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W O McMillan

Publications and source records attributed to W O McMillan.

15 recordsLinked to original sources
PubMed2006

Heliconius wing patterns: an evo-devo model for understanding phenotypic diversity.

Evolutionary Developmental Biology aims for a mechanistic understanding of phenotypic diversity, and present knowledge is largely based on gene expression and interaction patterns from a small number of well-known model organisms. However, our understanding of biological diversification depends on our ability to pinpoint the causes of natural variation at a micro-evolutionary level, and therefore requires the isolation of genetic and developmental variation in a controlled genetic background. The colour patterns of Heliconius butterflies (Nymphalidae: Heliconiinae) provide a rich suite of naturally occurring variants with striking phenotypic diversity and multiple taxonomic levels of variation. Diversification in the genus is well known for its dramatic colour-pattern divergence between races or closely related species, and for Müllerian mimicry convergence between distantly related species, providing a unique system to study the development basis of colour-pattern evolution. A long history of genetic studies has showed that pattern variation is based on allelic combinations at a surprisingly small number of loci, and recent developmental evidence suggests that pattern development in Heliconius is different from the eyespot determination of other butterflies. Fine-scale genetic mapping studies have shown that a shared toolkit of genes is used to produce both convergent and divergent phenotypes. These exciting results and the development of new genomic resources make Heliconius a very promising evo-devo model for the study of adaptive change.

Animals↗
PubMed2005

First-generation linkage map of the warningly colored butterfly Heliconius erato.

We report the first genetic linkage map of Heliconius erato, a species that shows remarkable variation in its warningly colored wing patterns. We use crosses between H. erato and its sister species, H. himera, to place two major color pattern genes, D and Cr, on a linkage map containing AFLP, allozyme, microsatellite and single-copy nuclear loci. We identified all 21 linkage groups in an initial genetic screen of 22 progeny from an F1 female x male H. himera family. Of the 229 markers, 87 used to identify linkage groups were also informative in 35 progeny from a sibling backcross (H. himera female x F1 male). With these, and an additional 33 markers informative in the second family, we constructed recombinational maps for 19 of the 21 linkage groups. These maps varied in length from 18.1 to 431.1 centimorgans (cM) and yielded an estimated total length of 2400 cM. The average distance between markers was 23 cM, and eight of the 19 linkage groups, including the sex chromosome (Z) and the chromosome containing the Cr locus, contained two or more codominant anchor loci. Of the three potential candidate genes mapped here, Cubitus interruptus (Ci), Decapentaplegic (Dpp) and Wingless (Wg), only Ci was linked, although loosely, to a known Heliconius color pattern locus. This work is an important first step for constructing a denser genetic map of the H. erato color pattern radiation and for a comparative genomic study of the architecture of mimicry in Heliconius butterflies.

Animals↗
PubMed2004

Historical demography of Mullerian mimicry in the neotropical Heliconius butterflies.

We compare the historical demographies of two Müllerian comimetic butterfly species: Heliconius erato and Heliconius melpomene. These species show an extensive parallel geographic divergence in their aposematic wing phenotypes. Recent studies suggest that this coincident mosaic results from simultaneous demographic processes shaped by extrinsic forces over Pleistocene climate fluctuations. However, DNA sequence variation at two rapidly evolving unlinked nuclear loci, Mannose phosphate isomerase (Mpi) and Triose phosphate isomerase (Tpi), show that the comimetic species have quite different quaternary demographies. In H. erato, despite ongoing lineage sorting across the Andes, nuclear genealogical estimates showed little geographical structure, suggesting high historical gene flow. Coalescent-based demographic analysis revealed population growth since the Pliocene period. Although these patterns suggest vicariant population subdivision associated with the Andean orogeny, they are not consistent with hypotheses of Pleistocene population fragmentation facilitating allopatric wing phenotype radiation in H. erato. In contrast, nuclear genetic diversity, theta, in H. melpomene was reduced relative to its comimic and revealed three phylogeographical clades. The pattern of coalescent events within regional clades was most consistent with population growth in relatively isolated populations after a recent period of restricted population size. These different demographic histories suggest that the wing-pattern radiations were not coincident in the two species. Instead, larger effective population size (N(e)) in H. erato, together with profound population change in H. melpomene, supports an earlier hypothesis that H. erato diversified first as the model species of this remarkable mimetic association.

Alleles↗
PubMed2002

Patterns of genetic diversity and biogeographical history of the tropical wetland tree, Pterocarpus officinalis (Jacq.), in the Caribbean basin.

Studies examining intraspecific variation in plant species with widespread distributions and disjunct populations have mainly concentrated on temperate species. Here, we determined the genetic structure of a broadly distributed wetland tropical tree, Pterocarpus officinalis (Jacq.), from eight Neotropical populations using amplified length fragment polymorphisms (AFLP). AFLPs proved highly variable with almost half (48%) of the genetic variation at these loci occurring among individuals within populations. Nonetheless, there was a strong geographical pattern in the distribution of AFLP variation within P. officinalis. Caribbean and continental populations fell into two well-defined genetic clusters supported by the presence of a number of unique AFLP bands. Within these two regions, there were also strong genetic differences among populations, caused mainly by frequency differences in AFLP bands, making it difficult to determine the evolutionary relationships among populations. In addition, our analysis of P. officinalis revealed striking differences in the levels of AFLP variation among the eight populations sampled. In general, Caribbean populations had lower genetic diversity than continental populations. Moreover, there was a clear loss in AFLP diversity with distance from the continent among Caribbean populations. The overall genetic pattern within P. officinalis suggests that past colonization history, coupled with genetic drift within local populations, rather than contemporary gene flow are the major forces shaping variation within this species.

Caribbean Region↗
PubMed1998

A phylogenetic approach to the identification of phosphoglucomutase genes.

The expanding molecular database provides unparalleled opportunities for characterizing genes and for studying groups of related genes. We use sequences drawn from the database to construct an evolutionary framework for examining the important glycolytic enzyme phosphoglucomutase (PGM). Phosphoglucomutase plays a pivotal role in the synthesis and utilization of glycogen and is present in all organisms. In humans, there are three well-described isozymes, PGMI, PGM2, and PGM3. PGM1 was cloned 5 years ago; however, repeated attempts using both immunological approaches and molecular probes designed from PGM1 have failed to isolate either PGM2 or PGM3. Using a phylogenetic strategy, we first identified 47 highly divergent prokaryotic and eukaryotic PGM-like sequences from the database. Although overall amino acid identity often fell below 20%, the relative order, position, and sequence of three structural motifs, the active site and the magnesium--and sugar-binding sites, were conserved in all 47 sequences. The phylogenetic history of these sequences was complex and marked by duplications and translocations; two instances of transkingdom horizontal gene transfer were identified. Nonetheless, the sequences fell within six well-defined evolutionary lineages, three of which contained only prokaryotes. Of the two prokaryotic/eukaryotic lineages, one contained bacterial, yeast, slimemold, invertebrate, and vertebrate homologs to human PGM1 and the second contained likely homologs to human PGM2. Indeed, an amino acid sequence, derived from a partial human cDNA, that fell within the second cross-kingdom lineage bears several characteristics expected for PGM2. A third lineage may contain homologs to human PGM3. On a general level, our phylogenetic-based approach shows promise for the further utilization of the extensive molecular database.

Amino Acid Sequence↗
PubMed1997

What initiates speciation in passion-vine butterflies?

Studies of the continuum between geographic races and species provide the clearest insights into the causes of speciation. Here we report on mate choice and hybrid viability experiments in a pair of warningly colored butterflies, Heliconius erato and Heliconius himera, that maintain their genetic integrity in the face of hybridization. Hybrid sterility and inviability have been unimportant in the early stages of speciation of these two Heliconius. We find no evidence of reduced fecundity, egg hatch, or larval survival nor increases in developmental time in three generations of hybrid crosses. Instead, speciation in this pair appears to have been catalyzed by the association of strong mating preferences with divergence in warning coloration and ecology. In mate choice experiments, matings between the two species are a tenth as likely as matings within species. F1 hybrids of both sexes mate frequently with both pure forms. However, male F1 progeny from crosses between H. himera mothers and H. erato fathers have somewhat reduced mating success. The strong barrier to gene flow provided by divergence in mate preference is probably enhanced by frequency-dependent predation against hybrids similar to the type known to occur across interracial hybrid zones of H. erato. In addition, the transition between this pair falls at the boundary between wet and dry forest, and rare hybrids may also be selected against because they are poorly adapted to either biotope. These results add to a growing body of evidence that challenge the importance of genomic incompatibilities in the earliest stages of speciation.

Animals↗
PubMed1997

Rapid rate of control-region evolution in Pacific butterflyfishes (Chaetodontidae).

Sequence differences in the tRNA-proline (tRNApro) end of the mitochondrial control-region of three species of Pacific butterflyfishes accumulated 33-43 times more rapidly than did changes within the mitochondrial cytochrome b gene (cytb). Rapid evolution in this region was accompanied by strong transition/transversion bias and large variation in the probability of a DNA substitution among sites. These substitution constraints placed an absolute ceiling on the magnitude of sequence divergence that could be detected between individuals. This divergence "ceiling" was reached rapidly and led to a decay in the relative rate of control-region/cytb b evolution. A high rate of evolution in this section of the control-region of butterflyfishes stands in marked contrast to the patterns reported in some other fish lineages. Although the mechanism underlying rate variation remains unclear, all taxa with rapid evolution in the 5'-end of the control-region showed extreme transition biases. By contrast, in taxa with slower control-region evolution, transitions accumulated at nearly the same rate as transversions. More information is needed to understand the relationship between nucleotide bias and the rate of evolution in the 5'-end of the control-region. Despite strong constraints on sequence change, phylogenetic information was preserved in the group of recently differentiated species and supported the clustering of sequences into three major mtDNA groupings. Within these groups, very similar control-region sequences were widely distributed across the Pacific Ocean and were shared between recognized species, indicating a lack of mitochondrial sequence monophyly among species.

Animals↗
PubMed1996

Mimicry meets the mitochondrion. Evolution.

A recent molecular study of the evolution of mimicry in tropical butterflies of the genus Heliconius proves that the mimics adapted to previously diverged 'model' species, but does not clearly distinguish between opposing views of how the model species diverged.

Animals↗
PubMed1996

The phylogeographic pattern of mitochondrial DNA variation in the Dall's porpoise Phocoenoides dalli.

We used 11 restriction endonucleases to study mtDNA variation in 101 Dall's porpoises Phocoenoides dalli from the Bering Sea and western North Pacific. There was little phylogeographic patterning among the 34 mtDNA haplotypes identified in this analysis, suggesting a strong historical connection among populations across this region. Nonetheless, mtDNA variation does not appear to be randomly distributed in this species. Both GST and AMOVA uncovered significant differences in the distribution of mtDNA variation between the Bering Sea and western North Pacific populations. These mtDNA results, coupled with differences in allozyme variation and parasite infestation, support the demographic distinctiveness of Bering Sea and western North Pacific stocks of Dall's porpoise. The lack of a strong phylogeographic orientation of mtDNA haplotypes within the Dall's porpoise is similar to the pattern reported in other vertebrates such as coyotes, blackbirds, chickadees, marine catfish, and catadromous eels. Like Dall's porpoise, these species are broadly distributed, and have large populations linked by moderate to high levels of gene flow. However, the more complex, deeply branched phylogenetic network of mtDNA haplotypes within Dall's porpoise, relative to these other vertebrates, suggests important differences between these species in the forces shaping mtDNA variation. One such force is the effective size of female populations, which appears to have been comparatively large and stable in Dall's porpoise.

Animals↗
PubMed1995

Concordant evolutionary patterns among Indo-West Pacific butterflyfishes.

Genetic differences within a 495 base pair section of the mitochondrial cytochrome b gene reveal a striking concordance among species in two monophyletic groups of Indo-west Pacific butterflyfishes. In both species groups, an approximately 2.0% genetic break clearly partitions individuals between the Indian Ocean and Pacific Ocean. However, levels of intra-Pacific mtDNA variation are low, on average less than 1.0%, and fail to cluster by species boundaries defined by colour pattern. Individuals from different species, separated by thousands of kilometers, often possess identical cytochrome b sequences, whereas conspecifics from the same reefs can show up to 1.5% difference. The discrepancy between the mtDNA gene tree and species boundaries may reflect retained ancestral variation or may be the result of hybridization. The strong temporal and phylogenetic concordance between these two independent species groups suggests that genetic differentiation was influenced by common environmental factors. Low levels of within- and between-species genetic differences imply a recent divergence time and suggest a link between speciation within each group and Pleistocene climatic fluctuations. These results paint a turbulent picture of the recent evolutionary history of the Indo-West Pacific.

Animals↗
PubMed1971

Phenobarbital-induced alterations in phosphatidylcholine and triglyceride synthesis in hepatic endoplasmic reticulum.

Biosynthetic pathways of phosphatidylcholine and triglyceride were studied in proliferating hepatic endoplasmic reticulum of rats pretreated with phenobarbital. Phosphatidylcholine accounted for the major increment in membrane phospholipid. In vitro measurements of hepatic microsomal enzymes which catalyze phosphatidylcholine biosynthesis revealed a significant increase in specific activity of the enzyme governing phosphatidylcholine synthesis by sequential methylation of phosphatidylethanolamine. The specific activity of phosphorylcholine-glyceride transferase, which catalyzes phosphatidylcholine synthesis from d-1,2-diglyceride and CDP-choline, was not altered. Specific activity of diglyceride acyltransferase, which catalyzes triglyceride biosynthesis, was increased to a degree comparable to the increase in specific activity found in the phenobarbital-induced drug-metabolizing enzyme which oxidatively demethylates aminopyrine. In vivo incorporation of methyl-(3)H from l-methionine-methyl-(3)H into microsomal phosphatidylcholine was significantly increased, resulting in an increased methyl-(3)H to choline-1,2-(14)C incorporation ratio of more than three times that found in control animals. A comparable increase in this incorporation ratio was noted in serum phospholipids. The in vitro enzyme studies, in agreement with in vivo incorporation data, indicate that the increase in phosphatidylcholine content of phenobarbital-induced proliferating endoplasmic reticulum is related to increased activity of the pathway of phosphatidylcholine biosynthesis involving the sequential methylation of phosphatidylethanolamine.

Acyltransferases↗
PubMedDate not supplied

Assessment of dilation methods in achalasia: large diameter mercury bougienage followed by pneumatic dilation as needed.

In a retrospective study, 33 achalasia patients were treated with dilation therapy using large diameter mercury bougienage (mean, 56 French) and/or pneumatic balloon dilation. Mean follow-up time was 35 months. Mercury bougienage, performed in 20 patients, was successful in 10 (50%) with no complications. Pneumatic dilation was performed as initial therapy or in those having failed previous pharmacologic therapy and/or bougienage. A successful response was achieved in 19 of 23 patients (83%), with a 3.2% complication rate. In addition, in four patients with eventual recurrence of symptoms after initial pneumatic dilation, bougienage was used as a successful alternative to repeat pneumatic treatment. The combined efficacy of both forms of dilation was 88% with a complication rate of 1.4%. These data indicate that mercury bougienage should be considered initial therapy for achalasia in view of its simplicity, safety, and acceptable efficacy, followed by pneumatic dilation if bougienage is unsuccessful. Bougienage also may be considered if eventual recurrent symptoms develop after initially successful pneumatic dilation. Surgery should be utilized only if dilation therapy fails to achieve a satisfactory response.

Catheterization↗