The control of embryonic diapause in the Australian sharpnose shark. Rhizoprionodon taylori

WALTRICK, D.; SIMPFENDORFER, C.; JONES, S. M.; AWRUCH C. A.

Buenos Aires

Simposio; 7th International Symposium on fish endocrinology; 2012

The arrest of development at any stage of embryogenesis, embryonic diapause, is widespread among species from unrelated taxa in all vertebrate groups. In elasmobranchs, diapause have only been confirmed in 2 species, however, the observation of fertilized eggs without visible embryos during extended periods suggests the occurrence of this trait in at least another 14 elasmobranchs. The control mechanisms of diapause have not been investigated in this group but, as in other vertebrates, it possibly involves hormones and environmental cues. Blood samples from 128 pregnant Rhizoprionodon taylori were collected for plasma steroid analysis. Levels of progesterone (P4), testosterone and estradiol will be measured by radioimmunoassay for all reproductive stages. In R. taylori, large and active corpora lutea (CL) are observed in the ovary during the early pregnancy, suggesting that, as in vertebrates, high levels of P4 are needed to induce diapause. At the end of gestation, a second peak of P4 is expected to induce the active development of the young and induce implantation, when the ovary is expected to be the main source of P4. Steroid levels during pregnancy will be discussed in regards to possible mechanisms controlling entry, maintenance and termination of diapause in R. taylori.