M. Justin O'Riain

Mammalian eusociality: a family affair

Comparative studies of two species of mole-rat are helping to clarify the ecological correlates of mammalian eusociality. Both species live in social groups composed of close kin, within which breeding is restricted to one female and one to three males. They inhabit xeric areas with dispersed, patchy food and unpredictable rainfall. During droughts, they can neither expand their tunnel systems nor disperse. In brief periods after rain the animals must cooperate and dig furiously to locate rich food patches. By living in groups, arid-zone mole-rats can take full advantage of windows of opportunity when conditions are right for burrowing. Thus, ecological factors and kin selection have apparently interacted in the evolution of eusociality in these species.

Landscape requirements of a primate population in a human-dominated environment

IntroductionAs urban and rural land development become widespread features of the global landscape so an understanding of the landscape requirements of displaced and isolated wildlife species becomes increasingly important for conservation planning. In the Cape Peninsula, South Africa, rapid human population growth, and the associated urban and rural land transformation, threatens the sustainability of the local chacma baboon population. Here we analyse spatial data collected from nine of the 12 extant troops to determine their population-level landscape requirements. We use hurdle models to ascertain the key landscape features influencing baboon occurrence and abundance patterns on two hierarchical spatial scales.ResultsBoth spatial scales produced similar results that were ecologically reliable and interpretable. The models indicated that baboons were more likely to occur, and be more abundant, at low altitudes, on steep slopes and in human-modified habitats. The combination of these landscape variables provides baboons with access to the best quality natural and anthropogenic food sources in close proximity to one another and suitable sleeping sites. Surface water did not emerge as an influential landscape feature presumably as the area is not water stressed.ConclusionsThe model results indicate that land development in the Cape Peninsula has pushed baboons into increasingly marginal natural habitat while simultaneously providing them with predictable and easily accessible food sources in human-modified habitats. The resultant spatial competition between humans and baboons explains the high levels of human-baboon conflict and further erosion of the remaining land fragments is predicted to exacerbate competition. This study demonstrates how the quantification of animal landscape requirements can provide a mechanism for identifying priority conservation areas at the human-wildlife interface.

VIRAL EPIZOOTIC REVEALS INBREEDING DEPRESSION IN A HABITUALLY INBREEDING MAMMAL

Abstract Inbreeding is typically detrimental to fitness. However, some animal populations are reported to inbreed without incurring inbreeding depression, ostensibly due to past “purging” of deleterious alleles. Challenging this is the position that purging can, at best, only adapt a population to a particular environment; novel selective regimes will always uncover additional inbreeding load. We consider this in a prominent test case: the eusocial naked mole-rat (Heterocephalus glaber), one of the most inbred of all free-living mammals. We investigated factors affecting mortality in a population of naked mole-rats struck by a spontaneous, lethal coronavirus outbreak. In a multivariate model, inbreeding coefficient strongly predicted mortality, with closely inbred mole-rats (F ≥ 0.25) over 300% more likely to die than their outbred counterparts. We demonstrate that, contrary to common assertions, strong inbreeding depression is evident in this species. Our results suggest that loss of genetic diversity through inbreeding may render populations vulnerable to local extinction from emerging infectious diseases even when other inbreeding depression symptoms are absent.

Organization of somatosensory cortical areas in the naked mole-rat (Heterocephalus glaber).

Multiunit electrophysiology was combined with histological analysis of cortical sections to investigate the organization of somatosensory areas in the naked mole‐rat. We provide new details for the organization of primary somatosensory cortex (S1) and identify cortical modules and barrels that correspond to the representations of different body parts. In addition, details of the location and organization of secondary somatosensory cortex (S2) are reported, and evidence for a third somatosensory representation, likely the parietal ventral area (PV), is provided and discussed. S1 contained a complete and systematic representation of the contralateral body surface and oral structures. The orientation of S1 was inverted, with the lower body represented medially and the face and oral structures located rostrolaterally. The S2 representation was found in caudolateral cortex forming a mirror image of S1. The two areas were joined at the representation of the vibrissae and snout, so that the orientation of S2 formed an upright representation of the body in cortex. Receptive fields for S2 were consistently larger than those in S1. Evidence for the presumptive parietal ventral area, lateral to S2, suggests that this area may be an inverted mirror image of S2. By aligning the electrophysiological maps of body representations with cytochrome oxidase‐reacted cortical sections we were able to identify modules related to the buccal pad, chin, vibrissae, forelimb, hindlimb, trunk, tongue, lower incisor, and upper incisors. The orofacial modules in lateral cortex resemble similar modules reported to relate to oral structures previously described in the laboratory rat, owl monkey, and squirrel monkey. J. Comp. Neurol. 495:434–452, 2006.

African Mole-Rats: Eusociality, Relatedness and Ecological Constraints

M. Justin O’Riain Zoology Department, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa justin.oriain@uct.ac.za Abstract Within the family of African mole-rats (Bathyergidae) there is a range of lifestyles from strictly solitary to eusocial. This variation correlates strongly with numerous ecological factors providing evidence in support of an ecological basis for the evolutionary inception and maintenance of sociality in mole-rats. Furthermore, recent studies on the relatedness of individuals both within and between neighboring colonies of social mole-rats suggest that previous arguments that expounded the importance of relatedness to the evolution of sociality were misleading. A close look at arguably the only eusocial mammal known to science, the naked mole-rat, provides a unique opportunity to study the similarities in the selective environment of insects and mammals without the associated phylogenetic noise of a close common ancestry. In addition, striking examples of convergent evolution between naked molerats and eusocial insects provides insight into why there are so few eusocial vertebrates.

Troop Size and Human-Modified Habitat Affect the Ranging Patterns of a Chacma Baboon Population in the Cape Peninsula, South Africa

Differences in group size and habitat use are frequently used to explain the extensive variability in ranging patterns found across the primate order. However, with few exceptions, our understanding of primate ranging patterns stems from studies of single groups and both intra‐ and inter‐specific meta‐analyses. Studies with many groups and those that incorporate whole populations are rare but important for testing socioecological theory in primates. We quantify the ranging patterns of nine chacma baboon troops in a single population and use Spearman rank correlations and generalized linear mixed models to analyze the effects of troop size and human‐modified habitat (a proxy for good quality habitat) on home range size, density (individuals/km2), and daily path length. Intrapopulation variation in home range sizes (1.5–37.7 km2), densities (1.3–12.1 baboons/km2), and daily path lengths (1.80–6.61 km) was so vast that values were comparable to those of baboons inhabiting the climatic extremes of their current distribution. Both troop size and human‐modified habitat had an effect on ranging patterns. Larger troops had larger home ranges and longer daily path lengths, while troops that spent more time in human‐modified habitat had shorter daily path lengths. We found no effect of human‐modified habitat on home range size or density. These results held when we controlled for the effects of both a single large outlier troop living exclusively in human‐modified habitat and baboon monitors on our spatial variables. Our findings confirm the ability of baboons, as behaviorally adaptable dietary generalists, to not only survive but also to thrive in human‐modified habitats with adjustments to their ranging patterns in accordance with current theory. Our findings also caution that studies focused on only a small sample of groups within a population of adaptable and generalist primate species may underestimate the variability in their respective localities. Am. J. Primatol. 74:853‐863, 2012.

The comparative anatomy of the abdominal gastrointestinal tract of six species of African mole‐rats (Rodentia, Bathyergidae)

The gastrointestinal tracts (GITs) of six species of African mole‐rats (Bathyergidae) were compared. The aim was to provide a comprehensive anatomical comparison between the different species. The relative shape, length, and surface areas were taken into account to determine whether the GITs are phylogenetically constrained or exhibit anatomical adaptations in response to diets. In all six species the stomach was simple and glandular. With the exception of Heterocephalus glaber, the caecum was coiled in a flat spiral, the ascending colon was arranged in a loop of varying lengths, and a mucosal colonic papillary‐lined groove was present in the ascending colon in all species. By contrast, the caecum in H. glaber was uncoiled, the ascending colon was not looped, and the groove was not papillated. A caeco‐appendix was observed only in Bathyergus suillus and Georychus capensis. Hierarchical multivariate cluster analysis on the presence/absence of nine anatomical structures associated with the GIT of mole‐rats revealed that H. glaber was anatomically the least similar of the six species (77.6% similarity) with respect to the nine GIT variables included. All Cryptomys species were the same (100% similarity), and two species B. suillus and G. capensis grouped together and were more similar to the Cryptomys genus (95% similarity) than they were to H. glaber. These findings support previous phylogenetic classifications. The voluminous caeco‐colon in B. suillus may be explained by its ingestion of grasses in addition to below‐ground storage organs of plants. We conclude that phylogeny and diet affect the GIT anatomy of the African mole rats studied here. J. Morphol., 2010.

Isotopic assessment of marine food consumption by natural-foraging chacma baboons on the Cape Peninsula, South Africa

OBJECTIVES Stable isotope analysis has been used to investigate consumption of marine resources in a variety of terrestrial mammals, including humans, but not yet in extant nonhuman primates. We sought to test the efficacy of stable isotope analysis as a tool for such studies by comparing isotope- and observation-based estimates of marine food consumption by a troop of noncommensal, free-ranging chacma baboons. MATERIALS AND METHODS We determined δ13 C and δ15 N values of baboon hair (n = 9) and fecal samples (n = 144), and principal food items (n = 362). These values were used as input for diet models, the outputs of which were compared to observation-based estimates of marine food consumption. RESULTS Fecal δ13 C values ranged from -29.3‰ to -25.6‰. δ15 N values ranged from 0.9‰ to 6.3‰ and were positively correlated with a measure of marine foraging during the dietary integration period. Mean (± SD) δ13 C values of adult male and female baboon hairs were -21.6‰ (± 0.1) and -21.8‰ (± 0.3) respectively, and corresponding δ15 N values were 5.0‰ (± 0.3) and 3.9‰ (± 0.2). Models indicated that marine contributions were ≤10% of baboon diet within any season, and contributed ≤17% of dietary protein through the year. DISCUSSION Model output and observational data were in agreement, both indicating that despite their abundance in the intertidal region, marine foods comprised only a small proportion of baboon diet. This suggests that stable isotope analysis is a viable tool for investigating marine food consumption by natural-foraging primates in temperate regions.

Beefing Up Species Richness? The Effect of Land-Use on Mammal Diversity in an Arid Biodiversity Hotspot

The transformation and fragmentation of natural land are considered to be major drivers of biodiversity loss and local extinctions. In this study we compare medium-to-large mammal diversity on rangeland, game farms and natural land within the Little Karoo, South Africa. Mammal diversity was assessed using camera traps set up at 141 sites, and compared across the three land-use types. There were no significant differences in mammal diversity across land-use types, although rangelands typically supported fewer species. Game farms had similar species richness to natural areas, suggesting that the introduction of large ungulate species and the erection of game-proof fencing has had little impact on mammal diversity to date. Importantly, our results suggest that land used for low-intensity grazing by cattle (Bos taurus) can support similar mammalian species richness to natural areas, which indicates a high level of compatibility between current economic activities and biodiversity conservation in this area. Although specific to the Little Karoo, our findings can inform management and conservation decision-making on a broader scale, as they support evidence of the biodiversity value of economically active land.

Shedding Light on Reflective Prisms as Potential Baboon (Papio ursinus) Deterrents in the Cape Peninsula, South Africa

Human-wildlife conflict is one of the emergent themes of contemporary conservation (Redpath et al., 2013; Sillero-Zubiri, Sukumar & Treves, 2007; Woodroffe, Thirgood & Rabinowitz, 2005) and has a number of negative side effects for both humans and wildlife. Where this conflict results in damages to crops, livestock or property (Gusset, Swarner, Mponwane, Keletile & McNutt, 2009; Hemson, Maclennan, Mills, Johnson & Macdonald, 2009), it may be financially beneficial to employ deterrents aimed at reducing spatial overlap between wildlife species and human-modified environments (e.g. King, Lawrence, Douglas-Hamilton & Vollrath, 2009; Hill & Wallace, 2012).