The functional morphology of species-specific male structures and lack of female coevolution in Lytta (Adicolytta) eucera (Chevrolat 1834) (Coleoptera Meloidae)

Abstract

Possible functions of several species-specific, sexually dimorphic male structures and of the male genitalia of Lytta eucera were deduced from observations of behaviour in the field and captivity, and were used to test theories of sexual selection. The male rubbed and tapped on the female’s antennae with sexually dimorphic segments of his antennae, and on her elytra with brushes of setae on his hind tarsi. He forcefully grasped the female’s prothorax and at least occasionally perforated the female’s prothoracic membranes with his modified middle tibiae, and her relatively uniform, membranous vaginal lining with his strong aedeagal teeth. His aedeagal teeth snagged her vaginal lining, and his gonostyli usually pressed against a featureless external female intersegmental membrane. None of these male structures was used as a weapon or in threat displays. No female structure fitted tightly in a “lock-and-key” manner with any of the male structures, nor was any female structure capable of selectively impeding their use, thus ruling out some hypotheses explaining their species-specificity in males. Female resistance to males, including occasional violent “tantrum” displays, was energetic, persistent, and highly effective; the functional significance of this resistance is unclear. If females distinguish the stimuli produced by species-specific traits of male genitalia, as supposed by some hypotheses, they likely use higher-level analyses in the central nervous system rather than the locations of the particular sense organs that are stimulated. HIGHLIGHTS The functional morphology of species-specific genital and nongenital sexually dimorphic traits of male Lytta eucera beetles was deduced using behavioural and morphological data. Two nongenital male traits function exclusively to stimulate females during courtship. Two other nongenital male traits may have mixed functions; one is unique in Meloidae in serving to grasp the female prothorax in a tong-like fashion. The traits were compared with predictions of hypotheses that have been proposed to explain species-specificity. No nongenital or genital trait fit well with mechanical versions of the species isolation or the sexually antagonistic coevolution (SAC) hypothesis. Inconsistency in the points of male–female genital contact indicated that stimulation versions of the cryptic female choice and SAC hypotheses could not be true unless female analyses of male stimuli occur not at the receptors themselves, but deeper in the female’s nervous system.