Patch leaving decisions by sexual and asexual strains of an insect parasitoid under different environmental conditions: A role in the coexistence of both reproductive modes?

AMAT, I.; CASTELO, M.K.; BERNSTEIN, C.

Leeds, Inglaterra

Congreso; Association for the Study of Animal Behavior: Easter Meeting; 2003

ASAB

Theory predicts that asexual reproduction has a competitive advantage over sexual reproduction because of the two-fold cost of producing males. In the parasitoid Venturia canescens (Hymenoptera: Ichneumonidae), both thelytokous (parthenogenetic) and arrhenotokous (sexual) wasps are known to co-occur in natural conditions. In this parasitoid, thelytoky is obligate and not induced by Wolbachia bacteria. What could be the ecological, short term, factors that favour the coexistence of arrhenotokous and thelytokous populations? In parasitoids, the strategies of host exploitation are directly linked to their reproductive success. Differences in efficiency of the adopted strategies, for instance under different conditions, could play a role in the competitive balance opposing both reproductive modes. Both arrhenotokous and thelytokous V. canescens populations are found in natural conditions. Conversely, in anthropic conditions (mills and granaries) populations are exclusively thelytokous. These locations provide a relatively constant environment and an ample supply of hosts. This makes temperature and host availability two pertinent factors in discriminating the two environments. In this work we compare patch exploitation by thelytokous and arrhenotokous females combining different temperatures, and host densities. Surprisingly, arrhenotokous and thelytokous females did not show any difference in the way they discriminate between patches of different richness. Conversely arrhenotokous females are more sensitive to changes in temperature. When suffering a decrease in temperature, they exploit patches more thoroughly while thelytokous females stay insensitive to temperature. These results suggest that the coexistence of thelytokous and arrhenotokous wasps in natural conditions could be facilitated by different host exploitation strategies adopted by females of each reproductive mode. These could have resulted from different selection pressure acting upon the optimal pattern of host exploitation of arrhenotokous and thelytokous females in their preferred habitat (field and anthropic conditions respectively).