What causes female bias in the secondary sex ratios of the dioecious woody shrub <i>Salix sitchensis</i> colonizing a primary successional landscape?

Che‐Castaldo, Christian; Crisafulli, Charlie; Bishop, John G.; Fagan, William F.

doi:10.3732/ajb.1500143

Cited by 29 publications

(44 citation statements)

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“…Nitrogen and phosphorus allocated to reproduction in riparian stems greatly exceeded that for upland stems (Che‐Castaldo et al. ). Willow reproductive phenology in riparian zones was typically delayed due to lingering snow that accumulates during winter in stream beds, and it is possible that these large nutrient pulses designated for reproduction were better synchronized with weevil oviposition and early instar feeding in riparian zones than upland areas.…”

Section: Discussionmentioning

confidence: 99%

“…, , Hjältén ), and does little to explain the strong female bias observed in reproductively mature willows on the Pumice Plain (Che‐Castaldo et al. ). Understanding the causes of sex ratio bias in dioecious plants populations is an open question of considerable interest in ecology and evolutionary ecology (Field et al.…”

Section: Discussionmentioning

confidence: 99%

“…On the Pumice Plain, female willow plants allocated equal or greater amounts of resources to reproduction than did males, despite being of similar size (Che‐Castaldo et al. ). We predicted that male willow stems should be preferentially attacked by weevils (as a possible explanation for the observed female bias in the Pumice Plain willow sex ratio), and that sex‐bias in weevil attack may vary with respect to plant water stress.…”

Section: Willow‐weevil Case Studymentioning

confidence: 99%

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Disentangling herbivore impacts in primary succession by refocusing the plant stress and vigor hypotheses on phenology

Che‐Castaldo

Crisafulli

Bishop

et al. 2019

Ecological Monographs

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The plant stress and plant vigor hypotheses are widely used to explain the distribution and abundance of insect herbivores across their host plants. These hypotheses are the subject of contentious debate within the plant herbivore research community, with several studies finding simultaneous support for both hypotheses for the same plant–herbivore interaction. We address the question of how such support is possible using dynamic site‐occupancy models to quantify the attack dynamics of Cryptorhynchus lapathi (poplar‐willow weevil) on Salix sitchensis (Sitka willow), a dioecious shrub colonizing Mount St. Helens, Washington, USA after the 1980 eruption, in relation to host plant stress, vigor, and sex. We also introduce several scaling criteria as a rigorous test of the plant vigor hypothesis and demonstrate why modeling insect detection is important in plant–insect studies. Weevils responded positively to water stress associated with seasonal dry‐downs, and this response was phenologically compartmentalized by larval feeding mode. Weevils preferentially attacked large and/or flowering stems, imposing an ecological cost on willow reproduction via increased stem mortality and susceptibility to future attack. We propose that the dual response to host plant stress and vigor is due to the synchronization between young weevil larval feeding and willow nutrient pulses that are mediated by environmental stress. In turn, this process drives successional dynamics, causing the juvenilization of upland willow plants and possibly delaying establishment of a willow‐dominated upland sere. These results highlight the common, but often overlooked, phenological basis of the plant stress and plant vigor hypotheses, which both focus on how stress changes the quality of plant resources available to immature insects.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Willow‐weevil Case Studymentioning

confidence: 99%

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Disentangling herbivore impacts in primary succession by refocusing the plant stress and vigor hypotheses on phenology

Che‐Castaldo

Crisafulli

Bishop

et al. 2019

Ecological Monographs

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“…Riparian systems tend to have higher nutrients and moisture than upland systems, which could also alter litter quality and potentially influence herbivore susceptibility or preferences (Danell et al 1985, Elmqvist et al 1988b, Boecklen et al 1990, Cornelissen and Stiling 2005. At Mount St. Helens, sex ratios are skewed female (2:1) across both upland and riparian habitats (Che-Castaldo et al 2015). At Mount St. Helens, sex ratios are skewed female (2:1) across both upland and riparian habitats (Che-Castaldo et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Plant sex influences aquatic–terrestrial interactions

et al. 2020

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A growing body of research shows that plant genetic factors can influence ecosystem processes and structure communities, but one aspect that has received little study is sex differentiation in dioecious plants. Since headwater streams are reliant on riparian leaf litterfall, plant sex differences in leaf traits may influence in-stream processes. Sitka willow (Salix sitchensis) at Mount St. Helens is dioecious and heavily infested with the stem-boring weevil (Cryptorhynchus lapathi), which causes branch dieback and summer litterfall. We found that female willow shrubs tend to grow closer to the stream bank, are more likely to be infected by the weevil, and have 42% higher litter C:N than male willows. These factors may lead to increased litter inputs and slower litter mass loss for female willows. The combination of colonization location, herbivore attack, altered litter quality, and slower mass loss results in female shrubs providing more sustained carbon and nutrient resources to microbes and invertebrates in the early successional streams at Mount St. Helens. In addition, since dioecy is a relatively common trait in riparian habitats, it is possible that plant sex plays a far more interesting role in structuring linked terrestrial-aquatic communities and ecosystem processes than previously understood.

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“…Sex‐ratio bias may be a consequence of sex‐specific differences in life‐history traits influencing survival, growth and reproduction (Allen & Antos, ; Delph, ; Field et al, 2013a; Lloyd & Webb, ; Putwain & Harper, ). Alternatively, bias may already be present in seeds as a result of mechanisms including meiotic drive, pollen competition or selective abortion (Che‐Castaldo, Crisafulli, Bishop, & Fagan, ; Correns, ; Field, Pickup, & Barrett, ; Stehlik & Barrett, ; Taylor, ). Stochastic forces can also contribute to variation in sex ratios, and populations may be in a non‐equilibrium state when sampled (Field et al, 2013b).…”

Section: Introductionmentioning

confidence: 99%

The spatial ecology of sex ratios in a dioecious plant: Relations between ramet and genet sex ratios

Timerman

Barrett

2019

Journal of Ecology

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In clonal dioecious plants, the frequency and spatial distribution of flowering ramets contains information on the underlying genet sex ratio. These measures can also provide insight on potential ecological mechanisms causing variation and bias in sex ratios among populations. We used a novel likelihood‐based approach and spatial clustering model to estimate the genet sex ratios from flowering ramet data collected from 32 populations of dioecious Thalictrum pubescens, a clonal species from eastern N. America that occupies moist wetland and forested environments. We investigated sex ratios of seed families, clone size, patterns of flowering and plant height to determine potential causes of sex‐ratio bias. Flowering ramet sex ratios varied considerably among populations but were significantly male‐biased. Seed families grown to flowering also exhibited the same degree of male bias. Both models predicted close correspondence between ramet and genet sex ratios. The likelihood model revealed that sex differences in ramet production could not account for biased ramet sex ratios. The spatial clustering model indicated that ramets were significantly clustered at two spatial scales and estimated similar cluster sizes and densities for both sexes. There was no evidence for spatial segregation of the sexes. Both sexes were equally likely to flower in consecutive years and repeated bouts of flowering had no effect on ramet height. Synthesis. Our analyses suggest that the widespread occurrence of male‐biased sex ratios in Thalictrum pubescens is unlikely to result from sexual differences in clonal growth or habitat preferences. The bias appears to become established early in the life cycle, perhaps at the seed stage as a consequence of local resource competition.

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What causes female bias in the secondary sex ratios of the dioecious woody shrub Salix sitchensis colonizing a primary successional landscape?

Abstract: We hypothesize that S. sitchensis secondary sex ratios depend on either early-acting genetic factors affecting the seed sex ratio or sex-specific germination or survival rates before maturity, as opposed to factors associated with reproduction in adult plants.

Cited by 29 publications

References 104 publications

Disentangling herbivore impacts in primary succession by refocusing the plant stress and vigor hypotheses on phenology

Disentangling herbivore impacts in primary succession by refocusing the plant stress and vigor hypotheses on phenology

Plant sex influences aquatic–terrestrial interactions

The spatial ecology of sex ratios in a dioecious plant: Relations between ramet and genet sex ratios

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