Cryptic diversity and phylogeographic patterns of the Bostrychia intricata species complex (Rhodomelaceae, Rhodophyta) along the coast of southeastern Australia

ABSTRACT

Marine phylogeographic studies have recently shown that historical events, oceanography and ecological factors shape patterns of biodiversity and population connectivity. In southeastern Australia a historical geographic barrier, the Bassian Isthmus, results in deep genetic differentiation between some marine taxa. Using partial mitochondrial cytochrome oxidase subunit I (COI) DNA sequences, we investigated the genetic diversity and phylogeography among 26 populations of the red alga Bostrychia intricata along the southeastern Australian coast. Our genetic data revealed the occurrence of five cryptic B. intricata species (lineages N5, N7, N8, N9 and N10), two of which (N9 and N10) are newly discovered and endemic to Tasmania, while cryptic species N5 and N7 were confined to mainland Australia. Species N8 was more genetically diverse and extensively distributed than the other cryptic species, because it occurred both on mainland Australia and in Tasmania. We also detected a clear east–west phylogeographic break between cryptic species N7 and N5, and between haplotypes of species N8 on either side of Wilsons Promontory (the southernmost tip of mainland Australia). Spatial analysis of molecular variance identified three clusters of populations of species N8 along the south coast of Australia, and the split among these groups corresponded to extensive sandy areas: Coorong dunefield and Ninety Mile Beach. Additionally, our study detected the separation between mainland Australian (species N5 and N7) and Tasmanian species (N9 and N10) across the Bass Strait. We suggest that phylogeographic breaks and genetic differentiation in cryptic B. intricata species likely correlate to the historical Bassian land bridge, present-day habitats and different oceanographic circulation patterns.

KEYWORDS:

• Distribution patterns
• Macroalgae
• Mitochondrial haplotype diversity
• Population connectivity
• Species delimitation

ACKNOWLEDGEMENTS

We thank Jonathan Bastard and Nathanael Walker-Hale for help with the sequencing of some samples.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

This work was supported via strategic research funds from the School of Biological Sciences at Victoria University of Wellington.