Genetic Variation in Sexual Size Dimorphism Is Associated with Variation in Sex-Specific Plasticity in .

AbstractThe difference in body size between females and males, or sexual size dimorphism (SSD), is ubiquitous, yet we have a poor understanding of the developmental genetic mechanisms that generate it and how these mechanisms may vary within and among species. Such an understanding of the genetic architecture of SSD is important if we are to evaluate alternative models of SSD evolution, but the genetic architecture is difficult to describe because SSD is a characteristic of populations, not individuals. Here, we overcome this challenge by using isogenic lineages of to measure SSD for 196 genotypes.

Genetic variation of morphological scaling in Drosophila melanogaster.

Morphological scaling relationships between the sizes of individual traits and the body captures the characteristic shape of a species, and their evolution is the primary mechanism of morphological diversification. However, we have almost no knowledge of the genetic variation of scaling, which is critical if we are to understand how scaling evolves. Here we explore the genetics of population scaling relationships (scaling relationships fit to multiple genetically-distinct individuals in a population) by describing the distribution of individual scaling relationships (genotype-specific scaling relationships that are unseen or cryptic).

Individual Cryptic Scaling Relationships and the Evolution of Animal Form.

Artificial selection offers a powerful tool for the exploration of how selection and development shape the evolution of morphological scaling relationships. An emerging approach models the expression and evolution of morphological scaling relationships as a function of variation among individuals in the developmental mechanisms that regulate trait growth. These models posit the existence of genotype-specific morphological scaling relationships that are unseen or "cryptic.

The (ongoing) problem of relative growth.

Differential growth, the phenomenon where parts of the body grow at different rates, is necessary to generate the complex morphologies of most multicellular organisms. Despite this central importance, how differential growth is regulated remains largely unknown. Recent discoveries, particularly in insects, have started to uncover the molecular-genetic and physiological mechanisms that coordinate growth among different tissues throughout the body and regulate relative growth.

Cryptic individual scaling relationships and the evolution of morphological scaling.

Morphological scaling relationships between organ and body size-also known as allometries-describe the shape of a species, and the evolution of such scaling relationships is central to the generation of morphological diversity. Despite extensive modeling and empirical tests, however, the modes of selection that generate changes in scaling remain largely unknown. Here, we mathematically model the evolution of the group-level scaling as an emergent property of individual-level variation in the developmental mechanisms that regulate trait and body size.