Page:The Gall Wasp Genus Cynips.pdf/11

 SUMMARY

investigation was undertaken with the conviction that an intensive study of any group of species should contribute to the elucidation of biologic problems of general concern. Ninety-three species represented by more than 17,000 insects and 54,000 galls have been available for this analysis of the genus Cynips and these have offered an opportunity for studying the nature of species, individual variation, mutation and hybridization in nature, and the factors affecting the origin of species.

Species are defined as populations with common heredity. The thesis is maintained that species, in this sense, are more than mental concepts—that species are realities which preserve a morphologic and physiologic identity under varying conditions, over vast areas, and thru periods of time that may extend beyond the present geologic epoch. Within these populations individuals are found to vary, mutations to occur, and Mendelian races to develop as they are observed to develop in the laboratory. It appears that in Cynips, at least, these mutations have been the chief source of new species, but only when they are isolated from close relatives with which they might have interbred. Altho hybrid individuals prove common, and local colonies which have arisen by hybridization between related species are not unknown, the isolation of such hybrid populations to form species seems to have occurred in only a few instances in this genus.

The data on which these conclusions are based constitute a taxonomic revision of the genus Cynips. The group as redefined is a homogeneous unit delimited by insect morphology, gall characters, host relationships, life histories, and geographic distribution. Published records are coördinated with a large body of new data on these several aspects of the group. Of the 93 species placed in this genus, 45 have previously been described (only 26 of which have heretofore been recognized in Cynips) and 48 are new to science. To the 5 instances of alternation of generations which have previously been published for the group, 6 additional cases are added.

It should be of some moment to correlate these conclusions, concerning the nature and the origin of the species of Cynips, with the studies that have been made or remain to be made on the evolution of other groups of organisms. (5)