Control of programed arrested development in embryos of the Australian sharpnose shark, Rhizoprionodon taylori

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

Durban

Congreso; Sharks International Conference; 2014

Thearrest of development at any stage ofembryogenesis, embryonic diapause, is widespread among species from unrelatedtaxa in all vertebrate groups. In elasmobranchs, diapausehave only been confirmed in 2 species, however,the observation of fertilized eggs without visible embryos during extendedperiods suggests the occurrence of thistrait in at least another 14 elasmobranchs. The control mechanisms of diapausehave not been investigated in this group but, as in other vertebrates, itpossibly involves hormones and environmental cues. Blood samples from 128pregnant Rhizoprionodon taylori werecollected for plasma steroid analysis. Levels of progesterone (P4),testosterone and estradiol will be measured by radioimmunoassay for allreproductive stages. In R. taylori,large and active corpora lutea (CL) are observed in the ovary during the earlypregnancy, suggesting that, as in vertebrates, high levels of P4 areneeded to induce diapause. At the end of gestation, a second peak of P4is expected to induce the active development of the young and induceimplantation, when the ovary is expected to be the main source of P4.Steroid levels during pregnancy will be discussed in regards to possiblemechanisms controlling entry, maintenance and termination of diapause in R. taylori.