Evolution and historical biogeography of a parasite–host assemblage: Alcataenia spp. (Cyclophyllidea: Dilepididae) in Alcidae (Charadriiformes)

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Abstract
The methodology of phylogenetic systematics was used to develop hypotheses for the evolution of eight species of Alcataenia, a group of host-specific cestodes of the Alcidae and, to a lesser extent, the Laridae (Charadriiformes). Concurrently, aspects of the early biogeography of alcids were reevaluated making it possible to study the historical and distributional relationships of parasites and hosts. The most parsimonious hypothesis for the phylogeny of Alcataenia suggested that sequential colonization or host switching with limited coevolution (coaccommodation) by parasites best explained the distributional patterns exhibited by Alcataenia spp. Morphological evolution of specific species of Alcataenia accompanied host switching, but was limited subsequent to the initial event of colonization. Thus evolution of these parasites following colonization lagged behind continuing diversification of the host group. Although alcids are an ancient group, as indicated by palaeontological and phylogenetic data, their cestode fauna is apparently not. It is postulated that Alcataenia spp. were acquired by their characteristic hosts in the late Pliocene and early Pleistocene, following diversification of the Alcidae at the generic level during the Miocene. Host distributions of respective Alcataenia spp. are more narrow than expected, considering the relatively young age of this assemblage. The current paradigm linking pronounced host specificity with coevolution of hosts and parasites in assemblages of great evolutionary age is not supported.