Sulikowski et al.: The reproductive cycle of Amb/yra/a radiata 



539 



Assessment of morphological parameters in 

 the male reproductive tract 



Histological stages III through VI (SIII-SVI) 

 of spermatogenesis were examined, and GSI 

 and HSI were determined for the 48 males col- 

 lected during 24 months of sampling. Although 

 the relative proportion of these four stages did 

 not differ among months, it is notable that the 

 production and maintenance of mature sper- 

 matocysts (SVI) within the testes persisted 

 throughout the year (Fig. 2A). Similarly, no 

 significant seasonal differences were found in 

 HSI or GSI (Fig. 2, B and C, respectively). In 

 addition, there were weak to no correlations 

 between spermatogenesis and either HSI or GSI 

 (r=-0.07 and 0.13, respectively). 



Synchronicity between male and female 

 reproductive cycles 



Results from the male and female morpho- 

 logical reproductive parameters indicated 

 that thorny skates are capable of reproducing 

 throughout the year in the western Gulf of 

 Maine. When GSI, follicle diameter in relation 

 to percent composition of SVI, or shell gland 

 weight in relation to percent composition of 

 SVI were compared between male and female 

 thorny skates, no apparent correlation was 

 detected (Fig. 3, A-C). In contrast, when per- 

 cent composition of SVI (spermatogenesis) was 

 plotted against percentage of captured female 

 skates with egg cases, a strong synchronicity 

 (r=0.51) was observed (Fig. 4). 



Discussion 



Elasmobranchs display a wide range of repro- 

 ductive strategies with morphological and physiological 

 specializations for oviparous or viviparous reproduction 

 (Wourms and Demski, 1993; Hamlett and Koob, 1999). 

 These strategies are associated with one of three basic 

 types of reproductive cycles: 1) reproduction throughout 

 the year, 2) a partially defined annual cycle with one 

 or two peaks, and 3) a well-defined annual or biennial 

 cycle (Wourms, 1977; Hamlett and Koob, 1999). Among 

 oviparous elasmobranchs, some species exhibit cycles 

 with clearly delineated period* s) of reproductive activity 

 interspersed between periods of little or no activity. For 

 example, in the clearnose skate (Raja eglanteria), the 

 patterns of estradiol concentrations and follicle dynamics 

 indicate the presence of a well-defined annual reproduc- 

 tive cycle, in which mating and egg deposition take place 

 from December to mid May (Rasmussen et al., 1999). 

 Likewise, hormone and morphological data also indicate 

 a defined annual cycle in the epaulette shark (Hemiscyl- 

 lium ocellatum) (Heupel et al., 1999) and that reproduc- 

 tive activities take place from July to December. 



Jan Feb Mar April May June July Aug Sept Oct Nov Dec 



34 - 



32 

 31 



Z 30 - 



29 



D 



8 6 



Jan Feb Mar April May June July Aug Sept Oct Nov Dec 



Figure 1 (continued) 



In contrast, other oviparous elasmobranchs exhibit re- 

 productive activity year round. For example, the present 

 study revealed that female thorny skates are capable of 

 reproducing throughout the year. This conclusion was 

 based on GSI, shell gland weight, diameter of the larg- 

 est preovulatory follicles, and the presence of egg cases 

 in specimens collected over the course of the study. We 

 also observed that GSI and shell gland weight were 

 highest in October. Thus, the period (or periods) of 

 enhanced reproductive activity appears to be an in- 

 tegral part of continuous cycles, although the specific 

 measured parameters or when these periods occur may 

 vary between species. 



In a study of thorny skates sampled from August to 

 December in NAFO Division 3N, females were found to 

 be reproductively active over the entire sampling inter- 

 val, and peak egg case production occurred in September 

 (Del Rio, 2002). In contrast, although large preovulatory 

 follicles were present and oviposition occurred through- 

 out the reproductive cycle of the lesser spotted dogfish 



