Behavioural and Physiological Studies of Fighting in the Velvet Swimming Crab, Necora puber (L.) (Brachyura, Portunidae)

Thorpe, Kathleen Elaine (1994) Behavioural and Physiological Studies of Fighting in the Velvet Swimming Crab, Necora puber (L.) (Brachyura, Portunidae). PhD thesis, University of Glasgow.

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The velvet swiming crab, Necora piiber (L.), is a marine brachyuran commonly found in shallow, rocky, sublittoral areas on the Atlantic coasts of Europe. In Britain, the commercial importance of N. puber has increased over the last fifteen years, following the collapse of the Spanish fishery for this species, and the crab now forms the basis of an important fishery based mainly off the west coast of Scotland. N. puber has traditionally been regarded as "aggressive", due mainly to its rapid defensive response of striking and grasping humans who attempt to handle them, but relatively little was known of their intra-specific agonistic behaviour until the work of Smith (1990; Smith & Taylor 1993; Smith et al. 1994) on males. The aims of the work in this thesis were: to describe the intra-specific agonistic behaviour of females in relation to the size of the interactants, and to investigate the initiation, outcome and content of fights; to describe the processes of escalation and communication during fights in males and females; to investigate the metabolic consequences of fighting and exercise in males; and, to investigate the behavioural consequences of any metabolic costs incurred by the contestants during agonistic behaviour by examining the effects of prolonged fights in subsequent agonistic responses. The agonistic behaviour of N. puber is compared with the predictions of game theory. The agonistic displays of female N. puber are similar to those described for other portunids, particularly the closely related Liocarcinus depurator, and identical to those of male N. puber. Female N. puber fight readily in the laboratory, with interactions being initiated equally often by the larger and smaller of two opponents, but with the larger usually being victorious. In some interactions, however, a smaller crab won against a larger opponent, and possible reasons for this are discussed. In two respects, the results are surprising in the context of insights gained from game theory: firstly, the fights do not show a gradual pattern of escalation through display to overt physical violence. Secondly, fights do not become more costly in terms of either potential for injury (intensity) or duration as the contestants became more evenly matched; indeed, as the contestants became more evenly matched, fight duration decreased. In both males and females, a short term escalatory process was apparent in intra-individual sequences, with winners and losers tending to follow their own previous low risk acts with high risk acts. However, this process was weaker and shorter lived in losers, which tended to de-escalate after performing high risk acts; winners sustained high intensity fighting by matching or escalating following the performance of high risk acts. Looking at inter-individual sequences to examine the process whereby crabs react to the behaviour of their opponent, one clear trend was a tendency for both winners and losers to match the behaviour of the opponent when this involved low risk acts, but winners and losers respond differently to high risk acts with the winners escalating or matching more frequently than losers. The different communicatory significance of the agonistic acts are discussed. The metabolic consequences of agonistic behaviour in male N. puber were quantified by measuring the concentrations of L-lactate and D-glucose in the haemolymph, and L-lactate, D-glucose and glycogen in the walking leg muscle. There were no significant differences between fought and unfought crabs in terms of the parameters measured, but concentrations in fought and unfought crabs were significantly different from those in crabs forced to exercise. There appears, therefore, to be a very limited metabolic cost associated with agonistic behavour in N. puber. There were no significant differences between winners and losers in the metabolic parameters measured, and it can be inferred from this that there is no metabolic threshold reached that forces crabs to give up. Previous agonistic behaviour did not alter the behaviour of male crabs in subsequent fights. Fought crabs were as likely to initiate a subsequent interaction as unfought crabs, and fought crabs were also equally likely to be successful as unfought crabs. First fights and subsequent re-fights were of similar duration, content and intensity. Again, this suggests that agonistic behaviour in male N. puher is not sufficiently metabolically expensive to impose constraints on any subsequent behaviour. The results of these studies are discussed on a functional basis in relation to the predictions arsing from game theory and on a causal level in relation to possible mechanisms underlying the behaviour.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Felicity Huntingford
Keywords: Zoology, Physiology, Behavioral sciences
Date of Award: 1994
Depositing User: Enlighten Team
Unique ID: glathesis:1994-76339
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 15:24
Last Modified: 19 Nov 2019 15:24

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