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 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 , 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.

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 population to interannual variation in salinity conditions observed in a coastal Maine lake. 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 isolated during a period of relatively low-ion conditions (2021). We hypothesize that 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.

AbstractMajor ongoing theoretical and empirical challenges are to predict impacts of immigration on extinction probabilities of remaining populations within fragmented habitats. Comprehensive prediction requires considering multiple genetic effects on demography, including inbreeding and resulting inbreeding depression, additive genetic variance in fitness and resulting adaptive microevolution, and local adaptation and resulting migration load. However, all such effects have not been quantified or modeled simultaneously, especially for small wild populations experiencing regular natural immigration. We used quantitative genetic individual-based simulations parameterized using long-term data from song sparrows () to show that contrary to broad expectation, increasing immigration could slightly increase short-term extinction probability. This outcome arose because while immigration reduced inbreeding and resulting expression of inbreeding depression, migration load stemming from apparent local adaptation was substantial and counteracted local adaptive microevolution, especially given heterosis-enhanced introgression. However, alternative self-reinforcing outcomes of rapid extinction due to an inbreeding-induced extinction vortex or migrational meltdown, as well as persistence due to microevolution of increased population growth, commonly arose. These results imply that altering dispersal rates among populations will not necessarily predictably affect local population persistence over short eco-evolutionary timeframes and highlight how remaining populations can lie on a knife-edge between persistence and alternative routes to genetically induced extinction.

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.

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 (), 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.

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 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 . 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.

AbstractGradient variation evolves when environmental and genotypic effects on a phenotype covary positively (cogradient variation) or negatively (countergradient variation) across locations, whereas gene-by-environment interactions (G × E) reflect nonadditive genetic and environmental influences on phenotypes. Spatial covariance in environmental and genotypic effects (Cov) shapes variation in quantitative traits, facilitates local adaptation, and provides insights into eco-evolutionary dynamics. Yet several debates regarding gradient variation remain unresolved, including whether qualitative patterns of reaction norms accurately reflect Cov, whether cogradient or countergradient variation occurs more frequently than G × E, and whether general patterns emerge according to taxonomic groups, forms of environmental gradient, or trait types. We conducted a quantitative survey of 556 phenotypes and measured Cov and G × E across various phenotypes, taxa, and environmental gradients. We found that the qualitative assessment of reaction norms was unreliable for identifying Cov and that Cov occurred as frequently as G × E. No distinct patterns in Cov emerged across environmental, taxonomic, or trait-based groups. Our results challenge prevailing views regarding Cov and suggest that gradient variation can evolve under any environmental condition, taxonomic grouping, or trait type. We suggest that broader application of quantitative methods for Cov across diverse systems will enhance our understanding of Cov in nature.

AbstractEukaryogenesis is the prototypical example of an egalitarian evolutionary transition in individuality, and endosymbiosis, more generally, is central to the origins of many complex biological systems. Why do only some symbioses undergo such a transition, and how does the host-symbiont relationship change during this process? Here, we characterize endosymbiosis by two emergent collective-level properties: host and symbiont survival as a collective ("mutual dependence") and the level of synchronized reproduction ("reproductive cohesion"). Using adaptive dynamics, we study the evolution of the traits underlying these properties. First, by adding a carrying capacity for the collective population-a realism omitted in previous models-we find novel reasons why complete dependence or cohesion might not evolve, thus providing further theoretical support for the rarity of transitions in individuality. Second, our model suggests that asymmetries in evolutionary outcomes of hosts and symbionts can be explained by a difference in their population growth parameters, coupled with their shared fate when in a collective. Last, we show that during the early stages of an endosymbiosis, even if investments in dependence and cohesion are uncorrelated, mutual dependence arises faster than reproductive cohesion. Our results hence shed light on three aspects of endosymbiosis: coevolution between the host and symbiont, coevolution between dependence and cohesion, and ultimately the opportunity to undergo an evolutionary transition. Connecting to ecological factors, this work uncovers fundamental properties of endosymbioses, providing a clear way forward for theoretical and empirical investigations.

AbstractAnimals employ various mechanisms for camouflage, including color change, that may facilitate habitat use. However, the extent to which these mechanisms operate under nocturnal conditions is unclear. To investigate this, we combined a background-induced color change experiment with visual modeling to test whether altering backgrounds for a tropical tree frog () could induce short-term color change under nocturnal conditions to match the viewing background, as perceived by three predator classes: snakes, mammals, and birds. We demonstrated that frogs can change color multiple times from green to brown and back across grass and leaf litter backgrounds in dim conditions. Frog visual contrast varied by predator and background. Brown frogs matched against leaf litter across all predators, whereas green frogs were more variable and comparatively less well matched against grass. Notably, frogs achieved near-optimal color matching against both backgrounds for avian predators, with green frogs matching into grass and brown frogs matching into leaf litter. Our study provides evidence that undergoes rapid background-induced color changes at night maintaining effective camouflage, at least against avian predators. We emphasize the need to assess rapid color change against visually guided predators in natural conditions and the importance of understanding viewing conditions for illuminating the ecology and evolution of camouflage.

AbstractIn simultaneous hermaphrodites, resource availability and the temporal distribution of mates determine male and female fitness and optimal sex allocation. In insect-pollinated plants, we expect individuals to allocate more to their female function when they are large and more to their male function when other individuals have many ovules available to be fertilized. Here, we studied the dependence of sex allocation and male and female components of reproductive success on both the size and the timing of reproduction in the plant (Ranunculaceae), accounting for inbreeding depression and variation in the mating system. Female reproductive success depended positively on size, whereas male reproductive success depended on mate availability and the timing of flowering, as predicted. Moreover, male reproductive success trended to a saturating function of allocation to stamens, whereas female reproductive success was a slightly accelerating function of pistil production. These results provide new insights into the reproductive strategies of perennial plants and help to explain the joint strategy in of andromonoecy (the production of both male and bisexual flowers by individuals over the course of their lives) and gender diphasy (a shift between a male and a hermaphrodite phase among seasons).

AbstractNatural selection is widely considered responsible for the fit between organisms and their environment. Lizard limb length variation is a paradigmatic example: studies have shown that limb length differences tightly correlate with habitat use among species, while small differences in limb length between individuals can affect biomechanical function, fitness, and survival within populations. It has therefore been surprising for many field biologists to find otherwise-healthy wild lizards with damaged or missing limbs, appearing to challenge associated expectations of substantial fitness costs. We document limb loss (from a foot to an entire limb) in 58 lizard species, with all cases showing healed limbs and many lizards appearing robust and healthy. Data indicate that limb-deficient lizards typically comprise less than 1% of populations and often exhibit body condition, sprint speed performance, and survival comparable to limb-intact individuals. We discuss the implications of these findings for how evolutionary adaptation is studied and understood in natural populations and provide a perspective on conventional assumptions about the strength and ubiquity of selection pressures on seemingly critical traits. Is natural selection always as omnipresent as Darwin envisioned it to be?

AbstractSince the late 1890s up until today, how phenotypic plasticity interacts with genetic adaptation has been a debated issue. Proponents of a positive causal role of phenotypic plasticity-James M. Baldwin in the first place-supported the view that in altered environmental conditions, phenotypic plasticity is a key factor allowing a population to avoid extinction and then genetic evolution to catch up ("original Baldwin effect" [OBE]). Opponents, such as Ernst Mayr, regularly pointed out that phenotypic plasticity, by masking genetic variation, slows gene-level evolution ("Mayr effect" [ME]). For decades, this opposition remained only verbal and qualitative. To resolve it, we propose here a stochastic model that, following Baldwin's intuitive take, combines the minimal number of ingredients to account for extinction, selection, mutation, and plasticity. We study evolutionary rescue of the population (arrival and invasion of an adaptive genetic mutant) in the altered environment for different values of phenotypic plasticity, here quantified as the probability that the maladapted genotype develops into the adapted phenotype. Our claim is that OBE can be a genuine evolutionary mechanism, depending on the level of phenotypic plasticity with respect to a threshold value . When , increasing promotes evolutionary rescue by delaying extinction ("strong" OBE); when , plasticity sustains population survival and increasing has two antagonistic effects: to accelerate adaptation by increasing the supply of adaptive mutants ("weak" OBE, intermediate values of ) and to slow down adaptation by decreasing their fitness advantage (ME, high values of ).

AbstractMany ecological models treat exploitative competition in isolation from interference competition. Corresponding theory centers around the * rule, according to which consumers that share a single limiting resource cannot coexist. Here we model motile consumers that directly interfere while handling resources, mechanistically capturing both exploitative and interference competition. Our analytical coexistence conditions show that interference competition readily promotes coexistence. In contrast to previous theory, coexistence does not require intraspecific interference propensities to exceed interspecific interference propensities or for interference behaviors to carry a direct (rather than merely an opportunity) cost. The underlying mechanism of coexistence can resemble the hawk-dove game, the dominance-discovery trade-off (akin to the competition-colonization trade-off), or a novel trade-off we call the "dove-discovery trade-off," depending on parameter values. Competitive exclusion via the * rule occurs only when differences in exploitative abilities swamp other differences between species, and it occurs more easily when differences in * reflect different search speeds than when they reflect different handling times. Our model provides a mathematically tractable framework that integrates exploitative and interference competition and synthesizes previous disparate models.

AbstractMetapopulations span environmental gradients and experience variable rates of environmental change, with populations differing in their tolerance and evolutionary capacity. Our study aimed to quantify the extent to which interactions between population-specific traits and spatial environmental heterogeneity affect metapopulation persistence under climate change. Using an eco-evolutionary model, we simulated 25 population types with varying thermal tolerance breadths and genetic variance, impacting the strength of selection and rate of evolutionary response, respectively. We applied this framework to marine ecosystems, which face significant threats from climate change, with many habitat-forming organisms such as coral, oysters, and kelp existing as metapopulations connected through propagule dispersal via ocean currents. We tracked the response of different populations under sea surface temperature spatial ranges and projected warming rates to 2100 that are specific to 49 large marine ecosystems. We found that the rate of warming was the strongest predictor of the number of persistent metapopulations, where faster warming reduced the population types that a region could support. We also found that cooler subpopulations outperformed warmer ones, likely due to immigration from warmer sites, suggesting that cooler sites may act as climate refugia.

AbstractUnderstanding and identifying factors influencing the likelihood of sudden transitions in ecological systems is a significant area of scientific research. Environmental fluctuations are particularly important, as they can trigger these transitions before reaching the system's condition to a deterministic tipping point. While there has been much focus on noise-induced tipping due to uncorrelated environmental noise, the impact of correlated noise on multispecies systems has been relatively overlooked. Specifically, studies have neglected the impact of correlations between species responses to environmental changes and a system's susceptibility to tipping. This study examines various two-species ecological models representing different interaction types in noisy environments. We reaffirm that elevated positive temporal autocorrelations in environmental fluctuations aggravate the chance of tipping. Conversely, our key findings suggest that elevated positive correlations in species responses generally delay the onset of tipping, except when the system dynamics is solely driven by positive interspecific interactions. The correlation of species responses is also critical in determining the reliability of early warning signals for predicting sudden ecological changes. Our findings highlight the importance of considering the similarity between species' responses to environmental variability, which significantly influences the likelihood and detectability of dramatic ecological transitions.

AbstractThe evolution of sexual dimorphism is predicted to resolve conflict that can arise from divergent evolutionary interests between sexes, enabling each sex to reach its fitness optimum. However, most of the genome is shared between sexes, which can lead to a genetic constraint for dimorphism evolution. Most studies of intersexual genetic constraints have focused on the effect of genetic correlations, , for single traits. However, multivariate studies of the matrix of intersexual genetic covariances suggest that sexual dimorphism may be more evolvable than inferred from because of the potential for indirect responses to selection from correlated traits. To comprehensively address this question, we collected and reanalyzed published estimates of using a recently developed approach to quantify the evolvability of sexual monomorphism and dimorphism. We find that across the traits and species we study, the evolvability of dimorphism is lower than that of monomorphism, but also that sexually concordant and antagonistic selection are almost equally capable of producing dimorphism. We also find that asymmetry in would affect the response to selection more in females than in males. Our results show that sexual dimorphism is more evolvable than studies of suggest and underscore that sexually antagonistic selection is not required for the evolution of sexual dimorphism.

AbstractElevational distributions have long fascinated scientists, an interest that has burgeoned with studies of predicted upslope range shifts under climate change. However, this body of work has yielded conflicting results, perhaps due to varied conceptual and statistical approaches. Here I explore how ecological processes and researcher decisions shape the patterns characterized by elevational ranges. I use community science data to illustrate (1) that elevational ranges include variation in abundance; (2) that elevational ranges are usually estimated, not observed directly; (3) that elevational ranges are dynamic across short distances and time intervals; and (4) that how we describe elevational ranges has consequences for inference of range shifts. I present a conceptual framework for understanding elevational ranges across multiple spatial scales and propose that elevational distributions are governed by scale-dependent processes. This framework implies that accurately quantifying elevational ranges and learning how they are formed or maintained requires matching questions to their appropriate scale domain. I provide a list of best practices for studying elevational ranges and highlight promising directions for future research into these complex phenomena.