Etude de l'influence des facteurs visuels sur les comportements sexuels et agressifs de Mollienesia (Poecilia) velifera (Pisces,Poeciliidae)

One of the most striking features of cave fishes is their pronounced ocular regression. They are, however, perfectly adapted since they multiply and display the behaviour patterns which are biologically important in their surroundings. It is therefore of interest to study the relative role of visual factors in the corresponding behaviour patterns in related epigean species.Other authors have previously demonstrated the dominant role of chemical stimuli in the releasing of sexual behaviour patterns in M. sphenops, of which some forms are cavernicolous. In M. velifera and M. latipinna, on the contrary, visual factors seem more important. The releasers of the aggressive behaviour patterns of these three species seem to be predominantly visual. In the present study, the importance of visual factors has been verified experimentally in M. velifera by comparing the observed behavioural differences in experimentally blinded individuals and normal controls.The results of the pre-experimental phase show that there is no difference between these two groups before blinding, neither in the frequency of the patterns, nor in their numerical values.The results of the first experimental phase confirm the importance of visual releasers in the sexual behaviour patterns of M. velifera. Thus, sexual approaches, mouth—abdomen contacts and copulation attempts are totally absent in blinded pairs. Sexual motivation however is still present since the gonopodal flexions are equally frequent in both groups. On the other hand, it seems that aggressive behaviour patterns are maintained in blinded individuals but only when the partners are very close to each other or when an actual contact has taken place.The comparison of pairs in which only one of the partners is blinded (second experimental phase), as well as results of the first phase, suggest that experimental blinding does not cause hormonal changes liable to influence the observed patterns. In addition to this, the role of the ♀ in courtship has been specified. When a ♀ individual is intact and receptive, it will initiate courtship when it is placed in the company of an inactive blinded partner.