid and show that the highly abundant NSPF proteins likely have a beneficial impact on fitness.

Complex eukaryotes generally express different traits as they grow and develop to facilitate their function in different ecological niches. Theory suggests the evolution of differentiation between life stages is facilitated by the expression of different genes at different points throughout ontogeny, which alleviates evolutionary constraints. Therefore, ascertaining what contributes to specialized patterns of gene expression across ontogeny is fundamental to understanding the evolution of ontogenetic complexity. Expression divergence between duplicate genes and gene organization have been identified as important features of relatively complex ontogenies. Therefore, one could predict that their link to transcriptional specialization may be weaker across relatively simpler ontogenies. Here, we investigated the links between gene duplication, gene organization, and stage-specific patterns of expression across the relatively simple Caenorhabditis elegans life cycle. We found that signatures of stage-biased chromosomal regions were weaker in C. elegans than what has been previously described in organisms with more complex ontogenies. Furthermore, we found the extent that duplicate genes varied in ontogenetic expression pattern was more constrained in C. elegans. Overall, these findings help generalize our understanding of the association between gene duplication, gene organization, and the evolution of complex ontogenies.