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Bold New World: urbanization promotes an innate behavioral trait in a lizard

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Abstract

Urban environments are novel landscapes that markedly alter animal behavior. Divergence in behavior in response to urbanization may provide advantages in navigation, exploiting resources, and surviving under a novel suite of selective pressures. Relatively few studies, however, have identified population-level behavioral changes in response to urbanization that are not confounded by rearing environment and prior experience (e.g., an urban upbringing). To address this, we used the Australian water dragon (Intellagama lesueurii) to test whether populations under varying levels of urbanization (urban, semi-natural, and natural populations) differ in their innate behavioral traits; acquired either heritably or due to population-specific maternal effects. Eggs were collected from wild mothers and hatched in the lab. Hatchlings were then reared in the lab under standardized conditions (a common-garden experiment). We then assayed individual behavioral traits (boldness, exploration, and neophilia) five times across their first year of development. We compared behavioral traits, as well as their expression (repeatability), between urban, semi-natural, and natural populations. Neophilia and explorative behavior was similar among all populations. However, dragons from semi-natural populations were significantly bolder than those from natural populations. Urban dragons were also bolder than dragons from natural populations, although this trend was not significant because of high variance in boldness. Dragons from semi-natural and urban populations had similar boldness scores, suggesting a potentially biologically relevant difference in boldness between them and natural populations. We also saw some differences in the consistency of the expression of behavior. Boldness in individuals from urban environments was also the only repeatable trait. Overall, our study suggests that boldness is an innate, urban-derived divergent behavioral trait that likely contributes to the success of these lizards in anthropogenically altered environments.

Significance statement

Lizards from human-modified areas are innately bolder than ones from natural habitats. To determine this, we raised lizards from eggs collected from urban, semi-natural, and natural populations in a standardized environment, removing the effects of prior experience and developmental environment, and examined their behavioral traits over time. The difference we found in boldness was related to their origin population, rather than being shaped through experience, suggesting this trait may be heritable and is being selected for in anthropogenic landscapes. Our study addresses an important gap in studies of urban behavioral ecology by examining behavioral differences among replicated, differently urbanized, sites after experimentally accounting for both rearing environment and prior experience.

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Data availability

The datasets generated during and/or analyzed during the current study are not publicly available due to logistical constraints, but are available from the corresponding author on reasonable request.

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Acknowledgments

We would like to thank P. Bolton, C. Fryns, F. Kar, S. Klopper, and D. Noble for their assistance in field. We are grateful to T. Damasio, M. Mühlenhaupt, C. Wilson, and the husbandry volunteers at Macquarie University’s Lizard Lab for their assistance in the lab, and P. Harlow and O. Lapiedra for providing their insights into this topic. Finally, we would like to thank the anonymous reviewers for their comments and suggestions.

Funding

This research was supported by scholarship from Macquarie University (JBG) and Natural Sciences and Engineering Research Council of Canada (JBG). JLR was supported by an Endeavor and Claude Leon Foundation postdoctoral fellowship during this work.

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Correspondence to James Baxter-Gilbert.

Ethics declarations

Ethical approval for lizard captures and our experimental protocols followed animal ethics guidelines that were approved by both the Macquarie University Animal Ethics Committee (ARA no. 2015/023) and Taronga Zoo Animal Ethics Committee (ARA no. 3b/08/15). Our research was approved by the New South Wales National Parks and Wildlife Service, Office of Environment and Heritage (License no. SL100570).

Conflict of interest

The authors declare that they have no conflict of interest.

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Communicated by T. Madsen

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Baxter-Gilbert, J., Riley, J.L. & Whiting, M.J. Bold New World: urbanization promotes an innate behavioral trait in a lizard. Behav Ecol Sociobiol 73, 105 (2019). https://doi.org/10.1007/s00265-019-2713-9

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  • DOI: https://doi.org/10.1007/s00265-019-2713-9

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