Host “cleansing zone” at secondary contact: a new pattern in
host-parasite population genetics.
We introduce a new pattern of population genetic structure in a
host-parasite system that can arise after secondary contact (SC) of
previously isolated populations. Due to different generation time and
therefore different tempo of molecular evolution the host and parasite
populations reach different degrees of genetic differentiation during
their separation (e.g. in refugia). Consequently, during the SC the host
populations are able to re-establish a single panmictic population
across the whole recolonized area, while the parasite populations stop
their dispersal at the SC zone and create a narrow hybrid zone (HZ).
From the host’s perspective, the parasite’s HZ functions on a
microevolutionary scale as a “host-cleansing filter”: while passing
from area A to area B, the hosts are rid of the area A parasites and
acquire the area B parasites. We demonstrate this novel pattern on a
model composed of Apodemus mice and Polyplax lice by
comparing maternally inherited markers (complete mitochondrial genomes,
and complete genomes of vertically transmitted symbiont Legionella
polyplacis) with SNPs derived from the lice genomic data. We discuss
circumstances which may lead to this pattern and possible reasons why it
has been overlooked in the studies on host-parasite population genetics.