Morphological and phylogenetic evidence for hybridization and introgression in a sea star secondary contact zone

• Published in: Invertebrate Biology
• Main Authors: Harper, Fiona M., Hart, Michael W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Northwest Atlantic
• Online Access: http://dx.doi.org/10.1111/j.1744-7410.2007.00107.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1744-7410.2007.00107.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1744-7410.2007.00107.x

Abstract. Glacial cycles and other climatic events have been widely invoked as factors promoting divergence, secondary contact, and hybridization between populations of terrestrial organisms, but the origin and fate of secondary contact in the sea is much less well understood. We studied the distribution of morphological and genetic variation in a northwest Atlantic zone of secondary contact between congeneric sea stars of Asterias that probably separated after the Pliocene as part of the trans‐Arctic interchange. These species have similar reproductive biology and can hybridize in the laboratory. However, multivariate analysis of morphological traits scored from sea stars inside and outside the zone of secondary contact clearly indicated two clusters of phenotypes that corresponded to the two taxonomic species. A quantitative analysis of this clustering pattern did not support the hypothesis of a third grouping that might correspond to intermediate hybrid phenotypes. Known F 1 hybrids from laboratory matings grouped with one of the two taxonomic species. However, a survey of mtDNA sequence variation clearly indicated that ∼13% of individuals of one species ( Asterias forbesi ) are descendants of hybridization events that resulted in introgression of haplotypes of Asterias rubens into populations of A. forbesi . We conclude that morphological phenotypes are inadequate to identify hybrids of Asterias and their descendants, and that hybridization and introgression might be common in this secondary contact zone.