Male Pregnancy in Seahorses and Pipefishes (Family Syngnathidae): Rapid Diversification of Paternal Brood Pouch Morphology Inferred From a Molecular Phylogeny

Abstract

In contrast to the majority of vertebrate species, primary male parental care is common in fishes and encompasses a remarkable diversity of adaptations. Seahorses and pipefishes (Family Syngnathidae) exhibit some of the most specialized forms of paternal care in animals and so are ideally suited to the study of the evolution of male parental care. During mating, female syngnathids transfer eggs to specialized morphological structures that are located on either the abdomen or tail of the male. The male provides all postfertilization parental care and has morphological and physiological adaptations to osmoregulate, aerate, and even nourish the developing embryos. While all syngnathid species are adapted for paternal care, the brooding structure with which this is accomplished varies between species, from simple ventral gluing areas to much more complex structures such as the completely enclosed pouches of the seahorses. Our combined cytochrome b-, 12S rDNA-, and 16S rDNA-based molecular phylogeny of syngnathid fishes demonstrates that rapid diversification of male brooding structures has been associated with the major evolutionary radiation of the group, suggesting that development and diversification of structures involved in paternal care may have been key evolutionary innovations of the Syngnathidae. Molecular analyses also highlight geographical centers of biodiversity and suggest interoceanic migration of Syngnathus pipefishes from their center of origin in the Pacific.

Genetic diversity and population structure of the pot-belly seahorseHippocampus abdominalisin New Zealand

“…Maximum likelihood and Bayesian phylogenetic trees were generated within Geneious with the use of the PhyML (Guindon & Gascuel 2003) and MrBayes (Huelsenbeck & Ronquist 2001) plugins to show the relationship of the new cytochrome b sequences in reference to other published Hippocampus genbank sequences by Casey et al 2004 (AF192642ÁAF192706; less six identical sequences in the set), Wilson et al 2001 (AF356049, AF356054, AF356057, AF356063, AF356065 and AF356071) and Kawahara et al 2008 (AP005985). Two sequences from different genera, Sygnathus typhle (AF356042) and Microphis brachyurus (AF356046) by Wilson et al (2001) were included as outgroups to root the trees.…”

“…Two sequences from different genera, Sygnathus typhle (AF356042) and Microphis brachyurus (AF356046) by Wilson et al (2001) were included as outgroups to root the trees. Within PhyML, the HKY85 substitution model was used with four categories and default estimations to run 1000 bootstraps.…”

Evolutionary ecology of pipefish brooding structures: embryo survival and growth do not improve with a pouch

“…2001; Coleman and Jones 2011). While in all species males brood the eggs on their bodies throughout the developmental period, syngnathids vary greatly in extent and form of brood care (Carcupino et al.…”

“…These different types of brood pouches have traditionally been thought to have evolved due to benefits of improved reproductive success via offspring survival (Wilson et al. 2001). For example, in several pipefish species with brood pouches, males are able to provide nutrients to the developing embryos (Haresign and Shumway 1981; Berglund et al.…”

Within species support for the expensive tissue hypothesis: a negative association between brain size and visceral fat storage in females of the Pacific seaweed pipefish

“…1986; Wilson et al. 2001; Stolting and Wilson 2007). Males of many syngnathids brood embryos for several weeks depending on the ambient temperature (Foster and Vincent 2004).…”