Résumé
Emerging pathogens constitute a severe threat for human health and
biodiversity. Determining the status (native or non-native) of emerging
pathogens, and tracing back their spatio-temporal dynamics, is crucial to
understand the eco-evolutionary factors promoting their emergence, to
control their spread and mitigate their impacts. However, tracing back the
spatio-temporal dynamics of emerging wildlife pathogens is challenging
because (i) they are often neglected until they become sufficiently
abundant and pose socio-economical concerns and (ii) their geographical
range is often little known. Here, we combined classical population
genetics tools and approximate Bayesian computation (i.e. ABC) to retrace
the dynamics of Tracheliastes polycolpus, a poorly documented pathogenic
ectoparasite emerging in Western Europe that threatens several freshwater
fish species. Our results strongly suggest that populations of T.
polycolpus in France emerged from individuals originating from a unique
genetic pool that were most likely introduced in the 1920s in central
France. From this initial population, three waves of colonization occurred
into peripheral watersheds within the next two decades. We further
demonstrated that populations remained at low densities, and hence
undetectable, during 10 years before a major demographic expansion
occurred, and before its official detection in France. These findings
corroborate and expand the few historical records available for this
emerging pathogen. More generally, our study demonstrates how ABC can be
used to determine the status, reconstruct the colonization history and
infer key evolutionary parameters of emerging wildlife pathogens with low
data availability, and for which samples from the putative native area are
inaccessible.