The Long chain Diol Index: A marine palaeotemperature proxy based on eustigmatophyte lipids that records the warmest seasons.

Long chain 1,13- and 1,15-diols are lipids which are omnipresent in marine environments, and the Long chain Diol Index (LDI), based on their distributions, has previously been introduced as a proxy for sea surface temperature. The main biological sources for long chain 1,13- and 1,15-diols have remained unknown, but our combined lipid and 23S ribosomal RNA (23S rRNA) analyses on suspended particulate matter from the Mediterranean Sea demonstrate that these lipids are produced by a marine eustigmatophyte group that originated before the currently known eustigmatophytes diversified. The 18S rRNA data confirm the existence of early-branching marine eustigmatophytes, which occur at a global scale.

PHYLOGENETIC POSITION OF ATTHEYA LONGICORNIS AND ATTHEYA SEPTENTRIONALIS (BACILLARIOPHYTA)(1).

The phylogenetic position of diatoms belonging to the genus Attheya is presently under debate. Species belonging to this genus have been placed in the subclasses Chaetocerotophycidae and Biddulphiophycidae, but published phylogenetic trees based on 18S rDNA, morphology, and sexual reproduction indicate that this group of diatoms may be a sister group of the pennates. To clarify the position of Attheya, we studied the morphology, 18S rDNA, 16S rDNA of the chloroplasts, the rbcL large subunit (LSU) sequences of the chloroplasts, and the sterol composition of three different strains of Attheya septentrionalis (Østrup) R.

The rise of the rhizosolenid diatoms.

The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 +/- 1.