IS OVULATION IN DOLPHINS, STENELLA LONGIROSTRIS 

 AND STENELLA ATTENUATA, ALWAYS COPULATION-INDUCED? 



K. Benirschke, ^' ^ Mary L. Johnson. ^ and Rolf J. Benirschke'"^ 



ABSTRACT 



This study of 58 nonpregnant uteri and ovaries of the spinner dolphin, Stenella longirostris , and the 

 spotted dolphin, S. attenuata, was undertaken to ascertain whether ovulation is copulation-induced 

 (reflex) or occurs spontaneously. Control specimens of immature, pregnant, and lactating females were 

 examined also and were used to define the normal reproductive events in uteri and ovaries of these 

 species. No differences were found between the two species. In about one half of the specimens we found 

 active corpora lutea of recent origin and in another 15^f of S. attenuata and 29'7c of S. longirostris, 

 corpora had fibrous centers but were hormonally active. No embryos were found and the endometrial 

 changes were such that early but unobserved pregnancies could be excluded. In 35% of the specimens 

 from S. attenuata the macroscopic diagnosis of corpus luteum was erroneous, while this was true of 21% 

 in S. longirostris. The corpora were degenerating and more resembled early corpora albicantia his- 

 tologically. In two of these specimens, endometritis was found and the endometrial histology gave 

 evidence of abortion in three. These findings are evidence that these Stenella species may sometimes 

 ovulate spontaneously and that macroscopic classification of corpora lutea in the past may frequently 

 have been erroneous. 



The reproductive physiology of the spotted dol- 

 phin, Stenella attenuata, and spinner dolphin, S. 

 longirostris, has not been fully elucidated. In par- 

 ticular, it is presently unknown whether these 

 dolphins ovulate spontaneously or on reflex after 

 copulation. Some reasons to believe the latter 

 have been presented for Tursiops truncatus (Har- 

 rison 1977) and the same is implied for other 

 Cetacea. The finding of corpora lutea almost ex- 

 clusively in pregnant animals is the basis for this 

 assumption, and the purpose of this study is to 

 examine the genital tracts of 58 nonpregnant 

 animals with corpora lutea in detail in an attempt 

 to resolve this question. In a detailed study of 

 spotted dolphin, Perrin et al. (1976) found that of 

 242 females with corpora lutea, 229 (95%) were 

 pregnant. In a similar study of spinner dolphins, 

 Perrin et al. (1977) found that 2.8% of 536 adult 

 females contained corpora lutea whose presence 

 could not be explained by pregnancy, lactation, or 

 abortion. 



The distribution of species with and without 

 reflex ovulation has been reviewed by Jochle 

 (1973). A surprisingly large number of species is 



listed as having exclusively or predominantly 

 reflex ovulation, including Cetacea. Only pri- 

 mates, mouse and rat are cited as exceptions; how- 

 ever, modern studies suggest this to be an incom- 

 plete list. In several papers on Camelidae, reflex 

 ovulation is well supported by experimental 

 studies and by observations from abatoirs. Al- 

 though camels and their South American rela- 

 tives must be accepted as being reflex ovulators, 

 the carefully controlled study by England et al. 

 (1969) showed that "occasional spontaneous ovu- 

 lation occurred during the height of the breeding 

 season" in the llama. Lama glama. 



In an attempt to gain additional information on 

 the reproductive physiology of S. longirostris and 

 S. attenuata, we examined the reproductive tracts 

 of animals recorded to possess corpora lutea while 

 not pregnant. Special attention was paid to ascer- 

 taining any reasons for the existence of these cor- 

 pora lutea, such as early undetected pregnancy 

 and an attempt was made to correlate the ovarian 

 status with endometrial changes. 



MATERIALS AND METHODS 



'Research Department, San Diego Zoo, P.O. Box 551, San 

 Diego, CA 92112. 

 ^University of California, San Diego, La Jolla, CA 92093. 

 3San Diego Chargers, P.O. Box 20666, San Diego, CA 92121. 



Manuscript accepted October 1979. 

 FISHERY BULLETIN: VOL. 78. NO. 2, 1980. 



Reproductive tracts of female S. longirostris and 

 S. attenuata were collected at sea by observers 

 during commercial tuna fishing operations in the 

 southeastern Pacific Ocean (Perrin et al. 1976, 



507' 



