Temperature tolerance and energetics: a dynamic energy budget-based comparison of North Atlantic marine species

Temperature tolerance and sensitivity were examined for some North Atlantic marine species and linked to their energetics in terms of species-specific parameters described by dynamic energy budget (DEB) theory. There was a general lack of basic information on temperature tolerance and sensitivity for many species. Available data indicated that the ranges in tolerable temperatures were positively related to optimal growth temperatures. However, no clear relationships with temperature sensitivity were established and no clear differences between pelagic and demersal species were observed. The analysis was complicated by the fact that for pelagic species, experimental data were completely absent and even for well-studied species, information was incomplete and sometimes contradictory. Nevertheless, differences in life-history strategies were clearly reflected in parameter differences between related species. Two approaches were used in the estimation of DEB parameters: one based on the assumption that reserve hardly contributes to physical volume; the other does not make this assumption, but relies on body-size scaling relationships, using parameter values of a generalized animal as pseudo-data. Temperature tolerance and sensitivity seemed to be linked with the energetics of a species. In terms of growth, relatively high temperature optima, sensitivity and/or tolerance were related to lower relative assimilation rates as well as lower maintenance costs. Making the step from limited observations to underlying mechanisms is complicated and extrapolations should be carefully interpreted. Special attention should be devoted to the estimation of parameters using body-size scaling relationships predicted by the DEB theory.     

Host sex and ectoparasites choice: preference for, and higher survival on female hosts

1. Sex differences in levels of parasite infection are a common rule in a wide range of mammals, with males usually more susceptible than females. Sex-specific exposure to parasites, e.g. mediated through distinct modes of social aggregation between and within genders, as well as negative relationships between androgen levels and immune defences are thought to play a major role in this pattern. 2. Reproductive female bats live in close association within clusters at maternity roosts, whereas nonbreeding females and males generally occupy solitary roosts. Bats represent therefore an ideal model to study the consequences of sex-specific social and spatial aggregation on parasites' infection strategies. 3. We first compared prevalence and parasite intensities in a host-parasite system comprising closely related species of ectoparasitic mites (Spinturnix spp.) and their hosts, five European bat species. We then compared the level of parasitism between juvenile males and females in mixed colonies of greater and lesser mouse-eared bats Myotis myotis and M. blythii. Prevalence was higher in adult females than in adult males stemming from colonial aggregations in all five studied species. Parasite intensity was significantly higher in females in three of the five species studied. No difference in prevalence and mite numbers was found between male and female juveniles in colonial roosts. 4. To assess whether observed sex-biased parasitism results from differences in host exposure only, or, alternatively, from an active, selected choice made by the parasite, we performed lab experiments on short-term preferences and long-term survival of parasites on male and female Myotis daubentoni. When confronted with adult males and females, parasites preferentially selected female hosts, whereas no choice differences were observed between adult females and subadult males. Finally, we found significantly higher parasite survival on adult females compared with adult males. 5. Our study shows that social and spatial aggregation favours sex-biased parasitism that could be a mere consequence of an active and adaptive parasite choice for the more profitable host.     

Asymmetry, reproductive success and parasitism of Pomatoschistus microps in a French lagoon

There was an allometry between length of nesting male Pomatoschistus microps and the size of the nest. There was also a positive relationship between parasite load and pectoral fin asymmetry. There was no marked relationship between the number of eggs in the nest and parasitism or level of asymmetry. These results are discussed in terms of energy allocation and fish reproductive success.     

Histology of the fusion area between the parasitic male and the female in the deep-sea anglerfish Neoceratias spinifer Pappenheim, 1914 (Teleostei, Ceratioidei)

The article deals primarily with the histology of the fusion area between the head of the male and the skin of the female in two female Neoceratias spinifer, each of which had a single parasitic male attached. In this area, comprising the whole flattened upper part of the male head, the dermis of the male is completely fused with that of the female, leaving no remnants of the epidermis of either. In all other known cases permanent attachment of the parasitic male is accomplished by fusion of separate outgrowths from the male snout and lower jaw and the female skin. In the fusion area of N. spinifer two interconnected blood vascular plexus are present, the one located in the connective tissue of the male head, the other in that of the female skin. It is not known, however, whether the plexus in the female skin is provided with blood from the female blood vascular system, i.e. there is no critical proof of a real continuity between the female blood vascular system and that of the male. The eyes of both parasitic males are very degenerate. There is no histological evidence of degenerative changes in the male digestive system, heart or gills.