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Strong selection barriers explain microgeographic adaptation in wild salamander populations
Jonathan L Richardson1, Mark C Urban
1School of Forestry & Environmental Studies, Yale University, 370 Prospect Street, New Haven, CT 06511, USA. jrichardson@aya.yale.edu
Summary
Microgeographic adaptation in spotted salamanders is driven by predation risk. Strong selection overcomes gene flow, allowing populations to adapt to local predator environments.
Area of Science:
- Evolutionary biology
- Ecology
- Population genetics
Background:
- Microgeographic adaptation, where populations adapt to local conditions, is increasingly observed.
- The drivers of adaptive divergence, such as gene flow and natural selection, are not fully understood.
- Predation risk is a known factor influencing trait variation in spotted salamanders (Ambystoma maculatum).
Purpose of the Study:
- To investigate the roles of selection, gene flow, and landscape structure in driving adaptive divergence in spotted salamanders.
- To determine how predation by marbled salamanders (Ambystoma opacum) influences genetic patterns in A. maculatum populations.
- To assess the relationship between foraging rates, genetic divergence, and landscape features in A. maculatum.
Main Methods:
- Analysis of 14 microsatellite loci to assess genetic divergence among A. maculatum populations.
- Quantification of predation risk based on the presence of A. opacum in sympatric ponds.
- Measurement of A. maculatum foraging rates and their association with genetic and landscape data.
Main Results:
- Significant genetic divergence was observed in A. maculatum populations, correlating with A. opacum predation risk.
- A. maculatum foraging rates were strongly linked to predation risk, genetic divergence, and pond spatial relationships.
- Evidence suggests selective barriers effectively limit gene flow, favoring local adaptation despite immigration.
Conclusions:
- Microgeographic adaptation in A. maculatum is shaped by divergent selection regimes imposed by predation.
- Strong selection against maladapted genotypes effectively counteracts gene flow, facilitating local adaptation.
- Selective barriers play a crucial role in maintaining adaptive divergence at small spatial scales.
Related Concept Videos
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...
01:21Frequency-dependent Selection
When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.
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.
02:04Conservation of Small Populations
Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less likely to...
01:32What is Natural Selection?
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01:31Formation of Species
Speciation describes the formation of one or more new species from one or sometimes multiple original species. The resulting species are discrete from the parent species, and barriers to reproduction will typically exist. There are two primary mechanisms, speciation with and without geographic isolation—allopatric and sympatric speciation, respectively.