Tuesday, March 8, 2011

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.

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