Habitat type determines the effects of disturbance on the breeding productivity of the Dartford Warbler Sylvia undata

Numerous studies have examined the causes and impacts of human disturbance on birds, but little is known about how these impacts vary among habitats. This is of applied importance both for predicting bird responses to changes in disturbance and in planning how to reduce disturbance impacts. The Dartford Warbler Sylvia undata , a key heathland breeding species, occupies territories in a range of heathland types. Three territory habitat groups were identified: heather-dominated territories, heather territories with significant areas of European Gorse Ulex europaeus and territories containing Western Gorse U. gallii . Productivity was significantly affected by the timing of breeding in all habitats, but disturbance only appeared to have a significant impact on the productivity of birds in heather territories. Disturbance events in heather territories delayed breeding pairs for up to 6 weeks. This significantly decreased both the number of successful broods raised and the average number of chicks fledged per pair. Nests situated close to territory boundaries in heather territories, with high numbers of disturbance events, were more likely to fail outright. It was determined that an average of between 13 and 16 people passing through a heather territory each hour would delay breeding pairs sufficiently to prevent multiple broods.     

Clarifying the Taxonomic Identity of a Phylogenetically Important Group of Eukaryotes: Planomonas is a Junior Synonym of Ancyromonas

ABSTRACT. Ancyromonas was first described in 1882 by Saville Kent, with the modern concept of the genus dating from 1979 with the work of Hänel. Since then, organisms assigned to Ancyromonas have been found to be common in diverse ecosystems, and the group's isolated phylogenetic placement renders it of considerable evolutionary interest. However, in 2008 Cavalier‐Smith et al. concluded that all modern accounts of Ancyromonas were of a different organism from that described by Saville Kent, and erected the new genus Planomonas to encompass modern observations of Ancyromonas, and several new species. We critique the rationale for creating this new genus, reexamining the original sources and making additional observations using light and electron microscopy. We find that almost all the differences between the genera are mistaken or insubstantial. In particular, (1) Cavalier‐Smith et al. characterized Ancyromonas sensu Saville Kent as anchoring and Planomonas as gliding, while we find that each type of organism actually does both, and (2) it was claimed that Planomonas is flattened while Ancyromonas sensu Saville Kent is not, but this argument is inconsistent. We treat Planomonas as a junior synonym of Ancyromonas, and Planomonas mylnikovi as a junior synonym of Ancyromonas sigmoides. We transfer Planomonas cephalopora, Planomonas micra, Planomonas howeae and Planomonas limna to Ancyromonas. The genus Ancyromonas therefore includes: A. sigmoides, Ancyromonas cephalopora n. comb., Ancyromonas melba, Ancyromonas sinistra, Ancyromonas micra n. comb., Ancyromonas howeae n. comb., and Ancyromonas limna n. comb.     

Measurement of Cell Wall Volume using Confocal Microscopy and its Application to Studies of Forage Degradation

The distribution of cell wall material between different plantcell types may contribute significantly to the variation indegradability of plant material with a similar overall chemicalcomposition but different anatomy. Assessment of the degradabilityof cell walls in a section suitable for digestion is a three-dimensional(3-D) problem because of the thickness of section required (50–100µm). Optical sectioning of thick sections using confocallaser scanning microscopy (CLSM) provides a method of estimatingthe volume of cell wall material present in tissue sectionsbefore and after digestion, and of visualizing the plant tissueusing 3-D image reconstruction. The use of CLSM enables degradabilitymeasurements to be made on cellsin situand can provide moreimmediate and relevant information than can be obtained by mechanicalfractionation of the tissues. The CLSM method has been usedto visualize thick sections taken from maize and barley internodesbefore and after degradation with cell wall degrading enzymes.Quantitative measurements of cell wall volume and mean cellwall thickness were made on a series of optical sections, andthe potential of the method for quantitation of cell wall degradabilityis assessed. Image analysis; plant anatomy; confocal microscopy; degradation; maize     

Anterior/Posterior Influences on Neural Crest-Derived Pigment Cell Differentiation

The neural crest of vertebrate embryos has been used to elucidate steps involved in early embryonic cellular processes such as differentiation and migration. Neural crest cells form a ridge along the dorsal midline and subsequently they migrate throughout the embryo and differentiate into a wide variety of cell types. Intrinsic factors and environmental cues distributed along the neural tube, along the migratory pathways, and/or at the location of arrest influence the fate of neural crest cells. Although premigratory cells of the cranial and trunk neural crest exhibit differences in their differentiation potentials, premigratory trunk neural crest cells are generally assumed to have equivalent developmental potentials. Axolotl neural crest cells from different regions of origin, different stages of development, and challenged with different culture media have been analyzed for differentiation preferences pertaining to the pigment cell lineages. We report region-dependent differentiation of chromatophores from trunk neural crest at two developmental stages. Also, dosage with guanosine produces region-specific influences on the production of xanthophores from wild-type embryos. Our results support the hypothesis that spatial and temporal differences among premigratory trunk neural crest cells found along the anteroposterior axis influence developmental potentials and diminish the equivalency of axolotl neural crest cells.