Getting a grip at the edge: recolonization and introgression in eastern PacificPoritescorals

Abstract

AbstractAimTo infer species identity, population isolation, and geographical variation in inter‐specific hybridization among corals of the genusPoritesfrom the central and eastern tropical Pacific, with a focus on the timing of separation between populations ofP. evermanniandP. lobatadivided by the Eastern Pacific Barrier.LocationHawaii, American Samoa, Panama and the Galapagos Islands of Ecuador.MethodsMaximum likelihood gene trees were obtained for mitochondrialDNA(COI), the internal transcribed spacer (ITS), and 5 single‐copy nuclear (scn) gene regions. Allelic networks were used to group multi‐locus scn data into species clusters despite some allele sharing. Coalescent analyses (IMa2) of the 5 scn markers were used to estimate the time of population divergence and test for introgression betweenP. evermanniandP. lobata.ResultsAllelic networks based on scn gene sequences agreed with mtCOIandITSdesignations. Divergence times between Hawaiian and eastern Pacific populations are consistent with an early Pleistocene recolonization of the eastern Pacific byP. evermannifollowed by a more recent arrival ofP. lobata. The two species were fully isolated in Hawaii/American Samoa populations, but introgression fromP. evermanniintoP. lobatawas evident in the eastern Pacific.Main conclusionsThese results are consistent with a scenario where a bout of introgression withP. evermanni,an early‐arriving colonizer of the eastern Pacific suited to marginal environmental conditions, facilitated the later colonization of the more sensitiveP. lobata.