User:JSLUCAS75/sandbox

Genetics

Early studies of COTS genetics used the available techniques of gel electrophoresis (Table ). They focused on the GBR and populations on reefs across the Pacific Ocean. They showed that COTS was very genetically heterogeneous, with a high level of genetic variability relative to a range of marine invertebrates (Birkeland and Lucas, 1990). Despite this, there was considerable uniformity across the Pacific Ocean with a general pattern of increasing genetic distance between populations with geographic distance. In line with this pattern of increasing genetic distance with geographic distance, the closely connected populations on the GBR were similar. Furthermore there were no distinctive genetic characteristics of outbreak populations or rogue populations giving rise to outbreak populations. The morphologically distinct COTS in the eastern Pacific, which had attracted a species name, A. ellissi, was not sufficiently genetically distinct to justify a separate species status. A. brevispinus, which had been considered to be a possible geographic variant of A. planci, was shown to be a separate sibling species by allozyme and hybridization studies (Birkeland and Lucas 1990), and more recently by the species’ DNA (Yasuda et al., 2006).

Population genetics studies extended to the Indian Ocean when (Benzie 1999) made a comprehensive study of 20 populations on coral reefs across the ocean, complementing the earlier studies of the Pacific. He found that the COTS populations of Western Australia and the Indo-Malaysian region had strong affinities with the western Pacific populations, including the GBR. There was very high affinity between the Ryukyu archipelago, southern Japan, and the GBR, such that he calculated the number of migrants per generation (Nem) between Japan and the GBR to be >40. There was, however, a strong discontinuity between the Pacific and eastern Indian Ocean populations and those further to the west across the Indian Ocean. Benzie calculated the number of migrants per generation (Nem) between the eastern Indian Ocean populations, with Pacific affinities, to the closest populations across the discontinuity to be < 1. Benzie observed that this genetic pattern was congruent with two colour morphs of COTS: a grey/green-red/brown pattern in the Pacific Ocean and a blue-pale red in the Indian Ocean. He calculated the separation of the central to western Indian Ocean populations and the Pacific Ocean, including eastern Indian Ocean populations, to be 1.0 to 2.9 Myr.

The marked discontinuity between the western Pacific and central to western Indian Ocean coincides with the very strong gene flow along the western edge of the northerly flowing North Pacific Gyre, including the Kuroshio current (Benzie 1999). To the west is the distinct Indian Ocean Gyre which services the central to western Indian Ocean populations. The advent of microsatellite analyses brought a greater level of discerning population genetics. They, however, broadly confirmed the fundamental division between Indian Ocean and Pacific Ocean (including north and Western Australia, and the Indo-Malaysian region) that was found by (Benzie 1999). They also consistently confirmed the status of A. brevispinus.

(Vogler et al., 2008) used the analysis of one mitochondrial DNA (CO1 fragment) to conclude that COTS was of complex of four clades or species, which may require different management strategies. The genetic groups (clades/species) were similar to those of (Benzie 1999). There was a pan-Pacific group extending into the Indo-Malaysian region and around into northern Western Australia. There were northern and southern clades in the Indian ocean, although these two clades co-occurred at two locations. These clades ere thus apparently reproductively isolated, which is surprising in a species that is a unpredictable spawner(Babcock et al., 1992), or genetically isolated, which doesn’t accord with degree of genetic isolation between A. planci and a sibling species (below). The Red Sea clade was distinct. The genetic distances between the clades ranged from 8.8-10.6%, which Vogler et al. observed was equivalent to the genetic distances between sibling species of other starfish. They went on to estimate that the clades diverged between 1.95 and 3.65 Myr. Within the genus Acanthaster, however, there is the sibling species, A. brevispinus, which is substantially genetically compatible with COTS (Lucas and Jones 1976). (Vogler et al., 2008) did not discuss their data on this sibling species and the genetic distances between their four clades/species are much less than the genetic distance they found between the established two sibling species, which retain a degree of genetic compatibility. Their four clades may warrant some status, but not the status of sibling species.

(Gerard et al., 2008) assessed the variation of three mitochondrial loci of COTS from three localities in the western Indian Ocean and comparable data from Japan and Mexico. They confirmed the colour morph and allozyme differentiation of Indian and Pacific populations. They estimated the divergence time between the Indian and Pacific Ocean populations as 1.56 Myr and 1.36 Myr according to the locus. They suggested that their western Indian Ocean populations may be genetically isolated from the two Pacific populations that they considered. The populations at the three locations in the western Indian Ocean had identical or closely related haplotypes as would be expected for populations in moderate proximity.

In another far reaching geographical study (Yasuda et al., 2009) analysed 32 COTS populations through the Indo-Pacific region using seven highly polymorphic microsatellite loci. They detected seven genetically distinct groups: southeast African group (Kenya and Mayotte); north-western Pacific group (the Philippines and Japan); Palau; north-central Pacific group (Majuro and Pohnpei); Great Barrier Reef; Fiji; French Polynesia. While this study identified regional groupings they found that there was a distinct genetic break between the Indian and Pacific Oceans. The Kuroshio Current up through the Ryukyu archipelago and the East Australian Current form a boundary of strong northerly and strong southerly currents, respectively. Genetic distances were again related to geographical distances in the Pacific.

Using analyses of mDNA control region sequence, (Timmers et al., 2011; Timmers et al., 2012) studied the genetics of COTS populations on the coral reefs of a variety of islands in the northwest Pacific, south-central Pacific and north-central Pacific. These included three regions and six localities with outbreak populations and  17 non-outbreak and six outbreak locations, six archipelagos, and three regions. They found substantial genetic structuring within the regions, between the archipelagos and within the archipelagos. They suggested that this indicates that larvae rarely achieve their dispersal potential. Clearly, however, there is sufficient long distance dispersal of larvae to maintain populations on both sides of the Pacific that constitute one of the clades identified by (Vogler et al., 2008). (Timmers et al., 2012) considered whether the six outbreak locations consisted of a ‘rouge’ subset of the total populations. This wasn’t the case as the populations with concurrent outbreaks were genetically independent.