Biotic triggers of female reproduction in the terrestrial isopodArmadillidium vulgareLatr. (Crustacea Oniscidea)

The environment can modulate the reproductive pattern of many arthropods by abiotic factors (e.g. temperature, photoperiod, moisture) or by biotic factors (e.g. male-effect, population structure). In the terrestrial isopod Armadillidium vulgare, reproduction is stimulated by environmental 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 parturial molting. This study is focussed on the influence of male or female 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 efficient as a permanent contact. The 4th week of the female preparturial inter-molt was the most sensitive time, since the presence of a male 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 inter-molt (appearance of white plates) accelerates vitellogenesis. Another main conclusion is that female-female intermittent crowding (1 day in 3) also showed a significant acceleration of vitellogenesis. In conclusion Armadillidium vulgare shows various biotic triggers of reproduction, which co-exist with classical abiotic ones. We discuss the relevance of these findings for natural populations, especially when the sex-ratio of the population is highly female-biased because of a parasitic distortion of sex-ratio.