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|Title:||Chemical and Physical Defense Traits in Two Sexual Forms of Opuntia robusta in Central Eastern Mexico||Keywords:||Opuntia;Ecology;Evolution;Mexico;info:eu-repo/classification/cti/2||Publisher:||PlosOne||Project:||9;3||Description:||In this study, we showed that the seed output is higher in hermaphrodites than in females of O. robusta but also has a higher variance. Furthermore, the hermaphrodite sexual form is on average spinier than the female form, and reproductive cladodes are spinier in hermaphrodites than in females. In addition, we showed that hermaphrodite empty cladodes contain a higher concentration of phenolic compounds than female empty cladodes and found a possible trade-off between the production of phenolic compounds in parental cladodes and their content in daughter cladodes. There also was a possible trade-off between the density of spines on areolae and average number of areolae per cladode, and a positive relationship between physical and chemical defense traits. With the current data, we cannot conclude that sexual polymorphism in the study population is herbivore mediated. In addition, we cannot make inferences about the possible evolution from gynodioecy to dioecy in O. robusta because of the need for accurate information concerning the costs of inbreeding, the entire costs of reproduction, the lifetime reproductive success, the estimation of vegetative growth traits, and possible competition for pollinators with other plant species.
Sexually dimorphic plants provide an excellent opportunity for examining the differences in the extent of their defense against herbivores because they exhibit sex-related differences in reproductive investment. Such differences enable comparison of the sex with high reproduction expenses with the sex that expends less. The more costly sex is usually also better defended against herbivores. Generally, females are considered more valuable than hermaphrodites in terms of fitness; however, hermaphrodites are more valuable if they can produce seed by autonomous selfing, provided that the inbreeding depression is low and pollen is limited. We studied a gynodioecious population of Opuntia robusta from Central- Eastern Mexico, which has been reported to be trioecious, dioecious, or hermaphrodite, and addressed the following questions: 1) Is the hermaphrodite’s reproductive output higher than the female’s, and are hermaphrodites thus better defended? 2) Are plant tissues differentially defended? 3) Do trade-offs exist among different physical defense traits? and 4) among physical and chemical defense traits? We found that 1) hermaphrodites had a higher seed output and more spines per areola than females and that their spines contained less moisture. Non-reproductive hermaphrodite cladodes contained more total phenolic compounds (TPCs) than female ones. In addition, 2) hermaphrodite reproductive cladodes bore more spines than female cladodes, and 3) and 4) we found a negative relationship between spine number per areola and areola number per cladode and a positive relationship between spine number per areola per plant and TPC concentration per plant. Non-reproductive hermaphrodite cladodes contained a higher concentration of TPCs than female cladodes, and parental cladodes contained fewer TPCs than both reproductive and empty cladodes.
UAEM project 2823/2009U CONACyT project 180694/2012
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