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Review: Phylogenetic Trees Support the Coevolution of Parasites and Their Hosts

Citation

  • Hafner, M. S. & Nadler, S. A. (1988). Phylogenetic trees support the coevolution of parasites and their hosts. Nature, 332, 258–259.
  • DOI

Abstract

Independent phylogenies were constructed for a group of pocket gophers and their chewing-louse ectoparasites from protein electrophoretic data. The branching patterns of the two trees are highly concordant, supporting a history of cospeciation in this host-parasite assemblage. In several parts of the trees the branch lengths are also similar, which, under a molecular-clock assumption, suggests that the corresponding host and parasite speciation events were roughly contemporaneous. A few associations depart from strict congruence and are attributed to host switching.

Fahrenholz's rule predicts that parasites and their hosts speciate in synchrony, so their phylogenies should match. Hafner and Nadler test this directly by building a phylogeny for pocket gophers and an independent phylogeny for their chewing lice from allozyme data, then comparing the two trees. The branching patterns are concordant to a degree unlikely by chance, evidence of cospeciation. Where branch lengths also agree, the authors read approximately contemporaneous speciation; where a parasite sits on the sister taxon of its host's true partner, they infer host switching (which they distinguish from true cospeciation as pseudo-cospeciation).

The methodological point that carries beyond the biology is that comparing two independently inferred phylogenies, in both branching order and branch length, avoids the circularity that afflicts coevolution studies built on a single combined analysis. Genetic distance supplies a common metric against which the timing of speciation events in the two groups can be compared.

Relevance to Hifuku

This paper is motivation for surveying several genes on one shared chart. Hifuku's survey command charts multiple genes on a single common frame: one shared taxon namespace and one set of neighbor-joining anchors, so each gene's trees land in the same coordinate system. The question Hafner and Nadler ask of a host tree and a parasite tree, whether two independently inferred phylogenies agree in topology and in branch length, is the question a reader asks of two gene maps on Hifuku's shared chart. The tree metric answers it in the same two parts: the Robinson-Foulds term measures topological agreement and the clade branch score measures branch-length agreement, mixed under the weight \( w \) (Section 5). See also Hafner et al. 1994 and Demastes et al. 2012 for the same system at finer resolution.