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UID:1776081600@ist.ac.at
DTSTART:20260413T140000
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DESCRIPTION:Speaker: Ksenia Khudiakova\nhosted by Mikhail Lemeshko\nAbstrac
 t: This Ph.D. thesis investigates how different forms of selection shape g
 enetic diversity in a constant environment that has led to evolutionary eq
 uilibrium. We progress from a non-epistatic case to increasingly complex m
 odels of epistasis and rely on stochastic and deterministic theory togethe
 r with simulations.We first show that in the non-epistatic case\, and in a
 n asexual population\, weak purifying selection leads to multiple-merger g
 enealogies\, and that the transition in genealogical properties coincides 
 with the onset of Muller’s ratchet.Then\, we apply a result from discret
 e Morse theory to prove that adding each next fitness peak to the landscap
 e requires at least one additional special pairwise interaction between lo
 ci\, called reciprocal sign epistasis.We then show that reciprocal sign ep
 istasis can extend the diversity-promoting effects of balancing selection 
 and delineate the parameter conditions under which this effect is expected
  to occur.Finally\, we demonstrate how epistasis that arises under stabili
 zing selection amplifies the effects of random genetic drift by causing th
 e selection coefficients of mutations to fluctuate through interactions wi
 th the changing genetic background.Together\, these results show that non-
 epistatic purifying selection reduces genetic diversity relative to neutra
 lity\, and that once Muller’s ratchet starts operating\, this reduction 
 cannot be captured by any simple rescaling of Kingman’s coalescent. On a
 n epistatic fitness landscape\, reciprocal sign epistasis is a key ingredi
 ent for generating multiple fitness peaks\, and it substantially alters wi
 thin-population dynamics at evolutionary equilibrium by extending the dive
 rsity-maintaining effects of balancing selection and driving temporal chan
 ges in selection coefficients. This Ph.D. thesis thus advances our underst
 anding of how epistasis shapes genetic diversity and evolutionary dynamics
  in populations at equilibrium.
LOCATION:Sunstone Bldg / Ground floor / Big Seminar Room B (I23.EG.102) and
  Zoom\, ISTA
ORGANIZER:
SUMMARY:Ksenia Khudiakova: Thesis Defense: How epistasis and purifying sele
 ction shape genetic diversity
URL:https://talks-calendar.ista.ac.at/events/6399
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