Theses and Dissertations

Advisor

Dapper, Amy

Committee Member

Gordon, Donna

Committee Member

Gout, Jean-Francois

Committee Member

Welch, Mark

Date of Degree

5-15-2026

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

Variation in reproductive traits and genome evolution reflects the interaction between selection, environment, and life-history. In the genus Caenorhabditis, recombination rate and sperm size exhibit a striking variation between strains and species. Here, Iintegrate three projects investigating recombination rate variation and recombination plasticity in C. elegans and sperm size divergence across Caenorhabditis species. First, I quantify recombination rates in two genetically distinct strains, N2 and CB4856, with different levels of laboratory adaptation using fluorescent markers spanning across gene-rich and gene-poor regions of the chromosome IV. I identify significant differences in recombination rate between the two strains within both gene-rich and gene-poor regions of the chromosome. My approach leverages strain-specific recombination rate estimates rather than inter-strain crosses, allowing us to directly identify patterns of variation in intra chromosomal recombination rates. Second, I examine the recombination rate plasticity in the same C. elegans strains under different stressors, revealing that recombination rates increase in the gene-rich regions and decrease in the gene-poor regions under stress. Although the direction of recombinationplasticity is similar, the magnitude of recombinationplasticity is specific to thestrain andstressor. Myresultsfurtherhighlighttheimportanceofhowexperimentsaredesigned,asstrain specific measurements of recombination rates are critical for accurately detecting plastic responses of intra-chromosomal recombination rates. Third, I investigate the dramatic variation in sperm sizes across Caenorhabditis species and test if the molecular evolutionary rates of sperm-associated genes differ amongthespermcategoriesusingcomparativephylogenetic methods. WhileIidentify several genes rapidly evolving in the medium- and large-sperm categories, my study fails to identify significant proportions of genes evolving rapidly in each sperm category. In conclusion, leveraging C.elegansasamodelforrecombinationrateevolutionopensnewavenuesfordissectingthegenetics and underlying mechanisms for variation in intra-chromosomal recombination and recombination plasticity. Additionally, comparative analyses across Caenorhabditis nematodes provide us with an excellent foundation for studying hypotheses about the evolutionary drivers shaping sperm size diversification.

Sponsorship (Optional)

NSF CAREER 2143063 by ALD

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