Cognitive Performance of Wild Eastern Gray Squirrels (Sciurus carolinensis) in Rural and Urban, Native, and Non-native Environments

Pizza Ka Yee Chow,Nicola S Clayton,Michael A Steele

doi:10.3389/fevo.2021.615899

Abstract

Enhanced cognitive ability has been shown to impart fitness advantages to some species by facilitating establishment in new environments. However, the cause of such enhancement remains enigmatic. Enhanced cognitive ability may be an adaptation occurring during the establishment process in response to new environments or, alternatively, such ‘enhancement’ may merely reflect a species’ characteristic. Based on previous findings that have shown ‘enhanced’ cognitive ability (i.e., higher success rate in solving novel food-extraction problems or, ‘innovation’) in Eastern gray squirrels (Sciurus carolinensis), a successful mammalian invader and urban dweller, we used an intraspecific comparative paradigm to examine the cause of their ‘enhanced’ cognitive ability. We conducted a field study to compare cognitive performance of free-ranging squirrels residing in rural and urban habitats in native (United States) and non-native environments (United Kingdom). By using established tasks, we examined squirrels’ performance in easy and difficult, novel food-extraction problems (innovation), a motor memory recall test of the difficult problem, and a spatial learning task. We found that the four groups of squirrels showed comparable performance in most measures. However, we also found that the native urban squirrels showed: (1) higher success rate on the first visit for the difficult problem than the non-native urban squirrels; (2) some evidence for higher recall latency for the difficult problem after an extended period than the non-native rural squirrels; and (3) learning when encountering the same difficult problem. These results suggest that the previously reported ‘enhanced’ performance is likely to be a general characteristic and thus, a pre-adaptive phenotypic trait that brings fitness advantages to this species in a new environment. Despite this, some cognitive abilities in gray squirrels such as solving novel problems has undergone mild variation during the adaptive process in new environments.

Highlights

We found that compared with the red squirrels, the gray squirrels showed higher success rates in solving the easy problem in the first visit, and higher success rates in solving the difficult problem in the first and subsequent visits to the testing apparatus
Lower and upper bound of highest posterior distribution (HPD), credible interval (CI) and Bayes factor (BF10)
The squirrels took significantly less time to solve the easy problem than the difficult problem (GLMM: χ21 = 7.38, P = 0.007)

Summary

Introduction

Enhanced cognitive ability has been shown to advance fitness measures in some contexts (Sol and Lefebvre, 2000; Sol et al, 2002, 2008; Nicolakakis et al, 2003; Keagy et al, 2009; Amiel et al, 2011; Cole et al, 2012; Cauchard et al, 2013; Webb et al, 2014; Preiszner et al, 2017). Other examples are individuals of some species that are more successful or faster in solving novel food-extraction problems, which have been reported in urban populations compared with their rural counterparts (e.g., Liker and Bókony, 2009; Papp et al, 2015; Audet et al, 2016; and see Preiszner et al, 2017; Prasher et al, 2019). Despite these examples, the possible causes of enhanced cognitive ability remain enigmatic. A non-mutually exclusive possibility is that ‘enhanced’ ability may be a species’ natural characteristic which has been shown in other traits such as competitive ability (the inherent superiority hypothesis by Elton, 1958)

Methods

Results

Discussion

Conclusion