SINO-AUSTRALIAN WORKSHOP

Brandt’s vole, Microtus brandti, is a major pest in the grasslands of Inner Mongolia and Mongolia (Zhang et al. 1999; Zhong et al. 1999; Zahler et al. 2004).  In the last 50 years in the grasslands of China there have been large increases in the numbers of livestock and associated increases in the numbers of outbreaks of small mammal species, resulting in degradation of the grasslands system.  Current management of the Brandt’s vole, a native species, involves broad-scale application of rodenticides or biological control agents such as botulin toxin which may have short term effects on population dynamics, but which also have non-target effects on livestock, people and biodiversity.  

We are interested in the development of ecologically-based pest management which focuses on having a broad understanding of the biology and ecology of the species of interest and its interactions in the environment (Singleton et al. 1999; Pech et al. 2003; Hinds et al. 2004).  From this understanding, management strategies can be devised which are economic, sustainable, socially acceptable, species-specific and environmentally safe.

One aspect of this approach is the development of alternative control techniques, including reproductive control.  Recently we have undertaken laboratory studies to determine the feasibility of developing fertility control techniques for Brandt’s voles.  Initial studies assessed the effects of immunisation with two reproductive proteins from the egg coats of the mouse and the pig. These proteins previously have been shown to have effects on the fertility of other species.  While good immune responses to these zona pellucida proteins were generated, no effects on the fertility of captive adult female voles were observed.  

Subsequently a Brandt’s vole ovarian cDNA library was produced and used to clone the vole zona pellucida 3 gene.  A full-length cDNA encoding Brandt’s vole zona pellucida glycoprotein subunit 3 (vZP3) was isolated.  The cDNA contains an open reading frame of 1254 nucleotides encoding a polypeptide of 418 amino acid residues.  The deduced amino acid sequence of vole ZP3 revealed high overall identity with the sequences of other species such as the hamster (82.1 per cent), mouse (81.3 per cent) and rat (80.6 per cent).

A specific peptide from a region of the vZP3 gene was identified for use in further studies. A synthetic version of this peptide was conjugated to an immune modulator, and used to immunize female Brandt's voles in order to test its efficacy as a contraceptive antigen. High antibody levels to the vZP3 peptide were present in the sera of immunized female voles and these also cross-reacted to the zona pellucida in the ovaries of Brandt’s vole. The fertility of the immunized voles was reduced by 50 per cent compared with control voles without evidence of significant ovarian pathology (Li et al. 2006).

Models of the population dynamics of Brandt’s voles have been used to simulate the application of fertility control or lethal control (Shi et al. 2002).  Fertility control would be effective if applied at the end of the preceding breeding season or twice at the start of an outbreak year and is equivalent to the effects of lethal control.  If applied in the preceding autumn, the effects of the infertility would need to be long-lasting.  A capacity to forecast outbreaks of voles would also be essential to the implementation of efficient control.

The results from the modelling and laboratory studies indicate that fertility control for Brandt’s vole using a self-antigen could be feasible.  We have been exploring the oral delivery of the vole-specific peptide in Brandt’s voles; however, the method is still a number of years from use in the field.   If it is possible to develop oral delivery formulations, then the approach will provide a species specific and environmentally friendly method of control.

Acknowledgements

The research on the development of fertility control for Brandt’s voles has been funded by ACIAR and AusAID.

References

Hinds, L., Pech, R. and Singleton, G. (2004). Ecologically based rodent management. In Proceedings of the International Seminar on Brandt’s vole management, Ulaanbaatar, 27-28 September, 2004, pp. 69-77, 98-102.

Li, H., Piao, Y., Zhang, Z., Hardy, C.M. and Hinds, L.A. (2006).  Molecular cloning and assessment of the immunocontraceptive potential of the zona pellucida subunit 3 from Brandt’s vole (Microtus brandti).  Reproduction, Fertility and Development, (In press).

Pech, R.P., Davis, S.A. and Singleton, G.R. (2003). Outbreaks of rodents in agricultural systems: pest control problems or symptoms of dysfunctional ecosystems?  In Rats, Mice and People: Rodent Biology and Management, (eds. G.R. Singleton, L.A. Hinds, C.J. Krebs and D.M. Spratt), ACIAR, Canberra, 2003. pp. 311-315.

Shi, D., Wan, X., Davis, S., Pech, R. P., and Zhang, Z. (2002). Simulation of lethal control and fertility control in a demographic model for Brandt’s vole Microtus brandti. Journal of Applied Ecology 39, 337-348.

Singleton, G.R., Leirs, H., Hinds, L.A. and Zhang, Z. (1999). Ecologically-based management of rodents – re-evaluating our approach to an old problem. In: Singleton, G.R., Hinds, L.A., Leirs, H. and Zhang, Z. (eds.), Ecologically-based management of rodent pests, Canberra, ACIAR, pp 17-29.

Zahler, P., Dolgormaa, L., Hinds, L.A. and Smith, A.T. (2004) The management of Brandt’s vole in Mongolia: towards an ecologically-based means of control. Mongolian Journal of Biological Sciences 2(2): 51-55.

Zhang, Z., Zhong, W. and Fan, N. (1999) Rodent problems and management in the grasslands of China. In: Singleton, G.R., Hinds, L.A., Leirs, H. and Zhang, Z. (eds.), Ecologically-based management of rodent pests, Canberra, ACIAR, 316-319.

Zhong, W., Wang, M. and Wan, X. (1999) Ecological management of Brandt’s vole (Microtus brandti) in Inner Mongolia, China. In: Singleton, G.R., Hinds, L.A., Leirs, H. and Zhang, Z. (eds.), Ecologically-based management of rodent pests, Canberra, ACIAR, 199-214.

¹CSIRO Entomology

²State Key Laboratory for Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences