Limited migration from physiological refugia constrains the rescue of
native gastropods facing an invasive predator
Abstract
Biological invasions have caused the loss of freshwater biodiversity
worldwide. The interplay between adaptive responses and demographic
characteristics is expected to be important for the resilience of
populations to biological invasions, but the interaction between these
factors is poorly understood. The native freshwater gastropod Amnicola
limosus is distributed along spatial variation in impact from an
invasive molluscivorous fish (Neogobius melanostomus), as well as in
calcium concentration, which limits the distribution of this invader and
thus provides refuges for the gastropods. We investigated if refuge
populations could provide migrants to declining invaded gastropod
populations through gene flow (i.e., demographic rescue), which could
also help maintain genetic diversity (i.e., genetic rescue). We also
tested for genetic adaptation of A. limosus to the invasive predator and
the low calcium habitats. We conducted pooled whole-genome sequencing of
twelve gastropod populations from the Upper St. Lawrence River,
complemented with a laboratory reciprocal transplant of wild F0 A.
limosus to measure survival and fecundity in treatments of water calcium
concentration (low/high) and round goby cue (present/absent). We found
that gene flow is restricted from the low-calcium uninvaded refugia
towards high-calcium invaded populations, implying that the potential
for demographic and genetic rescue is limited. We also detected
signatures of divergent selection between habitat types and evidence of
low fitness of individuals from refugia populations in both habitat
types, which could be either a cause or consequence of the population
structure between habitat types and highlights the potential conflict
between demographic/genetic rescue and adaptation.