ArticlePDF Available

Activity, overlap of range areas, and sharing of resting locations in the moon-toothed degu, Octodon lunatus


Abstract and Figures

The evolution of sociality across octodontid rodents remains puzzling Although basal species are solitary living, the most derived octodontids studied so far are social, implying that sociality evolved recently from solitaryliving ancestors. However, the social behavior of some octodontids remains anecdotal. We aimed to provide the 1st systematic data on activity, space use, and social behavior of the moon-toothed degu (Octodon lunatus), a derived octodontid rodent. We used livetrapping and radiotelemetry to monitor patterns of aboveground activity, aboveground range areas and overlap, and use of resting locations in a coastal population in north-central Chile. Activity of O. lunatus was statistically similar during nighttime and daytime, implying no clear diurnal or nocturnal activity. During daytime the animals used resting locations that were associated with high shrub cover and Pouteria splendens. Radiocollared males and females shared resting locations on multiple occasions. There was a nonsignificant trend in degus that used same resting locations to exhibit greater range overlap than degus using different resting locations. Associations based on resting locations revealed a total of 5 social groups. Taken together, these results indicate that adult O. lunatus exhibit some sociality, a finding consistent with a trend in which group living is more frequent in the most derived compared with basal octodontids.
Content may be subject to copyright.
BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research
libraries, and research funders in the common goal of maximizing access to critical research.
Activity, overlap of range areas, and sharing of resting locations in the moon-
toothed degu, Octodon lunatus
Author(s): Raúl Sobrero , Álvaro Ly Prieto , and Luis A. Ebensperger
Source: Journal of Mammalogy, 95(1):91-98. 2014.
Published By: American Society of Mammalogists
BioOne ( is a nonprofit, online aggregation of core research in the biological, ecological, and
environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published
by nonprofit societies, associations, museums, institutions, and presses.
Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of
BioOne’s Terms of Use, available at
Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries
or rights and permissions requests should be directed to the individual publisher as copyright holder.
Journal of Mammalogy, 95(1):91–98, 2014
Activity, overlap of range areas, and sharing of resting locations in the
moon-toothed degu, Octodon lunatus
Departamento de Ecolog´
ıa, Facultad de Ciencias Biol ´
ogicas, Pontificia Universidad Cat ´
olica de Chile, Casilla 114-D,
Santiago, Chile
The evolution of sociality across octodontid rodents remains puzzling. Although basal species are solitary living,
the most derived octodontids studied so far are social, implying that sociality evolved recently from solitary-
living ancestors. However, the social behavior of some octodontids remains anecdotal. We aimed to provide the
1st systematic data on activity, space use, and social behavior of the moon-toothed degu (Octodon lunatus), a
derived octodontid rodent. We used livetrapping and radiotelemetry to monitor patterns of aboveground activity,
aboveground range areas and overlap, and use of resting locations in a coastal population in north-central Chile.
Activity of O. lunatus was statistically similar during nighttime and daytime, implying no clear diurnal or
nocturnal activity. During daytime the animals used resting locations that were associated with high shrub cover
and Pouteria splendens. Radiocollared males and females shared resting locations on multiple occasions. There
was a nonsignificant trend in degus that used same resting locations to exhibit greater range overlap than degus
using different resting locations. Associations based on resting locations revealed a total of 5 social groups.
Taken together, these results indicate that adult O. lunatus exhibit some sociality, a finding consistent with a
trend in which group living is more frequent in the most derived compared with basal octodontids.
Key words: group living, nesting site, Octodon, range area, range overlap, space use
Ó2014 American Society of Mammalogists
DOI: 10.1644/13-MAMM-A-144.1
Most available data and theory developed to explain how
sociality (or group living) evolved in rodents come from the
study of a sample of taxonomic groups, typically from African
mole-rats (Bathyergidae) and North American squirrels and
marmots (Sciuridae—Ebensperger 2001). Evolutionary trends
in African bathyergids that generally support sociality and
cooperation during breeding are the consequence of ecological
restrictions associated to foraging and dispersal (Faulkes and
Bennett 2013). Sociality measures are associated with variation
in mean abundance and variation of food resources across
bathyergids (Faulkes et al. 1997). In contrast, life history may
have played a greater role in ecological constraints among
sciurids. In particular, sociality in sciurids seems associated
with the time required by the offspring to reach sexual maturity
and independence (Blumstein and Armitage 1998), implying
that sociality in these rodents is driven by life-history, species-
specific–level attributes. This potential difference in the
importance of ecology and life history as social drivers in
bathyergids and sciurids may, to some extent, reflect a focus on
single-hypothesis–driven studies. Collectively, however, these
studies highlight how sociality may be driven by multiple
factors (Ebensperger 2001). Clearly then, studies on the
sociality of other rodent clades are needed before strong
generalizations about these traits are made.
One potentially informative group of rodents to determine
the relative roles of ecological conditions and intrinsic, species-
specific attributes as drivers of social evolution are the
caviomorph (New World hystricognaths) rodents (e.g., guinea
pigs, degus, and viscacha rats—Ebensperger 1998; Tang-
ınez 2003). Intriguingly, both ecological conditions and
species-specific traits seem implied in caviomorph social
evolution (Lacher 1981; Rowe and Honeycutt 2002; Trillmich
et al. 2004). On the one hand, examination of data available on
6 caviomorph species shows that group size covaries with
differences in the abundance of food resources, flooded areas,
and predation risk within species (Maher and Burger 2011),
implying a role for ecological conditions. Across species,
however, variation in group size seems associated with
differences in body size, activity time, and the habit of digging
burrows when phylogeny is taken into account. These
associations support a role for predation risk (Ebensperger and
Blumstein 2006), but also for species-specific attributes. This
last alternative is further supported by comparative analyses
showing a nonsignificant association between habitat condi-
tions and sociality (Rowe and Honeycutt 2002).
Within caviomorphs, the octodontids (Octodontidae) consist
of 13 currently recognized species that are ecologically and
taxonomically diverse (Woods and Kilpatrick 2005). Although
3 species basal to the clade are solitary living, the most derived
octodontids studied so far are social (Lacey and Ebensperger
2007), implying that sociality evolved relatively recently from
solitary-living ancestors. However, data for some octodontids,
including derived species, remain anecdotal (Woods and
Kilpatrick 2005; Gallardo et al. 2007; Ojeda et al. 2013). Four
species comprise the Octodon derived clade, including the
degu (O. degus), a social and communally rearing species
(Ebensperger et al. 2004; Hayes et al. 2009). In contrast, the
social behavior of the other 3 species, the moon-toothed degu
(O. lunatus), Bridges’s degu (O. bridgesi), and the Pacific degu
(O. pacificus), remain virtually unknown (Woods and Kilpa-
trick 2005). The social behavior of O. lunatus remains critical
to determine whether ecological conditions and species-
specific attributes drove the evolution of group living in the
octodontids. The scarce available evidence suggests that O.
lunatus is restricted to rocky and highly dense coastal shrub
lands (Glanz and Meserve 1982; Contreras et al. 1987), does
not build underground burrows, and is suspected to be
nocturnally active (Ocampo-Garc´
es et al. 2003). These
ecological features of O. lunatus contrast with those of O.
degus, a species that forages in more open, unprotected areas
during daytime, and actively builds underground burrows.
Habitat openness has been shown to predict sociality in
relatively large terrestrial and marine mammals (Brashares et
al. 2000; Gygax 2002; Caro et al. 2004). However, the use of
unprotected habitat in terms of overhead cover is not strongly
associated with social living across species of caviomorph
rodents (Ebensperger and Blumstein 2006). Instead, social
behavior in these rodents seems associated with diurnality, as
well as the habit of actively digging burrows, with the
exception of capybaras (Herrera et al. 2011). Thus, the extent
to which O. lunatus exhibits sociality and remains active
during daytime may shed light on the roles of habitat cover,
aboveground activity, and burrow digging in shaping the
evolution of group living across the octodontids. In particular,
the apparently nocturnal activity, the absence of active burrow
digging, and the use of highly dense (with considerable
overhead cover) habitat predict a relatively low extent of
sociality in O. lunatus. Based on these considerations, we
predict that O. lunatus exhibits minimal range overlap and
minimal sharing of nest sites, 2 measures of sociality in
Study population.—Observations were made near the coastal
town of Los Molles, Chile (328130S, 718310W; Fig. 1) in 2010
and 2011. Los Molles is a semiarid, Mediterranean location
where annual rainfall does not exceed 300 mm and the ambient
temperature averages 14.48C (Mu˜
noz et al. 1996; Luebert and
Pliscoff 2006). The habitat used by O. lunatus is described as
complex, with patches of shrubs, grasses, and rocks (Luebert
and Pliscoff 2006). During 2010 and 2011 we used 5 randomly
placed 50-m transects and determined that shrub cover
averaged 54% 6SE 1.50% and grass cover averaged 41%
61.36%. The extent of bare ground was low and averaged
3% 60.49% and slab rock areas averaged 2% 60.24%. The
dominant plant species were Pouteria splendens (l ´
Bahia ambrosioides (manzanilla cimarrona), and Lithraea
caustica (litre). The total area examined at Los Molles was
nearly 15 ha and did not vary during the years of our study.
Initial trapping and radiotagging.—Animal trapping and
handling followed the guidelines of the American Society of
Mammalogists (Sikes et al. 2011). We used 13 days in 2010
and 14 days in 2011 to trap and radiocollar adult-sized
(assessed from body mass) male and female O. lunatus. During
the study period, the total number of traps used in 2010 and
2011 was 232 and 194, respectively. Animals were captured
using 14 314 340-cm Tomahawk traps (model 201;
Tomahawk Live Trap Company, Hazelhurst, Wisconsin).
Based on previous information, we placed traps inside
patches with high shrub cover and baited them with rolled
oats, fruity cereals, and sunflower seeds. We shifted traps to
adjacent areas (with similarly high cover of shrubs) if no
animals were trapped during 3 consecutive days. Traps were
opened near sunset (2000 h) and closed during early morning
FIG.1.—Known distribution of moon-toothed degu (Octodon
lunatus; gray shading) according to Contreras et al. (1987), Mares and
Ojeda (1982), Gallardo et al. (2007), and Ojeda et al. (2013); the cross
symbol indicates the location of the study site near Los Molles, Chile
(328140S, 718330W, elevation ¼33.58 m).
92 Vol. 95, No. 1
(0600 h). For each capture, we recorded sex, body mass, and
reproductive condition (e.g., whether females were perforate,
pregnant, or lactating), and each animal was assigned a unique
identification number. Upon 1st capture, each animal was
marked with ear tags (Monel 1005-1; National Band and Tag
Co., Newport, Kentucky). We used 2 ear tags (with identical
identification codes) because this minimized the probability
that an animal would lose both tags during the study period. In
addition, all adult-sized individuals were fitted with a
radiocollar weighing 7–9 g (RI-2D; Holohil Systems
Limited, Carp, Ontario, Canada; SOM-2190A and BR
radiocollars; AVM Instrument Co., Colfax, California) with
unique pulse frequencies. At the end of our study all
radiocollared animals were recaptured and radiocollars were
Temporal pattern of activity.—Moon-toothed degus are
reportedly nocturnal; however, this statement is based on
laboratory observations of a single individual (Ocampo-Garc´
et al. 2003). Thus, we recorded locations of all radiocollared
animals for a total of 3 days and 4 nights in 2010 and 3 days
and 4 nights in 2011. We recorded locations of collared degus
each hour between 2100 and 0700 h (nighttime) and between
0700 and 2100 h (daytime). Sunrise occurred at approximately
0630 h, whereas sunset occurred around 2030 h. Daily patterns
of activity were monitored using triangulation (Kenward
2001). We used 2 LA 12-Q receivers, each connected to a
null peak antenna system (AVM Instrument Co.). Every null
peak system had four 7-element yagi antennas. Distance
between antenna stations was about 120 m. To ensure
independence of data points (Swihart and Slade 1985;
Kenward 1987), intervals between fixes were approximately
1 h. Every hour, two 2-observer teams simultaneously recorded
bearings of every radiocollared subject (658) using the same
previously defined subject sequence. Bearings from both
antenna stations were then transformed into x–y locations
with the software Locate II (Nams 1990). Data points for each
degu were then mapped using the 95% minimum convex
polygon algorithm of the software Ranges 6 (Kenward et al.
Determination of social groups.—The main criterion used to
assign moon-toothed degus to social groups was the sharing of
resting locations (i.e., putative nest places). Given that activity
seemed lower during afternoon hours (see ‘‘ Results’’; Fig. 2),
the sharing of resting locations was inferred from trapping and
telemetry at this time. We defined resting location as areas of
4–9 m
covered by shrub vegetation, with signs of O. lunatus
(i.e., feces or dust-bathing spots) and where radiocollared
individuals were repeatedly found during daytime telemetry
and daytime trapping. The total number of resting locations
trapped per year at Los Molles was 8 in 2010 and 11 in 2011.
These areas were trapped for 13 consecutive days during late
November–early December 2010 and 14 consecutive days
during November 2011. Ten traps (Tomahawk model 201;
Tomahawk Live Trap Company) were used per day at each
resting location. Typically, traps were placed at locations with
putative evidence of O. lunatus, including runways and dust-
bathing spots. Traps were baited with rolled oats, fruity cereals,
and sunflower seeds, opened at sunset (2000 h), and closed in
the early morning (0600 h).
During 1700–1800 h, all radiocollared animals were radio-
tracked to their putative resting locations. We determined
resting locations with an LA 12-Q receiver (for radiocollars
tuned to 150.000–151.999 MHz frequency; AVM Instrument
Co., Colfax, California) and a handheld, 3-element yagi
antenna (AVM instrument Co., Colfax, California). On
average, 2 observers required 40 min to track all radiocollared
animals. Once located, the position of each animal was marked
with flagging material coded for individual animals. Each
radiofix location was then referenced twice with a Garmin
portable global positioning system (Garmin International Inc.,
Olathe, Kansas). The precision of global positioning system
readings was always within 5 m.
The determination of group composition required the
compilation of a symmetric similarity matrix of pairwise
association of the resting locations of all adult moon-toothed
degus during trapping and telemetry (Whitehead 2008). We
determined the association (overlap) between any 2 individuals
by dividing the number of evenings that these individuals were
captured at or tracked with telemetry to the same nesting area
by the number of evenings that both individuals were trapped
or tracked with telemetry on the same day (Ebensperger et al.
2004). To determine social group composition, we conducted
hierarchical cluster analysis of the association matrix in
SOCPROG software (Whitehead 2009).
To determine whether individuals assigned to the same
resting location also were socially cohesive when active, we
monitored patterns of space use by radiocollared animals. In
particular, we examined the prediction that spatial overlap of
range areas between individuals assigned to the same resting
location would be larger than overlap between individuals
assigned to different resting locations. The range area of each
radiocollared degu was determined from locations recorded
FIG.2.—Mean (61SE) distance moved (m) since previous scan of
moon-toothed degus (Octodon lunatus) monitored every 1 h for 6 days
and 8 nights at Los Molles, Chile. A total of 8 adult degus were
recorded in 2010 and 12 more degus were studied in 2011. Black bars
at the top of graphs indicate night hours.
February 2014 93
through triangulation during nighttime. Data points from each
individual were mapped using the 95% minimum convex
polygon algorithm in Ranges 6 (Kenward et al. 2003). Pairwise
estimates of the percent overlap between polygons for different
females also were calculated using Ranges 6.
Habitat and resting locations.—Resting locations (i.e.,
putative nest sites) always were located near the base of
shrubs and under the cover of dominant shrubs. Thus, for every
resting location (recorded to have been used by at least 1
radiocollared degu), we established 2 transects in a crossed
design and where each resting site corresponded to the
intersection point; these transects had north–south and east–
west orientations. We estimated the amount of overhead shrub
cover and recorded the maximum vegetation height (in m),
covering 1 m
of ground area. Soil penetrability as an index of
soil hardness (Ebensperger et al. 2012) was recorded at 1, 3,
and 5 m from the intersection point in the north–south and
east–west cardinal directions. These measures were taken with
the use of a handheld soil compaction meter (Lang
Penetrometer Inc., Gulf Shores, Alabama), and units were
transformed to kilopascals. These measures were averaged per
resting location before further analysis.
Data analyses.—We calculated distance between successive
scans as a measure of aboveground activity of the moon-
toothed degu. For each animal we calculated distance traveled
(in m) between each pair of successive scans. The same
individuals were monitored throughout consecutive days and
nights within each study year. As a result, locations recorded at
24-h intervals were not independent of one another.
Consequently, and for statistical analyses, we divided the
entire data collection period into 3 day and 4 night cycles,
defined on the basis of sunrise and sunset at each study site. For
the daytime portion of each activity cycle, we calculated the
mean distance travelled for each radiocollared individual
within each study year. We used a similar approach for the
nighttime portion of the activity cycle. As a result, each
radiocollared individual contributed 2 dependent data points to
our analysis of activity. We used repeated-measures analysis of
variance to examine the effect of activity time (day versus
night) on individual activity of females. Because activity of
individuals from the same resting locations may not be
statistically independent, the effect of group identification
was included in a preliminary analysis. Given that this analysis
revealed a statistically significant effect of group identification
(not reported), we conducted a subsequent analysis in which
activity of animals from the same resting locations was
averaged. Only females were included in this analysis because
only a single male was radiocollared during 2010. For
comparative purposes, we also examined how male activity
differed between daytime and nighttime during 2011.
We compared the mean size (in m
) of range areas and
percent range overlap by male and female moon-toothed degus
with Mann–Whitney U-tests. We used the relationship between
home-range size and the number of observation days to
determine sampling saturation (Quirici et al. 2010). Then we
used Wilcoxon matched-pair tests to compare percent overlap
in range areas of individuals assigned to the same resting
location associations and percent overlap that these individuals
had with individuals assigned to different associations in 2011.
We used Spearman rank correlation analysis to examine
potential associations between the number of degus that used
each resting location and plant cover, maximum vegetation
height, and soil hardness. We used the Dunn–Sidak correction
to prevent inflation of type I statistical error during these
explorative analyses.
All statistical analyses were calculated using Statistica 7.0
(StatSoft Inc. 1984–2004), Prism 5.0 (GraphPad Software Inc.
1992–2007), and Minitab 14.2 (Minitab Inc. 2005). Data are
reported as mean 6SE. All tests were 2-tailed, and unless
stated differently, we considered a significant difference at P,
Characteristics of radiocollared animals and trapping
effort.—A total of 44 adults (27 females and 17 males) and
13 juveniles (7 females and 6 males) were captured or
recaptured during this study. Overall, the number of captures–
recaptures per degu averaged 3.23 60.70 during 2010 and
5.48 60.61 during 2011. Eleven of the females trapped were
lactating, confirming breeding activity. A total of 20 adult-
sized individuals (2010: 7 females 169 618 g, and 1 male 128
g; 2011: 8 females 169 68 g, and 4 males 187 69 g) were
fitted with radiocollars.
Temporal pattern of activity.—Aboveground activity
recorded as distance moved between radioscans was variable
through time of day or night (Fig. 2). Although female activity
recorded during nighttime ( ¯
X6SE ¼216 690 m, range: 4–
1,571 m, n¼12) was 1.6 times greater than activity recorded
during daytime ( ¯
X6SE ¼136 667 m, range: 4–1,786 m, n¼
12), this difference was not statistically significant (F
P¼0.223). Likewise, the difference in male activity between
nighttime ( ¯
X6SE ¼374 6200 m, range: 20–1,521 m, n¼4)
and daytime ( ¯
X6SE ¼209 6122 m, range: 12–888 m, n¼4)
recorded in 2011 was not statistically significant (F
¼3.01, P
Resting locations and social groups.—We monitored 7
females and 1 male, and 8 females and 4 males during 2010
and 2011, respectively. A total of 24 radiotelemetry scan
sessions (2010: 10 sessions; 2011: 14 sessions) were completed
during daylight hours and used to assign radiotagged subjects
to resting locations. Daytime trapping of resting locations and
daytime telemetry revealed that animals used from 1 to 3
different resting locations ( ¯
X6SE ¼1.8 60.2; number of the
used nests ¼13), namely locations where an animal was found
repeatedly during 2 or more scans.
During 2010 we recorded 2 females using the same resting
place during the day on only 2 occasions. In contrast, during
2011 we recorded 45 occasions in which animals shared resting
locations. Of these, 27 observations involved male–female
pairs, 12 were female–female pairs, 1 involved 2 male–2
female associations, 4 involved 1 male–2 female associations,
94 Vol. 95, No. 1
and 1 involved 1 male–3 female associations. Provided that
resting location associations represent truly social groups, we
identified 1 social group in 2010 and 4 groups in 2011. Social
groups ranged from 2 to 4 adults throughout the study. Groups
contained 1–3 females and 1 or 2 males.
Range areas and overlap.—During 2010 and 2011, male
range areas (237,360 6158,780 m
,n¼5) were 2.4 times
larger than female range areas (100,833 647,203 m
although this difference was not statistically significant (Mann–
Whitney U-test, U¼23.00, P¼0.223; Fig. 3). When only
radiocollared females were considered, the size of 95%
minimum convex polygons did not differ between years
(2010: 85,743 636,909 m
,n¼7; 2011: 114,038 690,546
,n¼8; Mann–Whitney U-test, U¼22.00, P¼0.536).
Sampling saturation was recorded upon 3 days of observation
in 2010 and 2011. These findings suggested that range areas
recorded during the 2 years of study were appropriate estimates
of the true range areas of O. lunatus.
Range overlap among males with any other radiocollared
subject (20.68% 614.02%) was similar to that recorded in
females (14.69% 66.84%; Mann–Whitney U-test, U¼5,382,
P¼0.085). During 2011, a marginally significant difference
(Wilcoxon matched-pairs test, Z¼1.82, P¼0.068; Fig. 4)
indicated that overlap between range areas of degus assigned to
the same resting locations (61.9% 67.3%) tended to be
greater than overlap between range areas of degus assigned to
different resting locations (22.5 61.2, n¼4 social groups).
Characterization of resting locations.—A total of 13 resting
locations (putative nests) were identified during 2010 and
2011. Plant cover across all resting locations averaged 98.5%
61.0%, n¼13). Maximum shrub height averaged 3.5 6
0.2 m (n¼13), and soil hardness averaged 2,679.4 656.4 kPa
(n¼13). There was not a statistically significant association
between the number of degus that used each resting location
and plant cover (r
¼0.000, P¼1.000), maximum vegetation
height (r
¼0.140, P¼0.647), or soil hardness (r
¼0.383, P¼
ucumo (P. splendens) was present in 9 (60%) of 13 resting
locations, with a height that averaged 3.6 60.2 m (n¼9).
Resting locations included other plant species, such as Puya
chilensis and Escallonia pulverulenta. Rock outcroppings were
present in 2 of 13 resting locations.
Our results do not support previous claims describing
activity of O. lunatus as exclusively nocturnal (D´
ıaz 1999;
es et al. 2003; Begall 2005; Mu˜
noz-Pedreros et
al. 2010). In contrast, these results support other studies that
suggest that O. lunatus is active during daytime and nighttime
(Torres-Contreras et al. 1994; Jaksic et al. 1997; Mu ˜
Pedreros 2000). A more continuous pattern of activity
throughout the day and night in these rodents may be the
consequence of relatively stable microclimatic conditions.
Stable conditions may result from relatively high shrub cover
(e.g., Jensen et al. 2003), and from the relatively low thermal
amplitude due to ocean influence.
Relative to the range areas of similar-sized O. degus (Hayes
et al. 2007), O. lunatus exhibited extensive range areas, where
polygons generally matched the spatial distribution of shrub
patches (Fig. 3). Although several factors may contribute to
determining range areas in rodents (e.g., Getz et al. 2005),
overhead plant cover is likely to be the ultimate, major factor in
moon-toothed degus. Relatively high and continuous shrub
cover conditions likely provide O. lunatus with cover from
visual predators, stable microclimate, preferred food, and
appropriate nesting sites. Spatial and temporal variation in
these resources (e.g., food) or conditions should be examined
to determine how these predict the size of range areas in these
Both the sharing of resting locations and overlap of range
areas indicated these animals are social to some extent.
Pending studies aimed to confirm that sharing of resting
locations and range areas translate into communal nesting and
other affiliative aspects of group-living, social behavior of O.
lunatus seems intermediate between that of solitary (Mares et
al. 1997; Ebensperger et al. 2008) and highly social
(Ebensperger et al. 2004; Lacey and Ebensperger 2007)
octodontids studied so far. These findings represent an
FIG.3.—Range areas (95% minimum convex polygons) of the
moon-toothed degu (Octodon lunatus) recorded during a) 2010 (n¼8)
and b) 2011 (n¼12). Dashed lines represent adult males. Identical
colors are used to label individuals assigned to the same social groups
based on daytime telemetry and resting location trapping. The arrow
indicates geographic north.
FIG.4.—Mean (6SE) overlap in range areas between degus
(Octodon lunatus) assigned to the same or different social groups.
February 2014 95
important piece of information in the evolution of sociality in
octodontids, because they confirm the generally social nature
of the most derived octodontids compared with basal species
studied so far. Thus, differences in sociality across octodontids
are consistent with the pattern of social living in these animals
evolving relatively recently from solitary-living ancestors.
The amount of plant overhead cover has been linked to
sociality, with relatively large terrestrial mammals generally
being social in open habitats (Brashares et al. 2000; Caro et al.
2004). Group living would confer survival benefits in open,
more risky environments through several mechanisms, includ-
ing dilution or improved predator detection (Ebensperger 2001;
Krause and Ruxton 2002). In contrast, social living across
species of caviomorph rodents seems more associated with
diurnal activity and the habit of actively digging burrows
(Ebensperger and Blumstein 2006). The observation that social
O. lunatus uses habitats with relatively high plant overhead
cover remains inconsistent with the hypothesis that predation
risk drives social behavior in this species. Subsequent
comparative analyses are needed to determine the extent to
which this mismatch between the social phenotype and
ecological conditions in terms of predation risk represents
phylogenetic inertia.
Caviomorph rodents are known to exhibit intraspecific
differences in social systems that generally correlate with
variation in ecology (Maher and Burger 2011). Subsequent
studies are then needed to determine the extent to which social
behavior in O. lunatus may vary with density or other
ecological conditions, as shown in other rodents (Wolff
1994; Randall et al. 2005). In particular, the social behavior
of O. lunatus at Los Molles may be compared with that of O.
lunatus from Lago Pe˜
nuelas National Reserve, and where
abundance of this species seems lower based on the number of
captures reported there (Mu˜
noz-Pedreros et al. 2010).
In summary, our study yields insights into previously
unknown aspects of behavior, including general activity,
spatial ecology, and social behavior of O. lunatus. These
rodents exhibit locomotor activity during daytime and
nighttime and use 1 or more resting locations associated with
high shrub cover. The sharing of resting locations and overlap
of range areas support the idea that these rodents are to some
extent social compared with solitary and highly social
Nuestro conocimiento sobre la evoluci ´
on del comportamien-
to social en roedores octod ´
ontidos es a´
un fragmentario. La
on disponible indica que las especies filo-
eticamente basales son solitarias, mientras que las ma´s
derivadas tienden a ser sociales. Sin embargo, la informaci ´
sobre la estructura social disponible para varias especies es
otica, lo cual dificulta el establecimiento de conclusiones
robustas sobre la evoluci ´
on del comportamiento social en este
clado. Este es el primer estudio que cuantifica la actividad, uso
del espacio, y comportamiento social del deg´
u costino
(Octodon lunatus), una especie derivada de octod ´
Durante noviembre y diciembre de 2010 y 2011 se utilizaron
etodos de captura–recaptura y telemetr´
ıa para cuantificar el
on diario de actividad superficial, a´mbitos de hogar,
solapamientos entre a´mbitos de hogar, y uso compartido de
parches de descanso y nidificaci ´
on en una poblaci´
on costera
localizada en el centro-norte de Chile. La actividad de O.
lunatus, medida como desplazamientos individuales entre
localizaciones consecutivas, mostr ´
o una tendencia estad´
mente no significativa a ser mayor en horas de la noche.
Durante el d´
ıa los animales usaron 1 a 3 sitios de descanso y
anidamiento asociados con una alta cobertura arbustiva, donde
Pouteria splendens (l´
ucumo) fue la especie dominante. Machos
y hembras compartieron estos sitios de descanso en m ´
ocasiones. El solapamiento entre los a´mbitos de hogar tendi´
ser mayor en animales que adema´s compartieron sitios de
descanso comparado con animales que no compartieron estos
sitios. En base al uso compartido de refugios se identific ´
grupo social en 2010 y 4 grupos en 2011. La composici ´
on de
estos grupos fue de 1 a 3 hembras adultas y de 1 a 2 machos
adultos (2 a 4 adultos en total). Globalmente, los resultados
indicaron que O. lunatus muestra alg ´
un grado de sociabilidad,
on que apoya una tendencia en la cual el comporta-
miento social es ma´s frecuente en especies filogen´
derivadas de octod´
We especially thank V. Lahoz, who recently passed, for her
professional field assistance. We are very thankful to our colleagues
M. Palma, D. Rivera, and F. Vargas for field assistance. We also thank
L. D. Hayes for providing the Holohil radiocollars used in 2010. Two
anonymous reviewers made useful suggestions to improve a previous
version of this article. This study was supported partially by
FONDECYT grant 1090302 to LE, the Program 1 of Centro de
Estudios Avanzados en Ecolog´
ıa and Biodiversidad (FONDAP 1501-
001), and Chile government CONICYT doctoral fellowship (RS). A
research grant was provided by the IDEAWILD Foundation (RS). All
procedures that involved handling of live animals were approved by
the Pontificia Universidad Cat´
olica de Chile Bioethical Committee
(CBB-042/2011) and adhered to Chilean laws (permits 1-154.2010
[7989] and 1-109.2011 [6749] by the Servicio Agr´
ıcola y Ganadero).
BEGALL, S. 2005. The relationship of foraging habitat to the diet of
barn owls (Tyto alba) from central Chile. Journal of Raptor
Research 39:97–101.
BLUMSTEIN,D.T.,AND K. B. ARMITAGE. 1998. Life history
consequences of social complexity: a comparative study of
ground-dwelling sciurids. Behavioral Ecology 9:8–19.
BRASHARES, J., T. GARLAND,JR., AND P. ARCESE. 2000. Phylogenetic
analysis of coadaptation in behavior, diet, and body size in the
African antelope. Behavioral Ecology 11:452–463.
Adaptative significance of antipredador behaviour in artiodactyls.
Animal Behaviour 67:205–228.
EZ. 1987.
Biogeography of octodontid rodents: an eco-evolutionary hypoth-
esis. Fieldiana: Zoology 39:401–411.
96 Vol. 95, No. 1
´AZ, I. 1999. Food habits of the rufous-legged owl (Strix rufipes)in
the Mediterranean sclerophyllous forest of central Chile. Journal of
Raptor Research 33:260–264.
EBENSPERGER, L. A. 1998. Sociality in rodents: the New World
fossorial hystricognaths as study models. Revista Chilena de
Historia Natural 71:65–77.
EBENSPERGER, L. A. 2001. A review of the evolutionary causes of
rodent group-living. Acta Theriologica 46:115–144.
EBENSPERGER, L. A., AND D. T. BLUMSTEIN. 2006. Sociality in New
World hystricognath rodents is linked to predators and burrow
digging. Behavioral Ecology 17:410–418.
AND A. T. CHANG. 2004. Communal nesting and kinship in degus
(Octodon degus). Naturwissenschaften 91:391–395.
2008. Activity, range areas, and nesting patterns in the viscacha rat,
Octomys mimax: implications for its social organization. Journal of
Arid Environments 72:1174–1183.
EBENSPERGER, L. A., ET AL. 2012. Ecological drivers of group living in
two populations of the communally rearing rodent, Octodon degus.
Behavioral Ecology and Sociobiology 66:261–274.
FAULKES, C. G., AND N. C. BENNETT. 2013. Plasticity and constraints on
social evolution in African mole-rats: ultimate and proximate
factors. Philosophical Transactions of the Royal Society, B.
Biological Sciences doi:10.1098/rstb.2012.0347
AGUILAR,AND J. U. M. JARVIS. 1997. Ecological constraints drive
social evolution in the African mole-rats. Proceedings of the Royal
Society, B. Biological Sciences 264:1619–1627.
2007. The Octodontidae revisited. Pp. 695–719 in The quintessen-
tial naturalist: honoring the life and legacy of Oliver P. Pearson (D.
A. Kelt, E. P. Lessa, J. Salazar-Bravo, and J. L. Patton, eds.).
University of California Publications in Zoology 134:1–988.
2005. Factors influencing movement distances of two species of
sympatric voles. Journal of Mammalogy 86:647–654.
GLANZ, W. E., AND P. L. MESERVE. 1982. An ecological comparison of
the small mammal communities in California and Chile. Pp. 220–
226 in Dynamics and management of Mediterranean type
ecosystems (C. E. Conrad and W. C. Oechel, eds.). United States
Department of Agriculture and Forest Service, General Technical
Report PSW-58:1–637.
GRAPHPAD SOFTWARE INC. 1992–2007. Prism 5.0. GraphPad Software
Inc., La Jolla, California.
GYGAX, L. 2002. Evolution of group size in the dolphins and
porpoises: interspecific consistency of intraspecific patterns.
Behavioral Ecology 13:583–590.
HAYES, L. D., A. S. CHESH,AND L. A. EBENSPERGER. 2007. Ecological
predictors of range areas and use of burrow systems in the diurnal
rodent, Octodon degus. Ethology 113:155–165.
HAYES, L. D., ET AL. 2009. Fitness consequences of group-living in the
degu (Octodon degus), a plural breeder rodent with communal care.
Animal Behaviour 78:131–139.
INEZ. 2011. Capybara social structure and dispersal
patterns: variations on a theme. Journal of Mammalogy 92:12–20.
ERREZ. 1997. A
long-term study of vertebrate predator responses to an El Ni ˜
(ENSO) disturbance in western South America. Oikos 78:341–354.
JENSEN, S. P., S. J. GRAY,AND J. L. HURST. 2003. How does habitat
structure affect activity and use of space among house mice?
Animal Behaviour 66:239–250.
KENWARD, R. E. 1987. Wildlife radio tagging: equipment, field
techniques and data analysis. Academic Press, London, United
KENWARD, R. E. 2001. A manual for wildlife radio tagging. Academic
Press, San Diego, California.
KENWARD, R. E., A. B. SOUTH,AND S. S. WALLS. 2003. Ranges 6,
version 1.2: for the analysis of tracking and location data. Anatrack
Ltd., Wareham, United Kingdom.
KRAUSE, J., AND G. D. RUXTON. 2002. Living in groups. Oxford
University Press, Oxford, United Kingdom.
LACEY, E. A., AND L. A. EBENSPERGER. 2007. Social structure in
octodontid and ctenomyid rodents. Pp. 403–415 in Rodent
societies: an ecological and evolutionary perspective (J. O. Wolff
and P. W. Sherman, eds.). University of Chicago Press, Chicago,
LACHER, T. E., JR. 1981. The comparative social behavior of Kerodon
rupestris and Galea spixii and the evolution of behavior in the
Caviidae. Bulletin of Carnegie Museum of Natural History 17:1–71.
LUEBERT,F.,AND P. PLISCOFF. 2006. Sinopsis bioclima´tica y
vegetacional de Chile. Editorial Universitaria, Santiago, Chile.
MAHER, C. R., AND J. R. BURGER. 2011. Intraspecific variation in space
use, group size, and mating systems of caviomorph rodents. Journal
of Mammalogy 92:54–64.
MARES, M. A., J. K. BRAUN,AND R. CHANNELL. 1997. Ecological
observations on the octodontid rodent, Tympanoctomys barrerae,in
Argentina. Southwestern Naturalist 42:488–504.
MARES, M. A., AND R. A. OJEDA. 1982. Patterns of diversity and
adaptation in South American hystricognath rodents. Pp. 393–432
in Mammalian biology in South America (M. A. Mares and H. H.
Genoways, eds.). Special Publication 6, Pymatuning Laboratory of
Ecology, University of Pittsburgh, Linesville, Pennsylvania.
MINITAB INC. 2005. Minitab 14.2. Minitab Inc., State College,
NOZ, M., H. N ´
NEZ. 1996. Libro rojo de los sitios
prioritarios para la conservaci´
on de la diversidad biol´
Ministerio de Agricultura, Corporaci´
on Nacional Forestal, Santiago,
NOZ-PEDREROS, A. 2000. Orden Rodentia. Pp. 73–126 in Mam´
de Chile (A. Mu˜
noz-Pedreros and J. Ya´ ˜
nez, eds.). CEA Ediciones,
Valdivia, Chile.
´NCHEZ. 2010.
Diversidad de micromam´
ıferos en tres ambientes de la Reserva
Nacional Lago Pe˜
nuelas, Regi´
on de Valpara´
ıso, Chile. Gayana
(Chile) 74:1–11.
NAMS, V. O. 1990. Locate II user’s guide. Pacer Computer Software,
Tatamagouche, Nova Scotia, Canada.
Octodon lunatus: a nocturnal octodontid of northern Chile. Sleep
NENT. 2013.
Geographical distribution and ecological diversification of South
American octodontid rodents. Journal of Zoology 289:285–293.
QUIRICI, V., ET AL. 2010. Seasonal variation in the range areas of the
rodent Octodon degus. Journal of Mammalogy 9:458–466.
Flexible social structure of a desert rodent, Rhombomys opimus:
philopatry, kinship, and ecological constraints. Behavioral Ecology
February 2014 97
ROWE, D. L., AND R. L. HONEYCUTT. 2002. Phylogenetic relationships,
ecological correlates, and molecular evolution within the Cavioidea
(Mammalia: Rodentia). Molecular Biology and Evolution 19:263–
the American Society of Mammalogists for the use of wild
mammals in research. Journal of Mammalogy 92:235–253.
STATSOFT INC. 1984–2004. Statistica 7.0. StatSoft Inc., Tulsa,
SWIHART, R. K., AND N. A. SLADE. 1985. Testing for independence of
observations in animal movements. Ecology 66:1176–1184.
INEZ, Z. 2003. Emerging themes and future challenges:
forgotten rodents, neglected questions. Journal of Mammalogy
´NGUIZ,AND F. JAKSIC. 1994. Dieta
y selectividad de presas de Speotyto cunicularia en una localidad
semia´rida del norte de Chile a lo largo de siete a ˜
nos (1987–1993).
Revista Chilena de Historia Natural 67:329–340.
TRILLMICH, F., ET AL. 2004. Species-level differentiation of two cryptic
species pairs of wild cavies, genera Cavia and Galea, with a
discussion of the relationship between social systems and
phylogeny in the Caviinae. Canadian Journal of Zoology 82:516–
WHITEHEAD,H.2008.Analyzinganimal societies: quantitative
methods for vertebrate social analysis. University of Chicago Press,
Chicago, Illinois.
WHITEHEAD, H. 2009. SOCPROG programs: analyzing animal social
structures. Behavioral Ecology and Sociobiology 63:765–778.
WOLFF, J. O. 1994. Reproductive success of solitarily and communally
nesting white-footed and deer mice. Behavioral Ecology 5:206–
WOODS, C. A., AND C. W. KILPATRICK. 2005. Infraorder Hystricognathi.
Pp. 1538–1600 in Mammal species of the world: a taxonomic and
geographic reference (D. E. Wilson and D. M. Reeder, eds.). 3rd ed.
Johns Hopkins University Press, Baltimore, Maryland.
Submitted 31 May 2013. Accepted 25 September 2013.
Associate Editor was Ricardo A. Ojeda.
98 Vol. 95, No. 1
... Octodon degus is a diurnal, open field inhabitant, which exhibits an elaborate sociality, including communal nesting, cooperative burrowing, cooperative surveillance and alarm calls display (Ebensperger & Bozinovic, 2000;Ebensperger et al. 2004Ebensperger et al. , 2006Jesseau et al. 2009, Fulk, 1976Y añez, 1976;Cecchi et al. 2003). Octodon lunatus is a mainly nocturnal shrub inhabitant that is far less social than O. degus (Sobrero et al. 2014). In the field, O. lunatus form small groups consisting of two-four adult individuals, which occasionally share resting areas during daytime. ...
... Unlike O. degus, which have a preference to live in open areas, or savannas, of the mediterranean region of central Chile, O. lunatus is a shrub inhabitant, more frequently observed in the hills of the coastal range of this same region (Glanz & Meserve, 1982;Sobrero et al. 2014). Both species come to coexist, however, inhabiting different patches in xeric or sclerophic landscapes affected by the same climatic regime. ...
... In contrast, O. lunatus individuals do not share burrows nor do they form communal groups or engage in cooperative behaviours. However, males and females exhibit a partial overlap in their household domains, reflecting that social bonds, up to a certain degree, also take place in this species (Sobrero et al. 2014). Such contrasting social behaviours very likely imply differences in the frequency and diversity of the pheromonal interactions that take place during the lifespan of individuals of each species. ...
In mammals, the accessory olfactory or vomeronasal system exhibits a wide variety of anatomical arrangements. In caviomorph rodents, the accessory olfactory bulb (AOB) exhibits a dichotomic conformation, in which two subdomains, the anterior (aAOB) and the posterior (pAOB), can be readily distinguished. Interestingly, different species of this group exhibit bias of different sign between the AOB subdomains (aAOB larger than pAOB or vice versa). Such species-specific biases have been related with contrasting differences in the habitat of the different species (e.g. arid vs. humid environments). Aiming to deepen these observations, we performed a morphometric comparison of the AOB subdomains between two sister species of octodontid rodents, Octodon lunatus and Octodon degus. These species are interesting for comparative purposes, as they inhabit similar landscapes but exhibit contrasting social habits. Previous reports have shown that O. degus, a highly social species, exhibits a greatly asymmetric AOB, in which the aAOB has twice the size of the pAOB and features more and larger glomeruli in its glomerular layer (GL). We found that the same as in O. degus, the far less social O. lunatus also exhibits a bias, albeit less pronounced, to a larger aAOB. In both species, this bias was also evident for the mitral/tufted cells number. But unlike in O. degus, in O. lunatus this bias was not present at the GL. In comparison with O. degus, in O. lunatus the aAOB GL was significantly reduced in volume, while the pAOB GL displayed a similar volume. We conclude that these sister species exhibit a very sharp difference in the anatomical conformation of the AOB, namely, the relative size of the GL of the aAOB subdomain, which is larger in O. degus than in O. lunatus. We discuss these results in the context of the differences in the lifestyle of these species, highlighting the differences in social behaviour as a possible factor driving to distinct AOB morphometries.
... In these environments, O. degus excavate and use burrow systems connected aboveground by runways or trails used during foraging [Fulk, 1976;Lagos et al., 1995;Vásquez et al., 2002]. In contrast, O. lunatus is preferably associated with coastal shrubland, characterized by moist and high vegetative cover [Sobrero et al., 2014]. Compared with O. degus , O. lunatus seems to rely more on vegetation cover to hide from predators instead of building extensive burrow systems or using interconnected runways [Sobrero et al., 2014]. ...
... In contrast, O. lunatus is preferably associated with coastal shrubland, characterized by moist and high vegetative cover [Sobrero et al., 2014]. Compared with O. degus , O. lunatus seems to rely more on vegetation cover to hide from predators instead of building extensive burrow systems or using interconnected runways [Sobrero et al., 2014]. ...
... data], implying a high frequency of social interactions and probably a need for cognitive skills underlying these interactions. In contrast, the social behavior of O. lunatus is less well known, yet a recent study revealed how these rodents live in small social groups that range from 2 to 4 adults [Sobrero et al., 2014]. Therefore, if greater sociality is associated with greater cognitive demands to keep track of individual relationships, we predicted (ii) more social O. degus to exhibit a larger DG volume and density of cells than O. lunatus . ...
Full-text available
Navigational and social challenges due to habitat conditions and sociality are known to influence dentate gyrus (DG) morphology, yet the relative importance of these factors remains unclear. Thus, we studied three natural populations of O. lunatus (Los Molles) and Octodon degus (El Salitre and Rinconada), two caviomorph species that differ in the extent of sociality and with contrasting vegetation cover of habitat used. The brains and DG of male and female breeding degus with simultaneous information on their physical and social environments were examined. The extent of sociality was quantified from total group size and range area overlap. O. degus at El Salitre was more social than at Rinconada and than O. lunatus from Los Molles. The use of transects to quantify cover of vegetation (and other physical objects in the habitat) and measures of the spatial behavior of animals indicated animal navigation based on unique cues or global landmarks is more cognitively challenging to O. lunatus. During lactation, female O. lunatus had larger brains than males. Relative DG volume was similar across sexes and populations. The right hemisphere of male and female O. lunatus had more cells than the left hemisphere, with DG directional asymmetry not found in O. degus. Degu population differences in brain size and DG cell number seemed more responsive to differences in habitat than to differences in sociality. Yet, large-sized O. degus (but not O. lunatus) that ranged over larger areas and were members of larger social groups had more DG cells per hemisphere. Thus, within-population variation in DG cell number by hemisphere was consistent with a joint influence of habitat and sociality in O. degus at El Salitre.
... Accordingly, a detailed assessment of spatial relationships among free-living individuals is needed to determine if cururos are indeed group living and, additionally, if they engage in communal nesting. Clarifying the social organization of this species will contribute significantly to our understanding of the evolution of sociality within the Octodontidae (Rivera et al. 2014;Sobrero et al. 2014) and may reveal a phylogenetically distinct new system for comparative analyses of the adaptive bases for group living in subterranean rodents. ...
... In addition to cururos, other group-living octodontids include common degus (O. degus- Ebensperger et al. 2004), Andean degus (Octodontomys gliroides- Rivera et al. 2014) and, potentially, moon-toothed degus (Octodon lunatus- Sobrero et al. 2014). In contrast, the viscacha rat (Octomys mimax- Ebensperger et al. 2008) and the red viscacha rat (Tympanoctomys barrerae- Mares et al. 1997) are solitary. ...
Full-text available
Spatial relationships among conspecifics can provide insights into numerous aspects of social behavior. Spatial data may be particularly important for characterizing the behavior of difficult-to-study species such as subterranean rodents, direct observations of which are challenging. To characterize the social organization of the cururo (Spalacopus cyanus), a subterranean species in the rodent family Octodontidae, we used radiotelemetry to quantify spatial relationships within populations of this species located in Parque Nacional Bosque Fray Jorge and Santuario de la Naturaleza Yerba Loca, Chile. Specifically, we sought to determine if adults in this diurnal species share burrows and subterranean nests, the two criteria typically used to identify subterranean rodents as social. Analyses of radio fixes collected during February-March 2003 revealed that cururos at both Fray Jorge and Yerba Loca shared nighttime nest sites; cluster analyses of these data identified multiple spatially distinct subsets of adults in each population. Overlap of minimum convex polygons constructed from radio fixes collected during daylight hours suggested burrow sharing by animals in both populations. Cluster analyses of overlap values revealed the same spatially distinct groups of individuals identified from analyses of nest sharing; in addition, these analyses revealed one cluster of animals in each population that was not evident from analyses of nighttime data. Collectively, these results confirm that cururos are social, with adults in both study populations sharing burrow systems and communal nests. Our findings add to the growing understanding of social organization in octodontid rodents and reveal a new system for comparative studies of the ecology and evolution of behavioral variation in burrow-dwelling mammals.
... MCPs are a commonly used method for visualizing the areas occupied by free-living animals (Harris et al. 1990). Although MCPs may overestimate home range size, exclusion of the 5% of data points that are most distant from an individual's centroid of activity (95% MCPs) reduces this tendency and provides a generally robust procedure for determining if the areas used by different animals overlap, as expected in group-living species (Ebensperger et al. 2004;Sobrero et al. 2014). The minimum number of observations allowed per individual was 6, which exceeds the minimum number of data points required by adehabitatHR to construct a home range (Calenge 2015); during each year of the study, most (> 90%) of the individuals for which 95% MCPs were constructed were characterized by > 10 data points ( Table 1). ...
Full-text available
In some species, populations routinely contain a mixture of lone and group-living individuals. Such facultative sociality may reflect individual differences in behavior as well as adaptive responses to variation in local environmental conditions. To explore interactions between individual- and population-level variabilities in behavior in a species provisionally described as facultatively social, we examined spatial and social relationships within a population of highland tuco-tucos ( Ctenomys opimus ) at Laguna de los Pozuelos, Jujuy Province, Argentina. Using data collected over 5 consecutive years, we sought to (1) confirm the regular occurrence of both lone and group-living individuals and (2) characterize the temporal consistency of individual social relationships. Our analyses revealed that although the study population typically contained lone as well as group-living animals, individual spatial and social relationships varied markedly over time. Specifically, the extent to which individuals remained resident in the same location across years varied, as did the number of conspecifics with which an animal lived, with an overall tendency for individuals to live in larger groups over successive years. Collectively, these analyses indicate that population-level patterns of behavior in C. opimus are consistent with facultative sociality but that this variation does not arise due to persistent differences in individual behavior (i.e., living alone versus with conspecifics). Instead, based on changes in spatial and social relationships across years, we suggest that variation in the tendency to live in groups is shaped primarily by local ecological and demographic conditions. Significance statement Characterizing variation in conspecific relationships is critical to understanding the adaptive bases for social behavior. Using data collected over 5 successive years, we examined temporal variation in spatial and social relationships within a population of highland tuco-tucos ( C. opimus ) from northern Argentina. In addition to providing the first multi-year assessment of the behavior and demography of this species, our analyses generate important insights into relationships between individual behavior and population-level patterns of social organization. The behavioral variability evident in our study population suggests that C. opimus is an ideal system in which to explore the causes and consequences of individual differences in social behavior.
... hystricognath rodents, overlap of adult home ranges-particularly between males and females-has been reported for multiple surface-and burrowdwelling species, including wild guinea pigs (Cavia aperea- Asher et al. 2004 Adler et al. 1997). Studies of these taxa have revealed a variety of spatial arrangements, comparisons of which have been used to test hypotheses regarding the roles of ecological and phylogenetic factors in shaping the social biology of these animals (Ebensperger and Cofré 2001;Lacey and Ebensperger 2007;Sobrero et al. 2014). In contrast, truly subterranean rodents, including subterranean hystricognaths, have traditionally been assumed to be solitary (Nevo 1979;Lacey 2000). ...
Despite striking diversity in mammalian social behavior, studies of social organization have often dichotomized species by identifying them as either solitary or social (i.e., group living). This tendency has been particularly pronounced for subterranean rodents, the majority of which have long been assumed to be solitary. As a result, variation in social organization has likely been underestimated for these animals, particularly for species in which patterns of space use suggest limited or temporally dynamic opportunities for interactions among conspecifics. Here, we characterize patterns of space use in a population of tuco-tucos (Ctenomys sp.) from Anillaco, La Rioja Province, Argentina. Although these animals have been the subject of extensive research regarding circadian patterns of activity, spatial and social relationships among free-living individuals have not been documented. Analyses of radiotelemetry data from 17 individuals monitored during the breeding season (December 2015) revealed that partial overlap of individual home ranges was common, occurring between male–female as well as female–female pairs of animals. Spatial relationships, however, were dynamic, with both home range sizes and overlap changing on a daily basis. Although members of the study population did not meet the criteria typically used to identify group living in subterranean species, they were not completely solitary. Instead, the animals displayed an intermediate form of social organization characterized by persistent partial overlap of the areas occupied by different adults. These data add to the growing comparative picture of social variation in Ctenomys and suggest that further studies of these animals should contribute to improved understanding of the factors underlying differences in mammalian social systems.
Full-text available
We provide the first systematic data on behavior and ecology of Aconaemys porteri. We used telemetry to monitor patterns of activity, resting locations, and range areas. Rock rat movements were statistically similar during nighttime and daytime, implying no clear diurnal or nocturnal activity. Animals used from 2 to 9 putative resting locations, but one was used more frequently. Rock rats showed relatively smaller range areas and low to moderate spatial overlap with neighbors, compared to other rodent species. These results indicate that A. porteri exhibit an intermediate level of sociality, compared to other Octodontids.
Full-text available
This contribution is a tribute to José Yepes on the 75th anniversary of his description of the genus Tympanoctomys, and the 90th anniversary of his admission to the Argentine Museum of Natural Sciences “Bernardino Rivadavia”. Viscacha rats are the epitome of South American rodents adapted to desert habitats, and are a true model, not only to present different specialized attributes for life in xeric environments, but also as one of the mammals with the highest chromosomal number. In this chapter, we present an overview of the state of knowledge of the genus and related species, regarding aspects such as distribution, ecology, genetic and conservation. Perspectives focus on gaps and unresolved issues that are fascinating and promising research lines
Sociality, or group-living, results when conspecifics establish long-term (relative to lifespan) and spatially cohesive social units. Sociality theory states that group-living evolves whenever individuals attain net fitness benefits, or when individuals are forced to remain in groups. Among rodents, this theory comes from the study of a relatively small sample of taxonomic groups, typically from African mole-rats and North American squirrels and marmots. We reviewed published studies and data on the sociality of caviomorph rodents and argue that these rodents are particularly informative when refining a sociality theory. Our examination of evidence from caviomorphs indicated that resource heterogeneity (food, water pools) may act either as a constraint or a condition that promotes social benefits, depending on species. Instead, a benefit based on enhanced vigilance seems relatively common across species. Other predation benefits may have been overlooked. Benefits based on social thermoregulation or energetic savings during cooperative burrow construction come from the study of a few species and are restricted to laboratory settings. Evolutionary studies based on comparative approaches highlight that both ecological and life history traits have influenced sociality in caviomorphs. Besides, sociality was likely an ancestral condition across these rodents, implying that sociality in some extant species may be the legacy of social ancestors. Future research should determine multi-dimensional causes of social variation and intra-specific variation in sociality in well-studied taxa and examine the relationship between sociality, life-history, and ecology across taxa.
Multiple ecological factors are known to drive variation in social behavior. However, group-living in some species appears to be highly conserved, suggesting a phylogenetic influence. In this study, we evaluated both scenarios using intraspecific and interspecific comparisons across octodontid rodents. We first examined 2 different populations of Andean degu (Octodontomys gliroides), representing 2 extremes of a climate vegetation gradient across the Andes range. We evaluated how ecological variation in terms of abundance and distribution of food resources, predation risk, and burrowing costs predicted interpopulation variation in group size and range-area overlap (2 proxies of sociality). We estimated these measures of sociality from livetrapping and radiotelemetry. We then used phylogenetic methods to determine whether sociality exhibits a phylogenetic signal and reconstructed the ancestral state of sociality across the family Octodontidae. Overall activity of females and males of O. gliroides was greater during nighttime than daytime. Across populations we found significant differences in ecology, including abundance and distribution of food, predation risk, and burrowing costs. However, populations were similar in terms of group size and range-area overlap. The phylogenetic approach revealed a strong and significant phylogenetic signal associated with sociality, where this behavior was present early during the evolution of octodontid rodents. Together, these findings imply that sociality of O. gliroides is not linked to current population differences in ecology.
Full-text available
As evident from this review, comparative studies of octodontids and ctenomyids provide important opportunities to explore the adaptive bases for variation in rodent societies. In particular, the distinctive patterns of phyletic, ecological, and behavioral diversity evident in these families offer multiple opportunities to explore relationships between current environmental conditions and social structure. To date, analyses of sociality in octodontids have emphasized intrinsic benefits to group living, while studies of ctenomyids have focused on extrinsic constraints on natal dispersal that lead to the formation of social groups. Although the number of species for which quantitative data are available is small, neither soil conditions nor the spatial distribution of food resources appear to explain the occurrence of sociality in these animals. Similarly, no relationship is evident between social structure and key life history attributes of these families. The absence of a single, consistent ecological or life history predictor of group living suggests that multiple factors contribute to the social systems of octodontid and ctenomyid rodents. While resource distributions, burrowing costs, predation pressures, and the production of precocial young may all influence the behavior of these animals, the specific blend of selective pressures and adaptive consequences that shape social structure seems likely to vary among species. Acknowledging the multivariate nature of interactions between environment and social structure does not preclude the search for general correlations between environmental conditions and sociality, although it may render the identification of those relationships more challenging. Thus, while we suspect that many of the ecological and other potential selective forces identified here are important, we expect that their contributions to social structure vary not only between octodontids and ctenomyids but also within each family. To exploit fully the comparative opportunities afforded by these animals, we suggest that future studies of these animals should address the following objectives: 1. Characterization of social systems. At present, the behavior of most species in these families remains unknown and, thus, a primary goal of future research should be to generate comparative information regarding basic aspects of social structure such as the number of adults of each sex that live together, the kin structure of social units, and the social determinants of reproductive success. 2. Analyses of intraspecific variation in ecology and behavior. Comparative studies of conspecifics living in different habitats provide a powerful means of assessing the role of specific environmental variables in shaping social behavior. Because such comparisons effectively control for differences in evolutionary history that may confound cross-taxon analyses, identifying causal relationships between environmental conditions and behavior is facilitated. 3. Experimental manipulation of causal factors. Controlled manipulation of environmental variables is a compelling approach to testing proposed causal relationships between ecology, life history, and variation in social behavior. Experiments conducted in field settings are often challenging, but even relatively simple manipulations may yield important information regarding the effects of specific factors on social structure. Although much work is required to generate a comprehensive picture of the social biology of octodontid and ctenomyid rodents, the growing number of studies of these animals suggests that such data are forthcoming. As our knowledge of these families increases, we expect that octodontids and ctenomyids will come to play an increasingly prominent role in our understanding of rodent societies.
Full-text available
Chilean Mediterranean ecosystems, the only of this type present in South America of the four present in the world, are considered priority areas for conservation due to their high concentration of endemic species that have experienced accelerated rates of habitat destruction. They contain more than 39% of the mammal species, 47% of its endemic species, and 65% of the threatened species of Chile. Yet, these ecosystems are poorly represented in the system of protected areas, one of which is the Reserva Nacional Lago Peñuelas (RNLP) that is part of the Biosphere Reserve La Campana-Peñuelas, but whose mammal fauna is poorly documented. We studied both α and β diversity of the mammal assemblage in all three environments present at the RNLP (sclerophyllous forest, mixed shrub, and savanna of Acacia caven). Sherman traps grids were installed, pellets of two raptors (Tyto alba and Bubo magellanicus) were analyzed, tracks and signs were recorded, and direct observations were performed in the four seasons of the year 2001. We determined species richness (S), relative abundance, α diversity - considering its richness and structure (Shannon-Wiener and Pielou indexes)-, β diversity (Bray- Curtis index), and compared the diversity found with that documented for the same latitude from east to west. We recorded a total of 16 species: Thylamys elegans, Oligoryzomys longicaudatus, Abrothrix longipilis, A. olivaceus, Chelemys megalonyx, Phyllotis darwini, Myocastor coypus, Octodon degus, O. lunatus, Spalacopus cyanus, Abrocoma bennetti, Rattus norvegicus, R. rattus, Mus musculus, Lepus capensis, and Oryctolagus cuniculus. The coastal sclerophyllous forest was the most diverse with a species homogeneous distribution, followed by the mixed shrub, and finally the A. caven savanna. Also, the sclerophyllous forest is similar to the mixed scrub; in turn, both are very dissimilar to the savanna of A. caven. The diversity recorded in the study area is consistent with that of other areas of the Mediterranean areas. We discuss the status of these ecosystems and the diversity is compared to six documented locations at the same latitude.
Full-text available
The family Octodontidae (Rodentia, Hystricognatha) is an old group of low diversity, currently found on both sides of the Andean mountains between 16°S and 41°S. Information on the geographic distribution of the octodontid genera is presented and discussed, and the systematic status of each species and subspecies is given. An explanation is also proposed for the present distribution of the family, considering geological, climatic, floristic, faunistic, and ecological events that occurred after the first appearance of octodontids in the Deseaden age (early Oligocene) in Bolivia and Patagonia. Uplift of the Andes, formation of Patagonian pampas, disappearance of echimyids from the Patagonian Subregion, and appearance of ctenomyids seem to be the most important factors determining the present distribution of octodontids. -from Authors
Full-text available
Guidelines for use of wild mammal species are updated from the American Society of Mammalogists (ASM) 2007 publication. These revised guidelines cover current professional techniques and regulations involving mammals used in research and teaching. They incorporate additional resources, summaries of procedures, and reporting requirements not contained in earlier publications. Included are details on marking, housing, trapping, and collecting mammals. It is recommended that institutional animal care and use committees (IACUCs), regulatory agencies, and investigators use these guidelines as a resource for protocols involving wild mammals. These guidelines were prepared and approved by the ASM, working with experienced professional veterinarians and IACUCs, whose collective expertise provides a broad and comprehensive understanding of the biology of nondomesticated mammals in their natural environments. The most current version of these guidelines and any subsequent modifications are available at the ASM Animal Care and Use Committee page of the ASM Web site (
Caviomorph rodents represent one of the most distinctive groups of mammals in southern South America drylands; they colonized South America from Africa via trans-oceanic dispersions in the Eocene (40–50 Ma) and underwent an extraordinary ecological radiation after their arrival, thus making this group of great interest for biogeographic and evolutionary studies. The aim of this article was to provide a working hypothesis regarding the biogeographical history and ecological diversification of one of its conspicuous families, the Octodontidae. We reconstruct the evolutionary theater where their ecological diversification took place, and potential events of dispersal, vicariance and extinctions. We analyzed the historical biogeography of the Octodontidae across the eight ecoregions where they occur, based on species phylogeny and divergence times. Four approaches were used to reconstruct ancestral area: (1) Statistical Dispersal–Vicariance Snalysis (S-DIVA); (2) Bayesian binary Markov chain Monte Carlo (MCMC) analysis implemented in Reconstruct Ancestral State in Phylogenies (RASP); (3) Fitch optimization method; and (d) weighted ancestral area analysis (WAAA). Parsimony ancestral state reconstructions were implemented in order to explore the evolutionary history of an ecological character, mode of life. We propose the northern portion of the Monte desert ecoregion as the ancestral area in the evolution of the Octodontidae, with subsequent dispersal and enlargement of the family geographic range. The evolution of their ecological specialization (i.e. modes of life) suggests an ambiguous ancestral condition (saxicolous, generalist terrestrial, semifossorial) linked to species adaptation to arid environments, with fossoriality appearing later in octodontid evolution. The evolution of the Octodontidae is associated with contrasting environmental conditions (i.e. climate and vegetation) produced by the Andean Uplift between eastern and western sides.