Charles E. Dinsmore

Geographic variation in the limb skeleton of the red-backed salamander, Plethodon cinereus

Analysis of skeletal evolution is hampered by a lack of knowledge of the scope and nature of variation in natural populations. This is true even for a structure of such obvious adaptive and phylogenetic significance as the vertebrate limb. Recently, one of us documented extensive variation in the foreand hind limb skeleton in a single population of the Red-backed Salamander, Plethodon cinereus (Amphibia: Plethodontidae), from Glascow Mountain, Nova Scotia, in eastern Canada (Hanken, 1983). Salamanders from this population display numerous mesopodial (i.e., wrist and ankle) and digital patterns, many of which have never been observed in any other amphibian. Interpretation of the significance of this variation, however, is made difficult by the paucity of analogous, quantitative studies of natural limbskeletal variation in other urodele species, or even other populations of P. cinereus. In an attempt to rectify this problem, we quantified limb skeletal variation in samples of P. cinereus from three other localities. The results (1) document heretofore unreported variant mesopodial and phalangeal ci en. Richard Estes (San Diego State Univer) read the manuscript and disagrees with my clusions. I thank Arnold Bell (University of lifornia-Riverside) for taking the SEM photoaphs of the specimen.

Conceptual foundations of metamorphosis and regeneration: from historical links to common mechanisms

Metamorphosis and regeneration represent two familiar examples of developmental processes. In Western thought, their conceptual link with broader issues of generation or animal reproduction, including “spontaneous generation,” began with the ancient Greeks. Their ideas dominated scientific discourse on these topics until William Harvey, in the mid‐17th century, redefined and distinguished between epigenesis and metamorphosis as fundamentally different modes of reproduction. However, preformation theories, formulated in response to perceived threats of epigenetic concepts to religious doctrine, eclipsed epigenesis for much of the 18th century. Abraham Trembleys 1740 discovery of hydra regeneration helped to fuel the “epigenesis‐preformation debate” at that time. During that period, an exchange between C.F. Wolff, a young epigenesist, and A. von Haller, the reformed preformationist, saw robust models erected to comprehend generation, metamorphosis, and regeneration under each world view. Subsequent elaboration of experimental zoology and the incremental advance of biological knowledge saw the birth of divergent research traditions in pursuit of specialized problems. Embryology, regeneration, and metamorphosis, like genetics, identified independent study topics and elaborated new techniques, thereby creating their own research trajectories. Conceptual reintegration has slowly emerged with the evolution of current biotechnology. We have now begun to discern common molecular mechanisms underlying and reuniting metamorphosis and regeneration, as revealed in the accompanying symposium papers.

Correlations Between Phases of Deer Antler Regeneration and Levels of Serum Keratan Sulfate

SummaryA sensitive and highly specific enzymelinked immunosorbent assay with an inhibition step was used to monitor the concentration of keratan sulfate, a cartilage-related glycosaminoglycan, in the serum of three adult male deer. During the course of one complete annual antler regeneration cycle, keratan sulfate levels were found to fluctuate predictably in relation to the growth and maturation of the antlers: levels are substantially elevated during the growth phase and drop precipitously when growth ceases and the antlers become fully mineralized. In addition, an unanticipated elevation of serum keratan sulfate was observed in early spring prior to casting of the preceding years antlers and the initiation of regrowth. This suggests that changes in cartilage metabolism occur concomitantly, with this phase of the antlerogenic cycle. These results show predictable and physiologically regulated variation in serum keratan sulfate levels which correlate directly with specific phases of the antler regeneration cycle. Furthermore, the findings provide additional support for the assertion that measurements of keratan sulfate levels in serum can provide useful information about changes in cartilage metabolism in normal as well as diseased states.

Amputation Level-Dependent Patterning in Urodele Limb Regeneration

Comparison of mesopodial skeletal patterns found in native and regenerated limbs of the salamander Plethodon cinereus reveals variant patterns unique to each group. Variant patterns in native limbs are based on fusions between laterally adjacent elements (i.e., in the anteroposterior axis). Variant patterns in the mesopodia of regenerated limbs usually exhibit fusions among proximodistally adjacent elements. Analysis of regenerates derived from limb amputation at different levels shows that the axis of fusion between regenerated mesopodial elements remains the same (i.e., proximodistal) independent of amputation level. However, the frequency of specific fusion combinations is unexpectedly sensitive to amputation level. Proximal (stylopodial) amputation results in mesopodial patterns with predominantly preaxial fusion combinations; distal amputation produces mesopodial patterns with predominantly postaxial fusion combinations. This finding is discussed in the context of other recent studies in which amputation level influenced limb regeneration patterning.