542 ECOLOGY AND BEHAVIOR 



of selection such a patchy distribution of gene frequencies can occur by 

 random drift of neutral mutations, with some migration between adjacent 

 populations and an occasional, distant migration. Experimental verification 

 of this theory came from the work of Selander (1970), on whose results 

 Lewontin (1974) commented, "It would be absurd to imagine we are ob- 

 serving selection gradients. For this reason we cannot deduce selection 

 from patchy and mosaic gene frequency distributions." On the other hand, 

 Wallace (1968) and Lewontin (1974) have derived equations showing that 

 in two populations of 10 000 individuals each, the exchange of 10 indi- 

 viduals per generation is, in the absence of selection, sufficient to bring 

 the gene frequencies in the two populations to a common value. 



In the case of the two shark populations using the Sydney and Jervis 

 Bay breeding sites, the differences in gene frequencies could be due to 

 random genetic drift, for the distribution of gene frequencies appears 

 analogous to those described by Selander (1970). However, the migra- 

 tion of this shark between the two localities (McLaughlin and O'Gower 

 1971, and present authors) would seem to indicate that differences in 

 gene frequencies could be eliminated, unless the populations using the 

 two breeding sites are temporally isolated. The evidence to solve this possible 

 contradiction is not available. Interpretation of the data and resolution of 

 the problem depend entirely on which school of population genetics one 

 follows, the classical (Clarke 1975) or the non-Darwinian (Kimura 1975). 

 The conflicting approaches of the two schools are evident in the lack of a 

 definitive answer to the problem discussed herein. The first prerequisite for 

 resolving the issue is that the function of the polymorphic protein be deter- 

 mined, although even with this knowledge the detection of genetic selection 

 would be an enormous task. The second is that more and larger samples be 

 obtained, during a single season, from breeding populations which are in- 

 shore. From the present study one can conclude that within the two major 

 populations there is some division into smaller breeding units, but they are 

 not reproductively isolated. One can only conclude, in the absence of evi- 

 dence to the contrary, that the observed differences are the result of random 

 genetic drift. 



It therefore appears that further studies on the ecology of H. portus- 

 jacksoni do not warrant the effort involved. Nevertheless, even with the 

 very limited resources available, the application of scuba diving equipment 

 to the study of sharks has resulted in a considerable addition to our knowl- 

 edge of sharks in their own environment. 



