Abstract
Acanthocephalans, which are in the family Polymorphidae, are a globally distributed group of endoparasites whose adults reside in the intestines of fish-eating birds, waterfowl and marine mammals. Adults of Polymorphus brevis and Pseudocorynosoma constrictum are endoparasites of fish-eating birds (Ardeids) and waterfowl (Anatidae), respectively, and are considered one of the most abundant and widely distributed species of polymorphids in freshwater systems from the Nearctic and Neotropical regions of Mexico and the USA. In the present study, sequences of cytochrome c oxidase subunit 1 (cox1) from mitochondrial DNA were generated from 67 specimens of P. brevis and 32 of Ps. constrictum from 12 localities on 6 biogeographic provinces in Mexico (the Trans-Mexican Volcanic Belt, Pacific Lowlands, Veracruzan, Californian, Sierra Madre Occidental, and Sonoran), plus the Temperate Prairies biogeographical province in the USA. The phylogeographic analyses indicated that the populations of both species lacked phylogeographic structure and exhibited high haplotype diversity, low nucleotide diversity and low Fst values among the biogeographic provinces; in combination with negative values in the neutrality test, these findings suggest that the populations of both species of acanthocephalan are undergoing expansion. The current evidence indicates that the biology of the definitive hosts, in combination with their migration patterns, could play a key role in shaping the distribution of haplotypes and the population genetic structure of the studied 2 acanthocephalan species.