Towards a quantitative approach to research on kin recognition
Since the first documentation if kin recognition in plants (Dudley & File, 2007), and despite of mounting interest on this topic, there is still no consensus on how to define the distinction between ‘kin’ and ‘non-kin’. Many studies, especially those on wild species, reserve the word ‘kin’ for plants sharing the same mother, being either sibs or half-sibs (e.g. Lepik, Abakumova, Zobel, & Semchenko, 2012; Semchenko et al., 2014; Torices et al., 2018). But several studies with crop species also categorise kin and non-kin at the cultivar or variety level (e.g. Pezzola, Pandolfi, & Mancuso, 2020), while studies using the model species Arabidopsis thaliana separate kin and non-kin at the accession level (e.g, Biedrzycki, Jilany, Dudley, & Bais, 2010; Palmer et al., 2016). This variation in definition makes it difficult to compare results across studies, and could explain some of the discrepancies between different studies. Moreover, most studies on kin discrimination simply compare trait values and performance between discrete kin- and non-kin groups, often without actually quantifying the level of genetic relatedness (but see Karban, Shiojiri, Ishizaki, Wetzel, & Evans, 2013 and Xu et al., 2021 as notable exception). As kinship describes the extent of genetic similarity between individuals, it is rather arbitrary to categorise this relationship. We therefore propose that kinship should be expressed as a continuous quantitative measure in terms of genetic relatedness.
Furthermore, the level of replication at the genotypic is often insufficient (rarely more than 10 genotypes) to determine robust correlations of trait expression at different levels of relatedness. To our opinion addressing questions about kin discrimination and its consequences for agricultural or fitness entails firstly quantifying genetic variation in kin discrimination within a sufficiently large population of plants, and secondly, determining whether this variation correlates positively with performance in kin groups. We thus urge for a broader quantitative genetic approach to the research on the selection effects of kin recognition.
Keywords : allelopathy, Darwinian agriculture, ecological weed control, interference competition, kin recognition, rice