Sex role as factor of heterogeneity transmission in host-macroparasite system: The case study of Apodemus flavicollis

The predisposition of parasite to aggregate is generated by heterogeneity in exposure and susceptibility to infection. Among factors such age, body condition and diet that may influence the individual variations in transmission and establishment of parasite, sex is recognised to play a determinant role. Indeed in vertebrate, host parasite tend to be male biased. These evidences suggest sex differences in susceptibility, but whether sexes differs in their contribution in transmission is still debated. We analysed Apodemus flavicollis and its parasites Heligmosomoides polygyrus focusing whether sex is important in influencing the dynamics of infection in free living animal population. Methods: From April 2001 to September 2001 a field experiment was carried out on a population monitored with capture-mark-recapture live trapping (14 994 trap night) in 9 samples areas. The parasite burden was selectively reduced by anthelmintic treatment in all males of 3 areas in all females of other 3 areas while 3 remanding areas were used as control. During the experiment the dynamics of parasite infestations was monitored by individual faecal samples analysis. The multicapture data were analysed with generalised linear mixed models fitted with negative binomial errors and individual identification and temporal data as random factors. Results: A total of 143 A. flavicollis were trapped, with a total of 319 faecal samples analysed. During the experiments no significant changes in parasite prevalence and EPG was observed in control areas. In the manipulated areas the treated individual decreased the parasite burden. In the areas where females were treated males, compared with control males, did not change their parasite burden. While in areas where males were treated females decreased their parasites load respect to control females. Discussion: The experimental results suggests the role of the male A. flavicollis to drive the infection. Even if the mechanisms generating such pattern are not still clear, such findings suggest the importance of functional groups in maintaining the infections and thus their identification when programming control strategies.