MULTIVARIATE PHENOTYPIC DIFFERENTIATION AMONG BOTTLENECK LINES OF THE HOUSEFLY

Area of Science:

• Evolutionary Biology
• Population Genetics
• Quantitative Genetics

Background:

• Genetic bottlenecks can significantly impact the evolutionary trajectory of populations.
• Understanding how population size during bottlenecks affects phenotypic differentiation is crucial for evolutionary studies.

Purpose of the Study:

• To investigate multivariate phenotypic differentiation in housefly lines subjected to genetic bottlenecks of varying sizes.
• To assess the contributions of size and shape to total phenotypic distance following bottlenecks.

Main Methods:

• Examined eight morphometric traits in bottlenecked housefly lines founded by 1, 4, or 16 pairs.
• Utilized Mahalanobis' distance metric, scaled by additive genetic variance-covariance, to quantify genetic distance.
• Partitioned the genetic distance into contributions from size and shape components.

Main Results:

• All bottleneck lines showed significant divergence from the ancestral population.
• The direction of divergence varied with bottleneck size: single-pair lines diverged mainly in shape, 16-pair lines in size, and four-pair lines showed intermediate differentiation.
• Bottlenecks altered genetic relationships among traits, influencing evolutionary pathways.

Conclusions:

• Genetic bottlenecks reshape trait covariances, potentially facilitating evolutionary divergence.
• The initial population size during a bottleneck influences the mode of phenotypic differentiation (size vs. shape).
• These findings suggest bottlenecks can promote speciation by enabling access to novel evolutionary trajectories.