Species-Specific Daphnia Phenotypes: A History of Industrial Pollution and Pelagic Ecosystem Response

Abstract

Phenotypic differences among species, even closely related species, may translate into distinct effects on ecosystem dynamics. In lakes, the generalist grazer genus Daphnia often has marked effects on the abundance of primary producers, the rate of primary production, and rates of nutrient cycling. The effects are particularly distinct during the clear-water phase (CWP) when algal biomass is driven to extremely low values as Daphnia densities undergo an annual population increase. Here we show that the timing of the CWP in Onondaga Lake, New York, USA, has depended upon which Daphnia species were present in the water column. An analysis of the ephippia and diapausing eggs from the sediments reveals that long-term changes in the zooplankton species assemblage tracks a history of chemical (especially salt waste) pollution. Prior to 1930 the assemblage was dominated by native D. pulicaria and D. ambigua. From 1930 to 1980, these species were replaced by D. exilis and D. curvirostris, two salinity-tolerant exotic species native to shallow salt pools of the southwestern United States and coastal brackish ponds of Europe, respectively. As industry was progressively shut down by government action over the period from the 1970s to the 1980s, the exotic species disappeared, and the two native taxa returned (plus D. galeata mendotae, which is also native to the region). As we have shown previously, the exotic species were identified either by hatching and rearing diapausing eggs (D. exilis) or by analysis of eggs using mtDNA (D. curvirostris). We interpret their role in seasonal algal dynamics in Onondaga Lake retrospectively using data collected in prior studies of the lake. The native Daphnia currently cause a typical spring CWP in late May and early June, whereas the exotic species caused an unusual late-summer (August-October) CWP during the period of maximum cyanobacterial density.

Prey evolution on the time scale of predator–prey dynamics revealed by allele-specific quantitative PCR

“…However, the question remains whether the effects of rapid evolution on algalconsumer dynamics that we have documented here are important in nature. For example, are temporal changes in the densities of lake phytoplankton and zooplankton, such as the well-known clear-water phase dynamics observed in many tem-perate lakes (31,32), and the wide variation in algal food quality to grazers within and among lakes (33,34), influenced importantly by the level of algal genetic diversity available when acted upon by the natural selection imposed by grazers? (UTEX 26, 30, 265, 395, 396, 1803, 1809, 1911, and 2714).…”

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

“…Boronat et al (2001) demonstrated that cladoceran species have different halotolerances, ranging from fresh to saline water bodies, with D. longispina being estenohaline (range 0.5-1.2 g.L -1 ) and D. magna euryhaline (range 3.8-38 g.L -1 ). In fact, D. magna is one of the most halotolerant Daphnia species (Cowgill & Milazzo 1990, Rokneddine & Chentoufi 2004, Do Hong et al 2004, Hairston et al 2005. Tackx et al (2004) observed that cladocerans were mostly present in the freshwater part (<0.7 p.s.u.…”

“…(2) nia, in particular, is more or less tolerant to salinity and the differences among species can produce distinct effects in the system dynamics, such as in the abundance of primary producers, the rate of primary production and rates of nutrient cycling (Boronat et al 2001, Hairston et al 2005. As an example, euryhaline Daphnia magna lives in fresh, brackish and athalassohaline waters, while daphnids from the longispina group (D. longispina, D. galeata, D. cucullata) prefer waters with low mineralization and are very sensitive to magnesium, for example (e.g., concentrations above 0.6 g.L -1 become lethal for them) (Alonso 1996).…”

Multi-proxy studies in palaeolimnology

“…animal hairs Hodgson et al 1998, phytoliths Carnelli et al 2004, fish scales Davidson et al 2003), well-known proxies are being used in new ways, using newly developed analytical techniques and improved chronologies to estimate amounts and rates of change through time, and using new approaches to detect morphological or genetic changes in response to environmental change (e.g. Weider et al 1997;Kerfoot et al 1999;Cattaneo et al 2004;Hairston et al 2005). …”