Freshwater ostracodes in Quaternary permafrost deposits from the Siberian Arctic

Ostracode analysis was carried out on samples from ice-rich permafrost deposits obtained on the BykovskyPeninsula (Laptev Sea).A composite pro file was investigated that covers most of a 38-m thick permafrostsequence and corresponds to the last ca.60 kyr of the Late Quaternary.The ostracode assemblages aresimilar to those known from European Quaternary lake deposits during cold stages.The ostracode habitatswere small,shallow,cold,oligotrophic pools located in low centred ice wedge polygons or in small ther-mokarst depressions.In total,15 taxa,representing 7 genera,were identi fied from 65 samples.The studiedsection is subdivided into six ostracode zones that correspond to Late Quaternary climatic and environ-mental stadial-interstadial variations established by other paleoenvironmental proxies:(1)cold and dryZyrianian stadial (58 53 kyr BP);(2)warm and dry Karginian interstadial (48 34 kyr BP);(3)transitionfrom the Karginian interstadial to the cold and dry Sartanian stadial (34 21 kyr BP);(4)transition fromthe Sartanian stadial to the warm and dry Late Pleistocene period,the Allerød (21 14 kyr BP);(5)transition from the Allerød to the warm and wet Middle Holocene (14 7 kyr BP);and (6)cool and wetLate Holocene (ca.3 kyr BP).The abundance and diversity of the ostracodes will be used as an additionalbioindicator for paleoenvironmental reconstructions of the Siberian Arctic

Endemism, speciation and adaptive radiation in great lakes.

Evolution in great lakes has often been both quantitative (many endemic species of distantly related taxa often being present) and qualitative (outstanding levels of adaptive radiation having sometimes been achieved). These situations pose many questions, such as why there are so many endemics and so many superspecialists (and at the same time often many sibling species), as well as presenting problems relating to such matters as convergent evolution in different lakes, the possible role of key innovations, the nature of isolating mechanisms, competition and co-existence in complex communities, the roles of diverse mutualistic associations, and many others. These rich faunas also provide particularly favourable opportunities for studying patterns of speciation, while attempts to elucidate phylogenies in groups such as African cichlid fishes, that have radiated in several lakes, can be pursued on both a broad scale and at the intralacustrine level using both recently developed techniques and time-honoured methods. Rates of evolution, which differ widely between ecologically equivalent taxa in different lakes, have sometimes been extremely rapid, as attested by both molecular data and evidence from field studies. Notwithstanding their evolutionary exuberance, these rich faunas are fragile as demonstrated dramatically by the appalling tragedy that has befallen the haplochromine cichlid flock of Lake Victoria