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      Hypothesizing novel mating behaviours in the squaretail grouper based on direct behavioural observations

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      Rethinking Ecology

      Pensoft Publishers

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          Abstract

          Historically unfished, high-density spawning aggregations are vanishingly uncommon. Behavioural observations from such aggregations are rare, and may be sometimes novel and unexpected. Given the weight of evidence required to document spawning aggregations, how can we best report rare and unusual behavioural variations in spawning populations? 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 male alternative reproductive tactic (ART) and an inverse size assortment with large males courting several small females that shoaled mid-water (https://doi.org/10.1186/s12898-017-0120-5). In critiquing our manuscript, it has been suggested that our observations, methodologies and interpretation are inadequate, flawed, and do not fit within currently accepted theory (https://doi.org/10.1186/s12898-018-0206-8). While offering a detailed counter of the main methodological and theoretical criticisms we question how best to document and interpret novel behaviours in poorly known systems. Reporting novelty itself can hardly be the basis of criticism. Our report relied on direct in-water observations, conducted at peak densities over two spawning years. The critique ignores this, choosing instead to focus on a supplementary video which was not the basis of our conclusions. Like other researchers working on this species, we did not directly observe mating, but report courtship as a well-established proxy used 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 well-established frameworks showing that, at very high mating densities, a variety of tactics can emerge, that often vary considerably between populations and locations. In our original paper, we use this broader theory of sexual selection together with detailed behavioural data to propose plausible evolutionary explanations that bear testing in these novel, high-density systems. We agree with the authors that novel observations should be scrutinised carefully as they can challenge our current understanding of the range of behaviours populations display and serve as a springboard for theoretical advancement. Given their rarity, these observations should be evaluated against the rigour of their documentation and the transparency of their reporting. In this context, we hope our carefully documented observations serve as a useful addition to the fascinating and complex natural history of species like the squaretail grouper.

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          Most cited references 31

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          Sexual selection in males and females.

          Research on sexual selection shows that the evolution of secondary sexual characters in males and the distribution of sex differences are more complex than was initially suggested but does not undermine our understanding of the evolutionary mechanisms involved. However, the operation of sexual selection in females has still received relatively little attention. Recent studies show that both intrasexual competition between females and male choice of mating partners are common, leading to strong sexual selection in females and, in extreme cases, to reversals in the usual pattern of sex differences in behavior and morphology.
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            Reproductive strategies of coastal marine fishes in the tropics

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              Lonely hearts or sex in the city? Density-dependent effects in mating systems.

              Two very basic ideas in sexual selection are heavily influenced by numbers of potential mates: the evolution of anisogamy, leading to sex role differentiation, and the frequency dependence of reproductive success that tends to equalize primary sex ratios. However, being explicit about the numbers of potential mates is not typical to most evolutionary theory of sexual selection. Here, we argue that this may prevent us from finding the appropriate ecological equilibria that determine the evolutionary endpoints of selection. We review both theoretical and empirical advances on how population density may influence aspects of mating systems such as intrasexual competition, female choice or resistance, and parental care. Density can have strong effects on selective pressures, whether or not there is phenotypic plasticity in individual strategies with respect to density. Mating skew may either increase or decrease with density, which may be aided or counteracted by changes in female behaviour. Switchpoints between alternative mating strategies can be density dependent, and mate encounter rates may influence mate choice (including mutual mate choice), multiple mating, female resistance to male mating attempts, mate searching, mate guarding, parental care, and the probability of divorce. Considering density-dependent selection may be essential for understanding how populations can persist at all despite sexual conflict, but simple models seem to fail to predict the diversity of observed responses in nature. This highlights the importance of considering the interaction between mating systems and population dynamics, and we strongly encourage further work in this area.
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                Author and article information

                Journal
                Rethinking Ecology
                ReEco
                Pensoft Publishers
                2534-9260
                June 14 2019
                June 14 2019
                : 4
                : 103-114
                Article
                10.3897/rethinkingecology.4.33383
                © 2019

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