Sex chromosomes and sex determination

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Sex chromosomes are a genomic hotspot for evolutionary change in many groups of animals and plants.  Why do some species have XY, some ZW, and others polygenic sex determination?  Our models show that sex antagonistic selection, often driven by sexual selection, can play a key role.  We are testing that and other hypotheses in a long-term collaboration with Dr. Katie Peichel (University of Bern).  Together we are analyzing genomic data from several species of stickleback fishes to understand the forces driving the very rapid evolution of their sex chromosomes.

Featured papers:

Cheng & Kirkpatrick (2016)  Sex-specific selection and sex-biased gene expression in humans and flies.  PLOS Genetics 12: e1006170.

Pipoly, Bókony, Kirkpatrick, Donald, Székely, & Liker  (2015)   The genetic sex-determination system predicts adult sex ratios in tetrapods.  Nature 527: 91.

Kirkpatrick & Guerrero (2014) Signatures of sex-antagonistic selection on recombining sex chromosomes.  Genetics 197: 531.

Genome evolution

Why are chromosomes so evolutionarily dynamic?  In many taxa, chromosome rearrangements (such as inversions) are highly polymorphic within species and differ dramatically between species.  Our models show that local adaptation resulting from ecological forces can be a powerful driver of genome architecture.  We are quantifying the evolutionary forces acting on chromosome rearrangements using genetic and genomic data.

Featured papers:

Dagilis & Kirkpatrick (2016)  Prezygotic isolation, mating preferences, and the evolution of chromosomal inversions.  Evolution 70: 1465.

Ayala, Guerrero, & Kirkpatrick (2013) Reproductive isolation and local adaptation quantified for a chromosome inversion in a malaria mosquito.  Evolution 67: 946.

Species ranges

Why don’t species adapt to marginal habitats and expand their ranges outwards?  We work with models to explore mechanisms that put evolutionary limits on ranges.  These include gene flow, biotic interactions, and genetic constraints.

Featured papers:

Peischl, Kirkpatrick, Excoffier (2015) Expansion load and the evolutionary dynamics of a species range.  American Naturalist 185: E81.

Kirkpatrick & Barrett (2015) Chromosome inversions, adaptive cassettes, and the evolution of species’ ranges.  Molecular Ecology 24: 2046.

Sexual selection and speciation

We use models to learn how sexual selection can drive speciation, and we develop new statistical methods to quantify the evolutionary forces at work.  We are also interested in the rules that animals use to choose their mates.

Featured papers:

Hopkins, Guerrero, & Kirkpatrick (2014) Strong reinforcing selection in a Texas wildflower.  Current Biology 24: 1995.

Quantitative genetics

Traits like growth trajectories and reaction norms are “function-valued”: they are described by a continuous curve rather than a single measurement.  We work with models to predict how these traits evolve, and develop statistical methods to estimate patterns of genetic variation for them.  Another area of interest is to determine how patterns of genetic variation for multiple traits constrain evolution.  Here we ultimately aim to estimate the evolutionary dimensionality of organisms and learn what limits rates of adaptation.

Featured papers:

Stinchcombe, the Function-Valued Traits Working Group, and Kirkpatrick (2012) Genetics and evolution of function-valued traits:  understanding environmentally responsive phenotypes.  Trends in Ecology and Evolution 27: 637.