Bergmann's rule is maintained during a rapid range expansion in a damselfly

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Climate change causes species to shift their geographic ranges.
• Range shifts involve the movement of genotypes, influencing population divergence and adaptation.
• Phenotypic plasticity plays a key role in genotype-environment interactions during range expansions.

Purpose of the Study:

• To investigate phenotypic and genetic patterns during a natural range expansion.
• To quantify the relationship between latitude, body size, and genetic variation in damselflies.
• To understand the role of phenotypic plasticity in adaptation during range shifts.

Main Methods:

• Sampling of damselfly populations (Erythromma viridulum) across a latitudinal gradient in Northern Europe.
• Analysis of phenotypic variation using seven morphological traits to assess body size-latitude relationships.
• Genetic analysis using microsatellite loci to evaluate spatial genetic structure and gene flow.

Main Results:

• A weak spatial genetic structure indicating high gene flow during rapid range expansion.
• A strong positive correlation between latitude and body size (Bergmann's rule) despite homogenizing gene flow.
• Latitudinal body size variation was not explained by differences in larval development time (voltinism).

Conclusions:

• High gene flow during rapid range expansion does not prevent significant phenotypic divergence.
• Phenotypic plasticity in body size allows damselflies to respond to environmental factors correlated with latitude.
• Geographic patterns in damselfly body size are likely driven by phenotypic plasticity, facilitating adaptation during range expansions.