Saturday, May 30, 2015

Yuccas and their moths

"I get by with a little help from my friends."

Yucca schidigera
Yuccas are plants which define the Mojave Desert. The Joshua Tree (Yucca brevifolia),pictured below, is probably the most famous example of a Yucca, which are surprisingly close relatives of some Orchids and Asparagus.
The Joshua Tree, Yucca brevifolia

Yuccas rely on moths for a very interesting sort of mutualism. Unlike other pollinators where pollen often gets stuck to the body of the insect, the Yucca Moths seem to be more deliberate about the act. Actually scraping pollen off  Yucca Flower anthers and delivering it to another Yucca. The benefit to the moth being that they lay their eggs in the flower of the Yucca. The moths do not eat the pollen from the Yucca Flower. So by the act of purposely pollinating the Yucca flowers do not actually see any immediate benefit. It will be years before the pollination event spawns another mature Yucca and by that time it will be her great, great, great, grandchildren moths who are reaping the benefits. Talk about foresight!

One thing that puzzles scientists about mutualisms like this is their apparent instability. One could guess that evolution might favor moths that "cheat" and lay their eggs in the Yuccas but do not pollinate, which is labor intensive and potentially costly. Likewise how can a Yucca ensure that it is not providing shelter for the offspring of moths that didn't carry its pollen elsewhere?

In fact cheaters have evolved and entered this system. There are many species of moth which lay their eggs in the flowers or seeds of Yuccas but are not pollinators. Yuccas are able to respond and prevent this type of exploitation of their flowers and seeds by aborting ones which house large numbers of moth eggs.

Cheater moths do rely on the presence of the mutualist species because they rely on the persistence of the Yucca. If the mutualism between the Yucca and symbiotic moths were to break down and Yucca  were to fail to persist than the cheater species would likely go extinct, or would need to enter into the mutualism itself.

This interaction is incredibly complex and the behavior of the moth mutualists and cheaters is variable but well studied. If this subject interests you I suggest you take a look at some of the sources below. The system  has advanced theoretical work on the evolution of mutualisms and knowledge of how mutualistic interactions evolve and under what circumstances they break down.

References and further readings:

http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/yucca_moths.shtml

Pellmyr, Olle, and James Leebens‐Mack. "Reversal of mutualism as a mechanism for adaptive radiation in yucca moths." the american naturalist156.S4 (2000): S62-S76.

Ferriere, Régis, et al. "Cheating and the evolutionary stability of mutualisms."Proceedings of the Royal Society of London. Series B: Biological Sciences269.1493 (2002): 773-780.

Segraves, Kari A., David M. Althoff, and Olle Pellmyr. "Limiting cheaters in mutualism: evidence from hybridization between mutualist and cheater yucca moths." Proceedings of the Royal Society of London B: Biological Sciences272.1577 (2005): 2195-2201.

Addicott, John F., and Andrew J. Tyre. "Cheating in an obligate mutualism: how often do yucca moths benefit yuccas?." Oikos (1995): 382-394.

Friday, May 22, 2015

Rattlesnakes







"Always carry a flagon of whiskey in case of snakebite and furthermore always carry a small snake." -W.C. Fields

Sidewinder Rattlesnake, Photo by Alex Jones

Well it was only a matter of time. I live in the desert. I love snakes, and I especially love Rattlesnakes. There are lots of different types of these in the desert that live in lots of different places and make their livings in lots of different ways. There is nothing quite like the thrill and adrenaline rush associated with seeing and working with Rattlesnakes. I will always be fascinated by and respect these animals. I also think that they can answer many important biological questions.

Where to begin? Well I believe that Rattlesnakes are an excellent organism to start thinking about the importance of behavior. They have many interesting ones to deal with predators, prey, and to keep themselves cool and hydrated. Rattlesnakes are interesting in that they simultaneously have the tools to be go unnoticed (cryptic colors or camouflage) and the tools to be conspicuous and intimidating. They have to know when and where its best to go unnoticed, and in what circumstances its best to put on a show and scare potential predators away. 

Rattlesnakes also have a whole suite of other interesting behaviors. Perhaps most famous is the "sidewinding" movement exhibited by Crotalus cerastes (this movement also evolved in vipers in the Sahara Desert). Sidewinding is useful for thermoregulation, as the snakes are able to minimize contact with surfaces which can be incredibly hot. It is also very efficient, and is metabolically a cheap form of transportation compared to typical snake movement and movement in similarly sized lizards. Does the metabolic savings of this motion type also explain why "sidewinding" evolved many times? Deserts can be notoriously food limited, and minimizing metabolic costs of activity can be a way to deal with food limitations.

Young sidewinders also use their  tail movements to lure potential prey towards them. This type of mimicry has been observed in a few other snake species as well. The wiggling tail looks like a worm, and insectivorous lizards come to investigate and end up as a main course for the Sidewinder.

Behaviors are also important for dealing with the harsh environments in which they live. As skin exposure to dry air is the main way Rattlesnakes lose water to the environment they purposely minimize their exposure by taking cover under creosote bushes or covering part of their body with dirt or debris. 

Rattlesnakes have also found an interesting way to make sure they get enough water to drink on the rare occasions that is does become available in the desert. A variety of species have been observed coiling up on a rainy day, compressing part of their body, and in effect forming a water bowl with their own body. They then drink the water that collects in their own body depression.

Rattlesnakes and their complex behaviors continue to fascinate me, but there is another important reason why I love them so much. They are just so damn cute!
Newborn Diamonback Rattlesnake, photo by Alex Jones



References and further reading:

Cardwell, Michael D. Behavioral changes by Mohave rattlesnakes (Crotalus scutulatus) in response to drought. Diss. California State University, Sacramento, 2013.

Reiserer, Randall S., and Gordon W. Schuett. "Aggressive mimicry in neonates of the sidewinder rattlesnake, Crotalus cerastes (Serpentes: Viperidae): stimulus control and visual perception of prey luring." Biological Journal of the Linnean Society 95.1 (2008): 81-91.

Mata-Silva, Vicente, et al. "Rainwater-harvesting by the rock rattlesnake, Crotalus lepidus, in the Chihuahuan Desert of western Texas." The Southwestern Naturalist 59.2 (2014): 303-304.

Secor, Stephen M., Bruce C. Jayne, and Albert F. Bennett. "Locomotor performance and energetic cost of sidewinding by the snake Crotalus cerastes." Journal of experimental biology 163.1 (1992): 1-14.

Mosauer, Walter. "Adaptive convergence in the sand reptiles of the Sahara and of California: a study in structure and behavior." Copeia 1932.2 (1932): 72-78.

Friday, May 15, 2015

Chuckwallas


 "Do what you can, where you are, with what you have."-Theodore Roosevelt

                                Chuckwalla in Joshua Tree National Park, photo by Alex Jones

The Chuckwalla, Sauromalus ater, formerly Sauromalus obesus (thats right... "the bad, fat, lizard") is a species that I think is often overlooked. I think they are physiologically fascinating as they like it hot... literally. The temperature of normal activities in Chuckwallas is right around 37 degrees Celsius, right around our body temperature. Most ectotherms prefer it cooler, in fact 37 degrees is potentially very close to the thermal limits of some desert snake species. Chuckwallas live in rocky habitats which can often be hotter than ambient temperature, when ambient temperatures reach over 44 C or 110  Fahrenheit in the summer this presents quite an issue for these lizards despite their preference for hot places. They can thermoregulate through evaporative cooling to help with this(just like dogs do when they pant). There is much to be said about how these lizards deal physiologically with the hot desert temperatures that would be extremely taxing and often lethal for other organisms.

I however, would like to talk a little about another tool evolution has gifted the Chuckwalla. When most other lizards are frightened... they run. Lizards are fast, and HOT lizards tend to be even faster. Some species reach speeds approaching 30 MPH on hot days. The Chuckwalla (or if you prefer... the bad, fat lizard), is not built for speed. They are clunky, not fast. A fat Chuckwalla would provide a great meal for many a desert predator.

The Chuckwalla deals with threats not by fleeing but by finding a wedge between rocks, crawling inside, and inflating its body so that it cannot be pried out. How can it do this?

To understand this we have to reach farther back into evolutionary history and understand how frogs breathe. Stay with me here. Frogs breathe by buccal pumping, an extremely inefficient way to get air to your lungs. Imagine breathing not through your diaphragm but only by inflating your cheeks and then forcing that air into your lungs. This is essentially how frogs breathe. Its just a silly way to get oxygen to your lungs and is a reason why cutaneous respiration (breathing through your skin) is so important for amphibians.

Chuckwallas do not breathe this way. However, they still do have the ability to control their buccal cavity and to do this "buccal pumping" in the same way that frogs do when they breathe normally. When threatened a Chuckwalla finds a crevice,  inflates its "buccal cavity" and mouth in the same way a frog does when it breathes, and pumps that air into its lungs. This behavior is vastly different from normal breathing in Chuckwallas based on measurements of lung and buccal cavity pressures and volumes. Its ability to utilize its characteristic rocky habitat and this ancestral ventilation behavior enables the Chuckwalla to escape predators despite its lack of speed.


References and further reading:

Cowles, Raymond B., and Charles M. Bogert. "A preliminary study of the thermal requirements of desert reptiles." Bull. Am. Mus. Nat. Hist 83.5 (1944): 261-296.

Case, Ted J. "Thermoregulation and evaporative cooling in the chuckwalla, Sauromalus obesus." Copeia (1972): 145-150.

Gans, Carl. "Respiration in early tetrapods-the frog is a red herring." Evolution(1970): 723-734.

Tracy, Christopher R. "Differences in body size among chuckwalla (Sauromalus obesus) populations." Ecology 80.1 (1999): 259-271.

Sullivan, BRIAN K., and Keith O. Sullivan. "Common Chuckwalla (Sauromalus ater) in an urban preserve: Persistence of a small population and estimation of longevity." Herpetological Conservation and Biology 7.3 (2012): 437-441.

Deban, Stephen M., James C. O'Reilly, and Tad Theimer. "Mechanism of defensive inflation in the chuckwalla, Sauromalus obesus." Journal of Experimental Zoology 270.5 (1994): 451-459.

Thursday, May 7, 2015

Spadefoot Toads


"Our strengths grow out of our weaknesses"-Ralph Waldo Emerson


Spea multiplicata, Mexican Spadefoot, photo by Alex Jones

Arid areas are not supposed to be ideal places for aquatic or semi-aquatic organisms like amphibians. Amphibians have extremely permeable skin which makes them especially vulnerable to dessication (drying out) in the desert. The Spadefoot Toad family (Scaphiopodidae) is a group of amphibians that has been able to remarkably turn this perceived weakness of amphibians into a strength in the driest of places.

So named because they literally have spades on their foot. These spades are used for digging burrows where these animals will spend most of their lives and avoid the harshest times in the desert. Unlike other amphibians which have fixed breeding schedules, these animals will emerge from their burrows whenever conditions are favorable for reproduction (after significant rainstorms).

The entire life cycle of this animal is compressed into a few weeks. Quickly emerge, eat, breed, and burrow before conditions once again become unfavorable. For the tadpoles, its a matter of eating as much as they can as quickly as they can before they too head to the burrows.

Once in the soil the ultra-permeable skin of the Spadefoot toad no longer is a liability, but rather an advantage. These animals are able to absorb soil moisture at very low levels (~3% water content) and are able to manipulate urea and plasma levels as the soil dries in order to minimize water loss during dry periods. During the time that the animal is burrowed, its metabolism is reduced by about 80%, and based on the average fat content of a toad it is likely that at least some individuals could survive up to two years underground with no food.

Other interesting traits are present in Spadefoot toads, including a form of inducible cannibalism. Some species of Spadefoot have  tadpoles which become carnivorous (the great majority of tadpoles eat algae and plant matter) and specialize on eating the tadpoles of other Spadefoot toad species. It seems that if they get the taste of other tadpoles early, their appetite for their relatives grow according to researchers who were able to induce these cannibal tadpoles by providing them with tadpole meat early on.

Maybe the desert isn't a horrible place for amphibians after all. The spadefoots seem to have been able to take a trait which under normal circumstances would be a liability, and use it for their advantage. Some species are perhaps even able to reduce competition with other spadefoots by making their relationship with other toads predatory early on rather than competing with them throughout their lives. Spadefoot toads are a fascinating member of the desert community; living right beneath our feet, waiting patiently for the next rain.

References and further reading:
Levis, N. A., Serna Buzón, S., & Pfennig, D. W. (2015). An inducible offense: Carnivore morph tadpoles induced by tadpole carnivory. Ecology and Evolution, 5(7), 1405-1411.
McClanahan, L. (1967). Adaptations of the spadefoot toad scaphiopus couchi, to desert environments. Comparative Biochemistry and Physiology, 20(1), 73-99.
Ruibal, R., Tevis Jr, L., & Roig, V. (1969). The terrestrial ecology of the spadefoot toad scaphiopus hammondii. Copeia, , 571-584.
Seymour, R. S. (1973). Energy metabolism of dormant spadefoot toads (scaphiopus). Copeia, , 435-445.

Spotlights on deserts

Desert.
The word conjures a multitude of images both diverse and extreme. A traveler from elsewhere might picture a landscape that is brown and "dead". A snowbird pictures a place where it won't be so damn cold and snowy in the winter time. A traveler or laborer in such climes has to be well prepared. Water... lots of it....shade...awareness of limits (both physical and mental).

Plants and animals have adapted to live here... or in some cases perhaps have failed to adapt to live here. Death is an ever present threat here, to individuals, to populations, to species.

In an effort to promote enthusiasm and understanding about the desert and the organisms found here I have started this scientific blog. I will aim to include lots of good science and data, and to have some fun exploring how organisms survive and evolve in such places.

For my first spotlight, I will discuss one of my personal favorite desert organisms. The Spadefoot Toad family (Scaphiopodidae)
Photo from Wikimedia User Takwish