American Naturalist最新文献

AbstractEvaluating the evolutionary impacts of anthropogenic activity on populations is key to understanding species resiliency and to designing effective conservation strategies. Sequencing DNA from historical specimens provides the opportunity to establish a historical baseline and empirically assess changes in genetic diversity, changes in effective population size, and selection over time. Here, we sequenced historical and contemporary samples of the cardinalfish Taeniamia zosterophora collected in 1908 and in 2021-2022 across two sites with differing human impact in the Philippines. At both sites, genetic diversity increased over time, with contemporary samples having significantly higher Watterson's θ than historical samples. This diversity increase was primarily attributable to positive selection on low-frequency alleles such that they increased toward intermediate frequencies through time. For the putatively neutral fraction of the genome, in contrast, there was a slight but significant decline in Watterson's θ at both low and high human impact sites, suggesting that drift strengthened and effective population sizes declined through time. There was more evidence for selection and greater loss of neutral diversity at the site with higher human impact. Our results provide empirical evidence for the surprising preservation of genetic diversity through the action of natural selection in the face of anthropogenic impacts.

AbstractRensch's rule posits that sexual size dimorphism increases with overall body size among animal species with larger males and that it decreases with body size among species with larger females. The rule, originally based on patterns observed in a limited dataset rather than theory, has attracted much attention in the sexual selection literature. However, evidence for the rule has been equivocal. We test Rensch's rule with a recently published dataset on sexual size dimorphism in mammals using linear regressions with phylogenetic controls. We find that neither male-biased nor female-biased dimorphic species conform to Rensch's rule across mammals. When the analysis is restricted to within-family comparisons, as Rensch originally intended, the rule applies only to three of the 21 mammalian groups tested. We find very limited support for the "rule" in mammals and suggest that it is unlikely to be the general phenomenon that Rensch proposed.

AbstractVariation in colonization ability (comprising the dispersal and successful establishment of lineages in new regions) and its connection to species diversification may be one of the major reasons why clades vary widely in standing diversity. Diversity variation driven by colonization ability can be generated under two scenarios. Under a neutral model, high colonization ability enables some clades to colonize unoccupied areas and over time diversify into more species. Under a nonneutral model, some competitively superior clades are able to rapidly diversify into already occupied niches, both on continents they already occupy and on continents they are invading. Because entire lineages occasionally become extinct, including those that have colonized other landmasses, it can be difficult to distinguish between these models based on extant species. Here, we test these two alternatives using a species-level phylogeny of all extant and extinct species of the mammalian order Carnivora and related extinct groups. We find that species that colonize new continents leave more descendant species than noncolonizers and that colonizing species belong to clades that were diversifying faster than noncolonizers at the time of colonization. Our results suggest that variation in diversification may be partly driven by nonneutral processes with variable competitive ability between lineages. Our study highlights the importance of including extinct species in phylogenies when trying to understand evolutionary and biogeographic patterns.

AbstractMutualistic interactions between plants and pollinators play an important role in supporting biodiversity and ecosystem stability. However, these interactions are increasingly threatened by climate change, which can alter the phenology of species and cause temporal mismatches between interacting partners. Leveraging historical and contemporary datasets collected more than a century apart, we investigated phenological shifts in plants and pollinators and the impact of changes in temporal overlap of the interaction partners on the persistence of their interactions. We found that the onset of flowering and insect activity generally started earlier and has lasted longer in the present. We also found that greater temporal overlap of plant and pollinator species predicted a higher probability of persistence of their interaction between time periods. Our results document phenological shifts over a century and emphasize the importance of maintaining phenological matching for the persistence of plant-pollinator interactions. This illustrates the value of historical datasets for understanding long-term ecological dynamics in the face of accelerating environmental change.

AbstractFunctional diversity is expected to decrease following land conversion. Empirically, however, the consequences of such changes are highly variable. One possible explanation is that the magnitude and direction of functional diversity change depend on how agricultural land conversion interacts with the original determinants of community assembly (e.g., temperature and elevation gradients). We compared the functional structure of 50 Anolis lizard communities on the island of Hispaniola in both forested and deforested habitats along an elevation gradient, as elevation often determines community composition. We used morphological measurements of body size, limb and tail length, and toepad width to capture ecomorphological aspects of functional diversity. These traits are strongly linked to habitat use, which has been shown to be the primary axis of niche partitioning in anoles. We found that deforestation had little effect on functional (morphological) richness at low elevations but increased functional richness and evenness at high elevations, where natural communities are depauperate owing to thermal constraints. Simultaneously, deforestation reduced spatial turnover and eliminated morphologically peripheral species. These results suggest that how land conversion affects communities depends on whether it relaxes or reinforces a community's dominant environmental filters: at high elevations, as deforestation increases daytime temperatures, the filters that typically shape these communities are relaxed, allowing them to functionally resemble low-elevation communities. While this enriches high-elevation communities, it also removes morphologically unique species and homogenizes diversity across elevations. Our results highlight that how land conversion reorganizes the functional structure of a community depends on environmental context.

AbstractSexual size dimorphism (varying body sizes between males and females) and the operational sex ratio (ratio of sexually active males to receptive females) are key demographic traits influenced by complex selective pressures. Two hypotheses explain their relationship: the mating competition hypothesis posits that male-biased sexual size dimorphism intensifies with increasingly male-skewed adult sex ratios, while the mating opportunity hypothesis proposes that female-biased sexual size dimorphism escalates with greater male-biased adult sex ratios. We tested these hypotheses across 101 Chinese anuran species. Our results support the mating opportunity hypothesis, with enhanced female-biased sexual size dimorphism at more male-skewed operational sex ratios, particularly in monogamous species. We further explored the role of ecological factors and life history traits in shaping sexual size dimorphism and operational sex ratio. We found predation pressure to covary negatively with the male bias in operational sex ratios, while temperature variation, likely reflecting seasonal differences, negatively influenced both sexual size dimorphism and operational sex ratio. Our findings highlight the interplay between sexual selection, ecology, and life history in driving the evolution of sexual size dimorphism and operational sex ratio in anurans. Understanding these mechanisms is crucial for predicting how species may respond to future environmental changes.

AbstractAs environmental change accelerates globally, understanding concurrent organismal, species, and community responses is increasingly vital. Here, we examine these collective responses by incorporating genotype-specific thermal reaction norms into an eco-evolutionary predator-prey model, allowing us to track simultaneous phenotypic, ecological, and evolutionary responses to environmental change within ecological communities. We show that the reaction norms expressed by genotypes within a population determine how a community switches between different eco-evolutionary outcomes with changes in temperature. We identify how different components of phenotypic variation in thermal reaction norms-environmental (E), additive environmental and genetic ($E+G$), and gene-by-environment interactions ($G\times E$)-influence eco-evolutionary dynamics and outcomes as temperature changes. Our findings underscore how complex eco-evolutionary responses to environmental change ultimately emerge from variation in reaction norms among genotypes, offering new mechanistic insights into environmental impacts on adaptation, the maintenance of phenotypic and genetic variation, and ecological stability, which is crucial for understanding and predicting eco-evolutionary effects of rapid environmental change in the future.

AbstractThe extent of contemporary evolution, which is mediated by interactions with plasticity, will be an important determinant of biological responses to climate change. We synthesize two functional resurvey projects that, coupled with mechanistic models, evaluate the interplay of plasticity and evolution of pierid butterfly larval (thermal sensitivity of feeding) and adult (wing melanization) traits over recent decades. We characterize thermal environments over the resurvey periods, which we interface with developmental and (historical, current, and hypothetical) thermal sensitivity traits to examine the implications of evolutionary changes. We find that the evolution of photoperiod-cued plasticity of wing melanization in California Colias is consistent with avoiding thermal stress during warming springs. Plasticity has not evolved for Colorado Colias populations, which have experienced stronger increases in climate means relative to extremes in recent decades. Evolution in Colorado Colias larvae has improved tolerance to warm extremes, whereas evolution in California Colias larvae has broadened thermal sensitivity, consistent with capitalizing on expanded seasonal thermal opportunity. Our models predict that Washington Pieris larvae have experienced shifts in the direction of selection to increase performance at warm temperatures. The research highlights the importance of evaluating changes in climate change exposure and sensitivity to understand interacting organismal responses.

AbstractAbrupt ecosystem shifts during the Late Quaternary coincided with major climatic changes and intensified human activities, but the precise causes of these shifts remain debated. Here, building on previous hypotheses and work, we propose a new hypothesis that both plant beneficial and antagonistic soil microorganisms were the proximate drivers of Late Quaternary change. We synthesized evidence from paleoecological studies and contemporary ecosystems to understand how microbes and their interactions with plants shift ecosystem function. Because relevant paleoecological data are nonexistent, we reanalyzed a contemporary survey from grasslands and woodlands across Europe to test the general role of microbial diversity versus climate in controlling ecosystem function. Our models found that the richness of different microbial groups, including Proteobacteria, mycorrhizas, and plant fungal pathogens, were more strongly associated with the magnitude of direct effects on net primary productivity than temperature and precipitation. The richness of most of these groups was also influenced by climate, supporting our hypothesis that climate change may have indirectly caused past ecosystem shifts by changing microbial composition and function. We end by highlighting the potential of environmental DNA to reconstruct the biota and conditions of past ecosystems. Ultimately, improving our understanding of how microbes drove past ecosystem shifts may improve our ability to respond to future environmental changes.

AbstractAfter a fitful start, the conceptual study of mutualism (mutually beneficial interspecific interactions) is now flourishing. In 1994, I reviewed the status of the field as reflected in the peer-reviewed literature; I also laid out directions for future research. Here, I look back on that assessment and offer an updated perspective on our understanding of mutualism. Most of the open questions I identified now have significant literatures of their own. New questions have sprung from each of these, and methodological innovations have made it more possible than ever before to obtain answers. I identify one astonishing gap from 1994: the absence of attention, either in journals or in my own synthesis, to the fate of mutualisms in a changing world. I offer a brief assessment of the now-massive literature on this topic. Finally, I suggest some directions in which the field as a whole might profitably move in the future.