The wild rodent I will be working with is called a "degu." Degus are endemic to Chile and kind of look like guinea pigs with long, furry tails. In addition to being very smart and extremely social, degus are also diurnal (meaning they're awake during the day, like us). Degus sleep and breed in underground burrow systems, and the really cool thing about degus is that they utilize a unique breeding technique called "plural breeding with communal care." This means that several mothers give birth to and raise their pups in the same burrow system. In addition to raising their offspring in a common area, degu mothers will also provide care for offspring other than their own. This means that if you're a degu pup, you're groomed and nursed by your mother and several other females.
|This is a degu looking at a closed trap.|
So what's the benefit of plural breeding with communal care? If you're a degu mother, why would you invest some of your resources in pups that are not your own? If all the degus in a burrow system are closely related, then plural breeding with communal care may make some sense because it can be beneficial to provide care for your nieces and nephews since they share some of your genes. It appears that degu burrow systems usually contain several females that are closely related, but this is not always the case. So why do degus practice plural breeding with communal care? One hypothesis is that communal care increases the survival rate of all burrow offspring. However, researchers found that larger group sizes didn't lead to increased offspring survival.
Since I'm a physiologist, I'm interested in looking at some of the more proximate mechanisms in this reproductive strategy. Mainly, I'm going to be testing whether degus benefit from communal care because they gain a "buffering effect" against post-natal stress (meaning, stress that they encounter right after they're born when they're still young pups). Basically, after a pup is born, it's very important that they're licked and groomed a lot by their parent(s). If pups are not groomed enough when they're young, then they will have high stress hormone levels as adults. High, sustained stress hormone levels can lead to a decrease in health and survival. Stressed mothers lick and groom their pups less, so one benefit of communal care could be to buffer pups from a negligent mother. This mean that if you're a degu pup and your mother is really stressed out and is therefore not grooming you much, you'll still receive some grooming from the other females in the burrow system and you'll end up having a healthy stress response as an adult.
In order to test the hypothesis that plural breeding with communal care helps buffer degu pups from post-natal stress, I'll be studying wild degus in Chile this June through October. I'll be catching and marking pregnant females during the late summer and immediately after the females give birth (late September), I'll be implanting some mothers with stress hormone pellets and others with placebo pellets. These pellets will release a steady amount of cortisol (the main stress hormone in degus) over 60 days. Each burrow system will receive a different proportion of cortisol-implanted mothers; groups will have either 100%, 50%, or 0% of their lactating females receiving cortisol implants, with the rest of the females receiving placebo implants.
After the pups emerge from their burrows (October), I'll be trapping the pups to measure their stress responses. If my hypothesis is supported, then I expect to see healthy stress responses in all pups except for the pups from the burrow systems where all of the mothers received cortisol implants.
Because degus use multiple burrow systems, it's very difficult to figure out which degus are in which groups. To determine group membership, I have to do a lot of trapping and night-time radio telemetry to figure out where each individual spends most of their time and who with. Since there a limited number of radio collars and traps, I will probably have to work for two field seasons in order to get all of my data.
This is only one of the projects that I will be working on this field season, check out my next few posts to learn about the other experiments I'll be running. I also plan to go into more detail about field work, stress physiology, and Chilean culture. I hope you'll follow my blog through the next 5 months!
¡Hasta luego! (Spanish for "see you later")