American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Early sibling conflict may ultimately benefit the family”

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Alyssa Laney Smith, Daniel Z. Atwater, and Ragan M. Callaway (Oct 2019)

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Early sibling conflict via kin recognition may ultimately benefit the family for an invasive grass

Barbed goatgrass (<i>Aegilops triuncialis</i> L.).<br />(Credit: Andrew Dyer)
Barbed goatgrass (Aegilops triuncialis L.).
(Credit: Andrew Dyer)

Seeds of goatgrass, a European plant that is invading California, have the ability to chemically inhibit the germination of their siblings more than non-siblings. At face value, this seems like strong conflict among relatives. However, in experiments with no chemical suppression of germination, goatgrass seedlings even more strongly suppressed their siblings through competition. Thus, by suppressing germination, goatgrass may allow their close kin to remain dormant for a time, and by doing so to avoid competition within the family later in life.


Relatives often interact differently with each other than with non-relatives, and whether kin cooperate or compete has important consequences for the evolution of mating systems, seed size, dispersal, and competition. Previous research found that the larger of the size-dimorphic seeds produced by the annual plant, Aegilops triuncialis, suppressed germination of their smaller sibs by 25-60%. Here, we found evidence for kin-recognition and sibling rivalry later in life among Aegilops seedlings that places seed-seed interactions in a broader context. In experiments with size-dimorphic seeds, seedlings reduced the growth of sibling seedlings by ~40% but that of non-sibling seedlings by ~25%. These sequential antagonistic interactions between seeds and then seedlings provide insight into conflict and cooperation among kin. Kin-based conflict among seeds may maintain dormancy for some seeds until the coast is clear of more competitive siblings. If so, biotically induced seed dormancy may be a unique form of cooperation, which increases the inclusive fitness of maternal plants and offspring by minimizing competition among kin.