Sessional Committee on Environment and Sustainable Development Written Submissions Received Volume 2 Issues associated with the progressive entry into the Northern Territory of Cane Toads October 2003
Tabled Paper 1123
Tabled Papers for 9th Assembly 2001 - 2005; Tabled Papers; ParliamentNT
Tabled by Delia Lawrie
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Written Submissions Dr Mahony Volume 2 Cane Toad Inquiry Report 171 Another related matter that would be clarified in these steps and one that offers considerable potential for other means of biological control is the means of sex determination in cane toads. For the biocontol method we propose it is critical that only sterile males are produced. The sex determination mechanism in toads is not known, but it would be determined in step three above. This is a complex matter for which we have provided a brief outline at the end of the document. Research approach and proposed methods Two methods offer the greatest possibility to obtain large numbers of viable and hormonal competent but sterile triploids: Production of triploids by shock treatment, Production of triploids via intermediate tetraploidy. 1. Production of triploids by shock treatment Step one Artificial stimulation of gravid females to lay eggs. Achieved by hormonal injection of gonadotrophin. Step two In vitro fertilisation of eggs with sperm suspensions. Achieved by standard protocols. Step three Shock treatment of eggs immediately following fertilisation to prevent the extrusion of the second polar body from the egg. This effectively produces a diploid egg, with the incorporation of the sperm nucleus the zygote will be triploid. Triploids should grow and develop as normal but be sterile. Shock treatment usually involves sudden temperature or pressure change. Step four Monitoring growth and development of the triploids. 2. Production of triploids via intermediate tetraploidy Step one & two are the same as above. Step three Following fertilisation of the eggs shock or chemical treatment (Colchicine) applied at the time of first cleavage to produce autotetraploid individuals. Success tested by chromosomal analysis. Growth and development of the tetraploids needs to be investigated. Step four Tetraploids crossed to diploids (in vitro fertilisation) will produce triploid offspring. Work Plan 1. Production of triploids by shock treatment Step one Artificial stimulation of gravid females to lay eggs. We have developed the necessary protocols in our laboratory with the cane toad.