Aggressive Contests in Male Jumping Spiders
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Tutorial of Elias et al.'s "Assessment during aggressive contests between male jumping spiders"
Assessment strategies are a vital factor in game theoretical models of contests. In contests animals may engage in mutual assessment; where individuals assess both their own and their opponents resource holding potential (RHP) and make decisions based on estimated differences (Prenter et al, 2006; Briffa, 2008). Alternatively, they may partake in self-assessment, in which individuals set thresholds based on their own RHP (Prenter et al, 2006; Briffa, 2008). Using a statistical methodology which enables the distinction between assessment strategies, the study examined contests in Phidippus clarus, a common jumping spider.The study had three main aims: to determine whether substrate-borne signals are important in aggressive contests, the assessment strategies used in contests, and the factors that decide contest outcomes.
Adult and penultimate male and female P. clarus were collected. They were individually housed in the laboratory for a minimum of 4 days to allow them to acclimate prior to use. The experimental arena was a plastic cylinder with petroleum jelly on the inside of the wall to prevent spiders escaping. In order to avoid visual disturbances, an opaque paper ring was placed around the cylinder. Graph paper was used as the arena floor, this allowed movement to be measured. It was replaced after every two trials to prevent chemical cue build up. An empty female nest was placed in the center of the arena.
To begin with a removable barrier split the arena into two equal sections. Randomly selected males were placed in separate halves and left to acclimate for 5 minutes. The barrier enabled acclimation and removed potential ownership effects. Contests were observed and substrate-borne vibrations were recorded using a laser droppler vibrometer. Contests were terminated after three bouts, a male was considered to have won a bout when the rival male turned away and retreated more than two body lengths. Male behaviours during aggressive interactions were divided into two phases: the precontact phase and the contact phase. The contact phase began when the two spiders started to "leg fence". During the precontact phase males produced substrate-borne signals. The signals generally preceded movement toward rivals and rarely preceded retreat. Following the contests, males were weighed and digitally photographed to measure patella-tibia length and cephalothorax width. These measurements were used as an indicator of size. A range of statistical analysis was performed on the data.
A statistical methodology outlined by Taylor and Elwood (2003) and Morrell et al (2005) was used to distinguish assessment strategies. The results indicated that contest duration, particularly contact phases, were based predominantly on self-assessment and to a lesser degree mutual assessment. It was suggested that males may shift between self-assessment and mutual assessment as more information becomes available or more reliable. In the case of partial mutual assessment, as more rival assessment occurs, a negative correlation will grow between winner weight and contest duration (Prenter et al, 2006). The study found a nonsignificant negative relationship between winner weight and contest duration. This is congruous with partial mutual assessment.
It was suggested that relying more heavily on self-assessment to determine contest duration may be an economical strategy that avoids the costs of mutual assessment. Mutual assessment requires energetic demands to detect and process a rivals signals, as well as needing time to process the information in order to make accurate decisions. These costs would be heightened if the signals were unreliable. Hence, self-assessment enables the individual to pay only the costs they are willing to but maintain a high probability of winning against inferior rivals.
The male jumping spiders used multimodal signals during aggressive interactions: visual and substrate-borne. Substrate-borne vibrations appeared to be of particular importance, given that the number of vibratory signals accurately predicted the contest outcome. More actively signaling males were more likely to win.Â Additionally, precontact phase duration was based on relative vibration behaviour. Males which vibrated at similar rates had shorter precontact phases.
Figure.1 Effect of experience on contests. (a) Differences between contest phase duration in different bouts. Both precontact and contact phase duration were significantly reduced after initial contests. (b) Difference between vibrational signalling between different contest bouts. **P < 0.001. (Elias et al, 2008)
53/56 of the males that won the first bout went on to win all three bouts. The study found contest experience affected male's signalling rate. While winners signalled repeatedly at a similar rate, losers significantly decreased the rate at which they signalled after losing the first bout (Fig. 1b). As well as this, experience affected the time that males spent in contest. Both precontact and contact phases were notably shorter in the second and third bouts (Fig.1a). This indicates that experience effects are important for multiple contests with the same opponent in P. clarus. In the field, males would most likely escape after losing a single contest, so repeated bouts with the same individual may be rare. However, these results important because they highlight that experience, especially losing experience, can influence subsequent behaviours. Following these results an area that needed more research is the impact of experience on future contests with new rivals and the duration of these effects.
This is addressed in a later paper by Kasumovic et al (2010). They found that winner and loser effects have a similar magnitude, but loser effects persist longer. They also found previous experience alters actual fighting ability. They suggested that experience should be integrated into models, particularly when competitive signals or traits are unreliable.
Arnott and Elwood (2009) also wrote a subsequent paper which encouraged game theorists to update models. The paper explored how the abilities of contestants to assess RHP influences fights. The paper cited Elias et al (2008) to support the existence of partial mutual assessment. They stated that strategies, such as partial mutual assessment, point to limitations of current game theory models. Arnott and Elwood's (2009) work has been influential, with further work finding winner and loser effects change with age, which is often a disregarded factor in studies (Fawcett and Johnstone, 2010).
Arnott, G. and Elwood, R.W. (2009) 'Assessment of fighting ability in animal contests', Animal Behaviour, 77(5), pp. 991-1004.
Bridge, A.P., Elwood, R.W. and Dick, J.T.A. (2000) 'Imperfect assessment and limited information preclude optimal strategies in male-male fights in the orb-weaving spider Metellina mengei', Proceedings of the Royal Society B: Biological Sciences, 267(1440), pp. 273-279.
Briffa, M. (2008) 'Decisions during fights in the house cricket, Acheta domesticus: Mutual or self assessment of energy, weapons and size?', Animal Behaviour, 75(3), pp. 1053-1062.
Elias, D.O., Kasumovic, M.M., Punzalan, D., Andrade, M.C.B. and Mason, A.C. (2008) 'Assessment during aggressive contests between male jumping spiders', Animal Behaviour, 76(3), pp. 901-910.
Fawcett, T.W. and Johnstone, R.A. (2010) 'Learning your own strength: Winner and loser effects should change with age and experience', Proceedings of the Royal Society B: Biological Sciences, 277(1686), pp. 1427-1434.
Kasumovic, M.M., Elias, D.O., Sivalinghem, S., Mason, A.C. and Andrade, M.C.B. (2010) 'Examination of prior contest experience and the retention of winner and loser effects', Behavioral Ecology, 21(2), pp. 404-409.
Morrell, L.J., Backwell, P.R.Y. and Metcalfe, N.B. (2005) 'Fighting in fiddler crabs Uca mjoebergi: What determines duration?', Animal Behaviour, 70(3), pp. 653-662.
Prenter, J., Elwood, R.W. and Taylor, P.W. (2006a) 'Self-assessment by males during energetically costly contests over precopula females in amphipods', Animal Behaviour, 72(4), pp. 861-868.
Prenter, J., Elwood, R.W. and Taylor, P.W. (2006b) 'Self-assessment by males during energetically costly contests over precopula females in amphipods', Animal Behaviour, 72(4), pp. 861-868.
Taylor, P.W. and Elwood, R.W. (2003) 'The mismeasure of animal contests', Animal Behaviour, 65(6), pp. 1195-1202.
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