Regeneration from seeds with physical defects: Contrasts in survival strategies in recalcitrant and orthodox seeds

Seeds with different desiccation tolerance and their foraging animals present unique strategies for ensuring population growth and ecological fitness in the natural environment. While some seeds minimize physical injuries by having lignified thick coats or defensive compounds, others tolerate a certain degree of mass loss, with larger seeds enduring partial animal consumption better than smaller seeds, consistent with the reserve effect hypothesis, regardless of their desiccation tolerance. In endozoochory, aerial, terrestrial and aquatic fauna with appropriate gape sizes that consume whole fruits with mostly orthodox seeds are important for longer-distance seed dispersal as long as seed viability suffers little impairment following defecation. Some seeds even gain benefits from animal consumption when physical dormancy is overcome and germination occurs earlier. Dung beetles perform secondary spread and burial of seeds, reducing plant aggregation. On the other hand, highly nutritious recalcitrant seeds of a limited number of plant species show sprouting despite partial loss of embryonic axes to browsing animals, often with damage to radicles being less critical than to plumules. Some recalcitrant seeds even possess the unique ability to regenerate roots and shoots from the cotyledonary tissues devoid of embryonic axes. Such embryonic cell development, or 'stemness', from seed tissue fraction is rare in the plant kingdom, but evidently present in at least four families. Plant regeneration despite seed predation is a multi-trait adaptation that ensures species survival and fosters resilient natural ecosystems.