California Sea Grant College Program

Studies of invasive populations are often conducted with neutral loci, which may lack resolution. Here, we examine DNA sequence variation in a portion of the functional nuclear fusion/histocompatibility (FuHC) locus in the invasive colonial ascidian Botryllus schlosseri, and compare it to variation in the traditional barcoding locus, mitochondrial cytochrome oxidase I (COI). Using these two loci, we compare new invasive populations of B. schlosseri in Alaska to long-established populations in San Francisco Bay. Slightly higher COI diversity was detected in San Francisco Bay, but diversity was very low overall. FuHC revealed much higher variation, with similar levels of diversity between Alaska and San Francisco Bay populations, and no evidence of a genetic bottleneck. By genotyping FuHC, we also detected increased chimerism in Alaska, suggesting that fusions may play an important role in the establishment of very new populations.