Rodents in the arena: a critical evaluation of methods measuring personality traits

<p>The Open Field Test (OFT) and Mirror Image Stimulation (MIS) are used to measure behaviours related to an individual’s personality. These tests, carried out in a same novel arena, have been used for different taxa, but only a few papers underline the importance of method validation. Here we investigate how Eurasian red squirrels (<i>Sciurus vulgaris</i>) and Eastern grey squirrels (<i>Sciurus carolinensis</i>) behave during OFT and MIS. Next, we compare the performance between three analytical methods: the Principal Component Analysis (PCA), the Factor Analysis (FA) and an expert-based (EB) method. The EB approach classifies behaviours in groups relating on researchers’ knowledge and returns personality-trait values for each individual facilitating comparisons over studies and/or with new datasets. The comparison between the three methods gave similar results and high repeatabilities in some expert-based personality traits as well as PCA components and FA factors, showing that all three methods were valid to measure activity using OFT (both species) and sociability using MIS (grey squirrel). Repeatabilities of the other traits were less strong. Proportion of time spent in different behaviours did not differ with test duration, since shorter tests yielded valid measures of individual differences in personality. Shorter tests reduce operator time in the field, and are likely to reduce stress and arena-habituation of the animals. Test sequence affected the outcome of OFT: squirrels tested for the first time were more active than squirrels tested a second time. For the two squirrel species investigated, we recommend an OFT of 4 min and a MIS test of three and suggest to test an individual no more than 2 times per season with at least 2 months between repetitions.</p

Minimum selected model of the effects of host characteristics and environmental variables on parasite abundance (no. of parasites/host).

<p>Minimum selected model of the effects of host characteristics and environmental variables on parasite abundance (no. of parasites/host).</p

Variation of <i>S. robustus</i> abundance by host body mass.

<p>Relationship between <i>S. robustus</i> abundance and host body mass: observed values (blank circles) and values predicted by the model at different host densities (lines). Host body mass had a positive effect on <i>S. robustus</i> abundance (p = 0.0005; parameter estimate: 0.0059±0.0017 SE).</p

Most prevalent gastro-intestinal helminths and arthropods (excluding mites) parasitizing grey squirrels in North America.

<p>Only parasites that were recorded by more than one author and with maximum prevalence >5% are reported. Studies with sample size <50 hosts were excluded.</p

Variation of <i>C. sciurorum</i> abundance by season (A) and host density (B).

<p>Mean abundance of <i>C. sciurorum</i> (sample size above standard error bars) varied during different seasons (p<0.0001) and at different host densities (p<0.0001). Squirrels trapped in spring were more infested than in autumn and winter (both sequential Bonferroni adjusted p<0.0001) and animals living in high-density sites were more infested then those living in medium- and low-density populations (both adjusted p<0.008).</p

Helminth species infecting grey squirrels in Piedmont and Lombardy populations.

<p>N: number of host examined; n: number of infected hosts; p: prevalence; mI: mean intensity (no. parasites infected/hosts; when number of infected hosts <5, worm counts in italic).</p

Variation of <i>S. robustus</i> abundance by host density.

<p>Mean abundance of <i>S. robustus</i> (sample size above standard error bars) varied with density of hosts in the site (p<0.0001). Squirrels living in high-density sites were more infested than individuals living in medium- and low-density sites (both sequential Bonferroni adjusted p<0.0001) and squirrels living in medium-density sites were more infested than in low-density sites (adjusted p = 0.0008).</p