Male pregnancy in seahorses and pipefish: beyond the mammalian model

@article{Stlting2007MalePI,
  title={Male pregnancy in seahorses and pipefish: beyond the mammalian model},
  author={Kai N. St{\"o}lting and Anthony B. Wilson},
  journal={BioEssays},
  year={2007},
  volume={29}
}
Pregnancy has been traditionally defined as the period during which developing embryos are incubated in the body after egg–sperm union. Despite strong similarities between viviparity in mammals and other vertebrate groups, researchers have historically been reluctant to use the term pregnancy for non‐mammals in recognition of the highly developed form of viviparity in eutherians. Syngnathid fishes (seahorses and pipefishes) have a unique reproductive system, where the male incubates developing… 
The evolution and physiology of male pregnancy in syngnathid fishes
TLDR
The taxonomic distribution of syngnathid parity mode is assayed, the selective pressures that may have led to the emergence of male pregnancy are examined, the biology of synathids reproduction is described, and pressing areas for future research are highlighted.
Seahorse Brood Pouch Transcriptome Reveals Common Genes Associated with Vertebrate Pregnancy.
Viviparity (live birth) has evolved more than 150 times in vertebrates, and represents an excellent model system for studying the evolution of complex traits. There are at least 23 independent
Evolution of placentotrophy: using viviparous sharks as a model to understand vertebrate placental evolution
TLDR
Sharks are recommended as an outstanding model system to investigate the evolution of placentas and mechanisms for fetal nutrition during pregnancy in vertebrates.
Immunological tolerance in the evolution of male pregnancy.
TLDR
It is proposed that increased feto-paternal intimacy in pouched syngnathids commands immune suppression processes in early gestation, and that the elevated immune response during parturition coincides with pouch opening and reduced progeny reliance.
The evolution of pregnancy.
Paternal nutrient provisioning during male pregnancy in the seahorse Hippocampus abdominalis
TLDR
The results of this study support the hypothesis that nutrient transport occurs in the most advanced form of male pregnancy in vertebrates and suggest that lipid yolk reserves being depleted by embryonic metabolism are replaced by the brooding father.
Evolutionary ecology of pipefish brooding structures: embryo survival and growth do not improve with a pouch
TLDR
Negative effects of large egg size are suggested, despite the protection of brood pouches, in pipefishes that reproduce in water under hypoxia.
Post-copulatory sexual selection and sexual conflict in the evolution of male pregnancy
TLDR
Data indicate that post-copulatory sexual selection and sexual conflict occur in Gulf pipefishes, and the conflict seems to be mediated by a strategy of cryptic choice in which males increase rates of offspring abortion in pregnancies from unattractive mothers to retain resources for future reproductive opportunities.
...
...

References

SHOWING 1-10 OF 83 REFERENCES
Male pregnancy in seahorses and pipefishes (family Syngnathidae): rapid diversification of paternal brood pouch morphology inferred from a molecular phylogeny.
TLDR
A combined cytochrome b, 12S rDNA-, and 16S r DNA-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 diversified of structures involved in paternal care may have been key evolutionary innovations of the SyngnATHidae.
Testes investment and spawning mode in pipefishes and seahorses (Syngnathidae)
TLDR
All genera showed the same relationship between testes and body mass, regardless of brooding type, including the possibility that the mode of fertilization might have been misjudged for the pouchless syngnathids.
Reproduction and Development in Some Genera of Pipefish and Seahorses of the Family Syngnathidae
The members of the family Syngnathidae stand out among the bony fish for their specific parental care: the male bear embryos in a particular brood chamber or pouch. The physiological role of the
Dimorphic sperm and the unlikely route to fertilisation in the yellow seahorse
TLDR
Observations support the view that sperm competition in seahorses is not only non-existent but impossible, and speculate that spermatozoa are ejaculated into a mixture of ovarian fluid and eggs, while the male and female are in close contact.
Viviparity: The Maternal-Fetal Relationship in Fishes
TLDR
The maternal-fetal trophic relationships in each of the major groups of fishes are systematically reviewed and Pertinent anatomical, histological, ultrastructural, developmental, physiological, and biochemical studies are considered.
Maternal–embryonic relations in viviparous teleosts
TLDR
The ovarian wall becomes hypervascularized and the inner ovarian epithelium lining the ovarian cavity secretes embryotrophe, and Trophotaeniae provide extraembryonic endodermal exchange surfaces in many species undergoing intraluminal gestation.
The Yolkless Egg and the Evolution of Eutherian Viviparity
TLDR
Eutherian reproduction must have evolved in connection with genetic changes that caused fragility of the oocyte, instability of the follicle, and loss of the ability to produce vitellogenin, the main lipoprotein of yolk.
Reflections on the Evolution of Piscine Viviparity
Viviparity first makes its evolutionary appearance within the craniate-vertebrate line among fishes. We estimate that it has independently evolved at least 42 times in five of the nine major groups
Mating systems and sexual selection in male-pregnant pipefishes and seahorses: insights from microsatellite-based studies of maternity.
TLDR
Genetic studies of the genetic mating systems of pipefishes and seahorses have provided insights into important aspects of the natural history and evolution of these fishes, and suggest that the sexual selection gradient (or Bateman gradient) may be a substantially better method for characterizing the mating system than previously available techniques.
Effect of parental age and associated size on fecundity, growth and survival in the yellow seahorse Hippocampus kuda
TLDR
It is shown that large parents produce offspring whose initial postnatal growth rates were significantly higher than those of the offspring of younger and smaller parents, and suggested that male body size, and pouch size and function, may influence the future fitness and survival of their offspring.
...
...