Palaeolimnological evidence of Bosmina morphotypes appearance in the late Holocene

Lacustrine sediments retain Cladocera (Crustacea) subfossils (carapaces, ephippia, head shields, and postabdomens) from the Holocene, which allows reconstructing past aquatic communities and environmental changes. In late Holocene (Subatlantic) fossils, among many Cladocera species, we noticed the appearance of several Bosmina (Eubosmina) species in lakes surrounding the Baltic Sea. These species were never recorded in the early Holocene. The appearance of these species is a record of very recent speciation, which took place during the last millennium in lakes surrounding the Baltic Sea. Contemporary data show co-occurrence of several Bosmina (Eubosmina) species (longispina, kessleri, reflexa, ruehei, coregoni, gibbera, thersites). These species are not a product of invasion or introgressive hybridization, but in fact, they are probably a product of speciation. Here, we present the palaeolimnological evidence of this speciation from the only one species, Bosmina (Eubosmina) longispina, found in lacustrine sediments from the last interglacial and glacial periods.