Is developmental instability sex-specific? Case study in two spiny lizards with different reproductive modes.

Area of Science:

• Evolutionary developmental biology
• Morphological variation
• Animal development

Background:

• Developmental instability (DI) assesses an organism's capacity to buffer genetic and environmental changes during growth.
• DI can be sex-specific and influenced by reproductive modes, but their relative importance is understudied.
• Fluctuating asymmetry and canalization are key metrics for assessing DI.

Purpose of the Study:

• To investigate whether developmental instability is sex-specific in two spiny lizard species with contrasting reproductive modes.
• To compare the influence of sex versus reproductive mode on developmental instability and morphological buffering.
• To analyze head shape variation in relation to sex and reproductive strategy.

Main Methods:

• Analyzed 69 adult spiny lizards (Sceloporus grammicus - viviparous, Sceloporus aeneus - oviparous).
• Utilized landmark-based geometric morphometrics on dorsal head images to quantify shape.
• Assessed fluctuating asymmetry (Procrustes distances) and canalization (variance-covariance matrices, PCA).

Main Results:

• Fluctuating asymmetry did not differ between sexes within species but varied between species.
• Canalization analysis indicated stronger developmental buffering in male S. grammicus compared to both sexes of S. aeneus.
• No significant sexual dimorphism in head shape was detected in either species.

Conclusions:

• Developmental stability is more strongly associated with reproductive mode than sex in these lizards.
• Reproductive strategies, not sex, modulate morphological buffering during development.
• Size-related sexual differences do not necessarily lead to shape divergence.