Aquatic Invasive Species

Since being introduced to Australia to combat sugar cane crop destruction caused by the Frenchi cane beetle, the cane toad (Bufo marinus) has wreaked havoc on both native organisms and Australian ecosystems as a whole. Cane toads pose a particularly severe ecological threat due to their virtually limitless diets and poisonous qualities; they readily consume nearly anything in sight and release toxins that can eliminate most of their predators. However, previous research has shown that one of its predators, the meat ant (Iridomyrmex purpureius), can consume cane toads without being afflicted by its toxins.

In the past, researchers have implemented various methods in an effort to control cane toad populations, including certain forms of biocontrol. Unfortunately, their efforts have generally been met with limited success.

However, recent research has been revealed that may help lead to the development of a more effective method of preventing cane toad invasion. Scientists have discovered that cane toads primarily rely on their sense of smell when seeking out prey. This information may be a key component in a novel, innovative control method that utilizes certain odors to which both the cane toad and its predators are attracted.

Duke undergraduate Chris Rzeznik and his team are attempting to further develop this approach in an experiment that exploits both the cane toad’s vulnerability to meat ant consumption and its attraction to the scent of cat food. Building on the knowledge that both cane toads and meat ants have proven to be attracted to cat food, Rzeznik and his team have devised a procedure to lure both species together using their shared food preferences.

The researchers aim to assess how the cane toad’s sense of smell can be used to control its spread by identifying the foods to which both cane toad. To accomplish this, they will replicate the Australian environment in six simulated habitats, four of which will contain cane toads and two of which will contain meat ants. One will contain both species in order to examine the extent to which the ants will prey on the toads when adequately exposed to them. The corners of each habitat will emit the scent of cat food, and the researchers will record activity at each corner for one week to determine the level of attraction that both species exhibit to the odor.

The researchers speculate that if they are successful in using shared food preferences to lure these species together, they can deduce that small rodents and insects will be the most reliable bait in doing so in future studies. If their experiment ultimately produces no conclusive outcome, the researchers plan to retry it with modifications of certain variables, such as the use of insects like the lavender beetle (Cydnidae) as bait instead of cat food.

Although their study may have various motives, the researchers’ main concern is the welfare of the Australian environment. According to Rzeznik, “the overarching effect our team hopes to have is that by stopping the cane toad invasion, we will restore the uniqueness of Australia’s wildlife and rid this country of a pest that has caused problems for decades.”

Georgia Ward-Fear of the University of Sydney (Australia) and her colleagues have found that Cane Toads (bufo marinus) are in fact quite vulnerable to a native species of Australian ant. Although cane toads are poisonous to most of their predators, these ants are immune to the toxins secreted by the amphibians.

To measure the toad’s response to attack, they placed toads in a shallow plastic dish and tapped on it until it had completed five hops. They also measured the toads’ activity in the wild vs. the ants’ activity.

They concluded that because the toads have shorter, slower hops than other native frog species and share similar activity patterns with the ants, they are far more vulnerable to meat ant attack. As toads mature, they are active diurnally, which increases their encounters with meat ants. The experiment also showed that many toads failed to detect and evade approaching ants.

Functional Ecology Vol 23, Pages 559-568 (2009)

Ben Berg

Gene Expression Patterns, July 2008
The fight against cane toads has been waged since shortly after their introduction to the Australian continent in 1935. Many different strategies have been tried to limit population growth, but none deterred the poisonous toads’ invasion. New research led by Damian Halliday et al., however, attempts to find a weakness in the toad’s life cycle by examining changes in toad gene expression during metamorphosis.

Funded by the Australian Government’s Department of Environment and Heritage, the study identified changes in gene expression that occur during the somewhat miraculous metamorphosis from tadpole to toad. Transformations such as changing hemoglobin structures and creation of different digestive enzymes are known to occur between the stages. Halliday et al. were able to isolate the specific genes used in these transitions through the use of microarray analysis of toad DNA. Pending further research, the authors hope to find a method of preventing these genes from being expressed, inhibiting metamorphosis and thus eliminating the toad problem.

Ben Berg
Dr. David Lodge’s March 16th lecture was particularly interesting because of its relevance to the literature review I just finished writing. In the literature review I discussed the future direction of research on methods of controlling invasive cane toads in Australia. I ultimately recommended that methods involving the introduction of new species not be pursued because of the possible unknown consequences of doing so. Dr. Lodge began his lecture by saying that he thinks the introduction of non-native species could now be done in a safe manner, refuting my assumption that these introductions were as dangerous as ever.
The information Dr. Lodge went on to discuss turned out to validate much of the logic that led to my policy recommendation. He discussed the way in which models of invasion have been developed, and what limitations of these models exist. Essentially, among several weak points in invasion modeling, one of the most significant is modeling the spread of an invasive species. Many models claim to predict the potential spread of a species, but according to Lodge most of these models fail. When I asked about the contradiction between this statement and his claim that species could now be safely introduced, Dr. Lodge said that while modeling techniques have improved, we are far from knowing everything about species invasion. I therefore think that the assumptions made in my literature review are completely reasonable, and we cannot continue to introduce species with unknown consequences.

In his paper entitled “The war of the roses: demilitarizing invasion biology:, Brendon MH Larson argues that militaristic language used in invasive species articles to invoke a response in the reader can actually have negative effects. He claims that these metaphors contribute to public misunderstanding of invasive species, and that they support militaristic ways of thinking that make it hard to create a sustainable relationship between humans and the natural world. According to Larson, the problem with militaristic language relies on two fundamental facts about war. 1) A war requires opposing sides. 2) Wars are fought with the belief that good will triumph over evil. These assumptions are leading the public to have a misconstrued view of invasive species. They can also have a boomerang effect, where the readers have the opposite reaction to the language than is intended.

“Currently, the Australian government is preparing to spend between five and seven million dollars over the next 15 years to combat the cane toads…The economic loss resulting from the disturbance and destruction caused by invasive species is huge.” (Butler 2005). This quote is from author Tina Butler, a writer for an online newspaper, who comments about the importance of the elimination of cane toads from Australian ecosystems.

Although Larson raises a few valid points, I have to disagree with his argument. Militaristic language has inspired people to act and take up the “fight” in whatever they believe in for centuries. It’s psychological that more vivid and intense language will influence people’s opinions and possibly lead them to acting on them. I don’t think that the use of militaristic language is problematic nor is it ineffective. These metaphors do not incite riots or violence, but rather they convey the importance of the eradication and removal of invasive species and how large of an effect they have on the general public. Militaristic language is absolutely necessary to gain support from readers and to convince the general public that something must be done.

Butler, Tina. “Overstaying Their Welcome: Cane Toads In Australia.” Mongabay. http://news.mongabay.com/2005/0417b-tina_butler.html. Viewed February 23, 2010.

Proc. R. Soc. Vol. 276, 2813 – 2818, (2009)

A study done on Australian death adders shows how certain adaptations have become liabilities in reference to the invasion of cane toads. These snakes have adapted to their environments by developing lures on their tails, allowing them to attract more agile prey, and they have a delayed ingestion process, which allows them to circumvent the dangers of natural toxins.

Cane toads, however, pose a threat to these reptiles. Listed as a “top-ten global invader”, they are slowly decreasing Australian adder populations. Cane toads are typically bigger than native frogs, making it more attractive for adders to lure them in. They also move in slower, shorter hops, increasing their availability as prey. However, their toxins remain active for a long time after their death, increasing adder fatalities. More than half of the adders who tried to eat the toads died as a consequence. Cane toads are not only harming adders, but other Australian wildlife that typically prey on toads as well.

Chris Rzeznik

Ben Berg

Chemoecology 8.10.2009

Since their introduction to mainland Australia in 1935, the cane toad (Bufo marinus) has significantly decreased biodiversity amongst reptiles in Australia.  Scientists are now growing desperate in their attempts to limit the growth of this species.  Researcher Mattias Hagman conducted experiments involving biological control mechanisms to fight the toad invasion.

Working in conjunction with Team Bufo (a team of cane toad researchers) and receiving funding from the Australian government, Hagman tested lab results that suggested that a pheromone produced by larval toads lowered survival rates.  Toad larvae were placed into two groups in outdoor ponds, and the treatment group was exposed to the pheromone.  The pheromone, which is emitted by injured larvae to alert other individuals, caused the tadpoles to undergo accelerated metamorphosis, causing a smaller body size and reducing survivorship by 50%.  While this significantly effected cane toad populations, it appeared to have no effect on native species.  The authors have called for follow-up research on the topic.