Browsing by Author "Bernardi, Giacomo"

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    Evolutionary origin of the Atlantic Cabo Verde nibbler (Girella stuebeli), a member of a primarily Pacific Ocean family of antitropical herbivorous reef fishes
    (2021) Beldade, Ricardo; Longo, Gary C.; Clements, Kendall D.; Robertson, D. Ross; Perez-Matus, Alejandro; Itoi, Shiro; Sugita, Haruo; Bernardi, Giacomo
    Nibblers (family Girellidae) are reef fishes that are mostly distributed in the Indo-Pacific, with one exception: Girella stuebeli, which is found in the Cabo Verde Archipelago, in the Atlantic Ocean. We capitalized on this unusual distribution to study the evolutionary history of the girellids, and determine the relationship between G. stuebeli and the remaining nibbler taxa. Based on thousands of genomic markers (RAD sequences), we identified the closest relatives of G. stuebeli as being a clade of three species endemic to the northwestern Pacific, restricted to the Sea of Japan and vicinity. This clade diverged from G. stuebeli approximately 2.2 Mya. Two alternative potential routes of migration may explain this affinity: a western route, from the Tropical Eastern Pacific and the Tropical Western Atlantic, and an eastern route via the Indian Ocean and Southern Africa. The geological history and oceanography of the regions combined with molecular data presented here, suggest that the eastern route of invasion (via the Indian Ocean and Southern Africa) is a more likely scenario.
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    Phylogeography of the California sheephead, Semicossyphus pulcher: the role of deep reefs as stepping stones and pathways to antitropicality
    (2013) Poortvliet, Marloes; Longo, Gary C.; Selkoe, Kimberly; Barber, Paul H.; White, Crow; Caselle, Jennifer E.; Perez-Matus, Alejandro; Gaines, Steven D.; Bernardi, Giacomo
    In the past decade, the study of dispersal of marine organisms has shifted from focusing predominantly on the larval stage to a recent interest in adult movement. Antitropical distributions provide a unique system to assess vagility and dispersal. In this study, we have focused on an antitropical wrasse genus, Semicossyphus, which includes the California sheephead, S.pulcher, and Darwin's sheephead, S.darwini. Using a phylogenetic approach based on mitochondrial and nuclear markers, and a population genetic approach based on mitochondrial control region sequences and 10 microsatellite loci, we compared the phylogenetic relationships of these two species, as well as the population genetic characteristics within S.pulcher. While S.pulcher and S.darwini are found in the temperate eastern Pacific regions of the northern and southern hemispheres, respectively, their genetic divergence was very small (estimated to have occurred between 200 and 600 kya). Within S.pulcher, genetic structuring was generally weak, especially along mainland California, but showed weak differentiation between Sea of Cortez and California, and between mainland California and Channel Islands. We highlight the congruence of weak genetic differentiation both within and between species and discuss possible causes for maintenance of high gene flow. In particular, we argue that deep and cooler water refugia are used as stepping stones to connect distant populations, resulting in low levels of genetic differentiation.