Related Experiment Video
Updated: Aug 7, 2026
15:19
Effect of Male Accessory Gland Products on Egg Laying in Gastropod Molluscs
Published on: June 22, 2014
Strong natural selection causes microscale allozyme variation in a marine snail
K Johannesson1, B Johannesson, U Lundgren
1Tjärnö Marine Biological Laboratory, Strömstad, Sweden.
Summary
Natural selection significantly impacts molecular variation in marine snails. Even over short distances, allele frequencies at the aspartate aminotransferase locus demonstrate strong microclinal selection, influencing evolution.
Area of Science:
- Evolutionary biology
- Population genetics
Background:
- The role of natural selection in molecular evolution is debated.
- Limited data exists on selection acting on molecular traits compared to phenotypic traits.
Purpose of the Study:
- To investigate the importance of natural selection in driving molecular variation.
- To provide evidence for substantial contributions of natural selection to molecular variation at small spatial scales.
Main Methods:
- Studied allele frequencies of aspartate aminotransferase (Aat) in Littorina saxatilis populations over seven years.
- Observed population dynamics and allele frequency shifts following a toxic microflagellate bloom.
- Estimated the coefficient of selection for specific alleles in the surf zone environment.
Main Results:
- Steep microclines in Aat allele frequencies were observed between splash and surf zones.
- A toxic bloom temporarily shifted Aat allele frequencies in the surf zone.
- The frequency of the Aat120 allele returned to its original level within generations, indicating strong selection (estimated coefficient of 0.4).
Conclusions:
- Microclinal selection is a significant evolutionary force in this marine snail system.
- Natural selection can substantially shape molecular variation over short distances.
- Findings support the importance of selection on molecular traits, even at a microevolutionary scale.
Related Concept Videos
01:32What is Natural Selection?
Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.The Theory of Natural...
01:46Types of Selection
Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...
01:09Mutation, Gene Flow, and Genetic Drift
In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).Mechanisms of Genetic VariationThe original sources of genetic variation are mutations,...
01:38Limits to Natural Selection
Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
02:39Gene Flow
Gene flow is the transfer of genes among populations, resulting from either the dispersal of gametes or from the migration of individuals.
01:24Evolution of New Traits in Microbes
Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...