Seasonal changes in the concentration and colour of humic substances in some aquatic environments

SUMMARY. 1. Between February and September 1974, concentrations of fulvic and humic acids in waters from a cryoboreal region of the Precambrian Shield in Quebec varied between 0.5–6.1 mg 1⁻¹ and 0.1–6.5 mg 1⁻¹ respectively. Whereas the fulvic acids usually remained relatively constant during this period, humic acids showed appreciable increases.
2. The number and weight average molecular weights of the fulvic acids (∼5000 and ∼22,000 daltons respectively) were lower than those of the humic acids (∼20,000 and ∼75,000 daltons respectively). The average molecular weight of the aquatic humic matter often decreased during late summer and early autumn. During spring floods the molecular weight of fulvic acids increased and that of humic acids declined.
3. Because the aquatic humic acids were more intensely coloured than fulvic acids, they contributed more than 30% of the colour of the water even though they accounted for only 15% of the concentration of humic matter. The colour intensity of both fulvic and humic acids generally appeared to increase during the latter part of the summer, when there was normally a decrease in the value of the colour quotient (E₄/E₆ ratio), indicating the accumulation in the waters of more humified material.     

Genetic Architecture of Physiological Phenotypes: Empirical Evidence for Coadapted Gene Complexes

Physiological phenotypes are the result of the coordinated functionof many genes, some of which may be differentiated between conspecificpopulations. Within any one population, natural selection willfavor evolution of a coadapted set of alleles which optimizesphysiological performance and reproductive success. The existenceof such coadapted gene complexes may be assessed by assayingphenotypes of interpopulation hybrids: inferior performanceof hybrids suggests that the allelic combinations present inthe parental populations are coadapted. This approach has beenused to examine the genetic architecture of physiological traitsin the copepod Tigriopus californicus, a species characterizedby sharp genetic differentiation of populations. Developmentaltime and response to osmotic stress both show pronounced F₂hybrid breakdown, a result consistent with genetic coadaptationwithin populations. To better understand the biochemical andmolecular mechanisms underlying hybrid breakdown, we are investigatinga specific biochemical phenotype, the activity of the enzymecytochrome c oxidase (COX). COX (encoded by multiple nuclearand mitochondrial genes) catalyzes the oxidation of cytochromec (encoded by a nuclear gene). Two approaches are being usedto address the extent of coadaptation (both among nuclear genesand between nuclear and mitochondrial genes) underlying COXfunction: (1) studies of the DNA (and inferred amino acid) sequencesof component genes among populations in search of coordinatepatterns of amino acid substitution across loci, and (2) directstudies of COX function in interpopulation hybrids and backcrosses.These approaches provide evidence for the existence of nuclear/nuclearand/or nuclear/mitochondrial coadaptation within natural populationsof T. californicus.     

Use of Tetrahymena pyriformis to Evaluate the Effects of Purine and Pyrimidine Analogs1

SYNOPSIS Eighty-four purine and pyrimidine analogs were evaluated for growth inhibition of Tetrahymena pyriformis. The most toxic were 2-fluoroadenine, 2-fluoroadenosine, 6-methylpurine, a series of 5-fluoropyrimidines, and a series of adenine derivatives substituted in the 9-position. 2-Fluoroadenine was metabolized to the ribonucleoside triphosphate and was incorporated into nucleic acids; its inhibition of growth was reversed by high levels of adenine. 6-Methylthiopurine ribonucleoside was phosphorylated, but only to the monophosphate derivative. Contrasting T. pyriformis with mammalian cells gave clues to the mechanism of action of some of the agents. 6-Mercaptopurine, 6-methylthiopurine ribonucleoside, and 6-thioguanine, all potent pseudofeedback inhibitors of de novo purine biosynthesis in mammalian cells, are not toxic to T. pyriformis, which lacks the de novo purine pathway; this implies that inhibition of de novo purine biosynthesis by them underlies their growth inhibition of mammalian cells.     

The persistence of infectivity of conidia of the aphid pathogen Erynia neophidis on leaves in the field

Conidia of the aphid pathogen Erynia neophidis inoculated on to bean leaves in the field in 1980, 1981 and 1982, retained some infectivity for pea aphids for at least 14 days. Decline in infectivity occurred linearly with time. Inocula on leaves near the base of plants remained infective longer than those on leaves near the top and those on the abaxial surface remained infective for longer than those on the adaxial surface. Infectivity persisted longest in 1981 when conditions were coolest with least sun.     

Fire frequency regulates tussock grass composition,structure and resilience in endangered temperate woodlands

Abstract The importance of disturbance for regulating the structure and diversity of grassy ecosystems is widely recognized, but disturbance‐mediated interactions between grassland composition and grassland resilience, and consequent implications for conservation management, are less well documented. We established replicated burning, mowing and (non‐livestock) grazing regimes in two contrasting grassy woodland remnants in south‐eastern Australia, and monitored the dynamics and resilience of the matrix‐forming tussock grasses, Poa sieberiana (Poa) and Themeda australis (Themeda), over 12 years. Introduction of frequent burning to a Poa‐dominated understorey in a rarely burnt woodland enhanced dominance by Themeda, and conversely, reduced fire frequency in a frequently burnt Themeda grassland substantially increased Poa abundance. Burning was potentially detrimental in the Poa‐dominated woodland, but sward resilience (recovery after the 2002 burn) increased as Themeda increased with repeated burning. By contrast, the Themeda grassland was resilient to 4‐ and 8‐yearly burning, but biennial burning led to poor resilience and high tussock mortality under drought conditions. Contrary to other mesic grasslands, cessation of burning had not caused sward collapse by 14 years post‐fire despite high litter accumulation, potentially due to compensatory growth of Poa, lower site productivity and drought. Biennial mowing without slash removal was similar to 4‐yearly burning in effects, while exclusion from kangaroo and rabbit grazing significantly increased sward biomass and contributed to increased Poa cover and inflorescence production. We conclude that functional complementarity associated with mixed dominants enhances resilience to variable disturbance regimes, and that below certain thresholds of abundance of each dominant, this resilience declines. Conservation management of Themeda–Poa ecosystems should thus aim to maintain an effective balance of these dominants.     

Plasticity of functional traits varies clinally along a rainfall gradient in Eucalyptus tricarpa

Widespread species often occur across a range of climatic conditions, through a combination of local genetic adaptations and phenotypic plasticity. Species with greater phenotypic plasticity are likely to be better positioned to cope with rapid anthropogenic climate changes, while those displaying strong local adaptations might benefit from translocations to assist the movement of adaptive genes as the climate changes. Eucalyptus tricarpa occurs across a climatic gradient in south‐eastern Australia, a region of increasing aridity, and we hypothesized that this species would display local adaptation to climate. We measured morphological and physiological traits reflecting climate responses in nine provenances from sites of 460 to 1040 mm annual rainfall, in their natural habitat and in common gardens near each end of the gradient. Local adaptation was evident in functional traits and differential growth rates in the common gardens. Some traits displayed complex combinations of plasticity and genetic divergence among provenances, including clinal variation in plasticity itself. Provenances from drier locations were more plastic in leaf thickness, whereas leaf size was more plastic in provenances from higher rainfall locations. Leaf density and stomatal physiology (as indicated by δ¹³C and δ¹⁸O) were highly and uniformly plastic. In addition to variation in mean trait values, genetic variation in trait plasticity may play a role in climate adaptation.     

Perception of volatiles associated with sex and food by different adult forms of the black bean aphid, Aphis fabae

Abstract. Electroantennograms (EAGs) were recorded from adult male and asexual forms (winged and wingless virginoparae and gynoparae) of the black bean aphid, Aphis fabae , during stimulation with two sex pheromone components, (+)-(4a S ,7 S ,7a R )-nepetalactone and (-)-(1 R ,4a S ,7 S ,7a R )-nepetalactol, as well as six plant volatiles, i.e. ( E )-2-hexenal, ( E )-2-hexenol-1, ( Z )-3-hexenol-1, ( Z )-3-hexenyl acetate, hexanal and allyl isothiocyanate. The male antennae are 1000-10,000 times more sensitive to nepetalactol and nepetalactone than to the plant compound ( E )-2-hexenal. Besides this marked difference of EAG peak responses in males, the EAG rise and decay are slower for the sex pheromone components. Males are also much more sensitive to the sex pheromone components than asexual females. This high sensitivity correlates with a predominance of antennal secondary rhinaria, the major sites of pheromone perception in the male. However, it is the primary rhinaria on the antennae of the wingless asexual females that are responsible for pheromone perception. Male antennae are as responsive as the asexual female antennae to the plant volatiles. The specialization of the male for mate location is discussed.     

Life history and allozyme diversification in regional ecomorphs of the Hyalella azteca (Crustacea: Amphipoda) species complex

In North America, several species in the freshwater amphipod genus Hyalella occur as one of two alternative phenotypic types, or 'ecomorphs', each possessing life history traits that allow success in alternative habitats that differ in predation regime. This study documents life history diversification, reproductive isolation and allozyme differentiation of Hyalella ecomorphs in Oklahoma, and compares these results to previously reported patterns of phenotypic and systematic diversification in Michigan. As in Michigan, two ecomorphs are common in Oklahoma, with an early maturing, small sized ecomorph found in habitats containing Lepomis sunfish, which prey on Hyalella , and a late reproducing, large sized ecomorph found in fishless habitats and in very shallow margins of large reservoirs. Allozyme analysis and laboratory interbreeding trials demonstrated that ecomorphs in Oklahoma are reproductively isolated species. Phenotypically, these species are very similar to species of the same ecomorph in Michigan. Large ecomorph species in the two regions differ substantially in allozyme allele composition in a pattern consistent with reproductive isolation, yet these species did not differ in a comparison of phenotype. The small ecomorph in Oklahoma is similar in phenotype to two of three small ecomorph species in Michigan. Overall, this study supports the hypothesis that Hyalella diversification in North America is characterized by the evolution of similar phenotypic solutions to comparable ecological challenges.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 161–175.