This site-scale stochasticity is affected only by fecundity and therefore occurs even in infinitely large communities. In many cases where the establishment-longevity trade-off does not cause alternative stable equilibria, the trade-off still decreases the rate of convergence toward the single equilibrium, resulting in decades of transient dynamics that can appear indistinguishable from alternative stable equilibria in empirical studies.AbstractGenetic variability is essential for adaptation and could be acquired via hybridization with a closely related lineage. We use ants to investigate thermal adaptation and the link between temperature and genetic variation arising from hybridization. We test for differences in cold and heat tolerance between Finnish Formica polyctena and Formica aquilonia wood ants and their naturally occurring hybrids. Using workers, we find that the parental individuals differ in both cold and heat tolerances and express thermal limits that reflect their global distributions. Hybrids, however, cannot combine thermal tolerance of parental species as they have the same heat tolerance as F. polyctena but not the same cold tolerance as F. aquilonia. We then focus on a single hybrid population to investigate the relationship between temperature variation and genetic variation across 16 years using reproductive individuals. On the basis of the thermal tolerance results, we expected the frequency of putative F. polyctena alleles to increase in warm years and F. aquilonia alleles to increase in cold years. We find support for this in hybrid males but not in hybrid females. These results contribute to understanding the outcomes of hybridization, which may be sex specific or depend on the environment. Furthermore, genetic variability resulting from hybridization could help hybrid wood ants cope with changing thermal conditions.AbstractTransitions between sexual and unisexual reproductive modes have significant consequences for the evolutionary trajectories of species. These transitions have occurred numerous times in vertebrates and are frequently mediated by hybridization events. Triploid unisexual vertebrates are thought to arise through hybridization between individuals of a diploid unisexual lineage and a sexual species, although additional evidence that confirms this mechanism is needed in numerous groups. North American whiptail lizards (Aspidoscelis) are notable for being one of the largest radiations of unisexual vertebrates, and the most diverse group of Aspidoscelis includes numerous triploid lineages that have no known diploid unisexual ancestors. This pattern of "missing" ancestors may result from the short evolutionary life span of unisexual lineages or the selective advantages of polyploidy, or it could suggest that alternative mechanisms of triploid formation are operating in nature. We leverage genomic, morphological, and karyotypic data to describe a new diploid unisexual whiptail and show that it is likely the unisexual progenitor of an extant triploid lineage, A. opatae. We also resolve patterns of polyploidization within the A. sexlineatus species group and test predictions about the phenotypic outcomes of hybridization.AbstractBiodiversity in communities is changing globally, including the gain and loss of host species in host-pathogen communities. RGT-018 Increased host diversity can cause infection prevalence in a focal host to increase (amplification) or decrease (dilution). However, it is unclear what general rules govern the context-dependent effects, in part because theories for pathogens with different transmission modes have developed largely independently. Using a two-host model, we explore how the pathogen transmission mode and characteristics of a second host (disease competence and competitive ability) influence disease prevalence in a focal host. Our work shows how the theories for pathogens with environmental transmission, density-dependent direct transmission, and frequency-dependent direct transmission can be unified. Our work also identifies general rules about how host and pathogen characteristics affect amplification/dilution. For example, higher-competence hosts promote amplification, unless they are strong interspecific competitors; strong interspecific competitors promote dilution, unless they are large sources of new infections; and dilution occurs under frequency-dependent direct transmission more than density-dependent direct transmission, unless interspecific host competition is sufficiently strong. Our work helps explain how the characteristics of the pathogen and a second host affect disease prevalence in a focal host.AbstractSpecies-area relationships (SARs) describe how the number of species increases with the size of the area surveyed. They usually take the form of a power law on regional spatial scales. A metareview of empirical data has shown that the exponent of the power law is larger on average when the areas are sampled in a nested manner, compared with sampling of isolated areas such as islands or nature reserves of different sizes. Because this finding contradicts ecological reasoning, we performed computer simulations of three qualitatively different models that generate species distributions in space and time driven by the mechanisms of speciation, dispersal, and extinction. We find that in all cases and over a wide parameter range the SARs obtained by nested sampling have a smaller slope on the regional scale than those obtained by independent sampling. However, the slopes change considerably with spatial scale and in a different manner for the two sampling methods. By evaluating the spatial scales on which the two types of empirical data were taken, we can explain the discrepancy between simulation results and empirical data.AbstractEmpirical evidence suggests that coevolutionary arms races between flowering plants and their pollinators can occur in wild populations. In extreme cases, trait escalation may result in evolutionary switching from mutualism to parasitism. However, theoretical approaches to studying coevolution typically assume fixed types of ecological interactions and ignore the evolution of absolute fitness. Here, we introduce a novel approach to track the evolution of absolute fitness as a framework to determine when escalatory coevolution results in a switch from mutualism to parasitism. We apply our approach to two previously studied mechanisms mediating selection as a function of phenotype. Our results demonstrate that interactions mediated by a "bigger-is-better" mechanism evolve toward parasitism. In contrast, generalizing the classical trait-matching mechanism so that the fitness of each species is optimized when trait values mismatch by a particular amount, we find theoretical support for indefinite trait exaggeration that preserves mutualistic interactions.