BIOTIC TRIGGERS OF FEMALE REPRODUCTION IN THE TERRESTRIAL ISOPOD ARMADILLIDIUM-VULGARE LATR. (CRUSTACEA ONISCIDEA)

The environment can modulate the reproductive pattern of many arthropo ds by abiotic factors (e.g. temperature, photoperiod, moisture) or by biotic factors (e.g. male-effect, population structure). In the terres trial isopod Armadillidium vulgare, reproduction is stimulated by envi ronmental factors (e.g. photoperiod) and by the male's behaviour which plays two roles: first accelerating the onset of female reproduction by stimulating vitellogenesis, then mating with a female before the pa rturial molting. This study is focussed on the influence of male or fe male presence on the initiation of reproduction. We conclude that the intermittent presence of a male (1 day in 3, or 1 day a week) was as e fficient as a permanent contact. The 4th week of the female preparturi al inter-molt was the most sensitive time, since the presence of a mal e during this week only had as much effect as permanent contact. This particular sensitivity can be explained by the vitellogenesis cycle: a male present when the female is beginning the ''D'' period of its int er-molt (appearance of white plates) accelerates vitellogenesis. Anoth er main conclusion is that female-female intermittent crowding (1 day in 3) also showed a significant acceleration of vitellogenesis. In con clusion Armadillidium vulgare shows various biotic triggers of reprodu ction, which co-exist with classical abiotic ones. We discuss the rele vance of these findings for natural populations, especially when the s ex-ratio of the population is highly female-biased because of a parasi tic distortion of sex-ratio.