Predators on the Ecotone!

Light coloured male Collared Lizard (Crotaphytus collaris) temporarily in captivity

We're always interested in potential predators of lizards at White Sands- especially considering predation on mismatched, non-camouflaged lizards was probably an important selection pressure for crypsis (matching the white background). Usually the only signs of predators we observe are some scattered roadrunner tracks (it seems the populations of other winged reptile predators, shrikes and kestrels, have declined in the area).

Two days ago, I was pacing around a scrubby 'marginal' dune site and what I immediately thought was an oversized H. maculata, dashed bipedally towards a small cottonwood tree at the edge of a dune. I yelled at Mikki that I just saw something HUGE and I thought it was a Gambelia because of the size. We stalked up to the tree and Mikki pointed out a large A. inornata and suggested maybe that was what I saw. Pssh, field assistants, I thought. This dragon had a huge head and stood like four feet off the ground. Er, well, maybe four inches. Anyway, after a few minutes we were turning our backs on the cottonwood to hunt down less menacing creatures, when Mikki looked back and said she saw something HUGE on the dune. Now, I need remind you that when you're hunting dragons of a miniscule size (2 inches, 5 cm), anything > four looks mighty formidable. Well, we went after that beast of a lizard, soon discovering that it was a very lightly coloured male collared lizard- rarely seen this far into White Sands. Collared lizards have large heads for their size and a bite force to match. Perhaps it was my fear of being attacked by this chipmunk-sized reptile that made us take nearly forty-five minutes to catch the fellow. Or, it could have been something to do with our lack-of-water-induced exaggeration-hallucinations.

First of all, I had to create a new noose. Usually we use a 1.5 cm diameter slip-knot loop at the end of a pup-fish pole to capture lizards. I had to fashion a new, 4 cm noose to better accomplish the task. Turns out, getting a dental floss loop over something that large is actually pretty easy, and as I was pulling him out of the branches, my pole all a bent, his mouth all open, I thought, okay, what am I going to do with this biting machine?

So second I put him on the ground all tangled in floss and in quite a rage. As sort of a test I offered him the brim of Mikki's hat. Yeah. He chomped right into that and didn't let go. Well that made it easier. I wrapped my hand around him securely, thumb and forefinger pressing his jaws down onto the hat. I tried to loosen the noose around him, but quickly realized with the hat in his mouth, I could only get so far. So I remembered stomach flushing lizards last field season and how I used a toothpick to keep their mouths open while I induced them to barf... I took a thin stick and wedged it between his upper and lower jaw like a horse-bit. I then could get the loop over his head and drop him quickly into a cage.

We're going to take a tail tip (for genetic work), some colour specs and photos of our vicious fellow before returning him to the interdune. He was quite light for a collared lizard, and it will be interesting to see if he is unique genetically and morphologically. Perhaps these small-lizard predators are finally encroaching on the White Sands...


PS. Mikki saw ANOTHER light collared lizard in the same interdune today! The first is still in captivity, so we know that there is more than one possibly chomping on our study species!

Et. al. ~ Why my field assistants are the best ever!

Travis Morgan hiking up a dune just before sunset- pole at the ready!

Yes, it's that time. My assistants are fledging and often times out-catch me. Yesterday I sent them out alone to do some lizard noosing while I prepared a presentation for an outreach project. I sent them out with ten cages- we had only once caught ten lizards in a day before. Well. They showed me. They returned after only three hours with twelve individuals! They made an awesome make-shift cage out of a large water bottle poked with holes. 

Mikki Brinkmeyer showing off her mad noosing skills in the bushes.

So I ask myself- why do I go out at all? Why not retire in the cool apartment and wait for them to deliver the little friends to be processed and prodded? Well, turns out I need to work on my tan.

Here's to awesome field assistants!

~Simone

The Start of June

Just released male H. maculata at sunset.

We're roughly half way through the first part of our field season. We're up to 79 lizards- and hoping now for 150 before June 20. We had our best catching day today with 10 lizards!

I'll write again soon, but for now I have to sketch a Holbrook for some awesome slide shows!
~Simone

The Beginning

I've experienced some delays getting this blog up and off the ground- but I'll try my best to fill you in on our first two weeks.

~~~~~~~

The purple clouds finally descended on Otero County and the local grocery store parking lot. It has been four months without rain in the Tularosa Basin. As I write, acres of gypsum are dissolving on the surface of  White Sands... encouraging hydrophiles everywhere to crawl up from the depths of drought. The last few days the humidity has become more and more apparent. The air clings and so do the tiniest little flies who seem to bite everywhere from behind the ear to the arch of the foot. My supervisor, Luke Harmon's words ring true- insects aren't good for anything except food for lizards!

Handful of New Mexican Spadefoots (spadefeet? Spea multiplicata) who came up with the rains last year at
 Jornada Long Term Ecological Research Center

During a blog-writing break, we ventured outside and I snatched this little Mediterranean House Gecko (Hemidactylus turcicus) from the wall outside the apartment. While harmlessly identifying his sex, he quite suddenly and unexpectedly dropped his tail in my hand- right up to the base! The tail flopped around on the ground for minutes before we returned our little stubby friend outside. I felt a little guilty, but he's a bit of an invader anyway (yes, he.) 

We have captured, measured and marked 54 Holbrookia maculata on the ecotone between White Sands and the Chihuahuan Desert. To be honest, after nine or so full days of catching- I expected to have more lizards. To me, ecotone animals seem flighty, suspicious and less conspicuous than their counterparts in the heart of White Sands. Certainly, there are more birds, lizards and mammals on the ecotone, as evidenced by noisy chatter, numerous tracks and occasional sightings.

Common Nighthawk (Chordeiles acutipennis) Mikki spotted beside our ecotone site. Nighthawks are insectivores, usually feeding on moths at night.

Due to the lack of lizards we've seen on the ecotone, we may be moving on to sample further in the dunes where H. maculata is abundant. We'll spend at least one more day on the edge of White Sands returning lizards and scouting around. 

~Simone

The Researchers

Simone Des Roches
PhD Candidate, University of Idaho
BSc. Hon., University of British Columbia
Hunter of tiny-white-dragons
Biological-mythological illustrator extraordinaire
It's my third field season studying lizards down here in White Sands, NM and I'm thrilled to be back again, digging deeper into the life of the dunes. My current project, featured in this blog, *should* be the last of my dissertation and will take this year and the next to complete... indeed, the plan is to be a real DOCTOR (of philosophy) by August 2013... when the inevitable happens and my NSERC funding runs out. If you followed the link, you will rightly conclude that I am Canadian. Born and raised in Vancouver, BC, a spectacular city for someone like me. At age four I wanted to be a paleontologist and dig up the ancient reptiles. I remember asking my father if They (duh, Scientists) knew what colour dinosaurs were. And his best, most dangerous answer ever? His answer that probably put it in my mind to go to graduate school two decades later? My dad said, 'Well, Simone, They don't know that yet, but you could find out some day if you want to.' Thanks, pa. I'll surely make a living now. Way to foster my intellect. It seems fitting or ironic or something that I'm studying evolution and ecology of tiny, nearly colour-less dinosaurs... er, squamates anyway. The reptile-folk have also influenced my artwork- and if you're interested, my artwork blog can be found here.
~Simone
PS. I didn't do it, but someone did. And so did others.

Travis Morgan
BSc. Biology in progress, University of Idaho
Undergraduate Research Assistant, Teaching Assistant University of Idaho
Dunewalker Littlebeard
What’s-up people… Readin a sweet blog? That’s right! Soo, a small blurb about myself: My name is Travis Morgan. I come from the last frontier: Alaska. I attend the University of Idaho; my focus there is Biology. I am also an Undergraduate TA there, and I work in lab. My first goal here in the dunes is to survive among Shai-Hulud. I’ll keep you all posted on that… My main goals this summer are to learn as much as I can about working as a biologist in the field, observe and help the Grad students work, and finally to soak up as much knowledge about what it's like to be a Grad student; because I’ll be in those shoes some day soon. Anyway, I’m sure I’ll be writing here some time in the future, so until then… Peace.
~Travis

Michaela Brinkmeyer
BSc. Conservation Biology in progress, University of Idaho
Undergraduate Research Assistant, University of Idaho
Investigatory Lizard Finder
Hello everyone, 
My name is Michaela Brinkmeyer, but you can call me Mikki. I am just starting my journey to becoming a student of Biology. This is the end of my first year at the University of Idaho and the beginning of my first field experience!  I grew up in Boise, Idaho, the city of trees. Growing up in the West sparked my love of the outdoors from the beginning. My earliest memory is of Yellowstone National Park; I remember looking out our car window to find a moose with her newborn calf bathing at the edge of a lake front. I immediately fell in love with the relationship between wildlife and the natural world. This moment only lasted a few seconds in my mind, but has heavily influenced my interest in Conservation, Ecology and Biology. I have always held a deep appreciation for all forms of life; tree-hugger, bunny-lover, lizard-fanatic, call me anything you want! I fit all of those stereotypes and much more...I'm excited to start working, scouting out our little lizard friends.
~Mikki

The Experiment

Sunset at the ecotone

Like a newly emerged volcanic island, or a pristine glacial lake, White Sands formed rapidly, recently and supports an ecosystem physically and biologically distinctive from the surrounding scrubland desert. Its reptilian inhabitants colonized in the last few thousand years and in parallel, evolved longer legs, broader heads, and white colouration. The three species are only distantly related to one another, yet their convergent body shape and colour at White Sands suggests that natural selection may be acting on all of them in a similar fashion. 

The pale colour of White Sands lizards certainly makes them difficult to spot against the gypsum background. I have often come close to stepping on a little H. maculata, who only at the last moment appeared as a tiny ghost scuttling away from me over the sand. So colour loss may be an adaptation that allows camouflage from predators, and even prey. But the problem with ectotherms (cold-blooded animals) is that a change in colour means a change in how much time you must or must not spend in the sun. A little white lizard absorbs heat a lot slower than a darker lizard and that means it is exposed to predators longer, but may also be able to forage for longer.

Longer legs and toes enable many species of lizards to run faster on broad surfaces. Indeed, last year, I tested the hypothesis that White Sands lizards could run faster than their darker counterparts, especially on gypsum sand (stay tuned for the results!). Longer legs, however, maneuvering on smaller surfaces is more difficult. Perhaps the sparse vegetation in White Sands means that lizards must sprint long distances between cover. Lizards with longer legs may be at an advantage if they can run quickly across vast spaces.

The head and jaw of lizards will often affect how and what they eat. Typically, a larger head and jaw enable a more forceful bite; however, with the trade-off that the action of biting is slower. Thus, broad-headed lizards can often take large, tough prey – and perhaps that is what is available in White Sands. Head shape and size may also play a part in antagonistic behaviour with members of the same or different species.

Female H. maculata

Whether the original cause of selection on White Sands lizards was related to thermoregulation, evading predation, social interaction, or diet, we do not yet know. The form and strength of selection on White Sands lizards in the past may be the same or different to selection now. The aim of my experiment this year is to quantify current selection on H. maculata living on the ecotone between White Sands and the dark-soiled scrubland desert. My field assistants and I will be capturing individuals, measuring the traits I listed above (dorsal skin colour and body size and shape) and recording their survivorship over several seasons. From these data I hope to determine if individuals with certain traits are more likely to survive. 

I make three main predictions for any given trait: 

1. There is no selection acting and I observe no relationship between individual survivorship and their trait values.
2. Directional selection is acting and I record higher survivorship in individuals with more extreme trait values in one direction, e.g. the lizards with the lightest colour survive, and those that are darker are selected against.
3. Stabilizing selection is acting and I document highest survivorship in individuals with intermediate trait values, e.g. the lizards with intermediate leg length survive, and those with very long or very short legs are selected against.

Well that’s all the background information out of the way. I’m mighty behind on posting since we haven’t had the Internet for a while. We arrived in Alamogordo well over a week ago and have already begun catching, marking and releasing lizards. Our count is 22, with one unfortunate death. Please check back soon – I will introduce my stellar field assistants and let you know how we’re progressing! 

The Lizards

Three little lizard species live in White Sands. Each species is its own character, distantly related to the others. Yet all three have evolved similar features within the stark-white gypsum dunes of White Sands. Their darker counterparts, which live outside the dunes on the dark adobe soil typical of the Chihuahuan Desert probably resemble the ancestors of the White Sands residents that colonized less than 6000 years ago. Below are photos of both the white and dark form of each species.

Sceloporus undulatus, The Eastern Fence Lizard.
If I may go ahead and say so, Scelops has the most draconic-like attitude of the three White Sands lizards. Never reluctant to bite (which was actually ideal for testing their bite force last year), these little guys are feisty! They're sit-and-wait foragers, which means they hang around basking (mostly on yucca stalks*) until a tasty little arthropod morsel wanders their way. In White Sands, Scelops have lost their colour due to a mutation in the melanin gene, MC1r (1). They have slightly longer legs, and broader heads than their dark-soil counterparts, although the difference is not significant (2).



Aspidoscelis inornata, The Little Striped Whiptail
Otherwise known as, the very hardest little lizard to catch! These slender striped lizards are active foragers... instead of waiting around for their food to crawl by, they go hunting for it. They will even burrow into the soft sand in search of insect larvae. Both males and females are blue, and the colour is presumably used in signaling to other Aspis. In White Sands, Aspis are significantly larger than in the surrounding desert. They have longer legs, broader heads (2) and like Scelops have a mutation in MC1r (1) that has resulted in colour loss (although not in the same location in the gene).




Holbrookia maculata, The Lesser Earless Lizard.
Holbrooks is the protagonist of our story this field season. Holbrooks on White Sands are extremely divergent in colour from their darker cousins; however, the mutation which causes colour loss is unknown and not located in the coding region of MC1r (1). White Sands Holbrooks also have longer legs and broader heads (2). Like Aspis, they'll burrow in the ground, but like Scelops they are sit and wait foragers. This year, we'll be performing a mark-recapture experiment in which we evaluate current natural selection on Holbrooks. Stay tuned for my next blog where I will explain our very exciting experiment!


~ Simone

The Setting: White Sands, New Mexico

Welcome to White Sands, NM
712 square kilometers (275 square miles) of gypsum dunes. Situated in the centre of the Tularosa Basin, shouldered between the San Andres and Sacramento Mountains in southern New Mexico, USA.

White Sands is a young island, with deposition of calcium sulphate dihydrate having occurred between 6000 and 2000 years ago. Once a large inland water body (Lake Otero), White Sands is now the largest active gypsum dune field in the world. With some dunes crawling eastward as much as 9 meters (30 feet) every year, White Sands is one of the most dynamic and unusual ecosystems in North America. The ground is blinding white, vegetation is sparse and the little creatures that call White Sands home, are... different.