Conserved ecophysiology despite disparate microclimatic conditions in a gecko.

Microscale differences in the habitats organisms occupy can influence selection regimes and promote intraspecific variation of traits. Temperature-dependent traits can be locally adapted to climatic conditions or be highly conserved and insensitive to directional selection under all but the most extreme regimes, and thus be similar across populations. The opposing slopes of Nahal Oren canyon in the Carmel Mountains, Israel, are strikingly different: the south-facing slope receives intensive solar radiation, is hot and supports mostly annual vegetation, whereas the north-facing slope is ~10°C cooler, more humid, and supports Mediterranean woodland. We examined whether these differences manifest in the thermal physiology of a common gecko species Ptyodactylus guttatus in controlled laboratory conditions. We predicted that geckos from the hotter south-facing slope would prefer higher temperatures, have faster gut passage times, lower metabolic and evaporative water loss rates, and start diel activity earlier compared with north-facing slope conspecifics. Contrary to these predictions, there were no differences between any of the ecophysiological traits in geckos from the opposing slopes. Nevertheless, our data showed that individuals from the north-facing slope were generally more active in earlier hours of the afternoon compared with south-facing individuals. We suggest that P. guttatus individuals disperse between the slopes and either gene-flow or behavioral plasticity deter local adaptation, resulting in similar physiological traits. Perhaps a stronger contrast in climatic conditions and a stronger barrier are needed to result in interpopulation divergence in temperature-dependent traits.

Specialist versus Generalist at the Intraspecific Level: Functional Morphology and Substrate Preference of Mediodactylus kotschyi Geckos.

Populations of the same species occupying different microhabitats can either exhibit generalized traits across them or display intraspecific variability, adapting to each microhabitat in order to maximize performance. Intraspecific variability contributes to the generation of diversity, following selection and adaptation, and understanding such variability is important for comprehending how individuals choose their microhabitats. Compared with interspecific variability, however, intraspecific variability in functional morphology and its relationship with microhabitat preference and use have been relatively little studied. Here we examined whether populations of the gecko Mediodactylus kotschyi that differ in the substrates they occupy display habitat-specific behaviors and differing morphologies associated with functional adaptation to their microhabitats. We collected 207 geckos from under or on rocks or on trees from seven populations in Greece. On large islands individuals occupy both substrates; whereas small islets are devoid of trees and the geckos are restricted to rocks, while on the mainland they are only found on trees. We determined gecko substrate preferences in the laboratory, together with their clinging abilities to the different substrates. We measured their limbs, digits, and claws and assessed how these measurements relate to clinging ability. Geckos from all populations preferred the tree made available to them, but this preference was not statistically significant. Geckos from both large and small islands clung better to the tree than to the rock in the laboratory, while those from the mainland clung similarly to both substrates. Geckos collected from trees had longer manual digits and hind limbs. Geckos collected from large and small islands had taller (longer on the dorso-ventral axis; henceforth "deeper") claws. Longer digits and deeper but shorter claws were associated with a better ability to cling to rocks. Our findings suggest that while M. kotschyi is potentially preferentially arboreal, due to the great variation and plasticity it possesses, it can successfully also exploit the habitats available on the smallest, treeless islets in the Aegean Sea. Our study suggests that the dichotomous use of generalist versus specialist in describing species' habitat use is oversimplified, and we suggest the use of a generalist-specialist gradient instead.

Viviparity does not affect the numbers and sizes of reptile offspring.

Viviparity (live-bearing) has independently evolved from oviparity (egg-laying) in more than 100 lineages of squamates (lizards and snakes). We might expect consequent shifts in selective forces to affect per-brood reproductive investment (RI = total mass of offspring relative to maternal mass) and in the way in which that output is partitioned (number vs. size of offspring per brood). Based on the assumption that newly born offspring are heavier than eggs, we predicted that live-bearing must entail either increased RI or a reduction in offspring size and/or fecundity. However, our phylogenetically controlled analysis of data on 1,259 squamate species revealed no significant differences in mean offspring size, clutch size or RI between oviparous and viviparous squamates. We attribute this paradoxical result to (1) strong selection on offspring sizes, unaffected by parity mode, (2) the lack of a larval stage in amniotes, favouring large eggs even in the ancestral oviparous mode and (3) the ability of viviparous females to decrease the mass of uterine embryos by reducing extra-embryonic water stores. Our analysis shows that squamate eggs (when laid) weigh about the same as the hatchlings that emerge from them (despite a many-fold increase in embryo mass during incubation). Most of the egg mass is due to components (such as water stores and the eggshell) not required for oviductal incubation. That repackaging enables live-born offspring to be accommodated within the mother's body without increasing total litter mass. The consequent stasis in reproductive burden during the evolutionary transition from oviparity to viviparity may have facilitated frequent shifts in parity modes.

Intraspecific competition, not predation, drives lizard tail loss on islands.

Tail autotomy is mainly considered an antipredator mechanism. Theory suggests that predation pressure relaxes on islands, subsequently reducing autotomy rates. Intraspecific aggression, which may also cause tail loss, probably intensifies on islands due to the higher abundance. We studied whether tail autotomy is mostly affected by predation pressure or by intraspecific competition. We further studied whether predator abundance or predator richness is more important in this context. To test our predictions, we examined multiple populations of two gecko species: Kotschy's gecko (Mediodactylus kotschyi; mainland and 41 islands) and the Mediterranean house gecko (Hemidactylus turcicus; mainland and 17 islands), and estimated their abundance together with five indices of predation. In both species, autotomy rates are higher on islands and decline with most predation indices, in contrast with common wisdom, and increase with gecko abundance. In M. kotschyi, tail-loss rates are higher on predator and viper-free islands, but increase with viper abundance. We suggest that autotomy is not simply, or maybe even mainly, an antipredatory mechanism. Rather, such defence mechanisms are a response to complex direct and indirect biotic interactions and perhaps, in the case of tail autotomy in insular populations, chiefly to intraspecific aggression.