Well known for their ecological and evolutionary importance, the diatoms
(Bacillariophyceae) are ubiquitous eukaryotes that play key roles in global
primary production and biogeochemical cycling of nitrogen, phosphorus,
silica, iron and carbon. Diatoms alone account for 45% of the total
global primary production contributed by the ocean. Although the ecological
importance of diatoms is universally understood, little is known about
their cell biology, genome structure and the evolutionary strategy which
has afforded them competitive dominance in the modern ocean.
Attempts to
reconstruct diatom phylogenies have been ongoing in an effort to elucidate
the origins and evolutionary histories, but application of evolutionary
relationships to ecological studies has not been a major focus. The presence
of genetic diversity within a group of organisms has little ecological meaning
unless that diversity leads to phenotypic variation among species, subsequently
affecting their ecological success.
Our goal was to examine the scope of
phenotypic variation across genetically diverse diatom species and identify
the ecological drivers of diatom evolution. We examined the DNA content
of several diatom species and investigated how changes in genome size may be
related to the reported phenotypic variation in diatoms. We tested
hypotheses of correlated evolution between genome size and various other
character traits including habitat, distribution, life strategy and
cell volume.
Early genome size surveys of phytoplankton suggested a positive
relationship between cellular volume and DNA content; however our results
examine these relationships using phylogenetic analyses. A phylogeny
was built using the 18s rRNA region from 148 diatom species and phenotypic
trait data was analyzed using the comparative method. As a critical component
of the global ecosystem and the dominant eukaryotic group in the world ocean,
diatoms offer a platform for synthesizing evolutionary histories and ecology
in an effort to understand the origins of phenotypic variation.
