Early development of the longsnout seahorse Hippocampus reidi (Syngnathidae) within the male brood pouch

Abstract

Fertilized and unfertilized eggs and embryos of the longsnout seahorse Hippocampus reidi were collected at different stages of development and provided the basis for a description of morphological development from fertilization until release from the paternal pouch. Images of fertilized eggs, as well as their rupture after a few minutes in seawater are reported for the first time. The yolk sac transitioned from ovoid to spherical shape and was reabsorbed progressively until release. The tail began rising from the surface of the deuteroplasm while embryos were in the egg envelope. Embryos lacked a primordial fin fold and developed some species characteristics, such as rays in the dorsal fin, before resorption of the yolk sac. At release, juvenile seahorses were in an advanced stage of development even if they lacked important adult characteristics, such as ring plates and coronet. The tail was not prehensile in juveniles at release; a small caudal fin was present, although this fin is lost in adults.

Time-critical influences of gestational diet in a seahorse model of male pregnancy

“…The subsequent brood was thus examined for changes in response to dietary manipulation at the end of gestation. As embryos hatch from their chorions during the last few days of pregnancy (Novelli et al, 2018), the offspring would have been free-swimming 'yolk sac larvae' during this period of manipulation (Fig. 1C).…”

“…(C) Representative depiction of a well-developed seahorse embryo (yolk sac larva) as it would appear in the brood pouch during the last few days of pregnancy. Embryo drawings adapted from Novelli et al (2018).…”

“…Finally, although we have shown that seahorse reproduction is sensitive to paternal PUFA availability during specific time periods, we did not address the specific mechanisms that may explain this sensitivity. Although it is plausible that early (pre-hatching) embryos respond directly to paternally derived nutrients, especially given that nutrients can be transferred from father to developing offspring in the brood pouch of pipefish (Haresign and Shumway, 1981;Ripley and Foran, 2009), it has nevertheless not been established whether PUFAs, which are large molecules, are able to cross through the chorion-like envelope enclosing the seahorse embryo in early development (Novelli et al, 2018). It may be more likely that developmental changes result from differential resource utilisation to counteract stress imposed by impairments to osmoregulatory or gas exchange functions of the pouch (Ripley and Foran, 2009;Stölting and Wilson, 2007), or, additionally, in the case of BC treatment, differential maternal investment in response to a perceived reduction in male quality.…”

Embryonic development of the threatened freshwater pipefish Microphis deocata (Hamilton, 1822)

“…The characteristic banding pattern in M. deocata larvae prior to‐ and 1‐day post release is similar to earlier reports on the pigmentation on larvae of Gastrophori species like M. leiaspis and N. lumbriciformi s (Ishihara & Tachihara, ; Monteiro et al, ). Larval pigmentation in Hippocampus erectus is also band‐like, while uniform in Hippocampus reidi (Novelli, Otero Ferrer, Socorro, & Molina Domínguez, ). Development of pigmentation during early embryogenesis in M. deocata also corroborates with reports on H. reidi , M. leiaspis or N. lumbriciformes (Ishihara & Tachihara, ; Monteiro et al, ; Novelli et al, ).…”

“…Larval pigmentation in Hippocampus erectus is also band‐like, while uniform in Hippocampus reidi (Novelli, Otero Ferrer, Socorro, & Molina Domínguez, ). Development of pigmentation during early embryogenesis in M. deocata also corroborates with reports on H. reidi , M. leiaspis or N. lumbriciformes (Ishihara & Tachihara, ; Monteiro et al, ; Novelli et al, ).…”