Something Old, Something Novel, Something Stolen, Something Green

Last of our Summer 2017 Blog Series! Happy new semester!

Contributed by Rachael Wade

As scientists, we often accept DNA evidence as absolute truth.

The information we are able to elucidate from these data-packed molecules are undeniable and reliable. However, it’s important to remember the work that came before more modern techniques like DNA sequencing – the simple, yet elegant studies that illustrate the fundamentals we often take for granted, or, in whispered tones, may even consider outdated. There are incredible examples of how genetics has more accurately confirmed or perhaps elaborated on the findings of previous work, rather than defining the limits of our knowledge. I experienced this important realization during my dissertation work, and I continue to be reminded to consider all methods, both old and new, when doing research.

My dissertation research explores the diversity of algae recovered from the stolen chloroplasts, or kleptoplasts, of the sea slug Plakobranchus. Plakobranchus is what I like to call a specific-generalistic herbivore – it only feeds on siphonous green algae,

Plakobranchus with its wing-like parapodia open (left) to reveal the kleptoplasts retained in its tissues. PC: Sofia Suesue.

but is not very choosy within those groups. Siphonous algae are unicellular, yet macroscopic, which makes them prime choices for “sap sucking” sea slugs like Plakobranchus. These slugs use teeth and straw-like mouthparts to pierce these large, single-celled algae and suck out their cellular contents. Majority of their nutrition comes from sugars and proteins in the cytoplasm, but they also systematically filter the chloroplasts into specialized portions of their digestive track where they continue to photosynthesize and provide sugars, proteins, and lipids to their new sluggy host. Because of this novel trait and being non-picky eaters, we can use Plakobranchus as a unique sampling tool to explore the diversity of siphonous algae.

 

When I began my graduate work, I was surprised to find that I was not the first person in Hawai‘i to have explored this interesting slug-algae relationship. My committee member Dr. Celia Smith (UHM, Dept of Botany) shared with me that the director of UHM’s Microscope Facility, Dr. Marilyn Dunlap, completed her dissertation research on the same topic, but using very different methods. While I was using chloroplast DNA to identify Plakobranchus’ favorite snacks, she used traditional microscopy to examine chloroplast morphology and chromatography to explore pigment differentiation. Arguably the most compelling finding of Dr. Dunlap’s dissertation was the diversity of chloroplast sources she was able to identify simply by looking under the microscope, many down to the species level! I was even more excited to find that the genetic results of my Masters thesis, while adding several new records and putative new species of siphonous green algae to our knowledge of Hawai‘i’s marine flora, supported the findings of Dr. Dunlap’s dissertation.

Upon discovery of these parallel findings, I met with Dr. Dunlap to discuss the project and to hopefully find answers to some of the questions I had developed while formulating my study objectives and design. It was amazing to find that research conducted over 40 years ago was aligning with the work I was doing; it was a priceless opportunity to pick her brain and geek out about kleptoplasty with her. With several of my questions answered, and many new ones formulated that also mystified Dr. Dunlap, I couldn’t wait to begin my dissertation research, which uses a more cutting edge, next generation molecular technique to assess kleptoplast diversity across the Main Hawaiian Archipelago, including Plakobranchus specimens collected from the same site where Dr. Dunlap conducted her research. Now I could really put Dr. Dunlap’s microscopy results to the test in comparison with this more “modern” technique.

Rachael using a novel sampling technique to collect kleptoplasts from live Plakobranchus. PC: Yue Tang.

Though my dissertation work is ongoing, my preliminary findings support that yes, both classic techniques, like the microscopy used by Dr. Dunlap, and sophisticated molecular techniques can elucidate much of the same results. More remarkably, the methods combined provide a much greater breadth of information than either could provide alone: while molecular assessment of Plakobranchus’ kleptoplasts recovered greater overall diversity of algae, the chloroplast itself tells us some very interesting things about the algae Plakobranchus eats. Specifically, different pigments in the chloroplast, which correspond to different genera and often species, may suggest that Plakobranchus’ preferred food species are able to use more of the available light, allowing them to be more efficient photosynthesizers.

Cartoon artist: Jason Cantley.

Better photosynthesis means preferable food options when considering stealing and enslaving the chloroplasts as powerhouses, as Plakobranchus does when it steals and maintains algal chloroplasts internally as a secondary energy source. So not only do we have a better idea of overall algal diversity in Hawai‘i and those preferred by Plakobranchus, we also have a new and exciting avenue to explore the evolution of  this novel trait of kleptoplasty and herbivore-plant interactions. Without both methods, we would not have such a comprehensive picture of this unique relationship between an herbivore and its food.

Moral of the story: Partnering classic techniques with modern ones can help us have a deeper understanding of our work. So next time you have the opportunity to try out that snazzy new machine or cutting-edge technique, consider pairing it with a classic approach. You never know what interesting new discoveries you may stumble upon!

 

PC: Jason Cantley

Rachael is a Ph.D. candidate in the Department of Botany at the University of Hawai‘i at Mānoa. More information about Rachael and her research can be found on her website: rachaelmwade.wordpress.com.

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