Combat in a cave-dwelling wētā (Orthoptera: Rhaphidophoridae) with exaggerated weaponry

Fea, Murray; Holwell, Gregory I.

doi:10.1016/j.anbehav.2018.02.009

Cited by 21 publications

(9 citation statements)

References 63 publications

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“…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). In other species of Coelopid it has been suggested that longer midlegs may be advantageous in remaining attached to females during struggling behaviour as they are used in stabilisation or to clasp the females (Andre Gilburn -pers comm; Crean et al 2000).…”

Section: Discussionmentioning

confidence: 86%

“…It is possible that this behaviour makes it more challenging for other males to detect the presence of the female, and at the same time allows the guarding male to detect the presence of other males at a greater distance. 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).…”

Section: Discussionmentioning

confidence: 99%

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

LeGrice

Holwell

2022

Evol Ecol

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The need to respond quickly to the presence of an ephemeral resource required for breeding is often a feature of scramble competition mating systems. Scramble competition mating systems can feature extreme levels of sexual conflict and coercive mating by males. As a result, sexual selection can act on various traits used by males to overcome female resistance behaviours. Selection on these traits may result in significant intra and intersexual size variation and sexual dimorphism. Additionally, traits that influence mating success in males often show positive static allometry. Kelp flies (Coelopidae) are a small family of Diptera which specialise on wrack (beach cast marine macroalgae), a highly ephemeral resource. The mating system of these flies involves high levels of sexual conflict, with females rejecting all male mating attempts. In this study we describe intra and intersexual size variation and static allometry of traits in two of Aotearoa|New Zealand’s species, Coelopella curvipes and Chaetocoelopa littoralis. In addition, we investigate the mating behaviour of C. littoralis under ecologically relevant mating conditions. We found high levels of variation in both species with significant evidence of sexual dimorphism across all traits measured in C. littoralis, and in mid tibia length in C. curvipes. Furthermore, mid tibia length in both species exhibits positive static allometry and is disproportionally larger in larger males, suggesting that this trait in particular may be under strong sexual selection. We found that larger male C. littoralis which attempt to mate are significantly more likely to mate successfully demonstrating a large-size advantage in this species similar to findings across the Coelopidae. However, we only found a non-significant trend towards a mating advantage for males with longer mid-tibiae. We discuss these findings with reference to the population dynamics and ecology of these species.

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

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

LeGrice

Holwell

2022

Evol Ecol

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“…Despite their delicate appearance, the hind legs of males in this species are also used as armaments in intrasexual contests, where superior leg length is also advantageous [56]. Hence, sexual selection on this morphological trait arises from two sources, and favours the same result (leg exaggeration), which has probably contributed to the extreme morphology displayed by the males of this species.…”

Section: Discussionmentioning

confidence: 97%

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

Fea

Holwell

2018

Proc. R. Soc. B.

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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.

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“…(2018); 21 = Okada et al . (2006); 22 = Okada & Miyatake (2007); 23 = Walker & Holwell (2018); 24 = Fea & Holwell (2018); 25 = Ida & Wada (2017); 26 = O'Brien & Boisseau (2018); 27 = Nolen et al . (2017); 28 = Nguyen & Stahlschmidt (2019); 29 = Rink et al .…”

Section: General Meta‐analytical Proceduresmentioning

confidence: 99%

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

Palaoro

Peixoto

2022

Biological Reviews

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In many species that fight over resources, individuals use specialized structures to gain a mechanical advantage over their rivals during contests (i.e. weapons). Although weapons are widespread across animals, how they affect the probability of winning contests is still debated. According to theory, understanding weapon function during contests is essential to: (i) understanding its importance in determining the winner, and (ii) identifying what weapon traits (e.g. weapon length versus shape versus performance) are most relevant for contest success. However, quantitative evaluations of how weapon function affects the extent to which weapon traits influence contest success are still lacking. Here, we first develop an individual‐based model to evaluate how increasing the influence of the weapon in determining the winner translates to differences between winners and losers. Then, we use a meta‐analysis to identify: (i) whether different weapon measures influence contest outcome differently; (ii) how animals use their weapons during fights – i.e. weapon function; and (iii) if weapon function correlates to how weapons influence contest outcome. Our model showed that, as weapons increased the chance of determining the winner, the mean difference between winners and losers also increased. Therefore, in our meta‐analysis we used the mean trait difference between winners and losers as a proxy for the extent to which weapons influence contest success. The literature search identified 49 suitable studies, containing information for 52 species, totalling 107 effect sizes. Four main patterns emerged. First, most of the literature focuses on linear measures of weapons, while performance measures are concentrated on Crustacea and Squamata; other types of measures were rare. Second, differences between winners and losers in linear measurements were greater than differences in performance measurements when all species were combined (and when we used only a subset). Third, species that bear weapons almost always perform visual/tactile displays before engaging in physical contact. And fourth, while the way individuals display their weapons did not influence the importance of weapon size on contest outcomes, fighting style predicted when differences between winners and losers would be higher. Species that used their weapons to push or lift (even when combined with other functions) showed greater differences between winners and losers when compared to species that used their weapons to impact, pierce, pull or squeeze. Overall, our results show that we have an incomplete understanding of animal weapons built mostly on weapon size and a few select taxa. Thus, we should start focusing on measuring weapons according to how they are used during contests and in a wider diversity of species. One way forward is to conduct studies that integrate weapon morphology to weapon function to ensure we are measuring the most ecologically relevant variables.

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Combat in a cave-dwelling wētā (Orthoptera: Rhaphidophoridae) with exaggerated weaponry

Cited by 21 publications

References 63 publications

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

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

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

The hidden links between animal weapons, fighting style, and their effect on contest success: a meta‐analysis

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