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Abstract Plants demonstrate exceptional variation in genome size across species, and their genome sizes can also vary dramatically across individuals and populations within species. This aspect of genetic variation can have consequences for traits and fitness, but few studies attributed genome size differentiation to ecological and evolutionary processes. Biological invasions present particularly useful natural laboratories to infer selective agents that might drive genome size shifts across environments and population histories. Here, we test hypotheses for the evolutionary causes of genome size variation across 14 invading populations of yellow starthistle,Centaurea solstitialis, in California, United States. We use a survey of genome sizes and trait variation to ask: (1) Is variation in genome size associated with developmental trait variation? (2) Are genome sizes smaller toward the leading edge of the expansion, consistent with selection for “colonizer” traits? Or alternatively, does genome size increase toward the leading edge of the expansion, consistent with predicted consequences of founder effects and drift? (3) Finally, are genome sizes smaller at higher elevations, consistent with selection for shorter development times? We found that 2C DNA content varied 1.21‐fold among all samples, and was associated with flowering time variation, such that plants with larger genomes reproduced later, with lower lifetime capitula production. Genome sizes increased toward the leading edge of the invasion, but tended to decrease at higher elevations, consistent with genetic drift during range expansion but potentially strong selection for smaller genomes and faster development time at higher elevations. These results demonstrate how genome size variation can contribute to traits directly tied to reproductive success, and how selection and drift can shape that variation. We highlight the influence of genome size on dynamics underlying a rapid range expansion in a highly problematic invasive plant.
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Testing the Robustness of the ANES Feeling Thermometer Indicators of Affective Polarization
Affective polarization (AP)—the tendency of political partisans to view their opponents as a stigmatized “out group”—is now a major field of research. Relevant evidence in the United States derives primarily from a single source, the American National Election Studies (ANES) feeling thermometer time series. We investigate whether the design of the ANES produces overestimates of AP. We consider four mechanisms: overrepresentation of strong partisans, selection bias conditional on strong identification, priming effects of partisan content, and survey mode variation. Our analysis uses the first-ever collaboration between ANES and the General Social Survey and a novel experiment that manipulates the amount of political content in surveys. Our tests show that variation in survey mode has caused an artificial increase in the mixed-mode ANES time series, but the general increase in out-party animus is nonetheless real and not merely an artifact of selection bias or priming effects.
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- Award ID(s):
- 1835022
- PAR ID:
- 10479891
- Publisher / Repository:
- Cambridge University Press
- Date Published:
- Journal Name:
- American Political Science Review
- ISSN:
- 0003-0554
- Page Range / eLocation ID:
- 1 to 7
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/S0003055423001302
