Faculty Opinions recommendation of Experimental evolution reveals natural selection on standing genetic variation.

The effect of environment on adaptation and divergence was examined in two sets of populations of Escherichia coli selected for 1000 generations in either maltose- or glucose-limited media. Twelve replicate populations selected in maltose-limited medium improved in fitness in the selected environment, by an average of 22.5%. Statistically significant among-population genetic variation for fitness was observed during the course of the propagation, but this variation was small relative to the fitness improvement. Mean fitness in a novel nutrient environment, glucose-limited medium, improved to the same extent as in the selected environment, with no statistically significant among-population genetic variation. In contrast, 12 replicate populations previously selected for 1000 generations in glucose-limited medium showed no improvement, as a group, in fitness in maltose-limited medium and substantial genetic variation. This asymmetric pattern of correlated responses suggests that small changes in the environment can have profound effects on adaptation and divergence.

Download Full-text

Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait

Nature Communications ◽

10.1038/s41467-021-23804-7 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Kensuke Okada ◽

Masako Katsuki ◽

Manmohan D. Sharma ◽

Katsuya Kiyose ◽

Tomokazu Seko ◽

...

Keyword(s):

Sexual Selection ◽

Natural Selection ◽

Experimental Evolution ◽

Genetic Correlations ◽

Lifetime Reproductive Success ◽

Fundamental Theory ◽

Female Fitness ◽

Male Trait ◽

Flour Beetles ◽

Male Specific

AbstractTheory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters.

Download Full-text

Cryptic variation and its manifestation in the Lower Trentonian Rafinesquina lineage (Ordovician, New York State)

The Paleontological Society Special Publications ◽

10.1017/s2475262200008522 ◽

1992 ◽

Vol 6 ◽

pp. 292-292

Author(s):

Robert Titus

Keyword(s):

New York ◽

Genetic Variation ◽

Natural Selection ◽

New York State ◽

Ecological Factors ◽

Stabilizing Selection ◽

Rapid Population Growth ◽

York State ◽

Cryptic Variation ◽

Adaptive Peak

Species populations commonly carry a great deal of genetic variation which is not expressed in individual phenotypes. Cryptic variation can be carried in recessive alleles, in cases of heterosis, or where modifier genes inhibit expression of the hidden trait. Other genetic and ecological factors also allow cryptic variation. Stabilizing selection prevents the expression of hidden traits; normalizing selection weeds out the deviants and canalizing selection suppresses their traits. Together the two keep the species near the top of the adaptive peak. Cryptic variation balances a species' need to be well-adapted to its environment and also for it to maintain a reserve of variation for potential environmental change. Expression of cryptic traits is rare and is usually associated with times of greatly reduced natural selection and rapid population growth, when the lower slopes of the adaptive peak are exposed.A possible example of the manifestation of cryptic traits occurs within the lower Trentonian Rafinesquina lineage of New York State. The two most commonly reported species of the genus have been reappraised in terms of cryptic variation. Extensive collections of Rafinesquina “lennoxensis” reveal far more intergrading morphotypes than had hitherto been recognized. The form which Salmon (1942) described is broadly U-shaped with sulcate margins. It grades into very convex forms as well as sharply-defined or convexly geniculate types. Of great importance, all forms grade into the flat, U-shaped, alate R. trentonensis, which is, by far, the most common and widespread lower Trentonian member of the genus. The R. “lennoxensis” assemblage has a very narrow biostratigraphy, being confined to a few locations in the upper Napanee Limestone. This places it in a quiet, protected, low stress, lagoonal setting behind the barrier shoal facies of the Kings Falls Limestone.The R. “lennoxensis” assemblage does not constitute a natural biologic species; it is reinterpreted as an assemblage of phenodeviants occupying a low stress, low natural selection lagoon facies. All such forms should be included within R. trentonensis. Given the evolutionary plasticity of this genus, extensive cryptic variation is not surprising.

Download Full-text

Evolution and evolvability: celebrating Darwin 200

Biology Letters ◽

10.1098/rsbl.2008.0639 ◽

2008 ◽

Vol 5 (1) ◽

pp. 44-46 ◽

Cited By ~ 33

Author(s):

John F.Y Brookfield

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Time Scales ◽

Evolutionary Change ◽

Adaptive Mutation ◽

Genetic Covariances ◽

The Relationship ◽

The Way

The concept of ‘evolvability’ is increasingly coming to dominate considerations of evolutionary change. There are, however, a number of different interpretations that have been put on the idea of evolvability, differing in the time scales over which the concept is applied. For some, evolvability characterizes the potential for future adaptive mutation and evolution. Others use evolvability to capture the nature of genetic variation as it exists in populations, particularly in terms of the genetic covariances between traits. In the latter use of the term, the applicability of the idea of evolvability as a measure of population's capacity to respond to natural selection rests on one, but not the only, view of the way in which we should envisage the process of natural selection. Perhaps the most potentially confusing aspects of the concept of evolvability are seen in the relationship between evolvability and robustness.

Download Full-text

The genomics of adaptation

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2012.2322 ◽

2012 ◽

Vol 279 (1749) ◽

pp. 5024-5028 ◽

Cited By ~ 35

Author(s):

Jacek Radwan ◽

Wiesław Babik

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Royal Society ◽

Genetic Basis ◽

Genomic Data ◽

Evolutionary Change ◽

Introductory Article ◽

Technological Advances ◽

A Genome ◽

Genome Level

The amount and nature of genetic variation available to natural selection affect the rate, course and outcome of evolution. Consequently, the study of the genetic basis of adaptive evolutionary change has occupied biologists for decades, but progress has been hampered by the lack of resolution and the absence of a genome-level perspective. Technological advances in recent years should now allow us to answer many long-standing questions about the nature of adaptation. The data gathered so far are beginning to challenge some widespread views of the way in which natural selection operates at the genomic level. Papers in this Special Feature of Proceedings of the Royal Society B illustrate various aspects of the broad field of adaptation genomics. This introductory article sets up a context and, on the basis of a few selected examples, discusses how genomic data can advance our understanding of the process of adaptation.

Download Full-text

Evidence of between-population differences in natural selection on extra-floral nectaries of the shrub Anemopaegma album (Bignoniaceae)

Botany ◽

10.1139/cjb-2015-0201 ◽

2016 ◽

Vol 94 (3) ◽

pp. 201-213

Author(s):

Anselmo Nogueira ◽

Pedro J. Rey ◽

Julio M. Alcántara ◽

Lúcia G. Lohmann

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Evolutionary Ecology ◽

Common Garden ◽

Phenotypic Selection ◽

Population Differences ◽

Wild Populations ◽

Neotropical Savanna ◽

Foliar Damage ◽

Floral Nectaries

Extra-floral nectaries (EFNs) are thought to represent protective adaptations against herbivory, but studies on the evolutionary ecology of EFNs have seldom been conducted. Here we investigate the patterns of natural selection and genetic variation in EFN traits in two wild populations of Anemopaegma album Mart. ex DC. (Bignoniaceae) that have been previously described as contrasting EFN – ant adapted localities in the Neotropical savanna (Cristália and Grão Mogol). In each population, four EFN descriptors, foliar damage, and reproductive success variables were measured per plant (100–120 plants per population). To estimate the heritability of EFN traits, we crossed reproductive plants in the field, and grew offspring plants in a common garden. The results showed that ant assemblages differed between populations, as did the range of foliar herbivory. Genetic variation and positive phenotypic selection in EFN abundance were only detected in the Cristália population, in which plants with more EFNs were more likely to reproduce. An evaluation of putative causal links conducted by path analysis corroborated the existence of phenotypic selection on EFNs, which was mediated by the herbivory process in the Cristália population. While EFNs could be currently under selection in Cristália, it is possible that past selection may have driven EFN traits to become locally adapted to the local ant assemblage in the Grão Mogol population.

Download Full-text

Sex, amitosis, and evolvability in the ciliate Tetrahymena thermophila

10.1101/2021.12.21.473698 ◽

2021 ◽

Author(s):

Jason A Tarkington ◽

Hao Zhang ◽

Ricardo Azevedo ◽

Rebecca Zufall

Keyword(s):

Genetic Variation ◽

Experimental Evolution ◽

Evolutionary Biology ◽

Genetic Architecture ◽

Nuclear Division ◽

Tetrahymena Thermophila ◽

Laboratory Populations ◽

Evolutionary Success ◽

Sexual Progeny ◽

Open Question

Understanding the mechanisms that generate genetic variation, and thus contribute to the process of adaptation, is a major goal of evolutionary biology. Mutation and genetic exchange have been well studied as mechanisms to generate genetic variation. However, there are additional processes that may also generate substantial genetic variation in some populations and the extent to which these variation generating mechanisms are themselves shaped by natural selection is still an open question. Tetrahymena thermophila is a ciliate with an unusual mechanism of nuclear division, called amitosis, which can generate genetic variation among the asexual descendants of a newly produced sexual progeny. We hypothesize that amitosis thus increases the evolvability of newly produced sexual progeny relative to species that undergo mitosis. To test this hypothesis, we used experimental evolution and simulations to compare the rate of adaptation in T. thermophila populations founded by a single sexual progeny to parental populations that had not had sex in many generations. The populations founded by a sexual progeny adapted more quickly than parental populations in both laboratory populations and simulated populations. This suggests that the additional genetic variation generated by amitosis of a heterozygote can increase the rate of adaptation following sex and may help explain the evolutionary success of the unusual genetic architecture of Tetrahymena and ciliates more generally.

Download Full-text

Genetic Variation Explains Changes in Susceptibility in a Naïve Host Against an Invasive Forest Pathogen: The Case of Alder and the Phytophthora alni Complex

Phytopathology ◽

10.1094/phyto-07-19-0272-r ◽

2020 ◽

Vol 110 (2) ◽

pp. 517-525 ◽

Cited By ~ 1

Author(s):

Miguel A. Redondo ◽

Jan Stenlid ◽

Jonàs Oliva

Keyword(s):

Genetic Variation ◽

Natural Selection ◽

Transmission Rate ◽

Alternative Hypothesis ◽

Simulated Data ◽

Alnus Glutinosa ◽

Heritable Variation ◽

Narrow Sense Heritability ◽

Black Alder

Predicting whether naïve tree populations have the potential to adapt to exotic pathogens is necessary owing to the increasing rate of invasions. Adaptation may occur as a result of natural selection when heritable variation in terms of susceptibility exists in the naïve population. We searched for signs of selection on black alder (Alnus glutinosa) stands growing on riverbanks invaded by two pathogens differing in aggressiveness, namely, Phytophthora uniformis (PU) and Phytophthora × alni (PA). We compared the survival and heritability measures from 72 families originating from six invaded and uninvaded (naïve) sites by performing in vitro inoculations. The results from the inoculations were used to assess the relative contribution of host genetic variation on natural selection. We found putative signs of natural selection on alder exerted by PU but not by PA. For PU, we found a higher survival in families originating from invaded sites compared with uninvaded sites. The narrow sense heritability of susceptibility to PU of uninvaded populations was significantly higher than to PA. Simulated data supported the role of heritable genetic variation on natural selection and discarded a high aggressiveness of PA decreasing the transmission rate as an alternative hypothesis for a slow natural selection. Our findings expand on previous attempts of using heritability as a predictor for the likelihood of natural adaptation of naïve tree populations to invasive pathogens. Measures of genetic variation can be useful for risk assessment purposes or when managing Phytophthora invasions.

Download Full-text