American Naturalist最新文献

AbstractMost species distributions are dynamic, and as species distributions change they often encounter novel environments and resident species. To establish new populations, ecologically similar species compete with residents for resources while adapting to the environment. Yet local adaptation in residents can allow them to outcompete maladapted invaders and prevent their establishment. Indeed, local adaptation often improves male condition but also intensifies sexual conflict, a process where males increase their fitness while decreasing female fitness. Using an eco-evolutionary model, we show that sexual conflict can prevent adapted residents from monopolizing resources. This cost of adaptation in the residents opens a window of opportunity for the establishment of maladapted invaders. Female resistance to male harm can, however, prevent the invader from establishing. Sexual conflict can therefore reduce differences in competitive ability, facilitating establishment, but does not affect niche differences. However, when sexual conflict is density dependent, it can facilitate resident and invader coexistence, even when interspecific competition is stronger than intraspecific competition. Our results show that reproductive interactions may critically shape the dynamics of species invasions and species coexistence.

AbstractSeveral metrics have been proposed to measure phenotypic parallel evolution. All of these metrics stem from a geometric definition of parallel evolution in which two evolutionary trajectories are, literally, parallel or nonparallel to each other. Two metrics fit this definition: the interaction term between population and habitat in a two-factor ANOVA and a measure of the angle between two multivariate trajectories of evolution. A third metric is derived from the general direction of multivariate trajectories; although this might fit our intuition about parallel evolution, it does not fit the geometric definition. A fourth metric is based on the amount of variation explained by the habitat variable in a one-factor ANOVA (i.e., the R²). We show here that the R² metric does not reliably measure any aspect of parallelism and should be avoided. We also discuss the importance of establishing proper ancestor-descendent relationships in attempting to use any of the valid metrics to quantify parallel evolution. Finally, because different metrics measure different aspects of evolutionary trajectories, we recommend being explicit about what one is trying to measure (angle, direction, or length of trajectories).

AbstractMultitrait analyses can be used to measure the differential performance of phenotypic traits in species complexes. Hybridization within these complexes can result in a mismatch between mitochondrial and nuclear DNA that may lead to reduced performance and acclimation capacity in hybrids. To test the effect of this mismatch on physiology, we compared physiological performance and acclimation capacity of metabolic rate ($\dot{\mathrm{V̇}}{\mathrm{CO}}_2$) and total resistance to water loss (r_T) between two sexual Ambystoma species and a closely related unisexual lineage. We also separated unisexuals by their unique biotypes to determine how physiology varies with subgenomic composition. We found that unisexual biotypes exhibited phenotypes more like their related sexual species than other unisexuals. We also found a trade-off between r_T and $\dot{\mathrm{V̇}}{\mathrm{CO}}_2$, with increasing r_T resulting in a decrease in $\dot{\mathrm{V̇}}{\mathrm{CO}}_2$. Although we did not find evidence for mitonuclear mismatch, our results indicate that the genomic composition of hybrids may be a suitable predictor of hybrid trait performance. Multitrait analyses are imperative for understanding variation in phenotypic diversity, providing insight into how this diversity affects species responses to environmental change.

AbstractSynthetic gene drives are being investigated as tools to suppress pest populations, and it is important to understand how natural selection will act on variant drivers that may either arise by de novo mutation or be intentionally released. In this study, we extend previous spatially implicit stochastic models to examine the evolutionary dynamics of synthetic driving Y chromosomes in patchy environments when population size is responding dynamically to the spread of the driver and derive conditions for the existence of an evolutionarily stable strategy (ESS) for drive strength. Under broad conditions, an intermediate drive strength emerges as the ESS, capable of outcompeting both stronger and weaker variants. Additionally, we show how the intentional release of two drivers straddling the ESS can help stabilize population dynamics. Finally, inbreeding depression has the effect of expanding the range of conditions under which no intermediate ESS exists, with ever stronger drive being selected until the population is eliminated. These results provide insights into the expected evolutionary trajectories of gene drive systems, with important implications for the design and release of gene drives for pest and vector control.

AbstractHost-parasite theory is rooted in equilibrium dynamics. However, many host species exhibit "boom-bust" life histories or range expansions characterized by population booms and severe bottlenecks. The dynamic host density in boom-bust systems may disrupt the interactions between density-dependent processes such as parasite transmission and birth, resulting in unique dynamics compared with a host population at equilibrium. We subjected a simple compartment model to recurring host bottlenecks to approximate a boom-bust life history. We found that recurring bottlenecks suppressed disease spread by giving the host population an opportunity postbottleneck to expand faster than the disease could spread. As bottlenecks became more frequent and/or severe, disease spread was suppressed to such low levels that parasite extinction was virtually guaranteed. We found that our model was conservative and presented a near-best-case scenario for the parasite. Our results indicate that the dynamic host density of boom-bust systems creates new system behaviors that are not seen in equilibrium models. Additionally, we argue that our results generalize to any horizontally transmitted symbiont, including mutualists and commensals. We conclude that boom-bust dynamics must be explicitly modeled to accurately predict disease spread and the resulting evolutionary dynamics in hosts and their symbionts.

AbstractThermal preference (Tp) prevents ectotherms from encountering sublethal temperatures. Its plasticity likely modulates the importance of behavioral thermoregulation under changing conditions. While it has been widely recognized that Tp varies across ontogeny, the plasticity level of this trait across life stages is poorly understood. We propose a novel conceptual framework relating two plastic components of Tp: its mean, which indicates temperature affinity, and its variance, which informs on the precision of behavioral thermoregulation. We tested this framework at the population scale by measuring Tp variations across life stages of an insect model after several generations under contrasting developmental temperatures. Tp plastic responses differed among life stages. Generally, we obtained a bell-shaped relationship between temperature affinity and precision of thermoregulation, indicating a strategy to avoid suboptimal and supraoptimal temperatures in Drosophila melanogaster, but not in all life stages. We highlight the need to change the paradigm underlying the study of Tp plasticity beyond the use of a single metric (median or range) to better comprehend thermoregulatory strategies.

AbstractEndothermy is an energetically expensive trait, yet it has posed an evolutionary advantage across different lineages-a paradox that remains puzzling to biologists. Here, I investigate whether endothermy can evolve through life history optimization using a model of the balance between energy assimilation and energy allocation to somatic maintenance, thermoregulation, growth, or reproduction. The model displays bistable strategies when assimilation rates and thermoregulatory costs increase, respectively, exponentially and linearly with body temperature: the "heterothermic strategy" consists of minimizing the costs of thermoregulation by maintaining body temperature close to ambient temperature, and the "homeothermic strategy" consists of increasing body temperature until the costs of thermoregulation are fully compensated by the increased assimilation capacity at higher temperatures. These strategies produce similar fitness outcomes and thus emerge as alternative stable states of the system, maintained by strong stabilizing selection preventing transitions between them. Using quantitative genetics simulations, I show that a drop in ambient temperature may push populations toward an evolutionary branching point, enabling the rapid radiation of homeothermic lineages coupled with body size reductions. I thus propose that life history optimization of energy balance can explain the radiation of homeothermic endothermy associated with either climate cooling or migration to colder regions by early endothermic lineages.

AbstractThe decomposition of leaf litter is a major ecological process in terrestrial and aquatic ecosystems worldwide. Leaf litter generally enters ecosystems in annual pulses and is subsequently decomposed across many seasons. Yet investigations into this process are rarely conducted in parallel in aquatic and terrestrial ecosystems and over the full year, limiting our understanding of its phenological context across the blue-green interface. Here, we assessed the decomposition of three litter species by microorganisms and macroinvertebrates in temperate streams and forests across a year using repeated litterbag assays at 6-week intervals. We observed higher decomposition rates in summer in most combinations of ecosystem, litter species, and decomposer type, indicating positive effects of higher temperatures and low standing crops of labile litter. Furthermore, forests showed lower decomposition rates than streams. Last, we found that the relative litter species effects on both microbial and invertebrate decomposition were consistent across environments, suggesting that the fast microbial activity decreased the quality of the remaining tissue mass for invertebrates. Overall, our work places known drivers of the decomposition of leaf litter into a phenological context, providing evidence that changes in the timing or strength of these drivers could drive temporal shifts of this central ecological process.

AbstractPollinating seed predators are partners in a specialized plant-insect mutualism where insects pollinate the flower ovules of the seeds that they later consume. Such relationships have proven rare but provide a unique perspective on the mechanisms that drive (co)evolution. We combine natural history and community science observations to identify the red-shouldered bug (Jadera haematoloma) as the first member of the insect order Hemiptera to be classified in this guild. We use laboratory- and field-based experiments to demonstrate that J. haematoloma are consuming nectar and providing a pollination service for their host plants. However, the pollination benefit to the host is later reduced by seed predation from the pollinator's offspring. Furthermore, this study expands our perspective on the diet breadth of J. haematoloma, which is a model system for rapid ecological adaptation of feeding morphology that was historically attributed solely to selective pressures associated with accessing the seeds inside the fruit of their host plant.