Compound mimicry and trading predators by the males of sexually dimorphic Batesian mimics

Abstract

Sexual dimorphism is pronounced in Myrmarachne , a large genus of ant-like jumping spiders (Salticidae) and one of the major animal groups in which Batesian mimicry of ants has evolved. Although adult females and juveniles of both sexes are distinctly ant-like in appearance, Myrmarachne males have elongated chelicerae that might appear to detract from their resemblance to ants. Experimental findings suggest that the Myrmarachne male's solution is to adopt compound mimicry (i.e. the male's model seems to be not simply an ant worker but a combination of an ant and something carried in the ant's mandibles: an ‘encumbered ant’). By becoming a mimic of a particular subset of worker ants, Myrmarachne males may have retained their Batesian-mimicry defence against ant-averse predators, but at the price of receiving the unwanted attention of predators for which encumbered ants are preferred prey. Two salticid species were used as predators in the experiments. Portia fimbriata is known to choose other salticids as preferred prey and to avoid unencumbered ants and their mimics ( Myrmarachne females). In experiments reported here, P. fimbriata avoided encumbered ants and Myrmarachne males. Ants are the preferred prey of Chalcotropis gulosus . In our experiments, C. gulosus chose safer encumbered ants in preference to more dangerous unencumbered ants, chose Myrmarachne males more often than Myrmarachne females and showed no evidence of distinguishing between Myrmarachne males and encumbered ants. The cost of reconciling sexual dimorphism with Batesian mimicry appears to be that Myrmarachne males attract the unwanted attention of specialist predators of their compound model.

Newly emerged Batesian mimicry protects only unfamiliar prey

“…Evolution should favour Batesian mimics differing from their unprotected ancestors and resembling the model in as many features as possible. Some observations from nature, describing behavioural Batesian mimicry (e.g., similar way of movement in droneflies and hymenopterans- Golding and Edmunds 2000;Golding et al 2001;Srygley 2004 or the evidence of compound mimicry in ants and their spider mimic- Nelson and Jackson 2006), are in concordance with this prediction.…”

A Predator's Perspective of the Accuracy of Ant Mimicry in Spiders

“…Nevertheless, P. fimbriata generally avoided lures of male M. bakeri, suggesting that mimicry among males, despite possessing some cost in terms of diminished efficacy of mimicry due to their enlarged chelicerae, is still effective at deterring visually based predators. This supports the idea that the shape of the chelicerae of male Myrmarachne is in keeping with its mimicry because it looks like an ant worker carrying something in its mandibles [21], as is commonly observed in worker ants [6].…”

“…Although Myrmarachne can distinguish conspecifics and other mimics from ants [24][25][26], current evidence suggests that non-ant-like salticids are unable to make this distinction [4,21]. The question of interest in this study is whether accuracy of ant mimicry, as judged by humans, is reflected in predator behaviour.…”

“…Additionally, species in the large salticid genus Myrmarachne are sexually dimorphic as adults [20], with males seeming to be rather poor mimics due to their greatly enlarged chelicerae. Nevertheless, previous findings have suggested that males actually resemble ants carrying something in their mandibles [21]. In other words, they appear to be the Batesian mimics of a compound model (an ant plus the object it is carrying).…”

Regional Seismic Song Differences in Sky Island Populations of the Jumping Spider Habronattus Pugillis Griswold (Araneae, Salticidae)

“…E-mail: elias@utsc. utoronto.ca Forster 1982aForster ,1982bRichman 1982;Clark & Uetz 1990, 1993Tarsitano & Jackson 1992, 1997Edwards & Jackson 1994;Jackson & Pollard 1996;Harland et al 1999;Harland & Jackson 2000, 2002Nakamura & Yamashita 2000;Taylor et al 2000Taylor et al , 2001Clark & Morjan 2001;Jackson et al 2005;Li & Lim 2005;Nelson et al 2005;Hoefler & Jakob 2006;Nelson & Jackson 2006;Su & Li 2006). However, recent research has highlighted the utilization of seismic (vibratory) songs during courtship displays (Jackson 1977(Jackson , 1982Edwards 1981;Gwynne & Dadour 1985;Maddison & Stratton 1988a, 1988bNoordam 2002;Elias et al 2003) and a few studies have demonstrated that these seismic songs are crucial for mating success (Elias et al 2004(Elias et al , 2005(Elias et al , 2006a.…”