Host specificity driving genetic structure and diversity in ectoparasite populations: Coevolutionary patterns in Apodemus mice and their lice

Abstract

A degree of host specificity, manifested by the processes of host–parasite cospeciations and host switches, is assumed to be a major determinant of parasites’ evolution. To understand these patterns and formulate appropriate ecological hypotheses, we need better insight into the coevolutionary processes at the intraspecific level, including the maintenance of genetic diversity and population structure of parasites and their hosts. Here, we address these questions by analyzing large‐scale molecular data on the louse Polyplax serrata and its hosts, mice of the genus Apodemus, across a broad range of European localities. Using mitochondrial DNA sequences and microsatellite data, we demonstrate the general genetic correspondence of the Apodemus/Polyplax system to the scenario of the postglacial recolonization of Europe, but we also show several striking discrepancies. Among the most interesting are the evolution of different degrees of host specificity in closely related louse lineages in sympatry, or decoupled population structures of the host and parasites in central Europe. We also find strong support for the prediction that parasites with narrower host specificity possess a lower level of genetic diversity and a deeper pattern of interpopulation structure as a result of limited dispersal and smaller effective population size.

Host “cleansing zone” at secondary contact: a new pattern in host-parasite population genetics

“…First, we compare nuclear and maternally inherited markers (mitochondrial genomes, symbiotic genomes) to demonstrate a narrow HZ between the SW and SE lineages of the lice. Second, we address two possible causes of the SE/SW incompatibility suggested in our previous work (Martinů et al, 2018). P. serrata carries the intracellular obligate symbiont Legionella polyplacis (Říhová, Nováková, Husník, & Hypša, 2017) which could be incompatible with the non-native genetic background.…”

“…In Fig. 2, we summarize the main features of the population genetic pattern obtained by analysis of 379 bp mitochondrial haplotypes (Martinů et al, 2018). It shows that P. serrata is composed of several genetic lineages ( Fig.…”

“…Genetic background of Apodemus spp. and Polyplax serrata adopted from Martinů et al (2018). (a) The main genetic pattern of Apodemus hosts relevant to this study.…”

“…In fact, the presence of a parasite's HZ in the scenario described here is difficult to guess a priori, as it is not indicated by the host's HZ. However, in our previous work (Martinů, Hypša, & Štefka, 2018) we presented the genetic structure of postglacial Europe recolonization by the mice of the genus Apodemus and their ectoparasite, the louse Polyplax serrata, which corresponds to such scenario ( Fig. 2; see below for details).…”

“…Their samples collected across all of Europe form two genetically distant clusters, suggesting recolonization from two different refugia (the taxa designated by red and blue colours in the Fig. 2; see Martinů et al, 2018 for discussion).…”