The evolution of asymmetric genitalia in Coleoptera

Abstract

The evolution of asymmetry in male genitalia is a pervasive and recurrent phenomenon across almost the entire animal kingdom. Although in some taxa the asymmetry may be a response to the evolution of one-sided, male-above copulation from a more ancestral female-above condition, in other taxa, such as Mammalia and Coleoptera, this explanation appears insufficient. We carried out an informal assessment of genital asymmetry across the Coleoptera and found that male genital asymmetry is present in 43% of all beetle families, and at all within-family taxonomic levels. In the most diverse group, Cucujiformia, however, genital asymmetry is comparatively rare. We also reconstructed the phylogeny of the leiodid tribe Cholevini, and mapped aspects of genital asymmetry on the tree, revealing that endophallus sclerites, endophallus, median lobe and parameres are, in a nested fashion, increasingly unlikely to have evolved asymmetry. We interpret these results in the light of cryptic female choice versus sexually antagonistic coevolution and advocate further ways in which the phenomenon may be better understood.This article is part of the themed issue ‘Provocative questions in left–right asymmetry’.

Imperfect and askew: A review of asymmetric genitalia in araneomorph spiders (Araneae: Araneomorphae)

“…Liocranidae). Reports on insects suggest that genital asymmetry rarely appears isolated and is usually a shared trait between closely related species [3,4,90]. Here, we found some similar patterns with several species within a genus showing at least one type of genital asymmetry.…”

“…Changes in mating position have also been associated with many cases of DA in insect genitalia [1,4,12]. Unfortunately we were not able to test this in the case of T. politus using live specimens; nevertheless, observations in Agroeca [115] and other RTA spiders [13,116] suggest that copulation is achieved by the male climbing over the female and stretching over a side while the female slightly turns her abdomen; this process is alternated between right and left side.…”

“…Invertebrates show a wide range of genital asymmetries with probably thousands of independent origins. Many, sometimes not mutually exclusive, explanations have been proposed, namely: i) morphological compensation for selected changes in mating position; ii) sexually antagonistic co-evolution; iii) cryptic female choice for asymmetric male genitalia; iv) different functions for the left and right side; v) one-sided reduction to save space and resources; vi) functional constraints: to function properly, the separate parts of the genitalia need to connect in an asymmetric fashion [1][2][3][4].…”

New subgenus and three new species of soldier beetles from the Eocene of Baltic amber

“…nov. displays elongate elytra, which completely cover and overtake the abdomen. It is widely accepted that the shape of the aedeagus is an important phylogenetic character among the genera of soldier beetles (Brancucci, 1980;Liberti, 2011), and this feature even has some importance at the family level for many beetles (Schilthuizen et al, 2016). The morphology of the posterior most abdominal (1), ventral view, scale bar equals 400 μm (2), lateral view, scale bar equals 500 μm (3), lateral view, scale bar equals 500 μm (4).…”

The Phylogenetic Relationships of Tiaronthophagus n.gen. (Coleoptera, Scarabaeidae, Onthophagini) Evaluated by Phenotypic Characters

“…For the male genitalia, the arched, pointed parameres with a large, rounded ventral notch, and the phallobase with a plate-shaped ventral expansion allowed for optimal separation of the ingroup and outgroup taxa. Noteworthy, this well-developed, characteristic ventral projection of phallobase (Figure 6L,M) could suggest its involvement in the coupling mechanism, which is a complex phenomenon only marginally studied till now [59,60].…”