The Dynamics of Male Brooding, Mating Patterns, ad Sex Roles in Pipefishes and Seahorses (Family Syngnathidae)

Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Evolution (Impact Factor: 4.61). 07/2003; 57(6):1374-86. DOI: 10.1111/j.0014-3820.2003.tb00345.x
Source: PubMed


Modern theory predicts that relative parental investment of the sexes in their young is a key factor responsible for sexual selection. Seahorses and pipefishes (family Syngnathidae) are extraordinary among fishes in their remarkable adaptations for paternal care and frequent occurrences of sex-role reversals (i.e., female-female competition for mates), offering exceptional opportunities to test predictions of sexual selection theory. During mating, the female transfers eggs into or onto specialized egg-brooding structures that are located on either the male's abdomen or its tail, where they are osmoregulated, aerated, and nourished by specially adapted structures. All syngnathid males exhibit this form of parental care but the brooding structures vary, ranging from the simple ventral gluing areas of some pipefishes to the completely enclosed pouches found in seahorses. We present a molecular phylogeny that indicates that the diversification of pouch types is positively correlated with the major evolutionary radiation of the group, suggesting that this extreme development and diversification of paternal care may have been an important evolutionary innovation of the Syngnathidae. Based on recent studies that show that the complexity of brooding structures reflects the degree of paternal investment in several syngnathid species, we predicted sex-role reversals to be more common among species with more complex brooding structures. In contrast to this prediction, however, both parsimony- and likelihood-based reconstructions of the evolution of sex-role reversal in pipefishes and seahorses suggest multiple shifts in sex roles in the group, independent from the degree of brood pouch development. At the same time, our data demonstrate that sex-role reversal is positively associated with polygamous mating patterns, whereas most nonreversed species mate monogamously, suggesting that selection for polygamy or monogamy in pipefishes and seahorses may strongly influence sex roles in the wild.

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    • "It was difficult to know exactly where and how all seahorse samples were caught, so independent research on sex distributions and catch biases is needed. Clearly, sex-selective extraction is significant as many species maintain monogamous breeding pairs and male pregnancy is a rate-limiting step in some species (Vincent, 1994;Wilson et al., 2003;Harasti et al., 2012). With expanding trade, retention rates for females will probably increase, as females have only slightly less value than males and vessels are not limited in holding capacity. "
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    • "sexual dimorphism) appear to be associated with the delivery of parental care. Some examples include the brood pouch of pipefishes and seahorses (Syngnathidae; Wilson et al., 2003), the buccal cavity of mouthbrooding fishes (Opistognathidae; Hess, 1993; Apogonidae: Okuda et al., 2003) and the caudal and pectoral fins of nest fanning fishes (Gobiidae; Wantola et al., 2013; Gasterosteidae; Bakker & Mundwiler, 1999). These adaptations are generally associated with species providing uniparental care (Bakker & Mundwiler, 1999; Hechter et al., 2000; Okuda et al., 2003; van Lieshout & Svensson, 2013) and are often present only during reproduction (i.e. "
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    • "Rather, some species of pipefishes and seadragons carry the eggs attached to the ventral surface of the male with no outer covering. In addition, the brood-pouch structure is thought to have evolved at least twice in the Syngnathidae (Wilson et al. 2003; Wilson and Rouse 2010; Wilson and Orr 2011), so it provides an opportunity to study convergent evolution in a phylogenetic context. Thus, the brood pouch of the Family Syngnathidae provides a novel reproductive tissue, which has an interesting evolutionary history and has the potential to contribute to a better understanding of the role of positive selection in the evolution of reproductive proteins. "
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