Reproductive dependence of a branchiobdellidan annelid on its crayfish host: confirmation of a mutualism

The ectosymbiotic branchiobdellidan Cambarincola ingens Hoffman, 1963 can increase the growth and reduce mortality of the crayfish Cambarus chasmodactylus James, 1966. These results suggest that these two species are engaged in a cleaning symbiosis mutualism. However, the potential benefits C. ingens derives from the association, specifically its reproductive dependence on the crayfish, have not been examined experimentally. We conducted two experiments to determine if C. ingens was reproductively dependent on C. chasmodactylus. In the experiments, worms only laid cocoons on live crayfish. Also, significantly more cocoons were laid on larger crayfish which was consistent with a survey of worm and cocoon abundance on crayfish collected from a local river. These results suggest that C. ingens is dependent on its crayfish host for reproduction. The association between C. chasmodactylus and C. ingens is a mutualism, at least under environmental conditions in which crayfish survival and growth are enhanced by the worms.

Chemical Integration of Myrmecophilous Guests inAphaenogasterAnt Nests

Social insect nests provide a safe and favourable shelter to many guests and parasites. InAphaenogaster senilisnests many guests are tolerated. Among them we studied the chemical integration of two myrmecophile beetles,Sternocoelis hispanus(Coleoptera: Histeridae) andChitosa nigrita(Coleoptera: Staphylinidae), and a silverfish. Silverfishes bear low quantities of the host hydrocarbons (chemical insignificance), acquired probably passively, and they do not match the colony odour. Both beetle species use chemical mimicry to be accepted; they have the same specific cuticular hydrocarbon profile as their host. They also match the ant colony odour, but they keep some specificity and can be recognised by the ants as a different element.Sternocoelisare always adopted in other conspecific colonies ofA. seniliswith different delays. They are adopted in the twin speciesA. ibericabut never inA. simonelliiorA. subterranea. They are readopted easily into their mother colony after an isolation of different durations until one month. After isolation they keep their hydrocarbons quantity, showing that they are able to synthesize them. Nevertheless, their profile diverges from the host colony, indicating that they adjust it in contact with the hosts. This had never been demonstrated before in myrmecophile beetles. We suggest that the chemical mimicry ofSternocoelisis the result of a coevolution withA. seniliswith a possible cleaning symbiosis.