The solution to cane toad control is unlikely to come from only one source.  Short term strategies currently include various means of destroying toads - trapping, gassing, clubbing etc.  An anaesthatising spray that subsequently kills toads has recently been developed by our participant Pestat Pty Ltd. 

Medium-term strategies such as the use of the toad's own parasites or alarm pheromones are also being investigated.

In the longer term, scientists are also investigating the possibility of using gene modification technology to render toads unable to breed successfully.  One such concept is the "daughterless" strategy.

"Daughterless" is a sex skewing technology based on limiting the number of females in the wild population.  A genetically modified strain of cane toads are produced that are capable of  producing only male offspring.   This occurs through male tadpoles developing into fertile male toads normally, but female tadpoles reverse their sex and develop into fertile males also.  This, over time, makes it harder and harder for males to find mates with which to breed.   However, because the spread of the daughterless gene will be diluted in further generations, restocking of the wild population is required in order to ensure penetration of the gene throughout the population.

The strategy can be represented:

The benefits if this technique is successful are obvious - it is a non-toxic and humane way of bringing about a population decline, and has no impact on any other species or the environment. 

However, the development of this technology is exceedingly costly and time-consuming.  The steps involved include:

• finding the genetic target - the exact mechanism of sex determination in cane toads must be identified.  Several genes may be involved.  As in some other amphibians, temperature may play a role in sex determination.

• making the genetic construct - building a transgene - an engineered DNA molecule with two parts.  The effector part of the molecule will be the coding sequence of a gene that will promote male development in all offspring.  The other part of the DNA molecule will be a promoter or enhancer containing gene regulatory elements that will cause the effector to be expressed in the right cells at the right stage of development to bring about female-to-male sex reversal.

• generating transgenic toads - this will involve micro-injection of the modified DNA into fertilized cane toad eggs in the laboratory.

• determining fertility and heritability - the injected tadpoles must be raised to sexual maturity and tested for sex reversal.  Successful transgenic toads must also be red to ensure that the daughterless gene is heritable.

Data modelling is also taking place to work out how many transgenic toads would have to be released, when and where to make the strategy most effective should it be released into the wild.

Progress to date:

So far Professor Koopman's team (including IA CRC PhD student John Abramyan) have succeeded in defining the cellular and molecular steps involved in sex-specific development of cane toad young to a point where a control strategy based on this information can be designed.

They have established the stage of development at which sex is determined, isolated several of the key sex determining genes and determined their DNA sequence.  They have also been able to determine when and where some of these genes are active during sexual development.

Preliminary studies into the feasibility of hormonal sex reversal have been completed, and research is continuing into how to implement this in the laboratory.