Intron sequences provide a tool for high-resolution phylogenetic analysis of volvocine algae |
| |
Authors: | Michael Liss David L Kirk Kurt Beyser S Fabry |
| |
Institution: | Genetik, Universit?t Regensburg, Universit?tsstra?e 31, D-93040 Regensburg, Germany, DE Department of Biology, Washington University, St. Louis MO 63130, USA, US
|
| |
Abstract: | Three nuclear spliceosomal introns in conserved locations were amplified and sequenced from 28 strains representing 14 species
and 4 genera of volvocalean green algae. Data derived from the three different introns yielded congruent results in nearly
all cases. In pairwise comparisons, a spectrum of taxon-specific sequence differences ranging from complete identity to no
significant similarity was observed, with the most distantly related organisms lacking any conserved elements apart from exon-intron
boundaries and a pyrimidine-rich stretch near the 3′ splice site. A metric (SI50), providing a measure of the degree of similarity of any pair of intron sequences, was defined and used to calculate phylogenetic
distances between organisms whose introns displayed statistically significant similarities. The rate of sequences divergence
in the introns was great enough to provide useful information about relationships among different geographical isolates of
a single species, but in most cases was too great to provide reliable guides to relationships above the species level. A substitution
rate of approximately 3 × 10−8 per intron position per year was estimated, which is about 150-fold higher than in nuclear genes encoding rRNA and about
10-fold higher than the synonymous substitution rate in protein-coding regions. Thus, these homologous introns not only provide
useful information about intraspecific phylogenetic relationships, but also illustrate the concept that different parts of
a gene may be subject to extremely different intensities of selection. The intron data generated here (1) reliably resolve
for the first time the relationships among the five most extensively studied strains of Volvox, (2) reveal that two other Volvox species may be more closely related than had previously been suspected, (3) confirm prior evidence that particular isolates
of Eudorina elegans and Pleodorina illinoisensis appear to be sibling taxa, and (4) contribute to the resolution of several hitherto unsettled issues in Chlamydomonas taxonomy.
Received: 7 October / 25 November 1996 |
| |
Keywords: | Evolution Intron sequences Molecular clock Chlamydomonas Volvox Volvocales |
本文献已被 SpringerLink 等数据库收录! |
|