Reaction norms with bifurcations shaped by evolution.

Area of Science:

• Evolutionary Biology
• Theoretical Ecology
• Developmental Biology

Background:

• Seasonal polyphenism, where a single genotype produces different phenotypes in response to environmental cues, is a key area in evolutionary biology.
• Understanding the evolution of reaction norms, which map genotypes to phenotypes across environments, is crucial for explaining adaptive phenotypic plasticity.
• Previous models have explored reaction norm evolution, but the interplay between developmental constraints and adaptive branching remains an active research question.

Purpose of the Study:

• To investigate the evolution of reaction norm bifurcation and branching in seasonal polyphenism using two distinct modeling approaches.
• To determine the conditions under which branching reaction norms evolve and are maintained, considering population ecology and developmental pathways.
• To assess the impact of developmental submodels and constraints on the evolutionary trajectory towards branching reaction norms.

Main Methods:

• Development of two computational models for seasonal polyphenism evolution.
• Model 1: Unconstrained reaction norms defined by environment-phenotype probability matrices.
• Model 2: Incorporates an explicit developmental map, introducing potential constraints on evolutionary pathways.

Main Results:

• In Model 1, a branching reaction norm evolves under strong stabilizing viability selection with a cyclically fluctuating optimum, provided specific conditions on selection strength and developmental lag are met.
• In Model 2, branching reaction norms can emerge for certain developmental submodel parameters, but evolution is often constrained.
• Model 2 demonstrates that evolutionary trajectories can become trapped in local optima, hindering the evolution of advantageous branching patterns and leading to substantial developmental noise.

Conclusions:

• Developmental constraints can significantly limit the evolution of adaptive branching reaction norms, even when such patterns are theoretically favored by population ecology.
• The evolution of seasonal polyphenism is a complex interplay between selection pressures and the inherent constraints imposed by developmental systems.
• Future research should focus on integrating detailed developmental mechanisms into evolutionary models to better predict the evolution of phenotypic plasticity.