Genetic effects of forest fragmentation in high-density Araucaria angustifolia populations in Southern Brazil

Abstract

Araucaria angustifolia is an endangered tropical/subtropical coniferous of great interest for conservation due its economical, ecological, and social value. Only 3% of original Araucaria forests remain, which are generally confined to small forest fragments. Forest fragmentation can have serious consequences on genetic process in tree population, affecting long-term fitness and adaptability. To investigate the effects of forest fragmentation on genetic diversity and the structure of A. angustifolia populations, the genetic diversity of eight microsatellite loci was compared in four small fragmented populations (<22 ha), four tree groups (five to 11 trees) occurring in pastures and in three plots in a large continuous population. The clearest effect of fragmentation was the loss of rare alleles (p ≤ 0.05) in fragmented populations (19.4% to 47.2%) and intermediate frequency (0.05 < p ≤ 0.25) and rare alleles (p ≤ 0.05) in tree groups (19% to 86.1%) in comparison to continuous populations. Fragmented populations have significant higher fixation index ($\widehat{F}_{\text{IS}} = 0.121$, P < 0.05) than continuous populations ($\widehat{F}_{\text{IS}} = 0.083$, P < 0.05). High genetic differentiation was detected among tree groups ($\widehat{G}_{{{\text{ST}}}}^{\prime } = 0.258$, P < 0.01) and low among fragments ($\widehat{G}_{{{\text{ST}}}}^{\prime } = 0.031$, P < 0.05) and continuous populations ($\widehat{G}_{{{\text{ST}}}}^{\prime } = 0.026$, P < 0.05), showing a significant bottleneck effect in tree groups. Evidence that forest fragments have experienced a recent bottleneck was confirmed in at least two studied fragments. The implications of the results for conservation of the fragmented A. angustifolia populations are discussed.