The effect of maternal body size on embryo survivorship in the broods of pregnant male pipefish
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The occurrence of male pregnancy in the family Syngnathidae (seahorses, pipefishes, and sea dragons) provides an exceptionally fertile system in which to investigate issues related to the evolution of parental care. Here, we take advantage of this unique reproductive system to study the influence of maternal body size on embryo survivorship in the brood pouches of pregnant males of the broad-nosed pipefish, Syngnathus typhle. Males were mated with either two large females, two small females, a large then a small female, or a small then a large female. Our results show that offspring survivorship depends on an interaction between female body size and the number of eggs transferred by the female. Eggs of larger females deposited in large numbers are more likely to result in viable offspring than eggs of smaller females laid in large numbers. However, when females deposited smaller numbers of eggs, the eggs from smaller females were more likely to produce viable offspring compared to those from larger females. We found no evidence that this result was based on mating order, the relative sizes of competing females, or egg characteristics such as dry weight of eggs. Additionally, male body size did not significantly influence the survivorship of offspring during brooding. Our results suggest that the factors underlying offspring survivorship in pipefish may be more complex than previously believed, with multiple factors interacting to determine the fitness of individual offspring within the broods of pregnant males.
KeywordsBrood reduction Clutch size Parental care Sibling competition Sexual selection Syngnathidae
We thank Zach Cress, Laila Fröberg, Kenan Matterson, and Emma Planes for their extensive help with various aspects of this project. We are also grateful to Anna Billing, Inês Braga Gonçalves, Sarah Robinson-Wolrath, Gunilla Rosenqvist, and Tanja Strand for providing help with the field and husbandry aspects of this project. Jon Wright, Michael Jennions, and two anonymous reviewers provided valuable comments on earlier drafts of the manuscript. Also, we thank Kristineberg Marine Research Station and Klubban Research Station for the use of their facilities. Special thanks to Kristina Kruse, Joan Rowe, and the staff at the Nevada Genomics Center (Reno, NV, USA) for microsatellite technical support. This work was supported by Inez Johansson Foundation (IA), the Swedish Research Council to CK and AB, and the National Science Foundation to AGJ and KBM. All experiments were conducted in agreement with Swedish (permit number 103-2002; 68-2005) and American legislation on animal welfare.
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