Abstract
Disturbance has been found to play a critical role in the speciation, diversity, and dispersal of many species. The use of genetic techniques to study past events has given us the opportunity to understand the processes that lead to the biodiversity and geographic structure of species that we see today. The present study has two aims, firstly; to use genotyping-by-sequencing to examine the phylogeographic structure of the Australasian endemic brown alga, Hormosira banksii, around New Zealand coasts, and secondly; to assess the level of disturbance in Hormosira populations across the uplifted coastline of Akatore.
Three analyses are used to examine the SNP data in both datasets. To address the first aim, the analyses give a comprehensive view of the population genetic structure of Hormosira New Zealand wide and reveal the effects of past events. The full New Zealand dataset comprised 10,949 SNPs in total, which were able to explain 16.6% of the variation on the PC1 axis. The three analyses, together, were able to detect a recent northward range-expansion in Hormosira, from the South Island into the Wellington region. They also reveal the effects of a past earthquake event in the Wellington region, that resulted in a complete wipe-out of Hormosira. This removal was followed by recolonisation, likely from areas surrounding the uplifted zone in the Wellington region.
Similarly, the analyses of Hormosira in the Akatore region, for the second aim, confirms that the past uplift event in this region also resulted in extirpation of the species from that area. The PCA was able to explain 10.8% of the variation on the PC1 axis, and combined with the other analyses, suggests that the recolonising individuals came from at least two different Hormosira populations further south. Overall, the lower South Island in general displays a patchy phylogeographic pattern, suggesting a high rate of population turn over in some areas and frequent long-distance dispersal.
The results of this study contribute to what is known about disturbance, particularly in rocky shore species and their response to major earthquake uplift. Furthermore, the analysis provides evidence for how currents, storms, and other natural events may allow passively rafting buoyant species to migrate and colonise new areas.