[Coral-List] Cryptic Species/Introgression Paper

[Jason Thomas Ladner]

Dear colleagues,

We are writing to bring your attention to a paper that was recently
published in BMC Evolutionary Biology, which may be of interest to
many on this list. In the paper, we utilize high-throughput sequencing
data to compare the transcriptomes of two co-occurring types of
Symbiodinium with a focus on trying to identify some of the genes
involved in the thermotolerance of Clade D.

Protein evolution in two co-occurring types of Symbiodinium: an
exploration into the genetic basis of thermal tolerance in
Symbiodinium clade D
Jason T Ladner*, Daniel J Barshis and Stephen R Palumbi

http://www.biomedcentral.com/1471-2148/12/217


Abstract

Background

The symbiosis between reef-building corals and photosynthetic
dinoflagellates (Symbiodinium) is an integral part of the coral reef
ecosystem, as corals are dependent on Symbiodinium for the majority of
their energy needs. However, this partnership is increasingly at risk
due to changing climatic conditions. It is thought that functional
diversity within Symbiodinium may allow some corals to rapidly adapt
to different environments by changing the type of Symbiodinium with
which they partner; however, very little is known about the molecular
basis of the functional differences among symbiont groups. One group
of Symbiodinium that is hypothesized to be important for the future of
reefs is clade D, which, in general, seems to provide the coral
holobiont (i.e., coral host and associated symbiont community) with
elevated thermal tolerance. Using high-throughput sequencing data from
field-collected corals we assembled, de novo, draft transcriptomes
forSymbiodinium clades C and D. We then explore the functional basis
of thermal tolerance in clade D by comparing rates of coding sequence
evolution among the four clades of Symbiodinium most commonly found in
reef-building corals (A-D).

Results

We are able to highlight a number of genes and functional categories
as candidates for involvement in the increased thermal tolerance of
clade D. These include a fatty acid desaturase, molecular chaperones
and proteins involved in photosynthesis and the thylakoid membrane. We
also demonstrate that clades C and D co-occur within most of the
sampled colonies of Acropora hyacinthus, suggesting widespread
potential for this coral species to acclimatize to changing thermal
conditions via ‘shuffling’ the proportions of these two clades from
within their current symbiont communities.

Conclusions

Transcriptome-wide analysis confirms that the four main Symbiodinium
clades found within corals exhibit extensive evolutionary divergence
(18.5-27.3% avg. pairwise nucleotide difference). Despite these
evolutionary distinctions, many corals appear to host multiple clades
simultaneously, which may allow for rapid acclimatization to changing
environmental conditions. This study provides a first step toward
understanding the molecular basis of functional differences
betweenSymbiodinium clades by highlighting a number of genes with
signatures consistent with positive selection along the thermally
tolerant clade D lineage



Thanks,
Jason