Assessment of natural selection in a hybrid population of mussels: evaluation of exogenous vs endogenous selection models

Abstract A method for simultaneously estimating the admixture proportions of a hybrid population and Wright's fixation index, FST, for that hybrid is presented. It is shown that the variance of admixture estimates can be partitioned into two components: (1) due to sample size, and (2) due to evolutionary variance (i.e., genetic drift). A chi-square test used to detect heterogeneity of admixture estimates from different alleles, or loci, can now be corrected for both sources of random errors. Hence, its value for the detection of natural selection from heterogeneous admixture estimates is improved. The estimation and testing procedures described above are independent of the dynamics of the admixture process. However, when the admixture dynamics can be specified, FST can be predicted from genetic principles. Two admixture models are considered here, gene flow and intermixture. These models are of value because they lead to very different predictions regarding the accumulation of genes from the parental populations and the accumulation of variance due to genetic drift. When there is not evidence for natural selection, and it is appropriate to apply these models to data, the variance effective size (Ne) of the hybrid population can be estimated. Applications are made to three human populations: two of these are Afro-American populations and one is a Yanomamö Indian village. Natural selection could not be detected using the chi-square test in any of these populations. However, estimates of effective population sizes do lead to a richer description of the genetic structure of these populations.

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Sibling rivalry: Males with more brothers develop larger testes

10.1101/332775 ◽

2018 ◽

Author(s):

Heidi S. Fisher ◽

Kristin A. Hook ◽

W. David Weber ◽

Hopi E. Hoekstra

Keyword(s):

Natural Selection ◽

Perceived Risk ◽

Critical Factor ◽

Relative Number ◽

Hybrid Population ◽

Testis Size ◽

Sperm Production ◽

Multiple Partners ◽

In Captivity ◽

Generation Hybrid

ABSTRACTWhen females mate with multiple partners in a reproductive cycle, the relative number of competing sperm from rival males is often the most critical factor in determining paternity. Gamete production is directly related to testis size in most species, and is associated with both mating behavior within a system and perceived risk of competition. Peromyscus maniculatus is naturally promiscuous and males invest significantly more in sperm production than males of P. polionotus, their monogamous sister-species. Here we show that the relatively larger testes in P. maniculatus are retained, even after decades of enforced monogamy in captivity. While these results suggest that differences in sperm production between species with divergent evolutionary histories can be maintained, we also show that the early rearing environment of males can strongly influence their testis size as adults. Using a second-generation hybrid population to increase variation in testis size, we show that males reared in litters with more brothers develop larger testes as adults. Importantly, this difference in testis size is also associated with increased fertility. Together, our findings suggest that sperm production may be both broadly shaped by natural selection over evolutionary timescales and also finely tuned during early development.

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Adaptive divergence in shoot gravitropism creates hybrid sterility in an Australian wildflower

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2004901118 ◽

2021 ◽

Vol 118 (47) ◽

pp. e2004901118

Author(s):

Melanie J. Wilkinson ◽

Federico Roda ◽

Greg M. Walter ◽

Maddie E. James ◽

Rick Nipper ◽

...

Keyword(s):

New Species ◽

Natural Selection ◽

Hybrid Sterility ◽

Hybrid Population ◽

Adaptive Divergence ◽

Adaptive Traits ◽

Local Environments ◽

Locally Adaptive ◽

Evolutionary Connection ◽

Shoot Gravitropism

Natural selection is responsible for much of the diversity we see in nature. Just as it drives the evolution of new traits, it can also lead to new species. However, it is unclear whether natural selection conferring adaptation to local environments can drive speciation through the evolution of hybrid sterility between populations. Here, we show that adaptive divergence in shoot gravitropism, the ability of a plant’s shoot to bend upwards in response to the downward pull of gravity, contributes to the evolution of hybrid sterility in an Australian wildflower, Senecio lautus. We find that shoot gravitropism has evolved multiple times in association with plant height between adjacent populations inhabiting contrasting environments, suggesting that these traits have evolved by natural selection. We directly tested this prediction using a hybrid population subjected to eight rounds of recombination and three rounds of selection in the field. Our experiments revealed that shoot gravitropism responds to natural selection in the expected direction of the locally adapted population. Using the advanced hybrid population, we discovered that individuals with extreme differences in gravitropism had more sterile crosses than individuals with similar gravitropic responses, which were largely fertile, indicating that this adaptive trait is genetically correlated with hybrid sterility. Our results suggest that natural selection can drive the evolution of locally adaptive traits that also create hybrid sterility, thus revealing an evolutionary connection between local adaptation and the origin of new species.

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Selection Models and the Darwinian Theory of Natural Selection

Philosophie et Culture: Actes du XVIIe congrès mondial de philosophie ◽

10.5840/wcp1719883360 ◽

1988 ◽

pp. 108-112

Keyword(s):

Natural Selection ◽

Selection Models ◽

Darwinian Theory

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Natural Selection in a Bulked Hybrid Population of Upland Cotton 1

Crop Science ◽

10.2135/cropsci1978.0011183x001800050028x ◽

1978 ◽

Vol 18 (5) ◽

pp. 799-801 ◽

Cited By ~ 3

Author(s):

J. E. Quisenberry ◽

Bruce Roark ◽

J. D. Bilbro ◽

L. L. Ray

Keyword(s):

Natural Selection ◽

Upland Cotton ◽

Hybrid Population

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The effect of an intronic polymorphism on alcohol dehydrogenase expression in Drosophila melanogaster.

Genetics ◽

10.1093/genetics/138.2.379 ◽

1994 ◽

Vol 138 (2) ◽

pp. 379-385 ◽

Cited By ~ 3

Author(s):

C C Laurie ◽

L F Stam

Keyword(s):

Drosophila Melanogaster ◽

Natural Selection ◽

Alcohol Dehydrogenase ◽

Evolutionary Dynamics ◽

In Vitro Mutagenesis ◽

Allozyme Polymorphism ◽

Selection Models ◽

Intronic Polymorphism ◽

Lines Of Evidence

Abstract Several lines of evidence indicate that natural selection controls the frequencies of an allozyme polymorphism at the alcohol dehydrogenase (Adh) locus in Drosophila melanogaster. However, because of associations among sequence polymorphisms in the Adh region, it is not clear whether selection acts directly (or solely) on the allozymic site. This problem has been approached by using in vitro mutagenesis to distinguish among the effects on Adh expression of individual polymorphisms. This study shows that a polymorphism within the first Adh intron (delta 1) has a significant effect on the level of ADH protein. Like the allozyme, delta 1 shows a geographic cline in frequency, indicating that it may also be a target of natural selection. These results suggest that multisite selection models may be required to understand the evolutionary dynamics of individual loci.

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