Evolution of allometry in antirrhinum.

Area of Science:

• Evolutionary biology
• Developmental genetics
• Plant morphology

Background:

• Correlated variation in shape and size (allometry) is a fundamental aspect of biological diversity.
• Understanding the evolutionary and genetic underpinnings of allometry is crucial for explaining natural variation within species groups.

Purpose of the Study:

• To investigate the evolutionary and genetic basis of allometry in leaf and flower petal size within the snapdragon (Antirrhinum) species group.
• To determine the role of developmental constraints versus directional selection in shaping organ size diversity.

Main Methods:

• Development of a computational method to quantify shape and size variation in Antirrhinum leaves and petals.
• Analysis of an F2 population derived from interspecific crosses to assess the inheritance of correlated size traits.
• Identification of quantitative trait loci (QTLs) associated with organ size variation.

Main Results:

• The primary source of variation between Antirrhinum species involves positively correlated increases in leaf and petal size.
• This correlated variation was conserved in an F2 population, indicating the involvement of developmental constraints.
• Alleles increasing organ size were found at all identified QTLs in larger species.
• Simulations demonstrated that an undirected evolutionary process could explain the observed allele distribution, challenging the necessity of consistent directional selection.

Conclusions:

• Developmental constraints play a significant role in maintaining correlated allometry between leaf and petal size in Antirrhinum.
• The distribution of organ size alleles can be explained by evolutionary processes other than persistent directional selection, such as an undirected evolutionary walk.