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Male and female Uca tangeri (the only fiddler crab species to inhabit Europe) construct mudballs from mud excavated from within their burrows. Individual males placed similar patterns of mudballs each low tide, suggesting that there is some degree of stereotypy. When mudballs were experimentally moved further from the burrow or closer to it, males only repositioned those that were moved closer, placing them further away again. However, males did not replace mudballs that had been experimentally destroyed at the end of the mudballing phase when they had started to court females. In binary presentation tests, females showed no significant differences in response to mudballs made from different types of mud, or different numbers of mudballs. These results are consistent with earlier findings that male mudballs function as territory boundaries. However, we provide evidence that male mudballs have no function in female attraction, contrasting with previous studies. [ABSTRACT FROM AUTHOR]

Individual variation in the response to environmental challenges depends partly on innate reaction norms, partly on experience-based cognitive/emotional evaluations that individuals make of the situation. The goal of this study was to investigate whether pre-existing differences in behaviour predict the outcome of such assessment of environmental cues, using a conditioned place preference/avoidance (CPP/CPA) paradigm. A comparative vertebrate model (European sea bass, Dicentrarchus labrax) was used, and ninety juvenile individuals were initially screened for behavioural reactivity using a net restraining test. Thereafter each individual was tested in a choice tank using net chasing as aversive stimulus or exposure to familiar conspecifics as appetitive stimulus in the preferred or non preferred side respectively (called hereafter stimulation side). Locomotor behaviour (i.e. time spent, distance travelled and swimming speed in each tank side) of each individual was recorded and analysed with video software. The results showed that fish which were previously exposed to appetitive stimulus increased significantly the time spent on the stimulation side, while aversive stimulus led to a strong decrease in time spent on the stimulation side. Moreover, this study showed clearly that proactive fish were characterised by a stronger preference for the social stimulus and when placed in a putative aversive environment showed a lower physiological stress responses than reactive fish. In conclusion, this study showed for the first time in sea bass, that the CPP/CPA paradigm can be used to assess the valence (positive vs. negative) that fish attribute to different stimuli and that individual behavioural traits is predictive of how stimuli are perceived and thus of the magnitude of preference or avoidance behaviour.