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RESEARCH ARTICLE
Contents Vol 18(3)

Visual method for evaluating the state of sexual development in male grey squirrels (Sciurus carolinensis)

Mark Ferryman A B , Brenda A. Mayle A and Geoff W. Morgan A
+ Author Affiliations
- Author Affiliations

A Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH, UK.

B Corresponding author. Email: mark.ferryman@forestry.gsi.gov.uk

Reproduction, Fertility and Development 18(3) 383-393 https://doi.org/10.1071/RD05129
Submitted: 4 October 2005  Accepted: 8 December 2005   Published: 2 February 2006

Abstract

Stages of sexual development in grey squirrels were classified by scoring the presence of periscrotal hair and staining, as well as the position, size and colour of testes, to develop a visual breeding score (VBS). The VBS was a highly significant predictor of the presence and concentration of epididymal spermatozoa, which were produced from 12 months of age. Two classes of producers were identified: ‘high’ with spermatozoa levels >10 × 106 mL−1 and ‘low’ with spermatozoa levels <10 × 106 mL−1. Sperm motility was variable across all levels of productive males but was generally higher in the ‘high’ group, indicating that these were ‘functional’ males. Sexual regression was observed in two autumn periods. The VBS was less effective in determining states of regression and redevelopment; the confidence of classification improved when age class (adult or prepubertal) and date of capture was known. The use of the VBS to classify stages of sexual development in grey squirrels will improve selection of animals for studies of population biology and fertility control, and has potential application in captive breeding studies of rare Sciuridae species.

Extra keywords: age class, breeding condition, epididymal spermatozoa, sperm motility.


Acknowledgments

We would like to give special thanks to Jacqui Neal of Forest Research for her support in analysing the samples, Nick Jenkins of Sheffield University for technical guidance in assessing epididymal spermatozoa, and Professor John Gurnell of Queen Mary and Westfield College, London, for providing technical assistance and comments on an earlier draft of this manuscript. Stuart A’Hara and Chris Quine of Forest Research and two anonymous referees also provided helpful comments on earlier drafts of this manuscript.


References

Allanson, M. (1933). The reproductive processes of certain mammals. V. Changes in the reproductive organs of the male grey squirrel (Sciurus carolinensis). Philos. Trans. R. Soc. Lond. B Biol. Sci. 222, 79–96.
Dubock A. C. (1976). Reproductive cycles in the male and female grey squirrel (Sciurus carolinensis). Ph.D. Thesis, University of Reading, Reading, UK.

Dubock, A. C. (1979a). Male grey squirrel (Sciurus carolinensis) reproductive cycles in Britain. J. Zool. 188, 41–51.
Fagerstone K. A., Coffey M. A., Curtis P. D., Dolbeer R. A., Killian G. J., Miller L. A., and Wilmot L. M. (2002). ‘Wildlife fertility control.’ Wildlife Society Technical Review 02-2.

Fisher, E.W. , and Perry, A. E. (1970). Estimating ages of gray squirrels by lens-weights. J. Wildlife Manage. 34, 825–828.
Gurnell J. (1987). ‘The Natural History of Squirrels.’ (Christopher Helm: London, UK.)

Gurnell J. (1991). Grey squirrel. In ‘The Handbook of British Mammals’. (Eds G. B. Corbet and S. Harris.) pp. 186–191. (Blackwell Scientific Publications: Oxford, UK.)

Gurnell, J. (1996). The effects of food availability and winter weather on the dynamics of a grey squirrel population in Southern England. J. Appl. Ecol. 33, 325–338.
Home Office (1990). ‘Guidance on the Operation of the Animals (Scientific Procedures) Act 1986.’ (HMSO: London, UK.)

Kirkpatrick, C. M. (1955). The testis of the fox squirrel in relation to age and seasons. Am. J. Anat. 97, 229–255.
| Crossref | GoogleScholarGoogle Scholar | PubMed | Klevezal G. A., and Kleinenberg S. E. (1967). ‘Age Determination of Mammals from Annual Layers in Teeth and Bones.’ (Izdatel’stvo: Moscow, Russia.) [In Russian]

Koprowski, J. L. (1994). Sciurus carolinensis. Mamm. Species 480, 1–9.
Mayle B., Pepper H., and Ferryman M. (2004). ‘Controlling grey squirrel damage to woodlands.’ Forestry Commission Practice Note 4. (Forestry Commission: Edinburgh, UK.)

Middleton, A. D. (1930). The ecology of the American grey squirrel (Sciurus carolinensis, Gmelin) in the British Isles. Proc. Zoolog. Soc. London 1930, 804–842.
Payne R. W., Baird D. B., Cherry M., Gilmour A. R., Harding S. A., et al. (2002). ‘Genstat Release 6.1 Reference Manual.’ (VSN International: Oxford, UK.)

Pudney, J. (1976). Seasonal changes in the testes and epididymis of the American grey squirrel (Sciurus carolinensis). J. Zool. 179, 107–120.
| PubMed | Shorten M. (1954). ‘Squirrels.’ (Collins: London, UK.)

Siwela A. A., and Tam W. H. (1983). Reproductive cycle and seasonal changes in the prostate gland of the grey squirrel (Sciurus carolinensis Gmelin). In ‘Proceedings of the Ninth International Symposium on Comparative Endocrinology’. (Eds B. Lofts and W. N. Holmes.) pp. 289–292. (Hong Kong University Press: Hong Kong.)

Tait, A. J. , and Johnson, E. (1982). Spermatogenesis in the grey squirrel (Sciurus carolinensis) and changes during sexual regression. J. Reprod. Fertil. 65, 53–58.
| PubMed | Webley G. E. (1982). A study of aspects of the reproductive physiology in the male and female grey squirrel (Sciurus carolinensis). Ph.D. Thesis, University of Reading, Reading, UK.

Webley, G. E. , and Johnson, E. (1983). Reproductive physiology of the Grey squirrel (Sciurus carolinensis). Mammal Rev. 13, 149–154.