Journal of Evolutionary Biology最新文献

The time needed for the evolution of mating cues that distinguish species, such as species-specific songs or plumage coloration in birds, has received little attention. Aiming to gain some understanding of the timing of the evolutionary process we here present models of how mating cues evolve in populations split into subpopulations between which there may (parapatry) or may not (allopatry) be migration. Mating cues can be either neutral or directly selected. In models in which evolution commences with a substitution at a neutral mating-cue locus, under allopatry there is no selection on the mating cue, but under parapatry, selection may be induced on the mating cue by the selective conditions in the subpopulations, and the migration rates between them. We use simulation to calculate how selection pressures on mating cues then depend on selective conditions in subpopulations and migration rates between them. In the second part of the paper, we demonstrate quantitatively how the resulting selection pressures on new mating cues together with mutation rate affect speciation time. Our results suggest that species-specific songs or plumage colorations that are selectively neutral evolve faster under parapatry than under allopatry, and this may explain the short speciation times that are sometimes reported. Although our modelling assumptions are restrictive so that caution is needed in comparing the results to empirical data, we hope that our main results, showing quantitatively how parapatry can reduce speciation times, will encourage further work relaxing model assumptions or studying different models of mate choice.

Karyotype evolution might fuel speciation and can thereby contribute to species diversity. To test the hypothesis that speciation and karyotype change are linked, we estimated anagenetic and cladogenetic rates of karyotype evolution as well as speciation rates in Orthoptera. We compiled the male diploid chromosome number and the number of visible chromosome arms (the fundamental number) from published sources for 1,541 species. Chromosome-associated speciation rates were estimated by jointly modeling cladogenetic and anagenetic character evolution and the phylogenetic birth-death process in a Bayesian statistical framework using a subset of 516 species from 14 families. Our findings unveiled heterogeneity among orthopteran families in the pace of karyotype evolution and whether it was linked to speciation. In 6/14 clades we found evidence supporting speciation-associated (cladogenetic) karyotype changes, while in 6/14 clades karyotype evolution was primarily anagenetic. The remaining clades (2/14) showed uncertainty in favor of either model. We further analysed whether flightless phenotype, and thus less mobile species, showed higher rates of karyotype evolution. We showed that the flightless phenotype is associated with the rate of chromosome loss. The finding indicates contrasting patterns of karyotype evolution within specific orthopteran lineages, thus emphasizing substantial diversity in the pace of this evolutionary process. It also implies that substantial changes in chromosome number, arising from instances of chromosomal gains and losses, are recurring events in orthopterans that are associated with reproductive isolation and speciation, at least in some groups.

Inbreeding frequently leads to inbreeding depression, a general reduction in trait values and loss of fitness, and it appears that some sexually selected traits are especially sensitive to inbreeding, but sperm may be an exception. Additionally, because inbreeding depression is always in the direction of low fitness, it can reveal the direction of past selection acting on trait values. Here, we experimentally manipulate levels of inbreeding in a beetle (Tribolium castaneum) by full-sib mating for six generations. This breeding design allowed us to track the effects of increasing homozygosity on male reproductive traits (sperm and testes size), male size and lifespan, and reproductive output within inbred families, and on the heritability of these traits. All traits measured showed significant inbreeding depression and heritabilities tended to increase with inbreeding. Since inbreeding resulted in shorter sperm and smaller testes, it suggests that longer sperm and larger testes confer higher fitness in this beetle.

Through behavioural adaptation, organisms can alter their environment, and consequently, their exposure to selective pressures. In contrast, physiological traits adapt by accommodating environmental influences. Here, we examine how the coevolution of behavioural and physiological traits is shaped by their different relationships to the environment by modelling the adaptation of species with temperature-dependent sex determination to climate change. In these species, pivotal temperature and maternal nesting behaviour can evolve in response to rising temperatures that destabilise sex ratios. We used individual-based simulation modelling to ascertain the relative response to selection of these traits and determine how temperature-dependent embryonic survival and behavioural plasticity influence their coevolution. We found that pivotal temperature evolved to ameliorate sex-ratio bias more readily than nesting behaviour, though behaviour played an important role in adaptation to extreme environments. Selection favoured increased behavioural evolution when embryonic survival depended on nest temperature, while plasticity reduced the adaptive potential of behaviour. We demonstrate that the capacity of behavioural traits to respond to multiple selective pressures has a substantial impact on the coevolution of behavioural and physiological traits. Our findings highlight the complex interactions that occur when species adapt to new environments and the potential for plasticity to shape the course of evolution.

Kin recognition in plants may lead to plastic changes in their behavior, such as altering their floral display size. In this study, we conducted evolutionary simulations of the two floral tactics utilized by plants depending on the genetic relatedness of their neighboring plants. We found that the evolutionary consequences of the floral display size in plants can be classified into four types, based on whether the floral display size increased or decreased in comparison with the case plants disable of kin recognition. As a typical result, the plants that grew with kin behaved altruistically by increasing their floral display size, whereas those that coexisted with strangers behaved selfishly by reducing their floral display size, as is observed in the field. The kin recognition and resultant evolution of the floral display size had the spillover effect on the population scale. Kin recognition generally increased the intraspecific variation in the floral display size and seed production, and decreased the genetic diversity of plant populations.

Sex chromosomes are theorised to stop recombining and become fixed, yet many taxa show ambiguous genomic signals of sex consistent with either continuous recombination or sex chromosome turnover. Elucidating the basis of sex chromosome conservation or alternatively, turnover, requires comparative studies among natural populations with shared evolutionary histories. The African Great Lake radiations of cichlid fishes display an outstanding propensity to rapidly evolve novel sex-linked regions, yet older cichlid lineages external to these radiations seem to show conservation of a few sex chromosomes. Here, we studied sex-determining regions of species uniquely representing two older lineages within Lake Tanganyika; Oreochromis tanganicae (Oreochromini) and Tylochromis polylepis (Tylochromini). Using a combined SNP- and kmer-based approach, we confirm a ZW system on linkage group (LG) 3 in O. tanganicae, but not the previously proposed sex-determining gene. However, in T. polylepis, no clear region of sex-association could be identified, although kmer-based analyses point towards LG12 as a candidate sex chromosome. Additionally, we investigated four other species from older, non-East African radiation lineages and confirm LG3 to be frequently associated with sex, but also find stronger signals of sex association on different chromosomes not previously discovered. Combined, these results suggest that homomorphic sex chromosomes are a feature of African cichlids at large. LG3 frequently harbours regions of sex-linkage, but is often polygenic with more strongly sex-linked regions on other chromosomes, possibly denoting its ancestral function as sex-determining across African cichlids, that leaves traces as novel sex-determining regions emerge. Our investigation captures this in a phylogenetic context, from emergence, to fixation, or turnover to a new sex chromosome.

Phenotype-environment associations in neonatal animals may arise in wild environments by virtue of ecological dynamics within the nest. Such dynamics may be of special importance to the evolution of temperature-dependent sex determination (TSD), an enigmatic trait which can be adaptive when the incubation temperatures that affect sexual differentiation also have differential effects on fitness of the sexes. To infer causal effects of the nest environment on fitness-relevant phenotypes, we apply structural equation modeling (SEM) to a 14-year dataset of 3085 individual embryos whose position in 179 wild snapping turtle nests could be estimated. We find that temperature has a positive effect on hatchling size, and that the same temperatures that predict hatchling size also predict sex of hatchlings. Further, the probability that embryos develop as males is correlated with hatchling size in the wild, where across all environments, males are slightly and significantly larger than females at hatching. Our SEM reveals that the covariance between size and sex arises because of temperature effects on size, and because of a predictable covariance between egg placement within the nest coupled with maternal effects on egg size. Finally, embryos deep in the nest have a high probability of becoming male even in the hottest years. Our study suggests ecological dynamics occurring within the nest are an interesting and underappreciated source of phenotypic variation. Our study also supports the view that TSD is an adaptive trait, rather than a neutral trait, by showing consistent associations between phenotype and temperature in wild nests of a TSD reptile.

Investigating the evolution of complex traits in nature requires accurate assessment of their genetic basis. Quantitative genetic (QG) modeling is frequently applied to estimate the additive genetic variance (VA) in traits, combining phenotypic and pedigree data from a sample of individuals. Whether reconstructed from social links or molecular markers, empirical pedigrees differ in completeness, genealogical error rates and other attributes that can impact QG estimation. Here we investigate this impact using human genealogical data for six French-Canadian (FC) populations originating from the same genetic founding source but differing in their pedigrees' attributes. First, we simulated phenotypic values along pedigrees and under different trait architecture and 'true' parameter values (e.g. VA). Then we fitted mixed effects 'animal' models to these simulated data, to assess how QG estimation was impacted by pedigree attributes. Our results show that pedigree size and depth were important determinants of the precision, but not accuracy, of genetic parameter estimates. In contrast, pedigree completeness and entropy, two attributes related to the density of genealogical links, were not clearly associated with the performance of parameter estimation. Noticeably, a slight increase in the genealogical error rate was sufficient to cause a detectable underestimation of VA. Including maternal genetic effects into the simulations lead to a slight underestimation of VA with pedigrees of smaller size and depth. Despite originating from the same genetic source, the six pedigrees yielded wide variations in QG estimates under identical conditions. These findings highlight the importance of sensitivity analyses in pedigree-based genetic studies on natural populations.

Researchers have shown growing interest in using deep neural networks (DNNs) to efficiently test the effects of perceptual processes on the evolution of colour patterns and morphologies. Whether this is a valid approach remains unclear, as it is unknown whether the relative detectability of ecologically relevant stimuli to DNNs actually matches that of biological neural networks. To test this, we compare image classification performance by humans and 6 DNNs (AlexNet, VGG-16, VGG-19, ResNet-18, SqueezeNet, and GoogLeNet) trained to detect artificial moths on tree trunks. Moths varied in their degree of crypsis, conferred by different sizes and spatial configurations of transparent wing elements. Like humans, four of six DNN architectures found moths with larger transparent elements harder to detect. However, humans and only one DNN architecture (GoogLeNet) found moths with transparent elements touching one side of the moth's outline harder to detect than moths with untouched outlines. When moths took up a smaller proportion of the image (i.e., were viewed from further away), the camouflaging effect of transparent elements touching the moth's outline was reduced for DNNs but enhanced for humans. Viewing distance can thus interact with camouflage type in opposing directions in humans and DNNs, which warrants a deeper investigation of viewing distance/size interactions with a broader range of stimuli. Overall, our results suggest that human and DNN responses had some similarities, but not enough to justify widespread use of DNNs for studies of camouflage.