title: Major histocompatibility complex selection dynamics in pathogen-infected túngara frog (Physalaemus pustulosus) populations.
abstract: Pathogen-driven selection can favour major histocompatibility complex (MHC) alleles that confer immunological resistance to specific diseases. However, strong directional selection should deplete genetic variation necessary for robust immune function in the absence of balancing selection or challenges presented by other pathogens. We examined selection dynamics at one MHC class II (MHC-II) locus across Panamanian populations of the túngara frog, Physalaemus pustulosus, infected by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). We compared MHC-II diversity in highland túngara frog populations, where amphibian communities have experienced declines owing to Bd, with those in the lowland region that have shown no evidence of decline. Highland region frogs had MHC variants that confer resistance to Bd. Variant fixation appeared to occur by directional selection rather than inbreeding, as overall genetic variation persisted in populations. In Bd-infected lowland sites, however, selective advantage may accrue to individuals with only one Bd-resistance allele, which were more frequent. Environmental conditions in lowlands should be less favourable for Bd infection, which may reduce selection for specific Bd resistance in hosts. Our results suggest that MHC selection dynamics fluctuate in túngara frog populations as a function of the favourability of habitat to pathogen spread and the vulnerability of hosts to infection.
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul 08826, South Korea.
authors.forename: Tiffany A
authors.initials: TA
authors.lastname: Kosch
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul 08826, South Korea.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Bataille
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul 08826, South Korea.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Didinger
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul 08826, South Korea.
authors.forename: John A
authors.initials: JA
authors.lastname: Eimes
authors.affiliation: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA.
authors.forename: Sofia
authors.initials: S
authors.lastname: Rodríguez-Brenes
authors.affiliation: Department of Integrative Biology, University of Texas, Austin, TX 78712, USA Smithsonian Tropical Research Institute, Balboa, Ancón, Panama.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ryan
authors.affiliation: Laboratory of Behavioral and Population Ecology, School of Biological Sciences, Seoul National University, Seoul 08826, South Korea waldman@snu.ac.kr.
authors.forename: Bruce
authors.identifier: 0000-0003-0006-5333
authors.initials: B
authors.lastname: Waldman
mesh_terms: D000818:Animals; D001001:Anura; D008411:Chytridiomycota; D008285:Major Histocompatibility Complex; D009181:Mycoses
keywords: amphibian population declines; chytridiomycosis; directional selection; host–pathogen interactions; major histocompatibility complex; resistance alleles