Abstract
As an extension of the classic life history theory, the recently highlighted pace-of-life syndrome hypothesis predicts the coevolution of behavioural, physiological and life-history traits. For instance, bolder and shyer individuals do not only differ in personality profiles, but also in neuro-endocrinology and breeding patterns. While theory predicts that bolder (i.e. proactive), more aggressive individuals should colonize more rapidly urbanized habitats than shyer (i.e. reactive), less aggressive individuals, it is also predicted that across generations, adaptive selection processes could favour shyer individuals that are more sensitive to novel environmental cues. Here we compared two personality traits (handling aggression, exploration score in a novel environment), one physiological trait related to stress response (breath rate) and four breeding traits (lay date, clutch size, hatching success and fledging success) in a rural and an urban study population of Mediterranean great tits Parus major. Mixed models revealed strong phenotypic divergence between forest and city in most traits explored, in particular in personality, whereby urban great tits were more reactive to stress and faster explorers compared to rural birds (yet not more aggressive). Urban birds also laid smaller broods earlier in spring compared to their rural conspecifics, and city broods resulted in lower hatching success yet interestingly fledging success was similar. Nest-box centered measures of anthropogenic (artificial light, pedestrians and cars) perturbation and resource abundance allowed us to go beyond the classical forest/city comparison by exploring the phenotypic variation across an urbanization gradient. This revealed that high urbanisation in nest-box surroundings was associated overall with earlier breeding and smaller clutches, but also with faster breath rate, although these trends showed strong annual variation. Ongoing rapid urbanization and non-random gene flow between rural and urban great tits could both contribute to the high prevalence of bold breeders in the city. Our study suggests the existence of urban and rural great tit ecotypes with different pace-of-life, but also a finer-scale divergence along the degree of urbanisation within the city. Future studies are required to determine whether this phenotypic variation at different spatiotemporal scales is adaptive and whether it has a genetic basis or results from phenotypic plasticity.
Highlights
Understanding the mechanisms by which organisms adapt to spatiotemporal environmental heterogeneity remains a fundamental goal in evolutionary ecology
Using longitudinal data across 6 years from a great tit Parus major population monitoring in the city of Montpellier (France) and in a nearby rural oak forest (La Rouvière), we address in this study the following main questions: (i) Do great tits show divergent urban versus forest ecotypes for personality, physiological, and breeding traits?
Based on 6 years of great tit monitoring in an oak forest and the nearby city of Montpellier in southern France, our study reveals strong phenotypic divergence for a suite of breeding, behavioral and physiological traits, both when comparing forest and city birds, and for some of the traits, within the urban gradient
Summary
Understanding the mechanisms by which organisms adapt to spatiotemporal environmental heterogeneity remains a fundamental goal in evolutionary ecology. As an extension of the classic life history theory (Roff, 1992, 2002; Stearns, 1992), the recently highlighted pace-of-life syndrome (POLS) hypothesis (Ricklefs and Wikelski, 2002; Martin et al, 2006; Réale et al, 2010), predicts the coevolution of life histories with a suite of ecologically relevant co-varying traits in metabolism, immunology, and behavior. The POLS hypothesis provides testable predictions concerning the association between the slow-fast life history continuum and behavioral, physiological, and immunological traits. The POLS concept has attracted paramount attention in behavior ecology and eco-physiology, empirical support for the POLS hypothesis is currently mixed (Hille and Cooper, 2015), perhaps because POLS theory still lacks a conceptual framework to predict which ecological conditions will favor which syndromes. Many studies in the last decade have tested adaptive explanations for the evolution of repeatable individual differences in behavior (aka personality) (Wolf et al, 2007) and a number of theoretical studies have attempted to predict the conditions favoring the evolution of personalities (Dingemanse and Wolf, 2010)
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