Showing papers by "Allan J. Baker published in 1997"

CHAPTER 3 – Mitochondrial Control Region Sequences as Tools for Understanding Evolution

Abstract: The chapter summarizes what is known about the control region of birds in terms of its organization, the location of markers within it, and presents exemplars from laboratory observations illustrating the potential and problems of fast-evolving sequences in elucidating the population structure and molecular systematics of closely related taxa. In addition to transition and transversion substitutions and numerous small indels, length differences accumulate through variation in a number of tandem repeats, and relatively large duplication or deletion of events. Both inter- and intraspecific variations are more common in the two flanking domains than in the conserved central blocks, with tandem repeats occurring primarily in domain III and larger duplications restricted to among-species comparisons. A thorough analysis of intraspecific sequence variation leads inevitably to the consideration of the population genetic processes responsible for major phylogenetic subdivisions in gene trees and to consideration of taxonomic recognition of these discrete clades as subspecies, phylogenetic species, or biological species. A major difficulty illustrated by the knot sequences is that populations are unlikely to be in equilibrium with respect to mutation and genetic drift.

HISTORICAL DEMOGRAPHY AND PRESENT DAY POPULATION STRUCTURE OF THE GREENFINCH, CARDUEUS CHLORIS-AN ANALYSIS OF mtDNA CONTROL-REGION SEQUENCES.

Abstract: Genetic variability within and among 10 geographically distinct populations of Greenfinches (Carduelis chloris) was assayed by directly sequencing a 637 BP part of the mtDNA control region from 194 individuals. Thirteen variable positions defined 18 haplotypes with a maximum sequence divergence of 0.8%. Haplotype (h = 0.28-0.77) and nucleotide (r = 0.058-0.17%) diversities within populations were low, and decreased with increasing latitude (h:r, = -0.81; r: r, = -0.89). The distribution of pairwise nucleotide differences fit better with expectations of a "sudden expansion" than of an "equilibrium" model, and the estimates of long term effective population sizes were considerably lower than current census estimates, especially in northern European samples. Selection is an unlikely cause of observed patterns because the distribution of variability conformed to expectations of neutral infinite alleles model and haplotype diversity across populations was positively correlated with heterozygosity (HE) in nuclear genes (r, = 0.74, P mtDNA > allozymes).

A Phylogeny of Some Taxa of Masked Shrews (Sorex cinereus) Based on Mitochondrial-DNA, D-Loop Sequences

Abstract: Parsimony analysis of sequence variation in the mitochondrial (mt) DNA, D-loop region indicated that the masked shrew ( Sorex cinereus ) and the prairie shrew ( S. haydeni ) are monophyletic taxa, but mtDNA from S. cinereus has introgressed into S. haydeni . Within S. cinereus there was a lack of concordance between mtDNA clades and currently accepted subspecific designations. The taxonomic designation S. c. acadicus corresponded to a mtDNA clade composed of specimens found predominantly in Nova Scotia and New Brunswick. This clade shared a more recent ancestor with a lineage common to Ontario and Quebec than it did with mtDNA haplotypes from specimens sampled in Michigan and Alberta. S. c. cinereus is, therefore, a paraphyletic assemblage based on mtDNA haplotypes. Little support for currently recognized subspecific designations was found from an analysis of molecular variance among the populations of S. c. cinereus . The mtDNA clades fit a biogeographic hypothesis in which populations of shrews were isolated by factors associated with the Wisconsinan, glaciation and then reinvaded Canada from coastal and southern continental refugia. However, divergence times preceding the recent Wisconsinan glaciation are indicated by applying a molecular clock calibrated for shrews to observed genetic-distance values.

Evidence of a heritable component to body shape in the northern redbelly dace (phoxinus eos)

Abstract: Hypotheses about the role of selection on body-shape evolution assume a heritable component to this phenotypic character. To examine the influence of environmental induction on body shape, offspring form two morphologically differentiated populations of northern redbelly dace (Phoxinus eos) were reared in a common laboratory environment. Additionally, shape changes were monitored over 3 consecutive years in six populations. Offspring reared in a common environment retained the body shape of individuals from their natal pond, and shape changes among fish in different ponds were maintained in natural populations over years. These results strongly suggest a heritable component to body shape in P. eos. These results complement earlier work examining foraging tactics as a potential selection pressure on body shape and support the conclusion that body-shape differences among fish in different ponds are being maintained by selection for foraging ability.