Subfossil chydorid (Cladocera, Chydoridae) ephippia as paleoenvironmental proxies: evidence from boreal and subarctic lakes in Finland

Abstract

Chydorids (Cladocera, Chydoridae) have two reproductive strategies: asexual reproduction that prevails during favorable environmental conditions and sexual reproduction that is induced by environmental stimuli associated with seasonal or aperiodic environmental stresses. These modes of reproduction can be recognized in the subfossil sedimentary records as parthenogenetic shells of females (asexual reproduction) and by ephippia (sexual reproduction). We studied the interrelations between subfossil chydorid ephippia and environmental variables by analyzing surface sediment samples obtained from 76 Finnish lakes across a latitudinal gradient (60-70°N). The results showed that the total chydorid ephippia (TCE) increases along the climate gradient from *2 to 3% in the south to *25% in the north and suggested a significant dependence (r * -0.8, P \ 0.001) with several climate factors, especially that of mean July air temperature. We used this relationship to create a model for reconstructing past mean July air temperatures. A linear regression of the log 10 transformed TCE as a single independent variable explained 76% (SE ± 0.76°C) of the variance of the observed mean July air temperatures. Accordingly, we propose that this novel tool may be highly suitable for reconstructing paleotemperatures in cold-temperate environments.

Climate variability and lake ecosystem responses in western Scandinavia (Norway) during the last Millennium

“…The fossil Cladocera and ephippium analyses were performed in the laboratory according to the standard procedure described in Frey (1986). Microscope slides were prepared from 0.1ml of each sample and examined with a microscope (Olympus BX41 (Kultti et al, 2011;Nevalainen and Luoto, 2013).…”

Midge distribution patterns at multiple spatial scales in shallow Finnish lakes revealed through sedimentary records

“…The distance from the littoral vegetation (DLV) was measured and determined by examining aerial photographs and field observations and stream flow was determined simply by dividing the samples following their lotic or lentic distribution. For more details and other measured environmental parameters, consult the previous publications (Luoto 2009a, Luoto & Helama 2010, Luoto & Salonen 2010, Nevalainen & Luoto 2010, Kultti et al 2011.…”

Cladoceran (Crustacea) Niches, Sex, and Sun Bathing—A Long-Term Record of Tundra Lake (Lapland) Functioning and Paleo-Optics

“…suggesting less environmental stress (lower sexual reproduction) during the recent centuries. Sexual reproduction in Cladocera is evidenced in the fossil record through their ephippia and has previously been investigated in relation to climate oscillation, i.e., open-water season length, which dictates the relative importance of asexual (parthenogenetic) vs. sexual (gamogenetic) reproduction [28,43]. Accordingly, it has been suggested that sexual reproduction is less significant (lower sexual reproduction) during warm climate conditions as asexual reproduction prevails under long open-water season.…”