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Abstract
The incidence of tusklessness varies between free-ranging African elephant populations. Sex-linked genetic drift predicts 2 outcomes--the condition becomes fixed and sex-specific incidences diverge when populations are small and/or heavily poached. By contrast, for large and intact populations, tusklessness diminishes and there is no variation between sexes. We tested these predictions by comparing sex-specific incidences between 15 populations: a small one with a skewed founder effect towards tusklessness; 5 that had experienced intense levels of poaching; 2 that had been subjected to non-selective culling and 7 that are relatively pristine. Patterns of rainfall were studied of tusk fractures amongst these populations to correct for any effect that acquired tusklessness may have on our predictions. The incidence of tusk fractures was related to annual rainfall, but the mechanism that leads to an increase of the condition in drier areas was not clear Incidences of tusk fractures in free-ranging populations implied that the frequency of acquired bilateral tusklessness is low and should not affect our results. All males had tusks. Tusklessness in females was high in the small skewed founder population and some of those where there was a history of poaching. The incidence is expected to decline if the residual population is large.
Highlights
Tusklessness is common in some African elephant (Loxodonta africana) populations
Elephants that are bilaterally tuskless may act as an early warning sign of genetic drift in a population[24]
It was assumed that rainfall might serve as an index to some important variable such as nutrient levels of vegetation or as a crude estimate of humidity, that conceivably affect the incidence of tusk fractures
Summary
Tusklessness is common in some African elephant (Loxodonta africana) populations.The condition can be inherited (usually bilateral) or acquired (usually unilateral)[20].Incidences vary between populations[1,8,20], and over time, within populations[4,13]. Tusklessness is common in some African elephant (Loxodonta africana) populations. The condition can be inherited (usually bilateral) or acquired (usually unilateral)[20]. Incidences vary between populations[1,8,20], and over time, within populations[4,13]. Elephants that are bilaterally tuskless may act as an early warning sign of genetic drift in a population[24]. Tusklessness increases in heavily poached populations[8]. Tusklessness appears to be sex-linked to females[13,20,24]
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