The ability of animals to sync the timing and location of molting (the replacement of hair, skin, exoskeletons or feathers) with peaks in resource availability has important implications for their ecology and evolution. In migratory birds, the timing and location of pre-migratory feather molting, a period when feathers are shed and replaced with newer, more aerodynamic feathers, can vary within and between species. While hypotheses to explain the evolution of intraspecific variation in the timing and location of molt have been proposed, little is known about the genetic basis of this trait or the specific environmental drivers that may result in natural selection for distinct molting phenotypes. Here we take advantage of intraspecific variation in the timing and location of molt in the iconic songbird, the Painted Bunting (
Life history theory provides a framework for understanding how trade-offs generate negative trait associations. Among nestling birds, time spent in the nest, risk of predation, and lifespan covary, but some associations are only found within species while others are only observed between species. A recent comparative study suggests that allocation trade-offs may be alleviated by disinvestment in ephemeral traits, such as nest-grown feathers, that are quickly replaced. However, direct resource allocation trade-offs cannot be inferred from interspecific trait associations without complementary intraspecific studies. Here, we asked whether there is evidence for a within-species allocation trade-off between feather quality and time spent in the nest in Tree Swallows (Tachycineta bicolor). Consistent with the idea that ephemeral traits are deprioritized, nest-grown feathers had lower barb density than adult feathers. However, despite substantial variation in fledging age among nestlings, there was no evidence for a negative association between time in the nest and feather quality. Furthermore, accounting for differences in resource availability by considering provisioning rate and a nest predation treatment did not reveal a trade-off that was masked by variation in resources. Our results are most consistent with the idea that the interspecific association between development and feather quality arises from adaptive specialization, rather than from a direct allocation trade-off.
more » « less- NSF-PAR ID:
- 10369707
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Ornithology
- Volume:
- 139
- Issue:
- 3
- ISSN:
- 0004-8038
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Passerina ciris ) to investigate the genetic and ecological drivers of distinct molting phenotypes. Specifically, we use genome-wide genetic sequencing in combination with stable isotope analysis to determine population genetic structure and molting phenotype across thirteen breeding sites. We then use genome-wide association analysis (GWAS) to identify a suite of genes associated with molting and pair this with gene-environment association analysis (GEA) to investigate potential environmental drivers of genetic variation in this trait. Associations between genetic variation in molt-linked genes and the environment are further tested via targeted SNP genotyping in 25 additional breeding populations across the range. Together, our integrative analysis suggests that molting is in part regulated by genes linked to feather development and structure (GLI2 andCSPG4 ) and that genetic variation in these genes is associated with seasonal variation in precipitation and aridity. Overall, this work provides important insights into the genetic basis and potential selective forces behind phenotypic variation in what is arguably one of the most important fitness-linked traits in a migratory bird. -
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Abstract Roots are essential to the diversity and functioning of plant communities, but trade‐offs in rooting strategies are still poorly understood.
We evaluated existing frameworks of rooting strategy trade‐offs and tested their underlying assumptions, guided by the hypothesis that community‐level rooting strategies are best described by a combination of variation in organ‐level traits, plant‐level root:shoot allocation and symbiosis‐level mycorrhizal dependency. We tested this hypothesis using data on plant community structure, above‐ and below‐ground biomass, eight root traits including mycorrhizal colonisation and soil properties from an edaphic gradient driven by elevation and water availability in sandhills prairie, Nebraska, USA.
We found multidimensional trade‐offs in rooting strategies represented by a two‐way productivity‐durability trade‐off axis (captured by root length density and root dry matter content) and a three‐way resource acquisition trade‐off between specific root length, root:shoot mass ratio and mycorrhizal dependence. Variation in rooting strategies was driven to similar extents by interspecific differences and intraspecific responses to soil properties.
Organ‐level traits alone were insufficient to capture community‐level trade‐offs in rooting strategies across the edaphic gradient. Instead, trait variation encompassing organ, plant and symbiosis levels revealed that consideration of whole‐plant phenotypic integration is essential to defining multidimensional trade‐offs shaping the functional variation of root systems.
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Synopsis The allocation of limited resources among life history traits creates trade-offs that constrain the range of possible phenotypes of organisms. In animals, the cost of maintaining an effective immune response may reduce the ability to invest in reproduction, resulting in altered susceptibility to disease. However, not all members of a population face identical constraints because differences in an individual's environmental context or physiological state can influence the degree to which traits are negatively associated. Here, we evaluated how variation in timing of breeding, a correlate of fitness, may result in different patterns of trait associations between immunity and reproduction. We measured constitutive immunity in breeding female tree swallows (Tachycineta bicolor) using a bacteria killing assay with blood plasma to assess the relationships between bacteria killing ability (BKA), reproductive effort, and reproductive success. We found that timing of breeding can influence the association between BKA and reproductive effort, but its effects are not homogeneous among all traits. Late-breeding tree swallows with stronger BKA laid smaller clutches, a pattern that was not apparent in early breeders. Regardless of the timing of breeding, birds with stronger BKA fed their nestlings less. Despite a negative association with reproductive effort, we found no association between immunity and reproductive success. We provide evidence that individual tree swallows do not experience some trade-offs equally, and that timing of breeding likely plays a role in how costs of immunity are weighed. To understand how investment in immunity can limit life history traits, we must consider how a variation among individuals influences the relative costs of immunity.
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Abstract Despite theoretical advances, the ecological factors and functional traits that enable species varying in seed size and fecundity to coexist remain unclear. Given inherent fecundity advantages, why don't small‐seeded species dominate communities?
In perennial grasslands, we evaluated whether small‐seeded species are less tolerant of competition from the community dominant bunchgrass than large‐seeded species, but also less vulnerable to seed predation by mice. We also explored whether trade‐offs involving competitive tolerance include two other functional traits, height and leaf mass per area (LMA). We added seeds of 17 forb species to plots where bunchgrass competition and rodent seed predation were manipulated across sites varying in bunchgrass productivity and thus competitive intensity. Seeds were added at densities mimicking interspecific variation in fecundity among target species.
Standardizing for differences in fecundity (i.e. seed input, which enabled us to evaluate inherent interspecific differences in susceptibility to biotic interactions), bunchgrass competition more greatly reduced recruitment and establishment of small‐ versus large‐seeded species, whereas rodent seed predation more greatly reduced the recruitment of large‐ versus small‐seeded species. Plant height and LMA were unrelated to the competition effect size.
Small‐seeded species abundance decreased across sites increasing in bunchgrass productivity, whereas this was not the case for large‐seeded species. For adult plants but not seedlings, community‐weighted functional trait means (CWM) for seed size, height and LMA increased in plots with versus without bunchgrass competition and the CWM for seed size and height also increased at sites with greater bunchgrass productivity (for adults only). In contrast, rodent seed predation had no significant effects on CWM seed size.
At the end of the experiment, adult abundance positively correlated with plant fecundity in plots lacking bunchgrass, indicating the inherent advantages accrued to high fecundity small‐seeded species. However, with bunchgrass competition, abundances were equalized across species due to reduced competitive tolerance of high fecundity small‐seeded species.
Synthesis . Our results suggest that coexistence among subordinate forb species varying in seed size and fecundity is in‐part due to a trade‐off involving competitive tolerance and fecundity, mediated by seed size and associated functional traits. -
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All organisms experience fundamental conflicts between divergent metabolic processes. In plants, a pivotal conflict occurs between allocation to growth, which accelerates resource acquisition, and to defense, which protects existing tissue against herbivory. Trade-offs between growth and defense traits are not universally observed, and a central prediction of plant evolutionary ecology is that context-dependence of these trade-offs contributes to the maintenance of intraspecific variation in defense [Züst and Agrawal,
Annu. Rev. Plant Biol. , 68, 513–534 (2017)]. This prediction has rarely been tested, however, and the evolutionary consequences of growth–defense trade-offs in different environments are poorly understood, especially in long-lived species [Cipolliniet al. ,Annual Plant Reviews (Wiley, 2014), pp. 263–307]. Here we show that intraspecific trait trade-offs, even when fixed across divergent environments, interact with competition to drive natural selection of tree genotypes corresponding to their growth–defense phenotypes. Our results show that a functional trait trade-off, when coupled with environmental variation, causes real-time divergence in the genetic architecture of tree populations in an experimental setting. Specifically, competitive selection for faster growth resulted in dominance by fast-growing tree genotypes that were poorly defended against natural enemies. This outcome is a signature example of eco-evolutionary dynamics: Competitive interactions affected microevolutionary trajectories on a timescale relevant to subsequent ecological interactions [Brunneret al. ,Funct. Ecol. 33, 7–12 (2019)]. Eco-evolutionary drivers of tree growth and defense are thus critical to stand-level trait variation, which structures communities and ecosystems over expansive spatiotemporal scales.
