African Mole-rats. Ecology and Eusociality

Bennett & Faulkes provide an overview of the ecology and social structures of African mole-rats of the family Bathyergidae written in a readable style, and supplemented with many helpful illustrations, accessible to nonprofessional readers and scholars of the African molerats alike. The family Bathyergidae, with its five genera and many species of subterranean rodents endemic to sub-Saharan Africa, provides a fascinating evolutionary model for studying adaptation and speciation processes in nature. The range of social structures (from solitary to eusocial) that characterizes species of this taxon (including the naked mole-rat, Heterocephalus glaber, with its social structure reminiscent of social insects, such as bees and termites), offers a rare opportunity to study the evolution of sociality in Bathyergid rodents and mammals in general. This is the first book devoted to a description of the whole Bathyergidae family, following previous chapters by Jarvis & Bennett (1990, 1991). The first seven chapters survey the natural history and general biology of African mole-rats. Chapter 1 introduces the species that constitute the Bathyergid mole-rats and their systematics and distribution. This chapter is interesting and clear in describing the solitary species and the naked mole-rat but becomes more obtuse in the description of Cryptomys, when in some cases the divisions of species, subspecies and populations seem arbitrary and anecdotal and not supported by tests necessary for valid taxonomy. The second and third chapters describe life in the underground niche, which demands adaptations for burrowing through soil as well as physiological and behavioural adjustments to living in subterranean tunnels. The subchapter dealing with sensory adaptations is somewhat deficient. It would have been preferable to describe material on hearing and magnetic compass orientation (studied in Cryptomys) or to refer to the vast literature on senses and communication from studies of other subterranean rodents. Chapter 3 explores mole-rats’ foraging strategies, the nutritional value of their food sources, and the coevolution between mole-rats and the geophytes on which they feed. Special emphasis is given to the constraints of foraging in the subterranean niche, particularly the energetic cost of burrowing and the risks of unsuccessful foraging. Subsequent chapters describe various aspects of sociality, including types of social organization, reproductive strategies, physiological and behavioural means of reproductive suppression, and the genetic structure of populations. This background is a prelude to the main topic of the book, the evolution of sociality in Bathyergidae, in the context of the authors’ attempt to explain and promote a theory that connects the origin of sociality and cooperative breeding with increasing aridity, small body size, large and widely spaced food resources (geophytes), and high risks in solitary foraging and dispersal. The strengths of this hypothesis are presented in detail while its problematic aspects are minimized. For example, the authors claim that individuals in solitary species are generally larger and in social species generally smaller, which is only true for the largest (Bathyergus suillus) and the smallest (H. glaber), because it is clear from Figure 1.13 that other bigger species, for example, Cryptomys mechowi, C. damarensis and C. bocagei, are social and that the solitary Heliophobius, Georychus and Bathyergus janetta are among the smallest. At the same time, the authors trivialize the plausible alternative hypothesis of Burda (1990, see also Burda & Kawalika 1993). In addition, their categorization into eusocial (H. glaber and C. damarensis) and social (all other Crytomys) is puzzling as C. mechowi and C. hottentotus clearly fulfill the criteria of eusociality. Despite its many assets, the book has some shortcomings. Given the preface, the reader expects a synthesis of the current knowledge of Bathyergidae, but this is not fully achieved. Bennett & Faulkes tend to focus on their own work and describe studies with which they were involved, diminishing other investigators’ important work. By neglecting this part of the literature, their conclusions sometimes leave the less experienced reader with erroneous impressions. It would have been beneficial had they included more of the vast recent literature on systematics, ecology, senses, reproduction, etc., in Bathyergidae. Some ideas that contradict their own are omitted or misrepresented, including ideas about reproduction, systematics and taxonomy of Zambian Cryptomys. Finally, a discussion of aspects of convergence and divergence of the African mole-rats in comparison with those of various other intensively studied groups of subterranean mammals distributed on other continents would have provided a fascinating opportunity to explore evolution and natural selection in action. There is little meaningful comparison of African mole-rats with other subterranean mammals, and some descriptions of other subterranean rodents are incorrect (e.g. on page 124 on aggression and page 126 on longevity of the blind molerat, Spalax ehrenbergi). In spite of such criticisms, which hopefully will be considered in future revised editions, the book is important, fascinating and enjoyable. Bennett & Faulkes succeed in providing an attractive foundation that elicits the desire for a more extensive acquaintance with this unique group of African mole-rats and for deeper elucidation of questions concerning the evolution of sociality in mammals. This book, together with Nevo’s (1999) monumental tome, contributes to the burgeoning interest in subterranean mammals as an exceptional research model of organic evolution and thereby promotes the continuation of prolific and dynamic research on this group. GIORA HETH & JOSEPHINE TODRANK Institute of Evolution, University of Haifa, Haifa 31905, Israel