DSpace Angular :: Browsing by Author "Ebensperger, LA"

Browsing by Author "Ebensperger, LA"

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Communal burrowing in the hystricognath rodent, Octodon degus
(2000) Ebensperger, LA; Bozinovic, F
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.
Daily activity patterns of free-living cururos (Spalacopus cyanus)
(2005) Urrejola, D; Lacey, EA; Wieczorek, JR; Ebensperger, LA
Circadian patterns of activity have important implications for numerous aspects of a species' biology, including patterns of sociality and paternal care. The activity patterns of subterranean rodents are of particular interest because of the presumed lack of environmental entrainment cues available in underground habitats. We used radiotelemetry to monitor activity of adult cururos (Spalacopus cyanus) in 2 populations of this species from north-central Chile. The locations of radiocollared animals from Parque Nacional Fray Jorge (n = 10 adults) and Santuario de la Naturaleza Yerba Loca (n = 8 adults) were determined hourly for 72 consecutive hours during austral summer, 2003. Examination of these data revealed that surface and subterranean activity were largely restricted to daylight hours. Specifically, the following measures of activity were found to be significantly greater during daytime: percentage of animals outside of nest, distance from nest, and distance between successive locations at which an animal was detected. In addition, the occurrence of cururo vocalizations (typically given by animals at burrow entrances) was significantly associated with daylight. Collectively, these analyses indicate that, contrary to the behavior of captive S. cyanus, free-living cururos are diurnal. Physical and social environments in which captive animals are housed may contribute to observed differences in activity between field and laboratory populations of this species.
Do female rodents use promiscuity to prevent male infanticide?
(1998) Ebensperger, LA
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.
Dustbathing and intra-sexual communication of social degus, Octodon degus (Rodentia: Octodontidae)
(2000) Ebensperger, LA
I observed the behavior of captive male and fem ale 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 10-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.
Energetics and burrowing behaviour in the semifossorial degu Octodon degus (Rodentia: Octodontidae)
(2000) Ebensperger, LA; Bozinovic, F
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 sheer 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.
Grouping increases the ability of the social rodent, Octodon degus, to detect predators when using exposed microhabitats
(2002) Ebensperger, LA; Wallem, PK
We examined the hypothesis that a main benefit of group-living in the hystricognath rodent, Octodon degus (common degu), is to decrease individual risk of predation. During a first series of field observations, we contrasted group size of degus when using covered microhabitats with that of degus using exposed patches. During a second set of field observations, we assessed how distance to detection and to escape by degus varied with group size upon the approach of a potential human predator. Degus in exposed patches formed larger groups than degus in covered microhabitats. After excluding the influence of nearest burrow to focal subjects, we found that degus of larger groups detected an approaching human predator at a greater distance than degus of smaller groups. Likewise, degus of larger groups escaped to nearby burrows at a greater distance from the approaching predator than degus of smaller groups. All these pieces of evidence support the predatory risk hypothesis according to which group-living in degus functions to reduce the risk of predation.
Male degus, Octodon degus, modify their dustbathing behavior in response to social familiarity of previous dustbathing marks
(2002) Ebensperger, LA; Caiozzi, A
A previous experiment suggested that male degus, Octodon degus, use dustbathing during intrasexual communication. Herein, we assessed whether dustbathing by male and female degus is influenced by the social familiarity of previous marks. During 15-min tests, we contrasted the behavior of degus individually exposed during to an arena containing loose, previously dustbathed sand by a same-sex and socially familiar individual with that of degus exposed to an arena with soil previously dustbathed by a same-sex but socially unfamiliar conspecific. We measured the number of dustbathing events per min, the latency to first dustbathing event, and the location of dustbathing events by depositor and responder individuals. Both male and female degus dustbathe at a higher rate when subjected to soil previously used by a familiar conspecific than when exposed to a substratum previously dustbathed by an unfamiliar degu. The latency to first dustbathing event by responder male or female degus was unaffected by the social familiarity of previous marks left by depositors. Similarly, the place chosen by male and female responders to conduct their dustbathing behavior was unrelated to the micro-location of previous marks left by a familiar or an unfamiliar depositor degu. We conclude that degus are capable of discriminating socially familiar from unfamiliar scents of conspecifics and deposited in the substratum during dustbathing. We discuss the implications of such ability in the context of degu social behavior.
Nonparental infanticide in meadow voles, Microtus pennsylvanicus
(2000) Ebensperger, LA; Botto-Mahan, C; Tamarin, RH
The infanticidal behaviour of wild-caught male and female Microtus pennsylvanicus was studied in captivity to examine the hypothesis that nonparental infanticide provides perpetrators with nutritional gains after cannibalizing their victims. Voles of different breeding condition, age, and sex were tested for their behaviour toward unfamiliar vole and house-mouse pups in a neutral arena. Infanticide on unfamiliar vole pups was relatively frequent among pregnant, less frequent among reproductively active (nonpregnant-nonlactating) and immature females, and almost absent in lactating females. Most infanticidal females, particularly non-breeding and immature females, did not cannibalize the pups. Pregnant females often attacked and cannibalized vole and house-mouse pups. A majority of breeding male voles were infanticidal when exposed to an unfamiliar pup in an unfamiliar place, and at least half of them cannibalized their victims. Taken together, these results suggest that nutritional gains are an occasional but not the main motivation of pup-killing behaviour in female meadow voles. In contrast, the attainment of nutritional benefits could be one main benefit of infanticide by male meadow voles.
Seasonal changes in the time budget of degus, Octodon degus
(2005) Ebensperger, LA; Hurtado, MJ
The activity budget of an individual is the allocation of time to all its activities, and is expected to vary in response to both internal and environmental factors that influence its energy acquisition, breeding success, and survival. We recorded seasonal variation in individual and social behaviour of a natural population of degus (Octodon degus), a diurnal, semi-subterranean and social rodent from central Chile. We related changes in degu activity to differences in sex, seasonality (breeding activity, abundance of high quality food), and abundance of degu predators. On average, degus allocated most of their time while active above ground to foraging (46%) and alertness (32%); activities such as resting (8%), locomotor activity (7%), self-grooming (3%), burrow digging (0.2%), dust-bathing (1%), and social interactions (3%) occupied a relatively small percentage of degus' time budget. Time spent in foraging and total vigilance did not vary seasonally, but they were inversely related, reflecting a trade-off. Degus adjusted bipedal vigilance and locomotor activity partially to the presence of predators. Sex interacted with seasonality to influence degu behaviour. Male degus dust-bathed more and were more aggressive toward conspecifics than females during breeding time. We hypothesize that breeding activity is a more important predictor than abundance of high quality food to account for these interactions.
The potential effects of protected nests and cage complexity on maternal aggression in house mice
(1998) Ebensperger, LA
I studied the behavior of nursing house mice (Mus musculus) in captivity and used a two-by-two factorial design to test the hypothesis that the combination of a protected nest along with a chance for the intruders to retreat would improve the ability of resident females to defend their litters from infanticidal males. A chance for the intruder to retreat was manipulated by testing the resident females in either a single- or a two-compartment cage. The effect of a protected nest was examined by providing females with a nest box having a narrow entrance. During each test, an infanticidal adult male was introduced into the cage of a resident female and her pups. I observed that neither the presence of a protected nest nor the chance for the intruders to retreat to a different compartment, or a combination of the two, increased the ability of a female to defend her litter against an intruder male. Moreover, neither of these two factors influenced the overall behavior of the resident females. I obtained similar results after using data from previous studies to examine the influence of both of these factors on the efficiency of maternal aggression. Overall, these two approaches showed that females are often unable to prevent intruders from committing infanticide. I discuss the validity of the hypothesis that maternal aggression evolved as a mechanism to protect offspring from infanticide. (C) 1998 Wiley-Liss, Inc.

Browsing by Author "Ebensperger, LA"

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