Fitness-related traits are maximized in recently introduced, slow-growing populations of an invasive clam

Abstract

Many species are shifting their ranges being forced to rapidly respond to novel stressful environmental conditions. Colonizing individuals experience strong selective forces that favor the expression of life history traits notably affecting dispersal and reproductive rates in newly invaded habitats. Limited information is currently available on trait variation within the invasive range despite being critical for understanding ecological and evolutionary factors that drive the process of range expansion of invasive species. Here we evaluated life history shifts of the widely introduced Asian clam Corbicula within its invaded range. Through an exhaustive literature search, we obtained data for 17 invasive Corbicula populations from different ecosystems worldwide to test the relationship between population and individual parameters relevant to the process of range expansion. Our main results are that (i) recently introduced Corbicula populations are characterized by low conspecific density and low rate of population increase, (ii) clams reproduce earlier in slow-growing populations, and (iii) density had no effect on exponential population increase. All invasive Corbicula populations analyzed in this study (Form A/R) are mostly fixed for one genotype. Our results therefore suggest that adaptive phenotypic plasticity favored the expression of traits that maximize fitness in recently established populations facing stronger r-selective forces, thereby increasing their chances to overcome difficulties associated with low densities and low population increase in newly invaded areas.