Functional Morphology of Mammalian Mastication

SYNOPSIS. While chewing is not unique to mammals, it is oneof their most distinctive characteristics. Historically, studiesof food processing in mammals were intended to provide evolutionaryinsights, but more progress has been made in understanding mechanisticaspects. Mastication is considered under five headings. (1)Interaction of teeth with food.Knowledge of comparative dentalanatomy and function is advanced in comparison to understandingof foods and how they are broken down. (2) Chewing force andits resistance by the skull. The traditional assumption thatocclusal force is maximized is not always justified, and experimentalresults suggest that skull loading is far more dynamic and variablethan had been envisioned from theoretical analyses. (3) Howthe jaw moves. The most important masticatory movement is thatof the power stroke, and in most but not all species this isinfluenced more by the inclined planes of the teeth and jawjoints than by the musculature. (4) The role of muscles in producingboth force and movement. The most fundamental distinction amongjaw muscles is whether they have a rostral or caudal directionof pull, as this determines their role in transverse jaw movements.Reliance on anatomical names tends to obscure functional similaritiesand differences among species. (5) Intraoral structures. Becausethey are difficult to study, the actions of the tongue and pharynxare still debated. Even the fundamental question of whethermammals can breathe and swallow at the same time has not beendefinitively answered.     

Cell-Cell Interactions and Distal Outgrowth in Amphibian Limbs

SYNOPSIS. A current model concerning the process of limb regenerationin vertebrates is examined. According to this model (Bryantet al, 1981), new positional values in the proximal-distal limbaxis are laid down as a result of local interactions betweencells in the limb circumference. Cells with disparate circumferentialpositional values come together at the site of future outgrowthand intercalation between them generates more distal levelsof the pattern. The results of a number of experiments on surgicallycreated symmetrical limb stumps are discussed in relation tothis model. In addition, an extension of this model to accountfor digit formation is presented, and the implications of thisformulation for limb evolution are discussed.     

Isolation of Aeromonas caviae from ice-cream

Sixty-four samples of ice-cream were examined for the presence of Aeromonas species. Culture was by direct inoculation onto xylose deoxycholate citrate agar and into alkaline peptone water. Aeromonas caviae was isolated from three of the 64 samples (4–7%). The potential pathogenic significance of this organism in ice-cream is discussed.     

Phylogenetic analysis of eleven species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae) based on comparisons of allozymes

Freshwater snails in the genus Biomphalaria transmit Schistosoma mansoni in Africa, South America and the Caribbean region. Although considerable attention has been given to the identification of species, little is known of evolutionary relationships among the species. A phylogenetic analysis of 25 populations representing 11 species was performed on 25 enzyme loci examined using starch gel electrophoresis. A phylogenetic analysis of the individual populations produced 60 trees of equal length. The 60 trees have a consistency index value of 75.9% and a retention index value of 76.5%. The phylogenetic analysis provided strong support for the monophyly of Biomphalaria with either 14 or 15 synapomorphies uniting all of the species included and separating them from the outgroup, two species of Helisoma. Four nominal species represented by multiple populations formed monophyletic groups. Populations of B. sudanica, B. choanomphala, and B. alexandrina were interspersed. Ten arrangements were obtained for the populations of these three species. A variety of ingroup taxa were used to root the trees, and all provided support for the use of Helisoma species as an outgroup. In all of the trees obtained, the African species together formed a monophyletic group. In none of the trees obtained did the neotropical species form a monophyletic group. A constrained analysis requiring the monophyly of the neotropical species as well as the African species resulted in 90 trees just two steps longer than the shortest trees. Analysis of the species from either hemisphere alone resulted in decreased resolution, as measured by an increase in the number of trees obtained. This finding suggests that further comparisons of species from the two hemispheres will be of considerable value. Finally, two species which are resistant to infection with S. mansoni were included among the eleven studied. Neither of these species formed the sister group to all of the other species included, indicating that susceptibility is the plesiomorphic state, and that resistance is derived. Similarly, in none of the trees obtained did the two resistant species fall out as sister taxa, indicating that resistance arose independently twice.