Fluctuating optimum and temporally variable selection on breeding date in birds and mammals

Temporal variation in natural selection is predicted to strongly impact the evolution and demography of natural populations, with consequences for the rate of adaptation, evolution of plasticity, and extinction risk. Most of the theory underlying these predictions assumes a moving optimum phenotype, with predictions expressed in terms of the temporal variance and autocorrelation of this optimum. However, empirical studies seldom estimate patterns of fluctuations of an optimum phenotype, precluding further progress in connecting theory with observations. To bridge this gap, we assess the evidence for temporal variation in selection on breeding date by modeling a fitness function with a fluctuating optimum, across 39 populations of 21 wild animals, one of the largest compilations of long-term datasets with individual measurements of trait and fitness components. We find compelling evidence for fluctuations in the fitness function, causing temporal variation in the magnitude, but not the direction of selection. However, fluctuations of the optimum phenotype need not directly translate into variation in selection gradients, because their impact can be buffered by partial tracking of the optimum by the mean phenotype. Analyzing individuals that reproduce in consecutive years, we find that plastic changes track movements of the optimum phenotype across years, especially in bird species, reducing temporal variation in directional selection. This suggests that phenological plasticity has evolved to cope with fluctuations in the optimum, despite their currently modest contribution to variation in selection.L-M.C. and P.d.V. acknowledge support from the European Research Coun-cil (ERC) (Grant 678140-FluctEvol). The Montpellier tit group acknowledgesthe long-term support of the Observatoire des Sciences de l’Univers – Obser-vatoire de REcherche Montpelli ́erain de l’Environnement (OSU-OREME). Thebighorn, mountain goat, and eastern gray kangaroo studies were supportedby Natural Sciences and Engineering Research Council (NSERC) of Canada.Recent data collection for Wytham has been provided by grants fromBiotechnology and Biological Sciences Research Council (BB/L006081/1), ERC(AdG250164), and the UK Natural Environment Research Council (NERC)(NE/K006274/1, NE/S010335/1). The Columbian ground squirrel study wassupported by the National Science Foundation (Grant DEB-0089473). Traitand fitness data for hihi were collected/managed by John Ewen underNew Zealand Department of Conservation hihi management contracts andresearch permits AK/15073/RES, AK-24128-FAU, 36186-FAU, and 44300-FAUand with additional financial support via NERC UK, The Leverhulme TrustUK, Marsden Fund New Zealand, and the Hihi Conservation CharitableTrust. The data on reindeer were made available through the Reindeerhusbandry in a Globalizing North Nordic Center of Excellence, and thecrew at Kutuharju Experimental Reindeer Research Station in the ReindeerHerder’s Association are thanked for their valuable assistance and logisticsupport in data collection. The red deer, Silwood blue tit, and Soay sheepdatasets were supported by UK NERC. Lundy sparrow data were supportedby NERC, a Marie Skłodowska-Curie Action, and Volkswagenstiftung. Thered squirrel project was funded by NSERC of Canada and the NationalScience Foundation. J.C.S. was supported by a grant from the Ministry ofEconomy and Competitivity, Spanish Research Council (CGL-2016-79568-C3-3-P). J.T., T.K., and M.G. were supported by the Research Council of Norwaythrough its Centers for Excellence funding scheme, Project 223257. Researchon fairy wrens has been supported by the Australian Research Council

Temperature synchronizes temporal variation in laying dates across European hole-nesting passerines

Abstract Identifying the environmental drivers of variation in fitness-related traits is a central objective in ecology and evolutionary biology. Temporal fluctuations of these environmental drivers are often synchronized at large spatial scales. Yet, whether synchronous environmental conditions can generate spatial synchrony in fitness-related trait values (i.e., correlated temporal trait fluctuations across populations) is poorly understood. Using data from long-term monitored populations of blue tits (Cyanistes caeruleus, n = 31), great tits (Parus major, n = 35), and pied flycatchers (Ficedula hypoleuca, n = 20) across Europe, we assessed the influence of two local climatic variables (mean temperature and mean precipitation in February-May) on spatial synchrony in three fitness-related traits: laying date, clutch size, and fledgling number. We found a high degree of spatial synchrony in laying date but a lower degree in clutch size and fledgling number for each species. Temperature strongly influenced spatial synchrony in laying date for resident blue tits and great tits but not for migratory pied flycatchers. This is a relevant finding in the context of environmental impacts on populations because spatial synchrony in fitness-related trait values among populations may influence fluctuations in vital rates or population abundances. If environmentally induced spatial synchrony in fitness-related traits increases the spatial synchrony in vital rates or population abundances, this will ultimately increase the risk of extinction for populations and species. Assessing how environmental conditions influence spatiotemporal variation in trait values improves our mechanistic understanding of environmental impacts on populations