Unravelling the role of tropical cyclones in shaping present species distributions

Driven by climate change, tropical cyclones (TCs) are predicted to change in intensity and frequency through time. Given these forecasted changes, developing an understanding of how TCs impact insular wildlife is of heightened importance. Previous work has shown that extreme weather events may shape species distributions more strongly than climatic averages; however, given the coarse spatial and temporal scales at which TC data are often reported, the influence of TCs on species distributions has yet to be explored. Using TC data from the National Hurricane Center, we developed spatially and temporally explicit species distribution models (SDMs) to examine the role of TCs in shaping present-day distributions of Puerto Rico's 10 Anolis lizard species. We created six predictor variables to represent the intensity and frequency of TCs. For each occurrence of a species, we calculated these variables for TCs that came within 500 km of the center of Puerto Rico and occurred within the 1-year window prior to when that occurrence was recorded. We also included predictor variables related to landcover, climate, topography, canopy cover and geology. We used random forests to assess model performance and variable importance in models with and without TC variables. We found that the inclusion of TC variables improved model performance for the majority of Puerto Rico's 10 anole species. The magnitude of the improvement varied by species, with generalist species that occur throughout the island experiencing the greatest improvements in model performance. Range-restricted species experienced small, almost negligible, improvements but also had more predictive models both with and without the inclusion of TC variables compared to generalist species. Our findings suggest that incorporating data on TCs into SDMs may be important for modeling insular species that are prone to experiencing these types of extreme weather events.

Signals of differential introgression in the genome of natural hybrids of Caribbean anoles

Hybridization facilitates recombination between divergent genetic lineages and can be shaped by both neutral and selective processes. Upon hybridization, loci with no net fitness effects introgress randomly from parental species into the genomes of hybrid individuals. Conversely, alleles from one parental species at some loci may provide a selective advantage to hybrids, resulting in patterns of introgression that do not conform to random expectations. We investigated genomic patterns of differential introgression in natural hybrids of two species of Caribbean anoles, Anolis pulchellus and A. krugi in Puerto Rico. Hybrids exhibit A. pulchellus phenotypes but possess A. krugi mitochondrial DNA, originated from multiple, independent hybridization events, and appear to have replaced pure A. pulchellus across a large area in western Puerto Rico. Combining genome-wide SNP datasets with bioinformatic methods to identify signals of differential introgression in hybrids, we demonstrate that the genomes of hybrids are dominated by pulchellus-derived alleles and show only 10%-20% A. krugi ancestry. The majority of A. krugi loci in hybrids exhibit a signal of non-random differential introgression and include loci linked to genes involved in development and immune function. Three of these genes (delta like canonical notch ligand 1, jagged1 and notch receptor 1) affect cell differentiation and growth and interact with mitochondrial function. Our results suggest that differential non-random introgression for a subset of loci may be driven by selection favouring the inheritance of compatible mitochondrial and nuclear-encoded genes in hybrids.

Stronger evidence for genetic ancestry than environmental conditions in shaping the evolution of a complex signalling trait during biological invasion

Introductions of invasive species to new environments often result in rapid rates of trait evolution. While in some cases these evolutionary transitions are adaptive and driven by natural selection, they can also result from patterns of genetic and phenotypic variation associated with the invasion history. Here, we examined the brown anole (Anolis sagrei), a widespread invasive lizard for which genetic data have helped trace the sources of non-native populations. We focused on the dewlap, a complex signalling trait known to be subject to multiple selective pressures. We measured dewlap reflectance, pattern and size in 30 non-native populations across the southeastern United States. As well, we quantified environmental variables known to influence dewlap signal effectiveness, such as canopy openness. Further, we used genome-wide data to estimate genetic ancestry, perform association mapping and test for signatures of selection. We found that among-population variation in dewlap characteristics was best explained by genetic ancestry. This result was supported by genome-wide association mapping, which identified several ancestry-specific loci associated with dewlap traits. Despite the strong imprint of this aspect of the invasion history on dewlap variation, we also detected significant relationships between dewlap traits and local environmental conditions. However, we found limited evidence that dewlap-associated genetic variants have been subject to selection. Our study emphasizes the importance of genetic ancestry and admixture in shaping phenotypes during biological invasion, while leaving the role of selection unresolved, likely due to the polygenic genetic architecture of dewlaps and selection acting on many genes of small effect.

Evolutionary opportunity and the limits of community similarity in replicate radiations of island lizards

Ecological community structure ultimately depends on the production of community members by speciation. To understand how macroevolution shapes communities, we surveyed Anolis lizard assemblages across elevations on Jamaica and Hispaniola, neighbouring Caribbean islands similar in environment, but contrasting in the richness of their endemic evolutionary radiations. The impact of diversification on local communities depends on available spatial opportunities for speciation within or between ecologically distinct sub-regions. In the spatially expansive lowlands of both islands, communities converge in species richness and average morphology. But communities diverge in the highlands. On Jamaica, where limited highland area restricted diversification, communities remain depauperate and consist largely of elevational generalists. In contrast, a unique fauna of high-elevation specialists evolved in the vast Hispaniolan highlands, augmenting highland richness and driving islandwide turnover in community composition. Accounting for disparate evolutionary opportunities may illuminate when regional diversity will enhance local diversity and help predict when communities should converge in structure.

Appendicular morphology and locomotor performance of two morphotypes of continental anoles: Anolis heterodermus and Anolis tolimensis

Anolis lizards have been a model of study in ecomorphology in the Caribbean islands because species with the same type of microhabitat share similar morphological features. But despite their great diversity, little is known about continental species. We analyzed the relationship between the anatomical characteristics of the appendicular skeleton and the locomotor performance of two Anolis species found in Colombia that have different use of habitat. Anolis heterodermus, a strictly arboreal species, was compared with Anolis tolimensis, which inhabits the lower strata of vegetation. These two species differ in their body plan not only in body shape and external morphological features, but also in the skeleton and appendicular musculature. The results highlight the muscle and bone specializations associated with the use of habitat in this genus, such as the presence of more robust bones to enlarge the surface of muscle insertion, the thickening and loss of carpal parts, thickening of tendons associated with the manus, and greater development of muscle mass in the forelimbs by A. heterodermus with respect to A. tolimensis. These differences are related to the use of the microhabitat and the locomotor style of each species.

Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

The urban heat island effect, where urban areas exhibit higher temperatures than less-developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature-dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami-Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (T_e ), which estimates the distribution of body temperatures in a non-thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (T_b ). We found that urban areas had more open canopies and higher T_e compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field T_b that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available T_e within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.