It is notably thanks to its size (20% of the total surface liquid freshwater of the world and a depth of more than 1600m), age (at least 20 million years) and isolation of the lake Baikal that its amphipod crustaceans have developed an unprecedented adaptive radiation. More than 270 species have been described from the lake (totalling 20% of the world's freshwater species), and some Russian researchers speculate at least as many are still waiting to be discovered. Moreover, these amphipod species present a huge rate of endemism, as 95% of the Baikal gammarids are only known from that lake; the remainder 5% are Baikal-originating species which succeeed in invading the lake outlet, the Angara river (which flows into the Ienissei).
Another particularity: Baikal amphipods show an impressive variety of forms and sizes (see some pictures), of trophic types and habitats. It resulted in astonishing phenomena of evolutive convergence with the marine species, especially those of Antarctica.
Moreover, Baikal amphipods are characterised by the world's most extensive size range. The adult size of these animals varies from 2 to 90mm (the worldwide record for freshwater gammarids - compare with the maximum size of 37mm of the British species). The study of these organisms carried out at the Royal Belgian Institute of Natural Sciences has resulted in a new hypothesis explaining polar gigantism, according to which the amount of dissolved oxygen determines the maximum potential size of these animals.
Baikal amphipods are not only appreciated by biologists, but also by the fishes that live over the lake bottoms and widely prey on these crustaceans, some of which, in response, having developped large lateral spines (see pictures).
Two sucessive expeditions (1995 & 1996) to lake Baikal have yielded more than 100 species belonging to 25 genera, ranking the Royal Belgian Institute of Natural Sciences' collections amongst the richest in the world, particularly with respect to the biggest species. It is also at our Institute that a handful of species have been studied in captivity, for the first time outside the ex-USSR.
Conception: P. DAUBY &
G. CHAPELLE - © IRSNB, August 1999