Systematics and acoustics of North American Anaxipha (Gryllidae: Trigonidiinae)

Abstract

The genus Anaxipha has at least 13 North American species, eight of which are described here. Ten species fall into these three species groups: exigua group (exigua Say, scia Hebard and n. spp. thomasi, tinnulacita, tinnulenta, and tinnula); delicatula group (delicatula Scudder and vernalis n. sp.); litarena group (litarena Fulton and rosamacula n.sp.). The remaining three (imitator Saussure, fultoni n.sp., and calusa n.sp.) have no close relatives among the other species. Most new species were initially distinguished by their calling songs, and in most cases sympatric populations proved cleanly separable by features of male genitalia and tooth-counts of stridulatory files. Species groups were based mostly on comparisons of male genital structures and the results of DNA barcoding. Species are here characterized not only by their songs and morphology, but also by geographical, ecological, and seasonal distributions. At a given temperature the pulse rate (PR) of the male's calling song is a key aid to identification. PR at 25°C has a narrow range of variation within a species and among the 13 species its mean value varies from 5 to 79 p/s. As in other crickets, pulse rates plotted as a function of temperature have a positive, linear trendline. When trendlines for 11 Anaxipha species are extrapolated downward, the temperature at ŷ=0 p/s is 2.7+2.2 (mean±SD) - i.e., the lines tend to converge at about 3°C. This makes possible a simple formula for estimating the PR at 25°C from any Anaxipha calling song recorded at any temperature. Other aids to identifying species from their calling songs are the duration and regularity of breaks between pulse sequences and the relationship between PR and carrier frequency (CF). When CF is plotted as a function of PR, the relationship deviates noticeably from linear only in vernalis. We propose that in Anaxipha spp., as well as in six other genera in four gryllid subfamilies, the synchrony of tooth impacts and the fundamental vibrations of the CF is maintained by the scraper moving continuously over evenly spaced file teeth - rather than by the much-studied (and well-established) catch-and-release mechanism of Gryllus spp. Our proposal is based on the high rates of change in CF with temperature and on differences in the teeth of the stridulatory files. The PR at 25°C of each of the 13 species is remarkable in the degree to which it predicts the mean values of these five characters: file tooth number, tooth density, file length, pulse duration, and pulse duty cycle (Fig. 17). A neotype is designated for Gryllus pulicaria Burmeister (1838), the type species of the genus Anaxipha. With the e-version of this paper, extensive Supplementary Materials provide permanent access to data sets that are basic to our conclusions. These materials include detailed records of the specimens examined and of the more than 1300 recorded songs that were analyzed. Digitized versions of more than 450 of the recordings are archived in Cornell's Macaulay Library of Natural Sounds.