Luis A Ebensperger | Pontificia Universidad Catolica de Chile (original) (raw)

Research papers by Luis A Ebensperger

Multiple ecological factors are known to drive variation in social behavior. However, group-livin... more 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.

Two theoretical models, the 'economic' and the 'optimal' model, have been proposed to explain how... more Two theoretical models, the 'economic' and the 'optimal' model, have been proposed to explain how the fitness of prey changes in relation to flight initiation distance (FID): the distance between predator and prey when the prey initiates escape. Both hypotheses assume that the cost for the prey of remaining foraging (¼capture by a predator) influences their decision to escape and this cost should decrease as FID increases. Much qualitative research supports this prediction; however, no quantitative estimate of the cost of escape behaviour exists. Here, we used a seminatural experiment on predatoreprey interactions using the black field cricket, Teleogryllus commodus, as prey. We quantified the probability of survival of the prey as an ecological proxy of the cost of remaining at the foraging patch, and the FID of crickets at four different starting distances. The shape of the curve for the prey's cost of remaining foraging for the 'economic' model graphically fits the cost of staying in the patch most closely. The shape of the curve of survival of the prey, as proposed by the 'optimal model', is also appropriate, but the equation that best represents this curve is quadratic rather than exponential as suggested by the model mentioned.

While livetrapping is a vital field research tool, it is not a completely unbiased method of samp... more While livetrapping is a vital field research tool, it is not a completely unbiased method of sampling. Biased trapping arises during field endocrinological studies whenever hormone levels or response influence the probability of capture of a subject. We repeatedly captured wild, free-living adult degus (Octodon degus) from the same location over 12 days to determine whether individuals with a certain endocrine stress profile were more likely to be captured repeatedly than others. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy via a dexamethasone suppression test in adult male and lactating and nonlactating female degus upon initial capture. We successfully recaptured approximately half of the degus. None of the 3 indices of the stress response at initial capture predicted whether a degu would be recaptured. However, baseline CORT levels at 1st capture had a weak, negative relationship with the number of days between 1st and 2nd capture. Because most animals interpret capture and restraint as an acute stressor, we also analyzed the effect of recapture on the endocrine stress response. Baseline and stress-induced CORT concentrations were measured upon each subsequent recapture for up to 5 total captures. Upon subsequent recaptures, neither stress-induced CORT nor baseline CORT changed significantly. Additionally, individual stress-induced and baseline CORT titers were repeatable within our sample population. These findings suggest that livetrapping does not select for animals with certain endocrine stress profiles, and that degus fail to habituate to repeated capture and restraint stress. Aunque la captura viva de animales ha sido fundamental en estudios de campo, el método de captura puede incluir algunos sesgos. En estudios conductuales y endocrinológicos estos sesgos se producen cuando la probabilidad de captura de un individuo es afectada por su respuesta o por niveles hormonales. Se capturaron y recapturaron individuos silvestres del roedor Octodon degus durante 12 días para determinar si los individuos con un perfil hormonal particular en respuesta a estrés por captura tienen una mayor probabilidad de ser capturados. Se examinaron tres componentes de la respuesta fisiológica de estrés en degus hembras y machos: nivel basal de cortisol, nivel de cortisol inducido por estrés, y eficacia del sistema de retroalimentación negativa (a través de un ensayo con dexametazona). Durante el estudio se recapturaron cerca de la mitad de los individuos marcados originalmente. Ninguno de los tres componentes de la respuesta de estrés examinado fue capaz de predecir la probabilidad de recaptura en los degus examinados. Tampoco se detectó una relación entre los niveles de cortisol medidos en la primera captura y el tiempo transcurrido hasta la primera recaptura. También se examinó un posible efecto del número de recapturas sobre los niveles de cortisol basal y cortisol inducido por estrés. Aunque los niveles de cortisol inducido por estrés no cambiaron con el número de capturas, si se registró una disminución en los niveles basales de cortisol. Por último, detectamos que los niveles de cortisol basal y cortisol inducido por estrés son repetibles en la población estudiada. En conjunto, los resultados indicaron que el trampeo reiterado no selecciona degus con perfiles hormonales particulares y que estos animales no muestran hábito al estrés producto de captura e inmovilización reiteradas.

• No evidence that communal rearing enhances female reproductive success and survival • No eviden... more • No evidence that communal rearing enhances female reproductive success and survival • No evidence that communal rearing enhances offspring immunocompetence or survival • Females with high fecal glucocorticoids (FGC) increased lymphocytes and monocytes • Females with low FGC experienced increases in N:L ratios, neutrophils, and total IgG • Immunocompetence of females is sensitive to FGC but not to communal rearing a b s t r a c t One hypothesis largely examined in social insects is that cooperation in the context of breeding benefits individuals through decreasing the burden of immunocompetence and provide passive immunity through social contact. Similarly, communal rearing in social mammals may benefit adult female members of social groups by reducing the cost of immunocompetence, and through the transfer of immunological compounds during allonursing. Yet, these benefits may come at a cost to breeders in terms of a need to increase investment in individual immunocompetence. We examined how these potential immunocompetence costs and benefits relate to reproductive success and survival in a natural population of the communally rearing rodent, Octodon degus. We related immunocompetence (based on ratios of white blood cell counts, total and specific immunoglobulins of G isotype titers) and fecal glucocorticoid metabolite (FGC) levels of adults immunized with hemocyanin from the mollusk Concholepas concholepas to measures of sociality (group size) and communal rearing (number of breeding females). Offspring immunocompetence was quantified based on circulating levels of the same immune parameters. Neither female nor offspring immunocompetence was influenced by communal rearing or sociality. These findings did not support that communal rearing and sociality enhance the ability of females to respond to immunological challenges during lactation, or contribute to enhance offspring condition (based on immuno-competence) or early survival (i.e., to 3 months of age). Instead, levels of humoral and cellular components of im-munocompetence were associated with variation in glucorcorticoid levels of females. We hypothesize that this covariation is driven by physiological (life-history) adjustments needed to sustain breeding.

A growing body of evidence showing that individuals of some social species live in non-kin groups... more 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.

ing lactation, female O. lunatus had larger brains than males. Relative DG volume was similar acr... more ing 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.

Maternal stress and care significantly affect offspring's future behavior and physiology. Studies... more Maternal stress and care significantly affect offspring's future behavior and physiology. Studies in laboratory rats have shown that maternal stress decreases maternal care and that low rates of certain maternal behaviors cause offspring to develop hyperreactive stress responses. Plurally breeding rodents that practice communal care, such as degus (Octodon degus), may be able to buffer some of these effects since offspring receive care from multiple females. Directly after parturition, 0% (Control group), 50% (Mixed group), or 100% (CORT group) per cage of pair-housed female degus were implanted with 21-day release cortisol pellets. The amount of maternal care provided by females was determined from video recordings during the next 3 weeks. Females with cortisol implants did not alter rates of maternal care. However, females recently introduced to captivity had low rates of pup contact and pup retrievals compared to females of captive origin. When pups reached 4 weeks of age, we determined their baseline and stress-induced cortisol levels, in addition to assessing their negative feedback efficacy and adrenal sensitivity. Pups from mothers recently introduced to captivity had weak negative feedback. Within captive pups, those from CORT mothers weighed less compared to pups from either Control or Mixed mothers. Captive CORT pups also had weak adrenal sensitivity compared to captive Control pups. These findings demonstrate that maternal care and glucocorticoid elevation impact certain components of the degu pup stress response, but that plural breeding with communal care may buffer some of these effects.

Contrasting scenarios have been proposed to explain how resource heterogeneity influences group l... more Contrasting scenarios have been proposed to explain how resource heterogeneity influences group living or sociality. First, sociality may result from individuals in larger groups attaining net fitness benefits by monopolizing access to resources (" resource-defense " hypothesis). Second, sociality may be the fitness-neutral outcome of multiple individuals using a territory with sufficient resources to sustain a group of conspecifics (" resource-dispersion " hypothesis). While previous studies have tended to support the resource-dispersion hypothesis, these analyses have typically examined only 1 or a few predictions, making it difficult to distinguish between the 2 alternatives. We conducted a 4-year field study of Octodon degus to quantify the effects of spatial heterogeneity in food and refuge distributions on group size and 2 components of reproductive success (per capita number of offspring, offspring survival) in this plural breeding and communal rearing rodent. We found only a small effect of heterogeneity of food resources on group size; the effect food resource distribution on group territory size varied across years. Group size did not vary with spatial variation in group territory size and quality. Importantly, there was no covariation between group size and quality of an individual's territory (i.e., a measure of individual access to resources), or between this measure of territory quality and reproductive success, implying no resource-based benefits to social degus. Overall, our results were more consistent with fitness-neutral relationships among spatial heterogeneity of resources, sociality, and territory size. The resource-dispersion hypothesis, however, did not provide a complete explanation for degu socioecology. Se han propuesto distintas hipótesis para explicar cómo la heterogeneidad de los recursos afecta la vida en grupos, o sociabilidad. Esta puede surgir en situaciones donde individuos en grupos grandes se benefician al monopolizar el acceso a recursos (hipótesis de defensa de recursos). Por otra parte, la vida en grupos también puede ser el resultado neutro (en términos de adecuación) de individuos que comparten un territorio con recursos suficientes (hipótesis de dispersión de recursos). Aunque algunos estudios previos han validado la hipótesis de dispersión de recursos, estos solo han evaluado un número limitado de las predicciones de esta hipótesis, lo que ha dificultado distinguir entre esta y otras hipótesis alternativas. Durante un estudio de 4 años cuantificamos los efectos de la heterogeneidad espacial de alimento y distribución de refugios sobre el tamaño de grupo y dos componentes del éxito reproductivo (número per cápita de crías, supervivencia de las crías) en Octodon degus. Se registraron efectos relativamente pequeños de la heterogeneidad espacial del alimento sobre el tamaño de grupo, y variables entre años sobre el tamaño del territorio de cada grupo. El tamaño de grupo no fue afectado por la variación espacial en el tamaño y calidad del territorio de los grupos. No se registró co-variación entre el tamaño de los grupos y la calidad del territorio de cada individuo (una medida individual del acceso a recursos), o entre la calidad del territorio individual y el éxito reproductivo, lo que sugiere ausencia de beneficios derivados del uso social de recursos en degus. En general, los resultados fueron más consistentes con un escenario de efectos neutros de la heterogeneidad espacial de recursos sobre la sociabilidad. Sin embargo, la hipótesis de dispersión de recursos no explicó el conjunto de efectos (o su ausencia) asociados a la socioecología del degu.

The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhab... more The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhabiting pre-Andean pre-Puna and Puna environments of tropical South America. In order to understand the phylogeographic patterns of Octodontomys gliroides, we sequenced 579 bp of the mitochondrial DNA control region from 100 individuals collected from 20 populations across its entire distributional range. The phylogenetic and parsimony network, in conjunction with analysis of molecular variance (AMOVA), revealed a structured pattern of geographic differentiation of O. gliroides, with the occurrence of two well-defined evolutionary lineages: lineage A, restricted to Bolivia and Chile, and lineage B, restricted mainly to Argentina. Analysis of population structure inferred three genetic clusters along the distribution of O. gliroides that mostly agree with the four major barriers inferred by BARRIER analysis (e.g. rivers, salt flats, deserts, and mountain systems). In addition to the significant differentiation found among all levels studied, a positive correlation was identified between genetic and geographic distance, similar to as expected under the isolation-by-distance model. The most recent common ancestor of O. gliroides was estimated as c. 5.99 Mya, and the divergence between lineages A and B is estimated to have occurred by the Middle Pleistocene, about 0.69 Mya. The mismatch distributions and neutrality tests suggested a signal of population range expansion for both lineages coincident with major climatic changes that occurred during the wet–dry events of the Pleistocene in the Andean Puna region. Bayesian skyline plots (BSPs) for lineage A suggest a long history of constant population size followed by a period of slight to moderate demographic expansion at c. 0.04 Mya, whereas lineage B remained unclear after BSP analysis, probably because of the limited sample size.

1. Group size may influence fitness benefits and costs that emerge from cooperative and competiti... more 1. Group size may influence fitness benefits and costs that emerge from cooperative and competitive interactions in social species. However, evidence from plural breeding mammals indicates that group size is insufficient to explain variation in direct fitness, implying other attributes of social groups were overlooked. 2. We studied the natural population of a social rodent during 5 years to test the hypothesis that social stability – in terms of group composition – modulates the effects of increasing number of breeding females (a proxy of communal rearing) and males on the number of offspring weaned (sired) and on the number of offspring weaned (sired) surviving to breeding age (two proxies of direct fitness). We quantified the effects of social stability (measured as changes in female or male group members between mating and the onset of lactation) on these fitness measures. 3. We used live trapping, telemetry and DNA markers to determine social and fitness measures. 4. Social stability in degus was variable in terms of the number of changes in group composition across groups. Low stability was mostly due to mortality and emigration of group members. 5. Results supported a modulating role of social stability on the relationship between group size and the number of offspring weaned (sired). Stability in female and male group composition were both modulators of fitness to females and males. 6. The modulatory role of stability was sex specific, where high social stability was often fitness beneficial to the females. Instead, low social stability was fitness enhancing to the males.

1. Alternative morphotypes have been reported less frequently in females than in males. An except... more 1. Alternative morphotypes have been reported less frequently in females than in males. An exception to this rule is the gradient of phenotypical masculinization reported in some female mammals, in which feminized and masculinized females represent two opposite ends along this gradient. These phenotypical differences originate during prenatal development as the consequence of maternal effects. Feminized and masculinized females differ in several traits, including morphological, physiological, behavioural and reproductive traits. 2. Differences previously reported in reproductive traits between feminized and masculinized females come mostly from mechanistic studies performed in the laboratory, and not necessarily on social species. As a result, it is unclear to what extent these reported differences between female alternative morphotypes materialize in wild, natural populations. 3. We quantified the effect of female alternative morphotype on female reproductive traits in a natural population of Octodon degus, a highly social rodent. We assessed female alternative morphotype through a continuous gradient of anogenital distance. Thus, feminized females were close to the short end of anogenital distance, while masculinized females were close to the long end of this gradient. We also tested the hypothesis that the social environment interacts with female morphotype to influence female reproductive traits. 4. In female degus, only body weight affected litter size, where heavier females weaned more offspring. Masculinized females delivered male-biased litters and weaned heavier offspring. Lastly, masculinized females gave birth later in the breeding season compared to feminized females. 5. Contrary to previous claims, our findings do not support that masculinized females are less fertile than feminized females. Moreover, masculinized females produced heavier, potentially higher quality offspring compared with feminized females.

Maternal stress can significantly affect offspring fitness. In laboratory rodents, chronically st... more Maternal stress can significantly affect offspring fitness. In laboratory rodents, chronically stressed mothers provide poor maternal care, resulting in pups with hyperactive stress responses. These hyperactive stress responses are characterized by high glucocorticoid levels in response to stressors plus poor negative feedback, which can ultimately lead to decreased fitness. In degus (Octodon degus) and other plural breeding rodents that exhibit communal care, however, maternal care from multiple females may buffer the negative impact on pups born to less parental mothers. We used wild, free-living degus to test this hypothesis. After parturition, we manipulated maternal stress by implanting cortisol pellets in 0%, 50–75%, or 100% of adult females within each social group. We then sampled pups for baseline and stress-induced cortisol, negative feedback efficacy, and adrenal sensitivity. From groups where all mothers were implanted with cortisol, pups had lower baseline cortisol levels and male pups additionally had weaker negative feedback compared to 0% or 50–75% implanted groups. Contrary to expectations, stress-induced cortisol did not differ between treatment groups. These data suggest that maternal stress impacts some aspects of the pup stress response, potentially through decreased maternal care, but that presence of unstressed mothers may mitigate some of these effects. Therefore, one benefit of plural breeding with communal care may be to buffer post-natal stress.

Ethology Ecology & Evolution, 1998

It has been hypothesized that females could use promiscuity to prevent male infanticide: a female... more It has been hypothesized that females could use promiscuity to prevent male infanticide: a female will mate with several males as a way to confuse paternity of her offspring, so the males will tolerate these infants that might be their own. If so, and all other things being equal, a female should prefer an infanticidal over a noninfanticidal male as a mating partner. To test this prediction, I examined the social preferences of female meadow voles (Microtus pennsylvanicus) and house mice (Mus musculus) toward infanticidal and noninfanticidal conspecific males. In each trial, a female was allowed to visit two compartments containing either an infanticidal or a noninfanticidal male. Females of both species visited both kinds of males with the same frequency. Similarly, females of both species spent a similar amount of time inspecting the compartments of the infanticidal and the noninfanticidal male. The frequencies of other female behaviors such as self-grooming, scent marking, or aggression, were also similar. These results provide no support for the hypothesis that female promiscuity is a female strategy to prevent male infanticide in house mice or meadow voles.

Journal of Zoology, Sep 30, 2000

The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae... more The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae) were investigated and compared with that of more specialized fossorial rodents. An open-¯ow respirometry system was used to record energy expenditure of single degus inside respirometers partially ®lled with soft (moist) or hard (dry) soil. In addition, digging behaviour was recorded in groups of three animals inside a large terrarium under controlled conditions of food, photoperiod and temperature. In the ®eld, the digging activity of degus was monitored, along with seasonal variations in rainfall, content of soil moisture and soil hardness. Mass-speci®c metabolic rate during digging was found to be higher in animals burrowing in soft soils compared to hard soil. However, animals burrowing in soft soil removed more soil per min than animals in hard soil. Thus, gram per gram, excavating in hard soil was energetically more expensive. The digging cost of semifossorial degus tends to be either similar to or above those of similarly sized, but more fossorial, rodents. In the ®eld, heightened digging activity coincided with the occurrence of rainfall, greater content of soil moisture and relatively soft soil conditions. Degus generally use their front feet and teeth to shear the soil; disposal of accumulated debris being carried out by moving their front and hind feet backwards. We also observed the establishment of digging chains when two or three individuals burrowed at the same site. As far as digging is concerned, the behaviour of degus is similar to that of other fossorial rodents, such as African bathyergids and the more closely related South American ctenomyids.

Revista chilena de historia natural

Indicator species could help to compensate for a shortfall of knowledge about the diversity and d... more Indicator species could help to compensate for a shortfall of knowledge about the diversity and distributions of undersampled and cryptic species. This paper provides background knowledge about the ecological interactions that affect and are affected by herbaceous diversity in central Chile, as part of the indicator species selection process. We focus on the ecosystem engineering role of small mammals, primarily the degu Octodon degus. We also consider the interacting effects of shrubs, trees, avian activity, livestock, slope, and soil quality on herbaceous communities in central Chile. We sampled herbaceous diversity on a private landholding characterized by a mosaic of savanna, grassland and matorral, across a range of degu disturbance intensities. We find that the strongest factors affecting endemic herbaceous diversity are density of degu runways, shrub cover and avian activity. Our results show that the degu, a charismatic and easily identifiable and countable species, could be used as an indicator species to aid potential conservation actions such as private protected area uptake. We map areas in central Chile where degus may indicate endemic plant diversity. This area is larger than expected, and suggests that significant areas of endemic plant communities may still exist, and should be identified and protected.

Cold Spring Harbor Protocols, 2013

Journal of Zoology, 2000

Journal of Mammalogy, 2011

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Journal of Mammalogy, 2014

Ethology Ecology & Evolution, 1998

Journal of Zoology, Sep 30, 2000

Revista chilena de historia natural

Cold Spring Harbor Protocols, 2013

Journal of Zoology, 2000

Journal of Mammalogy, 2011

w w w . m a m m a l o g y . o r g

Journal of Mammalogy, 2014

Journal of Mammalogy, Mar 24, 2016

Contrasting scenarios have been proposed to explain how resource heterogeneity influences group l... more Contrasting scenarios have been proposed to explain how resource heterogeneity influences group living or sociality. First, sociality may result from individuals in larger groups attaining net fitness benefits by monopolizing access to resources ("resource-defense" hypothesis). Second, sociality may be the fitness-neutral outcome of multiple individuals using a territory with sufficient resources to sustain a group of conspecifics ("resourcedispersion" hypothesis). While previous studies have tended to support the resource-dispersion hypothesis, these analyses have typically examined only 1 or a few predictions, making it difficult to distinguish between the 2 alternatives. We conducted a 4-year field study of Octodon degus to quantify the effects of spatial heterogeneity in food and refuge distributions on group size and 2 components of reproductive success (per capita number of offspring, offspring survival) in this plural breeding and communal rearing rodent. We found only a small effect of heterogeneity of food resources on group size; the effect food resource distribution on group territory size varied across years. Group size did not vary with spatial variation in group territory size and quality. Importantly, there was no covariation between group size and quality of an individual's territory (i.e., a measure of individual access to resources), or between this measure of territory quality and reproductive success, implying no resourcebased benefits to social degus. Overall, our results were more consistent with fitness-neutral relationships among spatial heterogeneity of resources, sociality, and territory size. The resource-dispersion hypothesis, however, did not provide a complete explanation for degu socioecology. Se han propuesto distintas hipótesis para explicar cómo la heterogeneidad de los recursos afecta la vida en grupos, o sociabilidad. Esta puede surgir en situaciones donde individuos en grupos grandes se benefician al monopolizar el acceso a recursos (hipótesis de defensa de recursos). Por otra parte, la vida en grupos también puede ser el resultado neutro (en términos de adecuación) de individuos que comparten un territorio con recursos suficientes (hipótesis de dispersión de recursos). Aunque algunos estudios previos han validado la hipótesis de dispersión de recursos, estos solo han evaluado un número limitado de las predicciones de esta hipótesis, lo que ha dificultado distinguir entre esta y otras hipótesis alternativas. Durante un estudio de 4 años cuantificamos los efectos de la heterogeneidad espacial de alimento y distribución de refugios sobre el tamaño de grupo y dos componentes del éxito reproductivo (número per cápita de crías, supervivencia de las crías) en Octodon degus. Se registraron efectos relativamente pequeños de la heterogeneidad espacial del alimento sobre el tamaño de grupo, y variables entre años sobre el tamaño del territorio de cada grupo. El tamaño de grupo no fue afectado por la variación espacial en el tamaño y calidad del territorio de los grupos. No se registró co-variación entre el tamaño de los grupos y la calidad del territorio de cada individuo (una medida individual del acceso a recursos), o entre la calidad del territorio individual y el éxito reproductivo, lo que sugiere ausencia de beneficios derivados del uso social de recursos en degus. En general, los resultados fueron más consistentes con un escenario de efectos neutros de la heterogeneidad espacial de recursos sobre la sociabilidad. Sin embargo, la hipótesis de dispersión de recursos no explicó el conjunto de efectos (o su ausencia) asociados a la socioecología del degu.

Behavioral Ecology and Sociobiology, Oct 19, 2010

In social or group living species, members of groups are expected to be affected differentially b... more In social or group living species, members of groups are expected to be affected differentially by competition through the effect of group size (i.e., the "social competition hypothesis"). This hypothesis predicts an increase in the probability of dispersal with increasing size of social groups. At a more mechanistic level and based on the known effects of competition on stress hormone levels, a positive relationship between group size and glucocorticoids of juveniles should be observed. We used a demographic approach to test these predictions on a natural population of the communally rearing and semifossorial rodent-Octodon degus. Burrow systems provide degus with places to rear offspring and to evade stressful thermal conditions and predators. Thus, we predicted dispersal to increase with increasing number of degus per main burrow system used, a measure of habitat saturation in degus. The probability of dispersal increased with increasing number of degus per main burrow system used. Mean fecal metabolites of cortisol in offspring increased, yet not statistically significantly, with the number of juveniles in groups. These results were consistent with a scenario in which competition drives natal dispersal in juveniles in social degus. In particular, competition would be the consequence of high degu abundance in relation to the abundance of burrow systems available at the time of offspring emergence.

Global Ecology and Conservation, Dec 1, 2014

Journal of Zoology, Oct 1, 2000

The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae... more The energetics and burrowing behaviour of the semifossorial Octodon degus (Rodentia: Octodontidae) were investigated and compared with that of more specialized fossorial rodents. An open‐flow respirometry system was used to record energy expenditure of single degus inside respirometers partially filled with soft (moist) or hard (dry) soil. In addition, digging behaviour was recorded in groups of three animals inside a large terrarium under controlled conditions of food, photoperiod and temperature. In the field, the digging activity of degus was monitored, along with seasonal variations in rainfall, content of soil moisture and soil hardness. Mass‐specific metabolic rate during digging was found to be higher in animals burrowing in soft soils compared to hard soil. However, animals burrowing in soft soil removed more soil per min than animals in hard soil. Thus, gram per gram, excavating in hard soil was energetically more expensive. The digging cost of semifossorial degus tends to be either similar to or above those of similarly sized, but more fossorial, rodents. In the field, heightened digging activity coincided with the occurrence of rainfall, greater content of soil moisture and relatively soft soil conditions. Degus generally use their front feet and teeth to shear the soil; disposal of accumulated debris being carried out by moving their front and hind feet backwards. We also observed the establishment of digging chains when two or three individuals burrowed at the same site. As far as digging is concerned, the behaviour of degus is similar to that of other fossorial rodents, such as African bathyergids and the more closely related South American ctenomyids.

Journal of Mammalogy, Jun 5, 2015

Zoological Journal of the Linnean Society, Apr 20, 2016

The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhab... more The Andean degu, Octodontomys gliroides Gervais & d'Orbigny, 1844, has a broad distribution inhabiting pre-Andean pre-Puna and Puna environments of tropical South America. In order to understand the phylogeographic patterns of Octodontomys gliroides, we sequenced 579 bp of the mitochondrial DNA control region from 100 individuals collected from 20 populations across its entire distributional range. The phylogenetic and parsimony network, in conjunction with analysis of molecular variance (AMOVA), revealed a structured pattern of geographic differentiation of O. gliroides, with the occurrence of two well-defined evolutionary lineages: lineage A, restricted to Bolivia and Chile, and lineage B, restricted mainly to Argentina. Analysis of population structure inferred three genetic clusters along the distribution of O. gliroides that mostly agree with the four major barriers inferred by BARRIER analysis (e.g. rivers, salt flats, deserts, and mountain systems). In addition to the significant differentiation found among all levels studied, a positive correlation was identified between genetic and geographic distance, similar to as expected under the isolation-by-distance model. The most recent common ancestor of O. gliroides was estimated as c. 5.99 Mya, and the divergence between lineages A and B is estimated to have occurred by the Middle Pleistocene, about 0.69 Mya. The mismatch distributions and neutrality tests suggested a signal of population range expansion for both lineages coincident with major climatic changes that occurred during the wet-dry events of the Pleistocene in the Andean Puna region. Bayesian skyline plots (BSPs) for lineage A suggest a long history of constant population size followed by a period of slight to moderate demographic expansion at c. 0.04 Mya, whereas lineage B remained unclear after BSP analysis, probably because of the limited sample size.

Acta Theriologica, Jun 1, 2001

... resource-defense hypothesis. The formation of groups in the mara takes place as a consequence... more ... resource-defense hypothesis. The formation of groups in the mara takes place as a consequence of individuals concentrating their grazing activity around lagoons during the dry season (Taber and Macdonald 1992). Most green ...

Behavioral Ecology and Sociobiology, Apr 20, 2000

We examined the hypothesis that a main benefit of group-living in the semifossorial rodent, Octod... more 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 longterm benefits will be a consequence rather than a cause of degu group-living.

Revista Chilena de Historia Natural, Jun 1, 2000

Journal of Mammalogy, May 26, 2017

Ethology Ecology & Evolution, Apr 1, 1998

Do female rodents use promiscuity to prevent male infanticide? LUIS A. EBENSPERGER 1 ... This beh... more Do female rodents use promiscuity to prevent male infanticide? LUIS A. EBENSPERGER 1 ... This behavior has been noted in a wide variety of animal taxa, from invertebrates to vertebrates (HAUSFATER & HRDY 1984, ELGAR & CRESPI 1992, PARMIGIANI & VOM SAAL 1994). ...

Animal Behaviour, Jul 1, 2009

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

I observed the behavior of captive male and female Octodon degus to assess if dustbathing behavio... more I observed the behavior of captive male and female Octodon degus to assess if dustbathing behavior plays a role in social communication among unfamiliar, same-sex conspecifics. Degus of a first group (control responders) were individually exposed during 1 0-min tests to an arena containing loose, clean soil. I compared the latency to first dustbathing as well as the overall frequency of dustbathing events recorded to control responders with the corresponding figures recorded to a second group of degus (experimental responders) after they were individually introduced into the same arena but with soil previously used for dustbathing by a same-sex conspecific (depositor). I also compared the location of dustbathing events by experimental responders with that of depositor individuals. Although male degus tended to exhibit shorter latencies to first dustbathing event when in clean soil, this variable was not significantly influenced by sex of responders or the type of soil (clean or used). In contrast, a significant interaction between both factors revealed that males dustbathe at a higher rate than females when on clean soil, but similarly so when in a substratum previously dustbathed by a same-sex conspecific. The place chosen by both male and female responders to conduct their dustbathing behavior was unrelated to the presence of previous marks left by a depositor degu. I conclude that dustbathing is involved in communication during male-male, but not during female-female, interactions in the degu. I suggest that such male-male interactions represent competition for mates.

Revista Chilena de Historia Natural, 1996

La hip6tesis de resistencia a la deprivaci6n de alimento: el caso de dos especies de roedores de ... more La hip6tesis de resistencia a la deprivaci6n de alimento: el caso de dos especies de roedores de Chile central

Journal of Mammalogy, Nov 25, 2015

Behavioral Ecology, Dec 21, 2010

Variation in sociality may have an important impact on population genetic structure. In highly so... more Variation in sociality may have an important impact on population genetic structure. In highly social species, the formation of kin clusters leads to decreasing variation within but increasing genetic variation among social groups. Studies on less social species in which social groups may be more short lived have revealed a greater diversity of consequences on the genetic structure of populations. Thus, studies on populations of less social species can more precisely highlight how social structure and genetic structure covary in wild populations. We explored the relationship between natal dispersal and social structuring (i.e., whether social group are composed of kin) at the local population in a social rodent, Octodon degus, using a combination of direct (capture-mark-recapture) and indirect (codominat genetic markers) methods. Previous studies of degus indicated that social groups were characterized by high turnover rate of group members and no sex bias dispersal. As we expected, there was an absence of correlation between social and genetic structure; moreover, social groups were not characterized by high levels of genetic relatedness (R: no different form background population). Direct and indirect (corrected assignment index) methods revealed an absence of sex-biased dispersal. Moreover, this method reveled that our study population was composed of resident and immigrant individuals. Moreover, dispersal distances have no effect on kin structure as reveled by the spatial genetic autocorrelation analysis. Beside some degree of offspring association (R: among juveniles of a same group higher than background population), high turnover rate, dispersal, and perhaps a promiscuous or polyandry mating system seem to avoid a kin genetic structure, thereby limiting the opportunity for the evolution of kin-selected social behavior.

Aggressive Behavior, 1998

Journal of Ethology, Dec 7, 2006

The marine otter Lontra felina has been said to prefer wave-exposed habitats over more protected ... more The marine otter Lontra felina has been said to prefer wave-exposed habitats over more protected sites in response to a greater prey abundance in exposed habitat. We examined how the foraging activity of L. felina is affected by the regime of wave exposure and prey availability at Isla Choros, northern Chile. Through focal sampling we recorded time spent by otters in foraging, the duration of dives, and the hunting success on a wave-exposed and a wave-protected site on the island. In addition, we quantified the abundance of prey in both habitats. Marine otters spent more time foraging in the wave-protected site compared with the wave-exposed habitat. Successful dives reached 26.9% in the wave-exposed habitats, and 38.2% in the wave-protected habitat. Foraging dives were 18% shorter in wave-exposed as compared with wave-protected habitat. Numerically, available prey did not differ significantly with habitat. Our results are more consistent with the hypothesis that wave-exposed habitats represent a sub-optimal habitat to foraging marine otters. Marine otters' use of wave-exposed patches through northern and central Chile coastal areas probably reflects a low availability of suitable protected areas and greater human disturbance of more protected habitat.

Acta Ethologica, Apr 23, 2001

... ents, and it occurs in a wide variety of animal taxa, in-cluding invertebrates and vertebrate... more ... ents, and it occurs in a wide variety of animal taxa, in-cluding invertebrates and vertebrates (Hausfater and Hrdy 1984; Elgar and Crespi 1992; Parmigiani and vom Saal 1994). ... ORIGINAL ARTICLE Luis A. Ebensperger No infanticide in the hystricognath rodent, Octodon degus: ...