Tuesday, April 27, 2010
Monday, April 26, 2010
Recently, there has been research on color change and its effects on predator avoidance and social interaction. Specifically, one study, Colour change and assortment in the western rainbow fish, written by Rodgers et. al., looked at this dynamic interaction. The authors used controlled experiments to assess the influence that body pigmentation has on shoaling.
This area of research is not very recent, many studies on color change, mimicry, and coloration anomalies have been done. So what makes this one special? Well, many papers that have been published regarding color change in respect to predator defenses and other interactions have used artificial coloration of the fish (or other study organism) and not natural color change. The authors of this paper argued that the artificial coloration gives less conclusive results because predators in the wild use natural coloration to choose their prey. The major goal of this study was to investigate the relationship between color pattern change and grouping decisions. They tested the relationship by exposing the individuals to different colored environments for two weeks and observing their subsequent grouping behavior.
The results of the experiment supported the hypothesis.
One example from their results is that the fish exposed to the dark aquaria showed a darkened body color patterns and preferred to associate with other dark colored fish. The figure above was taken from the paper, showing the coloration differences between the fish that were kept in the dark aquaria (left) and the fish that were kept in the pale aquaria (right). The take home message from reading the paper was that there is more to the coloration than what it seems. This paper in particular focused on the impact of color on shoaling preferences and anti-predator defenses, but it also provided information on other related concepts. The paper is a great resource for information about color change in the wild, the benefits of color change, and the mechanisms behind schooling and shoaling preferences.
Colour change and assortment in the western rainbowfish
Tuesday, April 20, 2010
Do you have a friend whose laugh can be heard from miles away? Are you able to pick one of your friends or family members out of a crowd based on their laughter? Recent research has shown that humans are not the only animal with a distinct laugh. That’s right, dear reader, a study from the
Researchers Frederic Theunissen and Nicolas Mathevon have been studying the giggle calls of a group of spotted – also known as ‘laughing’- hyenas (Crocuta crocuta). Theunissen defines giggles as “short staccato outbursts they make when they are not getting what they want.”
Hyenas live in clans that vary from ten to ninety individuals. They can hunt on their own or they can collaborate to bring down larger prey. However, both forms of hunting cause intense competition.
Hyenas have ten different types of vocalization, including the giggle call. Hyenas giggle in response to stressful situations or to conflict. For example, a hyena will giggle when being chased away from a carcass by a larger animal or when it is fighting with another hyena over a carcass. After all, the only thing worth fighting over is food, and who wants to hand over a fresh carcass?
UC Berkeley has a colony with 26 hyenas. There were 14 adult females, 10 adult males, and 2 sub-adult males. The two sub-adult males were less than two years old when the study was conducted. The vocalizations of the hyenas are recorded during feeding time at the colony. The pitch variations in the vocalizations are then analyzed. One result of the analysis of these vocalizations is that a giggle can give clues to the age of the hyena. As a hyena ages, the pitch of the giggle goes down.
In a clan of spotted hyenas, there is a complex social system with separate male and female dominance hierarchies. Interestingly enough, males are not always dominant over females. There are examples of “hypermasculinized” females that dominate over males in the clan. Analysis of these vocalizations has shown that the giggle is not linked directly to the sex of the hyena- but instead to the social status.
Theunissen and Mathevon believe that these calls in addition to other sensory forms of communication allow for many channels of communication that supports the complex hierarchy and social system. It is not unheard of that several types of cues are used for communication. Many animals rely on sound cues in addition to chemical and visual cues. These cues can lead to information about other animals such as sex and kinship. Hyenas are no exception to this, except that the acoustic cues of the vocal calls have become very important in the social hierarchy. Subordinate hyenas have a giggle that is very different from the giggles of dominant hyenas.
Dominant hyenas have a giggle that can be described as stable and confident. On the other hand, subordinate hyenas have a giggle that is extremely variable and erratic. Think of it this way- you are in lecture and you hear the professor make a joke. The students who understand the joke laugh like there’s no tomorrow (they would be the dominant hyenas). The students who have slept the entire semester laugh quietly to themselves because they are not sure how funny the joke actually is (these people are like the subordinate hyenas). Every student in the class is now able to tell who knows the topic and who could not care less. This is exactly how a hyena clan works.
As an example, Theunissin says that the more dominant hyenas have giggles similar to “he -- he -- he -- he”. The subordinate hyenas have giggles that sound more like “he hi -- ha – he.” If you want to hear the differences yourself, follow this link to the UC Berkley News.
By listening to the vocalizations a hyena makes, other hyenas can assess a situation. Hyenas that hear the giggle then decide whether or not they should join forces with the hyena producing the vocalizations. It also can be a sign of submissiveness. The erratic giggle of a subordinate hyena may show that the subordinate hyena will act compliantly with the dominant hyena. There are countless situations in which a hyena will make decisions based on the giggle that is heard. Think of it in playground terms: wimpy kids will stay away from the bullies and the bullies will pick on the wimpy kids. Not that I’m in any way supporting bullying, it’s just a good metaphor for this hierarchy. In this case a carcass is similar to lunch money- that’s not too far of a stretch is it?
Alright, I’ll cool it with the metaphors and analogies from here on out.
The point is that the giggle calls of the spotted hyena carry information about the sender such as dominance and age. They may also allow for individual identification. Unfortunately, no one knows for sure exactly why hyenas produce giggle calls, but researchers can still hypothesize. Theunissen and Mathevon bring up many advantages of giggling in their paper; for example, giggling can rally other hyenas to a carcass which might be taken over by a lion. In addition, it is important to note that this study was carried out in captivity and therefore some bias is present. Overall, hyenas are extremely complex and interesting animals- despite the bad name that the Lion King has given them. There is a lot more work that can be done with hyenas which could lead to many discoveries and a greater understanding of social relationships and animal communication.
- Mathevon, Nicolas, Aron Koralek, Mary Weldele, Steve Glickman, and Frederic Theunissen. "What the hyena's laugh tells: Sex, age, dominance and individual signature in the giggling call of Crocuta crocuta ." BMC Ecology. 10.9 (2010). doi: 10.1186/1472-6785-10-9
- "Giggles give clues to hyenas social status." News Center. US Berkely News. US Berkley, 2010. Web. 20 April, 2010.
Friday, April 9, 2010
I will not be blogging about ethology or a specific article today, but about animal treatment instead. Animals are important, ok? I would be willing to bet that almost everyone I regularly come into contact with has heard about unethical treatment of animals on factory farms. But I would also be willing to bet that almost no one I come into contact with regularly is too worried about the treatment of animals on factory farms.
No, I am not a vegetarian or vegan. No, I am not going to tell you to watch some gruesome PETA video. No, I'm not asking you to give up meat for good.
All I want to do is raise awareness a little. At most, I'm just asking you to think about how you can make a difference without changing your daily habits. Is that too much, dear reader?
Factory farming is a huge issue all over the world, and the United States is no exception. Factory farms not only make animals live in terrible conditions, but they also cause air pollution, are sources for antibiotic resistant bacteria, and decrease biodiversity.
The Meatrix is a site that provides informative but still entertaining videos (using the Matrix movies as a basis) about the secrets and harms of factory farming. The site lists the issues and how you can help without changing your way of life- and without asking you to become vegetarian. Check out the video below- the first in a three part set- that exposes factory farming. Then check out the website to see what you can do to help diminish the unethical treatment of animals in factory farms.