192 



Increase in Number of Species 



species D. americana americana can be explained only as the result 

 of hybridization between D. americana texana and D. nova- 

 mexicana (Fig. 84) (Patterson and Stone, 1952). The hybrid sub- 



Fig. 84. Distribution of Diosophila novamexicana and the two subspecies of 

 D. americana. The subspecies americana americana is a hybrid between nova- 

 mexicana and americana texana. (Adapted from Patterson and Stone.) 



species americana occupies such a large range with so little over- 

 lap with the subspecies texana that it can justifiably be considered 

 an incipient species resembling the Plafysamia and Abies examples. 

 Many other plants and animals are called "hybrid species," but 

 in most instances they are probably the result of interspecific 

 hybridization which changed one or both parent species ( introgres- 

 sion) but which did not produce an additional third species. In the 

 thrips Stannard (1954) suggested that the genus Hybridothrips 

 may be the result of hybridization between the allied genera 

 Zactinothrips and ZeuglotJirips. The combination of characters in 

 certain species of the leafhopper genus Erythroneura can be ex- 

 plained most logically as a result of hybridization between two 

 fairly difi^erent parents (Ross, 1958fl). Of the 12 species of crab- 

 hole mosquitoes comprising the Neotropical genus Deinocerites, 

 Belkin and Ilogue (1959) consider that at least D. howardi and 

 possibly D. epitedius and species A. also are of hybrid origin. In 



