The genetic mating system of a sex-role-reversed pipefish ( Syngnathus typhle ): a molecular inquiry

Adam G Jones,Gunilla Rosenqvist,John C Avise,Anders Berglund

doi:10.1007/s002650050630

Abstract

In the pipefish Syngnathus typhle as in other species of Syngnathidae, developing embryos are reared on the male's ventral surface. Although much laboratory research has been directed toward understanding sexual selection in this sex-role-reversed species, few studies have addressed the mating behavior of S. typhle in the wild, and none has capitalized upon the power of molecular genetic assays. Here we present the first direct assessment of the genetic mating system of S. typhle in nature. Novel microsatellite loci were cloned and characterized from this species, and employed to assay entire broods from 30 pregnant, field-captured males. Genetic analysis of 1340 embryos revealed that 1–6 females (mean = 3.1) contributed to each brooded clutch, the highest rate of multiple maternity yet documented in any pipefish. Evidence of multiple mating by females was also detected. Thus, this population of S. typhle displays a polygynandrous mating system, a finding consistent with previous field and laboratory observations. Our results, considered together with similar studies of other syngnathid species, provide preliminary support for the hypothesis that the genetic mating system is related to the evolution of sexual dimorphism in the fish family Syngnathidae.

Highlights

In pipe®shes and seahorses, males provide all parental care
Females have the potential for a higher reproductive rate than males, and this species is sex role reversed
Sex role reversal provides unique opportunities to test sexual selection theory (Williams 1975; Andersson 1994), and S. typhle has been exploited in numerous laboratory studies to investigate various aspects of sexual selection and mating behavior (e.g., AhnesjoÈ 1992a, 1992b; Berglund 1995; Rosenqvist and Johansson 1995; Fuller and Berglund 1996)

Summary

Introduction

In pipe®shes and seahorses (family Syngnathidae), males provide all parental care. During copulation, a female transfers eggs to a male's ventral surface where they are fertilized (Vincent et al 1992). The relevance of mating pattern to the operation of sexual selection had long been appreciated (Darwin 1871; Clutton-Brock et al 1980; Payne 1984; BjoÈ rklund 1990; Oakes 1992), molecular studies of parentage underscored the need to distinguish between the social mating system and the genetic mating system (Mùller and Birkhead 1994; Avise 1996). The latter is often more germane to the operation of sexual selection (Andersson 1994). The approach has permitted the following: (1) determination of the rate of multiple mating by males; (2) documentation of multiple mating by females; (3) evaluation of a hypothesis, based on laboratory observations and the extent of sexual dimorphism, that S. typhle should be polygynandrous, and (4) a comparison of the results to the genetic mating systems of other previously studied syngnathids

Methods

Results

Discussion