Comportamento agonístico, deslocamento e padrões de atividade de lagostins neotropicais (Decapoda: Parastacidae)

Abstract

This study investigated the behavior of crayfishes of the genus Parastacus. Two experiments were performed: one describing and comparing the agonistic behavior of Parastacus brasiliensis and Parastacus pilimanus, in laboratory; and another experiment, in the field, where movement and activity of P. pilimanus were monitored through radio-telemetry. For the first experiment, individuals of both species were captured and taken to the lab, were they were paired according to carapace and cheliped length. Ten pairs of P. brasiliensis and thirteen of P. pilimanus, were formed, being acclimated individually. The pairs were allowed to interact for 20min, during which they were filmed. Quantifications of aggressiveness, relative aggressiveness, first bout duration, mean bout duration, number of bouts, latency period, representativity of aggressive behaviors, number of approaches, number of antennal whips and number of chela punches were made. The species were compared regarding the formation of dominance hierarchies. P. brasiliensis exhibited significantly higher values for all parameters, except latency, number of bouts and antenal whips (only winners), while P. pilimanus executed chela punch more frequently. Formation of dominance hieararchies was more frequent in P. pilimanus than in P. brasiliensis. These results point the fossorial species as less aggressive. The behavioral repertory differed from the expected for crayfish. Another difference was a non-escalated aggression. In the second phase, two campaigns were performed, one in the spring of 2010 and another in the spring of 2011. In each, five P. pilimanus were monitored for seven days through radio-telemetry. Verifications of position of crayfishes were made at 13, 19, 22, 1, 4 and 7h. Air temperature, water temperature, flow speed, dissolved oxygen, pH and conductivity were measured daily. Daily displacements were compared. The crayfish were tested for preferably diurnal/nocturnal activity, preferably upstream/downstream movements and permanence within burrows. The influence of abiotic parameters in the animal s displacement and the circadian activity were also checked. Only one crayfish presented significantly higher activity than two other crayfish. There were no significant differences between for movements. The permanence of the animals was higher within burrows than in the streambed, and none of the abiotic parameters affected movement. These results were the same for both campaigns. Between the campaigns, no differences were found for any parameters. The circadian activity analysis revealed that only three crayfish (one in 2010 and two in 2011) showed activity concentrated between 19h49min and 02h11min. The results point that P. pilimanus makes short, but frequent displacements. The high permanence within burrows characterizes this species as a primary burrower. The low dispersal potential of the studied population highlights its vulnerability towards a possible disturbs. This weak dispersion ability might also be related to the occurrence of intersexuality in the group. Both these studies relate to unknown subjects, when concerning the behavior of Neotropical crayfishes, which stand out for their differentiation, in relation to the general patterns within the Astacida, especially regarding the Northern Hemisphere species, better studied so far.