Story by Student Intern Rick Orozco

I had the opportunity to sit and talk to Dr. Ira F. Greenbaum about his research on Peromyscus maniculatus (deer mice) in the Pacific Northwest region. First, a little bit of background on Dr. Greenbaum: he attended Hofstra University where he acquired his Bachelor’s degree in Biology in 1973. After that, he worked on his Master’s and PhD in Zoology at Texas Tech University in 1975 and 1978, respectively. He then joined the Department of Biology at Texas A&M University and is currently Professor and Director of Lower Division Instruction where he is enhancing the education of undergraduate students.

When asked why he thought the Peromyscus study was important, Dr. Greenbaum mentioned how the original research was designed to do something very different. When he started his research, during the time of his PhD, all the deer mice in the Pacific Northwest were one species, Peromyscus maniculatus. Dr. Greenbaum’s research focus was on the chromosomal structure of the mice, such as short and long arms and how they influence chromosome pairing and how they segregate during meiosis. One point that Dr. Greenbaum mentioned dated back to Barbara McClintock’s work in the 1930’s, which revealed when you have heterozygosity for inversions you tend to have duplicated and deleted products during meiosis. This is problematic because individuals affected with this are generally less fit with low reproductive success due to half of their gametes being unbalanced. Dr. Greenbaum started finding frequent pericentric invesions within populations of Peromyscus maniculatus and wondered how this could be occurring? How could you get what’s called a meiotic under- dominant rearrangement, a chromosomal arrangement that should not be maintained at high frequencies within these Peromyscus populations? A problem Dr. Greenbaum encountered in preparing to answer this question was determining how to establish an experimental design that depends upon populations when you have a mouse that is distributed from the Atlantic to the Pacific and from the Northern Tundra to Central Mexico. Basically, it is difficult to study population genetics when you can’t recognize a population. Dr. Greenbaum solved this by creating the assumption that mice from one island are a different population than those on another island. His hypothesis was that “it’s not that the mice can’t swim, but the fish swim a lot better.”

Dr. Greenbaum sought to test the hypothesis that the type of chromosomal evolution observed in P. maniculatus was driven by genetic drift, which occurs much faster and intensely in smaller populations (i.e., islands) than large populations. What actually happened when the research started was that Dr. Greenbaum arrived at the Pacific Northwest region and discovered not just one species but two: Peromyscus maniculatus and Peromyscus keeni (he had no idea of this prior to the hypothesis). Keeping it short, he mentioned that no hybrids were found so it was clear that these two species were not interbreeding.

So how exactly did Dr. Greenbaum discover that there were two species? He wasn’t sure exactly where he did the first capture of both species but he thinks it was on Salt Spring Island, Canada. Dr. Greenbaum and his crew set Sherman traps in the afternoon, sat around the campsite, ate dinner, had a bourbon or two, and went to bed (to me this sounds like a perfect night). In the morning, the traps were collected and the live mice were placed in cages. What happened next baffled everyone; the mice started fighting one another. Since healthy mice were preferred, they sorted them into groups that didn’t try to kill each other. After some trial and error, they noticed some differences between the two groups: one group was smaller and lighter in color than the other. This conclusion was made with just physical characteristics; fast-forwarding through the entire lab process, bone marrow, hearts, livers, and kidneys provided the last sets of data to support the existence of two different species. Going back to his hypothesis, Dr. Greenbaum and his colleagues found several small islands where both species co-occurred and were both polymorphic for pericentric inversion at high frequencies (50%) for chromosomes 6 and 7. This revealed that genetic drift was not a primary factor in the chromosome evolution or chromosomal polymorphism.

Aside from the actual research, I was also interested in the behind-the-scenes events that weren’t reported in the published manuscripts. Dr. Greenbaum specifically mentioned Harry Sowchhuck a logger who showed them great hospitality by fixing their two flat tires, charging no fees, and then took them home so they can eat, bathe, and sleep. It’s not every day that one stumbles upon a special person like that. Another interesting event was when Dr. Greenbaum and his crew were staying at a motel in Washington. He said that they were thrown out of this motel due to taking live mice into the facility. Imagine what people thought when they saw some random guys getting off a truck carrying cages full of mice, centrifuges, test tubes, microscopes, liquid nitrogen tanks, and much more. Because of that, they started telling people what they were doing before they booked a room. When they told the owner of a motel in the city of Nanaimo, Canada, he said that they could continue but on the condition that they trapped the mice around the motel. Dr. Greenbaum said “we caught more mice around that motel than at many of our trapping localities.”

The way Dr. Greenbaum spoke about his time in the field was stunning. His tone showed me that he absolutely loved every moment out in the field. A good estimate of the time Dr. Greenbaum spent in the field was about 30 years, which included his time in Latin America. He said that there will always be difficulties during those trips such as getting a cold, food poisoning, and severe weather. Simply put, “stuff happens.” When I asked for Dr. Greenbaum’s top 5 favorite trips, he could not come up with a list because every trip was his favorite, except for that one trip with the extremely hot summer in Baja California. I was a little anxious before doing this interview since this was my first interview and I had not met Dr. Greenbaum previously. However, it turned to be a fun and great learning experience. Dr. Greenbaum is an easy-going, family oriented, big-time fisherman who does his best every day to make a societal contribution by helping young people educate themselves and get to where they want to go in life. He had always wanted to be a college professor and run a graduate research program. In fact, he loved his college years so much that he decided he was going to stay on a college campus for the rest of his life. When asked to describe his overall experience with his career, Dr. Greenbaum said “I can’t. I love it. It’s what I do.”

Read Rick’s reviews of two of Dr. Greenbaum’s research articles: Hogan et al 1993 summary Allard and Greenbaum 1988 Summary