Michele A. Johnson

A PHYLOGENETIC TEST FOR ADAPTIVE CONVERGENCE IN ROCK-DWELLING LIZARDS

Abstract Phenotypic similarity of species occupying similar habitats has long been taken as strong evidence of adaptation, but this approach implicitly assumes that similarity is evolutionarily derived. However, even derived similarities may not represent convergent adaptation if the similarities did not evolve as a result of the same selection pressures; an alternative possibility is that the similar features evolved for different reasons, but subsequently allowed the species to occupy the same habitat, in which case the convergent evolution of the same feature by species occupying similar habitats would be the result of exaptation. Many lizard lineages have evolved to occupy vertical rock surfaces, a habitat that places strong functional and ecological demands on lizards. We examined four clades in which species that use vertical rock surfaces exhibit long hindlimbs and flattened bodies. Morphological change on the phylogenetic branches leading to the rock-dwelling species in the four clades differed from change on other branches of the phylogeny; evolutionary transitions to rock-dwelling generally were associated with increases in limb length and decreases in head depth. Examination of particular characters revealed several different patterns of evolutionary change. Rock-dwelling lizards exhibited similarities in head depth as a result of both adaptation and exaptation. Moreover, even though rock-dwelling species generally had longer limbs than their close relatives, clade-level differences in limb length led to an overall lack of difference between rock- and non-rock-dwelling lizards. These results indicate that evolutionary change in the same direction in independent lineages does not necessarily produce convergence, and that the existence of similar advantageous structures among species independently occupying the same environment may not indicate adaptation.

BEHAVIORAL CONVERGENCE AND ADAPTIVE RADIATION: EFFECTS OF HABITAT USE ON TERRITORIAL BEHAVIOR IN ANOLIS LIZARDS

Most studies of adaptive radiations focus on morphological aspects of differentiation, yet behavior is also an important component of evolutionary diversification, often mediating the relationship between animal ecology and morphology. In species within radiations that are convergent in ecology and morphology, we then also expect convergence in behavior. Here, we examined 13 Anolis lizard species to determine whether territorial strategies have evolved convergently with morphology and habitat use. We evaluated two aspects of territoriality: behavioral defense of space via territorial displays, and territory overlap within and between sexes. Controlling for the phylogenetic relationships of the taxa in our study, we found that species similar in perch height and diameter convergently evolved patterns of territory overlap, whereas species similar in habitat visibility (the proportion of space that can be seen from a perch) convergently evolved display behavior. We also found that species with greater display time have more extensive male–male territory overlap. This study provides strong evidence for the role of habitat in the evolution of territoriality and suggests that the social structure of a species ultimately evolves in concert with habitat use and morphology.

Behavioural display systems across nine Anolis lizard species: sexual dimorphisms in structure and function

Relationships between structure and function are a primary focus in biology, yet they are most often considered within individual species. Sexually dimorphic communication behaviours and the morphology of associated structures can vary widely, even among closely related species, and these traits provide an ideal opportunity to investigate the evolution of structure–function patterns. Using nine Anolis lizard species, we addressed a series of questions regarding sex differences in and the evolution of relationships between extension of the throat fan (dewlap) and morphology of the muscles and cartilage controlling it. The main results indicated that within species, males displayed the dewlap more often than females and consistently exhibited larger associated structures. These data are consistent with work in other vertebrates in which corresponding sex differences in reproductive morphology and behaviour have been documented. Across species, however, we found no evidence that the rate of dewlap extension evolved in association with dewlap morphology. Thus, we provide an example of traits that, when considered in a phylogenetic framework, exhibited limited associations between behaviour and morphology, perhaps as the result of constraints imposed by the ecological contexts in which different species occur.

A phylogenetic perspective on foraging mode evolution and habitat use in West Indian Anolis lizards

Although many descriptive studies of foraging mode have been performed, the factors that underlie the evolution of foraging mode remain poorly understood. To test the hypothesis that foraging mode evolution is affected by habitat use, we analysed two data sets including 31 species of West Indian Anolis lizards. In this genus, the same suite of habitat specialists (or ecomorphs) has evolved on four islands, providing the replication necessary to evaluate the generality of the relationship between foraging mode and habitat use. Using habitat and behavioural data, we conducted phylogenetic comparative analyses to determine whether species of the same ecomorph have evolved similar foraging behaviour and whether differences in foraging mode are associated with differences in habitat use. We found that Anolis species show substantial variation in foraging behaviour, including differences in movement and eating rates. Furthermore, variation among ecomorphs indicates that foraging behaviour is related to habitat use, although the specific environmental factors driving foraging divergence are unclear. Our results show that foraging mode is an evolutionarily labile trait that is influenced by evolution of habitat use.

The behavioral ecology of sleep: Natural sleeping site choice in three Anolis lizard species

Summary Where animals sleep may be an important component of their behavioral ecology, as sleeping renders animals immobile and hypothetically vulnerable for long periods. Yet, sleep is rarely studied outside of the laboratory. To investigate factors that influence natural sleeping behavior, we examined sleeping locations of three sympatric species of territorial Anolis lizards (Anolis lineatopus, A. grahami and A. valencienni) that have evolved adaptations to different microhabitats. Results indicate that sleeping perch differences among these species are consistent with their diurnal specializations, and sleeping perches are generally higher, narrower, and more horizontal than diurnal perches. We find only limited evidence for sleeping site fidelity; although individuals of one species have apparent sleeping areas within their home ranges, few lizards repeatedly sleep on perches within 0.5 m of previous sleep perches. In a closer examination of the sleeping sites of A. lineatopus, we find that male nocturnal ranges are more dispersed from conspecific males than their diurnal ranges, and they typically sleep near their territory boundaries. We conclude that while Anolis sleeping site choice is strongly influenced by diurnal behavior (including territorial defense and microhabitat choice), differential diurnal and nocturnal microhabitat use may result from differing pressures during day and night.

Relationships among reproductive morphology, behavior, and testosterone in a natural population of green anole lizards.

Laboratory studies of reproductive systems have long supported the idea that neural and/or muscular structures used frequently are often enhanced in size. However, field studies integrating behavioral, morphological, and hormonal data are needed to better understand relationships in natural environments. We examined a natural population of green anole lizards (Anolis carolinensis) to determine whether variation in reproductive morphology both within and between the sexes paralleled differences in courtship and copulatory behaviors and circulating testosterone levels. Display rate in males was positively correlated with the sizes of the cartilage supporting the dewlap (a throat fan used in courtship and aggression) and renal sex segments (portions of the kidney that function similarly to the mammalian prostate), but correlated negatively with seminiferous tubule size. Plasma testosterone in males was negatively correlated with display behavior and was not correlated with any measures of morphology. Females, which display rarely, exhibited no relationships between morphology and frequency of behavior. Comparisons between the sexes show that males have consistently larger courtship and copulation morphologies than females, even when accounting for sex differences in body size. The results not only support the idea of relationships between increased function and enhanced structures, but also show the complexity of mechanistic interactions associated with reproductive behavior in wild animals.

Polymorphic microsatellite loci for the Puerto Rican crested anole (Anolis cristatellus) and their amplification in related Puerto Rican species

We isolate six highly polymorphic microsatellite loci for the Puerto Rican crested anole (Anolis cristatellus) from a genomic library enriched for CA repeats. The number of alleles per locus ranged from 14 to 19, with levels of observed heterozygosity ranging from 0.60 to 0.73. Most of these loci were successfully cross-amplified in other members of the cristatellus species group (A. evermanni, A. gundlachi, A. krugi, A. stratulus), but levels of polymorphism were lower.

Neuroendocrinology of Reptilian Reproductive Behavior

Publisher Summary Reptiles provide ideal opportunities for addressing many questions regarding the neuroendocrinology of reproduction. This chapter describes the use of comparisons among and within reptilian species that allow detailed investigations of the relationships between neuroendocrine mechanisms and reproductive behaviors. This chapter primarily focuses on the features associated with displays of sexual behavior, drawing mostly from research on the species that have been most extensively studied. It considers behavioral displays in their ecological contexts, associated seasonal and hormonal changes, the muscles and portions of the nervous system critical for production of the behaviors, and the development and plasticity of reproductive traits. It also attempts to integrate across the levels and discuss relationships among morphology, behavior, and the endocrine and other mechanisms regulating these traits. Territorial aggression and dominance (and the stress associated with these social behaviors) are also critical components of reproductive success that involve neuroendocrine mechanisms, including an important role for neurotransmitters.