UVB radiation affects growth, reproduction and tissue structure of Daphnia magna across several temperatures.

We examined the effects of daily exposure to UVB on growth, reproduction and histological characteristics of Daphnia magna over two generations at 20, 22, 25 and 30°C. Animals were exposed to 16 h of UVA and photosynthetically active radiation daily. Treated animals received 6 h of UVB during the light phase. Parental (P) generation growth and reproduction was impaired by exposure to UVB at all temperatures, with the poorest production at 30°C. First brood size decreased with UVB exposure; it was lowest at 30°C. Although F1 length at birth increased with P generation age, F1 produced by UVB-exposed mothers were smaller at all temperatures. The F1 generation was followed at 20 and 25°C; at both temperatures UVB exposure reduced F1 growth and reproduction. F1 growth and F2 production were lowest when both P and F1 generations were exposed to UVB. UVB exposure damaged ovarian and gut tissue at both 25 and 30°C; the consequences of this exposure were more severe at 30°C. The observed tissue damage may relate directly to the UVB-induced impairment of growth and reproduction. This study provides new insights into the effects of UVB on an important component of the pelagic zooplankton.

Maternal influences on population dynamics: evidence from an exploited freshwater fish.

We used a field experiment, population modeling, and an analysis of 30 years of data from walleye (Sander vitreus; a freshwater fish) in Lake Erie to show that maternal influences on offspring survival can affect population dynamics. We first demonstrate experimentally that the survival of juvenile walleye increases with egg size (and, to a lesser degree, female energy reserves). Because egg size in this species tends to increase with maternal age, we then model these maternal influences on offspring survival as a function of maternal age to show that adult age structure can affect the maximum rate at which a population can produce new adults. Consistent with this hypothesis, we present empirical evidence that the maximum reproductive rate of an exploited population of walleye was approximately twice as high when older females were abundant as compared to when they were relatively scarce. Taken together, these results indicate that age- or size-based maternal influences on offspring survival can be an important mechanism driving population dynamics and that exploited populations could benefit from management strategies that protect, rather than target, reproductively valuable individuals.

The effect of chronic exposure to artificial UVB radiation on the survival and reproduction of Daphnia magna across two generations.

We examined the effects of daily (chronic) exposure to artificial UVB radiation on the survival and reproduction of Daphnia magna over two generations. Control and experimental animals in each generation (parental and F1) were exposed to 16 h of UVA radiation and photosynthetically active radiation daily. In addition, experimental animals were exposed to 6 h of UVB during the middle of the light period. Survival and reproduction were followed for 12 days for each individual. Survival and production of F1 were significantly lower in the UVB exposed parental generation Daphnia than in controls. F1 exposure to UVB significantly decreased F1 survival and reproduction. Reproduction was lowest in UVB exposed F1 animals whose parents were also exposed to UVB. Adverse effects of UVB on offspring production may be magnified in successive generations suggesting that short-term experiments could underestimate the impact of increased UVB exposure on populations.

Age-dependent survival, reproduction and photorepair activity in Daphnia magna (Straus, 1820) after exposure to artificial ultraviolet radiation.

We examined age-related vulnerability of Daphnia magna to UV-B (ultraviolet-B radiation, 280-320 nm), the age-related relationships between UV-B dosage and reproduction, and the effects of duration of PRR (photorecovery radiation) on survival and fecundity. Animals were exposed to 0, 6, 9 or 12 h UV-B (peak emission 312 nm) at 1, 2, 3 or 4 days of age and followed to 12 days. Survival decreased with increasing exposure to UV-B, but increased with age at exposure. Duration of UV-B, but not age at exposure, decreased offspring production. Survival increased with an increase in duration of PRR for animals of all ages; however, the effect was not age related. Three-day-old animals were exposed to 6 h of UV-B followed by 0-600 min of PRR. Survival was greatest in controls, lowest in the group that received no PRR and similar for all other groups. Most mortality occurred within the first 72 h postirradiation. Offspring production was highest in light controls, lowest in the UV-B-exposed group that received no PRR and not significantly different among other groups. This study demonstrates the need to consider age when examining the effects of UV-B on zooplankton and the need to monitor responses over a sufficient length of time.

Effects of maternally transferred organochlorine contaminants on early life survival in a freshwater fish.

Laboratory research has shown that female fish can pass toxic organochlorines (OCs) from their bodies to their eggs, killing their offspring if sufficient quantities are transferred. We conducted a controlled incubation study using gametes from a wild, OC-contaminated walleye (Sander vitreus) population (Bay of Quinte, Lake Ontario, Canada) in order to assess among-female variation in offspring early life survival in relation to ova concentrations of planar OCs (polychlorinated dibenzo-p-dioxins and furans and planar polychlorinated biphenyls) and a suite of other maternal and ova characteristics. Equal volumes of ova from each female were fertilized, pooled, and incubated together as an experimental cohort. Relative survival of each female's offspring was estimated as the proportion of surviving larvae (at approximately 5 d posthatch) that she contributed to the cohort as determined by microsatellite DNA parentage assignment. Total planar OC concentration (expressed as toxic equivalency of 2,3,7,8-tetrachlorodibenzo-p-dioxin) of ova was positively related to maternal age and size and to ova lipid content. However, early life survival did not decline with increasing ova planar OC concentrations. Similarly, we observed no significant relationships between early life survival and ova thiamine content, ova fatty acid composition, or maternal age or size. Early life survival was more strongly correlated with date of spawn collection, thyroid hormone status of the ova, and ovum size. Maternally transferred planar OCs do not appear to negatively influence female reproductive success in this walleye population.