Paleogenetic evidence for a past invasion of Onondaga Lake, New York, by exotic Daphnia curvirostris using mtDNA from dormant eggs

Cladocerans possess traits such as resistant diapausing eggs and rapid part henogenetic reproduction that make them efficient invaders of new habitats. Nearly all known invasions have been successful, perhaps because failed in vasions are difficult to detect. It is possible, however, to identify past failed invasions, by studying the diapausing egg bank. Daphnia ephippia wer e found in the sediments of Onondaga Lake, New York that could neither be h atched nor identified using egg-case morphology. Instead, we used sequences of the 12S ribosomal ribonucleic acid (rRNA) gene of mitochondrial deoxyri bonucleic acid (mtDNA) extracted from diapausing eggs to identify the unkno wn Daphnia. We compared these DNA sequences with those generated from morph ologically identified Daphnia species collected in Onondaga Lake, and with published sequences for other North American Daphnia species. The invader w as identified as Daphnia curvirostris, a Eurasian species that has been onl y reported once before from North America, in extreme northwestern Canada. The discovery of it in Onondaga Lake signifies a greater than 4,500-km rang e extension for this species. On the basis of the sediment ephippial data, D. curvirostris first appeared in the lake about 1952, reached maximum abun dance during the period of peak pollution (1950s-1980s), and then essential ly disappeared after 1983 when lake water quality improved. As with the fin ding of another exotic cladoceran, D. exilis, in Onondaga Lake (Hairston et al. 1999a), it is likely that chemical industry activities on the lakeshor es were the original source of invading D. curvirostris, that pollution all owed this species to become established in the lake, and that the reduction in pollution ultimately led to its disappearance from the water column.