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The Bathyergidae
The family Bathyergidae (derived from the Greek bathys meaning deep and ergo to work) comprises subterranean hystricomorph rodents that are endemic to the continent of Africa. The family shows a wide spectrum of social structure ranging from strictly solitary species such as those belonging to the genera Bathyergus, Heliophobius and Georychus through to social and truly social species in the genera Cryptomys, Fukomys and Heterocephalus (Jarvis and Bennett, 1990; 1991).
The bathyergids occupy a range of habitat types from mesic through to arid environments (Jarvis & Bennett, 1990). However, a common underlying prerequisite for their occurrence is the presence of the underground storage organs of geophytes, for which there is a propensity in Africa (Jarvis & Bennett, 1991; Faulkes et al., 2004). In mesic regions the soil is workable for much of the year and thus there is essentially no necessity for mole-rats to be social, however, in more arid regions the rainfall is sporadic and unpredictable and in such instances there are few opportunities available to successfully burrow towards the food resources. These brief windows of opportunity require a number of mole-rats to excavate and tunnel to locate and harvest sufficient food resources.
Indeed, sociality in the African mole-rats has been hypothesized to have evolved in response to patterns of rainfall, the subsequent effects on food distribution and size and the consequent costs and risks of foraging (Jarvis et al., 1994; Faulkes et al., 1997; Bennett & Faulkes, 2000; Burda et al., 2000).
The Aridity Food Distribution Hypothesis (AFDH) has been put forward in an attempt to explain how sociality in African mole-rats may have evolved among some mole-rat species but not in others. The premise is that cooperative behaviour arose in some mole-rat species where the energetic costs of burrowing increase as the rainfall pattern becomes more unpredictable and the available food resource more clumped (Jarvis et al., 1994). Although Burda et al., (2000) argued against a causal relationship between cooperative foraging for food resources and the evolution of sociality in mole-rats [see Faulkes & Bennett (2007)] and O’Riain & Faulkes, (in press) for further commentary and debate), the AFDH has support from a number of empirical studies including long term field studies and associated molecular studies (Faulkes et al., 1997; Jarvis et al., 1998; Burland et al., 2002, Hess, 2004).
Sociality in mole-rats
The solitary species of southern and eastern African mole-rats (Georychus and Bathyergus, Heliophobius) generally inhabit environments that exhibit a marked seasonality or higher rainfall pattern (Jarvis & Bennett, 1990, 1991; Bennett & Faulkes, 2000; Šumbera et al., 2003a). A number of species of mole-rat that exhibit some degree of social behaviour may also occur in these mesic environments, but also in drier areas (Spinks et al., 1999; Janse van Rensburg et al., 2002). The truly social mole-rats occur in semi-arid and arid regions where rainfall is sporadic and unpredictable and hence the times available for successful foraging are restricted and a large workforce is required to sufficiently excavate the tunnel system to locate these patchily distributed food resources.
The species belonging to the genus Cryptomys (restricted to southern Africa) are generally composed of small family groups that incorporate up to three successive litters (Bennett, 1989). Colonies are usually around 8-10 animals and are transient in nature, with animals exhibiting regular periods of dispersal from the natal colony Spinks, (1998). The use of microsatellite libraries have revealed that multiple paternity of litters and extra-pair copulations are common in these environments where ecological constraints are not great Bishop et al., (2004). In the more highly social mole-rat species Fukomys damarensis, colonies have been found to number up to 40 animals but are usually around 12 -14, with reproduction restricted to small cohorts of breeding animals that constitute a single reproductive female and a small group of reproduc
Table of Contents
- Abstract
- Preface
- LIST OF FIGURES
- LIST OF TABLE
- Plate
Chapter 1-General Introduction
– Bathyergidae
– Sociality in mole-rats
– Burrow structure
– Burrow fractal dimensions
– Colony size
– Colony composition
– Reproductive strategies in mole-rats
– Patterns of ovulation in the Bathyergidae
– The giant mole-rat Fukomys mechowii
– Aims of study
Chapter 2-Materials and methods
– Study site
– Study animal
– Burrow architecture
– Burrow fractal dimensions
– Aseasonality
– Sexual dimorphism
– Ovulation methods
– Experimental design
– Creatinine determination
– Progesterone determination
– Electrone micrograph
– Statistical analysis
– Ethical note
Chapter 3-Burrow architecture, rainfall and foraging in colonies of the giant mole-rat Fukomys mechowii
– Abstract
– Introduction
– Materials and methods
– Results
– Discussion
Chapter 4-Craniometrics, sexual dimorphism and age variation of the giant mole-rat Fukomys mechowii
– Abstract
– Introduction
– Materials and methods
– Results
– Discussion
Chapter 5-Field evidence for aseasonality of reproduction and colony size in giant mole-rats Fukomys mechowii
– Abstract
– Introduction
– Materials and methods
– Results
– Discussion
Chapter 6-Ovulation pattern of the female giant mole-rats Fukomys mechowii Removed from the confines of the natal colony
– Abstract
– Introduction
– Materials and methods
– Results
– Discussion
Chapter 7-Synthesi
– List of references
