652 



ECOLOGY AND EVOLUTION 



feet of the physical environment, Talbot 

 (1934) shows that ants of the genus For- 

 mica inhabiting drier situations survived 

 experimental drying better than other spe- 

 cies of Formica that normally inhabited 

 more humid situations (see p. 335). In this 

 case, taxonomic correlation indicates again 

 that these physiological characters are in- 

 herited. 



Dobzhansky (1945, 1947) and Wright 

 and Dobzhansky (1946) report differential 

 survival of three chromosome races of 

 Drosophila pseudoobscura from the same 

 locality kept under artificial temperatures. 

 The experimental data conform to the 

 natural incidence of the chromosome types 

 (Dobzhansky, 1948) during summer, fall, 

 and winter (the spring incidence was not 



Fig. 238. Panamanian frog, Dendrobates tinctorius, exhibiting conspicuous dark brown and 

 blue markings (warning coloration) and provided with a poisonous mucus. (Photograph by 

 Ralph Buchsbaum.) 



Aldrich (1946) found that races of birds 

 are usually adapted to their respective en- 

 vironments and that transplantations of one 

 race to the range of another are not often 

 successful. 



Pond crayfish in eastern North America 

 (Cambarus diogenes, C. blandingii, C. im- 

 munis) are more tolerant of low oxygen 

 content of water and more resistant to heat 

 than are stream crayfish (C propinquus, 

 C. virilis) (T. Park, 1945a). It is possible 

 that such differences between crayfish from 

 different habitats are the result of natural 

 selection of physiologic characters. 



experimentally repeated). Natiiral selection 

 of these gene arrangements results in adap- 

 tive adjustment of the species to different 

 conditions. Selection of heterozygotes over 

 homozygotes results in the persistence of 

 several types in the same locahty, "buffers" 

 the species against environmental change, 

 and maintains a store of hereditary varia- 

 bihty. 



Dubinin and Tiniakov (1945, 1946, 

 1946a, 1946b, 1947) report seasonal varia- 

 tion in chromosome-inversion frequency in 

 urban populations of D. funebris under sea- 

 sonal selection pressures, but rural popula- 



