Data on parasites of rodents, collected over an 18-year period
on
the Iberian peninsula, were used to find the determinants
of parasite species richness. A total of 77 species of helminth parasites
(nematodes, cestodes and digeneans) was identified
among 16 species of rodents. Parasites were classified into groups according
to their specificity towards their host and their
life-cycle. A working phylogeny of the rodents was proposed on the basis
of molecular and paleontological data and for
each host the following parameters were recorded: sample size, weight,
geographical range, longevity, and life-style. Two
comparative methods were used, the independent comparisons method of Pagel
(1992) and the distance matrix method
of Legendre, Lapointe & Casgrain (1995). The second method has the
advantage of measuring the relative contribution
of phylogeny. Both methods gave similar results. Overall parasite species
richness correlated only with host sample size.
Host body size does not correlate with any subset of parasite species richness.
However, host phylogeny is a good predicator
of specific parasites and the species richness of digeneans correlates
with
host geographical range. 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 characters,
i.e. we made the assumption that the loss
of a parasite species is irreversible. The consensus tree obtained reflects
the major phylogenetic 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 hosts) in determining the structure of helminth parasite
fauna.