Showing papers by "Jonathan B. Losos published in 2019"

A roadmap for urban evolutionary ecology

Abstract: Urban ecosystems are rapidly expanding throughout the world, but how urban growth affects the evolutionary ecology of species living in urban areas remains largely unknown. Urban ecology has advanced our understanding of how the development of cities and towns change environmental conditions and alter ecological processes and patterns. However, despite decades of research in urban ecology, the extent to which urbanization influences evolutionary and eco-evolutionary change has received little attention. The nascent field of urban evolutionary ecology seeks to understand how urbanization affects the evolution of populations, and how those evolutionary changes in turn influence the ecological dynamics of populations, communities, and ecosystems. Following a brief history of this emerging field, this Perspective article provides a research agenda and roadmap for future research aimed at advancing our understanding of the interplay between ecology and evolution of urban-dwelling organisms. We identify six key questions that, if addressed, would significantly increase our understanding of how urbanization influences evolutionary processes. These questions consider how urbanization affects nonadaptive evolution, natural selection, and convergent evolution, in addition to the role of urban environmental heterogeneity on species evolution, and the roles of phenotypic plasticity versus adaptation on species' abundance in cities. Our final question examines the impact of urbanization on evolutionary diversification. For each of these six questions, we suggest avenues for future research that will help advance the field of urban evolutionary ecology. Lastly, we highlight the importance of integrating urban evolutionary ecology into urban planning, conservation practice, pest management, and public engagement.

Predator-induced collapse of niche structure and species coexistence

Abstract: Biological invasions are both a pressing environmental challenge and an opportunity to investigate fundamental ecological processes, such as the role of top predators in regulating biodiversity and food-web structure. In whole-ecosystem manipulations of small Caribbean islands on which brown anole lizards (Anolis sagrei) were the native top predator, we experimentally staged invasions by competitors (green anoles, Anolis smaragdinus) and/or new top predators (curly-tailed lizards, Leiocephalus carinatus). We show that curly-tailed lizards destabilized the coexistence of competing prey species, contrary to the classic idea of keystone predation. Fear-driven avoidance of predators collapsed the spatial and dietary niche structure that otherwise stabilized coexistence, which intensified interspecific competition within predator-free refuges and contributed to the extinction of green-anole populations on two islands. Moreover, whereas adding either green anoles or curly-tailed lizards lengthened food chains on the islands, adding both species reversed this effect—in part because the apex predators were trophic omnivores. Our results underscore the importance of top-down control in ecological communities, but show that its outcomes depend on prey behaviour, spatial structure, and omnivory. Diversity-enhancing effects of top predators cannot be assumed, and non-consumptive effects of predation risk may be a widespread constraint on species coexistence. Whole-ecosystem manipulations of Caribbean islands occupied by brown anoles, involving the addition of competitors (green anoles) and/or top predators (curly-tailed lizards), demonstrate that predator introductions can alter the ecological niches and destabilize the coexistence of competing prey species.

From low to high gear: there has been a paradigm shift in our understanding of evolution

Abstract: Experimental studies of evolution performed in nature and the associated demonstration of rapid evolution, observable on a time scale of months to years, were an acclaimed novelty in the 1980-1990s. Contemporary evolution is now considered ordinary and is an integrated feature of many areas of research. This shift from extraordinary to ordinary reflects a change in the perception of evolution. It was formerly thought of as a historical process, perceived through the footprints left in the fossil record or living organisms. It is now seen as a contemporary process that acts in real time. Here we review how this shift occurred and its consequences for fields as diverse as wildlife management, conservation biology, and ecosystems ecology. Incorporating contemporary evolution in these fields has caused old questions to be recast, changed the answers, caused new and previously inconceivable questions to be addressed, and inspired the development of new subdisciplines. We argue further that the potential of contemporary evolution has yet to be fulfilled. Incorporating evolutionary dynamics in any research program can provide a better assessment of how and why organisms and communities came to be as they are than is attainable without an explicit treatment of these dynamics.

Do the relationships between hindlimb anatomy and sprint speed variation differ between sexes in Anolis lizards

Abstract: The ability of an animal to run fast has important consequences on its survival capacity and overall fitness. Previous studies have documented how variation in the morphology of the limbs is related to variation in locomotor performance. Although these studies have suggested direct relations between sprint speed and hindlimb morphology, few quantitative data exist. Consequently, it remains unclear whether selection acts in limb segment lengths, overall muscle mass or muscle architecture (e.g. muscle fiber length and cross-sectional area). Here, we investigate whether muscle architecture (mass, fiber length and physiological cross-sectional area), hindlimb segment dimensions, or both, explain variation in sprint speed across 14 species of Anolis lizards. Moreover, we test whether similar relationships exist between morphology and performance for both sexes, which may not be the case given the known differences in locomotor behavior and habitat use. Our results show that the main driver of sprint speed is the variation in femur length for both males and females. Our results further show sexual dimorphism in the traits studied and, moreover, show differences in the traits that predict maximal sprint speed in males and females. For example, snout vent length and overall muscle mass are also good predictors of sprint speed in males, whereas no relationships between muscle mass and sprint speed was observed in females. Only a few significant relationships were found between muscle architecture (fiber length, cross-sectional area) and sprint speed in male anoles, suggesting that overall muscles size, rather than muscle architecture, appears to be under selection.

Parallel increases in grip strength in two species of Anolis lizards after a major hurricane on Dominica

Abstract: A recent study showed that hurricanes can act as selective agents affecting the phenotype of anole populations subjected to these extreme climatic events. Specifically, Anolis lizards that survived hurricanes were shown to have larger toepads than those that did not. To test whether hurricanes more generally impact populations of Anolis lizards, we collected data on toepad size, lamella number and grip strength for two species of Anolis on the island of Dominica in 2018 and compared them with data collected in 2016 before Hurricane Maria devastated the island. Our results show that populations of both species showed higher clinging forces in 2018, consistent with our predictions that lizards that are better clingers would be more likely to survive hurricanes. Unexpectedly, the increase in clinging force was not accompanied by an increase in toepad size or lamella number, suggesting that the increase in clinging strength is more likely driven by changes at the level of the setae microstructure. While the mechanism driving this pattern cannot be determined until future before/after hurricane comparisons are made, our data provide further evidence that hurricanes may be a previously overlooked driver of form and function in Anolis lizards.

Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel-based stereo-profilometry

Abstract: The skin surface structure of squamate reptiles varies greatly among species, likely because it plays a key role in a range of tasks, such as camouflage, locomotion, self-cleaning, mitigation of water loss and protection from physical damage. Although we have foundational knowledge about squamate skin morphology, we still know remarkably little about how intraspecific variation in skin surface structure translates to functional variation. This gap in our understanding can be in part traced back to: (i) our lack of knowledge on how body size determines skin surface structure; and (ii) the lack of means to perform high-throughput and detailed analysis of the three-dimensional (3D) anatomy of reptilian skin surfaces in a non-destructive manner. To fill this gap, we explored the possibilities of a new imaging technique, termed gel-based stereo-profilometry, to visualize and quantify the 3D topography of reptilian skin surface structure. Using this novel approach, we investigated intra-specific and intra-individual variation in the skin surface morphology of a focal lizard species, Anolis cristatellus. We assessed how various characteristics of surface topography (roughness, skew and kurtosis) and scale morphology (area, height, width and shape) scale with body size across different body regions. Based on an ontogenetic series of A. cristatellus males, we show that skin roughness increases with body size. Skin patches on the ventral body region of lizards were rougher than on the dorsum, but this was a consequence of ventral scales being larger than dorsal scales. Dorsal surface skew and kurtosis varied with body size, but surfaces on the ventral skin showed no such relationship. Scale size scaled isometrically with body size, and while ventral scales differed in shape from dorsal scales, scale shape did not change with ontogeny. Overall, this study demonstrates that gel-based stereo-profilometry is a promising method to rapidly assess the 3D surface structure of reptilian skin at the microscopic level. Additionally, our findings of the explanatory power of body size on skin surface diversity provide a foundation for future studies to disentangle the relationships among morphological, functional and ecological diversity in squamate reptile skin surfaces.

The role of bite force in the evolution of head shape and head shape dimorphism in Anolis lizards

Abstract: Patterns of convergent evolution in head shape, combined with performance measures, provide ideal opportunities to understand the processes driving its evolution. Anole lizards represent an excellent subject to test this, as recurrent habitat specialists or ecomorphs evolved independently across different islands. We show that phenotypic similarity corresponds to both phylogenetic similarity and similarity in habitat, indicating that there is convergent evolution in head shape among ecomorphs. Moreover, we show that the evolution of tall, wide heads correlate with the evolution of higher bite forces, driving head shape variation among and within ecomorphs. In addition, the processes affecting head shape variation can differ between sexes, leading to sexual head shape dimorphism. These processes might, however, still depend on the habitat. Consequently, there could also be convergent evolution in head shape dimorphism among ecomorphs. We found no evidence for convergent evolution in sexual head shape dimorphism. Moreover, the sexual head shape dimorphism correlates poorly with bite force, suggesting that intersexual head shape differences are related to other functions. Different processes are thus driving the evolution of head shape and head shape dimorphism. A free Plain Language Summary can be found within the Supporting Information of this article.

Head Size of Male and Female Lizards Increases with Population Density Across Island Populations in the Bahamas

Abstract: In polygynous lizards, male–male competition is an important driver of morphologic and behavioral traits associated with intraspecific dominance. The extent to which females engage in aggressive behavior and thus contribute to competition-driven morphologic variation is not well studied. We used injury frequencies of brown anoles (Anolis sagrei) in 16 island populations to test the hypothesis that injury-inducing aggressive encounters increase with population density in both male and female lizards. We further asked whether intraspecific competition is a potential driver of phenotypic traits related to dominance by using population density as proxy for intraspecific competition. We found that the proportion of individuals with injuries was greater in populations with higher densities, suggesting that agonistic competitive interactions increase with population density. Size-adjusted head length of male and female lizards increased with population density, suggesting that larger heads might be advantageous when intraspecific competition is strong. We detected differences in morphology and injury frequency among islands for both males and females, which suggests that agonistic competitive interactions among females may be stronger than previously appreciated. Further research is needed to determine whether aggressive encounters involving females are restricted to intrasexual competition or whether they also involve males, and how morphologic traits of females are related to competitive dominance and reproductive success.

Deadly cats down under

Abstract: The debate over the extent to which cats are an ecological problem and, if so, what solutions to pursue has become increasingly nasty. Underlying this unpleasantness has been a lack of enough good information. But there is a place where scientists do know, where research on cats and their impact and possible solutions has been deep and broad. That place is Australia, and two new books pro­vide insightful analysis of what we have learned and what can be done.