Contrasting the population genetic structure of a specialist (: Acanthocephala: Polymorphidae) and a generalist parasite () distributed sympatrically in Mexico.

Polymorphidae is a monophyletic group of acanthocephalans distributed worldwide. Within this family, is a specialist species that uses a single bird species as a definitive host. is a generalist species that uses a broad spectrum of definitive hosts to complete its life cycle. In the current research, sequences of cytochrome c oxidase subunit 1 () from mitochondrial DNA were generated from 44 specimens of and 76 of distributed sympatrically in 6 biogeographic provinces of Mexico with the objective of characterizing and comparing the population genetic structure of 2 acanthocephalan species with opposing life strategies. The phylogeographic studies indicated that the populations of both species lacked a phylogeographic structure and exhibited high haplotype diversity, low nucleotide diversity and low values among the biogeographic provinces; in combination with negative values on the neutrality test, this suggests that the populations of acanthocephalans are expanding. Paratenic hosts are key for the transmission from intermediate to definitive hosts in the generalist species. However, the inclusion of paratenic hosts does not play a principal role in the population genetic structure of within its distribution along the coasts of Mexico.