Molecular response to climate change: temperature dependence of UV‐induced DNA damage and repair in the freshwater crustacean Daphnia pulicaria

Abstract

In temperate lakes, asynchronous cycles in surface water temperatures and incident ultraviolet (UV) radiation expose aquatic organisms to damaging UV radiation at different temperatures. The enzyme systems that repair UV-induced DNA damage are temperature dependent, and thus potentially less effective at repairing DNA damage at lower temperatures. This hypothesis was tested by examining the levels of UV-induced DNA damage in the freshwater crustacean Daphnia pulicaria in the presence and absence of longer-wavelength photoreactivating radiation (PRR) that induces photoenzymatic repair (PER) of DNA damage. By exposing both live and dead (freeze-killed) Daphnia as well as raw DNA to UV-B in the presence and absence of PRR, we were able to estimate the relative importance and temperature dependence of PER (light repair), nucleotide excision repair (NER, dark repair), and photoprotection (PP). Total DNA damage increased with increasing temperature. However, the even greater increase in DNA repair rates at higher temperatures led net DNA damage (total DNA damage minus repair) to be greater at lower temperatures. Photoprotection accounted for a much greater proportion of the reduction in DNA damage than did repair. Experiments that looked at survival rates following UV exposure demonstrated that PER increased survival rates. The important implication is that aquatic organisms that depend heavily on DNA repair processes may be less able to survive high UV exposure in low temperature environments. Photoprotection may be more effective under the low temperature, high UV conditions such as are found in early spring or at high elevations.

Zooplankton vertical migration and plasticity of pigmentation arising from simultaneous UV and predation threats

“…In addition to pigmentation and vertical migration, zooplankton use other survival strategies as responses to UV radiation: for example, photo-enzymatic repair of DNA and screening substances like MAAs (MacFadyen et al 2004;Moeller et al 2005). Repair processes in copepods are reported by several authors, but the importance of these processes is not well understood (Zagarese et al 1997;Rocco et al 2002).…”

“…UV radiation may penetrate deeply into clear waters (Kirk 1994), and several studies show that suppressed reproduction and increased mortality among zooplankton (Crustacea) can be attributed to UV exposure (Williamson et al 1994;Zagarese et al 1994;Leech and Williamson 2000). In defense, zooplankton have a number of different UV protection strategies, including cell repair systems, vertical migration, and photo-protective pigments (Hairston 1976;MacFadyen et al 2004;Hansson et al 2007). Photo-protective pigmentation among copepod zooplankton is induced by UV radiation, resulting in increased carotenoid pigmentation (Hansson 2000).…”

Comparative physiological, biochemical, and molecular thermal stress response profiles for two Unionid freshwater mussel species

“…These declines most likely result from a combination of physical habitat modification, point source pollution, sedimentation, invasive species, and warming temperatures due to climate change (as reviewed by Hastie et al, 2003). Warming trends have already caused alterations in thermal structure and water quality (Cruise et al, 2000; reviewed by Caissie, 2006), resulting in downstream effects on primary producers, migratory fishes and macroinvertebrates (Davis et al, 2013;Harper and Peckarsky, 2006;MacFadyen et al, 2004;O'Reilly et al, 2003;Winder et al, 2009). Ecosystem-level functional alteration may be especially pronounced within the state of Alabama, a renowned biodiversity hotspot for freshwater fauna, particularly fishes, crayfish and mollusks (Lydeard and Mayden, 1995).…”

Effects of experimental warming and increased ultraviolet B radiation on the Mediterranean plankton food web

“…However, few multifactorial experiments have been dedicated to studying the effect of multiple global change stressors on aquatic ecosystems, and very few have studied the effects at several trophic levels. For example, it has been found that the effect of UVBR may be temperature dependent because temperature enhances photo-enzymatic repair (Williamson et al 2002;MacFadyen et al 2004). Another study (Doyle et al 2005) has shown that the effect of UVBR on phytoplankton growth is not only temperature dependent but also nutrient dependent.…”