REPRODUCTIVE CHARACTER DISPLACEMENT IN CALOPTERYX (ODONATA: CALOPTERYGIDAE).

Abstract

The search for examples of reproductive character displacement (as redefined by Grant, 1972) is motivated by the desire to reveal the role natural selection plays in the establishment and/or improvement of premating barriers to gene exchange between speciating populations. The search is severely limited by the need to examine closely related species whose geographic ranges overlap extensively but not completely (Walker, 1974) and by the difficulty in documenting expected examples (Grant, 1972). Considerable attention has been focused on the acoustical pair-forming signals of birds, anurans, and singing insects. Despite the suitability of these signals in quantitative surveys for patterns suggesting reproductive character displacement, few examples have been found (Alexander, 1969; Blair, 1974; Fouquette, 1975; Grant, 1972; Thielcke, 1969; Walker, 1974). To date only a few studies have focused on the displacement of: 1) pair-forming displays (Ferguson, 1973), 2) morphology associated with species discrimination (Grant, 1975), or 3) discrimination abilities within a species (Waage, 1975; Wasserman and Koepfer, 1977). This paper presents an example of displacement of morphological characters used in species discrimination for two species of damselflies, Calopteryx maculata (De Beauvois) and C. aequabilis (Say), and deals with the problems affecting previous efforts to document character displacement. Grant (1972, 1975) provided a critical review of these problems and presented an example of careful documentation in the classic case of the rock nuthatches (Sitta). There are four basic stages in the documentation of reproductive character displacement. These stages were stated or implied by Grant (1972, 1975) and others (e.g. Alexander, 1969; Littlejohn, 1965; Littlejohn and Loftus-Hills, 1968) and are summarized as follows: