Annual Abundances, Diversity and Growth Potential of Gymnamoebae in a Shallow Freshwater Pond

ABSTRACT. Abundance and diversity of gymnamoebae were assessed at monthly intervals for one year in the sediment surface layer of a shallow, highly productive, freshwater pond located in northeastern United States using laboratory culture enumeration techniques. The range in total abundance was 81/ml in January to 1,568/ml in June (spring peak) and 1,813/ml in October (autumn peak). The latter is equivalent to over 1.8 million per liter, one of the highest values reported for gymnamoebae from a freshwater pond. Maximum diversity (H = 3.3) occurred in April, July, and August. The growth potential of the gymnamoebae was determined in laboratory cultures (20° C) containing only the pond water (control culture) and pond water emended with malt-yeast extract and glucose (nutrient culture) using pond water collected in December. The total abundance of gymanmoebae increased from 363/ml in the initial pond water sample to approximately 1,800/ml in each of the culture conditions in the first week. Therafter, abundances reached 5,678/ml (control culture) and 8,016/ml (nutrient culture) by the third week indicating the vigorous growth potential from winter standing stock.     

Maximizing information in systematic revisions: a combined molecular and morphological analysis of a cryptic green pitviper complex (Trimeresurus stejnegeri)

Although the integration of DNA information in taxonomy has been invaluable, logistical problems relating to sampling can seriously limit its applicability. Here we describe the analysis of a morphologically cryptic species complex, in which we maximize the information present by using both a DNA phylogeny and a multivariate morphometric approach. The green pitviper Trimeresurus stejnegeri s.l. is widespread in Asia, with a number of described subspecies (some of which are considered full species by some workers) and two new species that have recently been described from Thailand. The phylogeny indicates three clades, which can also be discerned in the principal component analyses of morphological variation. Combining molecular and morphological information permits evaluation of the taxonomic position of populations not represented in the phylogeny − in particular, the subspecies T. s. chenbihui and T. s. yunnanensis . We discuss nomenclatural issues raised by this analysis, although these cannot be fully resolved until the holotypes of these subspecies can be examined. Finally, we apply a molecular clock calibrated in New World pitvipers, and discuss some of the palaeoclimatic changes that might have impacted upon diversification in this group.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 219–235.     

A Previously Undescribed Method of Song Matching in a Species with a Single Song “Type”, the Kentucky Warbler (Oporornis formosus)

The song of male Kentucky warblers consists of several repetitions of syllables containing 2 to 7 elements within a frequency range from 1.8 to 6.0 kHz. Each male has a single, individually distinctive song type that spans part or all of this frequency range. Song responses to playbacks of songs artificially elevated or lowered in frequency by 200 Hz show that a bird is able to alter its song in two ways. It may lower or raise the frequency range of the song or put more energy into the lower or higher frequencies within the song's elements to more closely match the energy distribution of the playback song. The syllable or element structure of the song is kept constant with only the song's energy distribution among frequencies changing. Thus, Kentucky warblers are able to alter their single song type to “match countersing” in a way similar to that of species with song repertoires who switch song types to match those of rivals. The Kentucky warbler may have a single songtype because of its ability to change its song's energy distribution. This ability may perform the same functions as song matching does in species with larger repertoires. This finding is discussed in relation to ideas on the evolution of song repertoires in intrasexual competition.     

Fish community changes after minimum flow increase: testing quantitative predictions in the Rhône River at Pierre-Bénite, France

1. Many aspects of the flow regime influence the structure of stream communities, among which the minimum discharge left in rivers has received particular attention. However, instream habitat models predicting the ecological impacts of discharge management often lack biological validation and spatial generality, particularly for large rivers with many fish species. 2. The minimum flow at Pierre‐Bénite, a reach of the Rhône river bypassed by artificial channels, was increased from 10 to 100 m³ s^?1 in August 2000 (natural mean discharge 1030 m³ s^?1), resulting in a fivefold increase in average velocity at minimum flow. Fish were electrofished in several habitat units on 12 surveys between 1995 and 2004. 3. Principal components analysis revealed a significant change in the relative abundance of fish species. The relative abundance of species preferring fast‐flowing and/or deep microhabitats increased from two‐ to fourfold after minimum flow increase. A change in community structure confirmed independent quantitative predictions of an instream habitat model. This change was significantly linked to minimum flow increase, but not to any other environmental variables describing high flows or temperature at key periods of fish life cycle. The rapidity of the fish response compared with the lifespan of individual species can be explained by a differential response of specific size classes. 4. The fish community at Pierre‐Bénite is in a transitional stage and only continued monitoring will indicate if the observed shift in community structure is perennial. We expect that our case study will be compared with other predictive tests of the impacts of flow restoration in large rivers, in the Rhône catchment and elsewhere.     

Very-broad-scale assessment of human impacts on river condition

1. Management of whole rivers and river catchments requires a comprehensive set of information about river condition and use, both existing and historical, and the links between them at regional, state or national scales. This paper outlines a new approach to the assessment of river condition, using a small team was able to assess 210 000 km of rivers across more than 3 million km² of Australia in little more than a year. 2. The approach was driven by a hierarchical model of river function, which assumed that broad‐scale catchment characteristics affect local hydrology, habitat features, water quality and, ultimately, aquatic biota. The model provided the basis for selecting important ecologically relevant features that indices should represent. For each reach of each river we derived a biological index and an environmental index based on measures quantifying catchment and hydrological condition, and habitat and water quality condition. Data came from existing state and national databases, satellite images, site measurements and process models. 3. All indices were calculated as deviation from a reference condition, were range‐standardised and were divided into equivalent bands of condition. Amalgamation of index components and of sub‐indices was determined by consideration of their ecological effects; for example, general degradation might be additive, but toxic effects of one component would override all others. 4. Several internal and external validation methods were employed, with the all‐important validation of the final assessments undertaken by comparison with a similar index based on locally measured data. 5. The environmental assessment classified 14% of reaches as largely unmodified, 67% as moderately modified and 19% as substantially modified by human impacts. The biological assessment based on site assessments and modelled data using invertebrates indicated that 70% of reaches were equivalent to reference condition and that 30% were significantly impaired. Catchment disturbance, elevated sediment and nutrient loads, and habitat degradation all contributed to these results. These impacts have all occurred during the last 200 years (post‐European settlement). 6. Partly as a result of the assessments of this study the Australian Government has begun to adopt a more environmentally sustainable approach to broad‐scale water management.     

Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa

Lystrosaurus is one of the few therapsid genera that survived the end-Permian mass extinction, and the only genus to have done so in abundance. This study identifies which species of Lystrosaurus have been recovered from Permian and Triassic strata to determine changes in the species composition across the Permo–Triassic (P–T) boundary in the Karoo Basin of South Africa. Data generated from museum collections and recent fieldwork were used to stratigraphically arrange a total of 189 Lystrosaurus specimens to determine which species survived the extinction event. Results reveal that L. curvatus and L. maccaigi lived together on the Karoo floodplains immediately before the extinction event. L. maccaigi did not survive into the Triassic in South Africa. L. curvatus survived, but did not flourish and soon became extinct. Two new species of Lystrosaurus , L. murrayi and L. declivis , appeared in the Early Triassic. It is possible that L. murrayi and L. declivis occupied different niches to L. maccaigi and L. curvatus , and had special adaptations that were advantageous in an Early Triassic environment. We suggest that L. maccaigi may be used as a biostratigraphic marker to indicate latest Permian strata in South Africa and that, in support of previous proposals, the genus Lystrosaurus should not be used as a sole indicator of Triassic-aged strata. Our field data also show that L. curvatus may be regarded as a biostratigraphic indicator of the P–T boundary interval.     

Mechanism of Mitochondrial Mutation in Yeast

THE yeast Saccharomyces cerevisiae can mutate to the respiratory-incompetent petite colony form. The mutation is probably caused by damage to, or loss of, the yeast's mitochondrial DNA, for petite mutants often lack mitochondrial DNA, possess it in abnormal amounts or with abnormal buoyant density¹. Some of the agents, such as acrifiavine or ethidium bromide, which induce the petite mutation interfere with mitochondrial DNA synthesis^2,3 whereas ethidium bromide also causes or permits degradation of Saccharomyces cerevisiae mitochondrial DNA^2,3. We have observed that nalidixate (50 µg/ml.), an inhibitor of DNA synthesis, can prevent or delay petite mutation induced by ethidium bromide⁴. A similar effect has been observed by Hollenberg and Borst using a higher nalidixate concentration⁵. We have investigated the mechanism of this effect. A diploid prototrophic strain of Saccharomyces cerevisiae (NCYC 239) was used throughout.     

Role of the Host Cell in Bacteriophage Morphogenesis: Effects of a Bacterial Mutation on T4 Head Assembly

In certain bacterial mutants, called groE, T4 phage head assembly is blocked specifically, implying that the host plays a direct role in head assembly. The block occurs early in the assembly process at the level of action of T4 gene 31.