NATURE AND EVOLUTION — HAWAIIAN INSHORE PISH FAUNA 355 



survived and interbred with the central Pacific form they did so in such 

 relatively small numbers as to leave no trace of intergradation on the 

 Johnston population. For the other three fishes the situation would 

 seem to be similar except that the Hawaiian form has either arrived 

 first or totally displaced the central Pacific type. 



The original immigrants to Hawaii that gave rise to the descend- 

 ant population may or may not have been aberrant members of the 

 ancestral stock. Furthermore, during at least the initial increase in the 

 population, random drift may have been effective. Finally, among 

 Hawaiian fishes, these possibilities of aberrant initial immigrants and 

 random drift may have occurred at least twice, once at the stepping 

 stone of Johnston (or possibly Wake) and again on first arriving in 

 Hawaii. 



The above factors (more fully treated in Zimmerman, 1948: 122- 

 125) may have caused differentiation through isolation per se, and this 

 differentiation would be of a non-adaptive type. Once arrived in the 

 Hawaiian Islands the fishes may have undergone further differentia- 

 tion in adapting themselves to the colder waters of this area. (Evidence 

 for one such adaptation has already been discussed.) Such adaptive 

 physiological differentiation would increase the ability of the residents 

 to compete with further immigrants, so that these would be able to 

 pass even fewer genes into the resident population than before (provid- 

 ing of course that they could interbreed at all). Consequently, I believe 

 that the integrity of a Hawaiian endemic species has been maintained 

 whether or not an occasional central Pacific immigrant has interbred 

 with it, and that the physiological adaptations of the endemics have 

 insured them from extermination through competition with the central 

 Pacific immigrants that may have arrived subsequently. 



References 



Arhhenius, G. 1952. Sediment cores from the East Pacific. Reports of the 

 Swedish Deep-Sea Expedition 19^7-194-8, vol. 5, fasc. 1, pp. 1-227. 



Ekman, S. 1953. Zoogeography of the sea. Sidgwick and Jackson Limited, 

 London: 417 pp. 



Fowler, H. W. 1928. The fishes of Oceania. Memoirs of the Bemice P. 

 Bishop Museum, vol. 10, pp. 1-540. 



Jordan, D. S. and B. W. Evermann. 1905. The aquatic resources of the 

 Hawaiian Islands. Part I. The shore fishes. Bulletin of the U.S. Fish 

 Commission for 1903, vol. 23, pt. 1, pp. 1-574. 



SCHULTZ, L. P., and L. P. Woods. 1948. Acanthurus triosteffus marquesensis, 

 a new subspecies of surgeonfish, family Acanthuridae, with notes on re- 

 lated forms. Journal of the Washington Academ]/ of Sciences, vol. 38, 

 pp. 248-251. 



