title: Ecological genomics of tropical trees: how local population size and allelic diversity of resistance genes relate to immune responses, cosusceptibility to pathogens, and negative density dependence.
abstract: In tropical forests, rarer species show increased sensitivity to species-specific soil pathogens and more negative effects of conspecific density on seedling survival (NDD). These patterns suggest a connection between ecology and immunity, perhaps because small population size disproportionately reduces genetic diversity of hyperdiverse loci such as immunity genes. In an experiment examining seedling roots from six species in one tropical tree community, we found that smaller populations have reduced amino acid diversity in pathogen resistance (R) genes but not the transcriptome in general. Normalized R gene amino acid diversity varied with local abundance and prior measures of differences in sensitivity to conspecific soil and NDD. After exposure to live soil, species with lower R gene diversity had reduced defence gene induction, more cosusceptibility of maternal cohorts to colonization by potentially pathogenic fungi, reduced root growth arrest (an R gene-mediated response) and their root-associated fungi showed lower induction of self-defence (antioxidants). Local abundance was not related to the ability to induce immune responses when pathogen recognition was bypassed by application of salicylic acid, a phytohormone that activates defence responses downstream of R gene signalling. These initial results support the hypothesis that smaller local tree populations have reduced R gene diversity and recognition-dependent immune responses, along with greater cosusceptibility to species-specific pathogens that may facilitate disease transmission and NDD. Locally rare species may be less able to increase their equilibrium abundance without genetic boosts to defence via immigration of novel R gene alleles from a larger and more diverse regional population.
authors.affiliation: Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.|Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: J H
authors.identifier: http://orcid.org/0000-0003-3796-2521
authors.initials: JH
authors.lastname: Marden
authors.affiliation: Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.|Smithsonian Tropical Research Institute, República de Panamá, 0843-03092, Panama, Panama.
authors.forename: S A
authors.initials: SA
authors.lastname: Mangan
authors.affiliation: Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.|Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Peterson
authors.affiliation: Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: E
authors.initials: E
authors.lastname: Wafula
authors.affiliation: Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: H W
authors.initials: HW
authors.lastname: Fescemyer
authors.affiliation: Department of Biological Science, California State University, Fullerton, CA, 92834, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Der
authors.affiliation: Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.|Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: C W
authors.initials: CW
authors.lastname: dePamphilis
authors.affiliation: Smithsonian Tropical Research Institute, República de Panamá, 0843-03092, Panama, Panama.|School of Forestry and Environmental Studies, Yale University, New Haven, CT, 06511, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Comita
mesh_terms: D000483:Alleles; D060467:Disease Resistance / Q000235:genetics*; D004463:Ecology; D065928:Forests; D017343:Genes, Plant; D014644:Genetic Variation; D057865:Plant Immunity / Q000235:genetics*; D011156:Population Density; D036226:Seedlings; D014197:Trees / Q000235:genetics* / Q000382:microbiology; D014329:Tropical Climate
keywords: demographic effects; eco-evolutionary feedback; ecological dynamics; forest research plot; fungi; genetic drift; immunity; long-term ecological study; plant-pathogen interaction; polymorphism; root microbiome