Endocrine Control of Embryonic Diapause in the Australian Sharpnose Shark Rhizoprionodon taylori

Abstract

The reproductive cycle of the Australian sharpnose shark, Rhizoprionodon taylori, includes a temporary suspension of development at the commencement of embryogenesis termed embryonic diapause. This study investigated levels of 17β-estradiol (E2), testosterone (T) and progesterone (P4) in plasma samples of mature wild female R. taylori captured throughout the reproductive cycle and correlated them with internal morphological changes. Levels of T were elevated through most of the embryonic diapause period, suggesting a role of this hormone in the maintenance of this condition. Increasing plasma T concentrations from late diapause to early active development were associated with a possible role of androgens in the termination of embryonic diapause. As in other elasmobranchs, a concomitant increase of E2 with ovarian follicle size indicated a direct role of this hormone in regulating vitellogenesis, while a peak in P4 suggested this hormone is associated with preovulation and ovulation. Additionally, significant correlations between photoperiod or water temperature and maximum follicular diameter and hepatosomatic index suggest that these abiotic factors may also play a role triggering and regulating the synchrony and timing of reproductive events.

The enigma of embryonic diapause

“…Information about the molecular control of diapause in non-mammalian vertebrates is limited. Similar to mammals, progesterone appears to maintain diapause in the Australian sharpnose shark (Rhizoprionodon taylori), but oestradiol is not involved and testosterone instead appears required for reactivation (Waltrick et al, 2014). Insulin-like growth factor binding protein (IGFBP1), which binds to IGFs, has also been implicated but its exact role is unknown (Rafferty and Reina, 2012).…”

Living on the edge: latitudinal variations in the reproductive biology of two coastal species of sharks

“…Previous studies of the reproductive biology of these species have been limited to tropical northern Australian waters, where both species have historically been by‐catch and by‐product species in a number of commercial gillnet and prawn‐trawl fisheries (Stevens & McLoughlin, ; Simpfendorfer, ; Stobutzki et al ., ; Harry et al ., ). Reproductive observations have been made for both H. australiensis and R. taylori from the Timor and Arafura Seas, and the North West Shelf, WA (Stevens & Cuthbert, ; Stevens & McLoughlin, ), and the reproductive biology (Simpfendorfer, ; Waltrick et al ., ), demography (Simpfendorfer, ) and habitat use (Munroe et al ., ) of R. taylori has been well‐studied in Cleveland Bay, Townsville, c . 1250 km north of Moreton Bay.…”

“…Previous studies of the reproductive biology of these species have been limited to tropical northern Australian waters, where both species have historically been by-catch and by-product species in a number of commercial gillnet and prawn-trawl fisheries (Stevens & McLoughlin, 1991;Simpfendorfer, 1999;Stobutzki et al, 2002;Harry et al, 2011). Reproductive observations have been made for both H. australiensis and R. taylori from the Timor and Arafura Seas, and the North West Shelf, WA (Stevens & Cuthbert, 1983;Stevens & McLoughlin, 1991), and the reproductive biology (Simpfendorfer, 1992;Waltrick et al, 2014), demography (Simpfendorfer, 1999) and habitat use (Munroe et al, 2014) of R. taylori has been well-studied in Cleveland Bay, Townsville, c. 1250 km north of Moreton Bay. Little is known, however, about these species' reproductive biology in the sub-tropical waters of southern Queensland, despite their abundance in Moreton Bay (Taylor et al, 2015) and harvest by commercial gillnet fishers operating in the Queensland East Coast Inshore Finfish Fishery (Taylor & Bennett, 2013;Harry et al, 2016).…”

Reproductive Strategy of the Giant Electric Ray in the Southern Gulf of California

“…Wourms (1981) proposed two reproductive modes, based on the type of embryonic nutrition: lecithotrophy, where the embryos depend exclusively on yolk, and matrotrophy, where in addition to yolk the mother secretes other nutritious substances. Additionally, the group has developed diverse reproductive tactics, and some species exhibit embryonic diapause (i.e., an interruption of embryonic development during gestation as defined by Simpfendorfer 1992), sperm storage in females (Pratt 1993;Pratt and Carrier 2001;Waltrick et al 2014), and selection of specific sites for parturition. Such sites are known as nursery areas and provide protection against predators to ensure better chances of survival of their offspring (Hueter et al 2004).…”