|
Systematic
Research in the Raphidophytes
The
raphidophytes are a
cosmopolitan group of microalgae in freshwater and marine
habitats. They are named for their
peculiar extrusive organelles, or trichocysts, which under light
microscopy,
resemble the raphides (thin crystals of calcium oxalate) of
plants. Currently, there are seven
genera belonging to the raphidophytes: Gonyostomum,
Vacuolaria, and Merotricha (freshwater); Chattonella, Heterosigma, Fibrocapsa, and Haramonas
(marine).
 Most
research and
discussion of the raphidophytes is centered around their known harmful
effects
on fisheries. Many marine raphidophytes
have been implicated in large fish kills around the world, particularly
in Japan.
While the exact mechanism
for causing fish mortality is currently under debate, some evidence
supports
production of a brevetoxin-like compound that interferes with the
autonomic
nervous system. Most
raphidophytes are not known to be toxic, and are relatively
understudied. As a
result of their potential economic importance, those few marine
raphidophytes
known to cause fish kills and harmful algal blooms have been studied
most extensively.
Our current research into the systematics of the raphidophytes is aimed
at answering 4 fundamental questions.
1. What is
the phylogenetic
relationship between raphidophytes, xanthophytes and phaeophytes
(brown
algae)?
2. How diverse is the genus Chattonella structurally
and
molecularly?
3. What are the structural
apomorphies that define raphidophyte genera?
4. What are the phylogenetic relationships
between freshwater and marine raphidophytes?
These
questions are being
answered using a two-fold approach of molecular phylogenetics and comparative
ultrastructure.
Currently, efforts are underway to sequence the HSP-90 and actin genes
from numerous raphidophytes, in
order to create a well-supported phylogeny of the group. This
will be coupled to a large RAPD (randomly amplified polymorphic DNA)
dataset to uncover infra-generic realtionships in Chattonella.
Finally the molecular data will be
coupled with structural characters such as flagellar root systems,
cortical cytoskeleton, flagellar transition region, pyrenoid
morphology, mucocyst ultrastructure, plastid morphology, and swimming
behavior. The end result will be a well-supported phylogeny that
will provide unique insights into pigment evolution, structural
innovation, and the evolution of toxicity in the raphidophytes.
All content © 2003 S.C.A.E.L. any
use of contents
requires permission from the Webmaster.
Algal Ecology Labs--331 Fort Johnson
Road--Charleston,
SC 29414.
|
