Invasion history of Caprella scaura Templeton, 1836 (Amphipoda: Caprellidae) in the Iberian Peninsula: multiple introductions revealed by mitochondrial sequence data

The caprellid Caprella scaura, native to the western Indian Ocean, is one striking example of a successful invader. It was first recorded in the Iberian Peninsula in Gerona (north-eastern coast of Spain), in 2005, and has recently been reported throughout the Mediterranean and Atlantic coasts of this region. The most likely vector of introduction and distribution is within the hull-fouling community on recreational craft. However, beyond the dates of detection, the introduction history of C. scaura remains unclear. Direct sequencing of mitochondrial DNA (cytochrome c oxidase subunit I) was used to compare genetic composition in native and introduced populations in order to infer the invasion history of this species. In addition, 18S rDNA sequences were used to resolve phylogenetic relationships within this species and with the morphologically closest species Caprella californica and Caprella scauroides. The high genetic divergence and population subdivision found between non-native Iberian populations together with a high level of genetic diversity in some populations indicate multiple geographical sources and introduction points for this caprellid. Our data suggest that Iberian populations may derive from at least two sources: (1) Pacific Australian, and (2) Indian Ocean, either directly, or, more likely, through stepping-stone events from central Mediterranean population(s). Atlantic Iberian populations seem to be the most recently established populations. On the other hand, this is the first study providing molecular evidence confirming C. scaura, C. californica and C. scauroides as distinct species. It also provides strong molecular evidence that C. scaura typica and C. scaura scaura correspond to the same subspecies, and the Japanese C. scaura diceros and the Chilean C. scaura spinirostris could merit specific rank.