The Inheritance of Female Dimorphism in the Damselfly, Ischnura Damula.

T H E genetics of sex-limited polychromatism in natural populations has been Investigated in only a few animals (see review by FORD 1961), none of the known instances including Odonata (damselflies and dragonflies). It is the purpose of the present paper to report the results of a breeding study of female dichromatism in Ischnura damula. This appears to be a case of balanced polymorphism, but its adaptive significance is not yet understood. The dimorphic forms of 1. damula have been described by WALKER (1953), and the color pattern differences on the dorsal synthorax are shown in Figure 1. One of the female types closely resembles the male. Homoeochromatic, isochromatic, and andromorphic are the terms applied to the male-like form, and the other form has been termed heterochromatic or heteromorphic in the literature of the Odonata (TILLYARD 1917; FRASER 1933; NEEDHAM and HEYWOOD 1929; LONGFIELD 1960). Although hommochromatic and heterochromatic are the terms most frequently employed by entomologists, andromorphic and hetermorphic have been adopted in this paper to avoid possible confusion with the cytogenetic meaning of the word heterochromatic.