Haidensis!
Wow, this is kinda a late update… sorry! I had a hard time thinking of what to write – significance has always been something that’s hard to explain for me. It makes sense in my head that understanding things is important, but when I try to explain that to anyone else, it ends up sounding trifling and lame. But that’s okay. It seems that I’m not the only one who’s curious about how things work, as the entire goal of the Willis Lab is to understand how speciation works in the grand scheme of evolution (Oh man, did you see that smooth transition??). In particular, they investigate why and how new species form, and why/how they stay as reproductively isolated new species, using Mimulus as a model. Mimulus is a really good model because the generation time isn’t too long and the genus is really diverse.
My project deals with a tiny species of Mimulus called “haidensis”. It’s found only on Queen Charlotte Island in BC, and the only other species of Mimulus on the island is guttatus. Jen, the grad student I’m working with, has already figured out that haidensis is a tetraploid – its cells have 4 copies of all the chromosomes instead of the normal 2 copies. What she doesn’t know yet is whether the 2 sets of chromosomes came from the same species (autotetraploid) or different species (allotetraploid), how the 2 plants came to form the tetraploid (Which one was the “mom”?), and what the path of evolution was (Did they all come from one original tetraploid that self-pollinated or did the same tetraploid form multiple times?). You might think the first question is obvious – after all, the only other species on the island is guttatus, so the tetraploid must just have a doubled guttatus genome. However, the plant lives in higher altitudes that guttatus can usually tolerate, and shares a lot of characteristics with another high altitude species, tilingii. This means that there could’ve been tilingii in the area before, but then haidensis formed as an allotetraploid and outcompeted the tilingii, causing it to go extinct in the area. Or it could mean that there were never tilingii in the area and haidensis formed as an autotetraploid of guttatus, then adapted to the high altitudes by evolving similar traits to tilingii. Either way, the evolutionary path of haidensis could show us at least a little bit about the capabilities of plants to evolve and speciate, which could contribute to our long-term understanding of polyploidization as it contributes to evolution. This could be very significant, since polyploidization is likely the most common path to speciation (tetraploids are considered a separate species from their diploid parents, since their different genome numbers keep them from interbreeding). Goldblatt et al. and Masterson et al. estimated that 70% of all angiosperms evolved into their current forms by doubling their genome at some point (or at multiple points). Therefore, understanding the process behind polyploidization is pretty significant.
As for why the polyploids stay new species instead of just dying out, it’s assumed that they must have some kind of competitive advantage. One theory is that polyploids adapt more quickly and have less inbreeding depression because the extra set of genomes allows for more heterozygosity. In allotetraploids, all the plants are initially heterozygous, since their 2 sets of chromosomes are from 2 different species. This is why figuring out how many times haidensis formed is important. If the tetraploid only formed once, and there’s only 1 set of diploid parents, the genetic diversity of haidensis is severely limited. However, if there were many sets of diploid parents that formed allotetraploids, that’s a lot larger of a gene pool, which would increase haidensis’ competitive advantage, if the theory I just mentioned is true.
I get the feeling that a lot of this doesn’t make sense hahah, so ask questions in the comments!
