Genetic and developmental basis of evolutionary pelvic reduction in threespine sticklebacks

Area of Science:

• Evolutionary biology
• Developmental genetics
• Evo-Devo

Background:

• Hindlimb loss has evolved multiple times across diverse animal lineages.
• The genetic underpinnings of pelvic reduction remain largely unknown in natural populations.

Purpose of the Study:

• To identify the genetic factors and molecular mechanisms responsible for pelvic girdle reduction in threespine sticklebacks.
• To investigate the role of the Pitx1 gene in this evolutionary process.

Main Methods:

• Conducted genetic crosses between threespine stickleback fish with complete and absent pelvic structures.
• Performed genome-wide linkage mapping to identify chromosomal regions associated with pelvic reduction.
• Analyzed Pitx1 gene expression patterns and protein sequences in pelvic-reduced individuals.

Main Results:

• Pelvic reduction is primarily controlled by a major chromosomal region containing the Pitx1 gene, with additional minor regions.
• Pelvic-reduced sticklebacks exhibit left-right asymmetry, similar to Pitx1 knockout mice.
• Genetic changes involve site-specific regulatory alterations in Pitx1 expression, not mutations in the protein-coding sequence.

Conclusions:

• Regulatory mutations in key developmental genes like Pitx1 can facilitate rapid skeletal evolution in natural populations.
• These regulatory changes allow for significant phenotypic changes (pelvic reduction) while preserving essential gene functions in other tissues.