Relatedness within clusters of a bird-dispersed pine and the potential for kin interactions

Abstract

Limber pine is a bird-dispersed species that frequently exhibits a multiple-trunk growth form. Previous studies have documented genetically distinct individuals within such groups of trunks, presumably resulting from bird seed caches. We surveyed every trunk of each tree in an isolated population of limber pine at 10 electrophoretic loci to determine how many trees were present and to estimate the relatedness of trees within clusters. Fewer than 20 per cent of the multi-trunk groups were found to contain multiple individuals. Damage to growing leaders (and possibly other unknown mechanisms) has apparently resulted in a multi-trunk growth form in single trees. Tree clusters contained from 2 to 4 individuals, and we estimate that trees within these clusters are related as slightly less than half-sibs, on average (r= 0.19 ± 0.10). The occurrence of kin groups in limber pine indicates the potential for interactions such as kin selection and sib competition. Examination of connections between these trees revealed frequent root and trunk fusion, usually between more genetically similar trees. We discuss the possibility that this trait evolved through kin selection. © 1991 The Genetical Society of Great Britain.