Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 7-Day Trial for You or Your Team.

Learn More →

THE ROLE OF DEME SIZE, REPRODUCTIVE PATTERNS, AND DISPERSAL IN THE DYNAMICS OF t‐LETHAL HAPLOTYPES

THE ROLE OF DEME SIZE, REPRODUCTIVE PATTERNS, AND DISPERSAL IN THE DYNAMICS OF t‐LETHAL HAPLOTYPES The t‐lethal haplotypes (t) found in house mouse (Mus musculus) populations are recessive lethals favored by gametic selection whereby male heterozygotes exhibit a non‐Mendelian transmission ratio of about 95% t. The expected equilibrium frequency is 0.385; however, empirical values are lower, averaging close to 0.13. We examined the hypothesis that interdemic selection is the cause of the low empirical values by using a deme‐structured simulation model that included overlapping generations, a realistic breeding system, differential deme productivity, and a large total population. We found that under some conditions interdemic selection could lower t frequency below 0.13 in the face of immigration rates up to 5%. Low frequencies were correlated with effective deme size (ne), regardless of whether ne was changed through changing deme size (n) or through changing the proportion of breeding adults. Earlier workers showed how the first two phases of interdemic selection (random genetic differentiation and mass selection) interacted to reduce the haplotype frequency, but here we show the importance of the third phase (differential productivity of demes) once demes are linked by dispersal. The effect of this phase is not due to the (negative) covariation between deme productivity and haplotype frequency, but occurs when differential deme productivity generates a difference in t frequency between the population of juveniles recruited into their natal deme and the population of juvenile dispersers. This difference was maximized when the average productivity of demes was low, either because few adult females bred at any one time and/or because fecundity was low. Contrary to an earlier prediction, male‐biased dispersal also reduced haplotype frequency, and this probably stems from the relative excess of wild‐type genotypes among dispersers compared to the deme residents. Another unexpected finding was that the randomly generated excess of heterozygotes (FIS < 0) found in small demes favored t haplotypes; however, the effect was only seen when the more powerful influence of the third phase of interdemic selection was removed. Simulations of neutral polymorphisms showed that a deme structure giving FST ≤ 0.6 is inconsistent with a haplotype frequency below 0.13. Based on current empirical estimates of FST (about 0.2), we concluded that immigration rates in the field are too high for interdemic selection alone to cause the observed deficit of lethal haplotypes. One factor that could combine with population structure effects is the observation that the transmission ratio is lowered to around 0.6 in litters produced from postpartum estrus (PPE). Incorporating this factor, we showed that interdemic selection could be effective in lowering the frequency of t below 0.13 when FST was above 0.43 even when migration rates were up to 10%. These results suggest that if empirical haplotype and FST estimates are accurate, then additional factors such as a lowered fitness of heterozygotes may be involved. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Evolution Oxford University Press

THE ROLE OF DEME SIZE, REPRODUCTIVE PATTERNS, AND DISPERSAL IN THE DYNAMICS OF t‐LETHAL HAPLOTYPES

Nunney, Leonard; Baker, Ann Eileen Miller
Evolution , Volume 47 (5) – Oct 1, 1993
Download PDF
18 pages

Loading next page...
 
/lp/oxford-university-press/the-role-of-deme-size-reproductive-patterns-and-dispersal-in-the-0GkAvMqlNu

References (82)

Publisher
Oxford University Press
Copyright
© Society for the Study of Evolution
ISSN
0014-3820
eISSN
1558-5646
DOI
10.1111/j.1558-5646.1993.tb02159.x
Publisher site
See Article on Publisher Site

Abstract

The t‐lethal haplotypes (t) found in house mouse (Mus musculus) populations are recessive lethals favored by gametic selection whereby male heterozygotes exhibit a non‐Mendelian transmission ratio of about 95% t. The expected equilibrium frequency is 0.385; however, empirical values are lower, averaging close to 0.13. We examined the hypothesis that interdemic selection is the cause of the low empirical values by using a deme‐structured simulation model that included overlapping generations, a realistic breeding system, differential deme productivity, and a large total population. We found that under some conditions interdemic selection could lower t frequency below 0.13 in the face of immigration rates up to 5%. Low frequencies were correlated with effective deme size (ne), regardless of whether ne was changed through changing deme size (n) or through changing the proportion of breeding adults. Earlier workers showed how the first two phases of interdemic selection (random genetic differentiation and mass selection) interacted to reduce the haplotype frequency, but here we show the importance of the third phase (differential productivity of demes) once demes are linked by dispersal. The effect of this phase is not due to the (negative) covariation between deme productivity and haplotype frequency, but occurs when differential deme productivity generates a difference in t frequency between the population of juveniles recruited into their natal deme and the population of juvenile dispersers. This difference was maximized when the average productivity of demes was low, either because few adult females bred at any one time and/or because fecundity was low. Contrary to an earlier prediction, male‐biased dispersal also reduced haplotype frequency, and this probably stems from the relative excess of wild‐type genotypes among dispersers compared to the deme residents. Another unexpected finding was that the randomly generated excess of heterozygotes (FIS < 0) found in small demes favored t haplotypes; however, the effect was only seen when the more powerful influence of the third phase of interdemic selection was removed. Simulations of neutral polymorphisms showed that a deme structure giving FST ≤ 0.6 is inconsistent with a haplotype frequency below 0.13. Based on current empirical estimates of FST (about 0.2), we concluded that immigration rates in the field are too high for interdemic selection alone to cause the observed deficit of lethal haplotypes. One factor that could combine with population structure effects is the observation that the transmission ratio is lowered to around 0.6 in litters produced from postpartum estrus (PPE). Incorporating this factor, we showed that interdemic selection could be effective in lowering the frequency of t below 0.13 when FST was above 0.43 even when migration rates were up to 10%. These results suggest that if empirical haplotype and FST estimates are accurate, then additional factors such as a lowered fitness of heterozygotes may be involved.

Journal

Evolution – Oxford University Press

Published: Oct 1, 1993

Keywords: ; ; ; ; ; ; ;

There are no references for this article.