Presentation Detail

Systematics and Inferred Phylogenies

Parkinson, John [1], Coffroth, Mary Alice [2], Baums, Iliana [1], LaJeunesse, Todd [1].

Moving toward a systematic revision of the genus Symbiodinium, the intracellular symbiont of corals.

Healthy coral reef ecosystems support incredible biodiversity in nutrient-poor waters. The success of reef-building corals depends upon an intracellular association with dinoflagellate microalgae (genus Symbiodinium). Climate change threatens the stability of such mutualisms, leading to stress-induced 'coral bleaching' events where the symbiont is lost and the host is compromised. Though initially characterized as a single, globally distributed species, subsequent molecular and physiological work has revealed extensive taxonomic and functional diversity among Symbiodinium. Much controversy remains as to how these data are interpreted in an ecological and evolutionary context. With the field plagued by confusing and arbitrary nomenclature, species delineation remains a critical step to ensure scientists are designing studies with appropriate taxonomic resolution and to facilitate the interpretation of findings from different labs.
We have taken steps to formally recognize the molecular genetic diversity within the genus Symbiodinium. We focused on representatives from a single clade with relatively low diversity and a high representation of monocultured strains. We developed a hierarchical molecular approach to delineate species boundaries in an easily replicated fashion. We sequenced both conserved and rapidly evolving nuclear, mitochondrial, and plastid genes to produce concordant phylogenies and assess inter- and intra-species levels of molecular variation. Patterns of reciprocal monophyly across all genes were used as primary evidence for a lack of sexual recombination among distinct lineages, satisfying the precepts of the Evolutionary and Biological Species Concepts. Where available, additional morphological, physiological, and ecological data supported the genetics-based species designations. These results demonstrate that molecular data provide a key line of evidence that is more reliable and rapid than traditional morphological approaches--an important consideration for diverse yet indistinct taxa such as Symbiodinium.
We have since moved on to more difficult categories: asymbiotic, culturable species, and symbiotic, unculturable species. In these cases, molecular data are available but supporting ecological or morphological evidence is lacking. Such situations are common and highlight both the spectrum of Symbiodinium lifestyles and the broad applicability of hierarchical molecular classification. With properly defined species, we can begin to examine the evolution of distinct dinoflagellate symbiosis strategies among closely-related lineages, informing far more relevant studies than the current paradigm of relying on 'clade'-level resolution, which essentially compares taxonomic families or orders. Species delineation lays the foundation for a systematic revision of Symbiodinium that more accurately reflects its evolutionary history and empowers researchers to appropriately investigate the future of reef-building corals in an era of climate change.

1 - Penn State University, 208 Mueller Lab, University Park, PA, 16802, USA
2 - State University of New York -- Buffalo, 447 Hochstetter Hall, Buffalo, NY, 14260, USA

Keywords:
coral symbiosis ecology
dinoflagellate evolution
species delimitation
Symbiodinium.

Presentation Type: Regular Oral Presentation
Session: 116
Location: Rendezvous B/Snowbird Center
Date: Monday, June 24th, 2013
Time: 11:45 AM
Number: 116006
Abstract ID:438
Candidate for Awards:Ernst Mayr Award