American Naturalist最新文献

AbstractPollinators are important drivers of floral variation and speciation in plants. Here we investigate the effects of functional trait matching on pollen receipt in two plant species, Tritoniopsis revoluta and Nerine humilis, each visited by long-proboscid nemestrinid flies and bees across their ranges. Using single visits by pollinators to flowers with increased variance in floral morphology, we construct performance surfaces based on pollen receipt. We find divergent pollen receipt surfaces mediated by functionally different pollinators, within and between plant populations. Our results illuminate the nuances of how plants adapt to increase reproductive output in multipollinator communities, in which pollinators vary in their effectiveness.

AbstractThe population-level consequences of predator-prey interactions include unstable equilibria and predator-prey cycles with an approximate quarter-period phase lag. Prior studies have found that inducible defenses and rapidly evolving defenses alter the stability and phase lags of predator-prey systems differently: inducible defenses are stabilizing and decrease phase lags more frequently than evolving defenses. Using predator-prey models, we show that inducible and evolving defenses have the same range of possible effects, but the effects of inducible defenses depend on induction stimuli, reversibility, and timing. Inducible defenses responding to predator density, predator and prey densities, or predation cues are often stabilizing, but they can be destabilizing when defense is overexpressed. Only inducible defenses responding to predator and prey densities or the fitness gradient can increase phase lags. Compared with intragenerational reversible defenses, irreversible and transgenerational inducible defenses are less stabilizing and increase lags more when defense costs are sufficiently high; the opposite holds for low defense costs. We predict that inducible defenses are destabilizing and increase phase lags less often than evolving defenses because induction is a negative feedback (a self-limiting effect), whereas disruptive selection on an evolving defense is a positive feedback (a self-amplifying effect).

AbstractHeterogeneity and seeming unpredictability in responses to environmental change is driving a push to understand the underlying organismal mechanisms. The 2024 Vice Presidential Symposium of the American Society of Naturalists aimed to catalyze a promising and underutilized approach to extend understanding: repeating historical experiments or otherwise quantifying organism function through time. Many physiological, behavioral, ecological, and evolutionary experiments or observations reported in journal articles and elsewhere offer the potential for repeating the data collection to detect responses to environmental change. The approach extends beyond resurrection studies, which revive organisms to compare function and performance of modern organisms to their historical counterparts but are severely taxonomically and logistically restricted. In this introductory article, we discuss the promise of functional resurveys and highlight exemplar research repeating physiological measurements, behavioral experiments or observations, selection and quantitative genetic experiments, and measurement of ecosystem function. We also feature novel approaches to infer function from both modern and historical specimens and data, including temporal genomics, quantifying composition or energy stores, and genomic reconstruction. The research reveals key organismal mechanisms that mediate responses to environmental changes and can be accounted for to improve ecological and evolutionary forecasts.

AbstractIn organisms with separate sexes, the expected evolutionary change in a trait due to selection can be expressed using sex-specific Robertson covariances (RCs), that is, the additive genetic covariance between the trait and female relative fitness and the additive genetic covariance between the trait and male relative fitness. Sex-specific RCs capture the effects of (1) direct and indirect selection acting on the trait in the sex it is measured in ("within-sex selection") and (2) direct and indirect selection experienced by the underlying loci when expressed in the opposite sex ("cross-sex selection"). Using hemiclonal analysis in Drosophila melanogaster, we investigated the expected response to within-sex and cross-sex selection for a suite of traits involved in interlocus sexual conflict (IeSC) at male-biased, equal, and female-biased adult sex ratios. Our results are consistent with the idea that IeSC and sexual selection become stronger with the degree of male bias in adult sex ratio. The expected responses to cross-sex selection were small and typically concordant relative to the expected response to within-sex selection, with no evidence of intralocus sexual conflict for the traits we investigated. On the contrary, our findings imply that cross-sex selection may substantially boost the rate of adaptation in females.

AbstractUnderstanding how prey camouflage, behavior, and habitat interact to affect predator perception will clarify the mechanisms underlying predator-prey interactions. These questions are particularly critical for seasonally polyphenic prey facing increased predation risk owing to camouflage mismatch under decreasing snow cover. Using falconry-trained goshawks (Accipiter atricapillus), we experimentally evaluate how raptors perceive white and brown lures in snowy and bare ground conditions and assess how motion and habitat influence attack distance. We find that mismatch influences raptor detection of stationary models but not moving lures. Attack distances were greater in open habitats compared with forest. Mismatch with ground color significantly increased detectability of white hare models relative to mismatched brown hare models, suggesting unequal predation risk for mismatched white and brown morphs. Our results may imply fitness differences for winter-white and invariant-brown morphs of seasonally polyphenic species under future climate scenarios and implicate behavior as a risk factor.

AbstractWhen vital rates are convex functions of environmental drivers, temporal variation in those vital rates could increase long-term stochastic fitness (so-called demographic lability). Yet no empirical cases of this phenomenon have yet been documented. We first outline three necessary steps to document lability: estimate how vital rates change with environmental drivers, quantify driver distributions, and compare the fitness effects of variation to a "no-variation" baseline driver value (typically its mean). We then review articles that presented evidence for lability and find that none fully documented it. In addition, we examine for the first time when natural selection would produce adaptive lability de novo, rather than other adaptations to stochastic environments, and we suggest that selection to better exploit the most frequent environmental states may often erode lability. Finally, we consider conditions (including life history "speed," shape of vital rate/environment relationships, and type of environmental driver) that might support lability. We argue that lability is less likely in response to abiotic than biotic drivers but question whether fast and slow life histories differ in their propensity for lability. Our principal aim is to suggest research directions that would put the intriguing idea of demographic lability on a firmer foundation.

AbstractThe sociosexual environment shapes the expression of same-sex sexual behavior (SSB). Empirical studies on SSB in insects often find that sex discrimination, when plastic, is weaker under male-biased sex ratios, ostensibly contradicting theory and experimental evolution that show that stronger sex discrimination evolves under male-biased sex ratios. We develop theoretical models to assess the role of the sex ratio on learned sex discrimination. We find that males have the strongest sex discrimination when they have the greatest opportunity to experience conspecifics from which they learn. Learned sex discrimination is most likely to evolve when innate discrimination is costly, costs to learning are low, mating with the opposite sex is costlier than attempted matings with the same sex, and late matings produce more offspring. Learning from unsuccessful mating attempts with males typically outcompetes other learning strategies, although learning from successful matings with females or learning from all mating attempts can evolve when individuals have few opportunities to mate or costs to discrimination are low. We argue that the life history of insects may favor learning from successful matings or all mating attempts and thus drive the apparent disconnect between the effect of the sex ratio on learned versus innate sex discrimination; we also provide nonadaptive alternatives.

AbstractIn animals, choosers assess the attractiveness of courting individuals based on multiple sexual traits rather than a single trait. To quantify mate choice toward combinations of these traits, it is essential to analyze choosers' responses. The chooser's responses can depend on the courter's identity, indicating that the mate choice of the chooser is based on the courter's overall attractiveness. In addition, examining mate choice across different mating stages (precopulatory, copulatory, and postcopulatory) by assessing courter identity effects on chooser behaviors can further clarify mating dynamics. Moreover, estimating the contribution of each sex to the variation in copulation frequency can provide insights into the mating system. Here, we examined the water strider Gerris gracilicornis and found that pre- and postcopulatory behaviors in both sexes did not vary with the identity of the opposite sex, indicating a lack of pre- or postcopulatory mate choice in either sex. Our results also suggested that copulation frequency was not influenced by males, thereby confirming the absence of forced copulation in G. gracilicornis. Overall, this study offers a novel approach for understanding the mating system of a species and assessing stage-specific mate choice based on overall attractiveness.

AbstractSalinization poses a widespread threat to freshwater ecosystems. Land use practices and sea level rise contribute added salt, while climate change may drive increasing fluctuations in salinity. Evidence of local adaptation to salt stress indicates that evolution may mitigate some of the ecological harm that salinization would inflict. However, the extent to which populations may adapt to fluctuating salinity conditions remains poorly understood. We performed a common-garden experiment examining the evolutionary response of a Daphnia population to interannual variation in salinity conditions observed in a coastal Maine lake. Daphnia isolated during peak salinity conditions (2022) and several months after another salinity peak (2019) showed substantially increased survival and reproduction under chronic sea salt stress relative to Daphnia isolated during a period of relatively low-ion conditions (2021). We hypothesize that Daphnia egg bank dynamics and a fitness cost of salt tolerance under low-ion conditions may explain these evolutionary dynamics.

AbstractReef halos are rings of sand, barren of vegetation, encircling reefs. However, the extent to which various biotic (e.g., herbivory) and abiotic (e.g., temperature, nutrients) factors drive changes in halo prevalence and size remains unclear. The objective of this study was to explore the effects of herbivore biomass, primary productivity, temperature, and nutrients on reef halo presence and width. First, we conducted a field study using artificial reef structures and their surrounding halos, finding that halos were more likely to be observed with high herbivorous fish biomass and that halos were larger under high temperatures. There was a distinct interaction between herbivorous fish biomass and temperature, where at high fish biomass, halos were more likely to be observed under low temperatures. Second, we incorporated environmental drivers into a consumer-resource model of halo dynamics. Certain formulations of temperature- and nutrient-dependent vegetation growth caused halo width and fish density to change from a fixed to an oscillating system, supporting the idea that environmental drivers can cause temporal fluctuations in halo width. Our unique combination of field-based and mechanistic modeling approaches has enhanced our understanding of the role of environmental drivers in grazing patterns, which will be particularly important as climate change causes shifts in marine systems worldwide.