The evolution of static allometry in sexually selected traits.

Area of Science:

• Evolutionary biology
• Quantitative genetics
• Sexual selection

Background:

• The evolution of morphological trait allometries, particularly under sexual selection, is not well understood despite theoretical discussions since Darwin.
• Existing theories often suggest sexual selection favors larger individuals with disproportionately larger traits (positive allometry) due to cost/benefit scenarios.

Purpose of the Study:

• To develop an allocation trade-off model predicting optimal allometry patterns under various selective regimes.
• To investigate the conditions under which different allometric patterns, including positive allometry, evolve.

Main Methods:

• Derived a general mathematical solution for optimal allometry based on an allocation trade-off model.
• Applied the model to various fitness functions to explore predictions under different selective pressures.

Main Results:

• The model predicts that positive allometry evolves only when marginal fitness gains from increased relative trait size are greater for larger individuals.
• The optimal allometric pattern (isometry, positive, negative, or polymorphic) is contingent on the specific nature of net selection.
• Model predictions align with the diversity of allometric patterns observed in empirical studies of sexually selected traits.

Conclusions:

• The evolution of allometry under sexual selection is complex and depends critically on the precise form of selection.
• Simple emergent patterns may obscure intricate underlying evolutionary processes.
• The model provides a framework for understanding the diversity of allometric patterns in sexually selected traits.