If you have the volition: How to assess vole testis mass asymmetry in non-targeted data sets

We determined the type of asymmetry and assessed its relationship with reproductive-age status in the testis mass of the bank vole (Clethrionomys glareolus (Schreber, 1780)), one of the most widely distributed rodent species. Testis mass varied from 1 mg in immature yearlings to 632 mg in actively reproducing overwintered individuals. Therefore, the high ontogenetic variability of this parameter was considered when analyzing asymmetry. To address the comparability issue of small testes mass (in immature males and males with gonadal involution) and the errors in their measurement, we categorized the animals into size classes and determined the minimum testis mass at which the measurement error did not exceed the detectable asymmetry. We found that testis mass greater than 30 mg in the bank vole exhibited only fluctuating asymmetry (FA), while directional asymmetry and antisymmetry were absent. FA was associated with the stage of sexual development (values were higher in males with gonadal involution) but did not differ among individuals with different ontogenetic stages (yearlings and overwintered). The increase in FA in males with gonadal involution can be viewed as a disruption of buffering processes that maintain the organism’s target phenotype. One such process may be the complexity (or even redundancy) of controlling cellular apoptosis in the involuting testis of reproductively old animals.