Sensory response patterns and the evolution of visual signal design in anoline lizards

 The evolutionary relationship between visual system response and visual signal design was investigated in four species of anoline lizards which occupy distinctly different habitats. Anoles display with motion patterns of a colorful throat fan called the dewlap. We assessed signal visibility by recording evoked potentials from the optic tectum in response to a moving stimulus flag (a dewlap-like stimulus), and, in one species, by testing behavioral response. The motion pattern, intensity and spectral quality of the stimulus flag, and the background against which it was viewed, were independently manipulated. In all cases, high-velocity motion patterns with a high percentage of brightness contrast between stimulus and background produced the greatest response. Differences in spectral quality between stimulus and background (color contrast) had no effect on tectal responses, but did influence the behaviorally measured detection probability. Using habitat light data we estimated the visibility of the dewlap of each species in different natural habitats. Each species' dewlap was highly visible in its own habitat, but some were much less visible in the habitats of some other species. Habitat light conditions and visual system response properties appear to have constrained the evolution of dewlap design, in at least some of the species. Accepted: May 1998     

A molecular phylogenetic analysis of diversification in Amazonian Anolis lizards

We present a mitochondrial DNA (mtDNA) haplotype phylogeny for Amazonian Anolis lizards, including geographical sampling within four species distributed across the Amazon basin (A. fuscoauratus, A. nitens, A. ortonii and A. punctatus). Approximately 1500 bp of mtDNA encoding ND2, COI and four transfer RNAs (tRNAs) are reported for 39 specimens representing four to five populations of each widespread species, plus eight outgroups. These new sequences are aligned with eight previously published sequences, yielding 914 variable characters and 780 parsimony-informative characters. Phylogenetic analyses using maximum parsimony and maximum likelihood reject the hypothesis that Amazonian anoles form a monophyletic group excluding Central American and Caribbean anoles, and suggest multiple faunal exchanges among these regions. Haplotype divergence among geographical populations of A. nitens, whose variation was influential in formulating the Pleistocene refuge hypothesis of Amazonian speciation, is very large (13-22% sequence difference), suggesting that these populations separated well before the Pleistocene. Haplotype divergences among geographical populations of A. fuscoauratus (3-4%), A. punctatus (4-9%) and A. ortonii (6-8%) also indicate pre-Pleistocene differentiation within each species, but temporally incongruent patterns among species.     

A phylogenetic analysis of body size evolution in the Anolis roquet group (Sauria: Iguanidae): character displacement or size assortment?

The important role that competition plays in structuring communities is well documented; however, the role of competition in an evolutionary context remains unclear. Evolutionary investigations into the role of competition have often focused on the process of character displacement, and a good example of this is the evolution of body size in the Anolis lizards of the Caribbean islands. Previous work on the A. roquet species group has taken a phylogenetic approach and concluded that patterns of body size differences are not caused by character displacement but are a result of size assortment. Using a phylogenetic reconstruction based on the sequence of the cytochrome b gene (cyt-b) and ancestral character-state reconstruction methods, we investigated the roles of character displacement and size assortment. Our results indicated that size assortment alone was insufficient to explain the observed patterns of body size differences. Furthermore, we found that change in body size was associated with a change in allopatry/sympatry, thus supporting the character-displacement hypothesis. We conclude that patterns of body size differences in the A. roquet species group appear to be the result of a combination of character displacement and size assortment because character displacement was only found to be possible on three occasions.     

The effect of prey availability on offspring survival depends on maternal food resources

Maternal nutrition can strongly influence embryo development and offspring fitness. The environmental matching hypothesis posits that developmental conditions affect offspring in ways that enable them to appropriately deal with similar post‐developmental conditions, although mismatches between developmental and post‐developmental environments will reduce fitness. To test this hypothesis, reproductive lizards (Anolis sagrei) were reared in environments with high versus low prey availability. The resultant offspring were then reared reciprocally under the same two prey conditions that their mothers experienced. High levels of prey available to mothers increased egg production, although the survival of eggs was low compared to those produced by mothers in the low‐prey treatment. Low prey availability to offspring reduced growth, regardless of the amount of prey available to their mothers. Low prey availability also compromised offspring survival, although this negative effect was only present when mothers experienced high‐prey conditions, whereas matching of low‐prey conditions in maternal and offspring stages resulted in high survival. However, because the mismatch of low maternal and high offspring prey availability resulted in similar offspring survival to the matched treatments, our results do not fully support the environmental matching hypothesis. Nevertheless, the present study highlights the interactive role of maternal and post‐hatching environments in generating variation in offspring fitness. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 437–447.     

Independent introductions and sequential founder events shape genetic differentiation and diversity of the invasive green anole (Anolis carolinensis) on Pacific Islands

Aim

Natural range expansions and human‐mediated colonizations usually involve a small number of individuals that establish new populations in novel habitats. In both cases, founders carry only a fraction of the total genetic variation of the source populations. Here, we used native and non‐native populations of the green anole, Anolis carolinensis, to compare the current distribution of genetic variation in populations shaped by natural range expansion and human‐mediated colonization.

Location

North America, Hawaiian Islands, Western Pacific Islands.

Methods

We analysed 401 mtDNA haplotypes to infer the colonization history of A. carolinensis on nine islands in the Pacific Ocean. We then genotyped 576 individuals at seven microsatellite loci to assess the levels of genetic diversity and population genetic differentiation for both the native and non‐native ranges.

Results

Our findings support two separate introductions to the Hawaiian Islands and several western Pacific islands, with subsequent colonizations within each region following a stepping‐stone model. Genetic diversity at neutral markers was significantly lower in the non‐native range because of founder effects, which also contributed to the increased population genetic differentiation among the non‐native regions. In contrast, a steady reduction in genetic diversity with increasing distance from the ancestral population was observed in the native range following range expansion.

Main conclusions

Range expansions cause serial founder events that are the spatial analogue of genetic drift, producing a pattern of isolation‐by‐distance in the native range of the species. In human‐mediated colonizations, after an initial loss of genetic diversity, founder effects appear to persist, resulting in overall high genetic differentiation among non‐native regions but an absence of isolation‐by‐distance. Contrasting the processes influencing the amount and structuring of genetic variability during natural range expansion and human‐mediated biological invasions can shed new light on the fate of natural populations exposed to novel and changing environments.

     

The value of comparative approaches to our understanding of puberty as illustrated by investigations in birds and reptiles

This article is part of a Special Issue "Puberty and Adolescence". Studies of birds and reptiles have provided many basic insights into the neuroendocrine control of reproductive processes. This research has elucidated mechanisms regulating both early development, including sexual differentiation, and adult neuroendocrine function and behavior. However, phenomena associated with the transition into sexual maturation (puberty) have not been a focus of investigators working on species in these taxonomic classes. Research is complicated in birds and reptiles by a variety of factors, including what can be extended times to maturation, the need to reach particular body size regardless of age, and environmental conditions that can support or inhibit endocrine responses. However, careful selection of model systems, particularly those with available genetic tools, will lead to important comparative studies that can elucidate both generalizability and diversity of mechanisms regulating the onset of reproductive maturity.     

Size but not relatedness drives the spatial distribution of males within an urban population of Anolis carolinensis lizards

The way that individuals are spatially organized in their environment is a fundamental population characteristic affecting social structure, mating system, and reproductive ecology. However, for many small or cryptic species, the factors driving the spatial distribution of individuals within a population are poorly understood and difficult to quantify. We combined microsatellite data, remote sensing, and mark–recapture techniques to test the relative importance of body size and relatedness in determining the spatial distribution of male Anolis carolinensis individuals within a focal population over a five‐year period. We found that males maintain smaller home ranges than females. We found no relationship between male body size and home range size, nor any substantial impact of relatedness on the geographic proximity. Instead, the main driver of male spatial distribution in this population was differences in body size. We also found no evidence for offspring inheritance of their parent''s territories. Males were never sampled within their father''s territory providing strong support for male‐biased dispersal. This study introduces a novel approach by combining standard mark release capture data with measures of pairwise relatedness, body size, and GPS locations to better understand the factors that drive the spatial distribution of individuals within a population.     

Phylogenetic signal and evolutionary correlates of urban tolerance in a widespread neotropical lizard clade*

Urbanization is intensifying worldwide, and while some species tolerate and even exploit urban environments, many others are excluded entirely from this new habitat. Understanding the factors that underlie tolerance of urbanization is thus of rapidly growing importance. Here, we examine urban tolerance across a diverse group of lizards: Caribbean members of the neotropical genus Anolis. Our analyses reveal that urban tolerance has strong phylogenetic signal, suggesting that closely related species tend to respond similarly to urban environments. We propose that this characteristic of urban tolerance in anoles may be used to forecast the possible responses of species to increasing urbanization. In addition, we identified several key ecological and morphological traits that tend to be associated with tolerance in Anolis. Specifically, species experiencing hot and dry conditions in their natural environment and those that maintain higher body temperatures tend to have greater tolerance of urban habitats. We also found that tolerance of urbanization is positively associated with toepad lamella number and negatively associated with ventral scale density and relative hindlimb length. The identification of factors that predispose a species to be more or less urban tolerant can provide a starting point for conservation and sustainable development in our increasingly urbanized world.     

Context-dependent changes in motor control and kinematics during locomotion: modulation and decoupling

Successful locomotion through complex, heterogeneous environments requires the muscles that power locomotion to function effectively under a wide variety of conditions. Although considerable data exist on how animals modulate both kinematics and motor pattern when confronted with orientation (i.e. incline) demands, little is known about the modulation of muscle function in response to changes in structural demands like substrate diameter, compliance and texture. Here, we used high-speed videography and electromyography to examine how substrate incline and perch diameter affected the kinematics and muscle function of both the forelimb and hindlimb in the green anole (Anolis carolinensis). Surprisingly, we found a decoupling of the modulation of kinematics and motor activity, with kinematics being more affected by perch diameter than by incline, and muscle function being more affected by incline than by perch diameter. Also, muscle activity was most stereotyped on the broad, vertical condition, suggesting that, despite being classified as a trunk-crown ecomorph, this species may prefer trunks. These data emphasize the complex interactions between the processes that underlie animal movement and the importance of examining muscle function when considering both the evolution of locomotion and the impacts of ecology on function.     

ADAPTATION AND PLASTICITY OF ANIMAL COMMUNICATION IN FLUCTUATING ENVIRONMENTS

Adaptations that facilitate the reception of long‐range signals under challenging conditions are expected to generate signal diversity when species communicate in different habitats. Although we have a general understanding of how individual communicating animals cope with conditions influencing signal detection, the extent to which plasticity and evolutionary changes in signal characteristics contribute to interspecific differences in signaling behavior is unclear. We quantified the visual displays of free‐living lizards and environmental variables known to influence display detection for multiple species from two separate island radiations. We found evidence of both adaptive evolution and adaptive plasticity in display characteristics as a function of environmental conditions, but plasticity accounted for most of the observed differences in display behavior across species. At the same time, prominent differences between the two island radiations existed in aspects of signaling behavior, unrelated to the environment. Past evolutionary events have therefore played an important role in shaping the way lizards adjust their signals to challenges in present‐day environments. In addition to showing how plasticity contributes to interspecific differences in communication signals, our findings suggest the vagaries of evolution can in itself lead to signal variation between species.