The ability of plants to distinguish self roots and kin roots from non-kin roots is shown in the growing body of research on plant identity recognition. In many species studied to date, roots respond differently to roots of the same individual, roots of a close relative, or roots of non-related competitors (Falik et al., 2003; Gruntman and Novoplansky, 2004; Holzapfel and Alpert, 2003; Mahall and Callaway, 1992, 1996; Maina et al., 2002). These responses are studied in the context of competition reduction among different parts of the same plant or those of a close relative. Kin selection theory is partly founded in the conception that individuals increase their collective fitness by behaving in a manner that increases the fitness of related individuals (Hamilton, 1964a, 1964b). This is realized by reducing investment in competition, which can increase the individual’s fitness because fewer resources are consumed for competing with neighbors and can similarly increase the neighbor’s fitness through altruism (Axelrod and Hamilton, 1981).
The most prevalent response variables in this body of research are various root growth traits. Other responses to belowground neighbor identity reported to date include plant biochemistry (Broz et al., 2010) and pollen quality (Lankinen, 2008).
Identity recognition capabilities of cycads have not been studied to date. A greater understanding of this phenomenon may be useful for planning the layout of garden and conservation plantings. The purpose of this study was to determine the presence of kin recognition capabilities in roots of a representative cycad species. Cycas edentata is a widespread cycad species that colonizes islands throughout its natural range (Lindström et al., 2008). It is one of two coastal species in the Philippines, and I selected this species because seeds from distinct islands could be easily secured to provide con-specific individuals. I predicted that root growth would be minimized when seedlings were forced to interact with close relatives and would be maximized when forced to interact with non-relatives.
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