Eastern Diamondback Rattlesnake (Crotalus adamanteus)

The eastern diamondback rattlesnake (Crotalus adamants) is the largest species of rattlesnake, with an average length of 34-72 inches. On the field trip, the class encountered a large female named Venus, in which ARC has been tracking and keeping an eye on for over a year. The eastern diamondback has a restricted territory ranging from North Carolina to Louisiana, staying strictly in the Southeastern United States. This species is classified as a pit viper, and possess large pits under their noses which act as a thermo-sensory organ which is used in hunting and thermoregulation. Eastern diamondbacks are not endangered, but have lost a lot of their natural habitat due to deforestation and human interference. I was very excited and impressed to actually find a rattlesnake in the wild, having never seen one outside of a glass enclosure before. Diamondback rattlesnakes possess a venom that contains crotalase, which inhibits strong hemorrhagic activity. This venom will cause intense pain, and can lead to death if not treated quickly. This was a new experience for me and I hope to get the opportunity to work closely with these animals again.

Spring Break Find

Over spring break after a nice rain storm on a humid day, I went to move the trashcans to the road, as it was a Monday morning. Once I moved it I noticed a small grey gecko under the trash can. I quickly identified it as the mediterranean gecko, Hemadactylus turcicus, the only species of gecko in our area.
This species was introduced to this area, so it is non-native. It had big toe pads, and as it crawled up my arm I could feel them put to use. They like to live near buildings so it is no wonder that I found him on a perfectly humid day hanging out under the trash cans.

Article Review: "Larger females are choosier in the gray treefrog (Hyla versicolor)"

This article was published on November 28, 2016 in the Behavioural Processes Journal . It was written by Michael C. Kuczynski, Thomas Getty, and Eben Gering. The article examines how the choosiness of the larger females of the H. versicolor impacts the species' trait diversity and the evolution of sexual traits. They tested the relationship between female choosiness and female body size, physical condition, and age with how far the different females were willing to travel to reach the attractive male call. They collected 50 (30 young and 20 old) sexually mature females of varying lengths and placed them in a chamber for the playback trials of male calls, which were created from recordings made in the summer of 2014. The unattractive call was set for a "near" amplitude for every test, and the speaker was placed opposite of the attractive speaker. The distance the female traveled was observed and their response time between the first and last trial was recorded after they were played four different call samples. They were able to vary the amplitude of the calls to simulate calls that were close or far away, so they did not have to move the speakers. After testing, length, weight after laying eggs, and physical condition of each female was recorded. Based on their weight and size the female frogs were placed into either the old or young category after testing. Female motivation was constant during the trials and no relationship was observed between response time and female length, weight, or condition through out the trials. Length of the female was the only strong predictor of choosiness. It was found that as predicted, the large female gray tree frogs were more likely to travel longer distances to reach the attractive male call than the small females were. Contrary to the prediction, female age and physical condition was not a concrete predictor of choosiness.

This research shows that there is deliberate size-dependent variation in choosing a mate in the gray tree frog species. Female preference can alter the population's sexual characteristics, this can help us to understand how certain male secondary sexual characteristics, like male calling properties, came about in this population, or how speciation was influenced. It is interesting to see how strong the influence of the general female preference of a frog population is and how it is able to determine the sexual trait  characteristics of the males in this species. This may open up new opportunities to understand how the influence of genes and the environment influence characteristics, like body size, to mold female's mate choice and the characteristics of the males and the evolution of female preference.
Link: https://www.researchgate.net/profile/Eben_Gering/publication/311158568_Larger_females_are_choosier_in_the_gray_treefrog_Hyla_versicolor/links/5a1ac2280f7e9be37f9be03d/Larger-females-are-choosier-in-the-gray-treefrog-Hyla-versicolor.pdf

Coluber constrictor

On March 27, 2018 our class encountered a Coluber constrictor at the Francis and Marion national park. It is most commonly known as a Southern Black racer. It was provided to us by some of our guides that had caught the snake for an upcoming group of schoolchildren in order to show them some of the common species. The weather was also quite cold so snakes were very hard to be found as most were burrowing to keep warm. The snake was't all that large as it was around 4 feet long indicating that it was an adult. This snake was remarkably docile as it bit no one when they handled it, and a seemed quite calm. It was easily identifiable as it's shiny black scales that covered it's entire body showed. If you look closely at the picture you see that there are some brown spots. This is normal as they are damaged scales but will appear like new once the snake sheds it's skin.

Article Review: "Do Green Treefrogs Use Social Information to Orient Outside the Breeding Season?" (2016)

     At the University of Wisconsin (Milwaukee), the Department of Biology performed an interesting experiment about the use of social information by anurans. This article was published in 2016, and details the investigation done on whether or not Green Treefrogs (Hyla cinerea), when in a non-reproductive state, respond to environmental acoustic stimuli.  According to the article, most animals seek and use environmental information to help them determine the most suitable places for them to rest, breed, or look for food. They do this by picking up signals from members of their same species, or members of different species, but that have the same or similar living/habitat requirements.
      Anurans, specifically, have been proven to have an auditory system that is very well developed. Also, they have been shown to use phonotaxis, which is basically movement in response to sound stimuli. Most research done before has shown that they use these two methods when they are in a sexually receptive, or reproductive state, however, this article is interesting because it looks at how and if Hyla cinerea use acoustic signals picked up from acoustic stimuli when not reproducing, or basically sexually inactive. Based on the article, there is a gap in the understanding of how anurans behave because of the lack of information on what they do during the non-reproductive season, which was a motivator for these investigators to do the research. Most of what is known about acoustic and vocal amphibian communication is tied to reproduction because the breeding season is when the communication occurs the most.
     According to the article, the researchers claimed that anurans are exposed to acoustic cues within their environment that belong to members of their same species, which could indicate to them that there are potential locations that would be good quality for them to settle. The question was if the frogs (in this case, Hyla cinerea) responded to these acoustic cues even when they are not reproductively active. To test this, according to the article, the investigators used 38 female Green Treefrogs who had no visible eggs or large follicles, and subjected them to four auditory exposures: playing back a call from their same species members, playing back a call from members of a different species (Barking TreeFrog; lives in same habitat and overlaps with Green Treefrog), playing back a white noise (control; a nonstop signal), and plain silence.
     Single frog calls were used instead of group frog calls, since the interest of the project was in responses to calls not related to mating in the frogs. The frogs tested were each placed in a dark box with the speaker outside the box, and the speaker was repositioned each round. Frog behavioral activity was measured in terms of whether or not they approached the wall of the arena, the frog's position to the speaker, and how long it took for the frog to touch the wall. After statistical analyses were performed, it was found that the female frogs did not approach the wall, or move to the speaker in response to the acoustic stimuli they were experimentally exposed to. Initially, the investigators had hypothesized that Hyla cinerea movements are influenced by acoustically obtained social information from the environment, but based on these results, their hypothesis was not supported. In every one of the experiments, they found that the frog subjects were randomly positioning themselves to the speaker; there was no trend.
    From the beginning of the experiment, investigators had thought that since Hyla cinerea have such a greatly developed auditory system for anurans, and also have been known to use phonotaxis, that they may also use their ability to hear and acoustically communicate in various other behavioral contexts. However, the experiment results showed no movement by the female Green Treefrogs to signals seemingly being emitted from other frogs, and also, their speed and positioning did not differ from the speed and positioning of other animals randomly moving around them. The studies that have been done before that were able to document significant frog behavior, according to the article, have used reproductively active frogs during their breeding season instead of reproductively inactive frogs outside of their breeding season. Based on the insignificant results in this experiment, the investigators concluded that Hyla cinerea's responses to social and sexual cues in their environment is limited only to times where it makes the most sense ecologically (finding a mate and/or a good place to breed), and that in frogs and toads, their reproductive hormone system impacts their vocal communication system. The article concluded that in anurans, the reproductive state the frog is in can affect its auditory system's receptivity to social or sexual acoustic signals, and ultimately, that non reproductive frogs may have a less receptive auditory system.
     This article was really neat in that it investigated acoustic communication in anurans, which was a topic discussed in class. When we discussed anuran acoustic communication in class, we talked about how the frogs were affected by noise pollution, and how they recognized calls from same and other species. This article was similar to what we talked about in class in that it investigated how frogs respond to calls from same and other species, except this one is more about when they are not in reproductive mode. This article adds some important information to our understanding of amphibians, and what we know about them because by reading this article, one can see how important reproductive activity is for the frogs' auditory system to be of most use. One can also see how dependent the events of mating and reproduction in frogs are on their receptivity to acoustic stimuli, as a result of the release of reproductive hormones when they are reproductively active. This work is interesting because it suggests that outside of reproduction time, these frogs may not really need to use acoustic communication as much, which is quite different from other animals, and even us.
     Most other animals, and humans, use communication and auditory information on a daily basis to help with non reproductive aspects of life, such as finding food and shelter, but it seems from this article that the frogs only really need it for mating and reproduction. Ultimately, this work is valuable for raising more questions/interesting topics for further research, such as: if frogs are not as receptive to acoustic signals when not reproductively active, what is it that allows them to continue being successful in finding food and shelter? It is also valuable because it helps us learn more about how the acoustic systems of frogs and the stimuli they are exposed to can affect (or, in this case, not affect) their behavior, which scientists are still trying to understand even more and more about. It's also cool to know these things about this particular species (Hyla cinerea) because they are a local species that live in our wetland areas here in SC, and in other parts of the southeastern US. Finally, it would be valuable for people studying how noise pollution can affect anuran acoustic receptivity and communication because it suggests that they can do that best when they are reproductively active. This means that it is important for noise pollution to be absent or minimal during times when these animals are reproductively active so that they can find a mate and reproduce successfully. Hyla cinerea are beautiful amphibians, and although they did not respond as expected to acoustic stimuli in this article, we can still learn from just that, and anything learned is valuable to the growing knowledge on these cool animals.

   
Author's names: Gerlinde Hobel and Ashley Christie
Journal: Zoological Studies
Link: http://www.frogbehaviour.org/wp-content/uploads/Hoebel-Christie-2016.pdf
Citation: Hobel, G., & Christie, A. (2016). Do Green Treefrogs Use Social Information to Orient Outside the Breeding Season? Zoological Studies, 55(17), 1-8. doi:10.6620/ZS.2016.55-17

Herps in the News: Fat-sensing hormone in tadpole metamorphosis

In a recent study done by the University of Michigan the influence of hormones on the developmental cycles of tadpoles was studied. This article discusses the findings of the article the University of Michigan, specifically relating to the eating habits of tadpoles and the hormones involved in these habits. The hormone leptin was studied, which influences the appetite of tadpoles during development. This chemical signals the brain that the organism is full and to stop leading. They found that this chemical is absent in tadpoles prior to metamorphosis as they are trying to digest and store as much energy from their environment as possible. Their insatiable appetite is evolutionarily advantageous because the more body mass they have before metamorphosis the better chance they have a surviving attacks from predators as well as becoming a more effective predator. As we know this energy comes form plant matter mainly as they are herbivores at this stage of their life. These tadpoles do not have any negative feedback controls, so their body never signals them to stop consuming. Through a study where they injected lectin vs. a saline control into the tadpoles they confirmed that leptin triggers this negative feedback signal for them to stop eating.

Leptin is also essential in metamorphosis as their is a peak in this hormone to stop the tadpoles from eating when they reach their metamorphosis peaks. The absence of food is necessary for their guts to develop and rearrange to be suited to consume animals for the next stage of their life as frogs. Interesting parallels have been drawn between the leptin pathway and regulatory function in both amphibians and mammals. Specifically neonatal rats maintain homeostasis in similar ways with leptin.

The intended audience for this article can range from a average interested news consumer with no scientific background to a well versed herpetologist. This article was very reader friendly and did a good job of communicating the information from the scientific study done in a "digestible" (pun intended) way. It also includes references and a link to the original article for a more experienced reader to take a look at the studies done. I do not believe there are any inherent biases in the article. It appears to be more of a summary and telling of an interesting new study done in the field of herpetology and its connection to mammals also makes it relatable to an everyday news reader. It could be interesting to look into this hormone and the obesity epidemic in america and do some research in it in humans and their eating habits.

Link:
https://www.sciencedaily.com/releases/2018/03/180329133110.htm

Natural History: Hemidactylus frenatus (Common House Gecko)

During a trip to Costa Rica, a specimen of Hemidactylus frenatus, also known as the Common House Gecko was spotted during the nighttime climbing a wall. The surrounding location was tropical, with temperatures from 80-90°F and primarily thick vegetation with an ocean nearby creating a wet, humid environment. The specimen was 10-12 cm long from mouth to tail. The specimen was identified by its lack of eyelids, broad toe pads extending the entire length of the toe, uni-coloration, smooth body and rough tail. To identify sex, hemipenile bulges located behind the hind legs and at the beginning of the tail are present indicating that this specific specimen is male. Adult H. frenatus range from 10-14 cm. indicating that this specimen was a fully-grown adult. Unique characteristics of H. frenatus are their brush-like toepads bearing microscopic setae, which increase surface are and friction with the surface. These unique characteristic aides in climbing in arboreal habitats as well as climbing into small cracks and crevasses.

Once spotted and approached, the house gecko quickly ran along the wall to the nearest object/painting in sight for cover. Geckos can perform true tail autotomy, in which they can release their tail when under sufficient stress. To avoid this, I captured the specimen by the torso. Once the specimen was captured, he quickly calmed down and was able to rest on my hand as shown in the image. He was very comfortable at this point, once he knew he was not being threatened.

This was one of many house geckos captured during the trip. They are a species thriving in the hot, humid, jungle environment of Costa Rica.