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From Soup to Systematics: Exploring the Phylogenetics and Extraordinary Evolution of Head and Genitalia of Nannocoiris Reuter (Hemiptera: Dipsocoromorpha) & Taxonomic Revision of Guapinannus Wygodzinsky (Hemiptera: Dipsocoromorpha)

Abstract

Evolutionary biologists have long been intrigued by exaggerated morphologies tied to sexual or natural selection. In insects, relatively few studies have investigated the evolution of such traits at the genus level and above and have used phylogenetic methods to do so. We here investigate the interspecific evolution of head length in the minute litter bug genus Nannocoris Reuter based on the first phylogenetic hypothesis of the group (25 ingroup species, five gene regions, 3409 bp) and ancestral state reconstruction. Head lengths in this speciose genus range from approximately one sixth of the total body length to more than a quarter of the body length, while the head and mouthpart (rostrum) lengths are correlated. Different species therefore possess a markedly different reach of the rostrum when extended. The analyses show that head length evolution in Nannocoris is plastic, with head length elongations and reductions occurring in several clades, derived from ancestors with moderately elongate heads. Evidence is provided that exaggerated head lengths evolved through elongation of either the genal (pricei group) or the tip (arimensis group) region of the head. The biology of species in the genus Nannocoris is unknown, but given the lack of sexual dimorphism of head lengths, we speculate that head evolution in this genus may be driven by natural selection, potentially in the context of prey capture. Studies on animal genitalia have long shaped our understanding of concepts, patterns and processes of morphological evolution. Coevolution between male and female genitalic structures is predicted to be ubiquitous, regardless of the evolutionary mechanism involved. However, studies that simultaneously evaluate male as well as female genitalic variation in a comparative phylogenetic framework have remained relatively scarce. We here investigate correlated male and female genital evolution in Nannocoris Reuter (Hemiptera: Schizopteridae), a minute litter bugs genus that may be unique among arthropods in the degree and variation of its exaggerated genitalic traits: we here show that the length of the male intromittent organ differs dramatically between species, ranging from 1/8th to 20 times the respective body length and that the female spermathecal duct also displays drastic length differences between species. Using a phylogeny of the genus, measurements of male and female genitalic features, and phylogenetically independent contrasts, we find that the length of male intromittent organ and female spermathecal duct are indeed correlated. The mode of evolution that has led to this striking phenotypes is unknown, but we stress that this system has potential for future research in the evolution of male and female genitalic features in general

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