West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

A putative driver of global amphibian decline is the panzootic chytrid fungus Batrachochytrium dendrobatidis (Bd). While Bd has been documented across continental Africa, its distribution in West Africa remains ambiguous. We tested 793 West African amphibians (one caecilian and 61 anuran species) for the presence of Bd. The samples originated from seven West African countries - Bénin, Burkina Faso, Côte d''Ivoire, Ghana, Guinea, Liberia, Sierra Leone - and were collected from a variety of habitats, ranging from lowland rainforests to montane forests, montane grasslands to humid and dry lowland savannahs. The species investigated comprised various life-history strategies, but we focused particularly on aquatic and riparian species. We used diagnostic PCR to screen 656 specimen swabs and histology to analyse 137 specimen toe tips. All samples tested negative for Bd, including a widespread habitat generalist Hoplobatrachus occipitalis which is intensively traded on the West African food market and thus could be a potential dispersal agent for Bd. Continental fine-grained (30 arc seconds) environmental niche models suggest that Bd should have a broad distribution across West Africa that includes most of the regions and habitats that we surveyed. The surprising apparent absence of Bd in West Africa indicates that the Dahomey Gap may have acted as a natural barrier. Herein we highlight the importance of this Bd-free region of the African continent - especially for the long-term conservation of several threatened species depending on fast flowing forest streams (Conraua alleni (“Vulnerable”) and Petropedetes natator (“Near Threatened”)) as well as the “Critically Endangered” viviparous toad endemic to the montane grasslands of Mount Nimba (Nimbaphrynoides occidentalis).     

Effects of the winter beechmast crop on bird occurrence in British gardens

Capsule Woodland birds were significantly less likely to occur in gardens in years of high beechmast crop.

Aim To test the hypothesis that woodland species that feed on beechmast will have significantly lower occurrence rates at garden feeders in mast years.

Methods Weekly winter occurrence rates at garden feeders between 1970/71 and 1999/2000 for 40 species were analysed in relation to annual beechmast abundance, classified into low, medium and high years. A repeated-measures logistic regression model was used to assess whether beechmast abundance explained further significant variation additional to underlying seasonal and annual trends.

Results Seven species that commonly feed on beechmast showed significantly lower occurrence in gardens in years of highest beechmast abundance: Great Spotted Woodpecker Dendrocopos major, Woodpigeon Columba palumbus, Great Tit Parus major, Coal Tit Periparus ater, Nuthatch Sitta europaea, Jay Garrulus glandarius and Chaffinch Fringilla coelebs. Blackbird Turdus merula and Siskin Carduelis spinus, which showed similar significant patterns, are likely to take beechmast as elements of their diet. Pied Wagtail Motacilla alba was the only insectivorous species to show significant effects, but occurrence was lowest in years of intermediate beechmast abundance. For the latter species, this may have been due to confounding effects of temperature, but there were no such confounding effects of either temperature, or the number of bird feeders provided in gardens, for the other nine species.

Conclusion Use of artificial food sources by birds in gardens is influenced by resources in the surrounding countryside, suggesting that food provided in gardens may play a significant part in the population dynamics of these species, that population monitoring without consideration of the garden habitat may be deficient, and that volunteer-based garden bird recording may provide data that can be used as an indicator of changes in the wider countryside.     

Isolation of sulfate‐reducing bacteria from deep sediment layers of the pacific ocean

Bacterial populations exist at great depths in marine sediments, but little is known about the type and characteristics of organisms in this unique bacterial environment. Cascadia Margin sediments from the Pacific Ocean have deep bacterial activity and bacterial populations, which are stimulated around a gas hydrate zone (215–225 m below sea floor [mbsf]). Bacterial sulfate reduction is the dominant anaerobic process within these sediments, and the depth distribution of sulfate‐reducing activity corresponds with distributions of viable sulfate‐reducing bacteria (SRB). Anaerobically stored sediments from this site were used to isolate sulfate‐reducing bacteria using a temperature‐gradient system, elevated pressure and temperatures, different media, and a range of growth substrates. A variety of enrichments on lactate were obtained from 0.5 and 222 mbsf, with surprisingly more rapid growth from the deeper sediments. The temperature range of enrichments producing strong growth from 222 mbsf was markedly wider than those from the near surface sediment (15–45°C and 9–19°C, respectively). This presumably reflects a temperature increase in deeper sediments. Only a few of these enrichments were successfully isolated due to very slow or no growth on subculture, despite the use of a wide range of different media and growth conditions. Psychrophilic and mesophilic sulfate‐reducing isolates were obtained from 0.5 m depth. As the minimum growth temperature of the mesophile (probably a Desulfotomaculum sp.) was above the in situ temperature of 3°C, it must have been present in the sediment as spores. A larger number of isolates (23) was obtained from 222 mbsf, and these barophilic SRB were closely related (based on 16S rRNA gene analysis), but not identical to, Desulfovibrio profundus, recently isolated from deep sediments from the Japan Sea. Bacteria related to D. profundus may be widespread in deep marine sediments.     

Microbial degradation of high and low molecular weight polyaromatic hydrocarbons in a two-phase partitioning bioreactor by two strains of Sphingomonas sp.

A mixture of six polyaromatic hydrocarbons (naphthalene, phenanthrene, fluoranthene, pyrene, chyrysene and benzo[a]pyrene), varying in size from 2 to 5 rings, was dissolved in dodecane, and used as the delivery phase of a partitioning bioreactor. Two species of Sphingomonas were then used individually, and as a consortium, to determine which of the PAHs were degraded. Only low molecular weight PAHs (naphthalene, phenanthrene and fluoranthene) were degraded by the individual strains, but the consortium degraded all substrates either to completion or near completion.     

Epstein-Barr virus, the TCL-1 oncogene and Burkitt's lymphoma

Epstein-Barr virus (EBV) is strongly implicated in the pathogenesis of several human malignancies, but notably in all endemic and some sporadic cases of Burkitt's lymphoma (BL). Although the virus's contribution to the development of BL remains unclear, evidence now suggests that a common feature of all BL tumours is the expression of the TCL-1 oncogene. A recent report shows that TCL-1 expression in virus-positive BL tumour cells is dependent on the presence of EBV. This finding suggests that the ability of EBV to induce TCL-1 would circumvent the need for the additional genetic or epigenetic changes that lead to the constitutive expression of this oncogene in EBV-negative BL tumours.     

Studies on glycosaminoglycans of regenerating rabbit ear cartilage

Cartilage regeneration in the adult rabbit ear was examined with respect to glycosaminoglycan (GAG) synthesis at various stages of the regeneration process. Increased hyaluronic acid and chondroitin sulfate synthesis was first seen 31 days after wounding, when a metachromatic cartilage matrix could be distinguished from blastemal cells. Analysis of cartilage and the overlying skin separately showed that 90% of the labeled chondroitin sulfate was found in the cartilage being regenerated. DEAE-cellulose chromatography of GAG preparations from 35-day regenerating cartilages showed hyaluronic acid and chondroitin sulfate peaks eluting in the same position as those isolated from normal cartilages. The identity of the hyaluronic acid and chondroitin sulfate peaks was confirmed by their susceptibility to Streptomyces hyaluronidase and chondroitinase ABC, respectively. Although the degree of sulfation in normal and regenerated cartilages was similar, the ratio of chondroitin 6-sulfate to chondroitin 4-sulfate was increased in regenerated cartilages. GAG preparations from unlabeled cartilages were digested with chondroitinase ABC and the disaccharide digestive products were identified and quantitiated. Normal cartilage had a $\text{Δ}\text{Di-6S}\text{Δ}\text{Di-4S}$ ratio of 0.27; the same ratio for the regenerated cartilage was 1.58.     

Mate Choice by Chemical Cues in Western Redback (Plethodon vehiculum) and Dunn's (P. dunni) Salamanders

Western redback and Dunn's salamanders (Plethodon vehiculum and Plethodon dunni, respectively) can distinguish between potential mates by using chemical cues. In laboratory choice tests, adult males of both species showed significant discrimination between chemical cues of gravid females over non-gravid females of equal body size. Furthermore, males of both species differentiated the odour of paired gravid females that differed by ? 5 mm snout-vent length (SVL). Given that clutch size is related to female body size in these species, adult males may be able to distinguish between females via cues that signal potentially high female reproductive success. In choice tests, P. vehiculum females did not discriminate between two relatively large males that differed by ? 5 mm SVL. However, females of P. vehiculum did discriminate between two relatively small males that differed by the same amount. Apparently, P. vehiculum females ranked males by both absolute and relative body size using chemical cues. This pattern could reflect a female preference for large males or that females avoid mating with the smallest males.     

The utility of behavioral models and modules in molecular analyses of social behavior

It is extremely difficult to trace the causal pathway relating gene products or molecular pathways to the expression of behavior. This is especially true for social behavior, which being dependent on interactions and communication between individuals is even further removed from molecular-level events. In this review, we discuss how behavioral models can aid molecular analyses of social behavior. Various models of behavior exist, each of which suggest strategies to dissect complex behavior into simpler behavioral 'modules.' The resulting modules are easier to relate to neural processes and thus suggest hypotheses for neural and molecular function. Here we discuss how three different models of behavior have facilitated understanding the molecular bases of aspects of social behavior. We discuss the response threshold model and two different approaches to modeling motivation, the state space model and models of reinforcement and reward processing. The examples we have chosen illustrate how models can generate testable hypotheses for neural and molecular function and also how molecular analyses probe the validity of a model of behavior. We do not champion one model over another; rather, our examples illustrate how modeling and molecular analyses can be synergistic in exploring the molecular bases of social behavior.     

Modular Skeletal Evolution in Sticklebacks Is Controlled by Additive and Clustered Quantitative Trait Loci

Understanding the genetic architecture of evolutionary change remains a long-standing goal in biology. In vertebrates, skeletal evolution has contributed greatly to adaptation in body form and function in response to changing ecological variables like diet and predation. Here we use genome-wide linkage mapping in threespine stickleback fish to investigate the genetic architecture of evolved changes in many armor and trophic traits. We identify >100 quantitative trait loci (QTL) controlling the pattern of serially repeating skeletal elements, including gill rakers, teeth, branchial bones, jaws, median fin spines, and vertebrae. We use this large collection of QTL to address long-standing questions about the anatomical specificity, genetic dominance, and genomic clustering of loci controlling skeletal differences in evolving populations. We find that most QTL (76%) that influence serially repeating skeletal elements have anatomically regional effects. In addition, most QTL (71%) have at least partially additive effects, regardless of whether the QTL controls evolved loss or gain of skeletal elements. Finally, many QTL with high LOD scores cluster on chromosomes 4, 20, and 21. These results identify a modular system that can control highly specific aspects of skeletal form. Because of the general additivity and genomic clustering of major QTL, concerted changes in both protective armor and trophic traits may occur when sticklebacks inherit either marine or freshwater alleles at linked or possible “supergene” regions of the stickleback genome. Further study of these regions will help identify the molecular basis of both modular and coordinated changes in the vertebrate skeleton.     

Intrinsic and Extrinsic Factors Influence Expression of Defensive Behavior in Plains Hog‐Nosed Snakes (Heterodon nasicus)

Animals failing to deter predation are eaten. Among the many deterrents to predation, antipredator behaviors are perhaps the most variable, ranging from active (fight or flight) to passive (immobility). We assessed variation in the expression of a passive defensive behavior, death‐feigning, in Plains Hog‐nosed Snakes (Heterodon nasicus) and predicted that intrinsic and extrinsic factors would influence the duration of this behavior and the latency to its onset. We simulated predatory attacks on 27 snakes encountered in the field, and analyzed the behavioral responses of snakes as a function of differences among individuals (sex and size) and environmental factors (temperature and microhabitat). Larger snakes death‐feigned for longer durations than smaller ones; this relationship was stronger for female snakes than for males. Death feints were initiated sooner when snakes were encountered at higher temperatures. Extrinsic factors had a greater influence on latency to death‐feigning behavior, whereas intrinsic factors more strongly influenced its duration. Because our results involved wild snakes, they provide an improved, highly relevant understanding of individual and environmental factors that regulate the expression of immobile defensive behavior. Furthermore, additional hypotheses can now be proposed that address the evolution of defensive behaviors that leave animals prone to attack.