The Physiological Effects of Agonistic Behaviour in the Shore Crab, Carcinus maenas (L.)

Sneddon, Lynne Ure (1998) The Physiological Effects of Agonistic Behaviour in the Shore Crab, Carcinus maenas (L.). PhD thesis, University of Glasgow.

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The effects of altering resource value on agonistic behaviour were investigated by staging fights between pairs of male shore crabs, Carcinus maenas (L.) in the presence and absence of food. The nature of the agonistic behaviour of Carcinus maenas is described. The behaviour of winners and losers appears to be different from an early stage in the fights. Contests do not begin with initial display followed by a progressive increase in intensity. The fights become very intense almost immediately at the start of a bout and display acts are performed throughout the fights. As expected, there appears to be an increase in intensity in the contests with food. The duration of fights is highly variable but is significantly lower for contests when food is present than in contests without food (mean fight length 559 +/- S.E. 53 and 1143 +/- S.E. 135 seconds respectively). The results are discussed in relation to current predictions from game theory models. Relative body size (carapace width) and weapon size (chela length) were used as indicators of resource holding potential (RHP) in the agonistic behaviour of male shore crabs, Carcinus maenas (L.). Weapon size was found to be a more reliable predictor of the outcome of pairwise fights than body size. Crabs with longer chelae than their opponents were more likely to win fights than crabs with relatively larger bodies. Body size had less influence on the outcome of fights. Relative body and weapon size did not influence initiation of contests but did have an advantage with respect to winning however, this was significant only for weapon size. Winning crabs had heavier claws with greater surface area than losing crabs. There was no relationship between relative size and fight duration. The frequency of cheliped display increased with chela length and winners performed significantly more displays than losers. Weapon size has been shown to be a better predictor of fight outcome than body size in the shore crab, Carcinus maenas. However, when the weapon size disparity is small between two opponents, it is still difficult to predict the victor. The role of weapon strength in pairwise fights between male shore crabs was investigated, to determine if relative force influences contest content, duration and outcome. Weapon strength was ascertained using a force transducer on live crabs, then fights between crabs were staged between size matched males. Winning crabs had major (crusher) claws and minor (cutter) claws which exerted a significantly greater force than losing crabs even when claw length was the same. Winners and losers were matched for body size and claw length but not claw height, or claw length to the dactyl, or dactyl length. Winners had greater claw height and claw length to the dactyl in the major claw giving them a mechanical advantage when closing the claw and thus exerting a greater force. The forces exerted by the major and minor claws were analysed for any relationship between force and morphological measurements. Winning crabs appear to be fitter in having a better claw structure which exerts a greater force and are more successful in agonistic interactions. Current game theory models and recent experimental evidence suggests that the strategy an animal adopts in agonistic encounters is determined by individual state. Therefore manipulation of an individual's state should elicit different behavioural responses. In this study, we also examine mechanisms which underlie state-dependent strategies using shore crabs, Carcinus maenas and how, by altering the environment, behaviour and physiology is affected. Fights were staged between pairs of male crabs under normoxic and severely hypoxic (<15 Torr) conditions to determine if the metabolic costs of fighting and resource acquisition are affected by water P02. After fighting, blood and tissue samples from each crab were taken and analysed for metabolites associated with anaerobiosis (L-lactate, glucose and glycogen). The spectrum of behavioural acts performed during contests was unaffected by hypoxic conditions. However, fight duration was significantly shorter in the hypoxic treatment. The phenomenon of being of a larger relative size and winning had a greater influence in the contests staged under hypoxia with 93% of the victors being of a larger size compared to 78% in normoxic conditions. Fight duration and intensity had no relationship with relative size in either treatments. The accumulation of L-lactate was significantly greater in the blood and tissues of crabs after fighting under hypoxia than in normoxic conditions. In addition, there was greater glycolytic activity in the tissues of these crabs, shown by elevated concentrations of glucose in the blood and increased breakdown of glycogen. This study demonstrates that the internal state of the crabs altered the length of time they were willing to engage in fighting and that fighting was energetically more expensive under hypoxic conditions.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Felicity Huntingford
Keywords: Zoology, Physiology, Behavioral sciences
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-75893
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Dec 2019 09:15
Last Modified: 19 Dec 2019 09:15

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