The Striped Mouse (Rhabdomys pumilio) From the Succulent Karoo, South Africa: A Territorial Group-Living Solitary Forager With Communal Breeding and Helpers at the Nest

Ecophysiological Studies Research Group, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa.
Journal of Comparative Psychology (Impact Factor: 2.34). 04/2004; 118(1):37-47. DOI: 10.1037/0735-7036.118.1.37
Source: PubMed


The authors studied the striped mouse (Rhabdomys pumilio) in the semiarid succulent karoo of South Africa. Mice forage alone, but they live in groups that share a common nest. Groups consist of 1 to 4 breeding females, 1 to 2 breeding males, and their offspring of both sexes, which remain in their natal group even after reaching adulthood, participating in territorial defense and nest building without showing signs of reproductive activity. Interactions are typically amicable and take place inside or in front of the nest. In contrast, encounters with mice from other groups are aggressive. Group living in the succulent karoo is possibly due to ecological constraints imposed by habitat saturation because of a year-round stable food supply as well as associated benefits of philopatry.

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    • "Females were weighed to the nearest gramme using an electronic balance, and we recorded whether their nipples were pink and elongated (characteristic of lactation), otherwise visible or not visible. Newly-trapped individuals were provided with numbered aluminium ear-tags (National Band and Tag, Newport, KY), and marked with non-toxic hair dye (Inecto, Pinetown, South Africa), so that they could be recognised during behavioural observations at their nest sites (described in Schradin and Pillay, 2004). All adults trapped during the breeding season were fitted with MD-2C radio-collars (Holohil, Canada). "
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    ABSTRACT: 1.Alternative reproductive tactics (ARTs) are discrete reproductive phenotypes governed by decision-rules called strategies. ARTs are fixed for life in species with alternative strategies, while tactic expression is plastic in species with a single strategy. ARTs have been investigated in males of many species, but few studies have tested whether the same theoretical framework applies in females. 2.Female striped mice (Rhabdomys pumilio) employ three ARTs: communal breeders give birth in a nest shared with female kin and a breeding male, and show allo-parental care; returners give birth away from the shared nest and later return to it; and solitary breeders give birth away from the shared nest and do not return to the group. 3.Here, studying free-living female striped mice over six breeding seasons, we tested whether ARTs arise from alternative strategies or a single strategy. 4.We also asked to what extent stochastic extrinsic factors explain whether individuals become solitary rather than group-living. 5.Females switched tactics, consistent with a single strategy, so we tested whether this represented a mixed or conditional single strategy. Only the latter predicts differences between ARTs in traits indicating competitive ability, such as body mass or age, before individuals adopt a tactic. We weighed females at conception when they were still group-living to eliminate potential confounding effects of gestation and subsequent social tactic (solitary- versus group-living) on body mass. 6.Females that went on to use a solitary ART were heavier than those that became communal breeders and returners, in support of a conditional strategy. 7.Solitary breeders also arose through extrinsic factors (mortality of all adult female group members). They weighed less than females that became solitary while relatives were alive, but did not differ in body mass from communal breeders and returners. 8.We conclude that ART theory applies to both sexes, with female striped mice following a conditional single strategy. Future studies should consider the possibility that phenotypes that superficially resemble evolved tactics might also arise through non-adaptive extrinsic causes. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
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    • "Philopatric helpers show lower testosterone and higher corticosterone levels than territorial dominant breeders and testosterone levels increase in male helpers with age (Schradin et al. 2009a,b). Interlitter intervals are 3–7 wk, and in the field, philopatric helpers can vary in age between 3 wk (juveniles) and 12 mo (fully adult) (Schradin & Pillay 2004). We first compared the amount of alloparental care with parental care by both parents and tested whether African striped mouse helpers show sex and age differences in providing alloparental care. "
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    ABSTRACT: Alloparental care of non-breeders is the main characteristic of cooperatively breeding species. While many studies have contributed to the understanding of the evolutionary reasons why individuals provide care to young that are not their own offspring, the variables influencing and causing alloparental care are less understood. We tested in African striped mice (Rhabdomys pumilio) whether age, sex, testosterone and corticosterone were correlated with alloparental care of non-breeding helpers. We studied 11 family groups under controlled conditions in the laboratory, each with two juvenile and two adult helpers, one being male and one being female in each age category. We predicted male helpers to show more alloparental care than female helpers, as males are the dispersing sex and might thus have to pay for staying. We also expected adult helpers to show more alloparental care than juvenile helpers and both corticosterone and testosterone to correlate negatively with alloparental care. We found high levels of alloparental care in non-breeding striped mice, which spent a significant amount of time in the nest, huddling and licking pups. There was neither a difference between the sexes nor between age categories (although both factors were significant in interaction terms), indicating either low costs and/or high benefits of alloparental care. Mothers showed significantly more care than helpers, and fathers showed similar levels of parental care as mothers but not significantly more than helpers. Although testosterone levels differed significantly between helpers of different age and sex, with adult male helpers showing the highest levels, we did not find any relationships between testosterone and the amount of alloparental care. Corticosterone levels were negatively correlated with alloparental care, and these effects were modulated by the sex and the age of helpers. In females, less alloparental care was shown with increasing corticosterone levels, while in males, the relationship was positive. Also, younger individuals with lower corticosterone levels showed more alloparental care than older individuals with low corticosterone levels. In sum, alloparental care is well developed in male and female non-breeding helpers of striped mice, both in adult and juvenile helpers, but independently of testosterone, with corticosterone showing an age- and sex-specific relationship with alloparental care.
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    • "The African striped mouse (Rhabdomys pumilio) in the Succulent Karoo semi-desert of South Africa is obligatory group-living during the dry hot season, which is characterized by both food and water shortage (Schradin and Pillay, 2004). However, this species shows high social flexibility during the moist and cold breeding season in spring (Schradin et al., 2012). "
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    ABSTRACT: Arginine vasopressin (AVP) is an important hormone for osmoregulation, while as a neuropeptide in the brain it plays an important role in the regulation of social behaviors. Dry habitats are often the home of obligately sociable species such as meerkats and Damaraland mole-rats, leading to the hypothesis that high plasma AVP levels needed for osmoregulation might be associated with the regulation of social behavior. We tested this in a facultative sociable species, the African striped mouse (Rhabdomys pumilio). During the moist breeding season, both solitary- and group-living reproductive tactics occur in this species, which is obligatory sociable in the dry season. We collected 196 plasma samples from striped mice following different reproductive tactics both during the moist and the dry season. Solitary mice did not have lower AVP levels than sociable mice, rejecting the hypothesis that peripheral AVP is involved in the regulation of alternative reproductive tactics. However, we found significantly higher AVP levels during the dry season, with AVP levels correlated with the abundance of food plants, the main source of water for striped mice. Plasma AVP levels were not correlated with testosterone or corticosterone levels. Our study underlines the important role that AVP plays in osmoregulation, particularly for a free ranging mammal living under harsh arid conditions.
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