Golden Moles

Order Afrosoricida | Family Chrysochloridae

Biological synopsis by Gary Bronner

Introduction

Namib Desert Golden Mole, Eremitalpa granti namibensis.

Photo by G. Rathbun.

Linnaeus first documented the existence of golden moles (family Chrysochloridae) nearly 250 years ago, yet current knowledge of these blind, subterranean small mammals is still limited, and based largely on a few more common and widespread species. This can be attributed to several factors:

The highly restricted distributions of some species, often in remote areas not easily accessible to biologists;

The cryptic and trap-shy nature of many species;

A historical tendency to focus biological attention on the larger, charismatic mammals while overlooking smaller-sized mammalian groups that are more diverse, ancient and often more deserving of conservation concern.

Phylogeny

Dobson (1882) first noted that golden moles resemble tenrecs in having zalambdodont molars, but that golden moles also show many important structural differences suggesting that they are not closely allied to any other family of extant mammals. Broom (1916) and several other authors subsequently showed that zalambdodonty has arisen independently several times in mammals, implying that the common possession of zalambdodont molars by golden moles and tenrecs is probably due to morphological convergence. On the basis of their unique cranial and nasal morphology, he proposed that chrysochlorids be classified in the distinct order Chrysochloridea (Broom 1915, 1916). This proposal received little attention, and until recently golden moles were generally regarded to be only specialized members of the (now defunct) Order Insectivora, with proposed affinity to the tenrecs of Madagascar based on their joint possession of zalambododont cheekteeth. However, recent studies of mitochondrial and nuclear gene sequences, rare genomic changes (indels, SINES and chromosome rearrangements; Springer et al. 2004) have conclusively demonstrated that chrysochlorids and tenrecs form a clade worthy of ordinal status. Stanhope et al. (1999) named this clade the Afrosoricida (African shrew-like mammals), a somewhat inappropriate name since it contains no soricids (shrews) and could engender confusion with the shrew subgenus Afrosorex, but Bronner & Jenkins (2005) accepted this name on the grounds that the alternative (and earlier) names "Tenrecoidea" and "Tenrecomorpha" are unsuitable at the ordinal level.

Divergence between golden-moles and tenrecs probably occurred about 50 million years ago, with the result that they share few morphological synapomorphies, warranting their allocation to distinct suborders (for which the names Tenrecomorpha and Chrysochloridea should be used).

Taxonomy

Most previous taxonomic revisions of golden moles were largely intuitive, or based on only elementary statistical evaluation of few specimens, leading to conflicting classifications that obscured rather than resolved inter-specific relationships. Based on phylogenetic analyses of morphometric and cytogenetic variation in three genera, Bronner (1995a,b) proposed a new classification including a newly-described species (Bronner 2000). Following Simonetta (1968), two subfamilies may be recognized, albeit with differing species allocations: the Chrysochlorinae, in which the malleus bone of the middle ear is enlarged with a spherical or club-like shape (Carpitalpa - 1 spp., Chlorotalpa - 2 spp., Chrysospalax - 2 spp., Chrysochloris - 3 spp., Cryptochloris - 2 spp. and Eremitalpa - 1 spp.); and the Amblysominae, in which the malleus is not expanded and has the typical mammalian shape (Amblysomus - 5 spp., Neamblysomus - 2 spp. and Calcochloris 3 spp.). This is the currently accepted taxonomy (Bronner & Jenkins 2005), though some minor changes may result when a phylogeny based on nuclear and mitochondrial gene sequences (currently being undertaken at the University of Pretoria by members of the Afrotheria Specialist Group) becomes available.

Distribution

Golden moles are endemic to subSaharan Africa, where the 21 known species inhabit a wide altitudinal, climatic and vegetational spectrum of subterrestrial habitats. They have a markedly southern African centre of diversity, with only three species occurring outside this region: Calcochloris leucorhinus in equatorial forest and woodlands of central Africa; Chrysochloris stuhlmanni in montane forests of east and central Africa; and Calcochloris tytonis, known from only a single specimen collected in Somalian woodland (Simonetta 1968). In southern Africa, the 18 known species fall into two broad ecological groups: a group of five species that occurs in semi-desert (Eremitalpa granti, Cryptochloris zyli and C. wintoni), karroid (Chrysochloris visagiei) or fynbos habitats (Chrysochloris asiatica) along the south-west coast; and 13 mesic-adapted species that inhabit indigenous forests, savanna woodlands and temperate grasslands in the eastern part of the subregion (Chrysospalax, Chlorotalpa, Calcochloris, Neamblysomus and Amblysomus). Only two species – the Hottentot golden mole (Amblysomus hottentotus) and the Cape golden mole (Chrysochloris asiatica) - are widespread. Some species, such as Stuhlmann’s golden mole Chrysochloris stuhlmanni and Juliana’s golden mole Neamblysomus julianae), are known from only scattered localities situated hundreds of kilometres apart, but connected by continuous favourable habitat. These may be more widespread than is indicated by the scant distribution data currently available. Other species, such as Sclater’s golden mole (Chlorotalpa sclateri), probably have more restricted ranges than general texts indicate, since the few populations known to exist occur at localities separated by wide expanses of seemingly inhospitable habitat; geographical continuity between these isolates seems unlikely. Click here for distribution maps.

Morphology

Golden moles are not all golden coloured! Fur colour varies from black to pale tawny-yellow; the colloquial name “golden mole”, and their family name “Chrysochloridae” (derived from Greek, meaning green-gold), refers to the iridescent sheen of coppery gold, green, purple or bronze on their fur. Despite differences in size and colour, all golden mole species have a similar appearance with compact fusiform or lozenge-shaped bodies, short and powerful forelimbs containing pick-like claws, and no external eyes, ears or tail (although internal caudal vertebrae are present). Their fur is dense and consists of guard hairs that are moisture repellent and woolly underfur for insulation. Their skin is thick and tough, particularly on the head, which contains a wedge-shaped muzzle with a leathery nosepad that protects the nostrils. They use upward thrust of their dorsally-flattened heads, together with powerful down thrusts of the foreclaws, to tunnel through the soil during subsurface foraging, creating raised ridges of soil that are visible aboveground. Some species (belonging to the genera Amblysomus and Neamblysomus) also use the head, together with their webbed hind feet, to move soil excavated when making deeper tunnels, and evict this soil on the surface in the form of small mounds.

Golden moles show many anatomical characteristics common to other fossorial mammals, these similarities being the result of ecological convergence rather than ancestry. The eyes are vestigial and covered by skin, and the optic nerve is reportedly degenerate (though there is some debate as to whether or not this is indeed so), a common tendency in animals living underground where sight is of little use. The external ear pinnae are absent (though there are small ear openings covered by dense fur), the external tail is lost, and the body has a streamlined shape to facilitate movement through the dense substratum.

Despite these superficial anatomical similarities to other fossorial small mammals, golden moles show many highly-specialized mammalian characters including: a unique hyoid-dentary articulation (Bronner et al. 1990); extremely hypertrophied malleus bones in the middle ear of some species that permit great sensitivity to both underground vibrations and airborne sounds (Mason & Narins 2001, Willi et al. 2005a,b); a third bone in the forearm (possibly an ossified tendon); a reduction in the number of phalanges in the fore- and hindfeet; and muscle arrangements not paralleled in the Mammalia (MacPhee & Novacek 1993). Most of the anatomical specializations shown by extant species are also found in 3 fossil species dating back as far as the Miocene (Broom 1941; Butler and Hopwood 1957; de Graaff 1957), and are so numerous and unusual that chrysochlorids have been described as "spectacularly autapomorphic" (MacPhee & Novacek 1993:26).

Physiology

Van Zyl’s Golden mole Cryptochloris zyli

Photo by Jennifer Jarvis

One of the reasons for the evolutionary success of golden moles may be their unique physiology. Despite a high thermal conductance, they have a low basal metabolic rate and are moderate (Chrysochloris asiatica, Amblysomus hottentotus) to extreme (Eremitalpa granti) thermoconformers (Bennett & Spinks, 1995; Seymour et al. 1998), thereby considerably reducing their thermoregulatory energy requirements. All species enter torpor, either daily or in response to cold temperatures. Body temperature in the thermal neutral zone is lower than in other similarly-sized mammals. The low metabolic rate of the Cape golden mole is achieved by lowering the body temperature, whereas in Grant’s golden mole it is also the result of intrinsic metabolic depression. Lowered metabolism and efficient renal function effectively reduce water requirements to the extent that most species do not need to drink. Far from being “primitive” characteristics, as was originally proposed by Withers (1978), such physiological specializations allow these moles to survive in habitats where temperatures are extreme and food is scarce, either seasonally or perennially.

Ecology

Like most other subterranean mammals, most golden mole species are restricted to a narrow range of habitats and environmental conditions, have very limited mobility and dispersal abilities, and specialized K-selected life history strategies. All species are opportunistic insectivores that feed primarily on earthworms, termites and/or millipedes, although their diets may vary in relation to the abundance of other prey items in specific habitats. Most are solitary and subterrestrial, and construct semi-permanent tunnel systems comprising two tiers: an upper level of subsurface burrows used for foraging and a lower level with chambers and inter- connecting tunnels used for resting and raising young. An exception to this pattern is found in the "Shark of the Dunes" - the small Namib golden mole (Eremitalpa granti namibensis) - which does not construct a permanent tunnel system but "swims" through the desert sands in search of the nests of subterranean termites (its favourite prey), often emerging onto the surface (Fielden et al. 1990). The giant golden mole (Chrysospalax trevelyani) is also a surface forager in the leaf litter of indigenous forests (Maddock 1986), whereas the closely related rough-haired golden mole (Chrysospalax villosus) often emerges to forage on the surface in dense grasslands after rains.

Populations of golden moles are often restricted to patches of suitable habitat with friable soils and abundant invertebrate prey, so that the distribution of demes is clumped, even within the more widespread taxa. Consequently, different species seldom coexist and compete for resources, even though their distribution may be broadly sympatric. If two species occur in the same area they tend to occupy different microhabitats, probably as a result of ecological displacement. Thus, for example, the Fynbos golden mole (A. corriae) and Cape golden mole (C. asiatica) occur together at Stellenbosch, but they inhabit different soil types. At Wakkerstroom, the Highveld golden mole (Amblysomus septentrionalis) is found only in grasslands and around marshes, whereas Sclater’s golden mole (Chlorotalpa sclateri) is restricted to scrub associated with montane cliffs and gorges (Roberts 1951).

The very limited reproductive data available (for only a few species) suggest that golden moles breed throughout the year, perhaps with a peak in the wetter months when prey is more abundant, and may be polyoestrous (Bernard et al. 1994; Schoeman et al. 2004). Litter sizes are small (usually 2) and post-natal development is extended, reaching up to 45 days in the Cape golden mole.

Behavior

The behavior of golden moles has not been studied in any detail, though it is known that most species are territorial and fight viciously if confined together. The only species whose behaviors have been documented is the Hottentot golden mole, in which adults are solitary and fight aggressively with individuals of either sex by wrestling their opponent using the foreclaws, and biting at the abdomen. Fighting is often accompanied by high-pitched squeaks. Individuals actively defend their burrow systems. Some amount of home range overlap is tolerated, and dominant moles sometimes take over neighbouring burrow systems to increase their home range. Courtship involves chirruping vocalizations, head-bobbing and foot stamping by the male, and rasping and squealing vocalizations by the female (Kuyper 1985).

The giant golden mole is the only species showing any indication of sociality (Hickman 1990), based on an unconfirmed report of several adult individuals dug out of the same nest in midwinter, which suggests that small groups may hibernate together. Duncan & Wrangham (1971) reported that burrow systems of Stuhlmann’s golden mole are used by more than one individual, since two golden-moles were caught in one trap in a burrow that showed signs of renewed use a week later. These two individuals, however, may have been a mother and her near-adult youngster, or the later capture could reflect colonization of the vacant burrow system by another individual.

Husbandry

Namib golden moles have been successfully kept in captivity (Fielden et al. 1990). Gary Bronner has kept individuals of several species (Neamblysomus julianae, Amblysomus hottentotus, Chrysochloris asiatica) successfully in captivity for periods ranging from a few weeks to nearly 2 years. Individuals should be housed separately in containers (the size of which depends on the species concerned, but should always allow the construction of at least 1m of burrows) with rich soil or sand changed weekly. They should be fed daily on a mixed diet of insects (e.g. mealworms, crickets, cockroaches) and earthworms, supplemented with diced lamb kidney, and provided with water ad libitum. (Most species probably do not drink in the wild, but require water in captivity). Some species will consume pinky mice with considerable enthusiasm, and giant golden moles will also take frozen day-old chicks.

When maintaining golden moles in captivity, room temperature is acceptable in moderate climates, but it is advisable to keep them in a temperature-controlled room if daily room temperatures drop below 15C or rise above 30C. As a general rule of thumb, a temperature of 15-25C is recommended; this range does not disrupt their endogenous daily torpor rhythms, and this torpor considerably reduces the amount of food they consume. Moles in torpor should not be handled excessively, as this awakens them, and seems to result in considerable stress, in extreme cases leading to the cessation of eating and physiological decline of the individual.

Conservation

Most of the species listed in threatened categories have restricted or fragmented distributions where populations are being subjected to increasing habitat degradation as a result of human activities, most notably mining, urbanization, agriculture and the poor management of indigenous forests.

Three species (Congo golden mole, Calcochloris leucorhinus; Somali golden mole, Calcochloris tytonis; Visagie’s golden mole, Chrysochloris visagiei) are listed as Data Deficient as so little is known about these species that their conservation status cannot be objectively assessed.

The 2006 IUCN Red List of Threatened Species includes 10 golden mole species, all from southern Africa, in threatened categories, as follows:

Critically Endangered De Winton’s golden mole (Cryptochloris wintoni) Endangered Marley’s golden mole (Amblysomus marleyi)

Giant golden mole (Chrysospalax trevelyani)

Van Zyl’s golden mole (Cryptochloris zyli)

Gunning’s golden mole (Neamblysomus gunningi)

Juliana’s golden mole (Neamblysomus julianae), although the topotypical population of Juliana’s golden mole is critically endangered Vulnerable Robust golden mole (Amblysomus robustus)

Arend’s golden mole (Carpitalpa arendsi)

Duthie’s golden mole (Chlorotalpa duthieae)

Rough-haired golden mole (Chrysospalax villosus) Near Threatened Grant’s golden mole (Eremitalpa granti)

Fynbos golden mole (Amblysomus corriae)

Highveld golden mole (Amblysomus septentrionalis)

Web Links

http://zoology.up.ac.za/samammals/ Detailed distribution maps for South African species of golden moles

http://afrotheria.net IUCN-SSC Afrotheria Specialist Group home page - portal for information on other representatives of the Afrotheria, including hyraxes, aardvark, tenrecs, and sengis

http://www.arkive.org/species/GES/mammals/Neamblysomus_julianae/ ARKive, images of Endangered Juliana’s golden mole

Animal Diversity Web Additional information on golden mole species

Digimorph Digiital morphology account of the golden mole skeleton (genus chrysochloris)

Literature Cited

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Bennett, N. C. & Spinks, A. C. 1995. Thermoregulation and metabolism in the Cape golden mole (Insectivora: Chrysochloris asiatica). Journal of Zoology, London 236: 521-529.

Bronner, G.N. 1995a. Cytogenetic properties of nine species of golden moles (Insectivora: Chrysochloridae). Journal of Mammalogy 76: 957-971.

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Bronner, G.N. 2000. New species and subspecies of golden mole (Chrysochloridae: Amblysomus) from Mpumalanga, South Africa. Mammalia 64: 41-54.

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Bronner, G.N., Hoffman, M., Taylor, P.J., Chimimba, C.T., Best, P.B., Mathee C.A., & Robinson T.J. 2003. A revised systematic checklist of the extant mammals of the southern African subregion. Durban Museum Novitates 28: 56-106.

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