Natasha Kelly, Visiting Scholar


I am interested in studying the variation in expression of condition-dependent secondary sexual traits present in both males and females. The condition-dependent costs and benefits associated with such traits may change over the course of an individual’s reproductive life span, affecting the level of choosiness that females should display and the reliability of these traits as indicators of genetic quality in males. My work is divided between empirical research and theoretical modeling.

Condition-dependent expression of sexually selected behaviours: If the expression of sexually-selected traits in both males and females is condition dependent, then we may expect the expression of a trait to vary as the fitness costs and benefits associated with its expression change. The cost of expressing a trait is dependent on the resources available to an individual and its genetic quality (the ability to use those resources efficiently). The resources available for an individual’s use (and the fitness costs and benefits of utilizing them) will be influenced by life history trade-offs. The costs and benefits associated with trait expression may change over an individual’s reproductive lifespan, resulting in individuals that differ in genetic quality producing the same level of trait expression at different points in their reproductive lifespan.

Theory and models: I explore theoretically how life history trade-offs will affect the expression of condition dependent traits. I aim to mathematically model how life history trade-offs affect both male sexually selected behaviour and female choosiness, and how the expression of a sexually selected trait in one sex affects the expression of a sexually selected trait in the other sex.

Empirical research: In conjunction with my theoretical work, I use the threespine stickleback system to investigate how the expression of condition dependent traits varies within and between sexes, and how variation in the condition dependent costs and benefits of a sexually selected trait in one sex affects the condition dependent expression of a trait in the other sex. For example, how does male courtship vary between low and high condition males, and how does this affect females’ choosiness?


  • Ph.D. candidate, Ecology & Evolutionary Biology. Yale University, 2005
  • M.Sc. Ecology & Evolutionary Biology. Yale University, 2007
  • B.A. (mod) 1st class, Zoology. The University of Dublin, Trinity College, 2004


Slotman, M.A., N.B. Kelly, L.C.Harrington, S. Kittahwee, J.W. Jones, T.W. Scott, A.Caccone, & J.R. Powell. 2007. Polymorphic microsatellite markers for studies of Aedes aegypti (Diptera: Culicidae), the vector of dengue and yellow fever. Molecular Ecology Notes 7(1), 168-171

Kelly, N.B. & Alonzo, S.H. 2009. Will male advertisement be a reliable indicator of paternal care, if offspring survival depends on male care? Proceedings of the Royal Society of London Series B – Biological Sciences 276, 3175-3183

Kelly, N.B. & Alonzo, S.H. 2010. Does a trade-off between current reproductive success and survival affect the honesty of male signalling in species with male parental care? Journal of Evolutionary Biology 23(11), 2461-2473

Visit Natasha’s personal website