Immune genes are hotspots of shared positive selection across birds and mammals

  1. Allison J Shultz  Is a corresponding author
  2. Timothy Sackton  Is a corresponding author
  1. Harvard University, United States


Consistent patterns of positive selection in functionally similar genes can suggest a common selective pressure across a group of species. We use alignments of orthologous protein-coding genes from 39 species of birds to estimate parameters related to positive selection for 11,000 genes conserved across birds. We show that functional pathways related to the immune system, recombination, lipid metabolism, and phototransduction are enriched for positively selected genes. By comparing our results with mammalian data, we find a significant enrichment for positively selected genes shared between taxa, and that these shared selected genes are enriched for viral immune pathways. Using pathogen-challenge transcriptome data, we show that genes up-regulated in response to pathogens are also enriched for positively selected genes. Together, our results suggest that pathogens, particularly viruses, consistently target the same genes across divergent clades, and that these genes are hotspots of host-pathogen conflict over deep evolutionary time.

Data availability

All data generated and analyzed during this study, including all source data for all figures are included in the manuscript, supporting files, Dryad repository (doi:10.5061/dryad.kt24554). All alignments used to perform analyses of PAML and HyPhy results are also available in the Dryad repository. Computing scripts for all analyses are available here:

The following data sets were generated
The following previously published data sets were used

Article and author information

Author details

  1. Allison J Shultz

    FAS Informatics, Harvard University, Cambridge, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-2089-4086
  2. Timothy Sackton

    FAS Informatics, Harvard University, Cambridge, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-1673-9216


The authors declare that there was no external funding received for this work.

Reviewing Editor

  1. Christian R Landry, Université Laval, Canada

Publication history

  1. Received: September 6, 2018
  2. Accepted: January 8, 2019
  3. Accepted Manuscript published: January 8, 2019 (version 1)
  4. Version of Record published: January 18, 2019 (version 2)


© 2019, Shultz & Sackton

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


  • 6,613
    Page views
  • 864
  • 62

Article citation count generated by polling the highest count across the following sources: Scopus, Crossref, PubMed Central.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Allison J Shultz
  2. Timothy Sackton
Immune genes are hotspots of shared positive selection across birds and mammals
eLife 8:e41815.

Further reading

    1. Ecology
    2. Evolutionary Biology
    Dakota E McCoy, Benjamin Goulet-Scott ... John Kartesz
    Tools and Resources

    Sustainable cities depend on urban forests. City trees-pillars of urban forests - improve our health, clean the air, store CO2, and cool local temperatures. Comparatively less is known about city tree communities as ecosystems, particularly regarding spatial composition, species diversity, tree health, and the abundance of introduced species. Here, we assembled and standardized a new dataset of N=5,660,237 trees from 63 of the largest US cities with detailed information on location, health, species, and whether a species is introduced or naturally occurring (i.e., 'native'). We further designed new tools to analyze spatial clustering and the abundance of introduced species. We show that trees significantly cluster by species in 98% of cities, potentially increasing pest vulnerability (even in species-diverse cities). Further, introduced species significantly homogenize tree communities across cities, while naturally occurring trees (i.e., 'native' trees) comprise 0.51%-87.3% (median=45.6%) of city tree populations. Introduced species are more common in drier cities, and climate also shapes tree species diversity across urban forests. Parks have greater tree species diversity than urban settings. Compared to past work which focused on canopy cover and species richness, we show the importance of analyzing spatial composition and introduced species in urban ecosystems (and we develop new tools and datasets to do so). Future work could analyze city trees and socio-demographic variables or bird, insect, and plant diversity (e.g., from citizen-science initiatives). With these tools, we may evaluate existing city trees in new, nuanced ways and design future plantings to maximize resistance to pests and climate change. We depend on city trees.

    1. Evolutionary Biology
    2. Genetics and Genomics
    Laura Katharine Hayward, Guy Sella
    Research Article

    Polygenic adaptation is thought to be ubiquitous, yet remains poorly understood. Here, we model this process analytically, in the plausible setting of a highly polygenic, quantitative trait that experiences a sudden shift in the fitness optimum. We show how the mean phenotype changes over time, depending on the effect sizes of loci that contribute to variance in the trait, and characterize the allele dynamics at these loci. Notably, we describe the two phases of the allele dynamics: The first is a rapid phase, in which directional selection introduces small frequency differences between alleles whose effects are aligned with or opposed to the shift, ultimately leading to small differences in their probability of fixation during a second, longer phase, governed by stabilizing selection. As we discuss, key results should hold in more general settings, and have important implications for efforts to identify the genetic basis of adaptation in humans and other species.