DOI: 10.5061/dryad.fbg79cp15
title: The timid invasion: Behavioural adjustments and range expansion in a non-native rodent

description: Animal behaviour can moderate or favour biological invasion processes, and
 the native fauna’s ability to adapt. The importance of behavioural traits
 for colonization success remains debated, as well as the nature of
 behavioural traits that facilitate colonization. We investigated
 behavioural responses associated with risk-taking and exploration, in both
 non-native bank voles (Myodes glareolus, N = 225) accidentally introduced
 to Ireland a century ago, and in native wood mice (Apodemus sylvaticus, N
 = 189), that decline in numbers with vole expansion. We repeatedly sampled
 behavioural responses in three colonization zones: source (2 sites),
 expansion edge (4) and pre-arrival(2).  Only source and edge
 zones are occupied by bank voles, for more than 80 years and 1-4 years,
 respectively. Individuals of both species varied consistently in
 risk-taking and exploration, and mice had not adjusted their behaviour to
 the presence of non-native voles, as their behaviour did not differ
 between the zones. Voles at the expansion edge were initially more
 risk-averse but habituated to the repeated testing situation, compared to
 voles that were consistently less risk-averse in the source population,
 indicating spatial sorting for risk-taking propensity along the expansion
 front We suggest that in non-native species under high predation pressure,
 the ability to develop timid phenotypes may thus represent a fundamental
 component for range expansions.
description: Trapping
 Rodents were trapped in
 single-capture Longworth traps (Penlon Ltd., Oxford, UK) which were
 pre-baited with seeds from commercial bird feed for 2 nights prior to
 trapping. At each site, 24 traps were set in lines with 10 m spacing
 between them. Traps were baited and set overnight and checked and
 deactivated in the morning. Animals were kept inside their traps in the
 shade until testing, with replenished food and pieces of carrots and
 cucumber as water sources. Trapping was not conducted during rainy days.
 Sites were visited for two trapping sessions within 4 days and re-visited
 after 2–4 weeks to allow repeated testing on recaptured
 individuals.  Behavioural tests<br> 
 For behavioural testing, we
 adopted two standardized behavioural tests that are commonly used in
 animal personality studies of small mammals to assess boldness and spatial
 exploration in a novel environment. The set-up combined the dark-light
 test and the open-field
 test and was adjusted to
 be executed under field conditions without prior handling of
 animals. Test arenas were
 always set in shady locations or under canvas roofs to avoid direct
 sunlight, shade patterns and open sky above the arena. At the end of each
 test, the arenas were cleaned with ethanol 70%. All tests were conducted
 between 1000 and 1800, under natural light
 conditions.  Dark-light test 
 We assessed boldness by
 measuring individuals’ willingness to emerge from a dark-covered shelter
 into an open, illuminated, and empty arena, which is perceived as
 dangerous for a rodent species with a plethora of
 predators. An opaque
 plastic tunnel (15 cm inner diameter, 30 cm long) was connected to an
 opening in the circular arena at ground level, blocked by a wooden door.
 Shortly before the tests, the animal was carefully transferred from the
 trap into a shuttle tube (15 cm outer diameter, 30 cm long, open at one
 side and blocked by a cylindrical sponge of the same diameter on the
 other) avoiding touching or shooing. The shuttle tube with the animal
 inside was then inserted with its full length into the plastic tunnel.
 After 1 minute of acclimatization to the dark tunnel, the door leading
 into the arena was opened and we measured the rodent’s latency to emerge
 (emergence) from the dark tunnel into the arena with its full body
 (without the tail). If animals did not emerge from the tunnel within 5 min
 (66% of tests in voles and 24% in mice), we slowly reduced the space in
 the tube by pushing in the soft, cylindrical sponge in order to gently
 displace the animal without touching it. 
 Open field
 test We quantified exploration by measuring the
 proportion of time each individual spent moving in the novel space of an
 experimental arena (activity), and also how often they crossed into its
 central part (crossings). We used round, plastic, foldable arenas (1.20 m
 diameter, 40 cm high) as portable test set-ups. Round arenas prevent animals sitting in
 corners. The central part of the arena (90cm diameter) was more exposed
 (open field) and could be perceived as potentially dangerous by the
 animal, compared to the area (15 cm wide) nearby the
 wall. We quantified
 exploration activity by measuring the proportion of time each individual
 spent moving in the novel space of an experimental arena, and also how
 often they crossed into its central part, which should be perceived as
 being even more exposed and potentially dangerous. Arenas were covered
 with mesh to prevent wood mice from jumping out. The open field test
 started as soon as the animals entered the arena from the dark tunnel of
 the dark-light test with the full body (without the tail). The door
 leading to the dark tube was closed quietly by the observer, or, if the
 animal was pushed out, the tube remained blocked by the sponge. For 5
 minutes after emergence, we counted the number of 10 sec intervals spent
 moving in the arena (activity), and the number of crossings of the line
 dividing the wall area and the central part of the arena with the whole
 body (crossings). After testing, animals were removed from the arena by
 offering a hiding place, either by pulling back the sponge in the tube or
 by placing their familiar trap in front of them.
 After the behavioural tests,
 animals were sexed and weighed, marked by an individual fur cut if not
 already marked, and photographed for later
 identification. The dataset represents the raw data on
 individual traits and behavioural measures taken in the field and was not
 in any way processed. 
description: Standard programm to open tables (e.g. Excel, OpenOffice
 Calc).
description: # The timid invasion: Behavioural adjustments and range expansion in a
 non-native rodent --- The dataset contains data on bank vole and wood
 mouse individuals captured on different sites in Ireland. Sites differed
 based on whether or not the invasive bank vole was present and for how
 long the invasive species had already been present. Captured individuals
 were tested in behavioural tests to assess exploration and risk-taking
 behaviour. Behavioural data was sampled repeatedly. Individuals of both
 species varied consistently in risk-taking and exploration, and mice had
 not adjusted their behaviour to the presence of invasive non-native voles,
 as their behaviour did not differ between the zones. Voles at the
 expansion edge were initially more risk-averse but habituated to repeated
 testing situation, compared to voles that were consistently less timid
 risk-averse in the source population, indicating spatial sorting for
 risk-taking propensity along the expansion front ## Description of the
 data and file structure Data represent raw data on individual body
 measures of captured individuals (weight, sex) and behavioural measured
 assessed directly in the field Variables shown: * date: capture date in
 2019; time: time of behavioural test at the same day; species: bv bank
 vole Myodes glareolus, wm- wood mouse Apodemus sylvaticus; ID individual
 identifier; sex: m-male, f-female, NA-not sexed; capture: n- new (first
 capture), * r- recapture; age: ad adult, juv juvenile (later removed from
 the analysis), wg: body weight estimate in grams; * DARK LIGHT TEST:
 lat.body: latency to emerge from the shelter in dark-light test, capped at
 300sec after which the animal was gently pushed out of the shelter into
 the arena, in seconds; * OPEN FIELD TEST: lat.centr: latency to cross the
 center line (15 cm from the wall), in seconds: intervals duration of test
 before escape or hiding in 10sec intervals, default: 30 intervals (300
 seconds); active.iv: number of intervals containing activity (walking,
 jumping, digging, not: fur cleaning); * centr.iv: number of intervals
 containing a crossing over the centre line, crossings: number of crossings
 over center line into the center; clean.iv: number of intervals with
 sitting and fur cleaning; jumps: number of jumps up the wall; * zone:
 categorisation of sites into edge, source and pre(colonisation) by
 non-native bank voles.