Integration of geometric with luminance information in the rat: evidence from within-compound associations.

In two experiments, rats first received preexposure to a rectangular arena in which the geometrically equivalent corner pairs (G1 and G2) were coincident with different luminance characteristics (C1 and C2, respectively). In Experiment 1, rats were then placed in a uniform gray rectangular arena where food was located in one geometrically equivalent pair of corners (G1), but not another (G2). Finally, rats were tested in a square arena with C1 and C2 and preferred to search in C1 rather than C2. In Experiment 2, following preexposure to G1C1 and G2C2, rats received pairings of C1 with food and C2 with no food in a square arena. During testing, rats preferred to search in G1 rather than G2 in a gray rectangular arena. These results demonstrate that reciprocal within-compound associations develop between geometric and luminance information and thereby challenge the view that there is a dedicated geometric module that is impenetrable to information that is not geometric.

COMPARATIVE PATTERNS OF GROWTH AND DEVELOPMENT IN CRICETINE RODENTS AND THE EVOLUTION OF ONTOGENY.

The quantitative description of growth curves for morphometric traits provides a basis for assessing the ontogenetic patterns underlying differences in morphological structure, as demonstrated with comparisons among neotomine-peromyscine rodents. Morphometric differences among contemporary rodent species are shown to result from relatively simple changes in relative growth rates and timing. Quantitative ontogenetic studies add a dynamic component to the assessment of morphological similarity, thus providing a more robust procedure for detecting homoplasy than static comparison of adult morphology. Applying the principles of phylogenetic systematics to studies of developmental timing among closely related taxa may be a useful and informative complement to studies based on molecular similarity or static comparison of adult morphology. Interspecific and intraspecific differences in allometric scaling of anatomical structures may reflect differences in growth patterns among the taxa compared; caution is warranted in inferring patterns of genetic correlation from data on phenotypic scaling.

Muscle enzyme profile, diet, and flight in South American bats.

Activities of four catabolic enzymes (citrate synthase, hexokinase, 3-hydroxyacyl-CoA dehydrogenase, and phosphorylase) were measured in the pectoralis muscles of 10 species of South American bats, representing four families. The pattern of enzyme activities in these tissues suggests that these muscles differ qualitatively with other mammalian and avian muscles in two respects. First, the muscles of all 10 bat species were much more highly oriented toward fat metabolism and away from glucose metabolism than in any previously measured skeletal muscle. Second, the species were divided into two major groups with respect to hexokinase activity. Primarily frugivorous species had hexokinase activities about 2-3 times as high as insectivorous species. It is suggested that the weight restrictions of flight limit glycogen storage and thus bias muscle metabolism toward fat. However, the extent to which pectoralis muscles have the capacity for glucose oxidation appears to be dependent on the intake of dietary glucose.