FISHERY BULLETIN: VOL. 81, NO. 2 



DISCUSSION AND SUMMARY 



Reproduction in Odontaspis taurus is typified by 

 the occurrence of both synchronous group and syn- 

 chronous individual physiological activities. Unisex- 

 ual male and female groups converge on a mating 

 ground, and intersexual behavioral activities such as 

 biting (i.e., typically male biting female) may serve as 

 a precopulatory release mechanism (Springer 1967; 

 Stevens 1974). Over several years some variation is 

 apparent, but the simultaneous presence of several 

 females in a similar reproductive state off the 

 Florida east coast indicates a definite seasonality for 

 reproductive activity. 



After mating, the oviducal glands produce six basic 

 types of egg capsules. Capsules without ova are pro- 

 duced initially, suggesting that oviducal gland activi- 

 ty precedes ovulation. Ova-laden egg capsules are 

 produced during the latter half of gestation, prin- 

 cipally as a food source for the remaining embryo in 

 each uterus. 



The synchronous occurrence of egg capsules of the 

 same type in the oviduct and the variation in ova 

 numbers per capsule could be partially explained by 

 three hypothetical physiological mechanisms, por- 

 tions of which have been documented in various 

 elasmobranchs: 



1) Extrinsic stimuli may cause the pituitary gland 

 to secrete hormones which eventually cause ovarian 

 ova to maturate. (Removal of the pituitary in 

 Scliorhinus caniculus prevents ovulation, Dodd et al. 

 1960.) During the period of ova maturation, luteal 

 tissue may form (TeWinkel 1950; Chieffi 1967) and 

 could possibly secrete hormones which initiate 

 oviducal gland activity preceding ovulation. E gg cap- 

 sules would then be produced initially without ova. 



TeWinkel (1950) similarly deduced that in Mustelus 

 canis, ". . . it is not unlikely, therefore, that ovarian 

 hormones present at the time of ovulation or slightly 

 preceding it, stimulate the secretion of a single egg- 

 case by each oviducal gland irrespective of the num- 

 ber of ova discharged." Sperm would have to be 

 stored if mating activity were the extrinsic stimuli af- 

 fecting the pituitary and if ova maturation took some 

 time. Although we have not documented if or where 

 sperm is stored in 0. taurus, the most likely location 

 would be the oviducal gland which has been shown to 

 be the site for sperm storage in other elasmobranchs 

 (Metten 1939; Prasad 1945; Pratt 1979). 



2) Extrinsic stimuli may cause the pituitary to se- 

 crete hormones which eventually cause ovarian ova to 

 maturate and, in addition, directly affect oviducal 

 gland activity. Steroid sex hormones (e.g., estrogen) 



have been shown to directly affect the secretory ac- 

 tivity of the oviduct in Squalus caniculus (Hisaw and 

 Abramowitz 1938; Dodd et al. 1960; Simpson et al. 

 1963). Mobilization of egg capsule production in the 

 oviducal gland may take less time than ova matura- 

 tion, therefore producing egg capsules without ova. 

 3) Sperm arriving at the oviducal gland may stimu- 

 late the gland to secrete ovalbumin and collagen cap- 

 sules preceding pituitary hormone release. However, 

 pituitary hormones and/or luteal hormones may 

 maintain ovarian and oviducal gland activity through 

 gestation. 



The staggered development of the 0. taurus em- 

 bryos indicates that sperm had been stored for 2-4 

 mo, and either fertilization of some ova took place as 

 late as July and August or development of fertilized 

 capsules was somehow delayed. 



Embryonic development may be divided into sever- 

 al phases within the developmental periods already 

 discussed, based on anatomical characteristics 

 and nutritive strategies (Fig. 19) Encapsulated 

 early embryos derive nutrition from internal coelomic 

 yolk supplies, although a yolk sac and stalk are pres- 

 ent. The presence of yolk sacs 6.0 mm in diameter or 

 larger in embryos 13-57 mm demonstrates little ap- 

 parent change in the external yolk supply during a 

 period of extensive growth and differentiation within 

 the egg capsule. In the 13 mm embryo, external con- 

 sumption of other encapsulated ova is improbable, 



1000 



CANNIBALISTIC 

 PHASE 



- YOLK SAC - UTERINE FLUID PHASE 

 HATCHING 



123456789 10 11 

 MONTH 



FIGURE 19. — Embryonic growth curve and nutritional phases in 

 development of Odontaspis taurus. 



222 



