Does it matter that some of the tetraploids the hatcheries are using to make triploids are mosaics? Does it affect the nature of the larvae?
Are there alternative means of inducing tetraploidy from triploid eggs besides the fairly toxic cytochalasin B? Is it better or worse than the standard operating procedure now in use?
These are some of the research questions that have real implications for the Virginia industry, especially hatcheries, that undergraduate scholars have addressed in a National Science Foundation sponsored Research Experiences for Undergraduates. Each year about a dozen promising young researchers come into the program at VIMS and hook-up with a mentor in anything from fish systematics to benthic ecology to – yes, I am happy to add – oyster aquaculture, specifically aquaculture genetics. While ABC’s only other REU student was in 2002, we have had the pleasure of hosting students in 2012 and 2013.
Last year, Joseph “Joey” Matt (Wake Forest University) took on a project stemming from a question we got from AJ Erskine about mosaic tetraploids (a mosaic has lost some of its chromosomes, a subject of AJ’s thesis at VIMS). Specifically, AJ questioned the idea that mosaic tetraploids were being used for spawning triploid production batches and asked whether it might be more apt to distribute “pure” tetraploids. (While this is an excellent question, the fact of the matter is that most tetraploids are mosaic, and sorting them out would be a logistical nightmare.) So, does it matter?
Joey spent the summer doing crosses using mosaic tetraploids (labeled M – often selected for their severity) and also using pure tetraploids (labeled 4) to make triploids. Triploid crosses were made all ways – M (♂) x 2n; 2n (♂) x M, 4 (♂) x 2n, 2n (♂) x 4, along with diploid controls. These crosses were replicated over and over, early larvae were analyzed by flow cytometry to look for abnormalities, and survival recorded. Three pairs of M(♂) x 2n and 4(♂) x 2n triploids were set and grown up to examine this summer. The bottom line of this 2012 research project was that we could detect nothing unusual about the larvae obtained from crosses that involved mosaic tetraploids. (The sperm from every male – M or 4 – were always ‘perfectly’ di-haploid.)
This year, Brittany Peachey (Grove City College) joined us for the REU summer. Brittany accomplished an experiment that may never be repeated again in the annals of polyploidy. Specifically, Brittany examined the effectiveness of using 6DMAP as an alternative to CB for chemical induction of tetraploidy in eastern oysters. The reason for the unique aspects of this work is that it corresponded precisely with ABC’s overall push to develop new tetraploid lines from some of our best diploid lines. This is a process that takes four generations: diploid -> chemical triploid -> chemical tetraploid -> mated tetraploids as brood stock.
As ABC just completed a study of 13 different varieties of triploids, we had an unprecedented supply of three year-old triploids for Brittany’s work, and the basic experiment was replicated nearly 20 times. The bottom line for Brittany’s project was that 6DMAP is very effective in making chemical tetraploids, it is also less dangerous to the user, and, it seems, survival is better. A paradigm has been changed. We will switch to 6DMAP.
Both Joey and Brittany were rising seniors as REU students. Both are writing up their results for publication – the results were that tight. Joey re-joined us for the summer to help operate our hatchery at KAC. He will stay next year in a new position we are calling the “tetraploid technician” to help keep track of our increasingly intense breeding program with tetraploids.
Brittany will complete her senior year at Grove City, and then – who knows?