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Communal burrowing in the hystricognath rodent, Octodon degus: A benefit of sociality?

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Abstract

We examined the hypothesis that a main benefit of group-living in the semifossorial rodent, Octodon degus (Rodentia: Octodontidae), is to decrease individual cost of burrow construction. We contrasted the digging behavior of groups of three same-sex, adult-sized individuals with that of solitary degus. The behavior of singles and trios was recorded inside a large terrarium partially filled with natural soil and under controlled conditions of food, light, and temperature. The observation that degus in groups do not decrease their burrowing time or frequency of digging compared with solitary diggers does not support the hypothesis that communal burrowing is a primary cause of degu sociality. On the other hand, the observation that degus in groups removed significantly more soil per capita than solitary digging degus, and that grouped individuals coordinated their digging – group members burrowed mostly in the same sites and formed digging chains –, suggests that social burrowing may potentially reduce the cost of burrow construction in the long term. We suggest that such long-term benefits will be a consequence rather than a cause of degu group-living.

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... In a search for further behaviorally relevant signals in the UV part of the spectrum, we measured the reflectance of degu urine, which these social animals use to for scent-marking of their foraging trails and meeting areas. 24,25 The spectral reflectance contrast of fresh degu urine monotonically increased with decreasing wavelength, reaching a maximum at approximately 310 to 360 nm (Fig. 7, continuous curve). Hence, fresh urine marks represent a strong visual UV signal. ...
... Behavioral studies in degus show that they are highly social. 24,25 For example, during alert call behavior degus raise upright on their hind paws and expose their thorax to the view of cospecifics. 4,28 In those circumstances, UV sensitivity may be relevant. ...
... 29 Among the social behavior patterns of degus is the use of common paths when moving around in their territory and the use of common wallowing places; these "public" trails and places are scent marked with urine and feces. 24,25 Our measurements show that fresh degu urine has a strong UV reflectance, whereas old dry urine does not. Hence these scent marks represent visual as well as olfactory cues to a UVsensitive animal-a potential advantage for longer-range orientation. ...
... Relatedness of colony members is also variable, ranging from 0.07 to 0.48 between females in one wild population, and averaging 0.25 which is equivalent to second-order kinship (Ebensperger et al., 2004). During the daytime, the group members roam above ground and coordinate their foraging activity by keeping visual contact (Ebensperger and Bozinovic, 2000;Ebensperger et al., 2002;Quirici et al., 2008;Vasquez, 1997) and emitting audible vocalizations (Long, 2007). They synchronize their digging activity to build complex underground burrows, which they share when night falls, and use routinely as refuges to raise their precocious but unweaned pups (Ebensperger et al., 2004;Fulk, 1976;Lee, 2004). ...
... As for other animal models, behavioral assessment should take species-specific characteristics into account. Under natural conditions, degus run from one burrow to another and travel across open areas during the day (Ebensperger and Bozinovic, 2000). Therefore, studies including the open field test and other tests aimed at assessing fear responses should be developed using suitable protocols. ...
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The scientific interest in caviomorph rodents as possible animal models for social and affective neuroscience is increasing in a remarkable way. The present contribution reviews the literature on the social behavior of caviomorph species, with an emphasis on domestic guinea pigs and Octodon degus. After providing an overview of the developmental milestones, we present current laboratory-based studies on the strength of social bonds, sensitivity to social environment, and the developmental and epigenetic factors involved in the expression of social behavior. Finally, we discuss possible lines of research to broaden our knowledge of the social behavior of these promising animal models. Keywords: degus; epigenetic; guinea pigs; social behaviour; social bonding
... If being active is costly, a share of this activity among several group members may lead to an individual decrease of these costs, benefiting a mouse by the possibility to allocate more time to sleep. They may, for example, share the costs of nest building and maintenance (Ebensperger & Bozinovic, 2000). Also, when individuals cooperate, less time is needed to achieve this task, saving energy that can be allocated to sleep. ...
... In order to estimate the group size effect on group activity, most of the previous studies were focusing on foraging effort, search for mates, antipredator behaviours or maintenance of burrow/den/nest systems (Pulliam, 1973;Jarman, 1987;Blumstein, 1999;Ebensperger & Bozinovic, 2000). This study opens a new perspective in understanding how group size can modify group activity because I was mainly interested in the nocturnal activity of groups inside the nest. ...
... (3) Burrow maintenance is energetically costly but a requirement for maintaining burrow integrity in ice rats, so we expected greater attention to burrow maintenance in smaller colonies. It is likely that each individual would have expended more energy and time maintaining the burrow in smaller colonies, whereas in larger colonies, individuals could expend comparatively less energy and lower their own maintenance behaviour (Ebensperger and Bozinovic 2000), given the greater number of individuals, an idea akin to the group vigilance or 'many eyes' hypothesis (Roberts 1996). ...
... For example, pocket gophers Thomomys bottae increase energy expenditure by 360-3400 times during burrowing (Gettinger 1984). There was a (weak) positive association between colony size and total investment by all ice rat colony members in burrow maintenance, however, indicating that in smaller colonies, each individual would have expended more energy and time maintaining the burrow, whereas in larger colonies, individuals shared in maintenance costs and would have saved energy (Ebensperger and Bozinovic 2000). ...
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The relationship between group size and fitness has attracted much interest, with many attempts made to detect an optimal group size. Group size is determined by the benefits and costs influencing group formation, which also influences whether groups persist or fail. We investigated whether group size is associated with success (individual survival and reproductive output) in the African ice rat Otomys sloggetti robertsi. Ice rats form mixed-sex plural-breeding colonies that trade off the benefits of huddling below-ground against within-colony resource competition above-ground. We measured behavioural correlates of individual success in summer and winter, focusing on energy saving (basking), acquisition (foraging) and use (burrow maintenance, distance travelled for foraging) behaviours. We predicted that (1) individuals in larger colonies would forage and travel more to find food because of greater within-colony competition for resources; (2) individuals in larger colonies would bask less than individuals in smaller colonies because of the greater energy savings generated from huddling in larger groups; and (3) burrow maintenance would be greater in smaller colonies because of fewer individuals engaging in this task. We showed that colonies succumbed or persisted as a group (i.e. most individuals present or all absent). In particular, in both seasons, individuals in smaller groups (≤5 individuals) were more likely to fail, while those in larger groups (≥12 individuals) were more likely to persist. The persistence of colonies was positively predicted by foraging and negatively by basking. Foraging was greater in larger colonies and burrow maintenance was greater in smaller colonies. While females of larger colonies produced more offspring in total, reproductive output (per capita offspring production) was not correlated with colony size. Individual ice rats in larger colonies accrued fitness benefits, which were predicted, proximally, by greater foraging and possibly energy savings in larger huddling groups. Statement of significance What proximally determines the relationship between group size, individual success and colony persistence? In ice rats, individuals in larger groups persist, which is correlated with more foraging. Larger groups possibly enjoy the benefits of huddling in larger groups, which are re-channelled into energy-intense activities. Groups failed or persisted as a unit. Investigating the behavioural correlates of the relationship between group size and persistence provides insight into the proximal underpinnings of this relationship.
... Satellite burrows could be distinguished from main burrows by their location close to the foraging area where animals can hide when threatened (Armitage, 1988;Branch et al., 1994). The higher number of entrances is important for animals to hide from predators (Ebensperger and Bozinovic, 2000a). Predation risk would be related to the structure of vegetation. ...
... When confronted with the fake predators, at both sites the cavies fled towards the burrow and/or hid in the galleries (Taraborelli et al., 2008). Ebensperger and Bozinovic (2000a) suggested that a higher number of entrances would be important for animals to hide more quickly from potential predators. Satellite burrows of Lagostomus maximus and Marmota flaviventris could also be distinguished from main burrows by their location close to the foraging area, where animals can hide when threatened (Armitage, 1988;Branch et al., 1994). ...
... Nevertheless, other observations suggest decreased burrowing costs may contribute to degu sociality. In particular, degus in groups coordinate their digging and remove more soil per capita than solitary diggers, implying an energetic benefit in terms of decreased burrowing costs (Ebensperger & Bozinovic 2000). In addition, degu groups were larger in a population with harder soil than in a population with softer soil conditions . ...
... Similarly, benefits based on decreased thermoregulatory costs and reduced costs of burrow construction have scarcely been addressed. Evidence consistent with benefits from social thermoregulation remains restricted to laboratory settings in coypus (Moinard et al. 1992) and degus (Canals et al. 1989); evidence for energetic savings during cooperative burrow construction comes from studies on southern mountain cavies and degus with disparate results (Ebensperger & Bozinovic 2000;Taraborelli 2009). Lacey and Sherman (2007) described the social systems of subterranean rodents with a three-dimensional model. ...
... In their natural living environments, degus pups are reared by both males and females (Ebensperger & Bozinovic, 2000;Ebensperger, Hurtado, Soto-Gamboa, Lacey, & Chang, 2004;Fulk, 1976) and are weaned at about postnatal day (PND) 45 (Ebensperger & Bozinovic, 2000;Ebensperger, Veloso, & Wallem, 2002;Fulk, 1976;Lee, 2004). Although pups receive parental care until about the sixth week of life, they start to eat solid food within the first week after birth (Reynolds & Wright, 1979). ...
... In their natural living environments, degus pups are reared by both males and females (Ebensperger & Bozinovic, 2000;Ebensperger, Hurtado, Soto-Gamboa, Lacey, & Chang, 2004;Fulk, 1976) and are weaned at about postnatal day (PND) 45 (Ebensperger & Bozinovic, 2000;Ebensperger, Veloso, & Wallem, 2002;Fulk, 1976;Lee, 2004). Although pups receive parental care until about the sixth week of life, they start to eat solid food within the first week after birth (Reynolds & Wright, 1979). ...
Article
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Octodon degus is a social caviomorph species that exhibits strong social bonds and robust distress responses to maternal separation. To understand the impact of early social isolation on social motivation, we investigated how social isolation during infancy, associated with repeated restricted interactions with mother and siblings, altered social motivation in young degus. In Experiment 1, three treatments were compared: complete isolation (ISOLATED group), nearly complete isolation, with daily half hour partition-restricted reunions with the mother and siblings (RESTRICTED group), and social-housing with the mother and siblings (FAMILY group). After 10 days of treatment, all subjects underwent a 5-day choice test between mothers and unfamiliar females. During the treatment period, the RESTRICTED animals emitted more isolation calls and spent more time close to the partition that separated them from mothers than ISOLATED animals. During the first social-choice day, FAMILY reared animals showed a preference for the mother for a few minutes, while the RESTRICTED animals preferred the mother for the whole session. Totally ISOLATED pups exhibited no social preferences. Since during successive testing periods the isolation calls decreased over the days, in Experiment 2 we investigated whether this decline was related to age or habituation to testing procedures. Animals were observed during a single exposure to isolation (ISOLATED) or restricted-reunion (RESTRICTED) at PND 21 and 31. The decrease of vocalizations was due to an age-effect. The findings clarify the nature of social bonds in degus. ß 2011 Wiley Periodicals, Inc. Dev Psychobiol 53: 657-669, 2011.
... Jones 1993). It has been proposed that building a new burrow system in which to rear offspring is energetically expensive (Ebensperger and Bozinovic 2000;Lovegrove 1989;Powell and Fried 1992). Because semifossorial rodents such as pine voles and subterranean rodents such as mole-rats do not have anatomical modifications to their forelegs for digging, burrow construction may be even more costly for these animals than for fossorial rodents. ...
... Additional factors such as soil characteristics, possession of digging adaptations, and frequency with which burrows need to be expanded or maintained may better predict delayed dispersal. Data from study of digging in degus (Octodon degus) by Ebensperger and Bozinovic (2000) also suggest that individuals may benefit by remaining philopatric because grouped individuals may be able to construct new burrows in less time or may be able to construct a more extensive burrow system than solitary degus. Spending less time digging could increase time allocated to vigilance and decrease the risk of predation. ...
Article
The costs and benefits of philopatry (remaining at the natal nest) have been discussed in numerous papers. Nevertheless, there is still debate about the relative importance of factors that favor philopatry, which can result in the formation of social groups. The decision to remain at the natal nest can be examined by using models such as the delayed-dispersal threshold model, which takes into account risks of dispersal, probability of becoming established on a suitable territory, and probability of finding a mate. These factors, in turn, are influenced by ecological variables such as distribution of critical resources and population density. The often-cited conclusion from this and similar models is that ecological or social constraints promote philopatry whereas relaxation of the constraints result in dispersal. More recent theoretical approaches have included not only some of these ecological factors but also life-history traits (e.g., survival and age of maturation). Some of the latter models suggest that external constraints alone are inadequate to explain interspecific variation in group living. I review existing data to evaluate the relative importance of variables proposed to influence philopatry in rodents and argue that future studies may benefit from a broad approach that encompasses life-history and ecological factors, such as adult survival and territory quality.
... Here, we performed a morphometric study of the subdomains of the AOB in Octodon lunatus and compared the resulting measurements with that of its sister species, O. degus. 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). ...
... Individuals of this species live in groups composed of a dominant male and two-five females, plus their offspring. Members of a group share the same burrow system, including a communal nest site, and exhibit a variety of cooperative behaviours, such as communal play, construction and maintenance of burrows, anti-predatory surveillance and alarm calls emission (Ebensperger & Bozinovic, 2000;Ebensperger et al. 2004Ebensperger et al. , 2006Jesseau et al. 2009). In contrast, O. lunatus individuals do not share burrows nor do they form communal groups or engage in cooperative behaviours. ...
Article
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.
... Satellite burrows could be distinguished from main burrows by their location close to the foraging area where animals can hide when threatened (Armitage, 1988;Branch et al., 1994). The higher number of entrances is important for animals to hide from predators (Ebensperger and Bozinovic, 2000a). Predation risk would be related to the structure of vegetation. ...
... When confronted with the fake predators, at both sites the cavies fled towards the burrow and/or hid in the galleries (Taraborelli et al., 2008). Ebensperger and Bozinovic (2000a) suggested that a higher number of entrances would be important for animals to hide more quickly from potential predators. Satellite burrows of Lagostomus maximus and Marmota flaviventris could also be distinguished from main burrows by their location close to the foraging area, where animals can hide when threatened (Armitage, 1988;Branch et al., 1994). ...
Article
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Burrows provide a stable microclimate and give small mammals protection from extreme temperatures and from predators on the ground surface. The objective was to determine the influence of biotic and abiotic factors on the structure of burrows used by the cavy Microcavia australis. The study was conducted on two sites with different climate conditions, predation risk and size of plant patches. A total of 18 main burrows and 13 satellite burrows were characterized at Ñacuñán, and 12 main and 3 satellite burrows at El Leoncito. The larger number of holes and higher development of main and satellite burrows at Ñacuñán is likely related to higher risk of raptor predation. At both sites burrows would function as shelter from the environment since temperature in the galleries is lower than soil temperature at the hottest time of the day. Moreover, active holes are east-oriented at Ñacuñán, avoiding SE and S winds, and northwest-oriented at El Leoncito, receiving the warm dry wind from the NW. Also due to gallery inclination the sun goes deeper into the tunnels in the coldest season (winter) than in the warmest one (summer). Burrows would afford cavies a refuge from predators and a stable microclimate.
... As for quantitative estimation of the degree of cooperation among group mates in rodent societies, very little data are available regarding the frequency or duration of cooperative interactions. Perhaps, the only proper example is a study conducted by Ebensperger and Bozinovic (2000) who examined the hypothesis that a main benefit of group living in degus is to decrease individual cost of burrow construction. The authors of the study compared burrowing time and frequency of digging of groups of two or three same-sex adult individuals with that of solitary degus under laboratory conditions. ...
... Suggestions concerning selective forces operating to form family groups in muroid rodents are rather debatable. To understand this evolutionary process more clearly, it would be useful to make a list of genera and species of highly social muroid rodents living in family groups (Gromov 2008 (Jarvis 1978(Jarvis , 1985Bennett and Jarvis 1988;Jarvis et al. 1994;Ebensperger 1998Ebensperger , 2001Ebensperger and Bozinovic 2000;Ebensperger and Cofré 2001). ...
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In rodent populations, there are two main types of complex social units – aggregations (breeding colonies) and family groups. The basic features of their social organization are quite different. Some species with a familygroup lifestyle have the most complex social structure and social organization. Impact of ecological factors, including predation and food resources, on the evolution of sociality in rodents (i.e., the transition from solitary living to a family-group lifestyle) is still unclear. It seems that a set of ecological conditions resulting in the evolutionary transition towards a family-group lifestyle is unique for any relevant rodent species, and there are no universal rules explaining the effect of external factors on speciesspecific social organization. It is very likely that social organization of any rodent species may reflect the combined effects of life-history and ecological constraints, social pressures, and phylogenetic history. Moreover, social factors alone, especially cooperation, may play a greater role in the evolution of sociality among rodents. The book should be interesting for ecologists, ethologists and evolutionary biologists as well as students.�� ��� � ������ ������ � � � � � ���� ��� �� ���������� ������ ����� ��� ��� � ����� � ����������� � � ���� ����������� � � � ���� � �� ���� � ��� ���� �� ��� ��! ���� � � "�� � ���� � � � #�� � �� �� ���� �� � � ����$ ������ ��� � �� � � � � � � ��� � ����� �� ���� �� � ��� �� � ��� ���� � ��� ��! ��� � ��� � � ��� ������� �� � � ����� ���������� �� � ���� ��� ���� � ����� ������ � � ���� ����������� �� �� ������ � �� � �� � � � ��� �������� ���� ��� ������� �� � � ����$������ ��� � �� � ��� � �������� � � � � � ��� � � � � ��� ������� �� ����� ����� � ��� ���� ��� � � ���� ��� ��� � ��� ���� �� ���� � ����$������ ��� � �� � ��� ���"� � ���� ��� � � � � � ��� � � �� �� ��� ��� � � � �������� �� �� ��� �� ��� ������ � � �� � ���� � �� �� � � ��������� �� �$ �� ������ ���� �� ��� ��! ��� � � � ��� � ��� ��% ��� � � ���� �� ��� ��! ���� ��� �� ��� � � �� �� �� � �� � �� � � � � ��� �� �� �� � �� ��� ��� $��� ���� �� ������� ������ � �� ������� ���� ���� ��� ��������� � ������ ��� �&�� �� �� ���� �� � � ���� ��� �� �� �� �������� � ������ ���� �� ��� �� ��� � ��� � ���� ���� ��� ���� �� �� ����� ��� � � � � � ��%
... haigi- Lacey and Wieczorek 2003). However, previous studies on degus found that the energetic cost of digging in hard soil is greater than digging in soft soils (Ebensperger and Bozinovic 2000a) and that degus digging in groups remove more soil per capita than solitary individuals (Ebensperger and Bozinovic 2000b). Further, while softer soil may provide better habitat and result in a greater degree of sociality, a previous study of degus at Rinconada and Los Molles does not support this relationship . ...
Article
A growing body of evidence showing that individuals of some social species live in non-kin groups suggests kin selection is not required in all species for sociality to evolve. Here, we investigate 2 populations of Octodon degus , a widespread South American rodent that has been shown to form kin and non-kin groups. We quantified genetic relatedness among individuals in 23 social groups across 2 populations as well as social network parameters (association, strength, and clustering coefficient) in order to determine if these aspects of sociality were driven by kinship. Additionally, we analyzed social network parameters relative to ecological conditions at burrow systems used by groups, to determine if ecological characteristics within each population could explain variation in sociality. We found that genetic relatedness among individuals within social groups was not significantly higher than genetic relatedness among randomly selected individuals in both populations, suggesting that non-kin structure of groups is common in degus. In both populations, we found significant relationships between the habitat characteristics of burrow systems and the social network characteristics of individuals inhabiting those burrow systems. Our results suggest that degu sociality is non-kin based and that degu social networks are influenced by local conditions. Es creciente la evidencia que apoya la ocurrencia de especies sociales donde los individuos no están emparentados genéticamente, lo que sugiere que la selección de parentesco no es indispensable para la evolución de la sociabilidad. En este estudio se examinaron dos poblaciones de Octodon degus , un roedor sudamericano donde los grupos sociales pueden o no incluir individuos cercanamente emparentados. Se cuantificó el parentesco genético entre individuos en 23 grupos sociales y en redes sociales de dos poblaciones para determinar si estos aspectos de la sociabilidad dependen del grado de parentesco. Además, se examinaron asociaciones entre los parámetros cuantificados de las redes sociales (asociación, fuerza, coeficiente de anidamiento) y las condiciones ecológicas a nivel de los sistemas de madriguera usados por cada grupo. El grado de parentesco genético dentro de los grupos no fue distinto del grado de parentesco entre individuos de la población tomados al azar, lo que apoya que una estructura de grupos no emparentada es la regla en Octodon degus . En ambas poblaciones se registró una asociación entre características ecológicas de los sistemas de madriguera y atributos de las redes sociales de los individuos que usan estas estructuras. Nuestros resultados indican que la sociabilidad en Octodon degus no está basada en relaciones de parentesco y que las redes sociales de estos animales dependen de las condiciones ecológicas.
... The use of closed habitat conditions coupled to a partially nocturnal activity in O. lunatus would reduce opportunities to decrease the predation risk through social vigilance or its potential benefit as suggested by species comparisons across caviomorph rodents [Ebensperger and Cofré, 2001;Ebensperger and Blumstein, 2006]. Second, an absence of burrow digging may prevent cooperation in terms of communal burrowing as recorded in O. degus [Ebensperger and Bozinovic, 2000]. Third, the observation that female O. lunatus from the same social groups were not simultaneously lactating [Sobrero et al., unpubl. ...
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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.
... Degus foraging in large groups detect approaching predators faster and spend more time foraging per capita ) than degus foraging in small groups. Degus in larger groups also experience lower per capita digging costs than degus in smaller groups (Ebensperger & Bozinovic 2000a, 2000b. In contrast, the effects of group-living on reproductive success are less clear. ...
... Evolutionary explanations to group living have relied on fitness advantages to group members including an increased access to resources, decreased predation risk, decreased burrowing costs, reduced cost of thermoregulation or even increased access to mates [5,8,9]. On the other hand, the evolution of group living itself has been attributed to the development of remarkable cognitive capacities [10,11]. ...
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Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.
... hartingi. Для этого подвида адаптивной может быть кооперация членов группы при копании, снижающая энергетические затраты каждой особи (Ebensperger, Bozinovic, 2000;Сморкачева, Орлова, 2011), а также обеспечение в норной системе необходимого уровня влажности и оптимальной температуры (Reichman, Smith, 1987). Известно, что многие поколения общественных полевок используют одни и те же норы, лишь обновляя их к сезону размножения (Касаткин и др., 1998; отмечено у полевки Хартинга в горах Странджа и Родопах: наши неопубликованные данные). ...
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Successful reproduction of two subspecies of Harting’s vole in monogamous pairs (monogamous groups, 35 pairs for each subspecies) was shown. The results obtained in modeling the experimental polygyny revealed a different attitude of females of the two subspecies to the formation of communal groups. In M. h. lydius polygynous groups, regardless of the relationship of the females (35 groups consisting of sisters and 20 groups of unrelated females), the intensity of reproduction and the proportion of successfully reared pups decreased significantly compared to the monogamous groups. With high energy costs for reproduction, there were significantly fewer reared pups per mother giving birth than in the monogamous groups, this suggesting the predominance of monogamy in this subspecies. On the contrary, related females of M. h. hartingi bred successfully in communal groups (35 groups of sisters), demonstrating high tolerance, a tendency to co-rearing and feeding the pups, and low infant mortality. In polygynous groups consisting of unrelated females (20 groups), reproductive success decreased due to increased infant mortality. Possible benefits of communal reproduction in this subspecies are discussed, as well as its probable relationship with habitat fragmentation under such conditions and with a lack of vacancies for the dispersal of young animals, which may be an important adaptation for this subspecies of voles. Keywords: communal nesting, monogamy, polygyny
... und Ebensperger(35) gehen jedoch davon aus, dass die Gruppen meist aus nur 2 bis 4 Individuen bestehen. Jede Gruppe hat ihr eigenes Territorium und Höhlensystem, das gegen andere Gruppen verteidigt wird(48). ...
... Simultaneous digging appeared to be a more efficient mode of burrow extension than two mice digging independently. The simultaneous digging behavior we observed in P. polionotus pairs is reminiscent of "chain digging" observed in communally burrowing mammals, such as eusocial mole-rats (Lovegrove 1989) and group-living degus (Ebensperger and Bozinovic 2000), and suggests that even distantly related rodent species may have converged upon a common strategy for efficiently excavating shared living space. ...
Article
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Animals often adjust their behavior according to social context, but the capacity for such behavioral flexibility can vary among species. Here, we test for interspecific variation in behavioral flexibility by comparing burrowing behavior across three species of deer mice (genus Peromyscus) with divergent social systems, ranging from promiscuous (Peromyscus leucopus and Peromyscus maniculatus) to monogamous (Peromyscus polionotus). First, we compared the burrows built by individual mice to those built by pairs of mice in all three species. Although burrow length did not differ in P. leucopus or P. maniculatus, we found that P. polionotus pairs cooperatively constructed burrows that were nearly twice as long as those built by individuals and that opposite‐sex pairs dug longer burrows than same‐sex pairs. Second, to directly observe cooperative digging behavior in P. polionotus, we designed a burrowing assay in which we could video‐record active digging in narrow, transparent enclosures. Using this novel assay, we found, unexpectedly, that neither males nor females spent more time digging with an opposite‐sex partner. Rather, we demonstrate that opposite‐sex pairs are more socially cohesive and thus more efficient digging partners than same‐sex pairs. Together, our study demonstrates how social context can modulate innate behavior and offers insight into how differences in behavioral flexibility may evolve among closely related species.
... Both Liopholis skink species use a sit-and-wait strategy where they sit inside the entrance of their burrows and wait for prey that pass by , although some L. striata are occasionally seen foraging at night. Sociality in subterranean animals has been shown to facilitate the partitioning of burrowing workload among multiple individuals, thereby reducing each individual's total energy cost (Hansell, 1993;Ebensperger and Bozinovic, 2000b). Sociality allows the construction of complex multi-entrance burrows, which provide protection from predators (Rand and Dugan, 1983) and, for endotherms, provides a greater ability to thermoregulate (Yahav and Buffenstein, 1991;Kauffman et al., 2003). ...
Article
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Burrowing is an important form of locomotion in reptiles, but no study has examined the energetic cost of burrowing for reptiles. This is significant because burrowing is the most energetically expensive mode of locomotion undertaken by animals and many burrowing species therefore show specialisations for their subterranean lifestyle. We examined the effect of temperature and substrate characteristics (coarse sand or fine sand) on the net energetic cost of burrowing (NCOB) and burrowing rate in two species of the Egernia group of skinks (Liopholis striata and Liopholis inornata) compared with other burrowing animals. We further tested for morphological specialisations among burrowing species by comparing the relationship between body shape and retreat preference in Egernia group skinks. For L. striata and L. inornata, NCOB is 350 times more expensive than the predicted cost of pedestrian terrestrial locomotion. Temperature had a positive effect on burrowing rate for both species, and a negative effect on NCOB for L. striata but not L. inornata. Both NCOB and burrowing rate were independent of substrate type. Burrows constructed by skinks had a smaller cross-sectional area than those constructed by mammals of comparable mass, and NCOB of skinks was lower than that of mammals of similar mass. After accounting for body size, retreat preference was significantly correlated with body shape in Egernia group skinks. Species of Egernia group skinks that use burrows for retreats have narrower bodies and shorter front limbs than other species. We conclude that the morphological specialisations of burrowing skinks allow them to construct relatively narrow burrows, thereby reducing NCOB and the total cost of constructing their burrow retreats. © 2015. Published by The Company of Biologists Ltd.
... Greater sociality also is expected in habitats with relatively low shrub cover, longer distance to the nearest refuge, and low density of burrow openings, all conditions that increase predation risk (Vásquez et al. 2002;Ebensperger and Hurtado 2005;Hayes et al. 2007;Taraborelli 2009;Ebensperger et al. 2012). Greater sociality is expected in populations experiencing harder soils due to costs of digging and burrowing (Ebensperger and Bozinovic 2000;Ebensperger et al. 2012). ...
Article
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.
... Burrow systems also could function as refugia from the extreme heat and aridity of the environment in which T. yonenagae occurs (Rocha 1991). Construction of subterranean burrows is thought to be energetically expensive (Ebensperger and Bozinovic 2000;White et al. 2006) and burrow sharing could allow individuals to reduce the costs associated with access to this critical resource. Future studies will evaluate these potential ecological influences on burrow sharing by T. yonenagae in greater detail. ...
Article
Among fossorial rodents burrow sharing is an important behavioral attribute that provides the foundation for multiple aspects of social structure. Within the family Echimyidae the torch-tail spiny rat (Trinomys yonenagae) is distinguished from closely related taxa by its tendency to live in burrows in desert habitats. Preliminary field studies have suggested that burrow systems of this species are shared by multiple adults. To test this hypothesis we used livetrapping and radiotelemetry to quantify patterns of burrow use in a population of torch-tail spiny rats located near Ibiraba, Bahia State, Brazil. Examination of our data indicates that 76.2% of 67 burrow systems monitored were occupied by >;1 adult, including same-sex pairs, male-female pairs, and multiple adults of both sexes. Spatial overlap among adults captured in the same cluster of burrow entrances was extensive (72.0% ± 27.0% based on 95% minimum convex polygons), with 66.7% of animals resident in the same burrow system using the same putative nest site. Collectively, examination of these data indicates that adult T. yonenagae share burrows and thus may be social. To place our findings in a comparative context and identify potential ecological correlates of burrow sharing in T. yonenagae we contrast our findings with data on space use by other fossorial, desert-dwelling rodents.
... We observed mole voles under laboratory conditions because this is the only way to illuminate the details of behavior of a cryptic species living underground. The same approach has been used in a number of captive animal studies addressing similar questions in other species (Bennett and Jarvis 1988;Jacobs and Jarvis 1996;Gaylard et al. 1998;Ebensperger and Bozinovic 2000;Smorkatcheva 2003, Serra et al. 2012etc.). The results allow us to estimate the contribution of weaned predispersal mole voles to important group activities. ...
Article
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The highly social subterranean voles of genus Ellobius (mole vole) represent a unique model to compare with both social bathyergids and surface-dwelling voles. Unlike most arvicolines, mole voles display the prolonged obligatory delay of dispersal. In subterranean rodents, this delay may be associated with benefits of cooperation (weaned offspring help their parents), an extended parental investment (parents care for weaned offspring), or both. To identify the role offspring aged \3 months play in mole vole families, we estimated their contribution to important group activities. We found that juveniles contributed very little to daily living activities up to the age of approximately 2 months. The older offspring carried objects at least as frequently as breeders, but they engaged in gnawing obstacles less frequently than their fathers. Male breeders and non-breeders engaged in gnawing more than the respective categories of females. Although young mole voles clearly did not surpass their parents in performing the more energetically costly activities, they gained body mass by 26 g (130 %) between days 30 and 90, often surpassing their parents in weight. Based on our results, in E. tancrei an extremely prolonged infancy is followed by intensive building of body reserves. This ontogenetic trajectory appears to be distinct from the patterns described for social bathyergids and for most voles.
... For example, wild female chimpanzees display increased cortisol response to both aggressive social interactions with conspecifics and the energetic demands of breeding (Thompson et al., 2010). In our study population, females that live alone must perform all activities associated with maintaining a burrow system, finding food, and caring for offspring; in contrast, group-living females share these tasks with conspecifics, potentially resulting in a per capita decrease in the effort expended on these activities (Ebensperger and Bozinovic, 2000;Ebensperger et al., 2007). In C. sociabilis, lone females also have higher per capita direct fitness than group-living females (Lacey, 2004), indicating that in addition to facing potentially greater challenges associated with survival, lone females are likely to be investing more in offspring care. ...
Article
The social environment in which an animal lives can profoundly impact its physiology, including glucocorticoid (GC) responses to external stressors. In social, group-living species, individuals may face stressors arising from regular interactions with conspecifics as well as those associated with basic life history needs such as acquiring food or shelter. To explore the relative contributions of these two types of stressors on glucocorticoid physiology in a communally breeding mammal, we characterized baseline GC levels in female colonial tuco-tucos (Ctenomys sociabilis), which are subterranean rodents endemic to southwestern Argentina. Long-term field studies have revealed that while about half of all yearling female C. sociabilis live and breed alone, the remainder live and breed within their natal group. We assessed the effects of this intraspecific variation in social environment on GC physiology by comparing concentrations of baseline fecal corticosterone metabolite (fCM) for (1) lone and group-living yearling females in a free-living population of C. sociabilis and (2) captive yearling female C. sociabilis that had been experimentally assigned to living alone or with conspecifics. In both cases, lone females displayed significantly higher mean baseline fCM concentrations. Data from free-living animals indicated that this outcome arose from differences in circadian patterns of GC production. fCM concentrations for group-living animals declined in the afternoon while fCM in lone individuals did not. These findings suggest that for C. sociabilis, stressors associated with basic life history functions present greater challenges than those arising from interactions with conspecifics. Our study is one of the first to examine GC levels in a plural-breeding mammal in which the effects of group living are not confounded by differences in reproductive or dominance status, thereby generating important insights into the endocrine consequences of group living.
... Many hypotheses that explain the evolution of sociality are based on the acceptance of a balance or a tradeoff between the positive and negative effects of the group living (Alexander, 1974;Bertram, 1978;Madison et al., 1984;Pulliam and Caraco, 1984;Ebensperger et al., 2011). Advantages include a decrease in the risk of predation, in particular due to specific alarm calls, e.g., in ground dwelling sciurids (Barash, 1973;Armitage, 1981;Hoogland, 1981); a reduction in energy spent searching for food, foraging, burrowing, and the maintenance of complex burrows (Jarvis, 1981;Jarvis et al., 1994;Ebensperger and Bozinovic, 2000); and the successful survival of the offspring due to collective thermoregulation, which acquire greater body weight before dispersal, the con tinuity of experience of adult individuals, and living through an adverse season within a group (Barash, 1974;Armitage, 1981Armitage, , 1999Armitage, , 2007Arnold, 1988Arnold, , 1990aArnold, , 1990bArnold, , 1993Hayes, 2000). This list may be supplemented with mutual help from related individ uals, e.g., in nursing pups (alloparenting); the inherit ance of territory occupied by one family; and the ben efits of collective protection of the territory and food resources (Sherman, 1980;Arnold, 1990b;Emlen, 1994;Lacey and Sherman, 2007). ...
Article
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An analysis of the published and his own data on the social behavior of rodents has allowed the author to conclude that the most social species among rodents are those with a family-group mode of life. The direct effect of ecological factors on the establishment of a complex social organization in rodents remains disputable. Presumably, the driving factor that determines the evolution of sociality in rodents is cooperation, which is promoted by proximate mechanisms of socialization. A complex social organization can be formed under any ecological conditions when families are more competitive than solitary individuals due to cooperation in various types of activities. The proximate mechanisms of socialization, especially early experience of tactile stimulation, create the preconditions for strengthening the pair bonds and elevating the level of parental care in the individuals of both sexes, which is necessary for establishment of extended family groups. The research into these mechanisms is most promising for a deeper insight into the processes associated with the evolution of sociality in rodents, and the relevant results should be integrated into the current socioecological concept.
... Among burrowing species, spatial heterogeneity in drainage and soil types may foster aggregation (Hare & Murie 2007). Burrowing species may additionally benefit from increased burrowing efficiency from digging chains (Ebensperger & Bozinovic 2000), further selecting for group living. ...
Chapter
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Caviomorphs occupy diverse ecological niches and exhibit diverse social organization. Studies and theory derived from better-studied mammalian taxa establish an integrative and comparative framework from which to examine social systems in caviomorphs. We synthesize the literature to evaluate variation in space use, group size, mating systems, and parental care strategies in caviomorphs in the context of current hypotheses. Across species, ecological lifestyles, including diet, habitat mode, space use, and activity period, are linked to variation in social systems including mating systems, breeding strategies, and associated parental care strategies. Within species, different populations and the same populations over time vary in space use, sociality, and mating systems, with most variation explained by differences in resource distribution, predation risk, or population density. We highlight unique aspects of caviomorph biology and offer potentially fruitful lines for future research both at the inter- and intra-specific levels. Among species, better-resolved phylogenies and collation of basic natural history information, including lifestyle characteristics, especially for underrepresented families such as spiny rats (Echimyidae) and porcupines (Erethizontidae), can advance comparative studies. Within species, future studies of caviomorphs can make use of recent technological advancements in data collection (e.g. proximity data loggers) and data analysis (e.g. model selection), as well as integration of laboratory and field studies. These complementary approaches will allow us to examine the diversity of social behavior in this rich taxon at multiple levels of analysis. In doing so, we can gain unique insights into the ecological drivers and evolutionary significance of diverse social systems.
... Unlike other fossorial hystricomorphs, the semi-fossorial degu does not have any obvious anatomical adaptations for digging despite building colonial burrows (Ebensperger and Bozinovic, 2000a). The degu has a generalized small mammal body plan in that their trunks are relatively short and limbs crouched. ...
Article
Animals that are specialized for a particular habitat or mode of locomotion often demonstrate locomotor efficiency in a focal environment when compared to a generalist species. However, measurements of these focal habitats or behaviors are often difficult or impossible to do in the field. In this study, the energetics and kinematics of simulated tunnel locomotion by two unrelated semi-fossorial mammals, the ferret and degu, were analyzed using open-flow respirometry and digital video. Animals were trained to move inside of normal (unconstrained, overground locomotion) and height-decreased (simulated tunnel, adjusted to tolerance limits for each species) Plexiglas chambers that were mounted flush onto a treadmill. Both absolute and relative tunnel performance differed between the species; ferrets tolerated a tunnel height that forced them to crouch at nearly 25% lower hip height than in an unconstrained condition, while degus would not perform on the treadmill past a ∼9% reduction in hip height. Both ferrets and degus exhibited significantly higher metabolic rates and cost of transport (CoT) values when moving in the tunnel condition relative to overgound locomotion. When comparing CoT values across small (<10kg) mammals, ferrets demonstrated a lower than predicted metabolic cost during both tunnel and terrestrial locomotion, whereas degus were very close to line of best fit. Although tunnel locomotion requires a more striking change in posture for ferrets, ferrets are more efficient locomotors in both conditions than mammals of similar mass.
... singularly breeding mammals (Harrington et al. 1983;Solomon and Crist 2008). Increased overlap during early morning trapping could suggest greater social cohesion and cooperation (Poirier et al. 1978;Drea et al. 1996) or could suggest that adults forage more closely together due to the benefits of reduced predation risk (Ebensperger and Wallem 2002 (Vleck 1979(Vleck , 1981Bennett and Faulkes 2000;Ebensperger and Bozinovic 2000a). Degu social groups often use the same burrow systems repeatedly or move into existing burrow systems, minimizing the current utility of coordinated digging among group members. ...
Thesis
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Evidence suggests that harsh and variable environmental conditions modulate the fitness benefits associated with increased group size in some species. Social network analysis is a more powerful approach to examine this relationship, as the quality of interactions is more important than quantity. Using 9 years of data, I determined how mean and coefficient of variation (CV) of nine ecological variables modulated the relationship between social network metrics on direct fitness in the plurally breeding rodent, Octodon degus. As predicted, increased social structure was most beneficial when food abundance was more variable, mean monthly rainfall was highest, predator abundance was more variable, soil hardness was more variable, and ectoparasitic flea intensity was low and more variable. In contrast, the observed effect of the CV of burrow density and mean food abundance on the relationship between strength and direct fitness contradicted our predictions. Overall, our results illustrate that the harshness and unpredictability of ecological conditions are not mutually exclusive explanations for social structure-direct fitness covariation.
... They are complex, comprising areas for socialising, sleeping, breeding and, for some SPM, food storage. In social species digging can be a cooperative activity (Ebensperger and Bozinovic 2000;Wolff and Sherman 2007). For rabbits, burrowing difficulty influences group size, being smaller where digging is easy but tunnels are prone to collapse, e.g. ...
Article
People have obligations to ensure the welfare of animals under their care. Offences under the UK Animal Welfare Act (HMSO 2006) are acts, or failures of action, causing unnecessary suffering. Veterinary professionals need to be able to provide current, scientifically-based prophylactic advice, and respect the limits of their expertise. The ethical concept of a life worth living and the Five Freedoms are core to welfare (FAWC 2009; Broom and Fraser 2015). Behaviour is a central component, both influencing and influenced by physical health. Keepers of small prey mammals (SPM) frequently misunderstand their behaviour and how to meet their needs. This review provides insight into the physical-social (external) and the cognitive-emotional (internal) environments of SPM, contextualised within an evolutionary perspective. This is extrapolated to captivity and practical suggestions given for meeting behavioural freedoms and enhancing client understanding and enjoyment of their animals, thereby improving welfare for both.<br/
... But unlike the Holarctic zone, a tropical climate is characterized by changes of wet and dry seasons. And harsh ecological conditions associated with the dry season are considered as one of the factors promoting formation of groups with complicated social structure among hystricognath rodents (Jarvis, 1978(Jarvis, , 1985Bennett & Jarvis, 1988;Jarvis et al., 1994;Ebensperger, 1998Ebensperger, , 2001Ebensperger & Bozinovic, 2000;Ebensperger & Cofré, 2001). ...
Article
There are two types of complex social units - aggregations and family groups - in rodent populations, with an essential difference in their social organization. The impact of ecological factors on the evolution of sociality in rodents (the transition from solitary towards family-group lifestyle) is still unclear. The inter-specific comparative analysis based on quantification of social traits related to the spatial-and-ethological population structure and cooperation allows author to propose a new conceptual approach to the assessment of differences between the species under consideration in terms of the evolution of sociality. A new conceptual model of the evolution of sociality in rodents should incorporate ecological conditions and social factors, including cooperation, operating as a complex of selective forces promoting formation of family groups.
... In addition, degu demonstrate social-affective bonds across a range of developmental stages (Colonnello et al., 2011). During the daytime, the group members are above ground and coordinate their foraging activity by keeping visual contact (Ebensperger and Bozinovic, 2000;Ebensperger et al., 2002;Quirici et al., 2008;Vasquez, 1997;Colonnello, 2011) and emitting audible vocalizations (Long, 2007;Colonnello et al., 2011). They synchronize their digging activity to build complex underground burrows, their sociality is non-kin based and social networks are influenced by local conditions (Vasquez et al., 2002). ...
Article
Alzheimer's disease (AD) is a multifactorial progressive neurodegenerative disease. Despite decades of research, no disease modifying therapy is available and a change of research objectives and/or development of novel research tools may be required. Much AD research has been based on experimental models using animals with a short lifespan that have been extensively genetically manipulated and do not represent the full spectrum of late-onset AD, which make up the majority of cases. The aetiology of AD is heterogeneous and involves multiple factors associated with the late-onset of the disease like disturbances in brain insulin, oxidative stress, neuroinflammation, metabolic syndrome, retinal degeneration and sleep disturbances which are all progressive abnormalities that could account for many molecular, biochemical and histopathological lesions found in brain from patients dying from AD. This review is based on the long-lived rodent Octodon degus (degu) which is a small diurnal rodent native to South America that can spontaneously develop cognitive decline with concomitant phospho-tau, β-amyloid pathology and neuroinflammation in brain. In addition, the degu can also develop several other conditions like type 2 diabetes, macular and retinal degeneration and atherosclerosis, conditions that are often associated with aging and are often comorbid with AD. Long-lived animals like the degu may provide a more realistic model to study late onset AD.
... developmental stages (Colonnello et al., 2011). During the daytime, the group members are above ground and coordinate their foraging activity by keeping visual contact (Ebensperger and Bozinovic, 2000;Ebensperger et al., 2002;Quirici et al., 2008;Vasquez, 1997;Colonnello, 2011) and emitting audible vocalizations (Long, 2007;Colonnello et al., 2011). They synchronize their digging activity to build complex underground burrows, their sociality is non-kin based and social networks are influenced by local conditions (Vasquez et al., 2002). ...
Book
Neurodegenerative diseases are the most frequent cause of dementia, representing a burden for public health systems (especially in middle and middle-high income countries). Although most research on this issue is concentrated in first-world centers, growing efforts in South America are affording important breakthroughs. This emerging agenda poses new challenges for the region but also new opportunities for the field. This book aims to integrate the community of experts across the globe and the region, and to establish new challenges and developments for future investigation. We present research focused on neurodegenerative research in South America. We introduce studies assessing the interplay among genetic, neural, and behavioral dimensions of these diseases, as well as articles on vulnerability factors, comparisons of findings from various countries, and works promoting multicenter and collaborative networking. More generally, our book covers a broad scope of human-research approaches (behavioral assessment, neuroimaging, electromagnetic techniques, brain connectivity, peripheral measures), animal methodologies (genetics, epigenetics, proteomics, metabolomics, other molecular biology tools), species (all human and non-human animals, sporadic, and genetic versions), and article types (original research, review, and opinion papers). Through this wide-ranging proposal, we hope to introduce a fresh approach to the challenges and opportunities of research on neurodegeneration in South America.
... In degus, soft soils require less energy to move than hard soils (Ebensperger & Bozinovic, 2000a). Degus that coordinate digging with other group members remove more soil per capita than solitary degus (Ebensperger & Bozinovic, 2000b). If plural breeding results in decreased costs of burrow construction and maintenance, we predict greater per capita number of offspring weaned and lower standardized variance in direct fitness with increasing number of adult females and adults males per group and when soil hardness is the greatest or most variable (Predictions 13 and 14, Table 1). ...
Article
We report the results of a 6-year study of social (number of adult males/females, relatedness of females, communal litter size) and ecological (mean/CV of food abundance, soil hardness, burrow openings) factors influencing the direct fitness of plurally breeding degu (Octodon degus) females. The best fit models for per capita offspring weaned and standardized variance in direct fitness (within-group variation) included the number of adult males per group. Per capita number of offspring weaned decreased and standardized variance in direct fitness increased with increasing number of adult males per group. Thus, females experience a cost associated with males that is not shared equally. Standardize variance in direct fitness decreased with increasing communal litter size. All other factors were not significant predictors of direct fitness variation. Our study suggests that plural breeding may not be as egalitarian as previously thought. Consequences of plural breeding may be influenced by intra- and inter-sexual conflict.
... In particular, opposite-sex pairs are more likely to dig simultaneously in the same burrow -a more efficient mode of burrow elongation that produces overall longer burrows despite no change in total digging duration. This simultaneous digging behaviour is reminiscent of "chain digging" observed in other communal burrowing mammals, such as eusocial mole rats 32 and group-living degus 33 , and suggests that distantly related rodent species may have converged upon a common strategy for the efficient excavation of shared living space. ...
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While some behaviours are largely fixed and invariant, others can respond flexibly to different social contexts. Here, we leverage the unique burrowing behaviour of deer mice (genus Peromyscus) to investigate if and how individuals of three species adapt their behaviour when digging individually versus with partners. First, we find that pairs of mice from monogamous (P. polionotus) but not promiscuous (P. maniculatus, P. leucopus) species cooperatively construct burrows that are approximately twice as long as those dug by individuals and similar in size to burrows found in the wild. However, the length of burrows built by P. polionotus pairs differs: opposite-sex pairs construct longer burrows than same-sex pairs. By designing a novel behavioural assay in which we can observe and measure burrowing behaviour directly, we find that longer burrows are achieved not by changing individual behaviour, but instead because opposite-sex pairs are more socially cohesive and thus more likely to dig simultaneously, which is a more efficient mode of burrow elongation. Thus, across social contexts, individual burrowing behaviour appears largely invariant, even when the resultant burrow from pairs of mice differs from expectation based on individual behaviour, underscoring the fixed nature of burrowing behaviour in Peromyscus mice.
... Thus, it appears that non-social rodent species subjected to harsh conditions tended to either retreat to milder niches or evolve sociality to cope with increasing aridity. The emergence of sociality would be adaptive in the context of facilitating cooperative behaviors that offset the physiological demands of living in a harsh environment (e.g., communal nesting, foraging, constructing shelters, engaging in group territory defense [21,[23][24][25][26]; Figures 3D-3F; Table S1). Moreover, cooperating as a group would be an effective strategy for individuals to offset the costs of reproduction [27][28][29]. ...
Article
Climate change is generating an intensification of extreme environmental conditions, including frequent and severe droughts [1] that have been associated with increased social conflict in vertebrates [2-4], including humans [5]. Yet, fluctuating climatic conditions have been shown to also promote cooperative behavior and the formation of vertebrate societies over both ecological and evolutionary timescales [6]. Determining when climatic uncertainty breeds social discord or promotes cooperative living (or both) is fundamental to predicting how species will respond to anthropogenic climate change. In light of this, our limited understanding of the order of evolutionary events-that is, whether harsh environments drive the evolution of sociality [6] or, alternatively, whether sociality facilitates the invasion of harsh environments [7]-and of how cooperation and conflict coevolve in response to environmental fluctuation represent critical gaps in knowledge. Here, we perform comparative phylogenetic analyses on Australian rodents (Muridae: Hydromyini) and show that sociality evolves only under harsh conditions of low rainfall and high temperature variability and never under relatively benign conditions. Further, we demonstrate that the requirement to cooperate under harsh climatic conditions generates social competition for reproduction within groups (reflected in the degree of sexual dimorphism in traits associated with intrasexual competition [8]), which in turn shapes the evolution of body size dimorphism. Our findings suggest that as the environment becomes more severe [1], the resilience of some species may hinge on their propensity to live socially, but in so doing, this is likely to affect the evolution of traits that mediate social conflict.
... Degu social groups lack kin structure (Quirici et al. 2011;Davis et al. 2016), implying that indirect fitness benefits are less likely. In contrast, evidence is consistent about degu sociality is linked to direct benefits, as enhanced ability to detect predators Ebensperger et al. 2006), or enhanced efficiency to build or maintain underground burrow systems (Ebensperger and Bozinovic 2000). ...
Article
Homophily by morphological and behavioral traits has been described in several species of vertebrates, but its functional consequences remain poorly studied. Homophily by plurally breeding females may improve direct fitness by enhancing reproductive success. Female mammals may exhibit phenotypical masculinization due to exposure to androgens during early development, a condition that is associated with maternal performance during subsequent breeding. Our goal was to assess whether female composition (in terms of masculinization) of plurally breeding groups influences female fitness in a natural population of degus (Octodon degus). We assessed if plurally breeding female degus assort themselves by anogenital distance (AGD), an accurate measure of masculinization level. We also quantified if homophily by AGD phenotype affects female reproductive success and the reproductive output of the group. Plurally breeding groups typically included similarly masculinized (i.e., long AGD) females or similarly feminized (short AGD) females, indicating a strong degree of homophily. Females weaned more offspring in plurally breeding groups with more masculinized females. Additionally, standardized variance in the number of offspring weaned decreased in plurally breeding groups with mostly masculinized females, indicating greater reproductive equality in these groups. We conclude that female degus organize into homophilic social groups of similar AGD, and that social groups of masculinized females exhibit a higher reproductive success.
... In natural conditions, the degu colony is comprised of an extended family group of 1-6 females and 1-3 males dwelling in open plains during the day and underground burrows at night (Ebensperger, Hurtado, Soto-Gamboa, Lacey, & Chang, 2004;Fulk, 1976). Both sexes care for the offspring, which are weaned at about the fifth week of age (Ebensperger & Bozinovic, 2000;Ebensperger, Veloso, & Wallem, 2002;Fulk, 1976;Lee, 2004). Like most herbivores but in contrast to common laboratory rodents, degu pups are relatively mature at birth: their sensory system is developed and they perform short travels around the nest from the first hours after birth (Wilson, 1982). ...
Article
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We investigated whether positive daily peer-interactions counteract the effects of isolation in Octodon degus. Twenty-five-day-old degus were either isolated (ISO), socially housed (SOCIAL), or isolated and allowed 1-hr daily peer interaction (PARTIAL-ISO). The animals were observed over 4 weeks. Just prior to isolation and after 2 weeks of individual housing, the subjects were assessed for response to pleasant stimuli via a sucrose preference test and to fearful situations in open field and startle tests. Two weeks after the previous tests, the subjects were retested as above and observed in novelty and sociability tests. Only the ISO group showed significant alterations in sensitivity to reward and increased risk-taking behavior in fearful situations. The ISO group consumed more sucrose, spent less time freezing in the startle test and exhibited increased exploration in open field and novelty tests compared to PARTIAL-ISO and SOCIAL groups. In the sociability test, the SOCIAL group vocalized more than the other two groups during encounters with an unfamiliar degus. Our findings suggest that (i) chronic isolation induces alteration of hedonic, emotional and social profiles, with a maturational delay in fear-related responses; (ii) friendly interaction attenuates most behavioral changes induced by total social isolation. However, the positive effects of daily social interactions did not fully counteract deficits in social vocalizations. Our study represents one of the few available studies focused not only on the consequences of negative life events in this species, but also the protective role of relatively short periods of positive social activity on subsequent emotional development. ß 2010 Wiley Periodicals, Inc. Dev Psychobiol 53: 280-290, 2011.
Article
The degu (Octodon degus) is a rodent that normally constructs burrows for nesting and rearing. To navigate inside these burrows, degus may use idiothetic and/or sensory cues more than visual information, which is less effective in burrows. Spatial information for navigation is processed in several key brain regions including the retrosplenial cortex (RS). However, the structural characteristics of the degu RS have not been previously reported. The present study measured the sizes of the RS and constituent areas 29 and 30 in the degu, and compared these to those found in the rat, which is a terrestrial rodent. The proportion of the rostrocaudal length of the entire RS relative to that of the entire cortex was significantly larger in degus versus rats. The proportion of the rostrocaudal length of the RS at levels rostral to the splenium of the corpus callosum relative to that of the entire cortex was also significantly larger in degus versus rats. Furthermore, the ratio of the estimated volume of area 29 relative to that of area 30 was significantly larger in degus versus rats. These results show that the degu has a rostrocaudally longer rostral RS with a larger area 29 compared to the rat, which suggests that these structural features may be relevant to differences in spatial information processing between the fossorial degu and terrestrial rat.
Book
In this unique book, Peter S. Ungar tells the story of mammalian teeth from their origin through their evolution to their current diversity. Mammal Teeth traces the evolutionary history of teeth, beginning with the very first mineralized vertebrate structures half a billion years ago. Ungar describes how the simple conical tooth of early vertebrates became the molars, incisors, and other forms we see in mammals today. Evolutionary adaptations changed pointy teeth into flatter ones, with specialized shapes designed to complement the corresponding jaw. Ungar explains tooth structure and function in the context of nutritional needs. The myriad tooth shapes produced by evolution offer different solutions to the fundamental problem of how to squeeze as many nutrients as possible out of foods. The book also highlights Ungar's own path-breaking studies that show how microwear analysis can help us understand ancient diets. The final part of the book provides an in-depth examination of mammalian teeth today, surveying all orders in the class, family by family. Ungar describes some of the more bizarre teeth, such as tusks, and the mammal diversity that accompanies these morphological wonders. Mammal Teeth captures the evolution of mammals, including humans, through the prism of dental change. Synthesizing decades of research, Ungar reveals the interconnections among mammal diet, dentition, and evolution. His book is a must-read for paleontologists, mammalogists, and anthropologists. © 2010 The Johns Hopkins University Press. All rights reserved.
Thesis
In this thesis selected aspects of the ecology of the common hamster (Cricetus cricetus [L.]) were investigated with reference to reasons for the decline of this species. The field study was carried out from 1994 to 2000 on the plot “Wartweg”, on a sub-population in the Hakel woodland area on the south edge of the Magdeburger Börde in Saxony-Anhalt, Germany. Burrow mapping, capture-mark-recapture and telemetric investigations were undertaken to study the mortality, the use of space and of burrows, the family break up and the effects of selected habitat factors like soil and agricultural management on the common hamster. Additionally, historical data from the adjacent area of the Hakel hinterland were evaluated. At that time these distributions were connected with the plot “Wartweg” in a metapopulation. The concentration of persistent pesticides were analysed on samples of carcasses from the whole of Saxony-Anhalt. Within the scope of the burrow mapping, the distribution of the hamster burrows around and on the plot “Wartweg” was analysed according to soil type. In the former district of Potsdam (state: Brandenburg) the decline of the hamster and its present distribution were compared with an agricultural soil map. Both investigations showed that the common hamster prefers the best agricultural soils with a high proportions of clay and silt. The distribution of burrows, especially of winter burrows, directly depends on the soil quality. The occurence of colour variations in the common hamster between 1915 and 1980 was investigated in a sample of 73 657 hamsters collected by a professional hamster trapper. Overall the percentage of variant individuals was 0.0855 % and the frequency decreased significantly over the observed period. The most frequent colour variants were white hamsters followed by piebald and yellow animals and only one black hamster. There could be a possible connection between the decline in hamster numbers during this period in the study area and the reduced frequency of colour morphs. None of the analysed liver and fat samples of common hamster carcasses was without any residues, but contamination with HCB, γ-HCH, pp-DDT, pp-DDE, pp-DDD, Dieldrin, PCB 101, PCB 138, PCB 153, PCB 180 was identified at only very low levels, often at or below the detection limit. The concentrations of metals (Pb, Cd, Hg, Cu) measured in muscle and kidney samples of common hamsters also occurred only in very low levels, often at or below the detection limit. One reason for the low contamination is the reduced application of the analysed substances in agriculture in recent decades. The low concentrations may therefore be a reflection of the ubiquitous distribution of these substances. At present the investigated substances do not play an important role in the health or vitality of the common hamster. The mortality of the common hamster was investigated in samples of radio tagged individuals and carcasses from two regions of Germany with different kinds of agricultural management. Predation and winter mortality turned out to be the main mortality factors, followed by disease and death caused by agricultural machinery during the harvest or other management measures. The main mortality factors were all directly or indirectly linked to agriculture. Present agricultural management exacerbates predation and increases winter mortality in this species. Crops with a prolonged vegetation cover and food supply are crucial for the survival of common hamsters on farmland with intense agricultural management. It was shown that in contrast to the commonly accepted opinion, females changed their burrows after breeding and left their breeding burrows to their young. At that time the young 89 had reached a mean age of about 5 weeks. From this time the juveniles of one litter started to separate and search for their own burrows. This sibling separation covered a period of about 3-5 weeks. The results of this study indicated that in the time after the family break up most juveniles got lost. Only 10 % of the juveniles were trapped again at other burrows. Juveniles leaving the birth burrow at an age of over 40 days had a higher chance of settling down in their own burrows. In addition the home range of and use of space by common hamsters were investigated. Median minimum convex polygons (95 % MCPs) for male adult hamsters were 1.85 ha and 0.22 ha for adult females. Most adult hamsters shifted home ranges after a time, sometimes over large distances. Despite their large home ranges, hamsters concentrated their activity (60 % of fixes) in small core areas. Male core areas were particularly multinuclear and could cover several female burrows. Higher levels of overlap of home ranges only occurred between the sexes due to the multigamous mating system. Most fixes during activity were at or near the hamster’s own burrow. The mean distance was significantly different between sexes, 33 m in males and 17 m in females. But also fixes of a greater distance of up to 300 m from the burrow normally used were not far away from a different hamster burrow, in the median 13 m. In Saxony-Anhalt male common hamsters inhabited, with 9.6, more burrows in the mean than females (3.6 burrows) in the course of the year. In June and July males used significantly more burrows per month and made more burrow changes than females. However, females also used more burrows during the summer, one more than in May or September. The reason for this sexual difference is the reproductive behaviour of this species. Due to the polygamous mating system males searched for and inhabited specifically female burrows for a shorter time period besides their own activity centre. Males successively used burrows which were situated at significantly greater distances than those of females. The maximum distance between two successively used burrows was 325 m in both sexes. Due to the high reuse of abandoned ones, hamster burrows can last for many years. In many behavioural patterns the common hamster has a high plasticity and in many factors a wide ecological valency. For that reason all results obtained refer to the specific circumstances of the research area. With different population densities, habitat and environmental conditions other behavioural pattern and population parameters in this species are possible.
Article
Mammals exposed to low temperatures increase their metabolic rate to maintain constant body temperature and thus compensate heat loss. This high and costly energetic demand can be mitigated through thermoregulatory behavior such as social grouping or huddling, which helps to decrease metabolic rate as function of the numbers of individuals grouped. Sustained low temperatures in endothermic animals produce changes over time in rates of energy expenditure, by means of phenotypic plasticity. However, the putative modulating effect that huddling exerts on the flexibility of the basal metabolic rate (BMR) due to thermal acclimation remains unknown. We determined BMR values in Octodon degus, an endemic Chilean rodent, after being acclimated either to 15°C or 30°C during 60 days, both alone and in groups of 3 and 5 individuals. At 15°C, BMR of huddling individuals was 40% lower than that of animals housed alone. Moreover, infrared thermography revealed a significant increase in local surface temperatures in huddled animals. Furthermore, individual thermal conductance was lower in individuals acclimated to 15°C than at 30°C, but no differences were observed between single and grouped animals. Our results indicate that huddling prevent an increase in BMR when animals are acclimated to cold conditions and that this effect is proportional to the number of animals grouped.
Article
We investigated factors leading to variation in social complexity or ‘social systems’ among plateau pika family groups within a contiguous local population across 2 years. Plateau pikas are small, diurnal, nonhibernating, sexually monomorphic lagomorphs that occupy family home ranges on open alpine meadows on the Qinghai-Tibetan Plateau. Expression of the social organization, social structure, mating system and parental care system in plateau pikas did not follow expectations from traditional ecological or evolutionary explanations. Variability in plateau pika family group size and the transitions of group size between years allowed us to investigate potential advantages and disadvantages of group living. Evidence that group living served to protect pikas against predation was weak. Although social huddling could have minimized thermoregulatory costs during the extremely cold Tibetan winters, there was no correlation of overwinter survivorship among pika families of different sizes. There was no apparent group-living benefit with regard to foraging, and the occurrence of cohesive social families on the flat, continuous meadow contradicts the hypothesis that sociality is related to patchiness of critical resources. Cost of maintaining burrows appeared unrelated to group size. Most interactions between pikas occurred within family groups and were affiliative (99% of adult interactions; 97% of adult–juvenile interactions), and most interactions between adult males of different family groups were aggressive (96% of interactions). Matings were primarily within families (88% of copulations). Pikas also possess a complex vocal repertoire that enhanced interactions within social families. Demographic constraints associated with variable overwinter survivorship appeared to be the dominant precondition that produced a given family size and mating system type, coupled with selective dispersal by some pikas before the start of the breeding season. Paternal care enhanced juvenile survival, and thus led to an equalization of reproductive success among adults in families with different mating combinations.
Thesis
The juveniles of the mound-building mouse, Mus spicilegus, build an imposing mound to overwinter. This structure is vital for the species, since only the animals tha tenter the mound will survive to the next reproductive season. The impressive work accomplished by these tiny animals is the result of a communal effort. Previous work had shown that, inside a group of six juveniles, there was a behavioural differentiation in a transport task of the building process, with animals transporting up to 80% of the proposed material. In the present work, by using the RFID technique, we determined the existence of a division of labour during the transport task with different individuals transporting two different materials. These two materials correspond to two different steps of the building process in the field. This division of labour in building tasks has rarely been described in mammals before. Three categories of animals were observed : carriers, occasional carriers and non-carriers. We did find that the affinity for the building material played a role in the determination of the specialists, with mice showing a higher level of affinity having a higher probability to become a specialist, pointing to a response thre shold. Other individual characteristics (i.e. levels of anxiety, neophilia and locomotion) were tested but do not seem to play an important role during the setting up of the specialization. In the other hand, when removing individuals from the group the identity of carriers changed, even if the removed individuals did not perform any transport. However, the work organization with a structure of carriers,occasional carriers and non-carriers was extremely robust and resisted the perturbations even at a low initial group size. So, the mechanism behind the work organization in this species seems to be modulated by a response thre shold as first instance, followed by self-organized processes that override the existing response thresholds and ensure the stability of the system when the group is disturbed. Morework is necessary in order to determine which are the mechanisms involved in the work organization of work of M. spicilegus and understand how they interact.
Article
Sociality and cooperative rearing may have evolved to increase direct fitness when conditions are challenging to reproduction and/or to reduce environmentally induced variance in fecundity. Examination of these hypotheses comes mostly from studies on singularly breeding birds where reproduction is monopolized by a male-female adult pair. Instead, little is known about plurally breeding species where most group members breed and rear their offspring communally. We used data from an 8-year field study to explore the relationship between the ecology and per capita offspring production and survival (2 components of reproductive success and direct fitness) of the plurally breeding rodent Octodon degus. We determined how mean and variance in food abundance, precipitation levels, degu density, soil hardness, predation risk, and thermal conditions modulated the effects of group size and number of breeding females (potential for breeding cooperation) on reproductive success. The effect of number of females per group on the per capita number of offspring produced was more positive during years with lower mean food and degu density. More positive effects of group size (on per capita number of offspring produced and on per capita surviving offspring) and of the number of females (on per capita number of offspring produced) occurred during years with decreasing mean precipitation levels. Thus, the hypothesis that group living and communal rearing are more beneficial (or less costly) under low mean habitat conditions is supported. In contrast, the social effects on reproductive success seem insensitive to variance in ecological conditions.
Article
Specialization can be defined as when specific individuals perform a specific task for a relatively long period of time. The mound-building mouse is a suitable species to study specialization during a collective construction task, as juveniles build imposing mounds in which to overwinter. The process includes several successive phases involving the transport and piling up of different kinds of materials along with covering up the mound with dirt and digging galleries. Laboratory studies revealed that within a group of six individuals, two individuals transported most of the material provided for building. We tested whether this behavioural differentiation corresponded to a real specialization. Mice were given two different transport tasks corresponding to different phases of the building process. Experimental groups received two different building materials in two consecutive periods while control groups received the same building material for both periods. As predicted, in experimental groups, carriers of one material were not the same individuals as the carriers of the second material. This shift in the identity of the carrier according to the material we provided indicates a specialization for a different transport task. By contrast, in control groups, mice tended to keep their carrier status during the two periods. We concluded that, at least under controlled laboratory conditions, a task-related specialization occurred during the collective construction of the mound. This specialization could be explained as part of a division of labour in the mound-building mouse.
Article
Parasite-mediated behavioral changes in their hosts have been documented in many species, but field evidence is scarce. The protozoan Trypanosoma cruzi is transmitted by insect vectors to several mammal species. Although previous studies have shown high levels of infection in hosts and vectors, it is unknown if this protozoan affects movement behavior of mammal reservoirs. Here we examine, under natural conditions, the existence of movement alterations in two species of rodents (Octodon degus and Phyllotis darwini) when infected with T. cruzi, evaluated for four consecutive years. We found that infected O. degus travelled shorter distances than those non-infected, the opposite was found for P. darwini. We also detected a strong inter-annual effect for both species. Our results show that rodent species respond differentially to T. cruzi infection in regard to their movements, which may have implications in disease spreading.
Chapter
Caviomorph rodents show a large diversity of living forms, with many social species, showing a large spectrum of cooperative behaviors. This chapter begins by reviewing the four mechanisms proposed for the evolution of cooperative behaviors, namely, kin selection, by-product mutualism, reciprocity, and group selection. Thereafter, it reviews examples of cooperative behaviors observed in caviomorph species, comprising anti-predator vigilance, communal breeding, and kin-biased behaviors. The review shows that most studies on cooperative behavior have been carried out in a few species, highlighting Octodon degus as the most studied species. Several studies have assessed antipredator vigilance within social groups, though results so far show that changing vigilance levels according to group size seems to be a group size effect rather than a cooperative strategy. Communal breeding is a commonly observed social system where some individuals provide care for offspring that are not their own, and several behaviors seem to be kin selected, though several studies show contradictory results. Future research should tackle a range of ecological conditions, using intra- and inter-specific studies.
Article
The unique social behavior of degus (Octodon degus) makes them a suitable animal model for social and emotional studies. Using degu pups, we examined the effects of repetitive short-term isolation on novel object exploratory behavior at 3, 4, 5, 6, and 7 weeks of age. Isolated pups were separated from their family 14 times for 30 min a day from 6–23 days post-birth. Non-isolated pups were reared with their families. A two-condition (with-mother or without-mother) object exploration test showed an isolation effect at 3 weeks. Compared with non-isolated pups, isolated pups showed longer start latency under the without-mother condition than under the with-mother condition, and less frequent contact with a novel object even when their mother was present. Non-isolated pups showed more frequent contact with the novel object under the with-mother condition than the without-mother condition. Repetitive maternal separation in early life negatively affected degu novel object exploratory behavior.
Chapter
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.
Chapter
Understanding the fitness consequences of group-living and breeding strategies is critical to advancing a theory for the evolutionary significance of animal social systems. To date, our understanding of the fitness consequences in caviomorphs is limited to six species. The available evidence suggests that sociality positively affects fitness in female capybaras and increases offspring survival in maras. Laboratory studies suggest that the number of males or the dominance status of females is an important predictor of female reproductive success in two cavies. In colonial tuco-tucos, per capita direct fitness is lower in groups than for solitary females, suggesting an immediate cost to sociality. In degus, the fitness consequences of sociality depend on the time frame of study. In studies encompassing two or three years, the direct fitness of degu females decreases with increasing group size. However, a recent study encompassing eight years revealed that the relationship between direct fitness and group size is most positive in years with low mean rainfall and food abundance, suggesting that sociality has evolved as a means to ensure reproductive success under harsh conditions. To advance our understanding, it is critical that researchers quantify fitness consequences of group-living in more species. In well-studied species, researchers have the opportunity to determine the extent of intra-specific variation in sociality–fitness relationships as well as use modern analytical tools to quantify how social interactions within groups influence individual reproductive success and reproductive skew.
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We examined intraspecific space use of free-ranging kangaroo rats (Dipodomys heermanni) during the breeding season using behavioral observations and radiotelemetry. Home ranges of males were significantly larger than those of females. Female D. heermanni maintained exclusive territories with essentially nonoverlapping home ranges, whereas home ranges of males overlapped with both same- and opposite-sex conspecifics, reflecting the different strategies of the different sexes. This follows a general pattern found in mammals in which spacing reflects limiting resources. There was, however, high individual variation in home range size for males, which may suggest a role for social interactions in determining spatial behavior in this species. D. heermanni, a medium-size species, appears intermediate in space use compared with the larger D. spectabilis and the smaller D. merriami.
Article
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We quantified the behavior of juvenile pine voles (Microtus pinetorum) in families maintained in outdoor enclosures protected from rain and predators and determined the effects of number of juveniles present (0-3) on their younger siblings and their parents. juveniles exhibited behaviors characteristic of helpers in cooperative breeding species: brooding, grooming, and retrieving younger siblings, and maintaining nests, runways, and food caches. The number of juveniles had no effect on weights, growth rates, or survival of younger siblings or on survival of parents, but families with three juveniles had shorter interlitter intervals than other families. There was a trend toward lower weights for younger siblings when juveniles continued to nurse from their mothers. juveniles brooded and groomed younger siblings more when their mothers were absent than when mothers were present. In families with juveniles, younger siblings were alone significantly less often than in families without juveniles, but number of juveniles in the family had little effect on duration or frequency with which juveniles brooded or groomed younger siblings. These data are consistent with cooperative breeding having evolved via individual selection for delayed dispersal. We argue that the limited availability of vacant tunnel systems and the high cost of digging new tunnel systems constrains dispersal in pine voles and has led to the evolution of cooperative breeding.
Article
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Summary Prolonged toleration of offspring in marmots was hypothesized to be (1) a means of preventing dispersal of undersized young (Barash 1974 a) or more generally (2) continued parental investment, increasing the probability of descendant survival and reproduction (Armitage 1981, 1987). These hypotheses are tested in this paper for one of the most social of marmot species, the alpine marmot. The animals studied lived in groups within territories defended by a dominant male and female, or as floaters lacking a well-defined home range. Offspring did not disperse before sexual maturity at age 2 (Fig. 1). Only territorial females bred, whereas territorial males were not able to monopolize reproduction likewise (Table 2). Dispersers had similar spring mass to nondispersers (Table 4). Hence, hypothesis 1 is not supported, at least not for adult-sized, > 2 years old animals. During their residency, 19% of subordinates obtained their natal territory or a neighboring one (Fig. 2). Long distance dispersal bore a high mortality risk. Thus, toleration of mature offspring could well represent parental investment. Other results, however, suggest additional influences on the timing of dispersal. (i) Males dispersed later than females (Fig. 3), possibly because of mate sharing by territorial males (see Emlen 1982). (ii) The higher mass loss of dispersers during the previous winter indicates that weak animals were forced to leave (Table 5) despite presumably lower chances of becoming territorial (Table 3). (iii) Subordinate animals which could not be the offspring of both territorials present were not more likely to disperse (Fig. 3). (iv) Lower dispersal rates when immatures lived in the group (Fig. 3) may indicate benefits from the subordinates' presence for rearing young.
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The trophic ecology of eleven predator species (Falconiforms: Buteo polyosoma, Elanus leucurus, Falco sparverius, Geranoaetus melanoleucus, Parabuteo unicinctus; Strigiforms: Athene cunicularia, Bubo virginianus, Tyto alba; Carnivores: Dusicyon culpaeus; Snakes: Philodryas chamissonis, Tachymenis peruviana) in two nearby localities of central Chile is analyzed. The localities exhibit the typical climate (hot-dry summers, coldrainy winters), and vegetation (chaparral), of mediterranean ecosystems. Densities of the staple prey (small mammals) were estimated by seasonal trapping during two years in both open and dense patches of chaparral. The trophic parameters examined are: 1) proportion of diurnal, crepuscular, or nocturnal prey found in the predators' diet; 2) relationship between abundance of different mammalian prey in the predators' diet, and in both open and densely vegetated habitat patches; 3) mean weight and variance of weight of small mammal prey consumed; 4) average weight of the predators; 5) food-niche breadth of the predators; 6) relationship between average weight of predators and mean weight of mammalian prey taken, its variance, and food-niche breadth; 7) overlap in food-niche between all the predator species; 8) guild packing of the predators. Parameters 1) and 2) are used to assess the importance of temporal and habitat segregation of the predators, respectively; parameters 3), 4), 5), and 6) provide information on the possibilities of partitioning the prey resources among the predators; parameters 1), 2), 7) and 8) are used to investigate the organization of the community in terms of guilds. Three niche dimensions seem to be important in determining the structure of the predator community: 1) hunting activity period (diurno-crepuscular, nocturno-crepuscular), 2) hunting habitat (open, or both open and dense patches), and 3) mean prey size taken. Segregation along these three axes results in generally low food niche overlaps (90% in pair-wise comparisons) can be recognized: a) the carnivorous-insectivorous guild formed by the diurnal raptors A. cunicularia and F. sparverius, which tend to hunt in open habitat patches; b) the herpetophagous guild formed by the diurnal snakes P. chamissonis and T. peruviana, which presumably hunt in open habitat patches; c) the carnivorous guild (highly specialized in the capture of two rodent species) formed by the diurnal raptors B. polyosoma, G. melanoleucus, P. unicinctus, and the carnivore D. culpaeus, which hunt in open habitat patches. The diurnal raptor E. leucurus is not clearly associated with any guild, and the only two nocturnal raptors in the community (B. virginianus and T. alba) exhibit marked differences in their trophic ecology.
Article
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The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only; 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September–November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.
Article
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Multi-variate analysis of life-history traits of 18 species of burrowing sciurids indicates that reproductive effort is determined by body-size energetics. Other traits, such as age adult weight reached, age of dispersal, length of time of gestation, were significantly correlated with body size. A principal component analysis suggested that the complex of life-history traits could be reduced to four components: body size (=weight), seasonality, specific reproductive effort, and maturity. The variation in the sociality index was best explained by age of first reproduction and age adult weight reached. Generally, species are more social when large body size combined with a relatively short growing season is associated with delayed dispersal and occurs in those species typically breeding for the first time at age two or older. Sociality in these species may have evolved through retention of daughters within the maternal home range as a means of continuing reproductive investment beyond weaning.
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We used giving-up densities in food patches to measure the effects of several direct (left by the predator) and indirect (environmental correlates of risk) cues of predatory risk on the foraging behavior of free-living fox squirrels ( Sciurus niger ) and thirteen-lined ground squirrels (Spermophihis tridtctmlineatus). Increases in giving-up density in response to stimuli allow quantitative comparisons of the effects of different types of cues. We used olfactory (urine of red fox) and visual (plastic models of owls) direct cues. As indirect cues, we used mkrohabitat (near or far from a refuge), background coloration (white, green, and brown tarpaulins), and escape substrate (canvas tarpaulins versus natural surrounding substrates). Both squirrel species responded most strongly to microhabitat Fox squirrels increased their giving-up density by 97&percnt; when feeding 4–6 m from a tree compared to feeding at the tree base. Thirteen-lined ground squirrels increased giving-up densities 84&percnt; when feeding 2 m from their burrows compared to feeding at the burrow entry. In response to an unfavorable escape substrate (canvas versus grass), fox squirrel giving-up densities increased 61&percnt;. Fox squirrels and ground squirrels increased giving-up densities 26&percnt; and 35&percnt;, respectively, in response to a plastic owL Background coloration had no demonstrable effect on the giving-up densities of fox squirrels. In contrast to other work on nocturnal mammalian herbivores and granivores, the diurnal fox squirrels did not respond to olfactory cues.
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Article
We examined the ways a small diurnal rodent, Octodon degus, copes with high environmental temperatures in a semiarid region in northcentral Chile. We hypothesized that degus are constrained in use of microhabitat by their limited tolerance to high environmental temperatures as well as by presence of predators. We recorded their activity from tracks on smoked tiles, under shrubs and in the open, and in large plots with predators either present or excluded. We monitored body temperature in the two microhabitats during warm and cool seasons. Our results support our hypothesis; degus chose covered areas even when predators were absent. We conclude that thermal restriction is a factor in determining use of space by degus.
Article
Data on activity and social behavior of the Chilean degu, Octodon degus, were gathered by direct observation of animals, some of which had been marked for individual recognition. Data from autopsies and external inspection of trapped animals suggested that most reproduction occurs in September at the latitude of Santiago. Degus are diurnal and show morning and evening activity peaks. Social organization is based on group territories, at least during the period after emergence of the young. Mound building (collecting a pile of sticks, stones, and cow dung) was associated with territorial marking. Females of the same social group may rear their young in a common nest burrow. Octodon degus burrows are sometimes used by Abrocoma bennetti, a similar sized rodent, and on two occasions nest burrows were found to be shared by young and mothers of both species.
Article
Preliminary studies indicate that the recently described colonial tuco-tuco (Ctenomys sociabilis) is social. As part of efforts to characterize the behavioral ecology of this species, we examined patterns of use of burrows by members of a free-living population of C. sociabilis located in southern Neuquen Province, Argentina. As many as five adults (one male, four females) were captured within a single colony (spatially distinct cluster of burrow entrances). Spatial relationships among eight adults from three colonies were monitored using radiotelemetry. Each animal was active in only a single colony. Within each colony, the areas used by different adults overlapped extensively (X ≥ 68%) and all animals shared a single nest site. Collectively, these data indicate that a colony of C. sociabilis consists of a single burrow system that may be inhabited by multiple adults. We suggest that comparative analyses of C. sociabilis and other colonial taxa (e. g., colonial African mole-rats; Bathyergidae) will significantly improve our understanding of the factors favoring sociality among subterranean rodents.
Article
Cryptomys damarensis had a digging metabolic rate (DMR) of 2.86 ± 0.31 cm3.g-1.h-1 in damp sand and of 2.58 ± 0.32 cm3.g-1.h-1 in dry sand. DMR was 4.53-5.03 times the resting metabolic rate (RMR). Burrowing speed was 3.53 ±0.75 m.h-1 in damp sand and 0.92 ± 0.33 m.h-1 in dry sand. Body temperature (Tb) increased by 1.3°C during burrowing in dry sand. Heterocephalus glaber had a DMR of 3.36 ± 0.25 cm3.g-1.h-1 in damp sand and of 2.78 ± 0.25 cm3.g-1.h-1 in dry sand. DMR was 4.34-5.25 times RMR. Burrowing speed was 0.75 ± 0.23 m.h-1 in damp sand and 0.30 ±0.02 m.h-1 in dry sand. There was a 2.3°C drop in Tb during burrowing in damp sand. For both species, the cost of burrowing was 1.5-3.7 times greater in dry than in damp sand. Cost of burrowing may be an important factor selecting for body size, differentiation of labour, and polyethism in bathyergids. -from Author
Article
Capybaras, Hydrochaeris hydrochaeris, live in groups of varying size averaging 10 adults of both sexes. Vigilant behaviour was studied in capybaras under natural conditions, using focal-animal sampling on individual females, dominant males and subordinate males from groups of different sizes. There was a significant negative correlation between group size and individual alert rate, and a positive correlation with total group alert rate. Although the reduction in individual rates of vigilance levelled off at group sizes of 9-10, total alert rate continued to increase. The behaviour of the females accounted for most of the variation in individual alert rate and the behaviour of subordinate males accounted for most of the variation in total alert rate. These results suggest that females benefit the most from being in larger groups due to reduced vigilance required, while subordinate males 'pay' for their group membership by the vigilance they perform.
Article
We used woodchucks (Marmota monax) to test predictions of a cost-benefit model of antipredator behavior that flight initiation distance would increase with distance to refuge and with predator approach velocity. We also examined the effects of distance to refuge and predator approach velocity on escape velocity and on both temporal and spatial margin of safety (expected time and distance between predator and burrow at the time of the woodchuck's arrival). The observer, assumed to be perceived as a potential predator, approached juvenile woodchucks from the direction opposite to the burrow at a slow (1.24 m/s) or fast (1.79 m/s) walking pace. When the woodchuck started to flee, the observer recorded the woodchuck's distance from the observer and from its burrow, the time spent running, and whether the woodchuck stopped before reaching its burrow. Flight initiation distance increased consistently with distance to the burrow over the entire observed range (0-25 m) but was not significantly affected by obs
Article
In a 6-yr study, I investigated possible selective bases for coloniality in two species of squirrels (Sciuridae): loosely colonial White-tailed Prairie Dogs (Cynomys leucurus) and densely colonial Black-tailed Prairie Dogs (C. ludovicianus). White-tail study sites were in Wyoming and Colorado, USA; Black-tail study sites were in Colorado and South Dakota. I examined three hypotheses that might explain the evolution of coloniality: (a) shortage of suitable habitat, (b) social facilitation of foraging, and (c) reduced predation. The apparent surplus of unused suitable habitat and the absence of isolated individuals both indicated that prairie dogs are not forced to live together because of habitat shortages. An analysis of prairie dog foraging patterns indicated that there is no social facilitation of foraging in terms of either (a) group hunting of either large or elusive prey, (b) the location of large, scattered food supplies, (c) modification of the soil in order to effect the growth of vegetation that is more favorable or more abundant than that which would otherwise result, or (d) group defense of foraging grounds. Three lines of evidence indicate that reduced predation may be the most important benefit of prairie dog coloniality. First, simulated predatory attacks by badgers (Taxidea taxus) indicated that individuals in large wards (subcolonies) detect predators more quickly than do individuals in smaller wards; further, Black-tails detect predators more quickly than do White-tails. Second, individuals in large wards devote proportionately less time to alertness (i.e., scanning for predators) than do individuals in smaller wards, and Black-tails are less vigilant than are White-tails. Third, breeding synchronization and center-edge differences in individual alertness both indicate the possible importance of self herd effects. Interspecific differences in ward size and ward density may ultimately result because White-tail habitats contain significantly more protective cover than do Black-tail habitats.
Article
The Cape ground squirrel (Xerus inauris) of southern Africa is a tropical species that does not hibernate. Field observations using scan and all-occurrence sampling revealed that this species was highly social. Female Cape ground squirrels formed social units of related females and their subadult young, as is typical for other ground squirrels. Female social groups were usually composed of 2–3 adult females and 2–3 subadults of either sex. Members of these female social groups shared sleeping burrows and feeding ranges. Female social groups did not cooperatively defend their feeding ranges from adjacent groups in other burrow clusters. Interactions within female social groups were highly amicable, and no dominance hierarchy was evident. Males in this species also lived in groups. These all-male bands of up to 19 individuals lived almost independently from female groups. The entire male band shared one home range, although ephemeral sub-bands were formed daily. The composition and size of these sub-bands changed daily. Interactions among males, which were largely amicable, included allogrooming and sleeping together. Analysis of interactions within the band indicated a stable, linear, dominance hierarchy among males. Dispersal in this species appeared to be male biased as is typical of other ground-dwelling squirrels, with males dispersing at reproductive maturity. Males joining male bands were thus dispersers and were not likely to be closely related. Sociality in the Cape ground squirrel may be summarized as highly social female kin clusters and associated social non-kin bands of males.
Article
Ecological data bases were searched for citations dealing with burrows, burrowing vertebrates, and the environmental impacts of this phenomenon. Results from this partial search were divided into categories with artificial boundaries depending on the primary focus of the cited paper. These categories were natural history, ecological theory, and the disciplines of geomorphology, pedology, plant ecology, and animal community ecology. Suggested research topics are presented as well as a simple conceptual model of the role of the burrow in the environment.
Article
In The Black-Tailed Prairie Dog, John L. Hoogland draws on sixteen years of research at Wind Cave National Park, South Dakota, in the United States to provide this account of prairie dog social behavior. Through comparisons with more than 300 other animal species, he offers new insights into basic theory in behavioral ecology and sociobiology. Hoogland documents interactions within and among families of prairie dogs to examine the advantages and disadvantages of coloniality. By addressing such topics as male and female reproductive success, inbreeding, kin recognition, and infanticide, Hoogland offers a broad view of conflict and cooperation. Among his surprising findings is that prairie dog females sometimes suckle, and at other times kill, the offspring of close kin. Enhanced by more than 100 photographs, this book illuminates the social organization of a burrowing mammal and raises fundamental questions about current theory. As the most detailed long-term study of any social rodent, The Black-Tailed Prairie Dog will interest not only mammalogists and other vertebrate biologists, but also students of behavioral and evolutionary ecology.
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