Paternal nutrient provisioning during male pregnancy in the seahorse Hippocampus abdominalis
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ORIGINAL PAPER
Paternal nutrient provisioning during male pregnancy in the seahorse Hippocampus abdominalis Zoe M. G. Skalkos1 · James U. Van Dyke2 · Camilla M. Whittington1 Received: 31 October 2019 / Revised: 22 April 2020 / Accepted: 18 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Vertebrates that incubate embryos on or within the body cavity exhibit diverse strategies to provide nutrients to developing embryos, ranging from lecithotrophy (solely yolk-provided nutrition) to substantial matrotrophy (supplemental nutrients from the mother before birth). Syngnathid fishes (seahorses, pipefishes and sea dragons) are the only vertebrates to exhibit male pregnancy. Therefore, they provide a unique opportunity for comparative evolutionary research, in examining pregnancy independent of the female reproductive tract. Here, we tested the hypothesis that the most complex form of syngnathid pregnancy involves nutrient transport from father to offspring. We compared the dry masses of newly fertilised Hippocampus abdominalis eggs with those of fully developed neonates to derive a patrotrophy index. The patrotrophy index of H. abdominalis was 1, indicating paternal nutrient supplementation to embryos during gestation. We also measured the lipid content of newly fertilised eggs and neonates and found that there was no significant decrease in lipid mass during embryonic development. Since lipids are likely to be the main source of energy during embryonic development, our results suggest that lipid yolk reserves being depleted by embryonic metabolism are replaced by the brooding father. The results of our study support the hypothesis that nutrient transport occurs in the most advanced form of male pregnancy in vertebrates. Keywords Brood pouch · Dry mass · Embryo incubation · Lipid mass · Matrotrophy · Parental care · Paternal investment · Patrotrophy · Syngnathid
Introduction Viviparity (live-bearing reproduction) has independently evolved from oviparity (egg-laying) over 150 times in vertebrates, including at least 13 independent origins in teleost fishes, all of which exhibit embryo incubation inside the female reproductive tract (Blackburn 2015). However, Communicated by Kathrin H. Dausmann. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00360-020-01289-y) contains supplementary material, which is available to authorized users. * Camilla M. Whittington [email protected] 1
School of Life and Environmental Sciences, The University of Sydney, Heydon‑Laurence A08, Camperdown, NSW 2006, Australia
School of Molecular Sciences, College of Science, Health and Engineering, La Trobe University, Wodonga, VIC, Australia
2
the teleost family Syngnathidae, which includes seahorses, sea dragons, and pipefishes, exhibits a unique form of male pregnancy, in which pregnant males incubate embryos inside a brood pouch (Stölting and Wilson 2007; Whittington and Friesen 2020). Syngnathids are important models for evolutionary rese
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