The naked truth: a comprehensive clarification and classification of current 'myths' in naked mole-rat biology.

The naked mole-rat (Heterocephalus glaber) has fascinated zoologists for at least half a century. It has also generated considerable biomedical interest not only because of its extraordinary longevity, but also because of unusual protective features (e.g. its tolerance of variable oxygen availability), which may be pertinent to several human disease states, including ischemia/reperfusion injury and neurodegeneration. A recent article entitled 'Surprisingly long survival of premature conclusions about naked mole-rat biology' described 28 'myths' which, those authors claimed, are a 'perpetuation of beautiful, but falsified, hypotheses' and impede our understanding of this enigmatic mammal. Here, we re-examine each of these 'myths' based on evidence published in the scientific literature. Following Braude et al., we argue that these 'myths' fall into four main categories: (i) 'myths' that would be better described as oversimplifications, some of which persist solely in the popular press; (ii) 'myths' that are based on incomplete understanding, where more evidence is clearly needed; (iii) 'myths' where the accumulation of evidence over the years has led to a revision in interpretation, but where there is no significant disagreement among scientists currently working in the field; (iv) 'myths' where there is a genuine difference in opinion among active researchers, based on alternative interpretations of the available evidence. The term 'myth' is particularly inappropriate when applied to competing, evidence-based hypotheses, which form part of the normal evolution of scientific knowledge. Here, we provide a comprehensive critical review of naked mole-rat biology and attempt to clarify some of these misconceptions.

The hypercholinergic brain of the Cape golden mole (Chrysochloris asiatica).

Studies detailing the anatomy of the brain of the golden moles are few. A recent study indicated that in the Hottentot golden mole (a member of the Amblysominae clade), there was a broad, atypical, distribution of cholinergic interneurons in the olfactory bulb, cerebral cortex, hippocampus and amygdala. To determine whether this broad distribution of cholinergic neurons is shared by other species of golden mole, we here examine the brain of the Cape golden mole (a member of the Chrysochlorinae clade, representing the second major clade within the family Chrysochloridae). Our analyses indicates the presence of a similar widespread distribution of cholinergic interneurons in the Cape golden mole. Thus, we conclude that these features are derived morphological traits in the brains of golden moles. In addition, we describe the nuclei generally considered to be part of the typical cholinergic system in mammals. Whereas the vast majority of these generally reported cholinergic nuclei were the same as recorded in other Eutherian mammals, it was noted that the cholinergic nuclei involved in oculomotion were substantially reduced in size, or absent in the case of the abducens nucleus. In addition, there was an absence of the cholinergic medial septal nucleus, but the presence of a cholinergic lateral septal nucleus. The laterodorsal and pedunculopontine tegmental nuclei evince regions where the cholinergic neurons are densely packed. These are atypical features of the mammalian cholinergic system, which when combined with the widespread atypical distribution of cholinergic interneurons, reveals a family-specific complement of cholinergic nuclei in the Chrysochloridae.

Comparative gastrointestinal morphology of seven golden mole species (Mammalia: Chrysochloridae) from South Africa.

Golden moles are small, fossorial, and primarily insectivorous mammals mostly endemic to South Africa. They belong to an ancient African clade of placental mammals (Afrotheria) that likely radiated from an herbivorous ancestor. Nearly half of the 21 golden mole species are listed as threatened; but remarkably little is known about their basic biology and gastrointestinal tract (GIT) morphology. This study provides a morphometric and histochemical analysis of the GIT of seven chrysochloridae species, including three threatened taxa. Macroscopically, all species examined had simple GITs with simple, wholly glandular stomachs and no cecum. Histologically, the pylorus was dominated by parietal cells. Neutral mucin cells were found on the luminal surface and in the gastric pits, while mixed acid and neutral mucin cells were found in the proximal parts of the gastric glands. The proximal intestine had typical small intestinal histological features such as villi. Typical colonic mucosal features were absent as villi were present throughout the intestinal tract. Goblet cells were abundant and increased toward the distal intestine. These intestinal goblet cells contained mostly mixed mucins. Stomach and intestinal content analysis confirmed the presence of arthropod exoskeleton material and possible small vertebrate remnants, commensurate with a low-fibre, protein-rich diet. This may account for their simple GIT morphology, as seen convergently in other unrelated insectivorous mammals. This study provides better representation of variation in GIT morphology among chrysochloridae and within the enigmatic Afrotheria clade. Additionally, it provides a better understanding of the mucin distribution in relation to diet and phylogeny of golden moles.

Phylogeography of a Morphologically Cryptic Golden Mole Assemblage from South-Eastern Africa.

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.

Faecal mimicry by seeds ensures dispersal by dung beetles.

The large brown, round, strongly scented seeds of Ceratocaryum argenteum (Restionaceae) emit many volatiles found to be present in herbivore dung. These seeds attract dung beetles that roll and bury them. As the seeds are hard and offer no reward to the dung beetles, this is a remarkable example of deception in plant seed dispersal.