TY - JOUR
T1 - Conditions for protection of an allele in linear homogeneous stepping stone models
AU - Walsh, James Bruce
N1 - Funding Information:
I thank Monty Slatkin and Tom Nagylaki for providing comments and discussion which greatly improved the manuscript. I especially thank Joe Felsenstein for help throughout this project, especially for subtle prodding at critical stages which helped me to sail through a seemly endless sea of algebra relatively intact. This research was supported in part by a National Science Foundation predoctoral fellowship and in part by test agreement DE-AT06-76EV71005 of contract DE-AM06-76-RL02225 between the U.S. Department of Energy and the University of Washington.
PY - 1983/8
Y1 - 1983/8
N2 - The one-dimensional linear homogeneous stepping stone migration structure is an important model in that it represents a short-range migration extreme for geographically structured populations and also serves as the underlying discretespace model for much of the work on continuous-space clines. We examine conditions for the protection of an allele under a stepping stone migration structure by using a recursive method based on Sturm sequences. Necessary and sufficient conditions for protection of an allele are found for a generalized step-cline selection gradient, which is the selection scheme used in much of the early cline work. Sufficient conditions for the protection of an allele are also found for (i) an advantageous patch at the stepping stone boundary which is followed by an arbitrary selection gradient, and for (ii) an advantageous patch embedded within an otherwise arbitrary selection gradient. We let m be the migration rate between neighboring demes. If within the advantageous patch WAa Waa = 1 + s, then for (i) s ≥ m (1 - m) is sufficient to protect allele A, even if the patch consists of only a single deme, while for (ii) s ≥ 2m (1 - 2m) guarantees that a single deme will protect A. If the advantageous patch consists of k demes, each with WAa Waa = 1 + s, then s ≥ ( π2 4) m k2 is sufficient for protection of A in (i), while s ≥ π2m k2 is sufficient for protection of A in (ii). Sufficient conditions for a protected polymorphism are found, and a bound on the level of migration is determined, below which a protected polymorphism exists, as predicted from Karlin and McGregor's (1972. Theor. Pop. Biol. 3, 186-209, 210-238) small parameter results. Finally, our patch swamping conditions (protection of an allele given a single advantageous patch) are compared to Nagylaki's (1975. Genetics 80, 595-615) conditions for the existence of continuous-space clines under analogous selection schemes and are shown to be identical for the two specific cases examined. We also discuss extensions of some of the above results to circular stepping stone migration structures.
AB - The one-dimensional linear homogeneous stepping stone migration structure is an important model in that it represents a short-range migration extreme for geographically structured populations and also serves as the underlying discretespace model for much of the work on continuous-space clines. We examine conditions for the protection of an allele under a stepping stone migration structure by using a recursive method based on Sturm sequences. Necessary and sufficient conditions for protection of an allele are found for a generalized step-cline selection gradient, which is the selection scheme used in much of the early cline work. Sufficient conditions for the protection of an allele are also found for (i) an advantageous patch at the stepping stone boundary which is followed by an arbitrary selection gradient, and for (ii) an advantageous patch embedded within an otherwise arbitrary selection gradient. We let m be the migration rate between neighboring demes. If within the advantageous patch WAa Waa = 1 + s, then for (i) s ≥ m (1 - m) is sufficient to protect allele A, even if the patch consists of only a single deme, while for (ii) s ≥ 2m (1 - 2m) guarantees that a single deme will protect A. If the advantageous patch consists of k demes, each with WAa Waa = 1 + s, then s ≥ ( π2 4) m k2 is sufficient for protection of A in (i), while s ≥ π2m k2 is sufficient for protection of A in (ii). Sufficient conditions for a protected polymorphism are found, and a bound on the level of migration is determined, below which a protected polymorphism exists, as predicted from Karlin and McGregor's (1972. Theor. Pop. Biol. 3, 186-209, 210-238) small parameter results. Finally, our patch swamping conditions (protection of an allele given a single advantageous patch) are compared to Nagylaki's (1975. Genetics 80, 595-615) conditions for the existence of continuous-space clines under analogous selection schemes and are shown to be identical for the two specific cases examined. We also discuss extensions of some of the above results to circular stepping stone migration structures.
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U2 - 10.1016/0040-5809(83)90047-3
DO - 10.1016/0040-5809(83)90047-3
M3 - Article
AN - SCOPUS:49049126988
SN - 0040-5809
VL - 24
SP - 78
EP - 106
JO - Theoretical Population Biology
JF - Theoretical Population Biology
IS - 1
ER -