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Inter-Population Variation in Hoarding Behaviour in Degus,
Octodon degus
Rene
´Quispe*, Camila P. Villavicencio*, Arturo Corte
´sà & Rodrigo A. Va
´squez*
* Instituto de Ecologı
´a y Biodiversidad, Departamento de Ciencias Ecolo
´gicas, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
Departamento de Biologı
´a, Facultad de Ciencias, Universidad de La Serena, La Serena, Chile
àCentro de Estudios Avanzados en Zonas Aridas, La Serena, Chile
Introduction
One of the most effective methods to assess the
adaptive value of phenotypes has been the quantifi-
cation of trait variation through comparisons
between populations occurring in contrasting ecolog-
ical conditions (Endler 1986; Foster & Endler 1999).
Species inhabiting large geographical areas covering
various habitat types must cope with diverse ecologi-
cal conditions, with large environmental differences
across their range (see e.g. Oswald 1998; Foster &
Endler 1999; D’Anatro & Lessa 2006; Ferguson &
Higdon 2006; Wingfield et al. 2007). Each popula-
tion may experience selective pressures different
from those experienced in populations elsewhere,
resulting in differences in phenotypic traits (e.g.
Correspondence
Rodrigo A. Va
´squez, Instituto de Ecologı
´a y
Biodiversidad, Departamento de Ciencias
Ecolo
´gicas, Facultad de Ciencias, Universidad
de Chile, Casilla 653, Santiago, Chile.
E-mail: rvasquez@uchile.cl
Received: July 1, 2008
Initial acceptance: October 6, 2008
Final acceptance: December 16, 2008
(D. Zeh)
doi: 10.1111/j.1439-0310.2009.01621.x
Abstract
Although foraging comprises a set of behaviours that typically vary with
resource availability and ⁄or climatic conditions, few studies have analy-
sed how foraging, particularly food hoarding, varies across populations
inhabiting different habitats. We carried out an inter-population study
on foraging behaviour with the caviomorph rodent Octodon degus col-
lected from two geographically separated populations in central Chile,
with contrasting climates. One population was located in a mountainous
zone (at 2600 m elevation) characterized by a high-altitude climate. The
other population was from a low-altitude Mediterranean climate zone
(450 m elevation). Under laboratory conditions, we measured popula-
tion-specific differences in food consumption and hoarding by recording
food utilization. We also assessed whether acclimation played a role in
behavioural differences, by using two different sets of animals that had
been in captivity for (1) 2 wk or (2) 6 mo, under common conditions.
The results showed variation in food hoarding between populations.
Individuals from the low-altitude population exclusively displayed scat-
ter hoarding behaviour. In contrast, high-altitude animals carried out
larder hoarding combined with scatter hoarding (37.4% and 62.6%
respectively). There was no intra-population variation between degus
with different acclimation periods under captivity, thus inter-population
differences in larder hoarding were maintained despite 6 mo of acclima-
tion to a common environment. The geographic variation observed sug-
gests that larder hoarding is favoured under harsher environmental
conditions. We discuss some probable causes for this variation. The lack
of effect of acclimation suggests that inter-population differences in lar-
der hoarding might be the result of local adaptation or, less likely, it
corresponds to an ontogenetically acquired irreversible behaviour.
Ethology
Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH 465
Solick & Barclay 2006; for reviews, see also Endler
1986; Foster & Endler 1999; Mosseau et al. 2000).
Such phenotypic traits include behavioural traits,
which can be quantified under laboratory conditions
(e.g. Tannenbaum 1987; Thompson 1990; Haim
1991). The study of the geographical variation of
behaviour can be an important tool allowing the
inference of the environmental factors influencing
the evolution of behaviour (Endler 1986; Foster &
Endler 1999), and can provide valuable insights into
the process of behavioural diversification across wild
populations.
Among the main types of behaviours that signifi-
cantly influence fitness (see Krebs & Davies 1997),
food foraging directly affects the energetic balance
and nutritional state of animals, which in turn influ-
ences growth, reproductive performance and other
traits closely related to fitness (Ritchie 1990; Lemon
1991; see also Stephens et al. 2007). Foraging is
defined as all those behaviours related to obtaining
and consuming resources such as food searching,
recognition, catching, manipulation, transportation,
hoarding and feeding (Stephens & Krebs 1986;
Hughes 1993). Moreover, foraging behaviour has
important implications for the colonization of new
territories and novel environments and hence it
plays an essential ecological role for the species’ dis-
tribution (Sol et al. 2005). Therefore, foraging repre-
sents an excellent topic for comparative studies of
geographical variation in behaviour because its
expression is closely related to environmental condi-
tions and resource availability. For example, popula-
tions from colder environments, or from areas
where food resources become seasonally scarce, may
exhibit higher levels of food hoarding activity (Barry
1976; Vander Wall 1990; Jenkins et al. 1995).
Food hoarding is a behavioural strategy that has
evolved independently in a wide range of taxa and
habitats (Vander Wall 1990), suggesting that it rep-
resents an adaptation to temporally variable or
unpredictable food supply due to weather, predation,
competition or to fluctuations in energy demands
(Vander Wall 1990; Jenkins & Peters 1992; Jenkins
et al. 1995). Two major patterns of food hoarding,
representing the extremes in the continuum of spa-
tial distribution of food storage, have been identified
(Vander Wall 1990; Jenkins et al. 1995). The storage
of food items in a protected central location, such as
a burrow or a nest, is known as larder hoarding,
whereas scatter hoarding refers to the concealment
of individual or small groups of food items in several
locations (Vander Wall 1990). As different popula-
tions of a given species may experience distinct
environmental conditions (Foster & Endler 1999),
behavioural differences in hoarding activity may
occur, particularly under contrasting climatic or
biotic conditions.
We carried out a study on the caviomorph rodent,
Octodon degus (common name: degu), which occupies
a wide distribution throughout north-central Chile
(Fulk 1976; Le Boulenge
´& Fuentes 1978). Octodon
degus is an endemic species commonly found in the
Chilean matorral, a biogeographical zone character-
ized by hot and dry summers and cool, moist winters
(Rundel 1981). It is a herbivorous diurnal rodent,
with a diet composed mainly of herbs, seeds and
leaves (Meserve 1981; Meserve et al. 1983). Degus
are generally associated with shrub cover and vari-
able amounts of open space where they forage (Le
Boulenge
´& Fuentes 1978; Jaksic et al. 1981;
Meserve et al. 1984; Iriarte et al. 1989). In these
habitats (at low elevation), degus usually construct
underground burrows and galleries that are used
communally (Ebensperger et al. 2004), and which
are connected above ground by a system of runways
(Fulk 1976; Vasquez 1997; Vasquez et al. 2002).
Despite the numerous studies of foraging in degus,
detailed descriptions of hoarding behaviour are lack-
ing. Some descriptive studies mention that degus
store food in their burrows, including grasses
and seeds (Woods & Boraker 1975; Fulk 1976; R. A.
Va
´squez, pers. obs.), and during field foraging experi-
ments they have been observed hoarding seeds to
their nests (larder hoarding) and ⁄or to a few scatter
sites digging a few (1–2) centimetres underground
(R. A. Va
´squez, unpubl. data). Fulk (1976) noticed
that adults can transport grasses to a burrow were
other subjects can consume it. There are no further
studies describing food hoarding in degus.
We assessed foraging behaviour by focusing on
hoarding carried out by animals captured in two
geographically separated populations that experience
highly contrasting winter seasons. One population
was collected nearby Santiago, in a typical degu site
located in the matorral of central Chile (450 m
elevation; see Methods for details), which is charac-
terized by Mediterranean-type climate. The second
population was located at a high altitude in the
Andes mountain range, to the east of the city of
Ovalle at 2600 m elevation, in an area that undergoes
long and cold winters that restrict the surface activity
of degus (see Methods for details). There are no pre-
vious studies in high-altitude populations of degus.
Secondly, we conducted a laboratory-based
within-population comparison between recently
captured wild degus and those that had been in
Inter-Population Variation in Hoarding Behaviour R. Quispe et al.
466 Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH
captivity for 6 mo (i.e. acclimated). Quantification of
behavioural phenotypes of acclimated and non-accli-
mated animals is a valuable technique to gain
insights into the flexibility of behaviour. Plasticity
studies in other taxa have demonstrated that this
can be an efficient approach to understand the
causes of variation in foraging behaviour (see Starck
1999; Honkoop & Bayne 2002). If acclimation to
common conditions does not produce convergence
in foraging behaviour among populations, then
inter-population differences in behaviour might be
due to local adaptation or irreversible phenotypic
plasticity (see Piersma & Drent 2003; David et al.
2004).
We predicted that, in comparison with the low-alti-
tude population, degus from the high-altitude popu-
lation experiencing more restrictive weather
conditions should be prone to a greater food hoarding
activity as an adaptive response to seasonal variability
in food availability and ⁄or accessibility. Previous stud-
ies describe degus as being able to modify their forag-
ing physiology and behaviour, and their daytime
activity budget according to seasonal and shorter
term variations (Bozinovic 1995; Bozinovic &
Vasquez 1999; Bozinovic et al. 2000; Kenagy et al.
2002a,b, 2004; Vasquez et al. 2006), but only a few
studies have dealt with spatial variation in the forag-
ing ecology of degus within a broad trophic spectrum
(Meserve et al. 1983, 1984; Zunino & Saiz 1991).
Materials and Methods
Subjects
We captured degus at each population using stan-
dard Sherman live traps, on sites where active
burrows were observed. The low-altitude population
is located at the University of Chile field station at
Rinconada de Maipu´ (7053¢W, 3328¢S), 30 km
south-west from Santiago. This area consists of a flat
topography dominated by scattered shrubs (Proustia
pungens, Acacia caven and Bacharis spp.) and contains
numerous degu burrows. Runways radiate from bur-
row entrances through the extensive herb cover via
which degus continuously travel (for degu studies
carried out in the area, see e.g. Fulk 1976; Vasquez
1997; Vasquez et al. 2002; Ebensperger et al. 2004).
The second population of Rio Los Molles (Bocatoma
area) occurs at high altitude in the Andes range
(7015¢W, 3045¢S), 98 km east from the city of
Ovalle, in the IV region in the north of Chile. In this
site the ground is rocky and mostly sloped, shrubs
and herbs occur at lower abundance, travel runways
are less frequent, and degus are rarely observed far
outside from their burrows. The two populations are
approx. 400 km apart, and there are several rivers
and large valleys that separate central from north-
central Chile. The captures were carried out between
December 2004 and April 2005. The traps were first
baited at dawn with a cereal and seed mix and
checked at midday. Traps were re-baited in early
afternoon and checked at dusk. Captured animals
were weighed, sexed, marked with numbered ear
tags (National Band & Tag Co., Newport, KY, USA)
and brought into captivity. Each animal was housed
in a standard metal cage (80 ·40 ·35 cm), with
wood shavings, under near-natural temperature and
photoperiod conditions. Captured animals were fed
commercial rabbit pellets ad libitum (Champion S.A.,
Santiago, Chile), with free access to water. Individu-
als were maintained in captivity grouped together by
their native populations. Experiments were con-
ducted during the light period. After the trials, ani-
mals were released back to their original sites of
capture.
Experimental Groups
Thirty-five wild-caught individuals were used for
experiments. Nineteen individuals were caught at
Rinconada de Maipu´ consisting of nine adult males
and 10 adult non-pregnant females. Sixteen individ-
uals were captured at Rio Los Molles, including 10
adult males and six adult non-pregnant females.
To investigate the behavioural flexibility to envi-
ronmental change and the reversibility of hoarding
behaviour under controlled conditions, two sub-
groups were formed within each population group.
One subgroup consisted of animals that had been
acclimated to captivity over at least a period of
6 mo. The second subgroup consisted of recently
caught individuals (2 wk before the commencement
of the experiments). From the Rinconada de Maipu´
population, nine individuals (five females and four
males) formed the ‘non-acclimated’ subgroup, and
10 animals formed the ‘acclimated’ subgroup (five
males and five females). From Rı´o Los Molles popu-
lation, six individuals belonged to the ‘non-accli-
mated’ subgroup (one female and five males) and 10
animals in the ‘acclimated’ subgroup (five males and
five females).
Procedure
We used four identical metallic arenas consisting of
a rectangular enclosure of 1 m ·1.5 m ·80 cm
R. Quispe et al. Inter-Population Variation in Hoarding Behaviour
Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH 467
(width ·length ·height). We poured sand into each
arena to a depth of 3 cm. One nest box of galvanized
metal measuring 25 ·25 ·10 cm was placed in a
corner of each arena; each individual had its own
artificial nest box burrow during the experiment.
We examined the foraging and food hoarding behav-
iour of subjects by providing an artificial seed patch
into the arena at the far side of the nest box. This
patch consisted in a metallic tray of 20 ·20 cm filled
with a mixture of 200 sunflower seeds (weighing a
total of 22.0 g) and fine sand, following the method
used by Vasquez (1996). Previous studies have dem-
onstrated that degus use these seeds (see Vasquez
et al. 2006). The distance from the burrow to the
food patch was 1 m.
Prior to each experiment, individuals were allowed
to become accustomed to their artificial burrow and
to the experimental food over a 4-d period. To stim-
ulate foraging activity during the experiments, we
enforced a fasting period, only with access to water,
for a 24-h period before the commencement of an
experiment. The trials were carried out during the
southern hemisphere fall season between March and
June 2005. We began a trial by randomly placing
animals of each population inside their own artificial
burrow in one arena. Each trial lasted 18–19 h,
beginning at about 17:00 h and ending at midday of
the next day, encompassing with the period of high-
est activity in this species (Kenagy et al. 2002a,b).
This length of time allowed subjects to become
accustomed, explore and forage in the arenas (see
e.g. Vasquez 1996). After each trial, we counted the
number of seeds larder hoarded in the burrow, and
then drained the sand with a manual sieve to count
the number of hoarded seeds that had been buried
throughout the arena. We also assessed the unhar-
vested seeds remaining on the food tray to calculate
seed consumption (see Vasquez 1994, 1996). Each
animal was tested individually and only once. After
each trial each arena was cleaned and sand
smoothed for next time.
Statistical Analysis
Given that body mass might affect several energy
intake variables, we first compared the body mass
between the two populations using a two-way anova
incorporating native population and acclimation sub-
group as factors. We used two-way factorial ancovas
for the three response variables: seeds consumption,
total seeds hoarded and seeds scatter hoarded. Origi-
nal population and acclimation level were included
as factors, and individual weight as a covariate. Data
were transformed when appropriate to meet the
assumptions of each analysis (see Sokal & Rohlf
1995). There was no need to carry out a statistical
analysis in order to demonstrate differences in larder
hoarding because only subjects from the high-alti-
tude population stored seeds inside the burrow. For
the analysis of the effect of acclimation within popu-
lations we used a nonparametric Wilcoxon signed
rank test, due to the lack of normality of data. To
test whether the number of seeds larder hoarded dif-
fered from seeds scatter hoarded within populations
we used a paired t-test.
Results
Because body mass might directly affect foraging,
we first analysed these data. Thereafter, body mass
was used as a covariate for inter-population com-
parisons. There was a significant effect of the popu-
lation’s origin and acclimation level on body mass.
Degus originating from the population at Rinconada
de Maipu´ had a larger body mass compared with
animals from Rio Los Molles (animals from the
low-altitude population were 52.3% and 37.2%
heavier, for non-acclimated and acclimated animals
respectively; see Fig. 1), while within each popu-
lation, individuals acclimated to captivity were
heavier than those that were not (two-way anova,
population: F
3,31
= 85.4, p < 0.001; acclimation:
F
3,31
= 69.4, p < 0.001; Fig. 1). There was no effect
of the interaction between population and acclima-
tion level (F
3,31
= 0.04, p = 0.83; Fig. 1).
Population
High elevation Low elevation
Body mass (g)
0
50
100
150
200
250
300
Non-acclimated
Acclimated
a
bb
c
Fig. 1: Body mass of degus originating from the two studied popula-
tions and with different levels of acclimation to captivity. Values are
means SE. Different letters represent statistically significant differ-
ences between groups, determined using Tukey’s post hoc test.
Inter-Population Variation in Hoarding Behaviour R. Quispe et al.
468 Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH
There was no difference in the number of seeds
consumed during each trial between both popula-
tions, nor among individuals that differed in accli-
mation level (two-way ancova with body mass as a
covariate, population: F
3,31
= 0.00008, p = 0.992;
acclimation: F
3,31
= 0.054, p = 0.816; Fig. 2a). All
degus of both populations, except one individual
from Rinconada de Maipu´ , hoarded seeds at several
places in the experimental arena. The amount of
seeds hoarded did not differ between populations,
and no differences were observed in the total
amount of seeds hoarded between the two levels of
acclimation within each population (two-way
ancova with body mass as a covariate, population:
F
3,31
= 3.105, p = 0.088, power = 0.42; acclimation:
F
3,31
= 0.347, p = 0.559; Fig. 2b).
No significant differences were found between
populations in the number of seeds that were scatter
hoarded (i.e. in the sand outside the burrow). There
was no effect of geographical population and of
acclimation group on amount of seeds scatter
hoarded (two-way ancova with body mass as a
covariate, population: F
3,31
= 0.514, p = 0.478; accli-
mation: F
3,31
= 0.955, p = 0.336; Fig. 3a).
No individual from the Rinconada de Maipu´ popu-
lation stored seeds in their burrows. In contrast,
individuals from the high-altitude population, in
addition to scatter hoarding, also frequently stored
N seeds consumed
0
20
40
60
80
100
120
140 Non-acclimated
Acclimated
a
aa
a
Population
High elevation Low elevation
Total seeds hoarded
0
20
40
60
80
100
a
a
aa
(b)
(a)
Fig. 2: (a) Total number of seeds consumed during the trials by
degus originating from two populations, and belonging to different
groups of acclimation time. (b) Total number of seeds hoarded during
the trials by degus originating from two populations, and belonging to
different groups of acclimation time to captivity within each popula-
tion. Values are means SE. The same letters represent no statisti-
cally significant differences between groups, determined using Tukey’s
post hoc test.
N seeds scatter hoarded
Non-acclimated
Acclimated
a
a
a
a
0
10
20
30
40
50
(a)
Population
High elevation Low elevation
N seeds larder hoarded
0
5
10
15
20
a
a
bb
(b)
Fig. 3: (a) Number of seeds scatter hoarded throughout the arena
during the trials by degus originating from two populations, and
belonging to different groups of acclimation time. (b) Number of seeds
larder hoarded inside the burrow during the trials by individuals origi-
nating from two populations, and belonging to different groups of
acclimation time to captivity within each population. Values are means
SE. The same letters represent no statistically significant differences
between groups, determined using Tukey’s post hoc test.
R. Quispe et al. Inter-Population Variation in Hoarding Behaviour
Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH 469
seeds inside the burrow (9 of 16 animals larder
hoarded; Fig. 3b). Subjects from the Rio Los Molles
population did not show a significant difference
between the number of seeds scatter and larder
hoarded (paired t-test: p > 0.05).
There was no significant difference in the number
of seeds that were larder hoarded between accli-
mated and non-acclimated subjects coming from the
high-altitude population (Wilcoxon signed rank test,
p > 0.05; Fig. 3b).
Discussion
Comparison Between Populations
Nearly all individuals displayed seed hoarding behav-
iour. Therefore, our results suggest that hoarding
behaviour occurs as a fundamental component of
foraging activity of this species. Degus appear to allo-
cate a significant amount of energy to hoarding
activities during foraging, and animals from both
populations often appear to hoard food given the
opportunity. This finding is important because there
is not previous information about hoarding in degus.
Furthermore, although no significant differences
were found in the total amount of seeds hoarded
between populations, we observed that degus from
the high-altitude population tended to hoard a
greater amount of seeds compared with the low-alti-
tude population (see Fig. 2b). Further studies in
degus could confirm this tendency, as it is known
that other species of small mammals modify their
behaviour in response to temperature, environmen-
tal condition and season, frequently hoarding greater
quantities of food under colder environmental condi-
tions (e.g. Schwaibold & Pillay 2006).
There was no difference in the total food intake of
individuals between the two populations. This result
may be due to similar energetic requirements for all
degus under common controlled conditions, when
food consumption is standardized to individual body
mass (i.e. with individual body weight as a covari-
ate). It should be noted that in the laboratory indi-
viduals experienced similar conditions in terms of
space availability, thermoregulatory costs and food
supply.
One prominent finding was that degus from the
low-elevation population exclusively scatter
hoarded, while degus originating from the high-alti-
tude population larder and scatter hoarded. This
inter-population difference is related to contrasting
ecological conditions. It is well known that the envi-
ronment in which animals inhabit can have a strong
impact on the development and evolution of
behavioural patterns (Foster & Endler 1999; Brown
& Braithwaite 2004). Even though we compare only
two contrasting populations, a difference between
them is sufficient to reject homogeneity in hoarding
behaviour (i.e. lack of geographical variation) among
populations (see e.g. Bell 2005). We think that the
observed inter-population differences were due to
intrinsic abiotic and ⁄or biotic features differing
between the studied populations, and that those dif-
ferences are not idiosyncratic, and they emphasize
the constraint of ecological conditions for shaping
foraging behaviour in degus. In this vein, there are
several factors (or a combination of them) that could
have driven the variation in hoarding strategies
observed between the two populations, and below
we briefly discuss the most evident.
First, the high-altitude population at Rio Los
Molles is located within the Andes mountain range,
and it is characterized by low annual temperatures,
long and cold winters with strong winds, storm
presence, rain and snow cover during winter time.
Feeding underground in cold weather may decrease
the time that degus are exposed to lethal above-
ground environmental conditions. Therefore, food
storage chambers in the degu burrow system might
be favoured in high-altitude populations, where
food is hoarded during clear days in preparation for
periods when above ground food is not accessible
(e.g. cold nights, rainy days, snow cover days). In
contrast, at low-altitude localities with milder
weather, degus could hoard outside their burrows
because individuals are able to recover the hoarded
food free from restrictive climatic conditions. Other
mammal species can modulate their foraging with
other activities depending on environmental tem-
perature; for example, rats can trade food for
warmth under generally cold conditions (Schultz
et al. 1999).
Previous research with Chilean rodents has
revealed changes in foraging behaviour due to pre-
dation risk cues (Vasquez 1994, 1996; Vasquez et al.
2002; Ebensperger et al. 2006). The high-altitude
population of Rı´o Los Molles is characterized by
lower availability of vegetation cover, a very rocky
and sloped topography and the presence of snow
during the winter. These factors could hinder the
movements of degus and could also increase the
conspicuousness to predators due to a higher con-
trast between the prey and background. These
aspects might have favoured a more cautious for-
aging behaviour (for a review, see Caro 2005),
resulting in degus directing their caches towards a
Inter-Population Variation in Hoarding Behaviour R. Quispe et al.
470 Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH
unique underground hidden point (i.e. they show
larder hoarding).
The travel cost to patch resources and the risk of
pilferage losses of the cached food are important fac-
tors that can affect hoarding behaviour as well (Daly
et al. 1992; Jenkins & Peters 1992; Jenkins et al.
1995; Tsurim & Abramsky 2004). The low-altitude
population has extensive meadows with larger and
more widespread vegetation. Individuals of this pop-
ulation travel longer distances as revealed by long
marked runways between burrow entrances and
shrubs (see Vasquez et al. 2002), and particularly
during the breeding season they can be highly terri-
torial (Soto-Gamboa et al. 2005). In contrast, degus
at the high-altitude population commonly build their
burrows near shrub trunks (R.A. Va
´squez, unpubl.
data), in shorter zones mostly limited to moist areas
associated with water run-offs or spring waters.
These restricted areas could favour larder hoarding,
suggesting that travel cost and pilferage risk could be
lower. The high-altitude population seem to be less
abundant and dense favouring a lower pilferage risk
as well. Although Fulk’s (1976) observation that
degus in a low-altitude population can share food
items with burrow mates challenges that idea.
Furthermore, given that degus nest communally
(Ebensperger et al. 2004), and that they can recog-
nize some level of genetic relatedness via familiarity
and kinship (Jesseau et al. 2008, Villavicencio et al.
in press), possibly pilferage occurs mainly among
non-relatives.
On the other hand, we found that degus originat-
ing from the low-altitude population had larger body
mass than those from high elevation. The observed
difference was maintained between acclimated sub-
jects despite the similar period of time that each
group experienced controlled captive conditions. We
stress that this is the first study reporting body size
differences between degu populations. Although it is
difficult to pinpoint the precise factors driving this
difference, possibly, smaller animals can cope better
with seasonal environments than larger individuals
because they are more likely to find enough food
during the lean season (see e.g. Lehman et al.
2005).
From an evolutionary perspective, the intraspecific
differences reported here may be explained in at
least two ways. First, these differences may represent
local adaptations and reflect genetic divergence, with
behavioural types well suited to the environmental
conditions (see e.g. Arnold 1981; Mosseau et al.
2000). On the other hand, the behavioural patterns
may reflect environmentally triggered phenotypic
variation (Stearns 1989; Pigliucci 2001). As a first
step to understand the source of this variation, we
assessed flexibility in the hoarding behaviour by
comparing individuals within each population under
two different levels of acclimation (see next section).
Comparison Within Populations
Several aspects of phenotypic flexibility deserve
attention because they influence the direction of the
organism–environment interaction, and subse-
quently can alter its ecological impact. These include
the time lag between changes in environmental cues
and plastic responses, reversibility of responses and
the shape of reaction norms with respect to environ-
mental gradients (see Pigliucci 2001; Piersma &
Drent 2003; David et al. 2004; Miner et al. 2005).
Our results show that there was no convergence in
the hoarding patterns between the two populations
living under captivity-controlled conditions. In other
words, the behavioural difference observed between
populations was maintained after 6 mo under
common conditions. Given that most behaviours,
including foraging, are reversible or flexible, the
maintenance of the hoarding patterns shown by
experimental animals suggests that it might be due
to genetic differentiation, thus supporting an expla-
nation based on local adaptation. This idea is also
supported by the long distance that separates both
studied populations. Therefore, further studies will
be needed to determine whether this hoarding
response is a consequence of local adaptation to
contrasting environments, or the result of a develop-
mental genotype–environment interaction.
In addition, we found a significant body mass dif-
ference within each population between the two
acclimated groups. The acclimated groups had larger
body masses than newly captured animals in both
populations. The longer captivity care, which
included ad libitum food availability, controlled tem-
perature, less space and therefore lower energetic
requirements, seems to be the principal cause influ-
encing the greater body mass of acclimated subjects.
However, these captivity environmental factors did
not influence the behavioural response expressed by
subjects from each population.
Although behaviour is frequently thought as the
most plastic or flexible phenotypic trait, our results
have shown that between two degu populations,
hoarding behaviour differs and it was not modified
after a long period of common conditions. Therefore,
larder hoarding seems to confer an adaptive advan-
tage to degus inhabiting high-altitude habitats.
R. Quispe et al. Inter-Population Variation in Hoarding Behaviour
Ethology 115 (2009) 465–474 ª2009 Blackwell Verlag GmbH 471
Acknowledgements
We thank M.C. Cecchi, I.N. Ma
´rquez, D. Parra, A.
Rivera, W. van Dongen and R. Zu´n
˜iga for their valu-
able assistance. ENDESA-Chile (Los Molles hydro-
electrical power station) kindly allowed us to
conduct fieldwork in its property. Research was con-
ducted under permit no. 5193 issued by the Servicio
Agrı´cola y Ganadero, Chile, with the supervision of
the Ethics Committee of the Faculty of Sciences,
Universidad de Chile, and was funded by FONDE-
CYT-1060186 to R.A.V., the Institute of Ecology and
Biodiversity ICM-P05-002, and PFB-23-CONICYT.
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