The ability to buffer detrimental effects of environmental stress on fitness is of great ecological importance because, in nature, pronounced environmental variation may regularly induce stress. Furthermore, several stressors may interact in a synergistic manner. In the present study, plastic responses in cold, heat and starvation resistance are investigated in the tropical butterfly Bicyclus anynana Butler, 1879, using a full factorial design with two acclimation temperatures (20 and 27 °C) and four short‐term stress treatments (control, cold, heat, starvation). Warm‐acclimated butterflies are more heat‐ but less cold‐tolerant as expected. Short‐term cold and starvation exposure reduce cold and heat resistance, and short‐term heat exposure decreases cold but increases heat resistance. Starvation resistance is not affected by any of the short‐term treatments. Thus, the effects of short‐term stress exposure are either neutral or negative, except for a positive effect of heat exposure on heat resistance, indicating the negative effects of pre‐exposure to stress. Interestingly, significant interactions between acclimation temperature and short‐term stress exposure for heat and cold resistance are found, demonstrating that larger temperature differences incur more damage. Therefore, animals may not generally be able to benefit from pre‐exposure to stress (through ‘hardening’), depending on their previously experienced conditions. The complex interactions between environmental variation, stress and resistance are highlighted, warranting further investigations.
Morphological classification and mitochondrial phylogeny of a pair of morphologically defined species of New Caledonian freshwater gastropods, Hemistomia cockerelli and Hemistomia fabrorum, were incongruent. We asked whether these two nominal species can be unambiguously distinguished based on shell morphology or whether the taxonomic discrepancy inferred from these character types was reflected in the variation of shell morphology. Our investigations were based on phylogenetic analyses of a fragment of the mitochondrial cytochrome c oxidase subunit I, geometric morphometric analyses as well as micro computer tomography. The species presorted to morphospecies by eye overlapped in shell shape. However, statistically, all shells were correctly assigned, but not all of them significantly. Qualitatively, both nominal species can be unambiguously distinguished by the presence/absence of a prominent denticle within the shell. In the phylogenetic analyses, individuals from three populations clustered with the “wrong” morphospecies. In the absence of data from multiple loci, it was assumed for the single specimen from one of these populations that its misplacement was due to a recent hybridization event, based on its very shallow position in the tree. For the other two cases of misplacement neither introgression nor incomplete lineage sorting could be ruled out. Further investigations have to show whether the morphological overlap has a genetic basis or is due to phenotypic plasticity. In conclusion, despite their partly unresolved relationships Hemistomia cockerelli and Hemistomia fabrorum may be considered sister species, which are reliably diagnosable by the presence or absence of the denticle, but have not yet fully differentiated in all character complexes investigated.
Facing increasing human demands on Earth, understanding how endangered species may survive in isolated remnants of natural habitat within heavily transformed landscapes is key to contemporary conservation biology. Against this background we here investigate the factors affecting pond occupancy in the endangered European tree frog (Hyla arborea L.) within an urban landscape, being located in north‐eastern Germany where the species is still fairly common. Our survey revealed that 58 out of 122 ponds were occupied by H. arborea. Ponds with a higher percentage of floating vegetation, being deeper and surrounded by higher percentages of crop fields and forests were more likely to be occupied, while factors associated with urbanization such as the percentage of built‐up area were strongly detrimental. Habitat requirements of H. arborea were complex as occurrence was simultaneously affected by different spatial scales, including the landscape scale, the immediate surroundings of ponds and the ponds themselves. H. arborea avoided highly urbanized areas, but occurred frequently in agricultural areas surrounding the city. The latter suggests that this species is fairly tolerant towards human‐induced transformations, and that vast arable fields yielded positive rather than negative effects on H. arborea occurrence. We conclude that the most important conservation issues for supporting H. arborea populations at the periphery of urbanized areas are (1) maintaining an open (agricultural) landscape structure, (2) providing undisturbed overwintering habitats, and (3) maintaining pond quality by halting shrub and tree encroachment.
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