Evolutionary co-variation of host and parasite diversity—the first test of Eichler’s rule using parasitic lice (Insecta: Phthiraptera)

The taxonomic richness of lice (Phthiraptera) varies considerably among their avian and mammalian hosts. Previous studies explored some factors shaping louse diversity; however, the so-called Eichler’s rule—according to which taxonomic richness of parasites co-varies with that of their hosts—has never been tested. Our study incorporates all families of birds and mammals and the whole order of lice to test this co-variation, thus we present the widest taxonomic range to test any correlates of louse richness. Louse richness data were controlled for uneven sampling effort. We used the method of independent contrasts to control for phylogenetic effects. We found a strong correlation between the species richness of avian and mammalian families and generic richness of their lice. We discuss some alternative macroevolutionary and macroecological hypotheses that may explain this phenomenon that may well be a general feature of parasitism and it seems possible that this effect contribute considerably to global biodiversity.