Larval development and poor trophic resource availability: Local adaptations and plasticity in a widespread amphibian species.

Theory predicts that, in organisms with complex life cycles, if the earlier-stage limiting factor induces weak later-stage phenotypes, the development of the later-stage trait should evolve to reduce carry-over effects. Local adaptations could thus favour decoupling of later stages. However, decoupling is not always possible. In this study, we used a widespread amphibian, the European fire salamander (Salamandra salamandra), to assess the role of local adaptations to environmental stressful conditions experienced at the larval stage. We exposed 150 larvae from different altitudes to two conditions: rich food and poor food condition. Conditions in early life stages can affect an individual's traits, either as a direct effect or mediated through outcomes in successive life stages. To distinguish between effects of rearing conditions and local adaptation, we searched for a causal model. The causal model detected effects of both food treatment and population origin (altitude) on all life stages. Larvae reared under rich food condition metamorphosed earlier, had higher growth rates and reached smaller size at metamorphosis. Significant differences occurred between larvae of different origin: low-altitude individuals performed poorly under the poor food treatment. Moreover, larvae from higher altitudes were slower with rich food and faster with poor food compared to those from lower altitudes. Our results underline that environmental conditions and local adaptation can interplay in determining the plasticity of larval stages, still adaptations can maximize the growth efficiency of early stages in oligotrophic environments, leading to divergent pathways across populations and environmental conditions.

Factors determining the dorsal coloration pattern of aposematic salamanders.

Aposematic bright colors have a key role for animal defense and can be expressed through metabolic production or by acquiring pigments from diet. Aposematic coloration can be related to both local adaptations and availability of trophic resources. The European fire salamander (Salamandra salamandra) shows significant color variability and occurs across a broad range of habitats. Here we combined field observations with common rearing experiments to disentangle the role of environmental conditions and local adaptations in determining aposematic coloration of salamander populations. We assessed color variation and measured habitat features and food availability in adults from 25 populations. Furthermore, we reared newborn larvae from 10 populations under different food availability and analyzed color of metamorphs. To assess color pattern, we measured the percentage of yellow covering the body, and the Hue, Saturation and Value of yellow coloration. Adult showed strong variation of color pattern; variation was strongly related to the individual's size, to habitat productivity and to food availability. Under common garden conditions, differences between populations were not anymore evident, and coloration was only affected by resource availability during larval development. Our results suggest that environmental conditions and food availability are more important than local adaptations in determining differences in aposematic color pattern.

Tolerance to cannabinoid response on the myenteric plexus of guinea-pig ileum and human small intestinal strips.

1. We studied tolerance to cannabinoid agonist action by comparing the in vitro inhibition of electrically evoked contractions of longitudinal muscle from small intestine of human and guinea-pig (myenteric plexus preparations) after 48-h incubation with the synthetic agonist (+) WIN 55,212-2. We also investigated the intrinsic response to the selective cannabinoid CB(1) receptor antagonist rimonabant in control and tolerant strips. 2. (+) WIN 55,212-2 inhibited guinea-pig (IC(50) 4.8 nM) and human small intestine (56 nM) contractions with similar potency before or after 48-h incubation in drug-free conditions; this effect was competitively antagonized by rimonabant (pA(2), 8.4, 8.2). A 48-h preincubation with (+) WIN 55,212-2, but not with (-) WIN 55,212-3, completely abolished the acute agonist response in both tissue preparations. The opiate K-receptor agonist U69593 inhibited human small intestine contractions with a similar potency in control and strips tolerant to (+) WIN 55,212-2, IC(50) 39 and 43 nM. 3. Unlike human tissue, in guinea-pig small intestine, which has a high level of endocannabinoids, rimonabant alone increased the twitches induced by the electrical field stimulation (EC(50) 100 nM) with a maximal effect of 123%. 4. In strips tolerant to (+) WIN 55,212-2, rimonabant markedly increased (155%) the electrical twitches in human ileum and in guinea-pig myenteric plexus smooth muscle (133%). 5. This study shows tolerance can be induced to the cannabinoids' action in intestinal strips of human and guinea-pig by long in vitro incubation with the agonist (+) WIN 55,212-2.