While sexual dimorphism has long received special attention from biologists, derived monomorphism, the condition in which both males and females express similar derived features, has been less well studied.  Historically, the appearance of “male-like” features in females has been explained by the genetic correlation between the sexes.  Recent work emphasizes the importance of studying the independent selective forces on both females and males to understand sexual dimorphism.  Sexual dimorphism and derived monomorphism in the genus Aneides are examined in light of predictions of social selection.  Aneides hardii shows the greatest degree of sexual dimorphism in snout-vent length and head width, with the other species of Aneides less sexually dimorphic. This reduced dimorphism, however, is not a return to an ancestral monomorphic state, but rather exemplifies derived monomorphism because females express traits that were limited in expression to males of ancestral species.  Instead of calling these “male-typical” traits in females, I suggest the term “derived monomorphic” traits, as these traits are typical in these females and “derived monomorphic” can apply to both sexes. Increased attention to studying the patterns and ecological significance of derived monomorphism will shed light on the underlying selective forces, including sexual selection, on both females and males. 

Preserved animals were measured with calipers and some animals were weighed. 

README file for Aneides morphological data.

All morphological measurements are in millimeters and weight is in grams.

SM123 column
    1 = adult male
    2 = adult female
    3 = juvenile
    7 = unknown

Mature column
    8 = mature
    7 = not mature

Morphological abbreviations
    SG = snout-gular length
    HW = head -width
    SVL = snout-vent length
    Tail = tail length
    AG = axilla-groin length
    WT = weight
    RHL = right hind limb length (excluding pes)
    RFL = right fore limb length (excluding manus)
    RG = regenerating tail

These files may include some outliers/typos that were later removed.