Field evidence for colony size and aseasonality of breeding and in Ansell’s mole-rat, Fukomys anselli (Rodentia: Bathyergidae)

Ansell’s mole-rat, Fukomys anselli, is a cooperatively breeding bathyergid endemic to the Lusaka Province of Zambia. During a 12-month field study involving the capture of 33 colonies of mole-rats, the number of occupants, breeding females and sex ratio within colonies were recorded. While thirty of these social groups contained a single breeding queen, three were found to exhibit plural breeding among females, having two queens present simultaneously. Mean±S.E.M. colony size was 8.7±2.2 (range  6–16,n=33). The occurrence of plural breeding and small group size is consistent with the predictions of the aridity food  distribution hypothesis for social species inhabiting mesic habitats. The sex ratio of the population was skewed towards females at 1.2:1. The mean mass of adult males was 63.0 ± 18.3 g (range 36.7–110.3, n=87) while that for adult females was 52.9±11.8 g (range 35.1–77.8, n=86). Pregnant and lactating females were found throughout the study period from February 2009 to  February 2010, indicating an aseasonal pattern of breeding in this species. Autopsy of individuals (n = 288) from the 33 colonies revealed a total of 19 pregnant females. Nine of these were in the latter stages of pregnancy and mean litter size was determined as 2.7 pups (range 1–4). Collectively, these new data reveal that Fukomys anselli share many similarities in life history and reproductive traits with the phylogentically closely related giant Zambian mole-rat, Fukomys mechowii.Key words: Fukomys anselli, Bathyergidae, reproduction, colony size, seasonality, reproductive skew

Ontogenetic variation and craniometric sexual dimorphism in the social giant mole-rat, Fukomys mechowii (Rodentia: Bathyergidae), from Zambia

The degree of maxillary molar tooth-row eruption and wear were used to assign samples of the social giant mole-rat, Fukomys mechowii, from Zambia, into nine relative age classes in order to assess ontogenetic (age) variation and craniometric sexual dimorphism, with reference to body mass. Univariate and multivariate statistical analyses showed craniometric differences between age classes 1–3 and age classes 5–9, with age class 4 being intermediate between these two age class groupings. This suggests that age class 4 lies at a point on a hypothetical growth curve where growth begins to stabilize. The intermediate placement of age class 4 in multivariate space broadly coincided with body mass categorizations into juveniles (age classes 1–3; 150 g). The analyses also revealed the absence of sexual dimorphism in the relatively younger age classes 1–4 but its presence in the relatively older age classes 5–9, and these results are supported by data on body mass. These results may have implications in our understanding of the population and social structures, and reproductive strategies in this little-studied giant mole-rat

Cladogenesis and endemism in Tanzanian mole-rats, genus Fukomys: (Rodentia: Bathyergidae): a role for tectonics?

Biological Journal of the Linnean Society, 2010; 100: 337–352.African mole-rats of the family Bathyergidae are subterranean hystricomorph rodents found throughout sub- Saharan Africa, where the distributional ranges of the most speciose taxa are divided by the African Rift Valley. In particular, mole-rats of the genera Heliophobius and Fukomys are distributed widely, and their adaptive radiation appears to have been strongly influenced by the geological process of rifting. As a result, virtually all members of the genus Fukomys occur in locations west of the Rift Valley. However, a small number of isolated populations occur east of the Rift Valley in Tanzania, where Heliophobius is widespread and is the predominant bathyergid rodent. Phylogenetic analysis of mitochondrial cytochrome b sequences of previously unstudied Tanzanian mole-rats (genus Fukomys) and geographically adjacent populations strongly suggests that vicariance in the Western Rift Valley has subdivided populations of mole-rats and, together with climatic changes, played a role in the isolation of extralimital populations of Fukomys in Tanzania. Together with molecular clock-based estimates of divergence times, these results offer strong support for the hypothesis that the observed patterns of cladogenesis are consistent with tectonic activity in the ‘Mbeya triple junction’ and Rungwe volcanic province between Lakes Rukwa and Nyasa

Cladogenesis and endemism in Tanzanian mole-rats, genus Fukomys: (Rodentia: Bathyergidae): a role for tectonics?

Biological Journal of the Linnean Society, 2010; 100: 337–352.African mole-rats of the family Bathyergidae are subterranean hystricomorph rodents found throughout sub- Saharan Africa, where the distributional ranges of the most speciose taxa are divided by the African Rift Valley. In particular, mole-rats of the genera Heliophobius and Fukomys are distributed widely, and their adaptive radiation appears to have been strongly influenced by the geological process of rifting. As a result, virtually all members of the genus Fukomys occur in locations west of the Rift Valley. However, a small number of isolated populations occur east of the Rift Valley in Tanzania, where Heliophobius is widespread and is the predominant bathyergid rodent. Phylogenetic analysis of mitochondrial cytochrome b sequences of previously unstudied Tanzanian mole-rats (genus Fukomys) and geographically adjacent populations strongly suggests that vicariance in the Western Rift Valley has subdivided populations of mole-rats and, together with climatic changes, played a role in the isolation of extralimital populations of Fukomys in Tanzania. Together with molecular clock-based estimates of divergence times, these results offer strong support for the hypothesis that the observed patterns of cladogenesis are consistent with tectonic activity in the ‘Mbeya triple junction’ and Rungwe volcanic province between Lakes Rukwa and Nyasa

Stress hormones and sociality: integrating social and environmental stressors

In cooperatively breeding species, reproductive decisions and breeding roles may be influenced by environmental (food resources) or social factors (reproductive suppression of subordinates by dominants). Studies of glucocorticoid stress hormones in cooperatively breeding species suggest that breeding roles and hormone levels are related to the relative costs of dominance and subordination, which are driven primarily by social interactions. Few studies, however, have considered how environmental factors affect glucocorticoid levels and breeding roles in cooperative breeders, even though environmental stressors modulate seasonal glucocorticoid release and often influence breeding roles. I examined baseline and stress-induced levels of the glucocorticoid corticosterone (CORT) across 4 years in the plural breeding superb starling, Lamprotornis superbus, to determine whether (i) environmental factors (namely rainfall) directly influence breeding roles or (ii) environmental factors influence social interactions, which in turn drive breeding roles. Chronic baseline and maximal stress-induced CORT changed significantly across years as a function of pre-breeding rainfall, but dominant and subordinate individuals responded differently. Pre-breeding rainfall was also correlated directly with breeding roles. The results are most consistent with the hypothesis that environmental conditions influenced the relative costs of dominance and subordination, which in turn affected the degree and intensity of social interactions and ultimately reproductive decisions and breeding roles

The number of subordinates moderates intrasexual competition among males in cooperatively breeding meerkats

For dominant individuals in cooperatively breeding species, the presence of subordinates is associated with both benefits (i.e. increased reproductive output and other group-living benefits) and costs (i.e. intrasexual competition on reproduction). The biological market theory predicts that dominant individuals are tolerant to same-sex group members when there are only a few subordinates, so as to maximize their own reproductive success. We investigated factors affecting aggression by dominant males and submission by subordinate males for a cooperatively breeding mammal, meerkats, Suricata suricatta. In this species, reproductive conflict occurs between the dominant male and the non-offspring males. As predicted, the number of subordinates in a group was positively associated with the aggression frequency by the dominant male and with the submission frequency by the subordinate males. Relative to the aggression frequency against male offspring, the frequency of aggression against non-offspring males was comparable in small groups, but was higher in large groups. These results indicate that reproductive conflict is present between the dominant male and the non-offspring males but is moderated in groups with small numbers of subordinates. This study provides an empirical data agreeing with the biological market theory in the context of intrasexual competition in cooperatively breeding species

Sociality and the telencephalic distribution of corticotrophin-releasing factor, urocortin 3, and binding sites for CRF type 1 and type 2 receptors: A comparative study of eusocial naked mole-rats and solitary Cape mole-rats

Various aspects of social behavior are influenced by the highly conserved corticotrophin-releasing factor (CRF) family of peptides and receptors in the mammalian telencephalon. This study has mapped and compared the telencephalic distribution of the CRF receptors, CRF1 and CRF2, and two of their ligands, CRF and urocortin 3, respectively, in African mole-rat species with diametrically opposed social behavior. Naked mole-rats live in large eusocial colonies that are characterized by exceptional levels of social cohesion, tolerance, and cooperation in burrowing, foraging, defense, and alloparental care for the offspring of the single reproductive female. Cape mole-rats are solitary; they tolerate conspecifics only fleetingly during the breeding season. The telencephalic sites at which the level of CRF1 binding in naked mole-rats exceeds that in Cape mole-rats include the basolateral amygdaloid nucleus, hippocampal CA3 subfield, and dentate gyrus; in contrast, the level is greater in Cape mole-rats in the shell of the nucleus accumbens and medial habenular nucleus. For CRF2 binding, the sites with a greater level in naked mole-rats include the basolateral amygdaloid nucleus and dentate gyrus, but the septohippocampal nucleus, lateral septal nuclei, amygdalostriatal transition area, bed nucleus of the stria terminalis, and medial habenular nucleus display a greater level in Cape mole-rats. The results are discussed with reference to neuroanatomical and behavioral studies of various species, including monogamous and promiscuous voles. By analogy with findings in those species, we speculate that the abundance of CRF1 binding in the nucleus accumbens of Cape mole-rats reflects their lack of affiliative behavior. © 2015 Wiley Periodicals, Inc