Living on the edge: Assessing the diversity of South African Pocillopora on the margins of the Southwestern Indian Ocean

Abstract

Scleractinia of the Maputaland reef complex (MRC) in South Africa exist at the margins of the Western Indian Ocean (WIO) coral distribution and are the only substantial hermatypic coral communities in South Africa. Pocillopora species occupy a conspicuous component of the MRC, and previous investigations identified three species of Pocillopora utilizing conventional taxonomy. Thus, our aims were four-fold: to elucidate Pocillopora species diversity using genetic techniques, primarily using species delimitation methods based on the ORF gene; to test for the presence of hybridisation within the Pocillopora community on the South-West margin of distribution in the Indian Ocean using two nuclear and two mitochondrial markers; to test the presence of cryptic species, using 13 microsatellite markers, finally, to elucidate the degree of genetic diversity within each Pocillopora species found and compare this to communities in lower latitudes. We illustrate taxonomic inconsistencies between these inventories and our phylogenetic data. The MRC harbours unique populations of Pocillopora , consisting of three species hypothetically co-occurring throughout the south WIO, namely: P . meandrina / P . eydouxi , commonly misidentified as P . verrucosa , P . verrucosa , sometimes correctly identified, but also commonly misidentified as P . damicornis sensu lato , and P . villosa , almost always misidentified as P . eydouxi . The hypothesis that hybrid swarms of Pocillopora occur in marginal environments such as the MRC was not supported, with low levels of introgressive hybridization reported instead. Analyses illustrate low genetic diversity at the species and population resolutions, suggesting a small founder population for each species. Nevertheless, these populations are demographically unique, exhibiting high levels of ITS2 haplotype endemism compared to higher latitude populations and the rest of the WIO. Pocillopora diversity on the MRC represents a unique assemblage and warrants further protection.

Strong horizontal and vertical connectivity in the coral Pocillopora verrucosa from Ludao, Taiwan, a small oceanic island

“…Markers PV2 , PV5 , PV6 , and PV7 successfully amplified P . verrucosa specimens from Southeast Africa [ 88 ], and most of these markers generally amplify Pocillopora species from the Western Indian Ocean, the Southwestern Pacific, Southeast Polynesia [ 55 , 58 , 89 ], and the Red Sea [ 90 ]. Among the 13 markers developed by Nakajima et al [ 53 ] for populations from Japan and predicted to amplify most Pocillopora species, four ( Psp_1 , Psp_2 , Psp_10 , and Psp_18 ) showed no or poor amplification (<25%), and an additional marker ( Psp_33 ) was found to have major additional products ( Table 1 ).…”

Coral Genus Differentiation Based on Direct Analysis in Real Time-High Resolution Mass Spectrometry-Derived Chemical Fingerprints

“…47 Thus, some doubts have been expressed about the sole use of either of these techniques. 13,47 These challenges are compounded by the time-and resourceintensiveness of the experimental process associated with the development of the barcodes.…”

“…In addition, the reported ability of some species of Sinularia to hybridize in the laboratory raises the possibility that naturally occurring hybridization events could contribute to the observed morphological diversity of this genus, as has been suggested for stony corals . Correlating genetic signatures to morphology in Pocillopora has proven difficult due to incongruencies between whole colony morphology and genetic lineages . Thus, some doubts have been expressed about the sole use of either of these techniques. , These challenges are compounded by the time- and resource-intensiveness of the experimental process associated with the development of the barcodes.…”

“…Correlating genetic signatures to morphology in Pocillopora has proven difficult due to incongruencies between whole colony morphology and genetic lineages . Thus, some doubts have been expressed about the sole use of either of these techniques. , These challenges are compounded by the time- and resource-intensiveness of the experimental process associated with the development of the barcodes.…”