MORPHOMETRIC VARIATION IN 13-LINED GROUND-SQUIRRELS, SPERMOPHILUS-TRIDECEMLINEATUS, FROM WEST TEXAS

Univariate and multivariate statistical tests were used to assess indi vidual and secondary sexual morphological variation in a sample of 99 Spermophilus tridecemlineatus from northwestern Texas. Based on multip le analysis of variance results, variation in standard morphological m easurements (condylobasal length, zygomatic breadth, mastoid breadth, and depth of skull) of adults was independent of age group, but depend ent on sex. Discriminant function analysis correctly assigned 95% of t he individuals to the correct sex when both cranial and external measu rements were used, whereas 86% of the individuals were assigned correc tly to sex based on cranial measurements only. Principal components an alysis confirmed the presence of two distinct groups based on sex; a c ombination of four cranial and five external measurements accounted fo r 95% of the variation between sexes. Consequently, sexes should be an alyzed separately when addressing systematic questions in this taxon f rom this area.