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POPULATION GENETIC STRUCTURE OF CECROPIA OBTUSIFOLIA , A TROPICAL PIONEER TREE SPECIES
Author(s) -
AlvarezBuylla Elena R.,
Garay Adriana A.
Publication year - 1994
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1994.tb01322.x
Subject(s) - biology , outcrossing , gene flow , cecropia , biological dispersal , genetic structure , inbreeding , population , isolation by distance , mating system , seed dispersal , ecology , mating , pollen , genetic variation , gene , genetics , demography , sociology
Theoretical analyses of the genetic organization of pioneer species have postulated two very different scenarios. Some models have predicted that such species would show strong population substructuring, whereas other models have suggested that extinction and recolonization can augment gene flow and reduce interpopulation differentiation. We tested these alternative scenarios by analyzing the genetic structure of eight loci from populations of the pioneer dioecious tree, Cecropia obtusifolia , in the tropical rain forest region of Los Tuxtlas, México. The populations studied exhibit low overall F ST values, no clear pattern of isolation by distance, and high estimates of gene flow. These results suggest either that the species is not at a genetic equilibrium under present levels of gene flow with populations derived from each other in the recent past, or that pollen and seed dispersal in this species occur over long distances (up to more than 100 km). Mating among relatives appears higher than expected by chance based on significantly positive fixation indices ( F ) and F IS values at some loci. However, no direct evidence for biparental inbreeding was found. The multilocus and single‐locus outcrossing rates for C. obtusifolia were estimated at t m = 0.974 (SE = 0.024) and t s = 0.980 (SE = 0.035), respectively. These are not significantly different from 1, and the difference, t m — t s = — 0.006 (SE = 0.018), is not significantly different from 0. These estimates, however, could be biased because in all enzymes, except PGM‐1 , we found statistically significant departures from the mixed‐mating model used to estimate them. Two rare alleles were found only in seeds collected from the soil, and the greatest number of different alleles were found also in soil seeds. It is hypothesized that the seed bank may play an important role in the genetic buffering of C. obtusifolia. Significantly positive or negative fixation indices in adults at some loci and significantly different heterozygosities among different life stages (from seeds to adults) suggest the action of selection at some loci.