Genetic structure and early acting effects of inbreeding in fragmented temperate forests of a self-incompatible tree, Embothrium coccineum.

MATHIASEN P, A. ROVERE & A. PREMOLI.

CONSERVATION BIOLOGY

Año: 2007 vol. 21 p. 232 - 240

0888-8892

Abstract: Deforestation of temperate forests has created landscapes of forest remnants in matrices of intense human use. We studied the genetic effects of such fragmentation in southern Chile for Embothrium coccineum, a bird-pollinated tree.  In particular, we tested the hypothesis that, because of self-incompatibility, E. coccineum in small fragments and isolated trees experience normal gene flow and do not suffer from inbreeding depression. We specifically studied the effects of reduced population size and increased isolation on population genetic structure and progeny performance. Samples were collected from six different sized fragments ranging from small 1 ha, medium 20 ha, and large >150 ha and spatially isolated trees separated at least 10 m from the nearest conspecific. Based on isozyme polymorphisms we estimated parameters of genetic diversity, divergence, and inbreeding for adults and progeny. We also measured seed germination, seedling growth, and outcrossing rates for seedlings maintained in progeny arrays. Eleven of the 22 loci analyzed were polymorphic. Genetic traits of adults did not vary significantly with population size, as expected, given that fragmentation occurred relatively recently. Progeny has a significant loss of total alleles as a result of genetic drift. They also have a tendency for greater polymorphism and lower within-population inbreeding than adults. Reduced but significant genetic divergence exists among adult and progeny populations. Hence fragmentation may reduce inbreeding while maintaining isolation in forthcoming generations. Seedling growth varied positively with the effective number of alleles, indicating deleterious effects of inbreeding on progeny. Seeds from small fragments had the highest germination success, suggesting that higher pollinator activity in such fragments reduces selfing, thereby buffering genetic erosion and maintaining adaptive variation. Our results highlight the importance of conserving remnants of native temperate forest to preserve genetic diversity, promote outcrossing, and conserve mutualistic interactions within fragmented landscapes.