We find that A. planci consists of four strongly differentiated and highly supported mitochondrial clades, from the Red Sea, the Pacific (Pac), the Northern (NIO) and the Southern Indian Ocean (SIO) (a and ), that together form a species complex. Although cryptic speciation is a widespread phenomenon in the marine realm, this finding is quite surprising for an organism as extensively studied as A. planci over the past decades.
Geographical distribution of COI haplotypes from the four putative COTS species. Pie charts indicate relative frequency of each species per sampling location. Colours are the same as in .
Assuming a COI divergence rate of 2.9–4.5%
), the four clades are estimated to have diverged in the Pliocene–Early Pleistocene (1.95–3.65
Myr ago). The speciation process was probably driven by sea-level changes (Pillans et al. 1998
), isolating populations between major oceans (e.g. Pac versus NIO; Voris 2000
). Additionally, restricted circulation patterns could have reduced larval interchange between populations (e.g. SIO versus NIO; Pollock 1993
). Furthermore, the strong patterns of regional differentiation may have been enhanced by ecological differences among lineages (Reid et al. 2006
). The populations of all four sibling species appear to be expanding, as supported by both the GMYC scaling parameter for the coalescent process (pj
<1; Pons et al. 2006
) and the overall star shape of each species' haplotype network (c
; Avise 2000
Our discovery of four highly differentiated clades in one of the world's most destructive coral predators has significant conservation implications. Identifying cryptic speciation is essential to adequately study and contain species that require management (Bickford et al. 2007
). Although the status of A. planci
is relatively poorly documented from the Indian Ocean and the Red Sea, outbreaks there do not appear to be as massive and widespread as in the Pacific (Zann 2000
), suggesting that outbreak patterns might vary between the different sibling species. Up to now, however, the overwhelming majority of COTS research has been performed in the Pacific. Failure to recognize the existence of the sibling species could have contributed to a lack of understanding of the processes that lead to outbreaks in the different COTS lineages, by extrapolating results obtained from the Pacific studies to A. planci
's entire distribution for both research and management purposes.
Future research will be required to investigate whether the life history, behavioural patterns and/or ecological requirements that may affect the outbreak dynamics of these four independent evolutionary COTS lineages have diverged sufficiently to necessitate lineage-specific management. This could prove to be crucial for the design of appropriate management strategies to minimize the impact of future catastrophic COTS outbreaks in different regions of the world.