Effects of maternal diet on offspring fitness in the bird cherry‐oat aphid

1. Maternal and offspring diet effects on life‐history traits of the bird cherry‐oat aphid Rhopalosiphum padi were tested on three wheat varieties. Using nine reciprocal combinations of wheat varieties, the effects of previous experience (maternal diet effect) on the aphid's response to resistant and susceptible varieties (offspring diet effect) were tested. Batis was susceptible, and Xiaoyan22 and Ww2730 were both resistant, but with different mechanisms. 2. Aphids produced the most alatae in the treatments with the most resistant maternal diet variety Xiaoyan22. The fecundity (F) and intrinsic rate of increase (r_m) of these alatae were at their greatest in the most resistant offspring diet variety, but these traits were not influenced in the apterae. 3. There were significant interactions in the alatae production and apterae life‐history traits, such as r_m, development time, weight gain, and mean relative growth rate, between the maternal and offspring diet varieties. The interactions in apterae responses between varieties, some of which were reciprocal, indicated phenotypic plasticity in these parthenogenetic aphids. 4. Rhopalosiphum padi produced more alatae on the most resistant variety; the alatae would disperse and were more fecund. The growth responses of the apterae showed phenotypic plasticity to the different combinations of maternal and offspring diet varieties. The phenotypic plasticity would allow R. padi to better utilise the variable environments represented by the small wheat plots of different varieties in China.     

Resting egg banks can facilitate recovery of zooplankton communities after extended exposure to saline conditions

1. Salinisation has had a major effect on the diversity of biota associated with freshwater wetlands. However, there is no information available about whether elements of the biotic communities would be able to recover if the concentration of salts within secondarily salinised wetlands was lowered to levels more typical of freshwater wetlands. 2. We tested the hypothesis that dormant eggs of zooplankton are able to persist in wetlands with elevated salinities for extended periods of time by using zooplankton communities that had developed in mesocosms exposed to either salt concentrations of 13 500 mg L^?1 or freshwater (<300 mg L^?1) for a period of 22 months. We measured the response of the zooplankton community as concentration was reduced along a gradient of decreasing salinity from 13 500 mg L^?1 to freshwater. 3. In the freshwater mesocosms, the zooplankton community was abundant and taxon rich. In comparison at the start of the experiment in the high salinity mesocosms, the zooplankton community had low abundances and very few taxa. Numbers remained low in these mesocosms until salinity was reduced to <2500 mg L^?1. Below this, there was a rapid increase in the abundance, and richness of zooplankton and communities became similar to the communities in the freshwater mesocosms. 4. These results indicate that dormant eggs of zooplankton are able to persist in wetlands exposed to high salinity levels for up to 22 months and provide a means for zooplankton communities to rapidly respond once a wetland returns to freshwater. 5. It is likely that if the underlying causes of secondary salinisation in wetlands are addressed, it will be possible to undertake restoration activities that allow the rapid return of some components of their biotic communities.     

Deep chlorophyll maxima and UVR acclimation by epilimnetic phytoplankton

1. It is well established that ultraviolet radiation (UVR) has many harmful effects on phytoplankton, but the factors controlling algal sensitivity to UVR are not fully understood. 2. We exposed phytoplankton communities from the epilimnia and deep chlorophyll maxima (DCM) of 2 Canadian lakes to 14 irradiance treatments of various spectral quality and monitored changes in the maximum quantum efficiency of Photosystem II photochemistry (F_v/F_m) using a pulse amplitude modulation fluorometer. 3. Phytoplankton from DCM did not show marked differences from epilimnetic communities in taxonomy or nutrient status, but exhibited substantially higher photosynthetic impairment under UVR exposure. 4. Our results suggest that epilimnetic phytoplankton acclimate to in situ light conditions in a spectrally‐specific manner, and that ultraviolet‐A radiation is a stronger stressor than ultraviolet‐B or photosynthetically active radiation in the mixed layers of our study lakes. Model estimates of damage and recovery rate constants revealed that the phytoplankton of the two lakes relied upon different strategies of UVR‐acclimation, in one lake minimising susceptibility to photodamage and in the other maximising recovery efficiency.     

Effect of Isoxanthopterin on the Activity of Transforming DNA in <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

WHEN an aqueous solution of the pteridine, isoxanthopterin, is incubated with salmon sperm DNA, an unstable association of the pteridine with the DNA can be demonstrated by chromatography on “Sephadex”¹. One interesting property of the complex is that the fluorescence of isoxanthopterin is enhanced ten-fold, a phenomenon which has been ascribed, in other cases, to intercalation of a planar heterocycle between base pairs in the DNA double helix². If such an intimate positioning occurred, it might be possible to disrupt the structure of DNA by using radiant energy of a wavelength (345 nm) which would be absorbed by the pteridine but not by the DNA. In a living organism the result would be expressed as a mutational event, or in the extreme case, cell death. We have tested this hypothesis using a sensitive biological indicator—bacterial transformation—to observe effects at specific gene loci. For experimental convenience, changes in DNA were detected by changes in transforming ability of wild type DNA.