The ear in subterranean insectivora and rodentia in comparison with ground-dwelling representatives. I. Sound conducting system of the middle ear.

Compared to acoustically unspecialized mammals (soricids and murids), the middle ear of subterranean insectivores and rodents (twelve species of six families examined) was clearly distinguished and characterized by many common features: rather round and relatively larger eardrum without a pars flaccida; reduced gonial; loose or no connection between the malleus and the tympanic bone; reduced and straightened transversal part of the malleus; enlarged incus; increased and rather flat incudo-mallear joint; rather parallel position of the mallear manubrium and incudal crus longum in some species (and their fusion in bathyergids); reduced or even missing middle ear muscles. Convergent occurrence of these structural features in taxa of different origin and their generally derived character suggest that they cannot be categorized as degenerative. The form of the stapes can be considered as a non-adaptive trait; it was taxon specific yet remarkably polymorphous in some species and exhibited no convergent features among subterranean mammals. Structural retrogression resulting in a columella-like stapes was observed in some species lacking the stapedial artery. The stapedial base was relatively larger than in unspecialized mammals. The subterranean mammals did not exhibit conspicuously enlarged eardrums as would be required for sensitive tuning to low frequencies. It is, however, argued that while selective pressures in the subterranean ecotope promoted hearing of low frequencies, hearing sensitivity did not have to be enhanced.

Adaptiveness of tunnel system features in subterranean mammal burrows.

Most moles and mole rats spend their lifetimes within the confines of tunnel walls, constructing, maintaining, and modifying burrow system structure in response to changing external circumstances and changing internal needs. Thus, anatomy, physiology, behavior, and distribution are all greatly affected by the burrow environment, with temperature, humidity, gas concentrations, living space, availability of food and mating partners, and protection from flooding and predation all being influenced by burrow architecture. Regrettably, the burrow structure of almost all subterranean mammals is unknown, or known only from several incomplete excavations. Moreover, existing data is often vague without any mention of particular structures or surrounding habitat, which makes the placing of burrow structure in an adaptive perspective difficult. Reasons for these short-comings are understandable: excavations require laborious excavation which can extend for hundreds of meters, reaching depths in excess of a meter; it is often difficult to remove the occupant prior to excavation which avoids modification of the system by the animal during excavation; particular types of subterranean mammals are limited in distribution to particular continents so that the literature is often localized and a global perspective difficult to obtain; and there is no standardization of terms relating to burrow structure, making intergroup comparison confusing. This paper addresses the above difficulties and encourages further investigation in this central area of study by making obvious the paucity of information for most subterranean mammals, presenting a synopsis of known burrow structures of major groups which will make particular gaps in our knowledge evident, providing a bibliography of major papers on burrow structure with coverage of most moles and mole rats, establishing a checklist of burrow features to better analyze future excavations and facilitate intergroup comparison, and lastly, to indicate possible adaptive significance of various burrow features to promote further observation, speculation and experimentation.

The Chrysochloridae: studies toward a broader perspective of adaptation in subterranean mammals.

Earliest chrysochlorids (from the Miocene) resemble contemporary members of the family. Unlike talpids, chrysochlorids have eyes covered with skin; pick-like foreclaws; a blunt, padded rostrum; and no external tail. Golden moles are an ancient lineage of mammals (related to tenrecs) with many unique features; it has been suggested that the Chrysochloridae constitute a separate order, the Chrysochloridea. In contrast, a constancy of structure within the group belies the wide range in habitat of the various species (including grassland, forest, and shifting desert sands), in contrast to the aquatic desmans and shrew-like talpids. Some species of golden mole are able to disperse over large distances, being accomplished swimmers (as are talpids) and having a wide range of diet; nonetheless, populations and species are patchily distributed throughout the range of the family (Africa south of the Sahara whereas talpids occur in the northern hemisphere). Diversity of chrysochlorid species is greatest in Southern Africa, from which emigrations to the north probably occurred. Although solitary, there is little evidence for competitive exclusion between the chrysochlorids, rhizomyids, or the more social and aggressive bathyergid rodent moles to explain the high incidence of endemism. Low litter sizes are indicative of the few predators known to effectively prey on golden moles. Physical factors which might restrict species from an area (such as food shortages and temperature extremes) may be overcome by becoming torpid, an ability unknown for other subterranean mammals. Clustering of largely immobile food resources and friable soils appear to be the major factors influencing chrysochlorid distribution. There is substantial need for basic studies on all aspects of the biology of chrysochlorids for a better understanding of evolutionary processes within the family, which will in turn contribute to a broader understanding and more balanced view of evolutionary processes in all subterranean mammals.

Water metabolism in the Namib Desert golden mole, Eremitalpa granti namibensis (Chrysochloridae).

1. Laboratory and field studies of energy and water metabolism employing isotopic dilution methods examined the ability of Namib Desert moles to survive on an insect diet without drinking water. 2. Water independence is achieved through efficient renal function while low rates of energy usage and torpor are further effective in reducing overall water requirements.