Calanus diapause, energetics, and development
Please check out our most recent publication:
Tarrant AM#, Baumgartner MF#, Hansen BH, Altin D, Nordtug T, Olsen AJ. (2014) Transcriptional profiling of reproductive development, lipid storage and molting throughout the last juvenile stage of the marine copepod Calanus finmarchicus. Frontiers in Zoology 11:91. Link to provisional pdf.
We have used Illumina-based high-throughput sequencing to compare transcriptome-wide gene expression patterns at two times during development in the fifth copepodid stage. We then conducted detailed qPCR-based expression profiling of a subset of the genes. We anchored these molecular measurements with observations of molt stage progress, oil sac volume and gonadal development. This project was funded by the Biological Oceanography Program at the National Science Foundation.
Why are we interested in calanoid diapause?
Calanoid copepods are among the most abundant animals on the planet, and they play a critical role in transferring energy from the base of the food chain to higher consumers. Being able to predict spatial and temporal patterns in copepod abundance is necessary for fisheries models.
||Some copepods, such as Calanus finmarchicus, can undergo a dormant period (diapause) during their juvenile development. As juvenile copepods develop, they accumulate lipid energy stores. Some of the copepods will then continue to develop to adulthood and become reproductively active. During periods of low food availability, other individual copepods will migrate to deep water, slow their metabolism and remain dormant for several months. When the copepods emerge from diapause, they swim to the surface, develop to adults and mate.
|Above cartoon shows C. finmarchicus life cycle in the Gulf of Maine. Based on an illustration by M. Baumgartner (Baumgartner, M.F., C.A. Mayo, and R.D. Kenney. 2007. Enormous carnivores, microscopic food, and a restaurant that's hard to find. pp. 138-171 in S.D. Kraus and R.M. Rolland (eds). The Urban Whale: North Atlantic Right Whales at the Crossroads. Harvard University Press). Modfied by A. Tarrant and K. Spencer Joyce.
It is not well understood how copepods "decide" whether to undergo diapause, or when to initiate and terminate diapause.
Copepod - Bacterial Interactions
The emergence of cholera epidemics has been shown to closely track with large blooms of copepods, which are abundant aquatic crustaceans that harbor the causative agent of cholera (the bacterium Vibrio cholerae). Attachment to copepods provides Vibrio and many other types of bacteria with a steady supply of nutrients and protection from environmental stresses, leading to increased growth rates and production relative to those “free-living” bacteria in the surrounding seawater. Therefore, copepods represent important environmental reservoirs of a wide range of bacteria, including many animal and human pathogens.
Amalia Aruda Almada has recently (Dec 2014!) completed a Ph.D. dissertation in which she probed the dynamic nature of the interactions between copepods and the bacteria that live on them. The ability to discriminate between beneficial and pathogenic microbes is critical to animal fitness, yet whether copepods are able to actively select for or against particular microbial colonizers is not well understood. She has identified transcriptomic responses of the estuarine copepod Eurytemora affinis to colonization by two distinct Vibrio species using RNA-Seq to identify the mechanisms by which copepod hosts may respond to and discriminate between colonizing Vibrio species. She has also characterized the microbiome of active and diapausing Calanus finmarchicus individuals. The ecological factors that control the assembly of microbial communities on zooplankton are poorly understood. The dramatic physiological changes associated with diapause in C. finmarchicus provide a unique system to study how a sustained physiological change of a copepod host may influence its bacterial associates. Watch for papers related to this work coming out soon! See this article in Oceanus decribing some of Amalia's work as a student.
We are collaborating on the "ENERGYBAR" Project – A dynamic energy budget approach to understand and predict potential long-term effects of produced water on copepods in the Barents Sea. Working with our Norwegian collaborators, our role is to use next-generation sequencing to explore possible second-generation effects of oil exposure on copepod nauplii. The project is funded by the Norwegian Research Council.
Other Relevant Publications
Tarrant AM, Baumgartner MF, Verslycke T, Johnson CL. 2008. Differential gene expression in diapausing and active Calanus finmarchicus (Copepoda). Marine Ecology Progress Series 355: 193-207.
Aruda AM, Baumgartner MF, Reitzel AM, Tarrant AM. (2011). Heat shock protein expression during stress and diapause in the marine copepod Calanus finmarchicus. Journal of Insect Physiology 57(5):665-75.