Every winter, tens of thousands of Sandhill Cranes from all over North America return from their breeding grounds to their overwintering grounds in the south. One of those sites is located southeast of Tucson, Arizona. I hit the road yesterday with a friend to check it out. We passed through the town of Tombstone (!) and up into the most beautiful golden grasslands that are peppered with yuccas in this part of the state, and eventually we coasted down into Whitewater Draw, run by the Arizona Department of Fish and Game. As we neared the Draw, I looked up at the horizon and could make out shape-shifting, pixelated lines in the sky--flocks of cranes, soaring on thermals and flapping slowly south, towards the Draw. They head out in the morning to eat in the agricultural valleys and return to these safe havens, the wetlands, about mid-day.I hit the gas peddle to make sure we made it to the Draw before they all had returned (it is a VW Golf Diesel--we weren't going anywhere fast!). Walking out to the berm along the draw, a few hundred feet away, the birds began circling in, by the tens, hundreds and thousands. With over six-foot wingspans, whirlwinds of birds swooped over us, dropping their long legs like landing gear, side-slipping to lose altitude, like falling leaves, and gently set themselves down. It took my breath away.
This species forms pair bonds, often mating for life, and can live for 20 years. The Arizona Department of Fish and Game should be applauded for acquiring this piece of land and helping the Sandhill Cranes endure, as they have, for millennia. Photos are below.
The view to the north, of the Catalina Mountains in Tucson from the Marley Building on Dec. 31, 2012.
The view to the east, of the Rincon Mountains in Tucson from Finger Rock Trail on Dec. 31, 2012.
The view to the south, of the Santa Rita Range, and Mt. Wrightson, covered in snow, with Tucson, some ocotillos and sagauros in the foreground, from Finger Rock Trail on Dec. 31, 2012.
A view of the Catalina's from the Finger Rock Trail as above.
Continuing up the trail, lots of saguaros, growing in the sweet spot of just enough water and warmth.
A small pool of water that survived through the day, will be gone by tomorrow...
Several weeks later, that snow was flowing through the beautiful Sabino Canyon as liquid water.
I hope that these photos do reflect the beauty of snow falling in these desert mountains, but they are also meant to show how dependent the lowland deserts and western U.S. in general are on these snowfalls. This snowmelt trickles through the canyons and the rocks, like a drip irrigation system used by every organism in this desert, from saguaros to humans. Snowmelt on mountains in western North America is advancing earlier and earlier. What will the impact be on the creatures that rely on that water? Change is coming and the future might be quite dry and hot out here in the West. See this remarkable report that used tree ring data to track the advance of spring due to global warming: http://www.sciencemag.org/content/333/6040/332.abstract
. Water molecules in these snow flakes will end up in the plants we study in the lowland desert, in the birds that feed on those plants, and maybe even in us, as it seeps into the aquifer under Tucson. This idea can be extended to the atoms in one's own body, which were created during the big bang and subsequent super novae. A new book called The Universe Within, highlights this fact if you are interested, by Dr. Neil Shubin, http://www.neilshubin.com/index.html
Yes, as a person with red-green colorblindness, this is an ironic post. This starfish (or sea star if you prefer, probably Pisaster ochraceus) is not from the Sonoran Desert. I saw it a few weeks ago on a beach in Olympic National Park. But, this post does get to Sonoran Desert organisms. The broader issue is color--and orange or red to be specific. In our department, we have one of the world's authorities on the evolution of color in animals--Professor Alex Badyaev. Alex and colleagues study the evolutionary ecology of color, including in birds, and especially in house finches, which gather carotenoid-bearing vegetation and eat it. These pigments are then processed (usually) and somehow end up where natural selection caused them to be--for example in the feathers of male house finches--females really like red males it seems, so males do what they can to make themselves red since they aren't born that way!
But what about this starfish, why is it orange? The biosynthesis of carotenoids is mainly the realm of bacteria and fungi. In fact, Professor Nancy Moran and colleagues recently showed that aphids, which can be orange, borrowed a gene from a fungus in order to produce this carotenoid, which may even allow the aphids to capture energy from the sun (time will tell if this is so). But back to the starfish...Well, their color is from a carotenoid--but I'm not sure who is making it--the starfish or a symbiont. If there is an adaptive value to advertising one's self, it may be to say 'stay away' to potential predators. Called aposematism, this might explain why monarch butterflies are orange (they are toxic). It is actually fairly unclear if orange starfish are aposematic, or if this due to a tradeoff that emerges during development. Regardless, it seems that carotenoids, from a biosynthetic perspective, are mostly the province of bacteria and fungi.
Ph.D. student Parris Humphrey in our laboratory group is studying Life in a Leaf at the Rocky Mountain Biological Laboratory (RMBL). In the leaves of just one species of plant, the mustard Cardamine cordifolia, he has been able to culture myriad species (see a photo of a plate that Parris brought back from RMBL below), but in a repeatable way. He is initially diagnosing bacterial phyllosphere species based on colony morphotypes when leaf extracts are plated on King's B media. Each colony was initially started from a single cell and then re-streaked on a new plate. Parris found that many of the leaf-dwelling bacteria in C. cordifolia are each able to produce pigments--yellow, green, pink and orange (there may be others that you can see below). Many of these pigments are carotenoids although some (the green) are not. The function of the siderophores (the green stuff), which has leaked into the media, is likely to allow the bacteria to utilize iron in the media. The carotenoids function in many different ways in bacteria and plants.
The genes that underlie these beautiful pigments have been shuffled around the tree of life, although some pigments that seem like they should be carotenoid-based are not--such as red or pink plant parts that obtain these colors from anthocyanins or betalains (although each is produced by plants in different lineages). Here are some beautiful betalains from the Sonoran Desert, in fact from a cactus (and I'm not sure of what species these beautiful plants are derived).
An absolutely astonishing story emerged from the journal Nature a few years ago that is relevant. Male squirrel monkeys (Saimiri sciureus) are red-green colorblind because in this diploid species, two copies of an opsin are required for red and green vision. However, only one copy is found on the X chromosome. Since males only have one X chromosome, they are red-green colorblind. Most females, having two copies of the X chromosome, can see red and green. Researchers used gene therapy, with the help of a virus, to infect the region of cells in and around the retina of the eye. These viruses had been engineered to contain a human opsin gene that allows red and green color vision perception. Because the clever authors had previously trained the very monkeys used in this experiment to find colors on a computer screen (and were rewarded with juice when they were correct) the authors were able to test if the monkeys, after the gene therapy, were able to see three instead of two shades. You can watch the monkey, here. I particularly liked that the monkeys used their noses to touch the screen when they saw red. Remarkably, the monkeys were able to detect green and red after only 20 weeks. Maybe there is hope for me after all! Until then, excuse the mis-matched clothing. I speak for about 1 in 12 men, by the way, who are lucky to have a great excuse for fashion faux pas. The evolution of color vision in primates (including humans of course), particularly in the New vs. Old World, is fascinating.
The land snail in this photo, which I found way up Mount Crested Butte in Colorado, has been feeding on the trunk of this quaking aspen tree. You can see the zig zag trail of the snail's feeding pattern all across this trunk.
What is it eating? I first imagined it might be feeding on the epiphytic microbes on the trunk (and it might be)--but then I read a bit more and it turns out that the green color on the trunk is due to the presence of chloroplasts from the tree! There are more chloroplasts per unit of tree trunk than in the leaves. Looking back at the photo it is easy to see why one might miss the greenish hues, which are covered up by that white powder. Thanks to the snail for lifting the veil of my ignorance regarding aspen trunks!
For more information on photosynthesis in aspen bark, see this study: http://cedarcreek.umn.edu/biblio/fulltext/Amer%20Jou%20Botany%20Vol%2045%201958%20Pearson.pdf
Aspens are remarkable in other ways--the oldest stand ("Pando") in Utah is probably tens of thousands of years old--the trees are clonal for the most part, sending up new trunks from underground stems. They reproduce sexually after fires or other stressful conditions. The clonal nature of the Pando stand was confirmed using molecular markers: http://naldc.nal.usda.gov/download/27665/PDFThis brings up another question--what is an individual in the case of clonal trees? Do somatic mutations that occur in some stems mean that they are genetically distinct enough from other stems to be individuals?
This stand of aspen to the right is up on the San Francisco peaks, a sky island in northern Arizona that has a Rocky Mountain flora and fauna. I can't tell if these trunks are really green, but if they are, they are using the sun's rays to photosynthesize!
The snail's radula is a funky thing. A chitinous structure studded with teeth, it allows the snail to scrape food from the smooth skin of the aspen. Nearly all molluscs have a radula, except bivalves. Bivalves can also live a long time, although not as old as an apsen clone. One, called a quahog, was found off the coast of Iceland, and the years of its life were catalogs by counting the rings of growth in its shell. It was 405 years old! See: http://news.nationalgeographic.com/news/2007/10/071029-oldest-clam.html. The rings of trees can be used to estimate age as well. We are quite proud of our legendary tree ring lab (The Laboratory of Tree-Ring Research: http://ltrr.arizona.edu/), established as a founding institution at the University of Arizona in 1937. By chatting with my colleague, Dr. Michael Nachman, however, I learned that creosote bushses, which are just a stone's throw from where I am typing this, can be quite old. Creosote, like aspens, grows in a colony and one has been estimated to be around 12,000 years old! Justly called the "King Clone" these plants, in addition to being relics, send volatile compounds that fill the heavy desert air of August with a heavenly scent that to me, is the smell of rain:http://www.jstor.org/discover/10.2307/2442649?uid=3739552&uid=2&uid=4&uid=3739256&sid=21101155747937
This is a photo of a creosote bush near the Arizona Inn, in my neighborhood.
One way that I've been thinking about our newest research effort, which is to use plant leaves as microcosms for ecological and evolutionary inquiry, is illustrated by this clip from the opening scene of Steven Spielberg's (2005) adaptation of The War of the Worlds (from H.G. Wells' remarkable 1898 book). To the microbes and arthropods that colonize plant leaves, and the microbes that in turn colonize those arthropods' guts, these are living, breathing islands. Do the same sets of ecological and evolutionary interactions play out on these islands compared to the familiar struggle for life on the Serengeti? Nature is red in tooth and claw in plant leaves too, probably. In our lab at the University of Arizona, we are dissecting these interactions in a plant-microbe-insect community at the Rocky Mountain Biological Laboratory and throughout the west including near Greer, Arizona. Our goal is to determine how infection with endophytic (living within plant leaves) bacteria influences whether and how plants are susceptible to herbivory by arthropods. We believe that plant-bacterial interactions that play out in the leaves of plants may be under-appreciated symbioses that are not unlike human gut microbiomes. Ph.D. candidate Parris Humphrey is focusing on this research for his dissertation. With Dr. Pete Gauss, a colleague from Western State College, Parris discovered that co-occuring bacteria often produce bacteriocins that can selectively kill some, but not all, species. Trench warfare in a leaf?We are also interested in understanding how bacterial communities on and in plant leaves assemble. Since they can disperse in the rain, snow, and clouds, these bacteria may simply not be limited by dispersal. Bill Hamilton and Tim Lenton wrote a paper on how bacteria may manipulate weather to their own advantage--a beautiful insight. The fact that ski hills used Pseudomonas syringae as ice-nucleators for snow-making until recently, suggests that this might not be so far-fetched as one might think at first glance (Bill thought of everything!). Such bacteria can increase the freezing temperature of water and often form the nuclei of snow crystals--they can also cause frost damage on plant leaves at temperatures higher than normal--allowing them access to the rich nutrients inside the leaves. Below is a fluorescent image containing yellowish-green bacteria that are living in an Arabidopsis thaliana mustard leaf. The beautiful green orbs and disks are chloroplasts and thykaloids, respectively, from this genetic model plant (and weed). The bacteria (there are at least four that I can find, can you find them?), are in the center and one is to the left. A pair of bacteria has just undergone binary fission. They swim (yes, swim) into the leaf through stomata or wounds and then replicate within the apoplast, that region between (not within) plant cells. Are they pathogens? Mutualists? Commensals? It depends on the ecological context. This world that normally remains unseen to our naked eyes is absolutely astonishing in its diversity, complexity and beauty. We are lucky to be able to study it--this will likely be a decades-long enterprise that will take us within the inner worlds of thousands of leaves. To give you an idea of the scale of the problem: there are typically between 10,000,000 and 100,000,000 bacterial cells per square centimeter of leaf tissue on every plant leaf, meaning that these cells outnumber the plant's own cells. Should the phyllosphere community and the plant together be thought of as a holobiont?--Crested Butte, Colorado, July 22, 2012
Last week, I accompanied PERT postdoctoral fellow Dr. Jen Koop and UBRP undergraduate researcher Lauren Johnston to our sampling site at Tumamoc Hill, part of the The Desert Laboratory run by EEB Professor Dr. Mike Rosenzweig in our College of Science at the University of Arizona. We were there to collect stems of mistletoe for population genetic analyses, which Dr. Koop and Lauren are conducting in our laboratory.
This amazing place affords us an opportunity to have a field site a mere 10 minute drive away. A small area of wildland within the city limits of Tucson, it is a treasure and we are lucky to be able to work there. We work amongst a plot of blue palo verde that Dr. Ray Turner has been studying for decades--luckily he accompanied us on our first trip out there to show us the ropes (with Dr. Larry Venable).
Once there, we stumbled upon a white-winged dove that was nesting in one of the mistletoes we needed to sample--here she is to the left with one of her two large nestlings (just to her lower left).
Below a foothills Palo Verde, Dr. Koop and Lauren ponder a flowering saguaro a few feet away (out of sight here). Above their heads are desert mistletoes that we were able to sample with the pruner (that thing leaning against the tree).
From humble beginnings (through the digestive tract of the Phainopepla), a new mistletoe sprouts a root radicle, which is boring into another mistletoe's stem--will it take hold? Time will tell...
Here, I am sampling desert mistletoe from a velvet mesquite using our pruner. The stems were placed into tubes that are frozen for future genetic analyses.
Dr. Koop and Lauren improvise, using an age-old technique for collecting a few stems from a mistletoe that is outside the reach of our pruner...
This one was hard to reach, but with the help of Dr. Koop and Lauren, I got it!
Although it is beautiful, this thing is not a native plant. The little dot to the left of the flowering stalk is a honeybee, which isn't native either. But, both are now part of the Sonoran Desert and they are here to stay. The agave sent up a ten foot stalk, over the matter of a few days, sending its whorls of flowers spiraling up to the sky to signal to the bees and the birds.
Not far from the agave, I found this male Phainopepla (Phainopepla nitens), glossy black and red eyes, hanging out in a blue palo verde tree. The backdrop is the Catalina Mountain range. He was on high alert, apparently, I was near his nest!
Next, I saw the female of this pair visiting her nest and dropping berries of the desert mistletoe into the mouths of their three chicks. Tufted with down, they seemed asleep as soon as I was able to peer over the top of the nest. All of these photos were taken in the wash near my friend's house, surrounded by homes in the foothills of Tucson.
I took these photos yesterday along a trickle of a waterfall, in an amazing box canyon in the Catalina Mountains near Tucson. At the top of this waterfall I found fly larvae, living under 1/4 of an inch of flowing water. These larvae in the first two photos are blackfly larvae--all one species in the family Simuliidae. They anchored themselves to this smooth quartz rock by using silk that they spin from their abdomens. They feed as barnacles do, by sweeping in algae and other small creatures using fan-shaped structures attached near their mouths. As adults, they feed on the blood of vertebrates. In other parts of the world, they vector terrible disease agents such as nematodes that cause river blindness. At the base of the waterfall, I found a long whirligig beetle waiting to capture prey that fell onto the surface film of a tiny pool the size of a dinner plate. Remarkably, species in this family of beetle (Gyrinidae) have two sets of compound eyes--one set that sees the world above the surface film (e.g., to detect giants with cameras) and one set that sees the world below. The beetle found itself next to a large carpenter ant soldier that had fallen down the waterfall, but was too big to feed upon. Especially in this desert, water plays a major role in shaping the distribution of plants and animals. Check out these links to see a drawing of blackfly larvae
, the compound eyes of a gyrinid beetle
, and a story on a convergently evolved four-eyed fish