Brett A. Goodman

LIFE ON THE ROCKS: HABITAT USE DRIVES MORPHOLOGICAL AND PERFORMANCE EVOLUTION IN LIZARDS

As a group, lizards occupy a vast array of habitats worldwide, yet there remain relatively few cases where habitat use (ecology), morphology, and thus, performance, are clearly related. The best known examples include: increased limb length in response to increased arboreal perch diameter in anoles and increased limb length in response to increased habitat openness for some skinks. Rocky habitats impose strong natural selection on specific morphological characteristics, which differs from that imposed on terrestrial species, because moving about on inclined substrates of irregular sizes and shapes constrains locomotor performance in predictable ways. We quantified habitat use, morphology, and performance of 19 species of lizards (family Scincidae, subfamily Lygosominae) from 23 populations in tropical Australia. These species use habitats with considerable variation in rock availability. Comparative phylogenetic analyses revealed that occupation of rock-dominated habitats correlated with the evolution of increased limb length, compared to species from forest habitats that predominantly occupied leaf litter. Moreover, increased limb length directly affected performance, with species from rocky habitats having greater sprinting, climbing, and clinging ability than their relatives from less rocky habitats. Thus, we found that the degree of rock use is correlated with both morphological and performance evolution in this group of tropical lizards.

Nowhere to run: the role of habitat openness and refuge use in defining patterns of morphological and performance evolution in tropical lizards

For species from open habitats with little cover and few refugia, selection should favour morphologies that enhance performance at tasks that enable rapid movement across open areas. Similarly, selection should also favour traits that enable rapid access and movement within suitable refugia. This study examined the relationship between habitat openness, refuge use, morphology and performance of 19 species representing 23 populations of tropical Lygosomine skink. Species from this group occupy a wide array of habitats from open forest and open rocky intertidal zones to high‐altitude heaths and dense, closed forests. Species that occupied open habitats were faster at sprinting, climbing and had better cling ability than species from more cluttered, closed habitats. In addition, species from habitats that used rock crevices as refuges had enhanced sprinting ability. This study shows the importance of both habitat openness and refuge type in the evolution of both the morphology and performance in lizards.

The Evolution of Body Shape in Response to Habitat: Is Reproductive Output Reduced in Flat Lizards?

Body size and shape are primary determinants of reproductive output in a variety of taxa, so selection favoring specific body sizes and shapes may, in turn, have a direct affect on reproductive output, and ultimately fitness. In reptiles, species that occupy rocky habitats are often flattened, a morphological character that aids locomotion and life on rocks, but which may constrain reproductive output by reducing the amount of abdominal space available to fill with eggs or offspring. Using 20 species of tropical skink from a wide range of habitats, we quantified habitat use, body height, body volume, and reproductive output, to determine whether the evolution of a flattened body was correlated with a reduction in abdominal volume, and, in turn, with reduced reproductive output. In this group of lizards, the occupation of rocky habitats has led (1) to the evolution of a flattened body, and this shift in body shape has (2) caused a reduction in abdominal volume. Despite this reduction in abdominal volume reproductive output was unaffected, as flatter species compensate by being more “full” of eggs. Thus, we demonstrate that morphological adaptation for enhanced performance in specific habitats did not cause a reduction in instantaneous reproductive output.

How hot do nest boxes get in the tropics? A study of nest boxes for the endangered mahogany glider

As hollow-bearing trees become scarcer due to habitat loss, the use of nest boxes as a management tool for hollow-dependent species is likely to increase. However, nest-box use can be variable among species and habitats, and one possible reason may be that nest boxes offer little protection against extreme temperatures compared with natural hollows; this may be particularly important in the tropics. Here, we measured the microclimate of 16 nest boxes, installed as part of a recovery program for an endangered arboreal marsupial, the mahogany glider, during the summer in tropical north Queensland. We also measured the microclimate of 14 naturally occurring refuges (hollows in standing and fallen trees) at the same study sites. Nest boxes were significantly hotter during the day than were natural refuges (either in fallen or standing live trees) and experienced a greater range of temperatures. The most important factors explaining variation in daytime temperature in boxes was box aspect and the amount of canopy cover directly above the box: boxes that faced north, and those with greater canopy cover, were up to 7°C cooler than those that faced south or had little cover. We discuss our results in relation to the use of nest boxes in management plans for arboreal marsupials in the tropics.

Microhabitat separation and niche overlap among five assemblages of tropical skinks

The niche axes of microhabitat use, activity and size for 21 skink species from five assemblages (Alligator Creek, Cairns, Chillagoe, Cooktown and Mt Bartle Frere) in the biodiverse tropics of north-east Queensland were examined. Species within the same assemblage separated predominantly along two structural microhabitat gradients; one that ranged from microhabitats dominated by large rocks to leaf litter and total ground cover, and a second defined by increasing leaf litter, ground cover, undergrowth, proximity to vegetation and increased canopy cover. All species used available microhabitats non-randomly, with species from the same ecotype (arboreal, generalist, litter-dwelling, rock-using) clustering in multivariate ecological space. Despite evidence of within-assemblage niche overlap, null-model comparisons revealed that only one assemblage (Chillagoe) had greater niche overlap than would be expected by chance. Assemblages with more species occupied smaller niche space, indicating species packing. However, species with more diverse niches were less evenly packed. While most species overlapped in activity time and body size, differences among species from the same ecotype were observed. Despite subtle differences in temporal activity and body size, differences in structural microhabitat use appears to be the dominant niche axis allowing the coexistence of species within these assemblages of tropical skinks.

Evaluation of offspring size-number invariants in 12 species of lizard

The optimal division of resources into offspring size vs. number is one of the classic problems in life‐history evolution. Importantly, models that take into account the discrete nature of resource division at low clutch sizes suggest that the variance in offspring size should decline with increasing clutch size according to an invariant relationship. We tested this prediction in 12 species of lizard with small clutch sizes. Contrary to expectations, not all species showed a negative relationship between variance in offspring size and clutch size, and the pattern significantly deviated from quantitative predictions in five of the 12 species. We suggest that the main limitation of current size–number models for small clutch sizes is that they rely on assumptions of hierarchical allocation strategies with independence between allocation decisions. Indeed, selection may favour alternative mechanisms of reproductive allocation that avoid suboptimal allocation imposed by the indivisible fraction at low clutch sizes.

Phenotypic Integration in Response to Incubation Environment Adaptively Influences Habitat Choice in a Tropical Lizard

Phenotypic integration, in which a suite of traits change in a correlated or covarying response to shifts in environmental conditions, may enhance an organism’s fitness. In skinks, rocky environments select for longer limbs and rapid running and climbing. We examined whether differences in nest temperature coincident with specific habitats caused phenotypically integrated effects on morphology, locomotor performance, and behavior in the skink Carlia longipes. Specifically, we determined whether microhabitat choices were integrated with adaptive morphology for each habitat. Using a split-clutch design, we incubated eggs at thermal regimes that mimicked the thermal environments of nests from two habitat types (forest = warm; rocky = cool). Hatchlings from cool incubation environments had longer limbs and greater running and climbing speeds, which are likely to be beneficial for rocky habitats. In addition, individuals from cool incubation environments selected rocky microhabitats more frequently than did hatchlings from warm incubation environments. We demonstrate phenotypic integration in response to nest temperature that affected morphology, performance, and ultimately habitat selection in a way that should increase hatchling fitness.