Baltic pipefish females need twice as many males as they get

• Published in: Behavioral ecology Vol. 28; no. 3; pp. 827 - 832
• Main Authors: Berglund, Anders, Sundin, Josefin, Rosenqvist, Gunilla
• Format: Journal Article
• Language: English
• Published: 01.05.2017
• Subjects: Biologi med inriktning mot zooekologi; Biology with specialization in Animal Ecology; brackish population; pipefish; potential reproductive rate; sex roles; sexual selection
• ISSN: 1045-2249; 1465-7279; 1465-7279
• DOI: 10.1093/beheco/arx046

Sex role reversal in 2 pipefish species, Syngnathus typhle and Nerophis ophidion , is potentially explained by females reproducing twice as fast as males. Moreover, in oceanic populations from the Swedish west coast, females compete for males with males pre- ferring to mate with larger females. However, in a brackish Baltic population of S. typhle , males do not prefer larger mates, whereas choosiness remains in the local N. ophidion population. We explore whether this absence of male choice in brackish S. typhle can be explained by males and females having more similar potential reproductive rates here, whereas the sex difference may remain in the local N. ophidion population. Contrary to our expectations, in both species, females out-reproduced males by a factor of more than 2, just as in the oceanic populations. We measured this experimentally as the number of males a female potentially could fill with eggs within the time span of 1 male pregnancy, in relation to males available in nature. Thus, we conclude that sexual selection on females is as strong in brackish as in oceanic populations of both species but that targets of selection via male choice are shifted to traits other than body size in S. typhle . Hence, costs and benefits of choice are probably more important than potential reproductive rates to understand mate choice. We suggest that it may be misleading to use targets of sexual selection, such as choice for large body size, as an indicator of the strength of sexual selection.