Parasite specialization from a phylogenetic perspective: a new index of host specificity

Abstract

The host specificity of a parasite is not merely a function of how many host species it can exploit, but also of how closely related these host species are to each other. Here, a new index of host specificity is proposed, one that takes into account the average taxonomic or phylogenetic distance between pairs of host species used by a parasite. The index is derived from measures of taxonomic distinctness used in biodiversity studies. It is easy to compute and interpret, ranging from a minimum value of 1 when all host species are members of the same genus, to a maximum of 5, when all host species belong to different classes. The variance of this measure can also be computed, and provides additional information on the taxonomic or phylogenetic structure of the host assemblage. Using data on helminth parasites of Canadian freshwater fishes, we show that the new index, unlike the mere number of known host species, is independent of study effort i.e. the number of published records of a parasite. Although the index and the number of known hosts are not entirely independent statistically, each captures a different aspect of host specificity. For instance, although acanthocephalans infect significantly more host species than trematodes, cestodes or nematodes, there is no difference in the average index value among these 4 helminth taxa, suggesting that the average taxonomic distances between the host species of a parasite do not vary among these higher taxa. We recommend the use of our new index in future comparative studies of host specificity, in particular when the focus is on the evolutionary history of parasites and of their past colonizations of host lineages.

Resource predictability and host specificity in fleas: the effect of host body mass

“…The association between flea host specificity and host body mass was revealed mainly when host specificity was considered in terms of the number of exploited host species and their taxonomic asymmetry. The latter parameter describes how much taxonomic heterogeneity there is among a group of host species (Warwick and Clarke, 2001 ;Poulin and Mouillot, 2003). A high variance usually means that one main branch in the taxonomic tree of host species contributes proportionally more species to the list than other branches.…”

“…For each flea species, 2 measures of host specificity were used : (1) the number of mammalian species on which the flea species was found, and (2) the specificity index, S TD , and its variance VarS TD (Poulin and Mouillot, 2003). The number of hosts examined often covaries with the number of parasite individuals and species found in a survey (Morand and Poulin, 1998).…”

“…We defined host specificity as the number, but also the identity, of host species that are exploited by a parasite species. In other words, rather than just taking the mere number of host species used by a flea as a measure of host specificity, we also applied a measure of host specificity that takes into account the taxonomic or phylogenetic affinities of the various host species (Poulin and Mouillot, 2003). This measure places the emphasis on the taxonomic distance between host species used by a flea rather than on their number, providing a different and complementary perspective on host specificity, one that truly focuses on the specialization of the flea for its host habitat.…”

Local parasite lineage sharing in temperate grassland birds provides clues about potential origins of Galapagos avian Plasmodium

“…2009), that accounts for the number of host species utilized by the parasite, the taxonomic distance among the host species, and the variance of the taxonomic distance among host species. ${\mathrm{S}}_{\mathrm{normalTD}}^{*}$ is a modification of the index, S TD , proposed by Poulin and Mouillot (2003). We compared the host breadth of parasite lineages found in Galapagos to the host ranges of non‐Galapagos lineages.…”

Helminth parasite communities of two Physalaemus cuvieri Fitzinger, 1826 (Anura: Leiuperidae) populations under different conditions of habitat integrity in the Atlantic Rain Forest of Brazil

“…Apart from habitat fragmentation (Hartvigsen and Halvorsen, 1994;Poulin and Morand, 1999), factors such as host biology (Aho, 1990;Hamann et al, 2006) and the composition of the host fauna can influence the composition of parasite communities (Poulin and Mouillot, 2003).…”