The association between breeding system and transposable element dynamics in Daphnia pulex

Area of Science:

• Evolutionary Biology
• Genetics
• Molecular Biology

Background:

• Transposable elements (TEs) are key drivers of genetic variation.
• Mating systems significantly influence TE dynamics.
• Sexual reproduction is hypothesized to limit TE proliferation compared to asexual reproduction.

Purpose of the Study:

• To investigate the impact of losing sexual reproduction on TE load in Daphnia pulex.
• To compare TE insertion numbers between obligate and cyclical parthenogens.
• To understand the recent activity and insertion patterns of the Pokey transposon.

Main Methods:

• Utilized the TE-Display PCR-based technique.
• Quantified Pokey transposon insertions in 22 obligate and 22 cyclical Daphnia pulex isolates.
• Analyzed insertion patterns across 46 isolates from eight cyclic populations.

Main Results:

• Pokey insertion copy number was significantly higher in cyclical parthenogens than in obligate parthenogens.
• TE distribution was similar within each breeding system, suggesting recent origin of obligate lineages.
• Most Pokey insertions were unique to individual isolates, indicating recent transpositional activity.
• Pokey inserts into both coding and noncoding genomic regions.

Conclusions:

• The loss of sexual reproduction in Daphnia correlates with an increased TE load.
• The Pokey transposon is actively inserting into the Daphnia genome.
• Obligate parthenogenesis likely evolved from cyclical parthenogenesis, leading to altered TE dynamics.