Browsing by Author "Oliveira, T."
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- Do cleaning organisms reduce the stress response of client reef fish?Publication . Bshary, Redouan; Oliveira, R. F.; Oliveira, T.; Canario, Adelino V. M.Marine cleaning interactions in which cleaner fish or shrimps remove parasites from visiting 'client' reef fish are a textbook example of mutualism. However, there is yet no conclusive evidence that cleaning organisms significantly improve the health of their clients. We tested the stress response of wild caught individuals of two client species, Chromis dimidiata and Pseudanthias squamipinnis, that had either access to a cleaner wrasse Labroides dimidiatus, or to cleaner shrimps Stenopus hispidus and Periclimenes longicarpus, or no access to cleaning organisms. For both client species, we found an association between the presence of cleaner organisms and a reduction in the short term stress response of client fish to capture, transport and one hour confinement in small aquaria, as measured with cortisol levels. It is conceivable that individuals who are more easily stressed than others pay a fitness cost in the long run. Thus, our data suggest that marine cleaning mutualisms are indeed mutualistic. More generally, measures of stress responses or basal levels may provide a useful tool to assess the impact of interspecific interactions on the partner species.
- A test of the ‘challenge hypothesis’ in cichlid fish: simulated partner and territory intruder experimentsPublication . Hirschenhauser, K.; Taborsky, M.; Oliveira, T.; Canario, Adelino V. M.; Oliveira, R. F.In male birds, the responsiveness of androgens to sexual and territorial behaviour is predicted to vary with mating system and the degree of paternal investment (‘challenge hypothesis’, CH; Wingfield et al. 1990, American Naturalist, 136, 829–846). The CH predicts a higher and longer lasting ‘breeding baseline’ androgen level in males of polygynous species with no or only short-term paternal investment than in males of monogamous species with a high degree of paternal investment. Since the applicability of the CH to nonavian vertebrates has been unclear, we experimentally tested its predictions in several cichlid fish (Neolamprologus pulcher, Lamprologus callipterus, Tropheus moorii, Pseudosimochromis curvifrons and Oreochromis mossambicus) using a simulated territorial intruder protocol. Androgens (11-ketotestosterone: 11-KT; testosterone: T) were measured from fish-holding water. In all species sampled, the 11-KT patterns confirmed the predictions of the CH originating from the avian literature, but T patterns did not. Males of all species sampled were highly responsive to territorial intrusions; however, the magnitude and duration of this response, that is, the rapid return to baseline 11-KT levels, could not clearly be explained by the degree of paternal care. 11-KT responses to interactions with ovulating females were observed in maternal mouthbrooders but not in biparental species (e.g. Lamprologini). At the interspecific level, androgen responsiveness was greater among males of monogamous species, as predicted, but also in species with more intense pair bonding (e.g. Tropheus moorii). Thus, this study confirms the predictions of the CH in cichlid fish at both the intraspecific and the interspecific levels.