Journal of Evolutionary Biology最新文献

Cork oak (Quercus suber) is an ecologically and economically important Western Mediterranean tree species in severe risk of decline due to aggravated tree mortality and lack of natural regeneration. In Q. suber, two distinct chloroplast lineages, one of them of trans-specific origin, occur in sympatry in the western half of its species distribution. We hypothesize that selection may drive the maintenance of the two lineages and investigate this hypothesis by sequencing chloroplast genomes of 259 Q. suber samples across 24 locations. Protein-coding chloroplast genes were scanned for selection signal using different codon-based methods. Selection signal was found at different sites and genes, and polymorphism in selected sites was shown to segregate between the two chloroplast lineages. We postulate that trans-specific chloroplast diversity in Q. suber is preserved by balancing selection, rather than resulting exclusively from ongoing introgression. These results correspond to an unusual case of balancing selection on whole plastid genomes in a long-lived woody plant species and have implications on conservation and management practices for Q. suber, which may benefit from taking into account genetic variation in plastid genomes as a possible source of increased adaptive potential for the species.

Phylogenetic comparative methods are a major tool for evaluating macroevolutionary hypotheses. Methods based on the mean-reverting stochastic Ornstein-Uhlenbeck process allow for modelling adaptation on a phenotypic adaptive landscape that itself evolves and where fitness peaks depend on measured characteristics of the external environment and/or other organismal traits. Here, we give an overview of the conceptual framework for the many implementations of these methods and discuss how we might interpret estimated parameters. We emphasize that the ability to model a changing adaptive landscape sets these methods apart from other approaches and discuss why this aspect captures long-term trait evolution more realistically. Recent multivariate extensions of these methods provide a powerful framework for testing evolutionary hypotheses but are also more complicated to use and interpret. We provide some guidance on their usage and put recent literature on the topic in biological rather than mathematical terms. We further show how these methods provide a starting point for modelling reciprocal selection (i.e., coevolution) between interacting lineages. We then briefly review some critiques of the methodologies. Finally, we provide some ideas for future developments that we think will be useful to evolutionary biologists.

Understanding the mechanisms that confer resilience to thermal stress is crucial in the context of climate change. Recently there has been increasing focus on sublethal effects of high temperatures, such as on reproduction. Male fertility is particularly sensitive to heat, and the upper Thermal Fertility Limit (TFL) is a better predictor of species' geographical ranges than lethal limits (LT) alone. Drosophila fruit fly species vary in their TFL and in the magnitude of difference between TFL and LT, but what drives this variation is unknown. We hypothesised that expression of Heat shock proteins (Hsps), known to play a role in both the heat stress response and spermatogenesis, may explain these species differences. We compared the effects of a short, moderate thermal shock on the expression of seven Hsps in the male reproductive tract versus the rest of the body, across six drosophilid species. Patterns of expression varied across tissues and species both before and after heat shock. There is some indication that species with lower lethal limits show greater upregulation in response to heat shock in somatic tissue. There was no clear pattern of differential regulation in relation to absolute TFL, but a suggestion that species with a larger TFL-LT gap lack differential regulation in reproductive tissue. Hence, whilst Hsp expression may play a role, there are clearly other mechanisms that underlie the sensitivity of species' fertility to elevated temperatures which need to be assessed.

Theory suggests that a population with a narrower niche can adapt more rapidly to environmental change, all else being equal. However, a narrow niche may be correlated with other factors that compromise evolvability, such as a smaller population size, and it is unclear if specialist mutants can succeed by virtue of greater evolvability when impeded by the ecological costs of a narrower niche. Here we use simulation models to show that specialist mutants can invade during periods of rapid environmental change, in some cases preventing extinction. Focusing on asexual populations, we show that successful specialist mutants typically enjoy two types of advantages over generalists: an immediate benefit of ignoring a habitat in which they are particularly unfit, and a longer-term benefit of greater evolvability. By understanding the mechanisms that yield these benefits, we are also able to show that evolutionary rescue by specialization can be largely prevented by manipulating the schedule of environment change. Our results demonstrate how a population may change fundamentally under strong pressure to adapt rapidly, with implications for both beneficial (e.g., conservation) and harmful (e.g., antibiotic resistance) examples of evolutionary rescue.

Symbiosis is considered a source of evolutionary innovation. Example innovations that have evolved in symbioses include new organs, morphological adaptations, and metabolic abilities. However, it is unknown whether symbiosis is special with respect to generating innovation. In other words, does having a symbiotic partner tend to result in more innovation relative to not having a partner? Here, I argue that there are two gaps standing in the way of understanding the role of symbiosis in the evolution of innovation: 1) we have not rigorously quantified whether symbiosis tends to increase innovation and 2) we have not fully articulated evolutionary mechanisms that operate differently in symbiosis that could lead to more innovation. To overcome these gaps, I suggest that experimental evolution and comparative methods can be used to quantify whether symbiosis is a source of innovation. I then describe some unique features of symbiosis that promote (or hinder) the evolution of innovations through effects on evolvability. Measuring innovation and integrating concepts of evolvability into the study of symbiotic interactions will allow us to understand when and how symbiosis drives innovation.

Echimyidae, the largest family of Hystricognathi rodents, comprises 28 genera and 103 species across South and Central America and shows significant karyotypic variation, with diploid numbers (2n) from 14 to 118 and autosomal fundamental numbers (FNa) from 14 to 168. However, eight genera still lack karyotype descriptions. This study describes the karyotype of Echimys chrysurus from Amazonian Brazil (Paragominas and Santa Bárbara do Pará), using G-banding, C-banding, and FISH with telomeric and 18S rDNA probes. The species has a 2n = 80/FNa = 134 karyotype. The autosomal set consists of 28 meta/submetacentric pairs (1-28) and 11 acrocentric pairs (29-39); the X chromosome is a large acrocentric and the Y chromosome is a small acrocentric. Constitutive heterochromatin is centromeric in all autosomes and the X. Telomeric probe signals are distal, and the 18S rDNA probe shows a single interstitial signal. Review of 118 published karyotypes (66 species, 20 genera) integrated with multilocus phylogeny reveals bidirectional chromosomal evolution from an inferred ancestral karyotype (2n ≈ 60), through multiple lineage-specific Robertsonian translocations, centric fissions, and pericentric inversions. Arboreal Echimyini have higher 2n values, while several terrestrial or semifossorial taxa display marked reductions; these changes align with Miocene-Pliocene dispersals, Andean uplift, and habitat transitions to canopy, open areas, and flooded forests, suggesting rapid chromosomal change and speciation driven by ecological and geographic factors.

Aerobic respiration in mitochondria is the source for most of the energy that powers complex animals, and maintaining energy flow from mitochondria near the optimum needed for life processes presents challenges for complex animals. Environments of most animals change rapidly. Moreover, individuals pass through developmental stages with different energy demands, and they shift life-history states that require modified production of adenosine triphosphate (ATP). To adjust to changing conditions, all complex animals display some capacity for acclimatization through phenotypic flexibility, whereby key aspects of mitochondrial respiration are reversibly altered. Phenotypic flexibility is a universal feature of the energy-production mechanisms of animals, but all animals face limitations in the range of environments and circumstances to which they can acclimatize. We discuss multiple examples of such phenotypic flexibility in animals, focusing on the different mechanisms employed that acclimatize mitochondrial respiration to exogenous and endogenous challenges. Genotype sets the range of phenotypes related to mitochondrial respiration that is available to an animal. Numerous studies document adaptive evolution of both mitochondrial and nuclear genes that directly affect the range of environments that will support oxidative phosphorylation. Phenotypic flexibility can obscure evolutionary changes in response to changing energy demands, and understanding the interplay of capacity for acclimatization and adaptive evolution of mitochondrial systems presents major challenges for physiological and evolutionary biologists.

Invasive plants often thrive in nutrient-rich environments because of their superior ability to capture and efficiently exploit nutrients. This fitness advantage is commonly explained by invasive species being more plastic than their non-invasive counterparts. However, the extent to which individual traits vary in their plastic responses to nutrient availability-and how these responses translate into fitness gains-remains poorly understood. We conducted a nutrient addition experiment in invasive Erythranthe guttata to determine how plasticity to nutrient levels varied among traits, among populations, and with growing conditions. Populations from both upland and lowland New Zealand were grown under "normal" and excessive soil nutrient levels, in an upland and a lowland common garden. We found no evidence of evolution in plastic responses between altitudinal groups. Common garden (growing environment) had a small but significant maladaptive interaction with nutrient responses; in the upland garden, plants growing under excess nutrients showed stunted growth, in contrast to the expected adaptive plastic response of larger leaves under high soil nutrients. The strength of nutrient responses among traits corresponded to their importance in the selection analysis, suggesting an adaptive plastic response. Additionally, in contrast to recent findings for other species, we found no relaxation of seed size and number trade-offs with nutrient addition, which suggests that this is not a consistent driver of invasive success. Overall, our findings increase our understanding of how invasive plants exploit high resource conditions through adaptive plasticity at the trait level, despite limitations in challenging environments.

Morphological differences between the sexes are frequently reported in wild populations, which can extend beyond overall body size and result in differences in the size and/or shape of specific traits. Sexually selected traits have historically been expected to display positive allometric scaling (i.e., relatively larger trait in bigger individuals), although recent works suggest that negative allometric scaling (i.e., relatively larger trait size in smaller individuals) are equally likely. We used a long-term dataset to quantify sexual dimorphism and sex-specific allometric scaling of morphometric traits in a wild bird described as monomorphic, the Alpine swift. We identified subtle sexual dimorphisms suggesting that the Alpine swift is rather a cryptically dimorphic species. Fork length was the most sexually dimorphic trait, with males displaying 7% longer forks than females. Furthermore, we found that the extent of sexual dimorphism in swifts has changed over the past two decades, such that male and female feather traits have become more similar. Finally, we show that fork length scaled negatively with wing length in both sexes, indicating that short-winged individuals had relatively larger forks. In line with selection on multiple sexual ornaments and the functional allometry hypothesis, which predicts that patterns of allometric scaling should depend on the function of the trait in question (i.e., negative allometric scaling does not need to accurately reflect body size but rather "attractiveness"), we suggest that short-winged individuals may have to compensate for their reduce attractiveness in body size by exaggerating their fork size.