Resource Limitation and Offspring Size and Number Trade‐offs in Cirsium Arvense (Asteraceae)

Abstract

We employed high and low pollination treatments to examine the effect of varying offspring number on the allocation of resources to individual seeds in 5 female clones of the dioecious perennial, Canada thistle (Cirsium arvense (L.) Scop.). In comparison to high pollination plants, low pollination plants displayed a significantly reduced seed set, an unchanged rate of seed abortion, a significant increase in mean achene weight, and an altered pattern of achene weight allocation across primary, secondary, and tertiary flowerheads. These data do not support theoretical predictions for a uniform level of provisioning to individual seeds and are most consistent with the hypothesis that limitation of available resources constrains the level of provisioning to individual seeds. We discuss some of the assumptions underlying offspring provisioning theory in light of our results and discuss the usefulness ofthis theory as a descriptor of plant systems. We are indebted to the following people for their constructive comments on an earlier draft of this manuscript: R. V. Cartar, E. L. Charnov, I. Fleming, M. McGinley, and M. L. Reid. Thanks also go to M. Mather, B. Seehra, J. Brooks, and M. Boyes who helped in the processing of the flowerheads. This work was supported by a Natural Sciences and Engineering Research Council operating grant to BDR and an NSERC postgraduate scholarship to RGL.

Sex‐Specific Trade‐Offs and Responses to Foliar Shade in the Gynodioecious Species Silene vulgaris (Caryophyllaceae)

“…Specifically., in reference to the current experiment, none of these traits (ovule size, ovule number, or anther size) exhibited a sigtiificant treatment effect or sex x trt-ntment interaction (table 1), suggesting that these are genetically fixed trade-offs. The observed ovule size-number trade-off indicated by our results is consistent with progeny size-number trade-offs predicted under life-history theory hut is rarely reported by empirical studies (Greenway and Harder 2Ü07), although some studies have shown a negative correlation between seed size and ovule number (Lalonde and Roitberg 1989;Lehtilä and Ehrlén 2005). Not surprisingly, females do not seem to experience a trade-off between anther and ovule production, as would be expected given that females derive fitness exclusively through female function and have presumably experienced (and apparently responded to) past selectioti to minimize allocation to vestigial stamens.…”

Correlated patterns of variation in phenology and seed production in populations of two annual grasses along an aridity gradient

“…BG plants originating in an environment intermediate between SB and AM with respect to productivity and unpredictability, are between these two extremes, and two-directional gene flow may have additional smoothing effect to the effect of natural selection. A negative correlation between seed mass and number has been documented in several studies comparing small-seeded versus large-seeded species (Shipley and Dion 1992;Greene and Johnson 1994;Turnbull et al 1999;Eriksson 2000, 2003), as well as within several species (van Groenendael 1985;Lalonde and Roitberg 1989;McGinley 1989). However, our study describes the dynamics of this relationship across an aridity gradient as a part of plant strategies.…”

Does Early Growth Cause a Phenotypically Plastic Response in Egg Production of Atlantic Salmon?

“…This has been demonstrated for a number of species from different taxa and trophic levels, e.g. Blue Tits Parus caeruleus (Dhondt, Kempenaers & Adriaensen 1992), Thistle Cirsium arvense (Lalonde & Roitberg 1989), Deep-water Prawn Pandalus borealis (Clarke, Hopkins & Nilssen 1991), Fruit-flies (Stearns 1992) and a cladoceran, Simocephalus vetulus (Perrin 1988(Perrin , 1989. In fishes, several studies have documented that food supply influences egg size and fecundity but the effect seems to vary among species.…”