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Alternative Seed Defense Mechanisms in Congeneric Plants
Author(s) -
Siemens David H.,
Johnson Clarence D.,
Ribardo Keve J.
Publication year - 1992
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1941463
Subject(s) - biology , seed predation , chemical defense , predation , herbivore , resistance (ecology) , botany , plant defense against herbivory , seed dispersal , ecology , population , biological dispersal , biochemistry , demography , sociology , gene
Plants in the same genus often differ by certain putative defense compounds even though they are attacked by the same or similar herbivores. We compared two such congeners in their interactions with the same seed predators. In the Sonoran Desert, seeds of the palo verdes Cercidium floridum and C. microphyllum (Leguminosae) were fed upon by the bruchid beetles Mimosestes amicus, M. ulkei, and Stator limbatus, several species of imperfect soil fungi, and at least one species of termite. Seed suitability was compared in field and laboratory experiments. Seeds of C. floridum were significantly more resistant except to a putative subpopulation of S. limbatus that normally feeds on C. floridum. Cercidium floridum seed resistance was located in the seed coat and was chemically based, as determined by a seed boat removal experiment and experiments in which we transferred extracts from resistant seeds to susceptible seeds. The resistance chemical(s) was not identified, though tests for tannins were negative. Alternatively, C. microphyllum abscised pods early, which significantly reduced attack by the seed predators. Early pod abscission was more effective at reducing seed predation than were resistant seed coats. We suggest that very different plant defense mechanisms may evolve under similar selection pressures within the same lineage, contrary to conventional wisdom.