#  Shraddha Lall Thesis Defense (Benjamin de Bivort, Advisor) 

 



    ![Shraddha Lall with long, curly dark hair, wearing blue sleevless top, in front of whitecabinet](/sites/g/files/omnuum6811/files/styles/hwp_5_4__480x385/public/2025-10/Shraddha%20Lall.jpeg?itok=M8BdF-Gi) 

 



 

####  calendar\_today Date and Time 

 **August 26, 2025** 

 03:30PM - 04:30PM EDT 

 



 

**Title:** Genetic and Evolutionary Basis of Behavioral Variability in *Drosophila melanogaster*

**Abstract:** Behavioral individuality is a ubiquitous phenomenon. Animals from genetically homogeneous populations reared in identical environments display persistent and variable behavioral phenotypes. This behavioral variability can be heritable and potentially adaptive through a bet-hedging strategy, wherein genotypes that produce a range of behavioral phenotypes enhance their long term fitness in unpredictably fluctuating environments by increasing the probability that some individuals will express traits well-suited to the current conditions. In this dissertation, I investigate the genetic and evolutionary basis of behavioral variability in *Drosophila melanogaster*, combining theoretical modeling with experimental approaches to test its evolvability and underlying mechanisms.

In Chapter 1, I develop a computational model to examine how variability responds to artificial selection. I compare family-based and individual-based selection strategies and show that family-based selection, where variability is measured across related individuals, is more effective than individual-based selection when the trait under selection is variance-based but not when it is mean-based. I further explore how population size, genetic architecture, and selection strength shape evolutionary outcomes.

In Chapter 2, I apply these insights in a 21-generation artificial selection experiment in fruit flies targeting increased variability in locomotor handedness. I observe a consistent increase in behavioral variability over selection without a shift in mean turn bias. This evolved variability is polygenic and potentially has some sex-linked basis. I also identify changes in central complex morphology and correlated tradeoffs in mating success.

In Chapter 3, we shift focus to thermal preference, an ecologically relevant behavior. Using a panel of inbred lines, we show that the mean and variability of thermal preference are both heritable, and genetically independent. Genome-wide association implicates *spag*, a co-chaperone of Hsp90, as a regulator of thermal preference variability.

In Chapter 4, we investigate the genetic basis of the offspring number–body weight tradeoff using a composite offspring index. We identify candidate genes influencing this tradeoff and demonstrate through functional experiments that specific mutations alter the balance between offspring size and number.

In the concluding chapter, I outline future directions, including experimental evolution approaches for studying bet-hedging. Together, this work shows that behavioral variability is an evolvable trait shaped by genetic and neuroanatomical factors.

**Committee:** Benjamin de Bivort (Advisor), Ian Dworkin, Naomi Pierce, John Wakeley



 

 



 

 See also:- [ OEB Thesis Seminar ](/event-type/oeb-thesis-seminar)
 
 

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