Cranial anatomy of ophiderpetontid aïstopods: Palaeozoic limbless amphibians

Oestocephalus , an ophiderpetontid from the Middle Pennsylvanian of both Europe and North America provides the best known basis for evaluating the relationships of the aïstopods. All aïstopods are united by the unique manner of attachment of the skull and the first cervical in which the articulating surface of the occiput is formed by the narrow circular rim of a notochordal pit. As in other aïstopods (but in contrast with all other early tetrapods), the otic-occipital portion of the braincase is ossified as a single element. The palatoquadrate ossification extends from the orbit to the back of the area of jaw articulation. These two characters may be retained from the osteolepiform sarcopterygians. Few, if any, unique derived characters unite aïstopods with other early tetrapods. Their phylogenetic position remains enigmatic.     

The effect of increased deposition of atmospheric nitrogen on Calluna vulgaris in upland Britain

Regular (monthly) additions of NH₄NO₃ (4–12 g N m⁻² yr⁻¹) were made over a period of 8 yr (1989–98) to areas of moorland in North Wales dominated by the ericaceous shrub Calluna vulgaris . Results from the early stages of the experiment (1990–94) have shown marked and dose-related increases in shoot extension and canopy height in response to the nitrogen treatments, with significantly higher shoot nitrogen contents. The nitrogen-related stimulation in the growth of the C. vulgaris canopy over this period has resulted in large accumulations of litter on the high-nitrogen-treated plots (6.6 kg m⁻² in plots treated with 12 g N m⁻² yr⁻¹, compared with 3.8 kg m⁻² for the water controls). Litter nitrogen concentrations were also significantly increased at the higher rates of nitrogen addition, leading to a doubling of the total return of nitrogen to the litter layer over the experimental period. These changes in vegetation structure were associated with large reductions in the abundance of the bryophyte and lichen species normally present under the untreated canopy. Results since 1994, however, show little increase in shoot extension in response to the nitrogen treatments, with no clear dose response to increasing levels of addition. These findings are associated with a dose-related increase in the susceptibility of the nitrogen-treated areas of the C. vulgaris canopy to late winter injury, characterized as browning of the shoot tips in early to late spring. These results indicate that deleterious effects are now accumulating as a result of the long-term addition of nitrogen to these moorland plots.     

Effects of Tissue Collection Methods on Morphometrics and Survival of Captive Neonatal Northern Bobwhite

ABSTRACT We assessed effects of tissue collection methods (i.e., patagial microbiopsy and down feathers) and chick age at sampling on morphometrics and 21-day survival of 600 captive neonatal northern bobwhite (Colinus virginianus). We observed minimal effects on morphometrics and no difference in survival among patagial microbiopsy (x̄ = 0.96 ± 0.03), down feathers (x̄ = 0.92 ± 0.04), and control (x̄ = 0.86 ± 0.05) methods. DNA analysis from patagial microbiopsy, down feather, and egg tooth samples showed greater concentrations of DNA from patagial microbiopsy (x̄ = 10.28 ± 1.74 μg/ml) than either down feather (x̄ = 4.10 ± 1.74 μg/ml) or egg teeth (x̄ = 2.35 ± 1.74 μg/ml).     

Patterns of abundance of fire ants and native ants in a native ecosystem

Abstract 1. This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2. Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3. Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4. The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants.     

Are avian eggshell colours effective intraspecific communication signals in the Muscicapoidea? A perceptual modelling approach

Diversity in the colour and appearance of avian eggshells has been proposed to serve a variety of visual functions, including crypsis from predation, mimicry and discrimination in facultative and obligate brood parasitism, and sexually selected intraspecific signalling of the extent of maternal investment in the egg. Here, we apply a photoreceptor noise-limited colour opponent model of avian perception to assess a necessary corollary of any intraspecific signalling hypothesis, namely that individual birds are able to discriminate between colours of eggs in different conspecific clutches. Clutches from 46 species in the superfamily Muscicapoidea were measured at the Natural History Museum collection in Tring, UK. The results demonstrate that, for these particular species, most eggs are predicted not to be easily discriminable from those in other conspecific clutches in terms of the shells' background coloration. These findings are of fundamental concern to any signalling hypothesis that looks to explain the evolution of avian-visible egg colour polymorphism through selection at the intraspecific level. Importantly, future studies should combine both the proximate mechanisms and the ultimate functions of trait variability when testing hypotheses of the variability in eggshell appearance.