Abstract
The freshwater snail Physella acuta is globally invasive. Within this species, however, cox1 haplotype markers distinguished a globally invasive population (A) from a non-invasive population (B) restricted to North America, the native range of P. acuta. This study investigated whether invasiveness is associated with differential population fitness. Field-collected P. acuta were genetically characterized to establish laboratory populations representing mito-haplotypes A and B. While the nuclear rDNA cassette (7,023 nt) differed only by 0.03% between populations A and B, the mitogenome haplotypes differed in size (14,383 vs 14,333 bp) and sequence content (~ 9%). Under controlled laboratory conditions, growth rate, age at maturity, size at maturity, and reproductive output did not show fitness differences between populations A and B (3 trials). Population fitness was also studied using a rewilding approach. Survival and fecundity of A and B snails were evaluated during one- or two-week intervals among cohorts of 20 laboratory-bred P. acuta adult snails in flow-through cages in the laboratory or exposed to natural field conditions. Only modest differences in fitness parameters were indicated under laboratory conditions, providing no clear association of population fitness with global distribution patterns. Under field conditions, however, population level fecundity differed with population A having a 3-fold greater fitness than population B in 5 of 7 trials (survival in 3 trials; realized fecundity in 2 trials). Whereas laboratory-based studies indicated only minor differences, the rewilding approach showed significant differential fitness between P. acuta populations A and B that differ in invasiveness.