Male seahorse pregnancy transcriptome reveals convergent genes underpinning viviparity
Identifiers: SRA: SRP049289
Viviparity (live birth) has evolved more than 150 times in vertebrates, and represents an excellent model system for the study of the evolution of complex traits. Although there have been at least 23 independent origins of viviparity in the fishes, there is only one instance of male pregnancy, in the syngnathid fishes. Male seahorses and pipefish have specialised brooding structures (pouches) that provide protection, aeration, and possibly osmoregulation and nutrient provisioning to developing embryos. Pouch structures differ widely across the lineage, offering an unprecedented opportunity to study the evolution of reproductive complexity. However, the physiological and genetic changes facilitating syngnathid pregnancy are largely unknown. We have used transcriptomic technologies to examine pouch gene expression at key gestational stages in our model syngnathid, the seahorse Hippocampus abdominalis. In this unique RNAseq data set, the first to represent different time points of pregnancy at such a fine scale in any species, we have identified a number of candidate genes involved in pregnancy in these fishes. These genes putatively function in brood pouch remodelling, nutrient and waste transport, gas exchange, osmoregulation, and immunological protection for developing embryos. We also identify genes that may trigger parturition and appear to be under mechanical and hormonal control. Many seahorse pregnancy genes have homology to genes of known reproductive function in pregnant mammals, reptiles, and other live-bearing fish. Our work suggests a common genetic basis for components of the reproductive machinery in divergent evolutionary lineages, and sheds light on the fundamental biology of the syngnathid brood pouch.