Individuality in Rodents: Research in the News

Being part of the crowd is what makes you unique. Say what?...

That’s the bottom line of a multi-year study I did with Dan as part of my dissertation research. We looked at eight different species of social ground-dwelling rodents, including marmots and their close cousins prairie dogs and ground squirrels. We found that as social group size increases over evolutionary time, so does the degree of individuality in the animals’ voices. Our study is the cover feature of the latest issue of Current Biology.

Pollard, KA & Blumstein, DT. 2011. Social group size predicts the evolution of individuality. Current Biology 21(5): 413-417. doi 10.1016/j.cub.2011.01.051 Available here.

Our study has been covered in popular press outlets, including:

Discover

NPR

Discovery News

The Daily Mail UK

Ars Technica

Science Daily

The Varsity

EurekAlert!

and more!

Mom and Dad: A story of hair part 2

Like Julien mentioned in the last blog entry, to understand what is happening evolutionarily with the marmots, we need to know their pedigree. To do this, we need to genotype all the new pups every summer to see who their mom and dad are. This is where I come in- I am in charge of doing all the lab work and analysis that will allow us to assign pups to their parents.

To start everything, we need a sample of DNA. When we are out in the field, we collect hair from every new individual we trap (this means all the newly emerged pups). We store these samples in a freezer till we can get back to UCLA and get in the lab.


Once back in Los Angeles, I take a bunch of hairs and stick them in a tube with a solution that lyses the cells and allows me to extract the DNA. Everything should be good now, right? I have my DNA and I should just be able to go get it genotyped, but hold on…there are a couple other steps involved before we get a pedigree.


The machine that tells us the genotype needs many, many strands of DNA to be able to read it, so we need to amplify it. We do this using PCR, or Polymerase Chain Reaction. We place our marmot DNA in a tube with nucleotides, primers, and DNA Polymerase and heat and cool the mixture several times. The heating and cooling make the DNA denature, or come apart, and come back together. At the end of the process, we have thousands of strands of DNA where we only had our original strands of marmot DNA.


We send this PCR product off to get genotyped. It takes about a day, and before you know it we get back a file that tells us the genotype of our marmot pups. The next step is going through all these genotypes and comparing them with potential mothers and fathers. To do this, we look at 12 microsatellites that are highly variable. What this means is that we look at 12 “sites” on their DNA and see what the allele is. We can then look at the potential parents and see what their alleles are at these corresponding sites. If they match, we can be pretty confident that we have found the right parent. Sometimes though, we can’t always be sure about the parents using molecular methods; that’s when we include our social observations to determine parental assignment.


Once this is done, we can start looking how different traits(morphological or behavioral) are changing over generations and we can make inferences about how marmots are evolving.

Here I am with pipette in hand, trying not to mess up the samples.

Photo by Amanda Lea

Mom and dad: A story of hair

When studying evolution, it is primordial to know the relatedness of the different individuals in a population. All least, we need to know who is the father and the mother of the different offspring we see every summer. Why it is so important? Simply because if you see a difference between the parents and their offspring and if this difference it due to genes then you are looking at evolution.

Marmot pups are really cute when they emerged from their burrow. Every year we asked them who are their mum and dad. However, no pups ever answered our questions. We tried to convince them to give us a nice drawing of their mum and dad, but we badly failed. Most of the time, when we approach they simply alarm-call or ignore us. One good thing for us is that when pups emerge from their burrow, they still hang-out most of the time with their mother and their brothers and sisters. By observing them, we are confident about who their mother is.

Telling who is the father is a totally different story. As in most animals, marmot males do not care about their offspring. After copulation, their main activity is getting big, fat, round, and plump. Males do not provide cares to the offspring. So observations could in no way give us information about paternity. Worth that than during the mating period, females copulate with different males, and in a same litter, pups could have different fathers. So to the different fathers of the pups, we are asking the question directly to the pups. Not truly to the pups, we asked the question to their hairs. Hairs provide all the information we need. Using some hair torturing techniques, also called molecular techniques, involving alcohol,burning and heating, we could extract DNA. With this DNA, we genotype the pups and by comparison with the genotype of the potential fathers, we could determine who is the father of whom. Basically, for a geneticist or a molecular biologist, hairs (or others samples with DNA) are really equivalent to the little paw-written pedigree we could ask to the pups. However, 'reading' the pedigree in hairs is more complex and need a large amount of work in the lab.

Maternity has been determined based on behavioral observations since 1962, and paternity was assigned using molecular techniques since 2000. The entire pedigree in the marmot population have 3500 individuals. We know the mother of 90% of the individuals since 1972 and we know 84% of the fathers since 2000.

This is a graphical representation of the marmot pedigree at RMBL. Each point represent an individual. Red lines stand for maternal link and blue one for paternal ones. To clarify the pedigree, I have made two graphs: one for the mums


and one for the dads




Below is a graphic of one of the longest patriline observed in our population (72 descendants over 5 generations). Squares are males and circles are females.