Browsing by Author "Bennett, Nigel C"

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    Facilitating golden mole conservation in South African highland grasslands : a predictive modelling approach
    (2016) Rampartab, Chanel; Bronner, Gary N; Bennett, Nigel C; Bloomer, Paulette; Robertson, M P
    Golden moles are subterranean mammals endemic to sub-Saharan Africa and threatened by anthropogenic habitat loss. At present, little is known about the biology, taxonomy, distribution and severity of threats faced by many of these taxa. In an attempt to raise awareness of these elusive grassland flagship taxa, the Endangered Wildlife Trust's Threatened Grassland Species Programme (EWT-TGSP) identified the need for more information on the distributions and conservation status of four poorly-known golden mole taxa (Amblysomus hottentotus longiceps, A. h. meesteri, A. robustus, A. septentrionalis) that are endemic to the Grassland Biome, and which may be heavily impacted by anthropogenic habitat alteration in the Highveld regions of Mpumalanga Province. This study employed species distribution modelling to predict the distributional ranges of these taxa, and involved four main processes: (i) creating initial models trained on sparse museum data records; (ii) ground-truthing field surveys during austral spring/summer to gather additional specimens at additional localities; (iii) genetic analyses (using cytochrome-b) to determine the species identities of the newly-acquired specimens, as these taxa are morphologically indistinguishable; and (iv) refining the models and determining the conservation status of these Highveld golden moles. Initial species distribution models were developed using occurrence records for 38 specimens, based on interpolated data for 19 bioclimatic variables, continuous altitude data, as well as categorical spatial data for landtypes, WWF ecoregions and vegetation types. These initial models helped to effectively focus survey efforts within a vast study area, with surveying during the austral spring-summer of 2013-4 resulting in the acquisition of 25 specimens from across Mpumalanga, nine individuals of which (A. h. meesteri n = 2; A. septentrionalis n = 5; unknown n = 2) were captured in five new quarter-degree-squares (QDSs) where no previous golden moles have been recorded. Additionally, observed activity was also recorded in nine new QDSs (see Appendix 3), showing that the model refinement methods used (variable selection, auto-correlation, non-repeated versus cross-validated models, jackknife of variable importance and localities, independent data testing) were effective in locating golden mole populations. By using genetically-identified historical golden mole records, predictive distribution models were calibrated in maximum entropy (MaxEnt) software to focus ground-truthing efforts.
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    How attractive is the girl next door? An assessment of spatial mate acquisition and paternity in the solitary Cape dune mole-Rat, Bathyergus suillus
    (Public Library of Science, 2012) Bray, Timothy C; Bloomer, Paulette; O'Riain, M Justin; Bennett, Nigel C
    Behavioural observations of reproduction and mate choice in wild fossorial rodents are extremely limited and consequently indirect methods are typically used to infer mating strategies. We use a combination of morphological, reproductive, spatial, and genetic data to investigate the reproductive strategy of a solitary endemic species, the Cape dune mole-rat Bathyergus suillus. These data provide the first account on the population dynamics of this species. Marked sexual dimorphism was apparent with males being both significantly larger and heavier than females. Of all females sampled 36% had previously reproduced and 12% were pregnant at the time of capture. Post-partum sex ratio was found to be significantly skewed in favour of females. The paternity of fifteen litters (n = 37) was calculated, with sires assigned to progeny using both categorical and full probability methods, and including a distance function. The maximum distance between progeny and a putative sire was determined as 2149 m with males moving between sub-populations. We suggest that above-ground movement should not be ignored in the consideration of mate acquisition behaviour of subterranean mammals. Estimated levels of multiple paternity were shown to be potentially as high as 26%, as determined using sibship and sire assignment methods. Such high levels of multiple paternity have not been found in other solitary mole-rat species. The data therefore suggest polyandry with no evidence as yet for polygyny.
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    A phylogenetic estimate for golden moles (Mammalia, Afrotheria, Chrysochloridae)
    (BioMed Central Ltd, 2010) Asher, Robert; Maree, Sarita; Bronner, Gary; Bennett, Nigel C; Bloomer, Paulette; Czechowski, Paul; Meyer, Matthias; Hofreiter, Michael
    BACKGROUND: Golden moles (Chrysochloridae) are small, subterranean, afrotherian mammals from South Africa and neighboring regions. Of the 21 species now recognized, some (e.g., Chrysochloris asiatica, Amblysomus hottentotus) are relatively common, whereas others (e.g., species of Chrysospalax, Cryptochloris, Neamblysomus) are rare and endangered. Here, we use a combined analysis of partial sequences of the nuclear GHR gene and morphological characters to derive a phylogeny of species in the family Chrysochloridae. RESULTS: Although not all nodes of the combined analysis have high support values, the overall pattern of relationships obtained from different methods of phylogeny reconstruction allow us to make several recommendations regarding the current taxonomy of golden moles. We elevate Huetia to generic status to include the species leucorhinus and confirm the use of the Linnean binomial Carpitalpa arendsi, which belongs within Amblysominae along with Amblysomus and Neamblysomus. A second group, Chrysochlorinae, includes Chrysochloris, Cryptochloris, Huetia, Eremitalpa, Chrysospalax, and Calcochloris. Bayesian methods make chrysochlorines paraphyletic by placing the root within them, coinciding with root positions favored by a majority of randomly-generated outgroup taxa. Maximum Parsimony (MP) places the root either between chrysochlorines and amblysomines (with Chlorotalpa as sister taxon to amblysomines), or at Chlorotalpa, with the former two groups reconstructed as monophyletic in all optimal MP trees. CONCLUSIONS: The inclusion of additional genetic loci for this clade is important to confirm our taxonomic results and resolve the chrysochlorid root. Nevertheless, our optimal topologies support a division of chrysochlorids into amblysomines and chrysochlorines, with Chlorotalpa intermediate between the two. Furthermore, evolution of the chrysochlorid malleus exhibits homoplasy. The elongate malleus has evolved just once in the Cryptochloris-Chrysochloris group; other changes in shape have occurred at multiple nodes, regardless of how the root is resolved.
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    Phylogeography of a morphologically cryptic golden mole assemblage from South-Eastern Africa
    (Public Library of Science, 2015) Mynhardt, Samantha; Maree, Sarita; Pelser, Illona; Bennett, Nigel C; Bronner, Gary N; Wilson, John W; Bloomer, Paulette
    The Greater Maputaland-Pondoland-Albany (GMPA) region of southern Africa was recently designated as a centre of vertebrate endemism. The phylogeography of the vertebrate taxa occupying this region may provide insights into the evolution of faunal endemism in south-eastern Africa. Here we investigate the phylogeographic patterns of an understudied small mammal species assemblage ( Amblysomus ) endemic to the GMPA, to test for cryptic diversity within the genus, and to better understand diversification across the region. We sampled specimens from 50 sites across the distributional range of Amblysomus , with emphasis on the widespread A . hottentotus , to analyse geographic patterns of genetic diversity using mitochondrial DNA (mtDNA) and nuclear intron data. Molecular dating was used to elucidate the evolutionary and phylogeographic history of Amblysomus . Our phylogenetic reconstructions show that A . hottentotus comprises several distinct lineages, or evolutionarily significant units (ESUs), some with restricted geographic ranges and thus worthy of conservation attention. Divergence of the major lineages dated to the early Pliocene, with later radiations in the GMPA during the late-Pliocene to early-Pleistocene. Evolutionary diversification within Amblysomus may have been driven by uplift of the Great Escarpment c. 5-3 million years ago (Ma), habitat changes associated with intensification of the east-west rainfall gradient across South Africa and the influence of subsequent global climatic cycles. These drivers possibly facilitated geographic spread of ancestral lineages, local adaptation and vicariant isolation. Our study adds to growing empirical evidence identifying East and southern Africa as cradles of vertebrate diversity.
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    Sociality in the common mole-rat, Cryptomys hottentotus hottentotus : the effects of aridity
    (1998) Spinks, Andrew Charles; Jarvis, Jennifer UM; Bennett, Nigel C
    This study addresses the extrinsic factors which have shaped the evolution and maintenance of sociality in the African mole-rats. Specifically, the common mole-rat was used as a model to assess the Aridity Food-Distribution Hypothesis (AFDH), as an explanation for the evolution of bathyergid sociality. The AFDH correlates mole-rat sociality with habitat aridity and the pattern of food distribution. Aspects relating to ecological constraints, foraging behaviour, population demography, reproductive biology and aggressive behaviour were compared between an arid and a mesic population of C. h. hottentotus, to assess how inter-habitat divergence in ecological attributes has influenced social behaviour within these two populations. In evaluating the AFDH as an explanation for the evolution of sociality within C. h. · hottentotus two broad questions were addressed: (1) do the assumptions of the AFDH hold true i.e. do arid and mesic habitats exhibit ecological differences, specifically with regard to the pattern of resource dispersion and the energetic costs of foraging, which influence foraging risks and consequently the costs of dispersal? and (2) do these inter-habitat differences have implications for bathyergid social evolution i.e. do the common mole-rat populations inhabiting arid and mesic areas exhibit regional differentiation in social behaviour? Substantial inter-site divergence in ecological characteristics, notably climate and resource attributes, were revealed in this study. Rainfall at the arid site was markedly lower and more sporadic, and evaporation levels significantly higher, than at the mesic site. Moreover, thermal constraints were more limiting at the arid site. These features will greatly elevate the costs of soil excavation and the risks of hyperthermia, severely restricting the occurrence of suitable burrowing opportunities at the arid locality. Consequently, foraging will be severely constrained in this area. At the mesic site, higher, more predictable rainfall, low evaporation rates and reduced thermal constraints will translate into more suitable burrowing opportunities for much, if not all, of the year. Regional differentiation in food resource characteristics was also evident. Although geophytes were clumped at both study localities, the density of geophytes was lower and the distance between geophytes or geophyte clumps concomitantly greater at the arid relative to the mesic site. Differences in resource dispersion in turn influenced the patterns of foraging. In response to the low geophyte density and associated longer foraging distances, burrow systems were notably longer and more linear at the arid site. Furthermore, food storage and in situ harvesting were essential components of cooperative foraging in C. h. hottentotus as they minimised the risks of starvation, particularly in arid habitats. Thus, resource characteristics together with the climatic restrictions on burrowing in arid areas may have a marked impact on foraging behaviour, imposing severe constraints on the mole-rats occurring there and ultimately shaping their foraging responses. Together, these factors satisfactorily account for the underlying premise of the AFDH, that arid and mesic habitats exhibit ecological differences with regard to the pattern of resource dispersion and the energetic costs of foraging, which are likely to influence foraging risks and the costs of dispersal. In evaluating the AFDH, the second question which needed to be addressed was whether the study populations exhibited divergence in their social behaviour. The populations revealed no differences in absolute group size or in reproductive characteristics which were related to the effects of aridity per se. However, distinct inter-population divergence was readily apparent in phenotypically plastic traits such as dispersal behaviour and xenophobia. Clear differences were evident between the arid and mesic sites in both the quantitative and qualitative nature of dispersal; dispersal was markedly constrained at the arid site and colonies demonstrated greater temporal stability, with more predictable temporal group membership. The ecological constraints on successful foraging at the arid site will curb opportunities for dispersal and promote cooperation in the C. h. hottentotus occurring there. Colony members should therefore maximise their inclusive fitness by natal philopatry, delayed dispersal and cooperative foraging. Inter-site differences were also apparent in the response of colony members to foreign conspecifics. Common mole-rats from the arid site were markedly more xenophobic than those from the mesic site, and aggressively rejected foreigners. For arid-occurring populations, the fitness penalties for failing to exclude foreigners from the colony burrow system and associated resources, will be more severe than for mesic-occurring populations, resulting in heightened levels of xenophobia. Again, colony cohesion and cooperation in arid areas are essential to individual survival and inclusive fitness. The regional differences in dispersal patterns and xenophobia revealed in this investigation may reflect adaptive variation in social behaviour between the study populations, and the results suggest that delayed dispersal and cooperation may be more crucial to individual survival in arid than in mesic areas. As such these findings provide support for the underlying contention of the AFDH that ecological constraints on foraging in arid areas have promoted a greater degree of social elaboration in mole-rats occurring there. This study provides persuasive support for the AFDH as an explanation for the adaptive significance of social behaviour and cooperation in the common mole-rat, and together with other investigations, suggests that the AFDH provides a valid explanation for the evolution of group-living in the Bathyergidae.