title: Post-copulatory opportunities for sperm competition and cryptic female choice provide no offspring fitness benefits in externally fertilizing salmon.
abstract: There is increasing evidence that females can somehow improve their offspring fitness by mating with multiple males, but we understand little about the exact stage(s) at which such benefits are gained. Here, we measure whether offspring fitness is influenced by mechanisms operating solely between sperm and egg. Using externally fertilizing and polyandrous Atlantic salmon (Salmo salar), we employed split-clutch and split-ejaculate in vitro fertilization experiments to generate offspring using designs that either denied or applied opportunities for sperm competition and cryptic female choice. Following fertilizations, we measured 140 days of offspring fitness after hatch, through growth and survival in hatchery and near-natural conditions. Despite an average composite mortality of 61%, offspring fitness at every life stage was near-identical between groups fertilized under the absence versus presence of opportunities for sperm competition and cryptic female choice. Of the 21 551 and 21 771 eggs from 24 females fertilized under monandrous versus polyandrous conditions, 68% versus 67.8% survived to the 100-day juvenile stage; sub-samples showed similar hatching success (73.1% versus 74.3%), had similar survival over 40 days in near-natural streams (57.3% versus 56.2%) and grew at similar rates throughout. We therefore found no evidence that gamete-specific interactions allow offspring fitness benefits when polyandrous fertilization conditions provide opportunities for sperm competition and cryptic female choice.
authors.affiliation: School of Biological Sciences , University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Alyson J
authors.initials: AJ
authors.lastname: Lumley
authors.affiliation: School of Biological Sciences , University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Sian E
authors.initials: SE
authors.lastname: Diamond
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, Trondheim 7491, Norway; Norwegian Institute for Nature Research, Trondheim 7485, Norway.
authors.forename: Sigurd
authors.initials: S
authors.lastname: Einum
authors.affiliation: School of Biological Sciences , University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Yeates
authors.affiliation: School of Biological Sciences , University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Danielle
authors.initials: D
authors.lastname: Peruffo
authors.affiliation: Island Ecology and Evolution Research Group (IPNA-CSIC) , C/Astrofísico Francisco Sánchez 3 , 38206 La Laguna, Tenerife, Canary Islands, Spain.
authors.forename: Brent C
authors.initials: BC
authors.lastname: Emerson
authors.affiliation: School of Biological Sciences , University of East Anglia , Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Matthew J G
authors.initials: MJ
authors.lastname: Gage
keywords: Atlantic salmon; cryptic female choice; fertilization; gamete; polyandry; sperm competition