AUTHOR=Fontana Silvia , Wang Wei-Lung , Tseng Kuang-Yu , Draisma Stefano G. A. , Dumilag Richard V. , Hu Zi-Min , Li Jing-Jing , Lai Pei-Husan , Mattio Lydiane , Sherwood Alison R. , Boo Sung Min , Liu Shao-Lun 

TITLE=Seaweed diversification driven by Taiwan’s emergence and the Kuroshio Current: insights from the cryptic diversity and phylogeography of Dichotomaria (Galaxauraceae, Rhodophyta)

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2024.1346199

DOI=10.3389/fevo.2024.1346199

ISSN=2296-701X

ABSTRACT=<p>Ocean currents play a role in both facilitating and impeding connectivity of marine organisms’ populations, serving as key drivers and potential barriers. The emergence of Taiwan around five million years ago (Mya) impacted the Kuroshio Current which later shaped the distribution of marine organisms. In this study, we examined how the Kuroshio Current influenced the distribution and population divergence of the marine red alga <italic>Dichotomaria elegans</italic> (Galaxauraceae, Nemaliales). Through phylogenetic analysis, species delimitation, and morphological comparison of Taiwanese species, we determined its phylogenetic position relative to other species within the <italic>D. marginata</italic> complex of the genus <italic>Dichotomaria</italic>. We uncovered the hidden cryptic diversity within the <italic>D. marginata</italic> complex in Taiwan and proposed the new combinations <italic>D. elegans</italic> and <italic>D. latifolia</italic> based on <italic>Galaxaura elegans</italic> and <italic>G. latifolia</italic>. Genetic analysis based on three loci (mitochondrial <italic>cox</italic>2-3 and <italic>cox</italic>1, and plastid <italic>rbc</italic>L) from 32 locations across the Philippines, Taiwan, and Japan revealed three allopatric lineages within <italic>D. elegans</italic>. The first lineage is restricted to the northern Philippines and southern Taiwan, while the second has a broader latitudinal range along the Kuroshio Current. The third lineage is found in southeast Luzon, Philippines, close to the bifurcation of the North Equatorial Current, near the start of the Kuroshio Current. The divergence of the first two lineages during the mid-Pliocene (~3.7 Mya) coincided with the emergence of Taiwan, with the current dynamics accentuating their separation. The Kuroshio Current exhibited a dual impact on the biogeography of <italic>D. elegans</italic>: promoting the dispersal of the second lineage towards higher latitudes and preventing the first lineage from moving northward. Principal component analysis showed that habitat conditions and morphologies differed between the two <italic>D. elegans</italic> lineages. This study provides insights into the cryptic diversity of <italic>Dichotomaria</italic> in Taiwan, as well as the genetic divergence, biogeographical patterns, and ecological associations of <italic>D. elegans</italic>, highlighting the interplay of island formation and currents shaping the diversification of seaweeds in the Northwest Pacific Ocean.</p>