Bigger Is Fitter? Quantitative Genetic Decomposition of Selection Reveals an Adaptive Evolutionary Decline of Body Mass in a Wild Rodent Population.

Article, Preprint English OPEN
Timothée Bonnet ; Peter Wandeler ; Glauco Camenisch ; Erik Postma (2017)
  • Publisher: Public Library of Science (PLoS)
  • Journal: PLoS Biology, volume 15, issue 1 (issn: 1544-9173, eissn: 1545-7885)
  • Related identifiers: doi: 10.1371/journal.pbio.1002592, doi: 10.1101/038604, pmc: PMC5268405
  • Subject: Probability Theory | Research Article | Natural Selection | Mathematics | Adults | Evolutionary Processes | Covariance | Rodents | Evolutionary Genetics | Population Groupings | Evolutionary Biology | Genetics | Physical Sciences | People and Places | Animals | Population Genetics | Biology and Life Sciences | Random Variables | Age Groups | Vertebrates | QH301-705.5 | bepress|Life Sciences|Biology | Amniotes | Phenotypes | Voles | Population Biology | Mammals | Organisms | Genetic Polymorphism | Biology (General)

In natural populations, quantitative trait dynamics often do not appear to follow evolutionary predictions: Despite abundant examples of natural selection acting on heritable traits, conclusive evidence for contemporary adaptive evolution remains rare for wild vertebrate populations, and phenotypic stasis seems to be the norm. This so-called ‘stasis paradox’ highlights our inability to predict evolutionary change, which is especially concerning within the context of rapid anthropogenic environmental change. While the causes underlying the stasis paradox are hotly debated, comprehensive attempts aiming at a resolution are lacking. Here we apply a quantitative genetic framework to individual-based long-term data for a wild rodent population and show that despite a positive association between body mass and fitness, there has been a genetic change towards lower body mass. The latter represents an adaptive response to viability selection favouring juveniles growing up to become relatively small adults, i.e. with a low potential adult mass, which presumably complete their development earlier. This selection is particularly strong towards the end of the snow-free season, and it has intensified in recent years, coinciding which a change in snowfall patterns. Importantly, neither the negative evolutionary change, nor the selective pressures that drive it, are apparent on the phenotypic level, where they are masked by phenotypic plasticity and a non-causal (i.e. non-genetic) positive association between body mass and fitness, respectively. Estimating selection at the genetic level thereby enabled us to uncover adaptive evolution in action, and to identify the corresponding phenotypic selective pressure. We thereby demonstrate that natural populations can show a rapid and adaptive evolutionary response to a novel selective pressure, and that explicitly (quantitative) genetic models are able to provide us with an understanding of the causes and consequences of selection that is superior to purely phenotypic estimates of selection and evolutionary change.
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