Toe pad morphology and mechanisms of sticking in frogs

Sticking ability in frogs was measured on a series of different substrates. Analysis of performance suggests that frogs use two sticking mechanisms: interlocking on rough surfaces and capillarity on smooth surfaces. There is a correlation between morphological specializations of the toe pad and sticking ability, but these morphological features are not unique to arboreal species. Terrestrial species that use leaves as resting sites during times of inactivity have many of the same morphological specializations and stick as well as the strictly arboreal species.     

A Man Out of Place: Herbert Spencer Jennings at Johns Hopkins, 1906-1938

Herbert Spencer Jennings (1868–1947) succeeded W. K. Brooksas Director of the Zoological Laboratory at Johns Hopkins Universityin 1910. His scientific work in the next two decades includedexperimental genetics of protozoa and mathematical analysisof the linear arrangement of chromosomes. At the same time,Jennings was involved in philosophical discussions of the natureof biological thought. His point of view expressed the biologist'sawareness of diversity and historical process, against boththe excesses of vitalism and of the modern reductionist methodsof physico-chemical biology. These philosophical discussionsare seen against the background of his difficulty in buildingup the zoological laboratory at Johns Hopkins in the 1920s,when the university tried unsuccessfully to return to the idealof pure research which had guided it under its first president.Moreover, Jennings faced strong competition for resources fromwithin the university itself, especially at the medical school.His position illustrates the predicament of the modern generalbiologist in an environment increasinglydominated by the medicalsciences     

The diversification of South American murid rodents: evidence from mitochondrial DNA sequence data for the akodontine tribe

Phylogenetic relationships based on 801 base pairs (bp) of the mitochondrial cytochrome b gene are examined for eight genera and 28 species of the akodontine tribe of South American murid rodents. The akodontine tribe comprises some 35% of the total diversity of the subfamily Sigmodontinae, but the current taxonomy at virtually all levels is uncertain because of inadequate generic diagnoses and assessments of variation and trends in traditional morphological characters. Monophyly of the tribe cannot be resolved by the sequence data, based on comparisons to outgroup taxa in three other tribes (Oryzomyini, Phyllotini, and Thomasomyini). However, highly corroborated monophyletic units within the group are obtained in a variety of both parsimony and distance analyses. These include a redefined and numerically dominant genus Akodon (with Microxus and Hypsimys as synonyms), Bolomys, Lenoxus, Oxymycterus, and a strongly supported assemblage that includes the central Andean Chroeomys and 'Akodon' andinus and the southern Abrothrix, 'Akodon' olivaceus, and the long-clawed mice of the genera Notiomys, Geoxus, and Chelemys. Sequence divergence within species is typically less than 5%, although levels can reach 10% for some highly polytypic forms. Divergence among genera within the tribe reaches 35% in corrected estimates, a level that is as great as that among representatives of different tribes. Changes in the current classification of akodontines are suggested based on these data, and the timing and place of origin of the tribe and its radiation is discussed.     

Evaluation of Rhodamine 123 As A Probe For Monitoring Mitochondrial Function In Trypanosoma Brucei Spp.

ABSTRACT. Rhodamine 123, a membrane potential-specific dye, has been evaluated as a probe to monitor the function of the mitochondrion in long slender bloodstream and procyclic trypomastigotes of several Trypanosoma brucei spp. By epifluorescence microscopy, mitochondrial development has been followed in long slender bloodstream and procyclic organisms stained with rhodamine 123. to photograph stained long slender bloodstream forms, it was necessary to develop a method to completely immobilize viable organisms. In both parasite forms, as the cell cycle progressed, the mitochondrion developed from a thread-like structure to a highly branched organelle. A dramatic reorganization occurred preceding cytokinesis to produce two progeny thread-like structures which were partitioned into newly formed daughter cells. the organelle within the long slender trypomastigote was found to stain optimally at 0.3 μ/ml of rhodamine 123, while the procyclic form required 3.0 μ/ml. the results suggest that the plasma membrane potential is higher in the long slender parasite than in the procyclic form. the effects of inhibitors that disrupt mitochondrial function were examined in long slender and procyclic parasites, and some of these agents were shown to affect rhodamine 123 accumulation and retention. In long slender trypomastigotes the trypanosome alternative oxidase does not appear to be coupled to proton pumping, whereas in procyclic organisms the effects of inhibitors indicate that this oxidase may be coupled to a pathway that is branched preceding an antimycin A₁-sensitive site.     

Assessment of diet choice by the yellow fever mosquito Aedes aegypti

To investigate feeding‐related decisions in Aedes aegypti (L.), adults are presented with simple diets of paired gustatory stimuli conveying information concerning energy content, nutrient richness, osmotic balance and food toxicity in a two‐diet matrix assay. Assessment of mosquito gut contents indicates that both sexes accept single sugar diets in a dose‐dependent manner. When presented with a choice between two different yet equimolar sugar solutions, more individuals of both sexes accept the disaccharides, sucrose and trehalose, than the monosacharrides, fructose and glucose. The combination of pyranose and furanose sugars in solution, either physically associated (as in sucrose) or present as monomers (as glucose and fructose), is accepted over solutions containing a single sugar moiety. Using the two‐diet matrix assay, mosquito diet‐choice is also tested between two equimolar sucrose ‘driver’ solutions in which one is presented with various concentrations of another potential feeding cue ‘test’ compound (i.e. each of the 20 naturally‐occurring amino acids, sodium chloride, quinine or caffeine). Diet‐choice between the ‘driver’ sucrose‐only solution and the solution of the ‘driver’ sucrose containing a ‘test’ amino acid is influenced by sex, amino acid concentration and sucrose concentration. There is also an example of synergism between the diet components, leucine and sucrose. Mosquitoes demonstrate a dose‐dependent acceptance of sucrose‐only diets over sodium chloride‐containing sucrose when presented together. Interestingly, the sucrose‐only diet is accepted by more mosquitoes than all concentrations of the saline‐containing sucrose diets except those approximately isotonic to mosquito haemolymph, at which concentration mosquitoes show no clear choice between the diets. More individuals of both sexes accept sucrose‐only diets than the diets of caffeine‐containing sucrose in a dose‐dependent manner. Only females, however, respond to quinine‐containing sucrose diets and modulate this behaviour in relation to the energetic reward: more females imbibed quinine‐containing sucrose at the higher sucrose concentration (1 m ). A systematic characterization of diet selection behaviour of A. aegypti is presented for 27 putative feeding cues potentially involved in nectar/honeydew feeding. This study will be used as a basis from which to investigate further the mosquito's assessment of food quality and ultimately host choice.     

Development in the Floating World: Defenses of Eggs and Embryos Against Damage from UV Radiation

Eggs and embryos of many aquatic organisms develop in the watercolumn and can experience ultraviolet radiation with potentiallydeleterious effects. This is especially vexing for floatingembryos that develop in the surface or neuston layer. Radiationdamage can be a particular problem for these embryos since thecell division cycle during the cleavage period is quite shortand often these cycles do not have mitotic checkpoints to insurefaithful transmission of DNA to the daughter cells. This couldresult in cell division with unrepaired DNA in the blastomeres,which could impact embryogenesis and the transmission of thegenome through the germ line. Described strategies to restrictradiation damage include mechanisms to limit oxidative damageand the use of sunscreens such as the mycosporines to curb radiationto sensitive targets. We describe a particularly ingenious useof sunscreens in the tunicate embryo, the use of extra-embryoniccells to shield the embryo from potentially harmful UV-A andUV-B radiation. We also raise questions regarding the natureof UV damage to embryos (is it DNA or also protein) and thecharacteristics of DNA repair in such embryos. It is likelythat unique mechanisms are present in floating embryos thatdevelop in this air-water interface to assure that cell andgenomic integrity are maintained in this challenging environment.     

Ultraviolet B screening potential is higher in two cosmopolitan moss species than in a co-occurring Antarctic endemic moss: implications of continuing ozone depletion

Concentrations of UVB (ultraviolet B) absorbing pigments and anthocyanins were measured in three moss species, over a summer growing season in Antarctica. Pigment concentrations were compared with a range of climatic variables to determine if there was evidence that pigments were induced by UVB radiation, or other environmental parameters, and secondly if there were differences between species in their pigment responses. Significant seasonal differences in the potential UVB screening pigments were found, with the two cosmopolitan species Bryum pseudotriquetrum and Ceratodon purpureus appearing better protected from the potentially damaging effects of ozone depletion than the Antarctic endemic Schistidium antarctici. B. pseudotriquetrum accumulated the highest concentration of UVB screening pigments and showed positive associations between UVB radiation and both UVB absorbing and anthocyanin pigments. The negative associations between water availability measures and UVB absorbing and anthocyanin pigments also suggest that B. pseudotriquetrum is well protected in the desiccated state. This could offer B. pseudotriquetrum an advantage over the other species when high UVB radiation coincides with low temperatures and low water availability, thus limiting physiological activity and consequently, active photoprotective and repair mechanisms. As these pigments could act as either direct UVB screens or antioxidants, the results suggest that B. pseudotriquetrum is best equipped to deal with the negative effects of increased exposure to UVB radiation due to ozone depletion. The most exposed species, C. purpureus, has intermediate and stable concentrations of UVB absorbing pigments suggesting it may rely on constitutive UVB screens. Anthocyanin pigments were more responsive in this species and could offer increased antioxidant protection during periods of high UVB radiation. S. antarctici appears poorly protected and showed no evidence of any UV photoprotective response, providing additional evidence that this endemic is more vulnerable to climate change.     

Molecular phylogeny of New World sheath-tailed bats (Emballonuridae: Diclidurini) based on loci from the four genetic transmission systems in mammals

Multiple unlinked loci are surveyed in a methodological approach for mammalian systematics that uses genes from the four pathways of genetic transmission: mitochondrial, autosomal, and X and Y sex chromosomes. Each of these components has different properties, such as effective population size, mutation rate, and recombination, that result in a robust hypothesis of evolutionary history. The utility of this experimental design is tested with bats in the family Emballonuridae and the hypothesis that the New World taxa are monophyletic. Parsimony and Bayesian analyses of the individual data sets give generally congruent topologies with high bootstrap proportions and posterior probabilities for monophyletic clades representing species and genera. The mitochondrial gene has significantly faster rates of substitution, higher levels of homoplasy, and a greater degree of saturation than the nuclear genes that contributed to the loss of phylogenetic signal at deeper branches of the tree. However, there is better resolution and support for the more slowly evolving nuclear introns including a New World clade, indicating a single origin of emballonurid bats in the Neotropics (tribe Diclidurini). One novel subtribe has a hard basal polytomy that is unresolved for all of the nuclear partitions, suggesting a rapid burst of evolution during the diversification of genera.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 189–209.