Résumé
Across different taxa, networks of mutualistic or antagonistic
interactions show consistent architecture. Most networks are modular, with
modules being distinct species subsets connected mainly with each other
and having few connections to other modules. We investigate the
phylogenetic relatedness of species within modules and whether a
phylogenetic signal is detectable in the within- and among module
connectivity of species using 27 mammal-flea networks from the
Palaearctic. In the 24 networks that were modular, closely-related hosts
co-occurred in the same module more often than expected by chance; in
contrast, this was rarely the case for parasites. The within- and
among-module connectivity of the same host or parasite species varied
geographically. However, among-module but not within-module connectivity
of host and parasites was somewhat phylogenetically constrained. These
findings suggest that the establishment of host-parasite networks results
from the interplay between phylogenetic influences acting mostly on hosts
and local factors acting on parasites, to create an asymmetrically
constrained pattern of geographic variation in modular structure.
Modularity in host-parasite networks seems to result from the shared
evolutionary history of hosts and by trait convergence among unrelated
parasites. This suggests profound differences between hosts and parasites
in the establishment and functioning of bipartite antagonistic networks.