Dr. David Barrington has been studying the evolution of plants for 40 years. Since the late 1970’s, he has been studying a particular genus of ferns known as holly ferns.

Barrington originally chose to study holly ferns because they were largely unstudied and scientists needed data on the different species, but his project quickly became an evolutionary hunt for the lineage of certain fern species.

Very early into his research, Dr. Barrington discovered an unusual trait of some ferns in this genus: polyploidy.

Polyploidy is a condition in which an organism has more copies of its genome than is normal (humans, for example, are diploid and have two sets of chromosomes). When a polyploid organism is formed, it can no longer reproduce with either of its parents, and is therefore a new species.

In the case of Dr. Barrington’s ferns, polyploidy is a survival mechanism for hybrid species. Normally, when two species of holly fern inter-breed (and each donate one set of chromosomes), an infertile hybrid results, and that hybrid then dies without having reproduced.

In response to this, the two species donate both sets of chromosomes to the offspring, and the resulting plants are viable, polyploid hybrids.

Now, in his laboratory at UVM, Dr. Barrington and a team of both graduate and undergraduate researchers are trying to trace the lineage of a particular species of holly fern – Polystichum talamancanum. Not only is this fern unique in that it has four sets of chromosomes, but it was named by Barrington himself, one of several new species Barrington has discovered and named.

The research team has identified one of the parents of this P. talamancanum – P. concinnum, by finding a conserved gene which was traced from parent to offspring. Barrington’s team is currently attempting to identify the other parent species of P. talamancanum.

To do this, the research team has collected samples from areas around Central America, where this polyploid species grows. Forty-one other species of fern have been collected in an attempt to identify one of them as the parent.

To identify which of the forty-one species may have combined to produce P. talamancanum, Barrington’s team must perform two simultaneous tasks: sequence a portion of the polyploid genome, and sequence the same portion of all forty-one possible parent species.

In order to identify the segment of the genome in P. talamancanum which originated in the unknown parent, Barrington’s researchers must isolate the set of chromosomes which originated in the known parent. This is done by identifying highly conserved genes in P. talamancanum and comparing them to the genome of the known parent, P. concinnum.

Once that portion of the genome is isolated, Barrington can then work with the remaining DNA to identify the plant’s other parent.

Despite the seeming simplicity of the process, Dr. Barrington’s team has run into several major problems along the way.

To start, no one has been able to successfully separate one set of chromosomes from the other in the species. To attempt to develop a technique for this, the researchers are using a sterile diploid hybrid between two known species, and attempting to separate the sets of chromosomes.

To this point, the attempts have yielded limited success, and the problem is proving to be a major roadblock to the successful completion of the project.

Another potential problem facing the team is finding a section of the genome which can be used to make an evolutionary connection between P. talamancanum and its unknown parent. If Barrington cannot find a viable segment of the genome for comparison, it will be impossible to correctly identify the species responsible for producing the polyploid.

Even if all of the techniques are perfected and all of the genomes are sequenced, there is still a possibility that no match will come out of the genomic comparisons. When asked what his next step would be should this occur, Barrington simply replied “I’ve gotta go back into the woods.”