Moulting cycles

Moulting in mammals is a cyclic phenomenon which often occurs in a wave–like pattern. The moult cycle depends upon an inherent rhythm of activity in the hair follicles, which may be modified by systemic factors. In laboratory rodents a number of hormones affect the timing of the moult, as well as affecting the amount of hair produced and the loss of club hairs.
In Microtus agrestis a seasonal moult results in a sparse coat with coarse hairs in summer and a dense coat with fine hairs in winter. The moult appears to be adjusted to the environment by way of the endocrine system, with adrenal and thyroid hormones, as well as sex hormones, involved in the regulation. The importance of such adaptive coat changes are discussed.     

Naegleria lovaniensis tarasca New Subspecies, and the Purepecha Strain, a Morphological Variant of N. I. lovaniensis, Isolated from Natural Thermal Waters in Mexico

Amoebae were isolated from a natural thermal water source in Michoacaan, Mexico, in September 1986. Two 500-ml samples were taken from pools with water at 45°C and 46°C and concentrated at 2,000 g for 15 min. The sediment was seeded on nonnutritive agar plates and incubated at 42°C. The isolates were axenized in bactocasitone-serum medium. The identification of the isolates was based on their morphology, total protein and isoenzyme patterns by agarose isoelectric focusing, serology, fine structure, agglutination with Concanavalin A, sensitivity to trimethoprim, capacity to kill mice, and their cytopathic effect in Vero cells. The results showed several morphophysiological, biochemical and serological differences between the isolates and the type strain Aq/9/1/ 45D of Naegleria lovaniensis. These remarkable differences provide sufficient evidence to consider one of the isolates a new subspecies, and the other one a morphological variant of N. l. lovaniensis, which can be differentiated from other Naegleriae by their morphology, biochemistry, serology and physiology. The authors propose the name tarasca for the subspecies and purepecha for the morphological variant.     

Myxosporidian Parasites from the Fish of the River Lugg

SYNOPSIS. Six different species of Myxosporidia were recorded from fish of the River Lugg. Myxobolus muelleri, M. artus, M. macrocapsularis, Henneguya zschokkei, H. psorospermica and H. oviperda .
Leuciscus cephalus, L. leuciscus and Rutilus rutilus infected with M. muelleri were common; of these 3 hosts, L. cephalus had the highest intensity of infection and the greatest number of infected organs and tissues. M. muelleri was compared from all the different infection sites each month where possible, from the same host ( i.e., L. cephalus ) and from the same site on different hosts (i.e. from the gills of all 3 hosts). No seasonal variation in occurrence, spore shape or size was found for M. muelleri , but spore size varied depending on the host and site of infection.
Tailed and tailless forms of H. zschokkei were found on L. leucicus and H. oviperda on E. lucius . Only tailless H. psorospermica were found.
Variations in spore form and size are discussed in relation to their use as taxonomic characters.     

Accessory Buds in the Genus Rubus with Particular Reference to R. idaeus L.

Accessory (secondary) axillary buds occurred in 21 out of 32Rubus species, including wild raspberry, R. idaeus L. The adaptivevalue of the secondary-bud character is discussed. Disbuddingexperiments on three raspberry cultivars and their inbred derivativesrevealed considerable variability in proportion of secondarylaterals developing and in numbers of flowers per secondarylateral, suggesting the possibility of selection for high secondarycrop potential.     

Production of benthic macroinvertebrate communities along a southern Appalachian river continuum

1. Annual production was estimated for macroinvertebrate communities of principle habitats along a first- to seventh-order river continuum in the southern Appalachian Mountains (U.S.A.). Annual production was relatively low in depositional habitats, pebble/gravel substrata, and on cobble devoid of plant biomass (mosses and hydrophytes). Production was greater in bedrock habitats and greatest on hydrophyte-covered cobble, with estimates reaching 364 g AFDM (ash-free dry mass)m^–2 yr^–1 in a sixth-order river reach. Annual production in depositional habitats was correlated to standing crops of benthic organic material (BOM) in low-order stream reaches but not in higher-order reaches, indicating differences in BOM availability with stream size. In cobble, pebble/gravel and bedrock habitats production was significantly correlated to standing crops of aquatic plants, which can stabilize substrata and enhance access of collector-filtering invertebrates to entrained food resources. 2. By accounting for proportional availability of habitats along the continuum, estimates of total production ranged from 5 to 154 g AFDM m^–2 yr^–1, and increased significantly with stream size. Annual production estimated for sixth- and seventh-order reaches of the continuum were amongst the highest reported thus far for lotic systems. Organization of the benthic community along the continuum, based on production estimates for individual functional feeding-groups, generally supported predictions of the River Continuum Concept (RCC): shredder contributions were greatest in low-order reaches and declined downstream; scraper percentages were greatest in the middle of the continuum; collector-filterer contributions increased with increasing stream size. Longitudinal trends for collector-gatherers and predators did not support RCC predictions; these groups appeared to be influenced by localized changes in habitat availability and occurrence of vertebrate predators along the continuum.     

Microsatellite DNA polymorphism confirms reproductive isolation and reveals differences in population genetic structure of cryptic pipistrelle bat species

Previous studies have indicated that the common European pipistrelle bat ( Pipistrellus pipistrellus ) comprises two cryptic species, P. pipistrellus and Pipistrellus pygmaeus , which differ in echolocation call frequency and mitochondrial DNA sequence. However, levels of divergence based on nuclear markers have not been examined, and hence the potential for male-mediated gene flow between the species cannot be discounted. Moreover, little is known about population structure and migration patterns in either species. Here, we describe the use of microsatellites to investigate nuclear DNA differentiation between, and the pattern of population genetic structure within, the two cryptic pipistrelle species. In total, 1300 individuals from 82 maternity colonies were sampled across the British Isles and Continental Europe. We show, using multivariate analyses, that colonies of the same species are generally genetically more similar to each other than to those from the other species regardless of geographical location. Our findings support the hypothesis that the species are reproductively isolated. Significant patterns of genetic isolation by distance were identified in both species, indicating that mating may occur before any long-distance autumnal migration. The presence of a sea channel does not confer higher levels of genetic differentiation among colonies over and above distance alone in either species. Differences in genetic population structure were identified between the species, with P. pipistrellus showing a wider range of levels of genetic differentiation among colonies and a stronger relationship between genetic and geographical distance than P. pygmaeus . Differences in dispersal, mating behaviour, colony size and/or postglacial colonization patterns could contribute to the differences observed.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 539–550.     

The effect of methanogen growth on mineral substrates: will Ni markers of methanogen‐based communities be detectable in the rock record?

Methanogens, thought to be present on early Earth, have a high requirement for Ni, suggesting that Ni utilization could be a potential biosignature for methanogens if enhanced Ni extraction from surrounding minerals accompanies methanogenic growth. To test the potential for such Ni extraction from minerals by methanogens, Ni release from Ni‐containing silicate glass was measured in Ni‐free growth medium in the presence of the methanogen Methanothermobacter thermoautotrophicus (average pH ∼7.0) and observed to be higher than an abiotic control (average pH ∼6.8). However, batch dissolution experiments and a siderophore assay indicate that cell exudates such as siderophores, low molecular weight organic acids, or lysates accompanying cell death are not responsible for the observed increase in Ni release rate. In addition, scanning electron microscopy (SEM) shows little to no evidence of direct microbe–mineral interactions such as biofilms or pitting. Instead, comparison with abiotic experiments suggests that changes in pH due to CO₂ uptake may be responsible for enhanced dissolution in the presence of metabolizing cells. These results document that methanogens may not preferentially extract Ni from surrounding minerals although they may indirectly affect mineral reaction rates that are pH sensitive. Thus identifiable Ni biosignatures may not exist in the rock record to document the presence of methanogens on early Earth or Mars.     

Taxonomy, distribution and nesting biology of species of the genus Dolichovespula (Hymenoptera, Vespidae)

The genus Dolichovespula consists provisionally of 18 species. Aerial nest site characteristics have been established for seven species but most of these species show flexibility in their choice of nest sites and two species often nest in shallow subterranean situations. Colony length is usually just over 3 months to approximately 4 months, but at lower latitudes may extend to more than 5 months. Mature colony size is usually approximately 1000 cells with more large cells than small cells. Parasitized colonies have a shorter colony cycle and smaller colonies. During the production of the sexual brood the larva/worker ratio reaches its lowest value of approximately 2.5 larvae per worker. Colonies often have upper mixed combs of small and large cells. Total adult production is usually less than 2000 adults. Colonies of D. arenaria and D. norwegica may specialize in mainly producing males or queens. Variations in mature colony size and production of queens is probably a consequence of the number of workers present, particularly early in the colony cycle.