Urbanization and its effects on personality traits: a result of microevolution or phenotypic plasticity?

Abstract

Human-altered environmental conditions affect many species at the global scale. An extreme form of anthropogenic alteration is the existence and rapid increase of urban areas. A key question, then, is how species cope with urbanization. It has been suggested that rural and urban conspecifics show differences in behaviour and personality. However, (i) a generalization of this phenomenon has never been made; and (ii) it is still unclear whether differences in personality traits between rural and urban conspecifics are the result of phenotypic plasticity or of intrinsic differences. In a literature review, we show that behavioural differences between rural and urban conspecifics are common and taxonomically widespread among animals, suggesting a significant ecological impact of urbanization on animal behaviour. In order to gain insight into the mechanisms leading to behavioural differences in urban individuals, we hand-raised and kept European blackbirds (Turdus merula) from a rural and a nearby urban area under common-garden conditions. Using these birds, we investigated individual variation in two behavioural responses to the presence of novel objects: approach to an object in a familiar area (here defined as neophilia), and avoidance of an object in a familiar foraging context (defined as neophobia). Neophilic and neophobic behaviours were mildly correlated and repeatable even across a time period of one year, indicating stable individual behavioural strategies. Blackbirds from the urban population were more neophobic and seasonally less neophilic than blackbirds from the nearby rural area. These intrinsic differences in personality traits are likely the result of microevolutionary changes, although we cannot fully exclude early developmental influences.

Urban Great Tits (Parus major) Show Higher Distress Calling and Pecking Rates than Rural Birds across Europe

“…This finding is in line with studies showing that urban great tits are more explorative and less neophobic than their rural counterparts (Tryjanowski et al, 2016;Charmantier et al, 2017;Riyahi et al, 2017), and display shorter flight initiation distances (Møller, 2008(Møller, , 2012, which represent other aspects of the proactive coping strategy. Findings on the great tit are also in line with data from other bird species, for which urban populations have also been found to display proactive behaviors (Evans et al, 2010;Carrete and Tella, 2017), but these studies compared few populations (Miranda et al, 2013). Our study included 14 populations from a large geographic area and revealed consistent results across localities, allowing to generalize the impact of urbanization on great tit coping styles.…”

Differences in measures of boldness even when underlying behavioral syndromes are present in two populations of the song sparrow (Melospiza melodia)

“…However, it is often unclear if such changes in urban animals represent evolutionary and genetically based adaptations, as suggested by several recent studies (Atwell et al 2012;Miranda et al 2013;Mueller et al 2013), or changes due to habituation or other forms of learning and plasticity.…”

An Approach to Distinguish between Plasticity and Non-random Distributions of Behavioral Types Along Urban Gradients in a Wild Passerine Bird

“…Most of these studies, however, have solely focused on differences in behavioral phenotypes at the population level. Researchers have only recently begun to assess individual variation in the context of urban ecology (Miranda et al, 2013). In this study we shed new light on relationships between urbanization and behavioral phenotypes by partitioning variation in behavioral phenotypes into within-and amongindividual components; this enabled us to investigate the relative roles of distinct mechanisms causing such associations.…”