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Broad species ranges that extend from the Western Indian Ocean to Polynesia define the Indo-Pacific as a cohesive biogeographic region. However, such distributions have often been found to be allopatrically differentiated complexes of cryptic species. Euraphia hembeli is one of the largest tropical rocky intertidal chthamalid barnacles and exhibits a broad distribution, from Madagascar to Hawaii. Using 121 sequences of 2 mitochondrial genes ( cox 1 and 12S) from 10 localities, we assess the genetic connectivity of E. hembeli across the Indo-Pacific. Our phylogeographic analyses recovered 2 clades: 1 widely distributed in the Indo-West Pacific from Madagascar to Guam (IWP clade) and 1 limited to the Hawaiian Islands (Hawaii clade). Molecular clock estimates divergence between the 2 clades occurred around 2.1 million yr ago in the early Pleistocene. Demographic analyses revealed that both clades have undergone population expansion, with more recent population growth in the Hawaii clade. The vast distribution and lack of geographic differentiation of the IWP clade suggest high dispersal capacity for E. hembeli , likely using oceanic islands as stepping stones. The Hawaiian clade, together with the other 2 Euraphia species, E. calcareobasis from the Tuamotu Islands and E. devaneyi from Easter Island, indicate that allopatric speciation in marginal populations is an important mode of diversification in this genus.
Shahdadi et al. (Wed,) studied this question.