Previous research

Most multicellular organisms go through a single cell bottleneck in development, a process that ensures subsequent clonality of the cells within the individual. Selection for clonality among cells could reduce costly intra-organismal conflicts that would occur in mixtures of unrelated cells (chimeras). Previous work on D. discoideum has shown that uniclonal slugs migrate further than chimeric slugs of the same size across agar, indicating a functional cost to chimerism. I tested whether this cost to chimerism results in a fitness cost under more natural conditions. First, I examined migration of slugs across decaying leaves or soil. Second, I examined migration up through layers of these substrates, which most closely mimics the natural migration of D. discoideum slugs to the soil surface. In most trials, chimeras performed worse than single clones. These results indicate that chimerism in D. discoideum has a real fitness cost in the wild, likely to be compensated for only by the larger size chimeras can attain in nature.

Current Work

D. discoideum cells that are grown in a glucose-rich environment are known to increase their allocation to spores when mixed with cells from a glucose-absent environment. If within a population of cells those that are most hardy and healthy are predestined to become spores and these spores are of a higher quality, it may allow for two interesting situations. Firstly, using health as a true measure of fitness could likely force mutant cells (which could potentially be genetic cheaters) into a prestalk role if that mutation has any negative pleiotrophic effects on health. Secondly, it ensures that D. discoideum clones could produce the best possible spores in mixes with other clones and thus retain the best chance of survival into the next generation.

In my current research, I explore whether amoeba condition is important in various aspects of development. I measured the spore production, spore germination and the ability to establish a new colony by healthy and unhealthy lines as well as the relative spore allocation when these lines are mixed.

For all tests, I grew an axenic lab strain (AX4) of D. discoideum cells in both healthful and unhealthful environments. I assessed health by measuring the growth of cells in both environments.

The first environment I tested was a standard media prepared with and without glucose. To determine relative spore allocation of mixed cells, I grew an AX4 strain that expresses GFP (green fluorescent protein). I mixed labeled cells with non-labeled cells and allowed them to develop on nitrocellulose filters. After development, the relative spore allocation by each line is determined via glowing spore proportions. I also tested cells that were grown in standard media at the optimal and a suboptimal low pH. For these experiments, I utilized a dye-based cell labeling technique, Cell Tracker (CMF) to determine relative spore allocation.

Quantifying the properties of spores created from both healthy and unhealthy cells is necessary to determine if health actually affects the quantity and/or quality of spore production. To measure the quantity aspect of spore production, I compared the relative number of spores produced by healthy and unhealthy cells. To determine the effect of health on quality of spore production I measured how many of these spores actually germinated when plated sparsely on a lawn of bacteria. I also measured another quality aspect of spore production, the ability of newly hatched cells to establish a population, through a proxy for early generation growth. When cells hatch on a lawn of bacteria, each new population clears a spot of bacteria. Since the spots tend to be circular, I measured the diameter of spots from both health and unhealthy lines and compared the relative areas. This research is being prepared for publication.