The dynamics of Wood mouse (Apodemus sylvaticus) populations in the Camargue

Hair as a noninvasive tool for risk assessment: do the concentrations of cadmium and lead in the hair of wood mice (Apodemus sylvaticus) reflect internal concentrations?

There is an increasing need for developing noninvasive markers of accumulation when studying the transfer of pollutants in wildlife, in response to problems caused by sacrifice of animals (disturbed population dynamics, respect of ethical protocols). Thus, the aim of this work was to determine whether trace metal (TM) concentrations in hair could be used as an accurate noninvasive estimator of internal and environmental concentrations. For that purpose, on a 40km² site surrounding an ancient smelter, 321 wood mice (Apodemus sylvaticus) were sampled on seven squares (500×500m) and 4 squares in fall 2010 and spring 2011, respectively. The relationships between the cadmium (Cd) and lead (Pb) concentrations in hair and those in the liver, kidneys, and soils were described. The results indicated that hair concentration was a relatively good predictor of Pb concentrations in organs (p<0.001, 0.46<R²<0.53). In contrast, Cd concentrations in organs were only weakly predicted by hair concentrations in session 2010 (p<0.001, R²=0.10 for both organs), and no significant relationship was found in session 2011 (p=0.252 for liver and p=0.971 for kidneys). The Cd and Pb concentrations in the soil and in hair were not linearly related, but concentrations in hair increased with soil concentrations (Spearman's rank correlations). Linear relationships between internal and hair concentrations differed significantly between the sampling sessions, especially for Cd. When they were included in models analyzing the relationships between TM concentrations in organs and in hair, individual characteristics (gender and body mass as a non-lethal estimation of relative age) increased the explained variability of Cd in organs but not of Pb. In conclusion, hair should be used cautiously to predict internal Cd concentrations but can be considered as an accurate noninvasive estimator of internal Pb concentrations. Further studies should be performed to develop, generalize, and apply this useful possible tool for risk assessment in ecotoxicology.

Transmission dynamics of Borrelia lusitaniae and Borrelia afzelii among Ixodes ricinus, lizards, and mice in Tuscany, central Italy

To estimate the basic reproduction number (R(0)) of Borrelia lusitaniae and Borrelia afzelii, we formulated a mathematical model considering the interactions among the tick vector, vertebrate hosts, and pathogens in a 500-ha enclosed natural reserve on Le Cerbaie hills, Tuscany, central Italy. In the study area, Ixodes ricinus were abundant and were found infected by B. lusitaniae and B. afzelii. Lizards (Podarcis spp.) and mice (Apodemus spp.), respectively, are the reservoir hosts of these two Borrelia burgdorferi sensu lato (s.l.) genospecies and compete for immature ticks. B. lusitaniae R(0) estimation is in agreement with field observations, indicating the maintenance and diffusion of this genospecies in the study area, where lizards are abundant and highly infested by I. ricinus immature stages. In fact, B. lusitaniae shows a focal distribution in areas where the tick vector and the vertebrate reservoir coexist. Mouse population dynamics and their relatively low suitability as hosts for nymphs seem to determine, on the other hand, a less efficient transmission of B. afzelii, whose R(0) differs between scenarios in the study area. Considering host population dynamics, the proposed model suggests that, given a certain combination of the two host population sizes, both spirochete genospecies can coexist in our study area. Additional incompetent hosts for B. burgdorferi s.l. have a negative effect on B. afzelii maintenance, whose R(0) results > 1 only with high mouse population densities and/or low lizards abundance, but they do not seem to influence B. lusitaniae transmission cycle on Le Cerbaie. Secondly, our model confirms the importance of nymphs' infestation, of host population density and diversity, and spirochetes host association for the maintenance of the transmission cycle of B. burgdorferi s.l.