DSpace Angular :: Browsing by Author "Ebensperger, Luis A."

Browsing by Author "Ebensperger, Luis A."

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Activational and organizational effects of testosterone on the number of mating partners and reproductive success in males of a social rodent
(2024) Correa, Loreto A.; Aspillaga-Cid, Antonia; Riquelme, Juan; Ly-Prieto, Lvaro; Hayes, Loren D.; Ebensperger, Luis A.
The timing of exposure to the steroid hormone, testosterone, produces activational and organizational effects in vertebrates. These activational and organizational effects are hypothesized to relate with the number of female mating partners and reproductive success in males. We tested this hypothesis by examining 151 wild degu ( Octodon degus) ) males across a 10-year study. We quantified the association between adult serum testosterone levels (i.e., an indirect index of adult activational effects) and anogenital distance (AGD) length (i.e., a direct index of fetal organizational effects), and their interaction on the number of female mating partners and reproductive success. We found no evidence of an association between adult male serum testosterone levels and the number of female mating partners, or between adult male serum testosterone levels and reproductive success. However, male AGD was positively associated with reproductive success, but not so with the number of female mating partners. Additionally, the positive association between male AGD and male reproductive success was mediated by the number of mates. Our findings do not support major roles of activational or organizational effects of testosterone on the number of female mating partners and its consequences on male reproductive success. Instead, our results suggest that compared with individual male attributes, the female social environment plays a more important role in driving male reproductive success.
Allosuckling allows growing offspring to compensate for insufficient maternal milk in farmed guanacos (Lama guanicoe)
(2010) Zapata, Beatriz; Correa, Loreto; Soto-Gamboa, Mauricio; Latorre, Etel; Gonzalez, Benito A.; Ebensperger, Luis A.
While allonursing, the provision of milk to non-offspring by females, involves a potential cost to their own offspring, allosuckling, the suckling from females other than their own mother may allow offspring to compensate for previous deficiencies in maternal milk. We tested this hypothesis in farmed guanacos. Under the compensation hypothesis we predicted that mothers of calves exhibiting allosuckling should be in poorer physical condition and should exhibit relatively low acceptance rates to filial sucking attempts compared to mothers whose calf did not allosuckle. We also predicted that calves exhibiting frequent allosuckling should show similar or greater rates of gain in body weight. but similar total (or final) weight in the long term than calves that nursed from their mothers exclusively. We examined the potential effects of sex and order of birth dates of calves on allosuckling, and the effect of female Success during agonistic encounters with other females on allonursing. Two stable groups of 15 and 14 mother-offspring pairs of farmed guanacos were studied from birth to approximately 3 months of age. Allosuckling events comprised 5.7% of all suckling events. Allonursing was performed by 52% of dams and 62% of calves exhibited allosuckling. We found similar gain rates in body weight and total weight at 60 days of age between allosuckling calves and filial sucking calves, irrespective of whether their mothers allonursed or not (P > 0.1). Body weight of mothers whose calf allosuckled was significantly lower than that of mothers whose calves nursed from them exclusively (P = 0.02). In addition, the percentage of acceptance of filial suckling bouts was significantly lower for allosuckling calves (P = 0.004). There was no correlation between the frequency of allonursing and the success of dams during agonistic encounters (P > 0.22). Our findings are consistent with the hypothesis that guanaco calves used allosucking to compensate for previous deficiencies in maternal milk. (C) 2009 Elsevier B.V. All rights reserved.
Burrow limitations and group living in the communally rearing rodent, Octodon degus
(ALLIANCE COMMUNICATIONS GROUP DIVISION ALLEN PRESS, 2011) Ebensperger, Luis A.; Chesh, Adrian S.; Castro, Rodrigo A.; Ortiz Tolhuysen, Liliana; Quirici, Veronica; Burger, Joseph Robert; Sobrero, Raul; Hayes, Loren D.
Group living is thought to evolve whenever individuals attain a net fitness advantage due to reduced predation risk or enhanced foraging efficiency, but also when individuals are forced to remain in groups, which often occurs during high-density conditions due to limitations of critical resources for independent breeding. The influence of ecological limitations on sociality has been studied little in species in which reproduction is more evenly shared among group members. Previous studies in the caviomorph rodent Octodon degus (a New World hystricognath) revealed no evidence that group living confers an advantage and suggest that burrow limitations influence formation of social groups. Our objective was to examine the relevance of ecological limitations on sociality in these rodents. Our 4-year study revealed no association between degu density and use of burrow systems. The frequency with which burrow systems were used by degus was not related to the quality of these structures; only in 1 of the 4 years did the frequency of burrow use decrease with decreasing abundance of food. Neither the number of females per group nor total group size (related measures of degu sociality) changed with yearly density of degus. Although the number of males within social groups was lower in 2008, this variation was not related clearly to varying density. The percentage of females in social groups that bred was close to 99% and did not change across years of varying density. Our results suggest that sociality in degus is not the consequence of burrow limitations during breeding. Whether habitat limitations contribute to variation in vertebrate social systems is discussed.
Early fitness consequences and hormonal correlates of parental behaviour in the social rodent, Octodon degus
(2010) Ebensperger, Luis A.; Ramirez-Otarola, Natalia; Leon, Cecilia; Ortiz, Maria E.; Croxatto, Horacio B.
Males are expected to assist their mates whenever this behaviour raises survival of offspring with little expense in terms of mating opportunities At a more proximate level cortisol and testosterone hormones seem involved in the expression of parental care in mammals We examined the consequences to postnatal offspring development and survival of the males presence in the social rodent Octodon degus Offspring quality and quantity and maternal condition of females were contrasted among females rearing their litters in the presence of the sire females breeding in the presence of a non-breeding female and females breeding solitarily We related these differences to variation in parental behaviour and plasma levels of testosterone and cortisol Twenty two females and their litters were studied under constant conditions of adult density nest availability food availability and breeding experience Males huddled over and groomed offspring However neither the number nor the mass of pups from dams that nested with the sire differed from those recorded to breeding females that nested with a non-breeding female and females that nested solitarily Body weight loss and associated levels of plasma cortisol in dams nesting with the sire were similar to those of solitary females but higher than mothers nesting with a non-breeding female Thus male care had no consequences to offspring and seemed detrimental to breeding females Circulating levels of cortisol and total testosterone were either poor (mothers) or no (fathers non-breeding females) predictors of parental care (C) 2010 Elsevier Inc All rights reserved
Ecological drivers of group living in two populations of the communally rearing rodent, Octodon degus
(2012) Ebensperger, Luis A.; Sobrero, Raul; Quirici, Veronica; Castro, Rodrigo A.; Ortiz Tolhuysen, Liliana; Vargas, Francisco; Burger, Joseph Robert; Quispe, Rene; Villavicencio, Camila P.; Vasquez, Rodrigo A.; Hayes, Loren D.
Intraspecific variation in sociality is thought to reflect a trade-off between current fitness benefits and costs that emerge from individuals' decision to join or leave groups. Since those benefits and costs may be influenced by ecological conditions, ecological variation remains a major, ultimate cause of intraspecific variation in sociality. Intraspecific comparisons of mammalian sociality across populations facing different environmental conditions have not provided a consistent relationship between ecological variation and group-living. Thus, we studied two populations of the communally rearing rodent Octodon degus to determine how co-variation between sociality and ecology supports alternative ecological causes of group living. In particular, we examined how variables linked to predation risk, thermal conditions, burrowing costs, and food avail-ability predicted temporal and population variation in sociality. Our study revealed population and temporal variation in total group size and group composition that covaried with population and yearly differences in ecology. In particular, predation risk and burrowing costs are supported as drivers of this social variation in degus. Thermal differences, food quantity and quality were not significant predictors of social group size. In contrast to between populations, social variation within populations was largely uncoupled from ecological differences.
Ecological predictors of range areas and use of burrow systems in the diurnal rodent, Octodon degus
(2007) Hayes, Loren D.; Chesh, Adrian S.; Ebensperger, Luis A.
Variation in animal space use patterns may be linked to numerous ecological factors affecting survival and reproduction. We examined the relationship between ecology and above- and below-ground components of space use by Octodon degus, a semi-fossorial rodent in Chile. We monitored the daytime minimum convex polygon and adaptive kernel range areas of 26 individuals and determined the number of burrow systems used by degus during night-time radiotelemetry and trapping of burrow systems on two study grids at Rinconada de Maipu, a semi-arid Matorral in central Chile. We quantified food biomass, soil hardness, distance to overhead vegetative cover, and density of burrow openings at putative nest burrows. Degus living on the grid with more shrub cover had larger range areas than degus living on the grid with less cover. The range areas of degus decreased with increasing distance from overhead vegetative cover. There was a weak (but statistically significant) negative relationship between the number of burrow systems used by degus and the distance to vegetative cover and density of burrow openings at burrow systems. Male and female degus had similar range areas. Our results suggest that overhead cover decreases the risk of predation to male and female degus. Degus probably balance the benefits of numerous burrow openings (reduced predation risk) with time and energy requirements of burrow construction and maintenance. Models of space use that consider the effect of multiple ecological variables should measure different dimensions of space use.
Effects of Radio-Collars are not Contingent on Socioecological Conditions in Degus
(2021) Ebensperger, Luis A.; Quirici, Veronica; Bunster, Valentina; Leon, Cecilia; Ramirez-Estrada, Juan; Hayes, Loren D.
Species-specific research on free-ranging mammals reveals a diversity of effects of radio-collars on behavior, body condition, and fitness. Although these studies indicate rather limited direct effects, radio-collars may cause effects influenced by socio-ecological conditions. Using a 7-year study on a natural population of group-living degus (Octodon degus), we tested the hypothesis that ecological (food availability, burrow density) and social (group size, group male-to-female ratio) conditions modulate effects of radio-collars on body condition (e.g., body mass, ecto- and endoparasite loads, fecal cortisol metabolites) and direct fitness (litter size, adult survival). We determined the effect of radio-collar use on degus by contrasting the presence or absence of radio-collars, quantifying the effects of the number of days carrying a radio-collar, and the relative mass of radio-collars worn by degus in central Chile between 2009 and 2015. Radio-collar use was not associated with direct effects on litter size, adult survival, or with body mass and fecal cortisol metabolites but was linked to low ecto- and endoparasite loads. These seemingly positive effects may reflect decreased mobility, or a research bias for radio-collaring larger, healthier individuals. There was no evidence that ecological and social conditions modulated radio-collar effects on degu body condition and direct fitness. These findings are consistent with evidence from other mammal studies that reported no appreciable detrimental direct or indirect effects of radio-collars. (c) 2021 The Wildlife Society.
Fecal cortisol levels predict breeding but not survival of females in the short-lived rodent, Octodon degus
(2013) Ebensperger, Luis A.; Tapia, Diego; Ramirez-Estrada, Juan; Leon, Cecilia; Soto-Gamboa, Mauricio; Hayes, Loren D.
The cort-adaptation hypothesis indicates that an association between glucocorticoid (cort) levels and fitness may vary with the extent to which reproduction or breeding effort is a major determinant of cort levels. Support for a context dependent association between cort and fitness comes mostly from relatively long-lived, bird species. We tested the hypothesis that there are gender and context (life-history) specific cort-fitness relationships in degus, a short-lived and generally semelparous social rodent. In particular, we used demographical records on a natural population to estimate adult survival through seasons and years and linked that to records of baseline cort (based on fecal cortisol metabolites). We found no evidence for a direct relationship between baseline cort and adult survival across seasons, and this lack of association was recorded irrespective of sex and life history stage. Yet, cort levels during early lactation predicted the probability that females produce a second litter during the same breeding season, supporting a connection between baseline cort levels and breeding effort. Overall, the differential effects of cort on survival and breeding supported that the extent of cort-fitness relationships depends on the fitness component examined. (C) 2013 Published by Elsevier Inc.
Female degus (Octodon degus) monitor their environment while foraging socially
(2008) Quirici, Veronica; Castro, Rodrigo A.; Oyarzun, Javiera; Ebensperger, Luis A.
Vigilance or scanning involves interruptions in foraging behavior when individuals lift their heads and conduct visual monitoring of the environment. Theoretical considerations assume that foraging with the "head down", and scanning ("head up") are mutually exclusive activities, such that foraging precludes vigilance. We tested this generalization in a socially foraging, small mammal model, the diurnal Chilean degu (Octodon degus). We studied spontaneous bouts of scanning of captive degus when foraging in pairs of female sibs and non-sibs. We examined the extent to which foraging (head down postures) and scanning (head up postures) were mutually exclusive in subjects exposed to none, partial, and complete lateral visual obstruction of their partners. In addition, we monitored the orientation of their bodies to examine the target of attention while foraging and scanning. Lastly, we examined the temporal occurrence of scanning events to assess the extent of scanning coordination, and whether this coordination is kin-biased. Visual obstruction had a significant influence on degu vigilance. Focal degus increased their quadrupedal and semi-erect scanning when foraging under a partially obstructed view of their partners. Degus oriented their bodies toward partners when foraging and scanning. Despite this, degus did not coordinate scanning bouts; instead, they scanned independently from one another. Relatedness among cage mates did not influence any aspect of degu behavior. Contrary to theoretical expectations, these results indicate that foraging and vigilance are not mutually exclusive, and that kinship per se does not influence scanning behavior and coordination.
Females of the communally breeding rodent, Octodon degus, transfer antibodies to their offspring during pregnancy and lactation
(2007) Becker, Maria Ines; De Ioannes, Alfredo E.; Leon, Cecilia; Ebensperger, Luis A.
Females in numerous rodent species engage in communal nesting and breeding, meaning that they share a nest to rear their young together. One potential benefit to communally nesting mot-hers is that infants improve their immunocompetence. Thus, suckling from two or more females might provide newborns with a more diverse array of antibodies and defensive cells. As a first step toward testing the immunocompetence hypothesis, we assessed whether female degus (Octodon degus), a communally nesting and breeding caviomorph rodent, transfer immunoglobulins to their young through the yolk sac or placenta while in the uterus and,during lactation, through milk. With this aim, adult degu females were immunized with four antigens, including two mollusk hemocyanins from Concholepas and Megathura (CCH and KLH, respectively), porcine thyroglobulin and tetanus toxoid. Specific antibodies against,the experimental antigens were used to track the origin of antibodies in the young. To establish the presence of specific antibodies of IgG and IgA isotypes in sera and milk of animals, an indirect enzyme-linked immunosorbent assay (ELISA) was developed. Degu females produced specific antibodies against antigens not found in their natural environment, and mothers were able to transfer the induced antibodies to their litters during pregnancy (IgG) and during lactation (IgA). However, we recorded only limited evidence of degu offspring acquiring antibodies from lactating mothers other than their own, giving little support to the increased immunocompetence hypothesis. (C) 2007 Elsevier Ireland Ltd. All rights reserved.
Fitness consequences of group living in the degu Octodon degus, a plural breeder rodent with communal care
(2009) Hayes, Loren D.; Chesh, Adrian S.; Castro, Rodrigo A.; Tolhuysen, Liliana Ortiz; Burger, Joseph Robert; Bhattacharjee, Joydeep; Ebensperger, Luis A.
The fitness consequences of plural breeding vary considerably among social vertebrates. We tested three hypotheses for the direct reproductive fitness consequences of group living in the degu Octodon degus, a social rodent endemic to central Chile. To test the 'benefits of communal care' hypothesis, we determined the relationship between the number of females per group, per capita direct fitness and offspring survival. To test the 'food abundance and quality' hypothesis, we determined the relationship between the biomass of preferred foods at burrow systems, group size, per capita direct fitness and offspring survival. To test the 'predation risk' hypothesis, we determined the relationship between group size, the density of burrow entrances to which social groups had access, per capita direct fitness, and survival of adults and offspring. Group size of core females (i.e. those with 50% or more nightly overlap) was negatively correlated with per capita direct fitness, but not with the number of females per group or total group size. Group living did not enhance the survival of offspring. Greater biomass of food (at 3 m and 9 m) and burrow density were not linked to larger groups and offspring survival. Our results did not support predictions of the 'benefits of communal care', 'food abundance and quality' or 'predation risk' hypothesis. Pending microsatellite analyses, we hypothesize that survival benefits linked to foraging group size and not reproductive fitness benefits may explain the evolution of sociality in degus. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Fitness consequences of variation in social group size are not population-specific but are associated with access to food in the communally breeding rodent, Octodon degus
(2024) Hayes, Loren D.; Strom, Madeline K.; Leon, Cecilia; Ramirez-Estrada, Juan; Grillo, Sara; Gao, Cuilan L.; Vasquez, Rodrigo A.; Ebensperger, Luis A.
Studies that concurrently investigate the functional benefits of group living in multiple populations of the same species are rare. Over a 3-year period (2014-2016), we examined two ecologically contrasting populations to test multiple hypotheses for the adaptive significance of group living in the communally breeding rodent Octodon degus. We quantified the size of social units (number of adults, number of adult females), edible vegetation at burrow systems, and per capita offspring weaned (PCOW) in each population. Contrary to expectations, we did not observe population-specific associations between group size and edible vegetation or PCOW nor universal benefits of group living. In one population, PCOW increased in mid-sized groups with more edible vegetation. However, this trend was not consistent across years. Notably, we observed a complete reproductive failure in one population during the first year of study, one that was characterized by low rainfall and no detectable edible vegetation. This result is important because reproductive failure occurred regardless of group size, suggesting that communal living may not buffer degus against the harshest of environmental conditions. Examining how social organization shapes individual reproductive success under extreme variation in food availability is an important step towards understanding how populations will respond to a changing climate.
Flight initiation distance is differentially sensitive to the costs of staying and leaving food patches in a small-mammal prey
(CANADIAN SCIENCE PUBLISHING, 2009) Lagos, Patricio A.; Meier, Andrea; Ortiz Tolhuysen, Liliana; Castro, Rodrigo A.; Bozinovic, Francisco; Ebensperger, Luis A.
Escape theory predicts that a prey should flee from an approaching predator at a point in which the cost of staying equals the cost of escape. We manipulated the cost of fleeing upon approaching human predators by providing the small mammal Octodon degus (Molina, 1782) with varying amounts of supplementary food likely to disappear while the animals are not in the food patch (e.g., hidden in their burrows). Simultaneously, we manipulated the risk of remaining in the patch by providing supplementary food at varying distances from the nearest burrow. Degus fled at a shorter distance to approaching predators when foraging in patches closer to the nearest burrow and supplied with relatively high abundance of food, but only when these rodents were foraging socially. Also, degus fled at a greater distance to approaching predators when foraging in patches far from the nearest burrow. Thus, functions linked to the loss of feeding opportunities and the risk of predation interact to influence flight initiation distance after a simulated attack. This study represented one of the few demonstrations of an interactive effect between cost and risks on antipredator behavior in a small, social prey mammal.
Habitat type influences endocrine stress response in the degu (Octodon degus)
(2013) Bauer, Carolyn M.; Skaff, Nicholas K.; Bernard, Andrew B.; Trevino, Jessica M.; Ho, Jacqueline M.; Romero, L. Michael; Ebensperger, Luis A.; Hayes, Loren D.
While many studies have examined whether the stress response differs between habitats, few studies have examined this within a single population. This study tested whether habitat differences, both within-populations and between-populations, relate to differences in the endocrine stress response in wild, free-living degus (Octodon degus). Baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy were measured in male and female degus from two sites and three habitats within one site during the mating/early gestation period. Higher quality cover and lower ectoparasite loads were associated with lower baseline CORT concentrations. In contrast, higher stress-induced CORT but stronger negative feedback efficacy were associated with areas containing higher quality forage. Stress-induced CORT and body mass were positively correlated in female but not male degus across all habitats. Female degus had significantly higher stress-induced CORT levels compared to males. Baseline CORT was not correlated with temperature at time of capture and only weakly correlated with rainfall. Results suggest that degus in habitats with good cover quality, low ectoparasite loads, and increased food availability have decreased endocrine stress responses. (C) 2013 Elsevier Inc. All rights reserved.
Immunocompetence of breeding females is sensitive to cortisol levels but not to communal rearing in the degu (Octodon degus)
(2015) Ebensperger, Luis A.; Leon, Cecilia; Ramirez-Estrada, Juan; Abades, Sebastian; Hayes, Loren D.; Nova, Esteban; Salazar, Fabian; Bhattacharjee, Joydeep; Ines Becker, Maria
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 immunocompetence) or early survival (i.e., to 3 months of age). Instead, levels of humoral and cellular components of immunocompetence 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. (C) 2014 Elsevier Inc. All rights reserved.
Individual behavioural variation does not affect social organization or reproductive success in a cooperative small mammal
(2024) van der Marel, Annemarie; Johnson, Nicholas E.; Grillo, Sara; Riquelme, Juan; Vasquez, Rodrigo A.; Gillam, Erin H.; Ebensperger, Luis A.; Hayes, Loren D.
Recent evidence indicates that individual behavioural variation in animals, defined as consistent individual differences in behaviour across contexts and time, influence ecological and evolutionary processes, and a growing number of studies demonstrate that individual behavioural variation can play a large role in shaping grouping dynamics among social animals. We studied the common degu, Octodon degus, a social rodent, to evaluate whether individual behavioural variation underlies social organization and the reproductive success of individuals within groups. We examined social groups in a population in central-north Chile during one breeding season, tested 67 adults in an open field test (i.e., the propensity to explore an unfamiliar environment) and 62 adults in determined assortment based on individual behavioural differences across 19 social groups, and performed genetic analyses to assess reproductive success. We found that the response to the poke test was repeatable, while none of the behaviours from an open field test were. The repeatable behaviour during the poke test was not associated to components of social organization (group composition), or to reproductive success. These findings imply that individual behavioural varia- tion did not affect grouping patterns or direct fitness in this degu population.
Instability Rules Social Groups in the Communal Breeder Rodent Octodon degus
(2009) Ebensperger, Luis A.; Chesh, Adrian S.; Castro, Rodrigo A.; Tolhuysen, Liliana Ortiz; Quirici, Veronica; Burger, Joseph Robert; Hayes, Loren D.
It has been hypothesized that animal groups in socially cohesive species are inherently unstable, ultimately the result of constraints to independent breeding, and proximately the product of adult fidelity and offspring philopatry. Other processes, including emigration of individuals that join pre-existing groups would be less important. We examined the persistence and variation in the composition of members of social groups in Octodon degus, a communal breeding rodent in which limitations to independent breeding are less obvious. This analysis was conducted during subsequent years, as well as during different seasons within years. Similar to social species in which constraints to independent breeding influence sociality, groups in degus were unstable in that they were short lived and ruled by an extensive turnover of group members across years. A relatively high turnover of group members was also recorded within years. Variation in the composition of groups was caused mostly by disappearance (presumably mortality) and immigration of adult members. Adult fidelity and offspring philopatry and dispersal played secondary roles in affecting the composition of social groups between and within years. Future studies should reexamine the importance of habitat limitations and its proximate determinant, natal philopatry, in driving the stability of social groups.
Lactating females do not discriminate between their own young and unrelated pups in the communally breeding rodent, Octodon degus
(2006) Ebensperger, Luis A.; Hurtado, Maria Jose; Valdivia, Isabel
Females in numerous rodent species engage in communal nesting and breeding, in which they share one or more nests to rear their young. A potential cost of communal nesting and breeding is that mothers divert resources to unrelated offspring. One way mothers could avoid this cost is to recognize and favour their own young over unrelated offspring when allocating maternal effort. We assessed whether female degus (Octodon degus), a communally nesting and breeding caviomorph rodent, discriminate between their own and unrelated offspring during lactation. Female degus previously have been shown to distinguish between their own and unrelated pups when exposed to odours from both. We measured pup discrimination based on differences in the retrieval behaviour of females that were in early or intermediate lactation directed towards their own and unrelated offspring; offspring presented were of similar or different age. Before any event of pup retrieval, lactating females spent similar amounts of time and interacted to a similar extent with their own and unrelated pups. During pup retrieval, all lactating females transported both pups to the nest. Neither relatedness to pups, nor pup-age differences, influenced the order in which pups were retrieved to the nest. Dams waited similar amounts of time before retrieving the first pup when the first transported young was their own or unrelated. Likewise, females waited similar amounts of time before retrieving the second pup when the pup transported first was their own or unrelated. The time between first and second pup transport events was longer when dams were in early when compared with intermediate lactation, but only when pups were of similar age. All experimental subjects nursed unrelated pups after they were retrieved. Collectively, our results do not support the hypothesis that communally breeding female degus use their recognition ability to discriminate against unrelated offspring in favour of their own young.
Nest and space use in a highland population of the southern mountain cavy (Microcavia australis)
(2006) Ebensperger, Luis A.; Taraborelli, Paula; Giannoni, Stella M.; Hurtado, Maria Jos; Leon, Cecilia; Bozinovic, Francisco
We examined the spatial and social structure of a high-altitude population of the scarcely known southern mountain cavy (Microcavia australis) in Argentina. We used radiotelemetry techniques to monitor nest use at night and daily home ranges and examine whether southern mountain cavies form nesting associations that are socially cohesive groups. We further timed our observations to breeding time of our study population (September-November) to assess opportunities for communal breeding. The nighttime telemetry of 24 radiotagged cavies revealed 7 nesting associations (i.e., communal nesting). These included 1-4 breeding females and I or 2 breeding males. Nesting associations were stable in terms of identity of individual members and in the location of putative nest sites. Most associations used a single nest site, but some shared 2 or 3. We noted that all nest sites were located under dominant shrubs, but use of nest sites was unrelated to variation in shrub cover. Nest sites with more burrow entrances were more frequently used by radiocollared cavies. During the day, home ranges of cavies overlapped more with ranges of nest mates than with those of non-nest mates, implying that nesting groups were socially cohesive units. This study confirmed that southern mountain cavies are communally nesting, and, because communal nesting occurs during breeding time, our findings support the idea that cavies engage in communal care of young.
One for all and all for one: phenotype assortment and reproductive success in masculinized females
(2021) Correa, Loreto A.; Leon, Cecilia; Ramirez-Estrada, Juan; Ly-Prieto, Alvaro; Abades, Sebastian; Hayes, Loren D.; Soto-Gamboa, Mauricio; Ebensperger, Luis A.
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.

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