Genetic diversity is a key factor that can influence mate choice in many species. We experimentally determined the influence of this factor on mate preference in the crustacean terrestrial isopod Armadillidium vulgare. This biological model is gregarious which could increase the risk of inbreeding by mating with closely related partners. Mechanisms of inbreeding avoidance during mate choice can thus be expected. Moreover, previous studies predict that males would be the choosy sex. We performed Y-choice tests giving males the choice between two females presenting different levels of heterozygosity and genetic similarity to the male. Our results show potential inbreeding avoidance according to the genetic characteristics of females presented to males. The higher the variation in genetic similarity to the male between females is, the higher the preference of the male towards the most dissimilar female is. Hence, male preferences may only be detectable when the difference between females' genetic characteristics is large enough. If heterozygosity is associated with fitness in A. vulgare (as in many organisms), the patterns of mate preference we observe may be adaptive.

Genetic diversity is known to be correlated to fitness traits, and inbred individuals often display lower values for life history traits. In this study, we attempt to quantify how inbreeding affects such traits in the terrestrial isopod Armadillidium vulgare by performing inbred and non-inbred crosses under laboratory conditions. We estimated genetic characteristics of parents and offspring, and related them to fecundity and fertility measures, as well as offspring growth and survival. Our study shows that a decrease in offspring number might result from mortality around birth, but not to changes in fecundity, fertilization rate, or developmental failure between inbred and non-inbred crosses. More heterozygous females tended to be bigger and had a higher fecundity, which could have implications in mate choice. No effect of inbreeding was detected on offspring growth and survival. These results can be related to previously observed effects of genetic characteristics on mating strategies in A. vulgare, and could shed light on mechanisms of inbreeding avoidance in this species.

Immune priming has been widely observed in invertebrates. However, this phenomenon remains incompletely characterized concerning the time course of the protective effect and immune responses. Here, we investigated the existence of a protective effect in the terrestrial isopod Armadillidium vulgare against a second infection with the bacterium Salmonella enterica. We primed animals with a low dose of living bacteria or with the bacterial culture medium. One day, 7 or 15 days later, we measured haemocytes concentration and viability and we injected a LD50 of living S. enterica to monitor the survival rates of infected individuals. We show that A. vulgare is better protected (i.e. survival improvement) upon secondary infection when it has encountered S. enterica 7 days before. This protection, which tends to persist 15 days after the first infection, is however not observed when the priming is performed only 1 day before the LD50 injection. Besides providing a new invertebrate example, we highlight this protection is dynamic and may be partly due to a high haemocyte production.