Bioacoustics of Neduba castanea

Fig. 19 (distribution), Fig. 21 (male and female habitus, calling song, drumming, male and female tremulation karyotype), Plate 2 B–C (live habitus), Plate 5A (male calling song), Plate 7I (male ventral sclerite), Plate 10B (male titillators), Plate 11K (female subgenital plate). Common name. Chestnut Shieldback. History of recognition. Scudder (1899) described Tropizaspis castanea from Los Angeles County, California . Caudell (1907) transferred this species to Aglaothorax based on habitus, in particular the pronotal shape, but the species was moved to Neduba once the male genitalia were examined ( Rentz 1988 ; Rentz & Birchim 1968 ). Our fieldwork shows that N. castanea is the only Neduba species found in mainland Los Angeles County (i.e. exclusive of the Channel Islands), where it is limited to the fringes of the Mojave Desert.

Distribution. Dry north slope of Transverse Ranges of California including the San Gabriel, San Bernardino, Liebre, and San Emigdio Mountains. Seasonal occurrence. Adult specimens have been taken from mid-June in foothill regions ( 13-VI-2003 , JA Cole & JN Hogue, LACM) into September at high elevation ( 12-IX-2015 , DA Gray, CAS). Females were last instar nymphs at the earliest date of occurrence listed above. Stridulatory file. (n = 5), length 3.7–4.6 mm , 79–99 teeth, tooth density 21.6 ± 1.1 (19.8–22.7) teeth/mm. Song. (n = 24) A continuous series of long MPTL (373.1 ± 51.5 ms) with widely spaced toothstrikes delivered at PTR of 2.6 ± 0.7 s- 1. The sound resembles a finger running along the teeth of a comb. The PTF of 13.7 ± 2.1 kHz extends comfortably into the audible range. There is a significant high frequency component, however, with 18.7 kHz PTF measured in one high frequency laboratory recording. Males begin calling at sunset. The population from McGill Campground on Mount Pinos , Ventura County , California has a significantly slower PTR than that of the type locality (2-sample t -test, P = 0.002). Males may also produce audible substrate vibrations via drumming. Drums precede bouts of stridulation ( Fig. 21 ) . Karyotype. (n = 5) 2n♁ = 22 ( 4m + 16t + XmYt), shared only with N. macneilli . T88-69, S88-72, topotype. Recognition. Morphological and color pattern differences thought to separate N. castanea from N. macneilli (per Rentz & Birchim 1968 ) are unreliable. The development of the styli on the subgenital plate, from absent to slight swellings to articulated, may vary within a population and even between the left and right sides of a single specimen. Both species exhibit the full range of variation in color patterns. Female N. castanea have round, highly convex subgenital plates, whereas those of N. macneilli are subtriangular with a bluntly pointed apex. Geographically N. castanea replaces N. macneilli , which is a Sierra Nevada species, in the Transverse Ranges of southern California . Notes. We treat N. castanea and N. macneilli as closely related sister species based on reproductive isolation via allopatry. Both inhabit the same life zone in different geographic regions of California . N. castanea and N. macneilli are sympatric with Aglaothorax ovata , and all three species share a similar robust habitus suggesting convergent evolution of body form in their habitat. Enlarged pronotal size may be adaptive for signal transmission in open habitats such as pinyon-juniper and Joshua tree woodlands, where trees and bushes are widely spaced, compared with the dense forest understories inhabited by other Neduba species Groups. Drumming was observed during courtship in the field at the Largo Vista Road locality (see Type material above), during which a male alternated drumming and stridulating. The signaling did not result in copulation in this observed instance (JAC pers. obs.).