The dynamics of male brooding, mating patterns, and sex roles in Syngnathidae

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THE DYNAMICS OF MALE BROODING, MATING PATTERNS, AND SEX ROLES IN PIPEFISHES AND SEAHORSES (FAMILY SYNGNATHIDAE)

Abstract. 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 likelihoodbased
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.
Key words. Comparative method, mating patterns, molecular phylogenetics, paternal care, sex-role reversal, sexual
selection, Syngnathidae.

Full article:
THE DYNAMICS OF MALE BROODING, MATING PATTERNS, AND SEX ROLES IN PIPEFISHES AND SEAHORSES (FAMILY SYNGNATHIDAE)