Blackwell Publishing Ltd Effective population size dynamics reveal impacts of historic climatic events and recent anthropogenic pressure in African elephants

Submitted by Archiver on Mon, 15/10/2018 - 16:44
Abstract

Two hundred years of elephant hunting for ivory, peaking in 1970–1980s, caused local
extirpations and massive population declines across Africa. The resulting genetic impacts
on surviving populations have not been studied, despite the importance of understanding
the evolutionary repercussions of such human-mediated events on this keystone species.
Using Bayesian coalescent-based genetic methods to evaluate time-specific changes in
effective population size, we analysed genetic variation in 20 highly polymorphic microsatellite
loci from 400 elephants inhabiting the greater Samburu-Laikipia region of northern Kenya.
This area experienced a decline of between 80% and 90% in the last few decades when ivory
harvesting was rampant. The most significant change in effective population size, however,
occurred approximately 2500 years ago during a mid–Holocene period of climatic drying in
tropical Africa. Contrary to expectations, detailed analyses of four contemporary age-based
cohorts showed that the peak poaching epidemic in the 1970s caused detectable temporary
genetic impacts, with genetic diversity rebounding as juveniles surviving the poaching era
became reproductively mature. This study demonstrates the importance of climatic history
in shaping the distribution and genetic history of a keystone species and highlights the utility
of coalescent-based demographic approaches in unravelling ancestral demographic events
despite a lack of ancient samples. Unique insights into the genetic signature of mid-Holocene
climatic change in Africa and effects of recent poaching pressure on elephants are discussed.

Author

J . B. A. OKELLO,*† G. WITTEMYER,*‡§ H. B. RASMUSSEN,‡¶** P. ARCTANDER,** S. NYAKAANA,* I .
DOUGLAS-HAMILTON‡ and H. R. SIEGISMUND**

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