Adaptive Radiation, Ecological Opportunity, and Evolutionary Determinism

Adaptive radiation refers to diversification from an ancestral species that produces descendants adapted to use a great variety of distinct ecological niches. In this review, I examine two aspects of adaptive radiation: first, that it results from ecological opportunity and, second, that it is deterministic in terms of its outcome and evolutionary trajectory. Ecological opportunity is usually a prerequisite for adaptive radiation, although in some cases, radiation can occur in the absence of preexisting opportunity. Nonetheless, many clades fail to radiate although seemingly in the presence of ecological opportunity; until methods are developed to identify and quantify ecological opportunity, the concept will have little predictive utility in understanding a priori when a clade might be expected to radiate. Although predicted by theory, replicated adaptive radiations occur only rarely, usually in closely related and poorly dispersing taxa found in the same region on islands or in lakes. Contingencies of a variety of types may usually preclude close similarity in the outcome of evolutionary diversification in other situations. Whether radiations usually unfold in the same general sequence is unclear because of the unreliability of methods requiring phylogenetic reconstruction of ancestral events. The synthesis of ecological, phylogenetic, experimental, and genomic advances promises to make the coming years a golden age for the study of adaptive radiation; natural history data, however, will always be crucial to understanding the forces shaping adaptation and evolutionary diversification.Organismic and Evolutionary Biolog

Seeing the Forest for the Trees: The Limitations of Phylogenies in Comparative Biology

The last 30 years have seen a revolution in comparative biology. Prior to that time, systematics was not at the forefront of the biological sciences, and few scientists considered phylogenetic relationships when investigating evolutionary questions. By contrast, systematic biology is now one of the most vigorous disciplines in biology, and the use of phylogenies is not only requisite in macroevolutionary studies, but has been applied to a wide range of topics and fields that no one could possibly have envisioned 30 years ago. My message is simple: phylogenies are fundamental to comparative biology, but they are not the be all and end all. Phylogenies are powerful tools for understanding the past, but like any tool, they have their limitations. In addition, phylogenies are much more informative about pattern than they are about process. The best way to fully understand the past—both pattern and process—is to integrate phylogenies with other types of historical data as well as with direct studies of evolutionary process.Organismic and Evolutionary Biolog

Convergence, Adaptation, and Constraint

Convergent evolution of similar phenotypic features in similar environmental contexts has long been taken as evidence of adaptation. Nonetheless, recent conceptual and empirical developments in many fields have led to a proliferation of ideas about the relationship between convergence and adaptation. Despite criticism from some systematically minded biologists, I reaffirm that convergence in taxa occupying similar selective environments often is the result of natural selection. However, convergent evolution of a trait in a particular environment can occur for reasons other than selection on that trait in that environment, and species can respond to similar selective pressures by evolving nonconvergent adaptations. For these reasons, studies of convergence should be coupled with other methods—such as direct measurements of selection or investigations of the functional correlates of trait evolution—to test hypotheses of adaptation. The independent acquisition of similar phenotypes by the same genetic or developmental pathway has been suggested as evidence of constraints on adaptation, a view widely repeated as genomic studies have documented phenotypic convergence resulting from change in the same genes, sometimes even by the same mutation. Contrary to some claims, convergence by changes in the same genes is not necessarily evidence of constraint, but rather suggests hypotheses that can test the relative roles of constraint and selection in directing phenotypic evolution.Organismic and Evolutionary BiologyOther Research Uni

Detective Work in the West Indies: Integrating Historical and Experimental Approaches to Study Island Lizard Evolution

Evolutionary biology is a historical science, like astronomy and geology. Understanding how and why evolution has occurred requires synthesizing multiple lines of inquiry. Historical studies, such as those that estimate phylogenetic trees, can detail the pattern of evolutionary diversification, whereas studies on living species can provide insight into the processes that affect ecological interactions and evolutionary change. The evolutionary radiation of Anolis lizards in the Greater Antilles illustrates the interplay between historical and modern-day approaches and strongly supports the hypothesis that interspecific interactions drive adaptive diversification. Studies of these species also demonstrate the role that manipulative experiments can play in understanding evolutionary phenomena.Organismic and Evolutionary Biolog

Stumped by trees? A generalized null model for patterns of organismal diversity

Journal ArticleEvolutionary biologists increasingly have become interested in the factors determining the structure of phylogenetic trees. For example, highly asymmetric trees seem to suggest that the probability of extinction and/or speciation differs among lineages

What Drives Variation in Habitat Use by Anolis Lizards: Habitat Availability or Selectivity?

Geographic variation in habitat availability may drive geographic variation in a species' habitat use; alternatively, species adapted to particular habitat characteristics may use a habitat regardless of its availability within an environment. In this study, we investigated habitat use of two sympatric species of Anolis lizards that are morphologically specialized to use different microhabitats. We examined variation in microhabitat use and availability among four distinct forest types. In each forest type, we quantified available microhabitats (i.e., perch diameter, angle of inclination, and visibility), as well as microhabitats actually used by each species. We found that species consistently differed in microhabitat use, corresponding to each species' morphological specializations. However, microhabitat use of both species varied among sites. This variation in Anolis gundlachi Peters, 1876 reflected differences in microhabitat availability, while the variation in Anolis krugi Peters, 1876 resulted from differential microhabitat selectivity. These results indicate that both habitat availability and habitat preferences must be examined in multiple localities for a species to understand the causes of variation in its habitat use.Organismic and Evolutionary Biolog

Anolis Newsletter VII

Newsletter for the 7th Anolis Symposium, Fairchild Tropical Botanic Gardens, Miami, Florida, 17-18 March 2018. It had been nearly a decade since the previous Anolis symposium was held in Cambridge, MA, at the Museum for Comparative Zoology, Harvard. A reunion of anole biologists en masse was long past due and it was decided that this symposium would be slightly different – we were going to hold it somewhere with anoles! And so, on the weekend of 17-18th March, 2018, nearly 70 anole biologists traveled to sunny south Florida to attend the 7th Anolis Symposium held at the beautiful Fairchild Tropical Botanic Gardens in Miami. In the grounds of the botanical gardens, attendees were presented with a diverse community of six (!) species of anole, both native and non-native, representing four distinct ecomorphs

Systematics, Natural History, and Conservation: Field Biologists Must Fight a Public-Image Problem

Organismic and Evolutionary Biolog

Adaptation, Speciation, and Convergence: A Hierarchical Analysis of Adaptive Radiation in Caribbean Anolis Lizards

This is the publisher's version, also available electronically from http://www.bioone.org/doi/abs/10.3417/0026-6493%282006%2993%5B24%3AASACAH%5D2.0.CO%3B2.Caribbean Anolis lizards are a classic case of adaptive radiation, repeated four times across islands of the Greater Antilles. On each island, very similar patterns of evolutionary divergence have occurred, resulting in the evolution of the same set of ecological specialists—termed ecomorphs—on each island. However, this is only part of the story of the Caribbean anole radiations. Indeed, much of the species diversity of Caribbean Anolis occurs within clades of ecomorphs, which contain as many as 14 ecologically-similar species on a single island. We ask to what extent the classic model of ecological interactions as the driving force in adaptive radiation can account for this aspect of anole evolutionary diversity. Our answer is that it can in part, but not entirely. More generally, the most complete understanding of evolutionary diversification and radiation is achieved by studying multiple hierarchical evolutionary levels from clades to populations

Climatic niche shift predicts thermal trait response in one but not both introductions of the Puerto Rican lizard Anolis cristatellus to Miami, Florida, USA

Global change is predicted to alter environmental conditions for populations in numerous ways; for example, invasive species often experience substantial shifts in climatic conditions during introduction from their native to non-native ranges. Whether these shifts elicit a phenotypic response, and how adaptation and phenotypic plasticity contribute to phenotypic change, are key issues for understanding biological invasions and how populations may respond to local climate change. We combined modeling, field data, and a laboratory experiment to test for changing thermal tolerances during the introduction of the tropical lizard Anolis cristatellus from Puerto Rico to Miami, Florida. Species distribution models and bioclimatic data analyses showed lower minimum temperatures, and greater seasonal and annual variation in temperature for Miami compared to Puerto Rico. Two separate introductions of A. cristatellus occurred in Miami about 12 km apart, one in South Miami and the other on Key Biscayne, an offshore island. As predicted from the shift in the thermal climate and the thermal tolerances of other Anolis species in Miami, laboratory acclimation and field acclimatization showed that the introduced South Miami population of A. cristatellus has diverged from its native-range source population by acquiring low-temperature acclimation ability. By contrast, the introduced Key Biscayne population showed little change compared to its source. Our analyses predicted an adaptive response for introduced populations, but our comparisons to native-range sources provided evidence for thermal plasticity in one introduced population but not the other. The rapid acquisition of thermal plasticity by A. cristatellus in South Miami may be advantageous for its long-term persistence there and expansion of its non-native range. Our results also suggest that the common assumption of no trait variation when modeling non-native species distributions is invalid.Organismic and Evolutionary Biolog