Genetic divergence of Pocillopora damicornis between temperate and subtropical regions: the need to monitor hidden genetic lineage distribution with regard to migration-load risks under climate change

Abstract

Climate change is significantly altering the distribution of corals in peripheral regions including temperate coral habitats in Japan, making it crucial to devise conservation strategies in response to these distribution shifts. Such peripheral populations are, however, often isolated, presenting opportunities for facilitating novel evolution and adaptation. If so, the northward migration of corals could not be just a matter of corals escaping northwards and increasing in abundance, but the northward migration of subtropical lineages might introduce a “migration-load”, potentially reducing the fitness of temperate lineages. To explore this aspect, we sampled Pocillopora damicornis extensively from subtropical to temperate zones, analyzing their genetic structure. Initial sequencing of mitochondrial Open Reading Frame (ORF) regions identified two ORF haplotypes; one predominating in subtropical regions and the other in temperate ones. Genotyping of nuclear microsatellite regions further confirmed a significant genetic break. Generalized Linear Models (GLM) using environmental data and genotypic distributions of different lineages suggested average water temperature indeed explain the distribution; incorporating other environmental effects such as chlorophyll-a concentration and particulate organic carbon (POC) further improved its predictive accuracy. Given the current sporadic hybridization and occasional invasions of the subtropical lineage into temperate zones, further invasions of the subtropical lineage of P. damicornis in the north under climate change might induce a migration-load with respect to adaptation. Our findings highlight the importance of monitoring genetic distribution with consideration for migration-load risks under climate change. Future research should focus on understanding ecological differences among morphologically identical lineages, monitoring genotype shifts in various climate zones, and evaluating the fitness of temperate populations in the face of climate change for effective coral conservation.