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 ( þ ) 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 ( þ ) 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 ( þ ) WIN 55,212-2, but not with (À) 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 ( þ ) 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 ( þ ) 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 ( þ ) WIN 55,212-2.

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.

Reduced trophic resources can pose relevant constraints to the development of freshwater animals with complex life cycles. For amphibians, food deprived environments, such as high-altitude ponds and springs and groundwaters are frequently used for breeding. The aim of this study is to outline trophic conditions leading to extreme cases of delayed larval development and increased size at metamorphosis of a European widespread amphibian, the fire salamander (Salamandra salamandra). We collected 150 fire salamander larvae, split them in two groups, one with high and one with low trophic resource availability. We then observed the effects of nutritional conditions on larval development recording time to metamorphosis and average day growth. Moreover, in the field, we surveyed larvae growth and size at metamorphosis in two artificial subterranean sites with low prey availability. Trophic conditions strongly affected larval development and under low food treatment time to metamorphosis reached up to 416 days. In the subterranean environments we observed a similar pattern, with larvae requiring more than one year to attain metamorphosis but reaching unexpected large sizes. Environmental trophic conditions experienced during early stages can induce strong delay in metamorphosis of the fire salamander; this plasticity makes fire salamander larvae optimal models for comparative studies and cross-environment experiments.

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Natural selection shapes the life features of organisms to suit the environment where they live, to take advantage of opportunities at different life stages, and to mitigate the risks (e.g., Via, 2009;Waddington, 1942). Environmental conditions early in life can have fitness consequences later in life, i.e., carry-over effects sensu O'Connor et al. (2014). Therefore populations living in different environments are expected to differentially allocate resources in order to minimise deleterious effects of early life on adult fitness (Stevens et al., 2000).