Different preference reactions of three Lake Baikal endemic amphipods to temperature and oxygen are correlated with symbiotic life

Thermopreference reactions and avoidance sensitivity to dissolved oxygen levels were measured in three endemic amphipod species from Lake Baikal: Eulimnogammarus verrucosus and E. vittatus, as well as Brandtia parasitica, which is a symbiont of the Baikalean sponge, Lubomirskia baikalensis. The benthic E. vittatus and E. verrucosus demonstrated highly developed thermopreference reactions, whereas B. parasitica did not show thermopreference behaviour. The experimental results also showed that E. vittatus and E. verrucosus avoid water with decreased dissolved oxygen levels, whereas behavioural reactions of B. parasitica did not depend on oxygen concentration. In the presence of sponge fragments, individual B. parasitica moved actively towards them, and concentrated on those fragments. Possible reasons for reduction of behavioural preference in B. parasitica are discussed with a focus on the species' symbiotic status. Les reactions de preferences a la temperature et la sensibilite d'evitement par rapport aux niveaux d'oxygene dissous ont ete mesurees chez trois especes d'amphipodes endemiques du lac Baikal: Eulimnogammarus verrucosus et E. vittatus, ainsi que Brandtia parasitica, qui est un symbiote de l'eponge endemique Lubomirskia baikalensis. Les especes benthiques E. vittatus et E. verrucosus ont demontre des reactions de preferences a la temperature hautement developpees, tandis que B. parasitica n'en montrait pas. Les resultats experimentaux ont aussi montre que E. vittatus et E. verrucosus evitaient l'eau ayant des niveaux bas d'oxygene dissous, tandis que les reactions comportementales de B. parasitica ne dependaient pas de la concentration en oxygene. En presence de fragments d'eponge, les individus de B. parasitica se deplacaient activement vers eux, et se concentraient sur ces fragments. Les possibles raisons de la reduction des preferences comportementales chez B. parasitica sont discutees avec une attention particuliere au statut symbiotique de l'espece.