Journal of Evolutionary Biology最新文献

In eukaryotes with separate sexes, sex determination often involves sex chromosomes which have diverged as a consequence of recombination suppression. In species with old heteromorphic sex chromosomes, the non-recombining Y(-W) chromosome is typically highly degraded and has lost most of its genes. However, the dynamics of how and how quickly this degradation occurs remain largely unknown because species with young sex chromosomes, characterised by recent recombination suppression, are understudied. We discovered such young sex chromosomes in the ant cricket Myrmecophilus myrmecophilus, which displays a neo-XY system stemming from an X-autosome fusion. We generated a chromosomal-level assembly of the female genome and compared it to male genomic data. We identified four distinct regions on the X, including two strata with varying degrees of Y chromosome degeneration. Phylogenetic studies and genomic comparisons with closely related species revealed two cases of taxonomic synonymies and that the Myrmecophilus neo-sex chromosomes likely evolved approximately 7 million years ago. The X strata subsequently emerged as a consequence of two localised events of recombination suppression. Ant crickets thus represent a promising new model for studying the early stages of sex chromosome degeneration.

Several studies have emphasized that phenotypic plasticity should be a key mechanism to cope with current rapid environmental changes by allowing individuals to quickly express new adaptive phenotypes. Yet, few studies have investigated the evolutionary potential of plasticity for multiple traits simultaneously and using several different environmental variables. Here, we assess the extent of variation in, and the selection acting on phenotypic plasticity of key ecological traits, laying date, and clutch size, using five environmental variables, in a Tree swallow (Tachycineta bicolor) population monitored since 2004. While we found some variation among females in their mean laying date and plasticity, we found evidence of selection acting only on mean laying date. We found no variation among females in mean clutch size or plasticity, such that we could not assess selection acting on either. Our results suggest that the evolutionary potential of plasticity in the population under study is limited, especially for clutch size. More studies investigating plasticity in wild populations and incorporating multiple traits and environmental variables are needed to understand the future responses of animal populations to environmental changes.

Sex allocation theory predicts the adaptive allocation of resources to male versus female reproduction in simultaneous hermaphrodites in response to individual characteristics or environmental factors. Because parasites uptake resources from their hosts, their presence could affect the sex allocation of the hosts. We investigated the effects of infestation status and infestation intensity by the rhizocephalan barnacle Boschmaella japonica on reproduction, including sex allocation, of the host intertidal barnacle Chthamalus challengeri. Feeding activity was also examined as a factor related to resource intake. Both male and female reproductive investment decreased with increasing parasite infestation, and the sex allocation of large-infested hosts was more male-biased than that of large uninfested hosts. Moreover, in contrast to the model prediction that male investment does not change under resource limitation, male investment decreased in infested hosts whose resources were taken by parasites. This reduction in male investment could be explained by changes in mating group size, since infested hosts have shorter penises and consequently are able to access fewer mating partners.

In ovipositing animals, egg placement decisions can be key determinants of offspring survival. One oviposition strategy reported across taxa is laying eggs in clusters. In some species, mothers provision eggs with diffusible defence compounds, such as antimicrobials, raising the possibility of public good benefits arising from egg clustering. Here we report that Drosophila melanogaster females frequently lay eggs in mixed-maternity clusters. We tested two hypotheses for potential drivers of this oviposition behaviour: (i) the microbial environment affects fecundity and egg placement in groups of females; (ii) eggs exhibit antimicrobial activity. The results partially supported the first hypothesis. Females reduced egg laying but did not alter egg clustering, on non-sterile substrates that had been naturally colonized with microbes from the environment. However, oviposition remained unaffected when the substrate community consisted of commensal (fly-associated) microbes. The second hypothesis was not supported. There was no evidence of antimicrobial activity, either in whole eggs or in soluble egg-surface material. In conclusion, while we found no behavioural or physiological evidence that egg clustering decisions are shaped by the opportunity to share antimicrobials, females are sensitive to their microbial environment and can adjust egg-laying rates accordingly.

Walnut is a significant woody oil tree species that has been increasingly affected by anthracnose in recent years. Effective anthracnose control is crucial for walnut yield and quality, which requires a comprehensive understanding of the response mechanisms to Colletotrichum gloeosporioides. The PR10/Bet v1-like proteins are involved in defense against various diseases, therefore, in this study, seven JrBet v1s were identified from the walnut transcriptome (named JrBet v1-1~1-7), whose open reading frame was 414~483 bp in length with isoelectric point ranging from 4.96 to 6.11. These JrBet v1s were classified into three groups, with the MLP/RRP and Dicot PR-10 subfamilies each comprising three members (the largest ones), indicating that the proteins within these two subfamilies may have evolved from a shared ancestral gene within the broader PR10/Bet v1 protein family. The cis-elements in the promoters of JrBet v1s were involved in response to hormones, coercive, and plant growth metabolism. Most JrBet v1s could be significantly upregulated by walnut anthracnose, JrBet v1-1, JrBet v1-2, JrBet v1-4, and JrBet v1-6 peaked at 12 days of anthracnose stress, showing a 2.85- to 63.12-fold increase compared to the control, while JrBet v1-3, JrBet v1-5 and JrBet v1-7 peaked at 9 days, with a 3.23- to 27.67-fold increase. Furthermore, the significant correlation of the upregulation under anthracnose stress of JrBet v1s and JrChit02-1 as well as JrChit02-2, the genes encoding chitinase, suggesting that during the long process of microevolution in walnut-C. gloeosporioides interactions, walnut has developed a Bet v1-chitinase defense mechanism to counteract pathogen invasion.

Differences in habitat use impose ecological constraints which in turn lead to functional and morphological differences through adaptation. In fact, a convergent evolutionary pattern is evident when species exhibit similar responses to similar environments. In this study, we examine how habitat use influences the evolution of body shape in lizards from the family Lacertidae. We divided our species into two categories: ground-dwellers and climbers, which encompasses the verticality and horizontality aspects of the habitat. We performed phylogenetic comparative analyses employing 186 species and seven linear morphological traits. Our results show contrasting patterns between head and limb shapes, which are considered distinct functional blocks. We observed differences in forelimb proportions, but not in hindlimb length, contrary to what was documented in other lizard groups, demonstrating a novel axis in the limb-locomotion-habitat relationship in this family. In addition, a clear effect of habitat use on head shape was detected. We observed that climbing species present on average flatter heads than ground-dwelling species, as well as different evolutionary trajectories. These findings suggest the complex interplay between habitat use and morphological evolution in lizards, highlighting how distinct selective pressures drive divergent adaptations in different functional traits.

Characterizing molecular underpinnings of plastic traits and balanced polymorphisms represent 2 important goals of evolutionary biology. Fire ant gynes (pre-reproductive queens) provide an ideal system to study potential links between these phenomena because they exhibit both supergene-mediated polymorphism and nutritional plasticity in weight and colony-founding behaviour. Gynes with the inversion supergene haplotype are lightweight and depend on existing workers to initiate reproduction. Gynes with only the ancestral, non-inverted gene arrangement accumulate more nutrient reserves as adults and, in a distinct colony-founding behaviour, initiate reproduction without help from workers. However, when such gynes overwinter in the natal nest they develop an environmentally induced lightweight phenotype and colony-founding behaviour, similar to gynes with the inversion haplotype that have not overwintered. To evaluate the extent of shared mechanisms between plasticity and balanced polymorphism in fire ant gyne traits, we assessed whether genes with expression variation linked to overwintering plasticity may be affected by the evolutionary divergence between supergene haplotypes. To do so, we first compared transcriptional profiles of brains and ovaries from overwintered and non-overwintered gynes to identify plasticity-associated genes. These genes were enriched for metabolic and behavioural functions. Next, we compared plasticity-associated genes to those differentially expressed by supergene genotype, revealing a significant overlap of the 2 sets in ovarian tissues. We also identified sequence substitutions between supergene variants of multiple plasticity-associated genes, consistent with a scenario in which an ancestrally plastic phenotype responsive to an environmental condition became increasingly genetically regulated.

Introgression is a highly influential process in evolution, where genes flow between species that are not fully reproductively isolated. Studies on introgression often focus on describing gene transfer and environmental changes that facilitate the meeting of species. However, the impact of mating systems and behaviour that facilitate gene transfer is less well-known. Dolomedes aquaticus and D. minor are sister species of fishing spiders undergoing one-way, geographically limited mitochondrial introgression, making them an excellent case study for the factors that promote and limit introgression. We used a combination of field observations and crossing experiments to systematically investigate potential prefertilization barriers that could limit introgression and explain the one-way and geographic barriers to introgression in these species. We found that habitat overlap and timing of reproductive maturity were not likely to be important limiting factors to introgression. However, behaviour was an important factor, with male mate choice being implicated in the geographic limitation, and female mate choice being implicated in the one-way limitation. Our results show the importance of using behavioural approaches in the investigation of introgression.

Polymorphic short insertions and deletions (INDELs ≤ 50 bp) are abundant, although less common than single nucleotide polymorphisms (SNPs). Evidence from model organisms shows INDELs to be more strongly influenced by purifying selection than SNPs. Partly for this reason, INDELs are rarely used as markers for demographic processes or to detect divergent selection. Here, we compared INDELs and SNPs in the intertidal snail Littorina saxatilis, focussing on hybrid zones between ecotypes, in order to test the utility of INDELs in the detection of divergent selection. We computed INDEL and SNP site frequency spectra using capture sequencing data. We assessed the impact of divergent selection by analyzing allele frequency clines across habitat boundaries. We also examined the influence of GC-biased gene conversion because it may be confounded with signatures of selection. We show evidence that short INDELs are affected more by purifying selection than SNPs, but part of the observed site frequency spectra difference can be attributed to GC-biased gene conversion. We did not find a difference in the impact of divergent selection between short INDELs and SNPs. Short INDELs and SNPs were similarly distributed across the genome and so are likely to respond to indirect selection in the same way. A few regions likely affected by divergent selection were revealed by INDELs and not by SNPs. Short INDELs can be useful (additional) genetic markers helping to identify genomic regions important for adaptation and population divergence.