title: Embryo oxygenation in pipefish brood pouches: novel insights.
abstract: The pipefish brood pouch presents a unique mode of parental care that enables males to protect, osmoregulate, nourish and oxygenate the developing young. Using a very fine O2 probe, we assessed the extent to which males of the broad-nosed pipefish (Syngnathus typhle) oxygenate the developing embryos and are able to maintain pouch fluid O2 levels when brooding in normoxia (100% O2 saturation) and hypoxia (40% O2 saturation) for 24 days. In both treatments, pouch fluid O2 saturation levels were lower compared with the surrounding water and decreased throughout the brooding period, reflecting greater offspring demand for O2 during development and/or decreasing paternal ability to provide O2 to the embryos. Male condition (hepatosomatic index) was negatively affected by hypoxia. Larger males had higher pouch fluid O2 saturation levels compared with smaller males, and levels were higher in the bottom section of the pouch compared with other sections. Embryo size was positively correlated with O2 availability, irrespective of their position in the pouch. Two important conclusions can be drawn from our findings. First, our results highlight a potential limitation to brooding within the pouch and dismiss the notion of closed brood pouches as well-oxygenated structures promoting the evolution of larger eggs in syngnathids. Second, we provide direct evidence that paternal care improves with male size in this species. This finding offers an explanation for the documented strong female preference for larger partners because, in terms of oxygenation, the brood pouch can restrict embryo growth.
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, Animal Behaviour, University of Zurich, Winterthurerstrasse 190, Zürich 8057, Switzerland Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, Gothenburg SE-40530, Sweden ines.goncalves@ieu.uzh.ch.
authors.forename: Ines Braga
authors.initials: IB
authors.lastname: Goncalves
authors.affiliation: Department of Ecology and Genetics/Animal Ecology, Uppsala University, Norbyvägen 18D, Uppsala SE-75236, Sweden.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Ahnesjö
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, Gothenburg SE-40530, Sweden.
authors.forename: Charlotta
authors.initials: C
authors.lastname: Kvarnemo
mesh_terms: D000818:Animals; D049628:Body Size; D004625:Embryo, Nonmammalian / Q000378:metabolism; D047108:Embryonic Development; D005260:Female; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D023701:Smegmamorpha / Q000196:embryology / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: Embryo development; Fish; Hypoxia; Male size; Normoxia; Paternal care; Syngnathidae