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Abstract Developmental and evolutionary processes underlying phenotypic variation frequently target several traits simultaneously, thereby causing covariation, or integration, among phenotypes. While phenotypic integration can be neutral, correlational selection can drive adaptive covariation. Especially, the evolution and development of exaggerated secondary sexual traits may require the adjustment of other traits that support, compensate for, or otherwise function in a concerted manner. Although phenotypic integration is ubiquitous, the interplay between genetic, developmental, and ecological conditions in shaping integration and its evolution remains poorly understood. Here, we study the evolution and plasticity of trait integration in the bull‐headed dung beetleOnthophagus tauruswhich is characterized by the polyphenic expression of horned (‘major’) and hornless (‘minor’) male morphs. By comparing populations subject to divergent intensities of mate competition, we tested whether mating system shifts affect integration of traits predicted to function in a morph‐specific manner. We focussed on fore and hind tibia morphology as these appendages are used to stabilize major males during fights, and on wings, as they are thought to contribute to morph‐based differences in dispersal behavior. We found phenotypic integration between fore and hind tibia length and horn length that was stronger in major males, suggesting phenotypic plasticity in integration and potentially secondary sexual trait compensation. Similarly, we observed that fore tibiashapewas also integrated with relative horn length. However, although we found population differentiation in wing and tibia shape and allometry, populations did not differ in integration. Lastly, we detected little evidence for morph differences in integration in either tibia or wing shape, although wing allometries differed between morphs. This contrasts with previous studies documenting intraspecific differentiation in morphology, behavior, and allometry as a response to varying levels of mate competition acrossO. tauruspopulations. We discuss how sexual selection may shape morph‐specific integration, compensation, and allometry across populations.
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Signals of selection beyond bottlenecks between exotic populations of the bull‐headed dung beetle, Onthophagus taurus
Abstract Colonization of new environments can lead to population bottlenecks and rapid phenotypic evolution that could be due to neutral and selective processes. Exotic populations of the bull‐headed dung beetle (Onthophagus taurus) have differentiated in opposite directions from native beetles in male horn‐to‐body size allometry and female fecundity. Here we test for genetic and transcriptional differences among two exotic and one nativeO. tauruspopulations after three generations in common garden conditions. We sequenced RNA from 24 individuals for each of the three populations including both sexes, and spanning four developmental stages for the two exotic, differentiated populations. Identifying 270,400 high‐quality single nucleotide polymorphisms, we revealed a strong signal of genetic differentiation between the three populations, and evidence of recent bottlenecks within and an excess of outlier loci between exotic populations. Differences in gene expression between populations were greatest in prepupae and early adult life stages, stages during which differences in male horn development and female fecundity manifest. Finally, genes differentially expressed between exotic populations also had greater genetic differentiation and performed functions related to chitin biosynthesis and nutrient sensing, possibly underlying allometry and fecundity trait divergences. Our results suggest that beyond bottlenecks, recent introductions have led to genetic and transcriptional differences in genes correlated with observed phenotypic differences.
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- Award ID(s):
- 1901680
- PAR ID:
- 10265537
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Evolution & Development
- Volume:
- 23
- Issue:
- 2
- ISSN:
- 1520-541X
- Format(s):
- Medium: X Size: p. 86-99
- Size(s):
- p. 86-99
- Sponsoring Org:
- National Science Foundation
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