title: Sexual selection protects against extinction.
abstract: Reproduction through sex carries substantial costs, mainly because only half of sexual adults produce offspring. It has been theorized that these costs could be countered if sex allows sexual selection to clear the universal fitness constraint of mutation load. Under sexual selection, competition between (usually) males and mate choice by (usually) females create important intraspecific filters for reproductive success, so that only a subset of males gains paternity. If reproductive success under sexual selection is dependent on individual condition, which is contingent to mutation load, then sexually selected filtering through 'genic capture' could offset the costs of sex because it provides genetic benefits to populations. Here we test this theory experimentally by comparing whether populations with histories of strong versus weak sexual selection purge mutation load and resist extinction differently. After evolving replicate populations of the flour beetle Tribolium castaneum for 6 to 7 years under conditions that differed solely in the strengths of sexual selection, we revealed mutation load using inbreeding. Lineages from populations that had previously experienced strong sexual selection were resilient to extinction and maintained fitness under inbreeding, with some families continuing to survive after 20 generations of sib × sib mating. By contrast, lineages derived from populations that experienced weak or non-existent sexual selection showed rapid fitness declines under inbreeding, and all were extinct after generation 10. Multiple mutations across the genome with individually small effects can be difficult to clear, yet sum to a significant fitness load; our findings reveal that sexual selection reduces this load, improving population viability in the face of genetic stress.
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: Department of Entomology, Institute of Zoology, Jagiellonian University, Gronostajowa 9, 30-387 Kraków, Poland.
authors.forename: Łukasz
authors.initials: Ł
authors.lastname: Michalczyk
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: James J N
authors.initials: JJ
authors.lastname: Kitson
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Lewis G
authors.initials: LG
authors.lastname: Spurgin
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Catriona A
authors.initials: CA
authors.lastname: Morrison
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Godwin
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Dickinson
authors.affiliation: ETH Zurich, Institute of Integrative Biology, D-USYS, Universitatsstrasse 16, CHN J 11, 8092 Zürich, Switzerland.
authors.forename: Oliver Y
authors.initials: OY
authors.lastname: Martin
authors.affiliation: Island Ecology and Evolution Research Group, Instituto de Productos Naturales y Agrobiología (IPNA-CSIC), C/Astrofísico Francisco Sánchez 3, 38206 San Cristóbal de La Laguna, Santa Cruz de 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: Tracey
authors.initials: T
authors.lastname: Chapman
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
mesh_terms: D000818:Animals; D005075:Biological Evolution; D053476:Extinction, Biological; D005260:Female; D056084:Genetic Fitness / Q000235:genetics / Q000502:physiology*; D007178:Inbreeding; D008297:Male; D052586:Mating Preference, Animal / Q000502:physiology*; D009154:Mutation; D012098:Reproduction / Q000235:genetics; D012641:Selection, Genetic / Q000235:genetics / Q000502:physiology; D014231:Tribolium / Q000235:genetics / Q000502:physiology*