Silvia Fontana1, Wun-Ruei Chang1, Shao-Lun Liu1
1Department of Life Science & Center for Ecology and Environment, Tunghai University, Taichung 40704, Taiwan
To understand speciation mechanisms in red seaweed, it is important to recognize cryptic species and assess their dispersal ability. Due to high morphological similarity, some species are only distinguishable via molecular analysis and/or microscopy. Dispersal ability in red algae is considered limited by the absence of flagella, yet dispersal barriers in marine environments are difficult to establish.
Here we present a case of possible incipient speciation within the red alga Dichotomaria elegans (Galaxauraceae, Rhodophyta), found in the Northwest Pacific. Three sequenced loci (plastid rbcL, mitochondrial cox1 and cox2-3) showed complete separation of two morphologically indistinguishable lineages. The two lineages are completely allopatric: lineage 1 is found in the northern Philippines and the southern/southwest coast of Taiwan, while lineage 2 has a wider latitudinal range, from the South China Sea, the eastern/northeast coast of Taiwan, to its highest latitude in Japan.
The split between the two lineages is dated approximately 1.5 – 3 Mya, suggesting their separation is due to geographic barriers raised during the Pleistocene. Molecular analysis showed that lineage 2 has a higher haplotype diversity than lineage 1. Ecological niche modeling showed that lineage 2 can tolerate a wider range of temperature, dissolved oxygen and phosphate, and lower salinity compared to lineage 1.
We hypothesize that lineage 2 has better adaptability to different water conditions, and its dispersal through the Kuroshio current led to its wider geographical range. We discuss implications on dispersal ability and allopatric divergence in marine red algae, both potential drivers of speciation within D. elegans.