Environmental heterogeneity generates fluctuating selection on a secondary sexual trait.
In any population in which resources are limiting, the allocation of resources toward increased reproductive success may generate costs to survival [1-8]. The relationship between a sexually selected trait and fitness will therefore represent a balance between its relative associations with fecundity versus viability [3, 6, 7]. Because the risk of mortality in a population is likely to be heavily determined by ecological conditions, survival costs may vary as a function of the prevailing environment [7]. As a result, for populations experiencing heterogeneous ecological conditions, there may not be a single optimal level of allocation toward reproduction versus survival [9]. Here, we show that early viability and fecundity selection act in opposing directions on a secondary sexual trait and that their relative magnitude depends upon ecological conditions, generating fluctuating selection. In a wild population of Soay sheep (Ovis aries), phenotypic and genetic associations between male horn growth and lifetime reproductive success were positive under good environmental conditions (because of increased breeding success) and negative under poor environmental conditions (because of reduced survival). In an unpredictable environment, high allocation to early horn growth is a gamble that will only pay off if ensuing conditions are favorable. Such fluctuating selection may play an important role in preventing the erosion of genetic variance in secondary sexual traits.
Robinson
Matthew R
MR
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom; Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, United Kingdom. Electronic address: matthew.r.robinson@ed.ac.uk.
Pilkington
Jill G
JG
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom.
Clutton-Brock
Tim H
TH
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom.
Pemberton
Josephine M
JM
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom.
Kruuk
Loeske E B
LEB
Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom.
D000818:Animals; D017753:Ecosystem; D005260:Female; D005298:Fertility / Q000502:physiology; D006733:Horns / Q000254:growth & development*; D008136:Longevity / Q000502:physiology; D008297:Male; D012606:Scotland; D012641:Selection, Genetic; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology; D012756:Sheep / Q000235:genetics / Q000254:growth & development*