Patterns of divergence in the olive sunbird Cyanomitra olivacea (Aves: Nectariniidae) across the African rainforest–savanna ecotone

In the debate over modes of vertebrate diversification in tropical rainforests, two competing hypotheses of speciation predominate: those that emphasize the role of geographical isolation during glacial periods and those that stress the role of ecology and diversifying selection across ecotones or environmental gradients. To investigate the relative roles of selection versus isolation in refugia, we contrasted genetic and morphologic divergence of the olive sunbird (Cyanomitra olivacea) at 18 sites (approximately 200 individuals) across the forest–savanna ecotone of Central Africa in a region considered to have harboured three hypothesized refugia during glacial periods. Habitats were characterized using bioclimatic and satellite remote‐sensing data. We found relatively high levels of gene flow between ecotone and forest populations and between refugia. Consistent with a pattern of divergence‐with‐gene‐flow, we found morphological characters to be significantly divergent across the gradient [forest versus ecotone (mean ± SD): wing length 60.47 ± 1.81 mm versus 62.18 ± 1.35 mm; tarsus length 15.51 ± 0.82 mm versus 16.00 ± 0.57 mm; upper mandible length 21.77 ± 1.09 mm versus 23.19 ± 0.98 mm, respectively]. Within‐habitat comparisons across forest and ecotone sites showed no significant differences in morphology. The results show that divergence in morphological traits is tied to environmental variables across the gradient and is occurring despite gene flow. The pattern of divergence‐with‐gene‐flow found is similar to that described for other rainforest species across the gradient. These results suggest that neither refugia, nor isolation‐by‐distance have played a major role in divergence in the olive sunbird, although ecological differences along the forest and savanna ecotone may impose significant selection pressures on the phenotype and potentially be important in diversification. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 821–835.     

Calanoid–cyclopoid interactions: evidence from an 11-year field study in a eutrophic lake

1. The interactions between calanoid and cyclopoid copepods were examined in an 11-year field study of a eutrophic lake (Heiligensee, Berlin, Germany).
2. A diminishing ratio of calanoids to cyclopoids was observed. The responses, however, were species specific. While two cyclopoid species responded with increased populations ( Cyclops vicinus, Thermocyclops oithonoides ), one species exhibited marked declines ( C. kolensis ). Other species extended the duration of their pelagic phase ( Mesocyclops leuckarti, Diacyclops bicuspidatus, T. oithonoides, C. vicinus ), leading to higher population overlaps. Eudiaptomus graciloides and E. gracilis, which used to be present throughout the year, were more frequently absent.
3. These changes coincided with a series of mild winters during which prey availability (algae and rotifers) was high.
4. Enhanced prey availability, in conjunction with a flexible diapausing strategy, are hypothesized to underly the increased success of C. vicinus . Predatory losses due to early occurrence and enhanced abundances of C. vicinus, rather than competition for the same food resources, are hypothesized to be responsible for the declines of C. kolensis and Eudiaptomus .
5. Summer species tended to develop higher abundances early in the season, which led to enhanced seasonal means during spring. These changes cannot be explained by the interaction between calanoids and cyclopoids alone, but were probably a result of changes in fish predation.     

Dose-rate and Mutation Frequency after Irradiation of Mouse Spermatogonia

Mathematical expressions relating dose-rate and mutation frequency and their fit to low dose-rate data are considered.     

Peroxidase and α-Amylase Activities in Relation to Germination of Dormant and Nondormant Wheat

Germination capacity, and α-amylase production in relation to the peroxidase and isoperoxidase activities in the grains of three varieties of wheat have been analysed and compared. A high percentage of germination and α-amylase producation at 25°C are associated with low peroxidase activity of the isolated embryo. This correlation is lacking when the intact grain is considered. A 2-day treatment at 4°C which further increases the percentage germination and enhances α-amylase synthesis, lowers the activity of peroxidase in the embryos. A general decrease in activity of all the isoenzymes is observed. Based on the above data and on differences in the activity of the most cathodic isoperoxidasic bands, a hypothesis is put forward which suggests that a sufficiently low peroxidase activity and a minimum auxin level of the embryo are responsible for the onset of germination.     

The circatidal rhythm of the estuarine gastropod Hydrobia ulvae (Gastropoda: Hydrobiidae)

Intertidal animals display a suite of cyclic behaviours that evolved as adaptations to the predictable cycle of inundation and exposure. In estuarine habitats, mud snails from the genus Hydrobia are among the most abundant grazers, and have received considerable attention with respect to the behavioural mechanisms mediating locomotion, dispersal, and feeding, although the nature of the control of these processes has remained elusive. In particular, it is not clear whether endogenous activity patterns are related to periodic changes of microphytobenthos biomass at the sediment surface, or whether they are timed to the tidal cycle at all. In the present study, we address the crawling activity of Hydrobia ulvae under constant conditions, as well as the effects of individual size and previous short‐term exposure to tides of different range, by recording immersed individual snails under constant dark conditions. We show that the species displays an overt circatidal pattern of crawling, with activity peaks around high water, and that the start of inundation may act as an entrainment agent of the rhythm. Moreover, the results obtained indicate that smaller snails display higher levels of activity, although neither the size nor previous in situ influence of tidal range has an effect on the period and on the amplitude of the rhythm. These findings suggest that fluctuations of microphytobenthos biomass are not a sufficiently strong selective pressure to have shaped locomotor activity in H. ulvae. Moreover, feeding of H. ulvae should take place mostly during high water and be independent of periodic fluctuations of microphytobenthos biomass at the surface of the sediment. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 439–450.     

α-Amylase in the Barley Grain Influenced by the Auxin-Cytokinin Interaction in the Coleoptile

Two phases are distinguished in the α-amylase production in barley (Hordeum vulgare) grains. There is an increase in activity extended to the third or fourth day of germination, then a slight decrease follows. This decrease is accelerated by kinetin while it is prevented by IAA applied at the top of the embryo coleoptile. IAA reverses partially the kinetin action. IAA applied in the germination medium has practically no effect. Removal of the coleoptile stops further increase in α-amylase activity and induces complete insensitivity to hormone treatment. The results indicate that auxin metabolism in the coleoptile participates in the control of α-amylase evolution in the barley grain and that kinetin could act through auxin metabolism in this coleoptile.