Friday, October 28, 2011

Getting Ready to Head Back to the U.S.

Well, my days in Chile are numbered- I'll be flying home on Monday, October 31st (and yes, Chileans do celebrate Halloween, so I'm hoping for some candy on the plane ride home). The last few days have been crazy busy since I've been scrambling to collect last-minute data, steadily writing up my thesis proposal which I'm defending a week after I get back to Tufts, and cleaning/packing/organizing for the trip home. This means I'll have to wait till next week to write about the endocrinology of parental care, so for this post I'll just be uploading a bunch of photos from my Chilean field season, enjoy!

Cueca dancers, the "cueca" is the traditional Chilean dance. 
Me in front of the Moneda (the president's house). Plus a stray dog, which are everywhere in Santiago.

Hiking in the Andes.

Black-billed shrike-tyrant
Parque Nacional La Campana

Pablo Neruda, Chile's famous poet and humanitarian.

Chilean swallow.

Magellanic horned owl

Street art in Valparaiso

Enormous male sea lion in Valparaiso (it smelled bad, too)

More cool street art, Valparaiso.

I've witnessed the sun rise pretty much everyday for the past two months.

And some days it's foggy and cold.

View from my apartment balcony after a student demonstration.

I caught an iguana with a TV antenna and some string a few days ago.

What a cutie!

Friday, October 21, 2011

Degu Sex

Reproductive physiology is amazingly super cool and fascinating. With the exception of stress physiology, I’d say that reproduction is the most interesting topic in biology. So, in honor of reproduction, let me tell you about the endocrinology behind mating, pregnancy, and lactation in the degu.

The mating period for degus is typically around the month of June. Because degus have a three-month gestation period, this means that the baby degus will be born around late August or September. Degus, like many seasonal animals, optimize their time for breeding so their offspring will be able to develop and grow in ideal conditions. The austral spring is a good time for degus to give birth because there’s plentiful food due to the rainy winter. The mattoral (that’s the habitat type I’ve been working in, it’s similar to the chaparral of Southern California) is very dry during the austral summer, so it’s important that the degus time their reproduction so all energetically expensive processes (growth in pups and lactation in mothers) will be completed before the dry season hits.

For male degus, testosterone is a key player during the mating season. Testosterone is an important hormone for spermatogenesis (sperm production) and several different mating behaviors such as gaining access to a mate, wooing a female, and performing the physical act of copulation. For species where mate access is competitive (elephant seals are a classic example), the more dominant and aggressive males are usually the most successful when it comes to reproducing. This aggressive behavior is partially modulated by testosterone, and dominant males oftentimes have higher levels of testosterone compared to subordinate males. Aggressive behavior is enhanced when testosterone binds to brain receptors (either by converting to 5-alpha-dihydrotestosterone and binding to androgen receptors, or by aromatizing to estradiol and binding to estrogen receptors). And while most of us think of aggressive behavior as fighting, aggression can also be displayed through song and other non-physical behaviors (ex: marine iguanas bob their heads up and down to caution other males encroaching on their territory).

Like many other seasonal vertebrates, male degus have high levels of testosterone during the mating season and low levels of testosterone during the rest of the year. Why do we see seasonal differences in testosterone levels, and if testosterone helps increase reproductive fitness through aggression and other behaviors, then why not pump out a ton of testosterone all the time? Well, the answer is that it’s costly; high circulating levels of testosterone create an energetically-expensive lifestyle, and it has been shown that testosterone-implanted animals can have low body mass, a suppressed immune system, and a higher rate of mortality.

The Challenge Hypothesis, posited by Wingfield and colleagues, states that the seasonal changes we see in testosterone levels are due to a tradeoff between aggression and parenthood. In bird species where males provide significant parental care (ex: providing chicks with food), testosterone levels usually fall after the chicks are born. After the chicks fledge, and if the parents are able to breed again, the male will then up-regulate his testosterone levels. For species where males don’t provide much parental care (like degus, who may do a little bit of thermoregulatory huddling, but that’s about it), the drop in testosterone is often longer and slower.

So what’s going on with the females during the mating season? Well, they’re probably checking out the males and judging them, but in addition to that, females are preparing themselves for pregnancy. Compared to male reproduction, the female reproductive cycle is quite complicated, but let’s see if I can break it down into the major steps (note: most of the information I’m providing is typical of guinea pigs, which are close relatives of degus):


This stage lasts a day or two, and the female is agitated and may mount other con-specifics. During this time period, the ovarian follicles are growing and the endometrium (lining of the uterus) is slowly building up. This follicle development is fueled by follicle stimulating hormone (FSH).

At the same time, the some outer cells in the follicles (specifically, the granulosa cells) are producing estrogens. Estrogen production is due to the work of two hormones: FSH and luteinizing hormone (LH), both of which are secreted from the anterior pituitary. LH stimulates the production of androgens from the theca interna (an inner layer of cells in the follicle), and FSH stimulates the production of an enzyme that takes the androgens and converts them to estrogens. This increase in estrogen levels is very important for the next stage:


First, the vaginal membrane opens, and after a few hours the estrous period begins. Estrous lasts 9-11 hours and this is when the female is sexually receptive (or “in heat”). In guinea pigs and other mammals, a female needs to be in estrous in order to perform “lordosis,” which is when the female arches up her back so the male can mount from behind. Copulation cannot occur without lordosis, so the males can only successfully mate with the females during this short time window. The binding of estradiol to certain neurons in the brain controls lordosis (note: I’m not sure if female degus perform lordosis, but it’s likely since guinea pigs do).


Right at the end of estrus, ovulation happens. Ovulation occurs when the estrogen levels reach a certain high point and activate a special control center in the hypothalamus. This control center causes a positive feedback cycle to start: the hypothalamus increases secretion of gonadotropin-releasing hormone (GnRH) which goes to the anterior pituitary and causes increased secretion of LH and FSH, which then go to the ovaries and cause the developing follicles to rupture and release the ova. The ova then begin their journey down the fallopian tubes where fertilization must take place (there’s about a 20 hour time window for fertilization to occur). The vaginal membrane may stay open for several more days, and then it will close until mid-pregnancy.

Immediately after ovulation, the ruptured follicles in the ovaries turn into corpus lutea. The corpus lutea produce high levels of estrogens and progesterone, which inhibit FSH and LH production (thus, preventing more follicles from developing). After about three days the corpus lutea start to degrade, and within six more days the corpus lutea are gone and the animal is ready to start the whole cycle again unless fertilization occurs and the ova successfully implant in the uterus lining, which brings us to:


The ova reach the uterus about three days after fertilization and take another three to four days to implant in the endometrium. The fertilized ova then begin to develop placenta, which produce and secrete a hormone called chorionic gonadotropin (CG). CG prevents the corpus lutea from degrading, so estrogens and progesterone levels stay elevated and no more follicles develop for the duration of the pregnancy. The estrogens and progesterone help stimulate development of the mammary glands for lactation, but lactation cannot begin until after the animals give birth because of the high levels of progesterone. (Question to think about: Birth control pills prevent ovulation from occurring. What hormone(s) do you predict are in birth control pills and how do these hormones prevent ovulation?)

Parturition and Lactation:

Degus have a gestation period of about 90 days (which can be longer or shorter, depending on the number of developing fetuses) and typically give birth during the night. During parturition (giving birth), each pup takes 10-30 minutes with 1-16 minutes between each pup. When parturition begins, the hormone “relaxin” helps the relax the cartilage holding the pubic bones together, and then oxytocin, released from the posterior pituitary gland, causes cervical distention and smooth muscle contraction in the uterine wall. Twelve to fifteen hours after parturition the mother has a post-partum estrous period of about 3 hours, which means she can get pregnant again right away. In humans, nursing and lactation are an effective means of inhibiting ovulation, but degus and some other small mammals can nurse their current young while carrying another litter. Milk production is stimulated by prolactin and glucocorticoids, while the effects of oxytocin cause milk letdown. During nursing, the stimulation of the nipple causes increased secretion of prolactin and oxytocin from the hypothalamus.

While I don’t have any photos of nursing degus, here are some pictures of degu pups:

The first degu pup capture of the year.

Getting ready to be released.

It will be hard to not take one home.

Thursday, October 13, 2011

What I’m Doing When I’m Not Trapping Degus

My advisor suggested that I talk a little bit about the challenges of working at an international field site. While it would be easy for me to list off the difficulties I’ve faced and the obstacles I’ve overcome, I feel that I should also talk about some of the terrific experiences that I only could have gained by traveling to Chile. So in this post, I’ll be writing about both the ups and downs of fieldwork and living in Santiago.


In Chile (and pretty much the rest of the world minus the U.S.) everyone drives stick shift. Because my parents didn’t want me to burn out the clutch on their old Volvo, I never really learned how to drive manual. Not long before I left for Chile, I was informed that I would have to drive a truck with manual transmission… surprise! So, after two short lessons with some trusting colleagues, I flew to Chile and prayed that I could “wing it.” I mean, where better to learn how to drive stick than in a major, South American city? (To be fair, Santiago drivers are no crazier than Boston drivers.)

Luckily, I didn’t have to start driving right away, so I had some time to practice before driving out to the field myself. Our daily commute takes about 45 minutes (depending on traffic) and involves driving through the heart of Santiago, taking a highway for a few miles, and then navigating a very long, bumpy dirt road. I started practicing on the dirt road and then one sleepy, Sunday morning my patient co-mentor, Dr. Loren Hayes, had me drive around the city until I got comfortable with shifting through all the gears. As time went on my stalls became less frequent and my shifting started working on a subconscious level, and so, thanks to the degus, I now know how to drive manual.

The truck in front of our cabin at Parque Nacional Fray Jorge 


Working at the same field site for five months has given me the chance to see many cool plants and animals. Spending hours upon hours in the same place has allowed me to observe some things that I would have never seen otherwise. Here are some of my favorite wildlife memories:

-While observing degus one day I saw little sprays of dirt flying into the air nearby. After a couple dirt sprays a tiny, shiny black head would pop out of a hole like a Whack-a-Mole. The culprit was a cururo, a type of subterranean rodent that has glossy black fur, tiny little ears, and large yellow teeth. The coruros construct little dirt mounds (kind of like molehills), which threaten to break my ankle every time I have to walk down one particular hill.

-One time while on my way to the boulder field I suddenly saw an enormous hummingbird. It was hovering in front of a tall, red flower, and it made a loud “PEEP!” every time it went in to drink some nectar. After consulting my bird book, I found out that I had seen a “Giant Hummingbird” (appropriately named, in my opinion).

-A few weeks ago my friend Meredith (she’s an American studying for her PhD here in Chile) found a Southern lapwing nest. The four eggs were very well camouflaged, so much so that we sometimes had difficulty re-finding the nest! But after checking on the eggs everyday, we were lucky enough to witness the baby lapwings hatching!

They look much cuter after their feathers dry.

-And sometimes I see things that are slightly cool/slightly disturbing, like the time I saw a tarantula walk in front of me (I’ve been told that they’re pretty rare in Chile), or the time I saw an eagle take out a degu (you just have to tell yourself that it’s the Circle of Life).

Student Protests

Chilean students have been waging a long protest against the government. The students are calling for more educational funding, both for public secondary schools and universities. Chile previously boasted an exceptional public education system, but when General Augusto Pinochet came to power in 1973 (through a military coup which ousted socialist president Salvador Allende) the government immediately cut education funding and encouraged privatization of the education sector. Because of the low number of public schools today, many young Chileans only have the option of attending a private school, which has subsequently saddled these student with lots of debt. The main aim of the protestors is to make education affordable for the middle and lower classes.

While the protests in Chile haven’t really affected my fieldwork, I have still felt a lot of the effects of the protests themselves. Not long after moving into my apartment, the university across the street was taken over by the students. One day I woke up and found that the students had blockaded the gate entrances with tables and chairs and had put up banners on the buildings. The next two weeks were rather annoying because the students put on their own little mini-concerts/rallies while I was trying to sleep. Earlier this month, some students also blocked my street with burning trash, but the police were quick to arrive and dispersed the protestors with water cannons and tear gas. I’ve gotten a few whiffs of tear gas while walking around the city, and let’s just say that it’s not a pleasant experience. 

The students.
And the police.
In addition to school takeovers, strikes, and random street fires, students have also been organizing many protest marches. The government denied a permit for one march in mid-July, so when the students tried to march without a permit the police immediately swooped in and used water cannons and tear gas to break up the protest. The citizens of Santiago sympathized with the students and showed their solidarity by banging pots and pans out of their windows and honking their car horns for several hours. Banging pots and pans was a form of protest during the food-shortages of Allende’s presidency, but was used as a way to anonymously protest during the dictatorship of Pinochet.

Public Transportation

Because of funding availability, I only had access to a field vehicle from June through August. For September and October, I’ve been getting rides to the field with the technicians of our Chilean host, Dr. Luis Ebensperger at the Pontificia Catolica Universidad de Chile. This has ended up working well, but I needed a little more time in the field during early September to collect the rest of my late-pregnancy seasonal samples. So, with the help of my friend Meredith, I learned how to use the public transportation system to travel to my field site.

Getting to my field site involved a 15-minute walk to the subway, a subway ride of approximately 30 minutes (with only one transfer), a bus ride of 30 minutes, and then an hour-long walk through the field. It was pretty exhausting to do the trek both there and back, but most days I had a ride to the field in the morning. I actually enjoyed the commute because I could see lots of cool animals during my walk (which was also good exercise) and I could read on the bus and subway. One of the frustrating things about fieldwork is that there are always limits on time and resources, so it’s always nice when you have backup plans.
Here's a burrowing owl I spotted while walking to the bus.
 Life in the City

Overall, I like living in Santiago. I can buy fresh bread from the corner store everyday, I can walk up a picturesque hill in the middle of the city and watch the sunset over the Andes, and I can even go to the university and practice my Spanish with the ecology department security guard. Some of the downsides of living in Santiago, though, are the air pollution, the earthquakes, and the loud traffic.

When we first arrived to Chile in June we found ourselves in the midst of a soccer-crazed nation; the Copa America was about to start! Whenever Chile played a match the whole city would watch, and we would immediately know when Chile scored a goal because we’d hear people cheering and taxi’s honking their horns. After every game, win or lose, there’d be an impromptu march on the Alameda (the city’s major street), which would be promptly dispersed with police water cannons and tear gas. It was really cool to see a whole city cheer for their country; I can’t really compare it to anything in the U.S. (sadly, Chile lost in the quarter finals, Uruguay went on to win the cup).

I was also lucky enough to be in Santiago for Chile’s independence day, the Dieciocho de Septiembre (September 18th). There are activities and events before, during, and after the Dieciocho that basically involve eating lots of BBQ and drinking chicha, a type of sweet, fermented wine. My Chilean friend Cecilia took me to a “fonda,” which is sort of like a U.S. fair but a little smaller. I looked at livestock animals, ate some BBQ, and tried some chicha. Rodeos are a big part of the Dieciocho celebration, but unlike a typical U.S. rodeo, Chilean rodeo only involves two cowboys on horseback trying to force a cow up against the arena wall. While they do knock the cow into a padded section of the wall, it does seem pretty hard on the cow so it was tough for me to sit through. I also watched the Chilean bomberos (firemen) do a little skit, but everything they did went wrong: they started a mini-fire so they could hose it down but the fire went out on its own, and then when a bombero holding a Chilean flag tried to zipline down from stage he got stuck. Nevertheless, I had a great time and I hope to be in Chile for another Dieciocho!

The cowboys are just about to knock the cow into the padded wall.

Thursday, October 6, 2011

Field Stress Techniques

One of my projects this field season is to determine the seasonal variation of cortisol concentrations in wild degus during the breeding season. As I blogged earlier, I’ll be collecting four blood samples from each degu: baseline, stress-induced, dexamethasone (DEX) challenge, and adrenocorticotropic hormone (ACTH) challenge. Here’s a quick overview of the four samples:

The baseline sample is taken within 3 minutes of capture (remember, CORT starts to increase 3 minutes after a stressor) and represents the typical levels of CORT an animal experiences throughout the day. The stress-induced sample is taken 30 minutes after capture and tells me how much an animal increases its CORT levels after encountering a major stressor. After the stress-induced sample, I then inject the animal with a DEX (a synthetic version of CORT) and wait 90 minutes before taking another blood sample. DEX binds to CORT receptors, thus initiating negative feedback, so the DEX sample gives me a good idea of how well the animal can turn of its stress response. After collecting the DEX sample, I then inject the animal with ACTH, wait 15 minutes, and then take my final blood sample. ACTH stimulates CORT release from the adrenal glands, so this sample will tell me the maximum amount of CORT an animal can release.

Now let me tell you in a little more detail of how I collected these samples. When I first came down to Chile in June I was working with another graduate student and three undergraduates (well, they’re really post-grads because all of the them had graduated from college that May). After a week or two of practicing our bleeding and handling skills, we set out 120 tomahawk traps at our first site and got down to business. Here’s how a typical trapping day went:

After arriving at our field site, we would set up a degu-processing station near our trapping area. Then, the five of us would each grab a bag of oats, spread out and start opening and baiting the traps. Once the traps were all open and baited, we would station ourselves around the trapping perimeter and begin monitoring the traps through our binoculars. Observing the degus could be boring and tedious- oftentimes we would go hours without catching a degu. The degus also liked to taunt us in various ways, usually by studiously avoiding the areas with traps. Some degus liked to enter the traps partway, gently rest their paw on the treadle, and then quickly run out of the trap. And occasionally, a few particular degus would sit by the traps for long periods of time, just staring back at us.

Degu processing station

Nevertheless, we did catch quite a few degus. When one of us saw a degu set off a trap, we would yell, “DEGU!” and then the closest graduate student (designated bleeder) and post-grad (designated handler) would run towards the trapped degu. The handler (using a gardening glove because the degus will bite) would get the degu out of the trap and hold it for the bleeder. The bleeder would use an electric razor to shave the degu’s leg and would then prick the saphenous vein (one of the main leg veins) with a needle. We first collected blood in a glass capillary tube for future cortisol analysis, and then we would switch over to an Eppendorf tube to collect blood for leptin and ghrelin analysis (these are two important hormones for energy regulation). After we collected the blood, the handler would hold a piece of cotton or gauze to the degu’s leg if it was still bleeding and then the degu would be taken to the processing center while the three other people continued to watch the traps.

Once at the processing center, the first thing we would do was ear-tag the degu so we could properly identify it (this is important because if the animal escaped during processing, then we could complete our measurements if we ever re-caught the animal). After ear-tagging the animal, we would then weigh the degu so we could figure out how much DEX and ACTH to inject. Then we would take a variety of measurements including ectoparasite levels (I covered this procedure in my last post), reproductive condition, glucose levels (we use the same monitor a diabetic might use), and anogenital distance (this is the distance from the top of the anus to the base of the penis or vaginal opening). By the time we were done taking all of these measurements, it was usually time to take the stress-induced blood sample and inject the degus with DEX. Then, we would stick a paper towel under the degu’s trap to collect any feces, cover the degu with a white sheet to keep off the sun, and head back to the trapping area to continue watching the traps.

After catching a few degus, the day would become a game of coordination between watching degus and taking further blood samples on the degus at the processing station. Because we had five people, we were usually able to keep the traps open the whole day. On the occasions when we caught multiple degus within a short period of time, we would have to close some traps for a while because there was no way we could watch all of the traps while processing the degus. This is one of the challenges of fieldwork; you often have long chunks of time where you’re essentially doing nothing, interrupted by brief periods of intense activity.

Fieldwork could sometimes be very frustrating, like when a degu would get caught in a trap and we didn’t notice. This mostly happened at the beginning of the field season- we eventually got better at preventing unnoticed captures by checking that all the traps were visible to at least one person before opening them, and also by tying a piece of orange flagging tape to the door of trap so we could easily tell from a distance whether the trap was open or closed. We also got better at watching the degus and recognizing the sound of a trap being triggered.

Other frustrations included when a degu would go into the trap, step on the treadle, but the trap would fail to shut. Some of the traps are better than others, and we oftentimes had to fiddle with the older traps to make then more sensitive. Sometimes we’d catch a degu but it’d escape from the trap while we were trying to get it out; it’s something that happens to everyone, no matter how long you’ve been working with the degus. And finally, the most frustrating thing about trapping degus is watching the birds eat all of the bait and set off the traps. Sometimes the birds would be so bad that we’d have to re-bait the traps every hour or so. Over the past few months, we’ve caught (in order of capture frequency) rufous-collared sparrows, common diuca-finches, long-tailed meadowlarks, band-tailed sierra-finches, Chilean mockingbirds, mustached turcas, mourning sierra-finches, white-throated tapaculos, eared doves, and shiny cowbirds. Here are some pictures of a few of these birds:

Rufous-collared sparrow 
My advisor, Dr. Michael Romero, holding a long-tailed meadowlark

Mustached turca

Common diuca-finch

White-throated tapaculo

Mourning sierra-finch

Chilean mockingbird

But even with the difficulties of trap-shy degus, unnoticed trappings, escaped animals, and hungry birds, we managed to get our first seasonal samples within two weeks (full stress series on 8 males and 14 females). Because we had a lot of time before gathering our next seasonal samples and preparing for my other project (examining the effects of poor maternal care on the pup stress response), we decided to do a side project to determine whether the stress response differs by habitat. We moved all of our traps up to a nearby field that had lots of boulders and began trapping up there. The boulder field, unexpectedly, was degu heaven, and we collected full stress series from 12 males and 8 females within just three days! Emboldened by our success, we decided to try trapping in an area with lots of trees and vegetation. This site proved to be more difficult, and it took a week to collect full stress series from 10 females and 5 males, after which we had to remove all of traps because it was time to start trapping at nearby national park. Which brings me to….

Parque Nacional Fray Jorge!

Fray Jorge is approximately 350km northwest of Santiago and is an interesting place because while the majority of the park is dry, dusty and covered with cactuses, there are also fragments of rain forest on top of some of the hills. The incoming fog from the ocean sustains these cloud forest fragments, which are more typically found in the southern part of Chile. Alas, we trapped the degus in the drier, scrubbier areas, here’s a good representative picture of our trapping habitat: 

Fray Jorge was a difficult place to trap because the degus rarely ventured out into the open, so we had to place most of the traps in and around the bushes and trap by ear instead of by sight. This usually worked fine, but on really windy days it was hard to hear the traps closing, so we ended up missing a few captures. The cactuses were also a real pain; by the end of the day we’d have tons of cactus spines embedded in the soles of our boots. But we persevered, and by the end of our time at Fray Jorge (about a week and a half) we managed to collect full stress series on 5 males and 13 females.

After we returned from Fray Jorge, we started prepping for my project examining the effects of poor maternal care on the pup stress response. We did some widespread trapping and radio collaring to help determine social groups (I went over these techniques in my last post), and then we started implanting the females with cortisol or placebo pellets after they gave birth.

I will start trapping and bleeding pups in a few days to determine if communal care helps buffer degu pups from negligent parenting. If this hypothesis is supported, then I expect to see high baseline and stress-induced CORT, plus poor negative feedback, from the pups belonging to social groups with cortisol-implanted mothers. You can read my first blog post for a fuller explanation of my experiment.

Buena suerte!

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