MORPHOLOGICAL DIFFERENTIATION IN WING VENATION AMONG BROODS OF 13- AND 17-YEAR PERIODICAL CICADAS.

Abstract

It has traditionally been assumed that morphological differences exist between the 13and 17-year life cycle forms of the periodical cicadas. Thus, differences among year-classes (broods) within a single species and life cycle would not be expected. In the first published description of the two life cycle forms, Walsh and Riley (1868) wrote, there are absolutely perceptible specific differences between the 17-year and the 13-year broods, other than in the time of maturing. The possibility of differentiation among broods, within a life cycle was never mentioned. Walsh (1870) asserted that, it has been impossible for me, on the closest examination of very numerous specimens to detect any specific differences between the two forms. Riley (1869) commented that, Mr. Walsh informs me that Charles Darwin, Asa Gray and Dr. Hooker all agree in the belief that the 17-year and 13-year forms ought not to be ranked as distinct species, unless other differences besides the period of development could be discovered. Although later authors (Alexander and Moore, 1962) did not completely reject the possibility of differentiation among the broods, Lloyd and Dybas (1966) noted that, no one has yet succeeded in demonstrating statistically significant differences between either broods or life cycles in any of the three species but modern methods of numerical taxonomy (Sokal and Sneath, 1963) have never been applied to this problem. In this paper I demonstrate that 13and 17-year periodical cicada broods