Predicting the winning or losing of symmetrical contests in the American lobster Homarus americanus (Milne-Edwards)

2007

Journal of Zoology

Mate choice is often assumed to be a prerogative of females because of their putatively larger reproductive investment than males. However, recent evidence suggests that spermatogenesis is far from being limitless and that males show a high selectivity towards their mates, thus maximizing their reproductive success. We investigated mutual mate choice in the crayfish Procambarus clarkii through two experiments. The first experiment explored the effects of body size, chelar size and chelar symmetry and social status of a potential partner. In the second experiment, we asked whether this species can discriminate between partners of the same body size but with different mating status. We used a binary choice test paradigm, in which two 'targets' with opposing characteristics were simultaneously presented to a test animal, the 'chooser'. The results showed that P. clarkii males are more selective than expected. Similar to the other sex, they were significantly attracted by targets with large body sizes, but not by individuals with larger and symmetric chelae or with a dominant status. An inter-sexual difference was found in the second experiment, in which only males seemed to select virgin potential mates. The several adaptive explanations for these preferences, still under debate, are finally discussed.

Section: Experiments 1: Morphological Characteristics and Hierarchicalsupporting

confidence: 89%

Mutual mate choice in crayfish: large body size is selected by both sexes, virginity by males only

Aquiloni

2007

Journal of Zoology

“…For instance, in the American lobster, Homarus americanus, the outcome of contests between size-matched individuals was predicted from subtle cues such as plasma protein level and exoskeleton calcium concentration (Vye et al 1997). These variables are not clearly visible to the rivals, but fighting lobsters may indirectly assess them by the effect of the above variables on claw contraction forces, the resistance of the exoskeleton to pressure, and general fighting vigour (Vye et al 1997). We did not measure these variables, so we cannot exclude their relevance in establishing dominance order and in maintaining it after the injection of bioamines.…”

Section: Discussionmentioning

confidence: 99%

Biogenic amines influence aggressiveness in crayfish but not their force or hierarchical rank

Tricarico

2007

Animal Behaviour

This study aimed at understanding the influence of biogenic amines on the agonistic behaviour of the crayfish Procambarus clarkii, a model organism for crustacean decapods. Specifically, we investigated whether the hierarchical rank of fighting individuals might be altered by injecting solutions of either serotonin or octopamine into their haemolymph. First, we assessed the effect and duration of the bioamines on the behaviour, posture, and chelar force of 60 adult males paired for size. Then, we examined their potential to modify dominance hierarchies by observing, for 2 h after the treatment, the behaviour of three categories of familiar size-matched pairs: (1) 20 'control pairs' (both individuals injected with a physiological solution), (2) 20 'reinforced pairs' (the dominant individual, alpha, injected with serotonin, and the subordinate individual, beta, with octopamine), and (3) 20 'inverted pairs' (alpha injected with octopamine and beta with serotonin). The results clearly show that the two bioamines were able to alter the posture and aggressiveness of the treated individuals in opposite directions without affecting their chelar force. However, the large majority of the 'inverted pairs' retained their former position in the hierarchy. The role that intrinsic characteristics and prior social experience play in maintaining dominance hierarchies in crayfish is discussed.

“…When the objective resource value and other factors are equal (see references in Vye et al 1997;Gherardi and Cioni 2004), body size is important in predicting the outcome of contests even when the larger crab occupies an inadequate shell (Expt. 4) (Hazlett 1966a,b;Elwood and Glass 1981;Dowds and Elwood 1985) and is more important than shell size when differences between contestants are small for these two attributes (Expt.…”

Section: Discussionmentioning

confidence: 99%

Fighting behavior in hermit crabs: the combined effect of resource-holding potential and resource value in Pagurus longicarpus

2005

Behav Ecol Sociobiol

A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of equal/ different RHP (i.e. 'body size') and equal/different RV (i.e. 'shell size' and 'shell quality'). In a fifth experiment, dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min. As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory of the previously held resource and behaved accordingly.