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

Abstract

Bilateral asymmetry in the genitalia is a rare but widely dispersed phenomenon in the animal tree of life. In arthropods, occurrences vary greatly from one group to another and there seems to be no common explanation for all the independent origins. In spiders, genital asymmetry appears to be especially rare. Most known species show almost perfectly symmetrical genitals with the right and left sides being mirror images of each other. However, some examples of asymmetric genitalia have been studied and many other reports are scattered in the taxonomic literature. Based on a broad literature survey, we found several species in thirteen families with evidence of genital asymmetry, mostly expressed only in females. Our review suggests that spider genital asymmetries, although rare, are more common than previously thought and taxonomic descriptions and illustrations are a useful but not entirely reliable tool for studying them. Here we also report on directional asymmetry in the liocranid spider Teutamus politus, the first known case of morphologically asymmetric male genitals in Entelegynae spiders. Generalities, evolution and categorization of asymmetry in spiders are further discussed.

Outside the pattern: Evolution of the genital asymmetry in Saicinae (Hemiptera: Heteroptera: Reduviidae)

“…The male genitalic asymmetry in Saicinae agrees with directional asymmetry or left-right asymmetry, which refers to the difference between the sides in a chiral form (Rivera-Quiroz et al, 2020;Schilthuizen, 2013). Directional asymmetry is the most common within insects with asymmetric genitalia, and several causes have been associated with it, such as the changes in mating positions and morphological compensation (Huber, 2004(Huber, , 2010Huber et al 2007;Rivera-Quiroz et al, 2020;Schilthuizen, 2013). Studies on the mating position and asymmetry suggest that driving from a symmetric mating position, with the female-above, to an asymmetric position with the male-above, false male-above (male on top but his abdomen contacting the female from below), side-by-side positions (male laterally to the female, locating the abdomen slightly turned to the side), or random-sided positions (change in the direction of the male genital structures during mating) might be a first step towards genital asymmetry, at least in insects (Huber, 2010;Huber et al 2007;Schilthuizen, 2013).…”

“…The male genitalic asymmetry in Saicinae agrees with directional asymmetry or left-right asymmetry, which refers to the difference between the sides in a chiral form (Rivera-Quiroz et al, 2020;Schilthuizen, 2013). Directional asymmetry is the most common within insects with asymmetric genitalia, and several causes have been associated with it, such as the changes in mating positions and morphological compensation (Huber, 2004(Huber, , 2010Huber et al 2007;Rivera-Quiroz et al, 2020;Schilthuizen, 2013).…”

First description of the female of Psalistopoides fulvimanus Mello-Leitão, 1934 (Araneae: Pycnothelidae)

“…One case of an anomalous spermathecae was detected. Anomalies are quite commonly reported in haplogyne spiders (see Huber, Sinclair & Schmitt 2007; Schilthuizen, 2013; Rivera-Quiroz 2020), but not commonly reported in mygalomorphs. In Fig.…”

First teratological case of the ocular pattern in the brown recluse spider genus Loxosceles Heineken & Lowe (Araneae, Sicariidae)

“…For a better description of this species, see Brescovit et al (2017). At this point, only teratological cases of the genitalia in Sicariidae (Loxosceles, Sicarius and Hexopthalma) have been published (Rivera-Quiroz et al, 2020), but cases of ocular abnormalities are completely unknown in this family (Jiménez & Llinas, 2002;Gonzalez-Moliné, 2008).…”