Novel mating behaviours in the squaretail grouper: Response to “Fake spawns and floating particles"

Based on two years of in-water observations of a high-density spawning aggregation of the squaretail grouper in the Lakshadweep Archipelago, we described a previously unreported inverse size assortment with large males courting several small females that shoaled mid-water (DOI 10.1186/s12898-017-0120-5). Critiquing our manuscript, Erisman and colleagues (DOI 10.1186/s12898-018-0206-8) suggest that our observations and interpretation are flawed, and do not fit within currently accepted theory. Here we offer a detailed counter of their main methodological and theoretical criticisms. Their criticism that this reproductive tactic has never been observed before is hardly a criticism since its novelty is precisely what we wished to highlight. The supplementary video that Erisman et al use to base much of their criticisms was not the basis of our conclusions, which relied on direct in-water observations. These observations were conducted over two spawning years, taking care to ensure that we sampled aggregations at peak densities. Like other researchers working on this species, we did not directly observe mating, but have used courtship as a proxy for mating success – a well-established proxy across mating systems studies. Apart from these methodological concerns, the authors suggest that there is no theoretical support for our observations. However, sexual selection theory provides a well-established framework showing that, at very high mating densities, a variety of tactics can emerge, that often vary considerably between populations and locations. We agree with the authors that novel observations should be scrutinised carefully. They challenge our current understanding of the range of behaviours populations display and serve as a springboard for theoretical advancement. We stand by our observations and hope they serve as a useful addition to the fascinating and complex natural history of species like the squaretail grouper.