Question

Cane toads have been introduced to Australia and many of the Pacific islands. Their skin contains glands that secrete poisons that are toxic to most vertebrates. Discuss how evolution might operate on potential predators of cane toads in areas like Australia in which the predators have no prior evolutionary history of interactions with these toads. Phillips and Shine (2006) discuss this issue.

Short answer

Evolution can result in predator adaptations such as toxin resistance or behavioral changes to avoid cane toads. Natural selection will favor predators that survive interactions with toads. These favorable traits will become common over generations.

Step-by-step solution

Understand the Context

When organisms interact with new species, especially invasive ones like cane toads in Australia, it triggers evolutionary pressures. These foreign toads have skin that secretes poisons toxic to native predators that have not previously encountered this type of threat.

Identify Evolutionary Mechanisms

Evolution acts primarily through mechanisms such as natural selection, mutation, genetic drift, and gene flow. In the case of Australian predators encountering cane toads, natural selection will be significant as those predators unable to deal with the poison are less likely to survive and reproduce.

Discuss Natural Selection

Natural selection would favor any predators that by chance (or mutation) do not attempt to eat the toads or are less affected by the poison. Over time, these traits become more prevalent in the predator population, leading to a gradual shift.

Consider Mutation

Mutations in the DNA of predator species might randomly occur, potentially giving rise to genetic traits that allow them to better handle or avoid the toxicity. If beneficial, these mutations would be passed on to subsequent generations.

Evaluate Potential Outcomes

Predators might evolve physiological resistance to the poison, behavioral changes to avoid eating toads, or other adaptations. Evolution requires many generations, so initially, there may be significant predator population impacts.

Key concepts

Natural Selection

Natural selection is a key driver of evolution, particularly when new environmental pressures emerge, such as the introduction of an invasive species like the cane toad in Australia. When predators are faced with the toxic cane toads, they are suddenly under pressure to survive and reproduce in this new challenge.

In natural selection, traits that increase an organism's probability of surviving and reproducing tend to become more common in the population over time. Predators that are less affected by or avoid the cane toad's poison are more likely to survive. Here's how natural selection could manifest in this scenario:

• Predators who instinctively avoid cane toads might live longer to reproduce.
• Predators that have a tolerance or resistance to the toxins survive better than others.
• Over generations, the genes of those that survive are passed on, gradually shifting the population.

Natural selection essentially acts as a filter, increasing the prevalence of beneficial traits and removing those less suited to the environment.

Mutation

Mutations are changes in DNA that can introduce new traits into a population. In the context of Australian predators dealing with cane toads, mutations offer a possibility for new and potentially beneficial traits to arise.

Mutations occur randomly and can affect an organism's fitness—its ability to survive and reproduce. Here’s how mutations may play a role in this situation:

• Some mutations might result in a physiological change that offers resistance to the toad's poison.
• Behavioral mutations could arise, causing predators to avoid the toads due to taste aversion or learned behavior.
• Mutations that don't imbue some advantage tend to be eliminated through natural selection.

Although any single mutation might appear rare, when beneficial, it can have a large impact over many generations, as the traits spread within the population.

Adaptation

Adaptation is the process where organisms become better suited to their environment. When it comes to cane toads in Australia, the predators may eventually adapt through both physiological and behavioral changes to this new threat.

Here are some potential adaptations that might emerge as predators encounter cane toads:

• Physiological adaptations might include developing enzymes that detoxify the toad poison.
• Behavioral adaptations could involve changing prey preferences to avoid the toads entirely.
• There might also be a shift in feeding times if cane toads are active at particular times, leading predators to hunt during different periods.

Adaptation involves a complex interplay of natural selection and mutation. Over time, what are beneficial traits for survival become more prominent, leading to a more fit and resilient predator population.