Exaggerated male legs increase mating success by reducing disturbance to females in the cave wētā Pachyrhamma waitomoensis

Abstract

Mate guarding is a widespread behaviour resulting from sperm competition and conflict over optimal remating rates. It is a key way in which males exhibit differential mating investment, and represents a complex interplay between mating effort, intrasexual competition, opportunity costs and sexual conflict. Nevertheless, although there are many examples of exaggerated male structures used to fight rivals, few animals have developed specialized male morphological adaptations for directly sheltering females from disturbance by non-rivals. Here we report on the use of sexually dimorphic, elongated male hind legs, which are used to guard females in the New Zealand cave wētā (Orthoptera: Rhaphidophoridae). We found that male hind legs alongside the female failed to deter rivals from accessing her or disrupting copulation. However, they did reduce the disturbance to females from other, non-rival animals such as juveniles and heterospecifics. Males with longer hind legs were more effective in reducing disturbance, and remained with females for longer. Longer guarding periods also led to higher numbers of matings between pairs. Models of males with artificially altered hind leg dimensions also showed a benefit to greater leg length, and artificially altering the disturbance rate to females also had a significant effect on pair duration. Our results indicate that nuisance disturbance to females may play an important role in driving sexual selection on male leg length and its exaggeration in this species.

Size variation, allometry and mating success in Aotearoa|New Zealand kelp flies (Coelopidae)

“…In other species including crane flies (Adler and Adler 1991), harlequin beetles (Zeh and Zeh 1992) and cave wētā (Fea and Holwell 2018a), males extend their legs in a similar fashion during mating and mate-guarding. The male hindlegs of cave wētā Pachyrhamma waitomoensis are highly exaggerated relative to females, yet are hypoallometric (Fea and Holwell 2018b). While male hindleg length in this species has no influence over mating interruptions by rival males, it does correlate with the number of matings a male can achieve by deflecting heterospecific animals in the densely populated communities occurring on cave walls (Fea and Holwell 2018a).…”

Mating Behavior and Sexual Selection in Monochamus saltuarius (Gebler)

“…In some species, the hind leg plays an important role in mate selection; for example, in the ambush bug (Heteroptera: Reduviidae), sexual selection appears to act on the length of the male hind leg [75]. In Pachyrhamma waitomoensis Richards (Orthoptera: Rhaphidophoridae), males with the longest hind legs could accrue approximately triple the number Phymata wolffii Stal of copulations [76]. Female bean bugs Riptortus pedestris (Fabricius) prefer males with higher frequencies of courtship display and larger hind legs, which indicate better abilities to compete for mates.…”

Static allometries do not reflect evolutionary allometry in exaggerated weaponry of male New Zealand sheetweb spiders (Cambridgea spp.)

“…Sexually selected weapons (hereafter: weapons) evolve via selection resulting from intrasexual competition over mates or resources important to mates. The majority of studies investigating the use of sexually selected weaponry have focused on males competing for access to females, which is common in insects (dung beetles, Onthophagus taurus , Moczek & Emlen, 2000 ; potter wasps, Synagris cornuta , Longair, 2004 ; giraffe weevils, Lasiorhynchus barbicornis , Painting & Holwell, 2013 , cave wētā, Pachyrhamma waitomoensis , Fea & Holwell, 2018 ), spiders (jumping spiders, Lyssomanes viridis , Tedore & Johnsen, 2012 ; sheetweb spiders, Cambridgea foliata , Walker & Holwell, 2018 ), crustaceans (shore crabs, Carcinus maenas , Sneddon et al, 1997 ; fiddler crabs, Uca spp., Swanson et al, 2013 ) and mammals (bighorn sheep, Ovis canadensis , Coltman et al, 2002 ), among other animals. However, females are also known to compete for mates with sex‐specific weaponry, such as occurs in jacanas (Berglund, 2013 ; Jenni & Collier, 1972 ).…”