Cane Toad Dispersal

(Rhinella marina, formerly Bufo marinus) was introduced into Queensland in the 19305 in a failed attempt to control insect pests that were damaging sugar cane crops. In this practical, we will discuss the impact that cane toads have had on native vertebrates, and how the invasion process might be assisting the evolution of improved dispersal ability in this highly invasive pest. Impact on native vertebrates In light ofthe attached readings, consider the following questions on the impact of cane toads on Australian vertebrates: 1. What kinds of selective pressures are cane toads exerting on native wildlife? 2. What do these selective pressures mean for populations of native vertebrates (both in the short and longer term)? Invasion and dispersal ability (Practical Report) In this section of the practical, we will be taking various morphometric measurements of cane toads (snout-vent length; hind limb length) collected from two locations, populations “A" and “B". Recent evidence suggests that cane toads at the front line of the invasion (i.e. those that are spreading into new areas) have longer hind limbs than those from populations near where the toads were first released in the 193os. This indicates that selection may be favouring greater dispersal ability. Your task is to use the data from today's practical to infer which specimens of the two groups (A or B) were collected from a new population and which were collected from a longer, more established one. Apart from inferring the likely source ofthe two cane toad populations, you will also be expected to use the data to make some generalisations about the adaptability ofthis highly invasive pest. Toad measurement 1. Work in pairs. One student can take notes while the other does the measuring. 2. Take a toad from either the container labelled “Population A" or “Population B" and bring it back to your work area. 3. We will be using a ruler to take our measurements (to the nearest1 mm). To measure snout vent length (SVL), measure the length from the tip ofthe snout to the cloaca. To measure hind limb length, stretch the leg out sidewards and measure from the tip of the longest toe to the cloaca. Measure both the left and right legs separately (don't forget to note which leg you are measuring). a. After measuring, place the toad into the ‘used' container and repeat the procedure with a new toad. 5. Towards the end ofthe class, enter the population (A or B), SVL, right leg length and left leg length of each toad you have measured onto the Excel spreadsheet provided.