Disentangling the relative contributions of factors determining seed physical defence: a global-scale data synthesis

Physical defence investment in seeds varies greatly among plant species and is affected by many potential factors. However, the relative importance of influential factors has not yet been systematically evaluated. Here, we compiled a global database of the seed coat ratio (SCR), a proxy of seed physical defence, for 1,357 species. Using partial R2 calculation that can estimate the reduction in explained variance of a given factor after removing it from a full model containing all the other factors, we disentangled the relative contributions of seven factors commonly used to explain variation in the SCR. Seed desiccation response and phylogeny explained a large amount of SCR variation among species, with a partial R2lik value of 13.31% and 10.62%, respectively. Seed dormancy, plant growth form, seed mass, climate region, and fruit type showed little power to explain SCR variation, although they are often cited in the literature as potential factors. Our results highlight the important roles of seed desiccation response and phylogeny in shaping interspecific variation in the SCR. These findings provide a detailed interpretation of both evolutionary and ecological patterns underlying the physical defence mechanisms and allocation strategies of plant seeds.seed desiccation response 1 means desiccation-tolerant, 0 means desiccation-sensitive, blanks mean lack of information. growth form 1 means woody, and 0 means herbaceous. fruit type 1 means fleshy, 0 means dry, blanks mean lack of information. climate region "Both" means the species occurs in both temperate and tropical regions. nondormant 1 means nondormant, 0 means dormant, blanks mean lack of information. physical dormant 1 means physical dormant, 0 means non physical dormant, blanks mean lack of information. other dormant 1 means other dormant (include physiological dormancy, morphological dormancy and morphophysiological dormancy), 0 means nondormant or physical dormant, blanks mean lack of information. Funding provided by: Anhui Provincial Natural Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100003995Award Number: 2208085J28Funding provided by: Research Grant from Wuhan Botanic Garden*Crossref Funder Registry ID: Award Number: E1559902Funding provided by: Southeast Asia Biodiversity Research Institute, Chinese Academy of Sciences*Crossref Funder Registry ID: Award Number: Y4ZK111B01Funding provided by: Yunnan Provincial Science and Technology DepartmentCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100008871Award Number: 202203AP140007Funding provided by: China Postdoctoral Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100002858Award Number: 2022T150694Funding provided by: Postdoctoral Fellowship of Xishuangbanna Tropical Botanical Garden, CAS*Crossref Funder Registry ID: Award Number: Funding provided by: National Natural Science Foundation of ChinaCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809Award Number: 31971444Funding provided by: National Natural Science Foundation of ChinaCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809Award Number: 32171533Data on the SCR and seed mass were collected from the literature published up until June 5, 2022. We used ((diaspore$ or "seed* coat$" or (seed$ and (kernel$ or reserve$)) or (seed$ and "embryo* endosperm$")) and (ratio$ or proportion$ or fraction$ or tissue$ or percent* or weigh* or mass*)) or (seed$ and (defen* or protect*) and (physical* or mechanical*)) as search terms in the ISI Web of Science and further restricted our search to be consistent with the 'Study Field Categories' of Wu et al. (2019), with the additional category 'anatomy morphology'. Google Scholar was also searched with the same keywords to expand our dataset. The nomenclature of the species was checked against the Plant List version 1.1 (TPL, http://www.theplantlist.org) using the function 'TPL' in the R package 'Taxonstand' and Plants of the World Online (POWO, https://powo.science.kew.org/). Mean values of the SCR and seed mass were used when a species had multiple records. In total, 1,758 records of the SCR were collected, comprising 1,357 species from 720 genera and 150 families. Information on the seed desiccation response, seed dormancy, growth form, fruit type, and climate region of the 1,357 species was also compiled either from published papers or from available online databases