Limited genetic signal from potential cloning and selfing within wild populations of coral-eating crown-of-thorns seastars (Acanthaster cf. solaris)

Population outbreaks of crown-of-thorns seastars (CoTS; Acanthaster spp.) are contributing to extensive coral loss and reef degradation throughout the Indo-Pacific, but the causes and underlying mechanisms of population maintenance and outbreaks are equivocal. Two recent publications suggest that, in addition to outbreeding sexual reproduction, asexual reproduction through larval fission and selfing may contribute to rapid increases in the local abundance of Acanthaster spp. We re-analysed two large microsatellite datasets (collectively representing 3714 individuals) that investigated connectivity in the Great Barrier Reef and wider Pacific region to investigate if potential cloning or selfing can be evidenced in the population genetic structure. Within this dataset, we identified only a small number (18, < 0.5%) of putative clones (repeated multilocus genotypes). We argue that several of these are due to sampling and processing errors rather than direct evidence of cloning. Analysis of the population genetic structure (i.e. pairwise genetic differences between individuals, deviations from Hardy-Weinberg Equilibrium, and linkage disequilibrium) also yielded no genetic evidence for asexual reproduction. There was a tendency towards slight heterozygote deficits, so we cannot refute that selfing does occur, but observed patterns are most likely attributable to sampling artefacts. Although we cannot exclude that asexual reproduction occurs to some extent in Acanthaster populations, we find no evidence that these processes make a contribution to population structure or directly enhance larval supply.

Automated summary

Population outbreaks of crown-of-thorns seastars (CoTS; Acanthaster spp.) are causing extensive coral loss and reef degradation in the Indo-Pacific. Recent studies suggest that in addition to sexual reproduction, asexual reproduction through larval fission and selfing may contribute to rapid increases in local abundance, but genetic analyses found limited evidence for cloning or selfing in the population. The slight heterozygote deficits observed are likely due to sampling artefacts rather than actual evidence of selfing. There is no evidence that these processes contribute to population structure or larval supply.