Allozyme diversity in the endangered shrub Linderamelissifolia (Lauraceae) and its widespread congener Linderabenzoin

Abstract

Allozyme diversity was assessed in 15 populations of the endangered clonal shrub Linderamelissifolia (Walt.) Blume (pondberry; Lauraceae) throughout its range in the southeastern United States and in five populations of spicebush (Linderabenzoin (L.) Blume), a sexually reproducing, co-occurring congener. Low levels of allozyme variation characterize both dioecious species. Although genetic diversity was moderately high (HT = 0.239) at polymorphic loci for L. benzoin, few of the 42 loci were polymorphic (Ps = 35%; Pp = 25%), and thus overall estimates of genetic diversity were relatively low (Hes = 0.083; Hep = 0.070). Little genetic variation was detected at 27 loci within L. melissifolia (Hes = 0.025; Hep = 0.015). Nine L. melissifolia loci (33%) were polymorphic but genetic diversity was low (HT = 0.074) at these loci, and few were polymorphic within populations (mean = 6.7%). The number of multilocus genotypes detected in L. melissifolia populations ranged from 1 to 18, with a mean of 4.5. Mean genetic identities between populations within each species were high (I = 0.98 and 0.99 for L. benzoin and L. melissifolia, respectively), a result of the high numbers of monomorphic loci. Despite the high genetic similarity of populations, estimates of gene flow were low to moderate (Nm = 0.82 and 1.25 for L. melissifolia and L. benzoin, respectively). The lower genetic diversity within L. melissifolia may be primarily due to bottlenecks during its evolutionary history. The recent loss of populations and of genets within populations have probably further eroded genetic diversity. To reduce the risk of extinction, effective population sizes of L. melissifolia could be enhanced by increasing genotypic diversity within populations.