COMPARATIVE-ANALYSIS OF PARASITE SPECIES RICHNESS OF IBERIAN RODENTS

Data on parasites of rodents, collected over an 18-year period on the Iberian peninsula, were used to fmd the determinants of parasite speci es richness. A total of 77 species of helminth parasites (nematodes, c estodes and digeneans) was identified among 16 species of rodents. Par asites were classified into groups according to their specificity towa rds their host and their life-cycle. A working phylogeny of the rodent s was proposed on the basis of molecular and paleontological data and for each host the following parameters were recorded: sample size, wei ght, geographical range, longevity, and life-style. Two comparative me thods were used, the independent comparisons method of Pagel (1992) an d the distance matrix method of Legendre, Lapointe & Casgrain (1995). The second method has the advantage of measuring the relative contribu tion of phylogeny. Both methods gave similar results. Overall parasite species richness correlated only with host sample size. Host body siz e does not correlate with any subset of parasite species richness. How ever, host phylogeny is a good predicator of specific parasites and th e species richness of digeneans correlates with host geographical rang e. A phylogenetic reconstruction of host relations was performed using the parasites belonging to subgroups in which richness is correlated with host phylogeny. These parasite species were treated as Dollo char acters, i.e. we made the assumption that the loss of a parasite specie s is irreversible. The consensus tree obtained reflects the major phyl ogenetic divisions of the host group. Finally, this study illustrates the relative importance of processes acting at different temporal and spatial scales (evolutionary time and actual geographical range of hos ts) in determining the structure of helminth parasite fauna.