Fruit size decline from the margin to the center of capitula is the result of resource competition and architectural constraints

Abstract

Plants produce repeated structures, such as leaves, flowers, and fruits, which differ in size and shape. One example of this is fruit size, which is commonly observed to decrease from proximal to distal positions within an inflorescence. The resource limitation hypothesis proposes that because proximal fruits usually develop first, they have temporal priority on access to resources over distal fruits. The non-mutually exclusive architectural effects hypothesis suggests that these position effects in fruit size may also be due to inherent architectural variation along infructescence axes. We separated out the effects of resource competition and inflorescence architecture by removing the outer or the inner flowers within capitula of Tragopogon porrifolius. We also studied if fruit position influenced germination and seedling performance in order to assess fitness consequences of position effects. Inner fruits were significantly heavier when outer flowers were removed. However, outer fruits did not significantly increase when inner flowers were removed, suggesting later fruits were limited by the development of early fruits. Our findings also suggest that architectural constraints restricted the size of inner fruits in comparison with outer ones. We found that both resource competition and inflorescence architecture affected the fruit size of T. porrifolius, even though this species does not have linear, indeterminate inflorescences. We advance the hypothesis that, when such effects on fitness occur, resource competition-mediated position effects could turn, in evolutionary time, into architectural position effects.

Extremely Long-Lived Stigmas Allow Extended Cross-Pollination Opportunities in a High Andean Plant

“…42, 43], it is likely that there would be a cost of increasing achene output in years of abundant pollinators in this species. As shown by Torices & Méndez [44] achenes within a capitulum can compete by resources, therefore, if fewer achenes compete by resources these may achieve a larger size. In a recent meta-analysis, García-Camacho & Totland [33] showed that although alpine plants suffer significant pollen limitation, there is no difference in pollen limitation between alpine and lowland species, and between self-compatible and self-incompatible species.…”

Not only size matters: achene morphology affects time of seedling emergence in three heterocarpic species of <i>Anacyclus</i> (Anthemideae, Asteraceae)

“…Besides variation in morphology, achenes may also vary markedly in size (Venable & al., 1987;McGinley, 1989;Maxwell & al., 1994;Imbert & al., 1996;Van Mölken & al., 2005;Brändel, 2007 ly the heaviest ones, whereas those adapted for greater dispersal are generally lighter (McEvoy, 1984;Tanowitz & al., 1987;Venable & al., 1987;Imbert & al., 1996;Imbert & Ronce, 2001;Brändel, 2004Brändel, , 2007Bastida & Menéndez, 2004, Bastida & al., 2010 among others). With regard to germination performance, recent research suggests that variation in achene size may be the main driver of divergent behavior exhibited by seeds from different achene morphs (Van Mölken & al., 2005;Torices & Méndez, 2010). Achene size can also affects performance in post-dispersal life-history traits, particularly in competitive conditions (McEvoy, 1984;Andersson, 1996;Ruiz de Clavijo & Jiménez, 1998;Meyer & Carlson, 2001;Ruiz de Clavijo, 2005;Van Mölken & al., 2005;Benard & Toft, 2007).…”

Sequential decline in fruit resource allocation within inflorescences of Sagittaria trifolia: a test of non‐uniform pollination hypothesis

“…Overall, we found a proximal‐to‐distal decline in seed quantity and quality within inflorescences of S. trifolia , which was not caused by ovule limitation or decreases in quantity and quality of pollination on sequential flowers, thus rejecting the non‐uniform pollination hypothesis. The present study did not design an experiment to test whether the declining pattern was due to an architectural effect or resource competition, two independent and non‐mutually exclusive components of position effects (Lee ; Torices & Méndez ). However, two observations support the possibility of both.…”

“…Especially, flowers within an inflorescence are not equal in some aspects, including floral organs, sex allocation, fruit and seed properties (Medrano et al . ; Diggle ; Guitián ; Buide ; Torices & Méndez ; Dai et al . ).…”