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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.


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