Monday February 13, 2006

Transcription

1 Analysis of the CBC news article: Empty stomach, visual memory guides ants to food Professor: Dr. Houseman Monday February 13, 2006 Department of Biology Faculty of Science University of Ottawa

2 1 Introduction The CBC News article titled Empty Stomach, visual memory guides ants to Food was posted on November 16, The purpose of the article is to explain how ants use visual cues to find food when hungry and to return to the nest when full (Health & Science 2005). The article is based on a study conducted at the University of Sussex in England by Thomas Collett and three colleagues. Thomas Collett is a Professor of Neurobiology whose research interest is the analysis of mechanisms underlying insect navigation and visual learning, using behavioural techniques (Collett 2004). Several of Dr. Collett s studies have been published by various journals. This particular study was published in the November 17, 2005 issue of Nature with the title, Ant navigation: priming of visual route memories. The study was performed on the wood ant Formica rufa. Using a variety of different pathways and landmarks, Collett and colleagues demonstrated that F. rufa chooses a particular path depending on whether or not it has been fed and by priming the selective retrieval of visual landmark memories (Collett et al. 2005). The story from CBC news does a reasonable job at describing the procedure of the study. For the most part, it does not embellish on Collett s observations or conclusions. Background Scientific Information Social hymenopterans, which include ants, may travel hundreds or thousands of meters from their nests on foraging trips (Wehner et al. 1996). Because of the great distance some of them travel, how they manage to consistently go back to food resources

3 2 and find their ways back home has been of interest for quite some time (Wehner et al. 1996). It has been found that ants use several navigational strategies during their foraging trips. Of interest in this case, is the use of path integration (Hill et al. 2004) with the landmarks they acquire en route (Bisch-Knaden et al. 2003). Path integration involves the animal keeping a running tally of its past directions and distances traveled. The animal integrates this information to allow it to set a direct route back to its starting point (Hill et al. 2004). Reading the CBC article, gives one the impression that the foraging path of ants is based predominantly on landmarks and their hunger state. There is no mention of the path integration system ants may use, even though this type of system may be of crucial importance. In a study done on Cataglyphis fortis (desert ants), it was found that although C. fortis may construct a somewhat meandering pathway when looking for food, when going back to their nests they set out upon a straight course, relying on vector information (Wehner et al. 1996). A more recent study done on C. fortis has shown that landmark cues are used in addition to the vector method that is laid out (Bisch-Knaden et al. 2003). Though the results are somewhat different, both these studies (and others) emphasize the ant s incorporation of both systems of navigation. The CBC article however, does not mention the vector based or path integration system, while referring to ants. One section of the article tries to relate the honeybee s navigational system to the ant study. It describes the honeybee s use of the sun as a compass. Although this is correct and supported extensively in the literature (Hill et al. 2004), it gives the reader the impression that this is the only or predominant method used by bees to find food, which is not the case. For example, bees often associate locations with scents of flowers or

4 3 possibly with colours (Reinhard et al. 2004). Like ants, they can also use familiar landmarks, which can even be recognized from different angles (Menzel 2005). Therefore, the honeybee s way of navigating itself is much more complex than the article suggests. All this emphasis on honeybees in an article about wood ants brings up another issue: Should there really be such a comparison made between the two insects? To entomologists, this comparison makes perfect sense, since they would be well aware of the similarities between ants and bees. Both these insects are social Hymenopterans (Gullan 2005). They are also both central-place foragers, which means that they have fixed positions in their environment from which they regularly depart and return (Wehner et al. 1996). The original study submitted to Nature does not provide this background information. However, this is not a significant concern, since the target audience of Collett s paper is composed of fellow biologists. The popular press article however, makes the assumption that the average reader would understand why bees and ants are being compared the way they are, since the taxonomical and behavioral similarities between the two insects is not addressed. Possible Improvements As discussed previously, the article from CBC news reflects the content of the piece published in Nature quite closely. There is no scientific evidence that has been misinterpreted. However, there are several ways the article could have been improved. Unfortunately, given the length constraint, there is not too much information that could have been added.

5 4 CBC news seemed to exaggerate this particular study s contribution to its field. The first sentence of the article reads, Ants use visual cues to find food when hungry and to return to the nest when full, researchers have found (Health & Science, 2005). This gives the idea that the study is the first in its kind. How ants manage to find their way back to their nests from foraging areas has actually been a topic of interest for quite some time. Even at the beginning of this century, Pièron reported the first experiment to reveal that ants perform path integration (Collett et al. 2000). The study of ant navigation has advanced considerably since Pièron. As discussed in the previous section, various studies have shown that ants use a variety of mechanisms to navigate themselves. In order to avoid the delusion that this study is the first one to be done on ant navigation, a background section should have been included to give readers a chance to compare new developments to what had already been established. In addition, some types of ants do not use path integration or landmarks at all. For example, trail-laying ants use chemical signals that provide olfactory cues so that they can establish a profile of their travel paths (Hill et al., 2004). Hence, there should have been more emphasis in the CBC article on the fact that this study does not apply to all ant species. In Nature, the part of the study that is reported in the most detail is the methodology applied to study the use of visual cues by F. rufa. When compared to the original paper, the CBC article reads almost like a summary or an abridged version and therefore focuses primarily on the methodology of the experiments as well. The last section of both articles, which talks about the use of a Y-shaped maze, is incomplete in the CBC article and hence very incoherent. In the original article, the set-up of the Y- shaped maze is clearly explained. The authors give pertinent details about the design of

6 5 the maze such as, each arm of the Y led to a different visual pattern. One of the two patterns signaled the way to food, and the other the way home (Collett et al. 2005). A diagram of the maze is also provided in Nature. With the length constraint the popular press article seems to face, it would have been a more useful read had there been more background information on previous studies rather than specific details on the methods used, some of which is too incomplete to be of use. Conclusion The story found on the CBC news website gives a concise summary of the study performed by Collett and his colleagues, as reported in Nature. There are no scientific errors made in reporting the study, and it is easily understood by the average reader. There is however, a slight glorification of the results found, making it seem as though this is the first such study done on navigational strategies. If more background information on the field had been provided in the popular press article, the reader would have been more likely to not be left with questions or misinterpretations.

7 6 References: Bisch-Knaden S, Wehner R Local vectors in desert ants: context-dependent landmark learning during outbound and homebound runs. Journal of Comparative Physiology A 189: Collett TS Prof Thomas Collett. Available from: [cited 4 February 2006] Collett TS, Harris RA, Hempel de Ibarra N, Graham P Ant navigation: priming of visual route memories. Nature 438: 302 Gullan PJ, Cranston PS The insects: an outline of entomology. 3 rd edition. Oxford, UK: Blackwell Publishing Ltd Health & Science Empty stomach, visual memory guides ants to food. CBC News [online]. Available from ants html [cited 4 February 2006] Hill RW, Wyse GA, Anderson M Animal Physiology. 1 st edition. Sunderland, Massachusetts: Sinauer Associates, Inc Menzel R, Greggers U, Smith A, Berger S, Brandt R, Brunke S, Bundrock G, Hülse S, Plümpe T, Schaupp F, Schüttler E, Stach S, Stindt J, Stollhoff N, Watzl S Honey bees navigate according to a map-like spatial memory. Proceedings of the National Academy of Sciences 102: Reinhard J, Srinivasan MV, Guez D, Zhang SW Floral scents induce recall of navigational and visual memories in honeybees. The Journal of Experimental Biology 207: Wehner R, Michel B, Antonsen P Visual navigation in insects: coupling of egocentric and geocentric information. The Journal of Experimental Biology 199: