Diversity and distribution of genetic variation in gammarids: Comparing patterns between invasive and non-invasive species

Abstract

Biological invasions are worldwide phenomena that have reached alarming levels among aquatic species. There are key challenges to understand the factors behind invasion propensity of non-native populations in invasion biology. Interestingly, interpretations cannot be expanded to higher taxonomic levels due to the fact that in the same genus, there are species that are notorious invaders and those that never spread outside their native range. Such variation in invasion propensity offers the possibility to explore, at fine-scale taxonomic level, the existence of specific characteristics that might predict the variability in invasion success. In this work, we explored this possibility from a molecular perspective. The objective was to provide a better understanding of the genetic diversity distribution in the native range of species that exhibit contrasting invasive propensities. For this purpose, we used a total of 784 sequences of the cytochrome c oxidase subunit I of mitochondrial DNA (mtDNA-COI) collected from seven Gammaroidea, a superfamily of Amphipoda that includes species that are both successful invaders (Gammarus tigrinus, Pontogammarus maeoticus, and Obesogammarus crassus) and strictly restricted to their native regions (Gammarus locusta, Gammarus salinus, Gammarus zaddachi, and Gammarus oceanicus). Despite that genetic diversity did not differ between invasive and non-invasive species, we observed that populations of non-invasive species showed a higher degree of genetic differentiation. Furthermore, we found that both geographic and evolutionary distances might explain genetic differentiation in both non-native and native ranges. This suggests that the lack of population genetic structure may facilitate the distribution of mutations that despite arising in the native range may be beneficial in invasive ranges. The fact that evolutionary distances explained genetic differentiation more often than geographic distances points toward that deep lineage divergence holds an important role in the distribution of neutral genetic diversity.

Keywords: Gammaridae; aquatic invasive species; biological invasions; genetic diversity; population differentiation.

Figure 1

Average F_ST between invasive and non‐invasive species. Visual representation of the average and standard deviation calculated from pairwise F_ST estimates of each species group. Native refers to species that remain strictly in their native range, while invasive are those that have shown capacity to colonize or expand its range after introduction. The status native included G. locusta, G. salinus, G. Oceanicus, and G. zaddachi. The group invasive included G. tigrinus, P. maeoticus, and O. crassus

Figure 2

Visual representation of the statistically significant relationships inferred with linear models. Linear relationships were estimated and tested according to the following formula: F_ST ~ evolutionary distance + geographic distance for each species. The x‐axis represents population differentiation while the y‐axis depicts the variable or variables that were found to relate x‐axis variation