Journal of Evolutionary Biology最新文献

Allometry, the relationship between body size and the size of other body parts, explains a significant portion of morphological variation across biological levels, at the individual level, within and between species. We used external morphology measurements of 6 Triturus (sub)species, focussing on the T. marmoratus species group, to explore allometric parameters within and between taxa. We tested for allometry of sexual size dimorphism in body, head, and limb dimensions and examined whether intraspecific allometry directed evolutionary allometry, as described by Rensch's rule. Our findings indicated that female-biased trunk and head dimensions exhibited positive allometry, whereas male-biased limb dimensions showed isometric relationships or weak correlations with body size. Morphological divergences between sexes occurred along common allometric slopes, most often through changes in the intercepts. Among taxon, comparisons revealed that (sub)species diverged in the direction of the allometric slopes. In line with Rensch's rule, sexual size dimorphism in female-biased traits significantly decreased as overall body size increased. However, the observed intraspecific allometric parameters deviated from theoretical expectations because the steepest allometric slopes for female-biased traits were recorded in the larger species. Our results contribute to understanding the dynamics of allometric relationships and sexual dimorphism in amphibians and provide a robust baseline for future comparative analyses.

Identifying the presence and strength of reproductive isolating barriers is necessary to understand how species form and then remain distinct in the face of ongoing gene flow. Here, we study reproductive isolation at two stages of the speciation process in the closely related mushroom-feeding species Drosophila recens and Drosophila subquinaria. We assess 3 isolating barriers that occur after mating, including the number of eggs laid, the proportion of eggs laid that hatched, and the number of adult offspring from a single mating. First, all 3 reproductive barriers are present between D. recens females and D. subquinaria males, which are at the late stages of speciation but still produce fertile daughters through which gene flow can occur. There is no evidence for geographic variation in any of these traits, concurrent with patterns of behavioural isolation. Second, all 3 of these reproductive barriers are strong between geographically distant conspecific populations of D. subquinaria, which are in the early stages of speciation and show genetic differentiation and asymmetric behavioural discrimination. The reduction in the number of eggs laid is asymmetric, consistent with patterns in behavioural isolation, and suggests the evolution of postmating prezygotic isolation due to cascade reinforcement against mating with D. recens. In summary, not only may postmating prezygotic reproductive barriers help maintain isolation between D. recens and D. subquinaria, but they may also drive the earliest stages of isolation within D. subquinaria.

Communication via evolved signals is ubiquitous (both within and between species) in the natural world. However, how honest we should expect signals to be remains an open question. Hybrid equilibria are a form of equilibria predicted by discrete signaling games in which signalers are sometimes dishonest and signals do not completely reliably convey information on signaler quality. While these equilibria have been theoretically demonstrated in several signaling games, their dynamics in a stochastic simulation of evolutionary trajectories (that include representation of the inherent noise expected in evolution in the natural world) have not previously been studied. In this paper, we present an agent-based simulation of a discrete signaling game which exhibits hybrid equilibria. We find that while hybrid equilibria are evolutionarily attractive where they exist, populations exhibit variable and often drastic oscillating behavior around the predicted equilibrium values. We discuss how these dynamics might offer valuable opportunity for detecting hybrid equilibria in natural populations.

Contact zones between genetically divergent lineages offer a unique opportunity to explore gene flow and speciation dynamics. Because satellite DNAs (satDNAs) have high evolutionary rates, they may be useful for comparing related taxa and assessing contact zones. Here, we analysed the distribution of chromosomal clusters of PcP190 satDNA across a contact zone between two distinct genetic lineages of a Neotropical species complex of frogs. The parental lineages, Physalaemus ephippifer and lineage 1B (L1B), exhibited pronounced divergence in the number of PcP190 clusters. We further expanded the geographic scope of this species complex by including two additional Brazilian localities in previously available cytogenetic and mitochondrial DNA datasets. The contact zone exhibited remarkable variation in the chromosomal distribution of PcP190 clusters among the autosomes; the only fixed autosomal site was found on chromosome 3. The highest numbers of PcP190 clusters were observed in specimens collected at sites near (approximately 320 km from) the distribution of L1B, whereas specimens from Dom Eliseu, which is near (approximately 330 km from) the distribution of P. ephippifer, had the lowest numbers of such clusters. Mitochondrial haplotypes also exhibited geographical variation across sites. Our findings expand the known contact zone of these Physalaemus lineages from 1,500 km2 to over 6,200 km2, demonstrating its extensive area, and emphasize the usefulness of satDNAs in studying contact zones.

Identifying the factors that contribute to reproductive isolation among closely related species is key for understanding the diversification of lineages. In this study, we investigate the strength of premating and postmating reproductive isolation barriers between Disa ferruginea and Disa gladioliflora, a pair of closely related species, often found co-flowering in sympatry. Both species are non-rewarding and rely on mimicry of different rewarding model flowers for the attraction of pollinators. We constructed abiotic niche models for different forms of each taxon to measure ecogeographic isolation. Using experimental arrays in sympatry, we recorded pollinator transitions to measure ethological isolation. We performed hand pollinations to measure postpollination isolation. We found strong, but not complete, premating isolation associated with abiotic niches and absolute pollinator-mediated isolation based on pollinator preferences in sympatry. Pollinator preferences among the orchids could be explained largely by flower colour (orange in D. ferruginea and pink in D. gladioliflora) which matches that of the pollinator food plants. Post-mating barriers were weak as the species were found to be inter-fertile. Coexistence in the orchid species pair is due mainly to pollinator-mediated reproductive isolation arising from flower colour differences resulting from mimicry of different rewarding plants. These results highlight the importance of signalling traits for the pollinator-mediated isolation of closely related species with specialized pollination systems.

This paper evaluates recent work purporting to show that the "agency" of organisms is an important phenomenon for evolutionary biology to study. Biological agency is understood as the capacity for goal-directed, self-determining activity-a capacity that is present in all organisms irrespective of their complexity and whether or not they have a nervous system. Proponents of the "agency perspective" on biological systems have claimed that agency is not explainable by physiological or developmental mechanisms, or by adaptation via natural selection. We show that this idea is theoretically unsound and unsupported by current biology. There is no empirical evidence that the agency perspective has the potential to advance experimental research in the life sciences. Instead, the phenomena that the agency perspective purports to make sense of are better explained using the well-established idea that complex multiscale feedback mechanisms evolve through natural selection.

Complex eukaryotes vary greatly in the mode and extent that their evolutionary histories have been shaped by the microbial communities that they host. A general understanding of the evolutionary consequences of host-microbe symbioses requires that we understand the relative importance of host phylogenetic divergence and other ecological processes in shaping variation in host-associated microbial communities. To contribute to this understanding, we described the bacterial communities hosted by several Drosophila species native to the Sonoran Desert of North America. Our sampling consisted of four species that span multiple dietary shifts to cactophily, as well as the dietary generalist D. melanogaster, allowing us to partition the influences of host phylogeny and extant ecology. We found that bacterial communities were compositionally indistinguishable when considering incidence only but varied when considering the relative abundances of bacterial taxa. Variation in community composition was not explained by host phylogenetic divergence but could be partially explained by dietary variation. In support of the important role of diet as a source of ecological selection, we found that specialist cactophilic Drosophila deviated more from neutral predictions than dietary generalists. Overall, our findings provide insight into the evolutionary and ecological factors that shape host-associated microbial communities in a natural context.

When mating is promiscuous, the ejaculate volume allocated to each female is expected (intuitively) to be linked with the presence and number of rival males. Previous theories have indicated that, in the absence of rival males, males will allocate the minimum ejaculate volume sufficient for fertilization of all available oocytes. However, it is unclear if this ejaculation strategy is still effective where females have a mechanism to remove sperm after copulation ("female sperm rejection"). In the Japanese pygmy squid, Idiosepius paradoxus, female sperm rejection was observed to occur frequently, but males were able to increase the remaining sperm volume available for fertilization, suggesting that there is no significant impact of female sperm rejection on male ejaculation strategy. However, males decreased ejaculate volume in the presence of rival males and increased it in their absence, a pattern counterintuitive to predictions from previous theories. Females reject sperm at every copulation, so after copulation, the amount of a given male's sperm remaining with the female may decrease after each subsequent rival copulates with the female. Perhaps in this species, the presence of rivals signals the risk of further sperm rejection, so males choose to conserve their resources and move on.

Rensch's rule describes a pattern of interspecific allometry in which sexual size dimorphism (SSD) increases with size among closely related species (i.e., among a group of related species, the largest ones tend to show more male-biased SSD). Sexual selection is often invoked to explain Rensch's rule, as larger male body size is assumed to be favoured by sexual selection for increased fighting performance in contests for mating opportunities. Often, however, the correlation between size and performance is not well described. We studied a sexually selected performance trait, bite force in Anolis lizards, to determine whether patterns of SSD are linked to size-associated patterns of performance dimorphism at the macroevolutionary level, as expected under the sexual selection hypothesis for Rensch's rule. Additionally, we tested whether allometric patterns of performance dimorphism differ between mainland and island species, as the latter have likely evolved under a stronger sexual selection regime. We found that SSD overwhelmingly explains the relationship between performance dimorphism and size in anoles, as expected under a sexual selection model for Rensch's rule. However, residual performance dimorphism was higher in island than in mainland species, suggesting that these groups differ in performance dimorphism for reasons unrelated to size. Head size dimorphism was associated with residual performance dimorphism, but did not fully explain the difference in performance dimorphism between island and mainland species. Together, these findings highlight the need to interpret Rensch's rule patterns of body size evolution cautiously, as allometric patterns of performance dimorphism and size dimorphism might not be equivalent.