Heterozygosity for recessive lethals in homosporous fern populations: Thelypteris palustris and Onoclea sensibilis

Sporophytes from natural populations of Thelypteris palustris and Onoclea sensibilis were subjected to breeding tests to reveal the presence of recessive lethal alleles in their genotypes. All sporophytes were found to be heterozygous for recessive sporophytic lethals. Despite the capability for producing completely homozygous genotypes by intragametophytic self-fertilization, ferns in natural populations seem to retain considerable genetic loads of deleterious recessive alleles. It is suggested that natural selection operates to strongly favour heterozygous rather than homozygous sporophytes under most conditions.     

Cardiopulmonary Gas Exchange in the Turtle: A Model Analysis

The performance of the cardiorespiratory gas exchange systemof the turtle, Pseudemys scripla, at rest and at three bodytemperatures (15, 25, 35°C), was assessed in reference totheory and experimental data. The primary processes governinggas exchange(ventilation, perfusion, diffusion) were found tobe uniformly balanced in regard to CO₂ exchange. This was nottrue for O₂ transport where, at higher body temperature, thesystemis characterized by underventilation and overperfusionin conjunction with declining O₂ saturation levels. Adjustmentsin convection of air or blood, which favor improvement in arterialO₂ saturation levels, are incompatible with stability of theCO₂stores and acid-base state. The latter were preserved acrossthe temperature range. Comparisons between bird, mammal, andturtle illustrate close similarity in the relative roles ofthe primary processes governing CO₂ exchange. This persistsin the face of wide differences inmetabolic intensity, cardiopulmonaryarchitecture and complexity, and body temperatures characterizingthe species which were compared. The close control of carbondioxide transport may reflect a fundamental adjustment to airbreathing by lungs as primitive vertebrates emerged from waterto the terrestrial domain. From a regulatory point of view thestudy emphasizes the importance of both structural and functionalcontrol of CO₂ homeostasis. It does not rule out regulatoryfeatures which may insure more effective O₂ transport; however,the latter are not evident within the context of the steadystate assumptions underlying this analysis.     

Transmission of the Trypanosomatid Flagellate Phytomonas davidi,a Symbiont of the Euphorbiaceae,by the Hemipteran Bug Pachybrachius bilobata scutellatus1

ABSTRACT. Phytomonas davidi is found in the latex of species of the plant family Euphorbiaceae, including Chamaesyce hirta and C. hyssopifolia, to latitude 32°N in the southeastern United States. The hemipteran Pachybrachius bilobata scutellatus (family Lygaeidae) serves as an agent of transmission from plant to plant. Heavy infections of flagellates in the salivary glands were observed; trypanosomatids were less than one-half the size seen in the plants and in the gut of the bug.     

Evolutionary relationships among the Pulmonate land snails and slugs (Pulmonata, Stylommatophora)

We have incorporated an additional 56 species of land snails and slugs in our ribosomal (r) RNA molecular phylogeny. The new taxa include representatives of several important groups. The molecular tree now includes 160 species of stylommatophoran land snails and slugs in 144 genera in 61 families. In the rDNA tree, the Stylommatophora are principally divided into an 'achatinoid' and a 'non-achatinoid' clade. Within these clades, several major land snail groups, including the Orthurethra, Elasmognatha, Limacoidea, and Helicoidea, are supported. Overall, the rDNA molecular phylogeny has remained stable following the incorporation of the additional taxa, with these additions having little impact on the major evolutionary patterns in the tree. Taxonomic coverage of the Orthurethra, Orthalicidae, Camaenidae, and Bradybaenidae is increased significantly. The camaenids and bradybaenids form a complex, and both appear to be paraphyletic. Several families of uncertain affinity, such as the Sagdidae and Thyrophorellidae, are included for the first time. The Sagdidae are shown to belong to the Helicoidea, and the Thyrophorellidae to the Achatinoidea.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 593–610.     

A COMPARISON OF THE MOLLUSCAN COMMUNITIES ON INTERTIDAL SAND FLATS IN OYSTER HARBOUR AND PEEL INLET, WESTERN AUSTRALIA

Intertidal molluscs on sandflats in Oyster Harbour and PeelInlet, Western Australia, were compared using transects. Twenty-fourspecies of molluscs were recorded in Oyster Harbour and only7 in Peel Inlet. Two groupings were foundin Oyster Harbour:a midlittoral component and infralittoral fringe. There wasno vertical community structure in Peel Inlet. Molluscs retainedon a 1 mm sieve had about the same mean density and biomassin the two areas but molluscs retained on a 2 mm sieve had amean density of 203/m² and a biomass of 132 g/m² in Oyster Harbourand were absent in Peel Inlet. Several possible reasons forthe absence of large molluscs in Peel Inlet are discussed. PeelInlet is on the west coast in a faunal overlap zone where thenumber of species is reduced. The mean temperature in Peel Inletis 2-3°C higher than in Oyster Harbour and salinity variationsare much more pronounced. (Received 20 November 1979;     

A Primer on Interpreting Regression Models

Abstract: We perceive a need for more complete interpretation of regression models published in the wildlife literature to minimize the appearance of poor models and to maximize the extraction of information from good models. Accordingly, we offer this primer on interpretation of parameters in single- and multi-variable regression models. Using examples from the wildlife literature, we illustrate how to interpret linear zero-intercept, simple linear, semi-log, log-log, and polynomial models based on intercepts, coefficients, and shapes of relationships. We show how intercepts and coefficients have biological and management interpretations. We examine multiple linear regression models and show how to use the signs (+, -) of coefficients to assess the merit and meaning of a derived model. We discuss 3 methods of viewing the output of 3-dimensional models (y, x₁, x₂) in 2-dimensional space (sheet of paper) and illustrate graphical model interpretation with a 4-dimensional logistic regression model. Statistical significance or Akaike best-ness does not prevent the appearance of implausible regression models. We recommend that members of the peer review process be sensitive to full interpretation of regression models to forestall bad models and maximize information retrieval from good models