Human disturbance reduces genetic diversity of an endangered tropical tree, Prunus africana (Rosaceae)

Abstract

Human activities such as fragmentation and selective logging of forests can threaten population viability by modification of ecological and genetic processes. Using six microsatellite markers, we examined the effects of forest fragmentation and local disturbance on the genetic diversity and structure of adult trees (N = 110) and seedlings (N = 110) of Prunus africana in Kakamega Forest, western Kenya. Taking samples of adults and seedlings allowed for study of changes in genetic diversity and structure between generations. Thereby, adults reflect the pattern before and seedlings after intensive human impact. Overall, we found 105 different alleles in the six loci examined, 97 in adults and 88 in seedlings. Allelic richness and heterozygosity were significantly lower in seedlings than in adults. Inbreeding increased from adult tree to seedling populations. Genetic differentiation of adult trees was low (overall F ST = 0.032), reflecting large population sizes and extensive gene flow in the past. Genetic differentiation of seedlings was slightly higher (overall F ST = 0.044) with all of the 28 pairwise F ST -values being significantly different from zero. These results suggest that human disturbance in Kakamega Forest has significantly reduced allelic richness and heterozygosity, increased inbreeding and slightly reduced gene flow in P. africana in the past 80-100 years.

Fine-scale spatial genetic dynamics over the life cycle of the tropical tree Prunus africana

“…Polymerase chain reaction protocols followed Farwig et al (2008) with annealing temperatures ranging from 54 to 62 1C and the number of cycles ranging from 44 to 46. For loci UDP97-403 and EMPaS06, a final extension step of 60 1C for 30 min was added to the standard protocol.…”

“…For example, if the extent of seed dispersal has declined across generations, owing to, for example, anthropogenic disturbance, juveniles may show stronger SGS than adults (for example, Farwig et al, 2008). In contrast, if the adult population results from a generation with few founder trees it may show stronger levels of SGS than the present day juveniles Pardini and Hamrick, 2008).…”

“…africana is a common species in Kakamega Forest, considered a late pioneer or an early climax tree species (for example, Swaine and Whitmore, 1988). Farwig et al (2008) studied genetic structure of P. africana seedlings and adults at a larger spatial scale among eight populations distributed over Kakamega Forest and adjacent fragments. They found stronger genetic differentiation among seedling populations than among adults, showing that genetic diversity and structure of the species is sensitive to processes reducing gene flow, such as forest fragmentation and local disturbance (Farwig et al, 2008).…”

“…Farwig et al (2008) studied genetic structure of P. africana seedlings and adults at a larger spatial scale among eight populations distributed over Kakamega Forest and adjacent fragments. They found stronger genetic differentiation among seedling populations than among adults, showing that genetic diversity and structure of the species is sensitive to processes reducing gene flow, such as forest fragmentation and local disturbance (Farwig et al, 2008). To better understand these patterns, we used parentage analyses to investigate the extent of gene flow across different life stages mediated by insect pollinators and vertebrate seed dispersers (Berens et al, 2013).…”

“…In this study, we used a multi-stage approach to determine whether the observed patterns of SGS are consistent with expectations deriving from the observed biological processes. We hypothesize (i) strong SGS at the seed stage because of distance-restricted seed dispersal; (ii) a continuous decrease of SGS across older recruitment stages because of mortality and the thinning of clusters of related individuals; and (iii) an increase in SGS across generations (between adult trees and seedlings of the next generation) resulting not only from restricted dispersal but also from proposed changes in gene flow across generations (Farwig et al, 2008).…”