288
Yoshinari Tanaka
lation should take into account the extinction risk aggravated by inbreeding
depression.
Conclusions
Throughout the conservation genetics literature, it is frequently stated that inbreeding depression may induce rapid extinction due to positive feedback between inbreeding depression and reduction of population size (i.e., an extinction
vortex by inbreeding depression). This chapter has demonstrated that an extinction vortex is likely to occur with realistic parameter values of the genomic
mutation rate of lethals or semilethals, the equilibrium population size, the intrinsic rate of natural increase, and the rate of population decline due to nongenetic
extrinsic factors. The magnitude of the equilibrium population size, the intrinsic
rate of natural increase, and the rate of population decline are especially important
in determining whether a population becomes extinct by inbreeding depression.
Simulation models incorporating stochastic fluctuations of population size further indicated that extinction by inbreeding depression is facilitated by environmental fluctuations of population size. The results suggest that there is a positive
interaction between genetic and environmental stochasticity that can lead to population extinction by inbreeding depression.
Acknowledgments. I thank Yasushi Harada and Yoh Iwasa for helpful discussions
on the topic. I am grateful to the editors, who provided me with the opportunity to
contribute to this volume. This work is supported in part by CREST (Core Research for Evolutional Science and Technology) of the Japan Science and Technology Corporation (JST), for which the principal investigator is J. Nakanishi.
Literature Cited
Avise JC, Hamrick JL (1996) Conservation genetics: case histories from nature. Chapman
and Hall, New York
Barrett SCH, Charlesworth D (1991) Effects of a change in the level of inbreeding on the
genetic load. Nature 352:522–524
Burgman MA, Ferson S, Ak¸ cakaya HR (1993) Risk assessment in conservation biology.
Chapman and Hall, New York
Britten HB (1996) Meta-analyses of the association between multilocus heterozygosity and
fitness. Evolution 50:2158–2164
Caughley G, Gunn A (1996) Conservation biology in theory and practice. Blackwell
Science, MA
Crow JF, Kimura M (1970) An introduction to population genetics theory. Harper and Row,
New York
Crow JF, Simmons MJ (1983) The mutation load in Drosophila. In: Ashburner M, Carson
HL, Thompson JN Jr (eds) The genetics and biology of Drosophila, vol 3C. Academic
Press, New York, pp 1–35
Yoshinari Tanaka
lation should take into account the extinction risk aggravated by inbreeding
depression.
Conclusions
Throughout the conservation genetics literature, it is frequently stated that inbreeding depression may induce rapid extinction due to positive feedback between inbreeding depression and reduction of population size (i.e., an extinction
vortex by inbreeding depression). This chapter has demonstrated that an extinction vortex is likely to occur with realistic parameter values of the genomic
mutation rate of lethals or semilethals, the equilibrium population size, the intrinsic rate of natural increase, and the rate of population decline due to nongenetic
extrinsic factors. The magnitude of the equilibrium population size, the intrinsic
rate of natural increase, and the rate of population decline are especially important
in determining whether a population becomes extinct by inbreeding depression.
Simulation models incorporating stochastic fluctuations of population size further indicated that extinction by inbreeding depression is facilitated by environmental fluctuations of population size. The results suggest that there is a positive
interaction between genetic and environmental stochasticity that can lead to population extinction by inbreeding depression.
Acknowledgments. I thank Yasushi Harada and Yoh Iwasa for helpful discussions
on the topic. I am grateful to the editors, who provided me with the opportunity to
contribute to this volume. This work is supported in part by CREST (Core Research for Evolutional Science and Technology) of the Japan Science and Technology Corporation (JST), for which the principal investigator is J. Nakanishi.
Literature Cited
Avise JC, Hamrick JL (1996) Conservation genetics: case histories from nature. Chapman
and Hall, New York
Barrett SCH, Charlesworth D (1991) Effects of a change in the level of inbreeding on the
genetic load. Nature 352:522–524
Burgman MA, Ferson S, Ak¸ cakaya HR (1993) Risk assessment in conservation biology.
Chapman and Hall, New York
Britten HB (1996) Meta-analyses of the association between multilocus heterozygosity and
fitness. Evolution 50:2158–2164
Caughley G, Gunn A (1996) Conservation biology in theory and practice. Blackwell
Science, MA
Crow JF, Kimura M (1970) An introduction to population genetics theory. Harper and Row,
New York
Crow JF, Simmons MJ (1983) The mutation load in Drosophila. In: Ashburner M, Carson
HL, Thompson JN Jr (eds) The genetics and biology of Drosophila, vol 3C. Academic
Press, New York, pp 1–35