Effects of salinity on the life history and fitness of Daphnia magna: variability within and between populations

Abstract

The life history traits of Daphnia magna were studied in laboratory experiments under freshwater and brackish (5%o salinity) conditions . The variability of responses within and between populations was examined by comparing 11 clones from a brackish lake and 10 clones from a freshwater pond . Experimental clones were hatched from ephippia collected from the sediment and thus represent random samples of the clone banks of each population .Most clones with a high salinity tolerance were from the population of the brackish habitat, but some were also found in the freshwater population . Thus, freshwater populations appear to have the potential to invade brackish habitats . A proportion of clones from the brackish population had very low fitness (measured as er) under freshwater conditions . This unexpected result means that freshwater adaptation can be lost by the freshwater cladoceran Daphnia magna . The effects of unfavourable conditions on growth and reproduction varied among clones and were not correlated . This clonal variation in growth and reproduction indicates that the environmental sensitivities of these traits are independent . The pattern of fitness reaction norms showed no trade-off between fitness under brackish and under freshwater conditions for either population . Thus, euryhaline generalists should be favoured in habitats with salinity fluctuations between freshwater and brackish conditions . 33

Genetic variability in the tolerance of natural populations ofSimocephalus vetulus(Müller, 1776) to lethal levels of sodium chloride

“…Many studies have shown that locally acting selective forces (particularly predation) lead to the formation of local races or "ecotypes" (local adaptation, see Weider and Hebert, 1987;De Meester, 1996a, 1996bBoersma et al, 1999;Cousyn et al, 2001;De Meester et al, 2002). This has also been reported in Daphnia populations from brackish vs. freshwater environments (Weider and Hebert, 1987;Teschner, 1995;Barry et al, 2005).…”

Salinity effects on survival and life history of two freshwater cladocerans (Daphnia magna and Daphnia longispina)

“…Additionally, growth rate of both daphnid species was also negatively affected and maturation was delayed at the highest concentrations. Similarly, Teschner (1995) concluded that clones of D. magna under brackish conditions grew more slowly and matured on average later than under freshwater conditions. Nevertheless, our results demonstrated that D. magna reproduces and lives well at salinity concentrations below 4.55 g.L -1 .…”

“…Other studies (Barron et al 2002) proved phytoplankton can adapt to salinity conditions, although this process becomes slower as NaCl concentration increases. Some algae (such as the ones belonging to the genus Dunaliella) are haloterant, growing at high saline media due to physiological adaptations, such as glycerol intracellular accumulation (Avron 1986) and a salt-induced protein (p60) present in the plasma membrane (Fisher (Teschner 1995, Schallenberg et al 2003, Rokneddine & Chentoufi 2004.…”

Environmental stress and local adaptation in Daphnia magna

“…The German clones were collected from the Großer Binnensee, a shallow slightly brackish and hypertrophic coastal lake, which contains unknown densities of mainly bream, roach, and perch (Lampert 1993), and from the Rixdorfer Pferdetränke, a small eutrophic fishless pond. These clones were used previously in life-table experiments involving different levels of salinity (Teschner 1995) and fish kairomones (Teschner unpubl. data).…”