Demographic genetics of the American beech (Fagus grandifolia Ehrh.) III. Genetic substructuring of coastal plain population in Maryland

Spatiotemporal genetic substructurings were investigated in the American beech population of the east-central coastal plain in Maryland. All trees including seedlings, various sizes of juveniles, and mature trees within the study site (10 × 100 m) were mapped, diameters measured, and leaves collected for allozyme analyses. Eleven polymorphic loci in eight enzyme systems were examined: 6Pgdh2, 6Pgdh3, Acp2, Adh1, Adh2, Fum, Got1, Got3, Lap, Pgi, and Pgm2. A total of 1945 trees were analyzed and 595 multilocus genotypes were detected. Six size-classes and 10 spatial blocks were discriminated for spatiotemporal analyses. Parameters for genetic variations (heterozygosity, Simpson's index, Shannon-Weaver's index, and inbreeding coefficient) decreased in larger size-classes. These genetic parameters fluctuated in spatial blocks of 10 m intervals, in which certain alleles were characteristic of specific blocks. The spatial autocorrelation by Moran's I and coancestry revealed the ranges of genetic relatedness to be only 20–30 m. Multilocus genotype analyses showed that higher genetic variations occur in larger size-classes and at gap openings where seed shadows for mother trees are overlapped. The relationships among reproductive trees, seedlings and juveniles suggested that the seed dispersal range of the American beech is normally in the range of 30–40 m. The mechanisms of a remarkably high genetic polymorphism maintained in this once artificially disturbed and grazed forest are discussed as related to conservation biology.     

Neuromuscular Organization for "Wing" Control in a Mollusc (Clione limacina) and a Bird (Columba livia): Parallels in Design

Flapping as a means of locomotion is shared by divergent groupsranging from pteropod molluscs to birds. The pteropod, Clionelimacina, exhibits two modes of locomotion, slow and fast swimming.The motor units which control swimming consist of small motoneuronsand relatively nonfatigable muscle fibers, while those involvedin fast swimming consistof large motoneurons and relativelyfatigable fibers (Satterlie et al., 1990).The pectoralis muscleof the pigeon, Columba livia, consists of two populations ofmuscle fibers distinguished by histochemistry and size. Cinematographicand electromyographic experiments suggest that the large fibersare used for takeoff and landing and the small fibers for levelflight (Dial et al., 1988). We have employed a suite of experimentaltechniques similar to those used for studies of the neuromuscularsystem of Clione to analyze a limited sample of motor unitsfrom the pectoralis of Columba. The peak tetanic tension andcontractile fatigue resistance during electrical stimulationof single alpha axons, functionally isolated from nerve filaments,was studied in 30 motor units. All units but one generated peaktetanic tensions which were less than 0.22% of whole muscletension. A high proportion (75%) of units demonstrated fatigueresistance, reflective of the demands of sustained flappingflight. These preliminary data suggest that the peripheral neuromuscularsystems of Clione and Columba share some common components forthe execution of at least two distinct modes of flapping locomotion.     

Colony Specificity in the Colonial Tunicate Botryllus and the Origins of Vertebrate Immunity

SYNOPSIS. Colonies of the compound tunicate Botryllus show thecapacity for self—nonself discrimination by fusion betweenseparated pieces of the same colony and rejection between piecesof unrelated colonies. We have found that genes controllingthis colony specificity are similar to those which cause transplantrejection in the vertebrates. Like the loci within the vertebratemajor histocompatibility complex (MHC), Botryllus fusibility(or histocompatibility) genes are highly polymorphic. In Botryllus,the histocompatibility complex also controls self—sterility,and limits cross—fertilization between colonies sharinghistocompatibility alleles. The mouse MHC, the H-2 region, islinked to loci which also affect the frequencies of allelesat H-2 loci in mouse populations. Thus both systems containcharacters which could act to promote the heterozygous conditionat the linked histocompatibility loci. We suggest that suchlinked characters are responsible for the evolution of allogeneicpolymorphism in vertebrates (however currently maintained),and that tunicate fusibility loci may be the evolutionary precursorsof vertebrate MHC genes.     

Correlations between habitat use and body shape in a phrynosomatid lizard (Urosaurus ornatus): a population-level analysis

Recent ecomorphological studies have shown that the predicted correlations between morphology and ecology on broad taxonomic levels are often obscured when comparing more closely related groups. Among species, comparisons of lizards often indicate very little support for adaptive radiations into novel habitats. As few population level studies have been performed, we compared body, head and limb shape between four populations of Urosaurus ornatus living in structurally distinct habitats (cliffs, rocks, trees and boulders). Surprisingly, clear correlations between habitat use and body shape among populations were found, most of which were in good accordance with a priori biomechanical predictions (e.g. flat body and head for extreme climbers; long distal hindlimb segments for jumpers and runners; narrow body and long tail for tree dwelling lizards). This indicates that populations of Urosaurus ornatus are seemingly 'adapted' to the habitat they live in. However, quantification of performance and behaviour are needed to determine the adaptive nature of these observations.