Molecular Biology and Evolution, Vol 7, 315-326, Copyright © 1990 by Society for Molecular Biology and Evolution
MJ Smith, JD Boom and RA Raff
We have investigated the differences between nuclear genomes of two
purportedly congeneric species of sea urchin that differ radically in early
development. Heliocidaris tuberculata develops by means of a typical
pluteus larva, whereas H. erythrogramma develops directly from an egg that
is 100-fold the volume of the H. tuberculata egg. Reassociation kinetic
analysis shows that the kinetic components of the genomic DNA from the two
species are essentially the same. No single repeat component explains the
30% difference between the H. erythrogramma and H. tuberculata genomes.
Reciprocal hybridization of tracer-labeled single-copy DNA fractions
between these species indicates that approximately 50% of the single-copy
DNA is sufficiently similar to form hybrids at standard hybridization
criterion. Thermal denaturation profiles of the hybridized single-copy DNA
sequence yields median (T50H) values of 13.8 degrees-16.5 degrees C. This
result suggests a divergence time of 10-13 Mya, which is comparable to
divergence times between congeneric sea urchin species in other genera that
do not differ significantly in development. Radical differences in early
developmental processes can evolve rapidly between closely related forms.
ORIGINAL ARTICLE
Single-copy DNA distance between two congeneric sea urchin species exhibiting radically different modes of development
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
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