PERRIN ET AL.: GROWTH AND REPRODUCTION OF SPOTTED PORPOISE 



a requirement of hypothesis 1, above, but does not 

 eliminate hypotheses 2 and 3. 



The three groups do not differ in average esti- 

 mated number of tooth layers. This may, in part, 

 be due to the difficulty of accurately counting the 

 innermost layers in teeth with more than 12 

 layers (the number of layers is probably undere- 

 stimated by as much as one-third in teeth with 

 large amounts of convoluted secondary dentine), 

 but careful comparison of the teeth of the three 

 groups in terms of other features presumably cor- 

 related with age, such as tip wear, degree of clo- 

 sure of the pulp cavity, and amount of secondary 

 dentine does not indicate that any group is older 

 than any other. This evidence is against 

 hypothesis 1, which requires that group C be 

 older than A, and hypothesis 2, which requires 

 that B be older than A and C. 



Groups A and B have reached asymptotic 

 length (-190 cm). The animals in group C aver- 

 aged about 3 cm less. A statistical comparison of 

 A with B using Student's t indicates that the dif- 

 ference is significant at a = 0.05. These results do 

 not eliminate or support directly any of the 

 hypotheses. Since A, B, and C are about the same 

 age, the length data indicate that asymptotic 

 length may be less for females that become senile 

 with 10 to 15 corpora. This indirectly supports the 

 idea of considerable individual variation in life 

 history. 



The most convincing evidence against hy- 

 pothesis 1 has to do with number of corpora in 

 right versus left ovaries. If the emphasis in cor- 

 pus deposition shifts from left to right at about 10 

 corpora, and if group C regresses from group B 

 (animals with about 20 corpora) losing about 6 

 corpora in the process, then group C should have 

 about equal numbers of corpora in the right and 

 left ovaries. If most corpora of ovulation come in 

 early reproductive life (as data analyzed below 

 indicate) and, as suggested by Sergeant (1962), 

 are more likely to disappear than corpora of preg- 

 nancy because of smaller initial size, then the 

 regressed group C should have, on the average, 

 more corpora on the right than on the left, be- 

 cause most of the corpora of preg- 

 nancy would be in the right ovary. Forty-one per- 

 cent of the corpora in 14 individuals having 18 to 

 22 corpora (average 19) were on the right. Only 

 2^c of the corpora in group C were on the right. 

 The difference between C and A (29 and 24% ) can 

 be accounted for simply by the difference in aver- 

 age total corpora count (12.9 and 11.2). These re- 



sults eliminate the hypothesis (number 1 above) 

 of loss of corpora with regression of ovaries. 



The various lines of evidence largely speak 

 against hypotheses 1 and 2 and support hy- 

 pothesis 3, that of great individual variation in 

 life history and of persistence of corpora albican- 

 tia. This is in line with findings by some other 

 workers in small cetaceans (Sergeant 1962, 1973; 

 Brodiel971). 



The data on the relationship of percent occur- 

 rence of corpora lutea to number of corpora (Fig- 

 ure 28) also support the hypothesis of widely 

 varying rate of accumulation of corpora albican- 

 tia. After stabilization at about 50% at 3 to 4 cor- 

 pora, the rate declines after 8 to 9 corpora to 20% 

 at 13 corpora; but the rate for females with 17 to 

 27 corpora is again 50%. Assuming that fecundity 

 is inversely related to age, this pattern suggests 

 that the females in the 17 to 27 group are about 

 the same age as those in the 3 to 9 group. 



Ovulation Rate 



Even assuming that corpora albicantia persist 

 and represent various ovarian events, estimating 

 average rates of accumulation is difficult because 

 of 1) the above-mentioned unreliability of age 

 estimates based on more than 12 tooth layers, 2) 

 the evident individual variation in accumulation 

 rate, and 3) change in ovulation rate during the 

 reproductive span. All of these factors must con- 

 tribute to the scatter in a plot of corpora number 

 (including corpus luteum) on estimated age (Fig- 

 ure 32). Several workers have pointed out that 

 cetacean ovaries often contain two or more cor- 

 pora of the same size and same stage of regres- 

 sion. It has been suggested that these are the 

 result of multiple infertile ovulations or luteali- 

 zation of atretic follicles in newly mature ani- 

 mals (Harrison et al. 1972). Many in the present 

 series of ovaries had two or more corpora (of Type 

 1 or 2) that were very similar in size and struc- 

 ture and must have resulted from nearly contem- 

 poraneous events. One probable multiple ovula- 

 tion is apparent in Figure 32. This female, field 

 number CW0R8, possessed 7 or 8 well-defined 

 layers in its teeth. In spite of its extreme youth, it 

 had a small corpus luteum, three Type 1 corpora, 

 two Type 2 corpora, one Type 3 corpus, and one 

 Type 4 corpus. The uterus was empty, and there 

 was no milk in the mammaries. The animal could 

 not have been reproductively active for more than 

 about a year, but had already experienced eight 



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