The University of Sydney, School of Life and Environmental Sciences, Sydney, New South Wales, 2006, Australia.
The University of Sydney, Sydney School of Veterinary Science, Sydney, New South Wales, 2006, Australia.
Biol Rev Camb Philos Soc. 2020 Oct;95(5):1252-1272. doi: 10.1111/brv.12607. Epub 2020 May 5.
The seahorses, pipefishes and seadragons (Syngnathidae) are among the few vertebrates in which pregnant males incubate developing embryos. Syngnathids are popular in studies of sexual selection, sex-role reversal, and reproductive trade-offs, and are now emerging as valuable comparative models for the study of the biology and evolution of reproductive complexity. These fish offer the opportunity to examine the physiology, behavioural implications, and evolutionary origins of embryo incubation, independent of the female reproductive tract and female hormonal milieu. Such studies allow us to examine flexibility in regulatory systems, by determining whether the pathways underpinning female pregnancy are also co-opted in incubating males, or whether novel pathways have evolved in response to the common challenges imposed by incubating developing embryos and releasing live young. The Syngnathidae are also ideal for studies of the evolution of reproductive complexity, because they exhibit multiple parallel origins of complex reproductive phenotypes. Here we assay the taxonomic distribution of syngnathid parity mode, examine the selective pressures that may have led to the emergence of male pregnancy, describe the biology of syngnathid reproduction, and highlight pressing areas for future research. Experimental tests of a range of hypotheses, including many generated with genomic tools, are required to inform overarching theories about the fitness implications of pregnancy and the evolution of male pregnancy. Such information will be widely applicable to our understanding of fundamental reproductive and evolutionary processes in animals.
海马、海龙和叶形海龙（海龙科）是少数几种雄性怀孕孵化胚胎的脊椎动物。海龙科鱼类在性选择、性别角色逆转和生殖权衡的研究中很受欢迎，现在作为研究生殖复杂性的生物学和进化的有价值的比较模型而崭露头角。这些鱼类为研究胚胎孵化的生理学、行为学意义和进化起源提供了机会，而无需考虑雌性生殖道和雌性激素环境。这些研究使我们能够通过确定支持雌性妊娠的途径是否也被孵化雄性所采用，或者是否为了应对孵化发育中的胚胎和释放活幼体的共同挑战而进化出了新的途径，来检查调控系统的灵活性。海龙科也是研究生殖复杂性进化的理想选择，因为它们表现出多种复杂生殖表型的平行起源。在这里，我们检测了海龙科的雌雄同体模式的分类分布，检查了可能导致雄性怀孕出现的选择压力，描述了海龙科的生殖生物学，并强调了未来研究的紧迫领域。需要对一系列假设进行实验测试，包括许多使用基因组工具产生的假设，以便为怀孕的适应性和雄性怀孕的进化提供全面的理论依据。这些信息将广泛适用于我们对动物基本生殖和进化过程的理解。
