The tarsus of erythrosuchid archosaurs, and implications for early diapsid phylogeny

The morphology of the erythrosuchid ankle joint is reassessed. Two specimens, recently thought to have been incorrectly referred to Erythrosuchus africanus , are shown without doubt to belong to this taxon. Furthermore, the morphology is essentially similar to that of other early archosaurs. The tarsus of Erythrosuchus is poorly ossified and consists of a calcaneum, astragalus, and two distal tarsals. The calcanea of Erythrosuchus, Vjushkovia triplicostata , and Shansisuchus shansisuchus are all similar in being dorsoventrally compressed, possessing a lateral tuber, and lacking a perforating foramen. The astragalus of V. triplicostata is currently unknown. The astragalus of Shansisuchus is apparently unique in form. The erythrosuchid pes is therefore more derived than has been recently proposed. The tarsal morphology of several other archosauromorph taxa is reviewed and many details are found to be at variance with the literature. The plesiomorphic condition for the Archosauromorpha consists of four distal tarsals and a proximal row of three elements; two of which articulate with the tibia. These proximal elements are interpreted as the astragalus, calcaneum, and a centrale, and the same pattern is retained in the earliest archosaurs. This reassessed tarsal morphology has implications for the homology of the centrale and reconstruction of early diapsid phylogeny.     

The taxonomic significance of leaf micromorphology in the genus Eugenia L. (Myrtaceae)

Leaf micromorphological features of both the Old and New World representatives of Eugenia L. have been studied by light microscopy and scanning electron microscopy. The leaves are hypostomatic and, in the majority of species, the stomata are raised above the epidermis. Trichomes are usually present on the abaxial surface of the New World species. The patterns of abaxial surface sculpturing and arrangement of outer stomatal rims are unique in the New World species. The majority of the Old W'orld species showed different anticlinal wall patterns on the adaxial and abaxial epidermises. In the majority of the New World species the anticlinal wall patterns are more or less the same except in E. axillaris. The paracytic type of stomata, with a non-prominent T-piece cutinization at the poles of the guard cells, is a characteristic feature of the New World species. The taxonomic significance of these features in identification and elucidation of species from both areas is discussed.     

Phenology determines seasonal variation in ectoparasite loads in a natural insect population

1. The extent to which individuals are parasitised is a function of exposure to parasites and the immune response, which in ectotherms may be associated with temperature. 2. We test the hypothesis that seasonal variation in ectoparasite burden is driven by temperature using an extensive mark‐release‐recapture study of adult Coenagrion puella (L.) (Zygoptera) as a model system. Mite counts were taken both at capture and on a subset of subsequent recaptures over two entire, consecutive breeding seasons. 3. Emergence date was the most significant factor in determining individual differences in mite burden, and mean counts for individuals emerging on the same days showed strong unimodal relationships with time of season. Subsequent recounting of mites on a subset of individuals showed that patterns of loss of mites were similar between seasons. 4. While temperature did not significantly affect mite burdens within seasons and ectoparasite prevalence was very similar across the two seasons, intensity of infection and rate of mite gain in unparasitised individuals were significantly higher in the cooler season. 5. We demonstrate that, while temperature may modulate the invertebrate immune response, this modulation does not manifest in variations in mite burdens in natural populations.     

Testing the Adaptive Significance of Acclimation: A Strong Inference Approach

Acclimation is a common phenotypic response to environmentalchange. Acclimation is often thought to enhance performanceand thus to be adaptive. This view has recently been formalizedas the "Beneficial Acclimation Hypothesis" and predicts thatindividuals acclimated to one environment perform better inthat environment than do individuals acclimated to a differentenvironment. Although Beneficial Acclimation is appealing andwidely supported, recent studies with E. coli and Drosophilahave challenged its general validity. Although these challengescould be dismissed as mere exceptions, they encourage a re-evaluationof the adaptive significance of acclimation. Our philosophicalapproach differs from that of most previous studies of acclimation,in which the prediction derived from a Beneficial Acclimationperspective (e.g., heat tolerance is positively correlated withacclimation temperature) is tested against the null hypothesis("single hypothesis approach"). Instead, we follow Huey andBerrigan (1996) in advocating a strong inference approach (sensuPlatt, 1964), which recognizes that Beneficial Acclimation isactually one of a set of competing hypotheses that make differentpredictions as to how developmental temperature influences thethermal sensitivity of adults ("developmental acclimation").Using this perspective, Huey and Berrigan proposed a factorialexperimental design (3 developmental by 3 adult temperatures)designed to discriminate among all competing hypotheses. Wenow derive a formal statistical model (ANOVA with orthogonalpolynomial contrasts) for this experimental design and use itto evaluate simultaneously the relative impact of each competinghypothesis. We then apply this model to several case studies(Drosophila, Volvox, Trichogramma), and we review also a recentstudy with E. coli. The influence of Beneficial Acclimationis supported (albeit often weakly) in most cases. Nevertheless,other hypotheses (especially the Optimal Developmental TemperatureHypothesis) often have a greater impact. Even so, however, BeneficialAcclimation usually predicts relative performance at extremetest temperatures. We conclude that, although rumors of itsdeath are premature, Beneficial Acclimation cannot be viewedas the dominant expectation, at least with regard to developmentaltemperature acclimation. Moreover, our findings reinforce theview that a strong inference approach provides a more comprehensiveportrait of complex biological responses than do single-hypothesisapproaches.     

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.