Constraints on the jumping and prey-capture abilities of ant-mimicking spiders (Salticidae, Salticinae, Myrmarachne)

Abstract

Accurate morphological ant mimicry by Myrmarachne jumping spiders confers strong protective benefits against predators. However, it has been hypothesized that the slender and constricted ant-like appearance imposes costs on the hunting ability because their jumping power to capture prey is obtained from hydraulic pressure in their bodies. This hypothesis remains to be sufficiently investigated. We compared the jumping and prey-capture abilities of seven Myrmarachne species and non-myrmecomorphic salticids collected from tropical forests in Malaysian Borneo and northeastern Thailand. We found that the mimics had significantly reduced abilities compared with the non-mimics. The analysis using geometric morphometric techniques revealed that the reduced abilities were strongly associated with the morphological traits for ant mimicry and relatively lower abilities were found in Myrmarachne species with a more narrowed form. These results support the hypothesis that the jumping ability to capture prey is constrained by the morphological mimicry and provide a new insight into understanding the evolutionary costs of accurate mimicry.

Mimicry in motion and morphology: do information limitation, trade-offs or compensation relax selection for mimetic accuracy?

“…If a good signal compensates for a poor signal (the increased deception hypothesis [ 2 ]), or if the generation of one signal constrains another (the multitasking hypothesis [ 2 ]), the two signals will be negatively correlated. Spider locomotion depends on muscles contained within the legs, but also on hydraulic power developed by muscles in the head, and thus hydraulic power depends on head morphology [ 22 ]. Indeed, the constricted morphology of ant-mimicking spiders limits their ability to jump [ 22 ], so it would not be unreasonable to expect similar constraints on locomotion, or the inverse: ant-like locomotion constraining the evolution of mimetic morphology.…”

“…Spider locomotion depends on muscles contained within the legs, but also on hydraulic power developed by muscles in the head, and thus hydraulic power depends on head morphology [ 22 ]. Indeed, the constricted morphology of ant-mimicking spiders limits their ability to jump [ 22 ], so it would not be unreasonable to expect similar constraints on locomotion, or the inverse: ant-like locomotion constraining the evolution of mimetic morphology. However, we found that accuracy of morphology and locomotion were not negatively correlated, failing to support either hypothesis.…”

Relationship between model noxiousness and mimetic accuracy in myrmecomorphic spiders

“…Even though spiders acquire protection by resembling ants, the defensive advantage comes with costs, such as constraints on circadian rhythm, lower fecundity due to abdominal narrowing and/or constrictions (see Cushing 2012), reduced jumping and hunting abilities (Hashimoto et al 2020), and the spider becoming a target for ant specialist predators (Nelson et al 2006a, b;. Mimicry is expected to occur only if the benefits of closely resembling the model exceed the costs.…”

An arachnid’s guide to be an ant: morphological and behavioural mimicry in ant-mimicking spiders

“…The extent to which ant-mimicking spiders resemble ants is constrained by predation pressure and several other factors. Slender body shape and thin legs may constrain accurate mimics in their jumping and prey capturing abilities (Hashimoto et al 2020), while constricted abdomen may reduce fecundity (McIver & Stonedhal 1993). Developmental, genetic and life history parameters also impose constraints (Pekár & Jarab 2011, McClean et al 2019).…”

“…Recent studies have measured various traits such as body shape, size, color, movement, and walking trajectories that contribute to mimicry. (Shamble et al 2017, Hashimoto et al 2020, Pekár et al 2020. However, these studies have not compared all three players (model, mimic, and non-mimic) in the mimetic system, nor have they included multiple traits that contribute to mimicry (but see Kelly et al 2021).…”