Wednesday, February 17, 2010

History Of Green Anaconda

The green anaconda is the largest snake in the world. Although famous, very little is known about its life history. Until I began my research, no field studies had been carried out on the species. Due to the skin trade and habitat degradation its numbers have declined in places where they are not protected. In an effort to protect the species I, with a team of friends and colleages, began the Anaconda Project in 1992, with the aim to learn the basic aspects of the anaconda’s biology in order to create guidelines for its protection and possible management.

At first, to work with anacondas seemed like a formidable challenge that I could not overcome. However, I chose to work in the llanos where the strong dry season makes the animals much easier to find and catch. Later I learned how to find, catch, and restrain them in the field. The areas of my research are: population dynamics, habitat use and mobility, diet preferences, predation of adults and juveniles, mating system and reproduction; however I have collected information on a large number of other fields of the life of the animals.

Among the many aspects that I have learned in a casual way from the snake, just by following them for so long is the presence of cannibalism, how often they are wounded by their own prey, the posibility that they can attack a human being. I have also learned several tricks to work with them such as how to measure, how to implant a transmitter on them with 777minimun disturbation of the behavior, among many others. My ultimate goal is to learn all the secrets of the life history of the animal and get a more first hand knowledge of it.

I have gathered eleven years worth of data catching and processing more than 900 animals and with more than 170 recaptures. I have followed with radio transmitter more than 38 animals, collected more than 100 diet samples, I have also found 51 breeding aggregations and studied the mating, pregnancy and delivery of more than 47 females. With the information gathered I hope to develop a management plan for the conservation of the species and the area in general.

I discovered that anacondas make breeding aggregations of one female and several males. Despite the uneven sex ratio, no conflicts, fights, or agonistic interactions occur between the males other than perhaps pushing each other away from the mating position. I also found that anacondas have an amazing Sexual Size Dimorphism (SSD) where the female is much larger than the males. Indeed anacondas show the largest SSD found in any tetrapod. This SSD is surprising due to the high likelihood that males compete physically for the females (by pushing each other). Physical competition would produce selection pressure for large size in males, however this is obviously not seen in anacondas. One of the aims of my research is to explain why we find this SSD despite the physical competition among males. So far I have found that males seem to rely on tactile cues in order to identify who the female is in the breeding ball. I have found evidence that larger males are mistaken for females and courted by smaller males. Courted males, as well as courting males, will be in disadvantage. Thus, there seems to be an optimal male size where it can outcompete other males but it is not too large to be mistaken (click here to read the whole article).

By studying anacondas in a integratred way I learned not only several aspects of their secret life but also that they can be excellent models for the study of relevant issues in the ecology of snakes and vertebrates in general. Having the largest Sexual Size Dimorphism of any species I can hardly think of any animal that would be a better model for SSD research. Anacondas also present a surprising ontogenetic change in biomass from birth to adulthood, with a 500-fold increase it is much higher than the increase we find in any other species of snakes. This makes anacondas an excellent model to study the ontogenetic changes and develop predictions regarding this issue. Due to their large size, anacondas offer advantages for study that are not found in other snakes, including easy extraction of blood samples sufficient for study of physiological processes and genetic analyses, and possibility of implanting radio transmitters for

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