Host generalists and specialists emerging side by side: an analysis of evolutionary patterns in the cosmopolitan chewing louse genus Menacanthus

Parasites with wide host spectra provide opportunities to study the ecological parameters of speciation, as well as the process of the evolution of host specificity. The speciose and cosmopolitan louse genus Menacanthus comprises both multi-host and specialised species, allowing exploration of the ecological and historical factors affecting the evolution of parasites using a comparative approach. We used phylo- genetic analysis to reconstruct evolutionary relationships in 14 species of Menacanthus based on the sequences of one mitochondrial and one nuclear gene. The results allowed us to validate species identi- fication based on morphology, as well as to explore host distribution by assumed generalist and specialist species. Our analyses confirmed a narrow host use for several species, however in some cases, the sup- posed host specialists had a wider host spectrum than anticipated. In one case a host generalist (Men- acanthus eurysternus) was clustered terminally on a clade almost exclusively containing host specialists. Such a clade topology indicates that the process of host specialisation may not be irreversible in parasite evolution. Finally, we compared patterns of population genetic structure, geographic distribu- tion and host spectra between two selected species, M. eurysternus and Menacanthus camelinus, using haplotype networks. Menacanthus camelinus showed limited geographical distribution in combination with monoxenous host use, whereas M. eurysternus showed a global distribution and lack of host speci- ficity. It is suggested that frequent host switching maintains gene flow between M. eurysternus popula- tions on unrelated hosts in local populations. However, gene flow between geographically distant localities was restricted, suggesting that geography rather than host-specificity is the main factor defin- ing the global genetic diversity of M. eurysternus.