Examining the effects of fragmentation on genetic variation inPlatanthera leucophaea(Orchidaceae): Inferences from allozyme and random amplified polymorphic DNA markers

Abstract

Species that have become rare or endangered due to human disturbance are at increased risk of extinction as a result of environmental, demographic, and genetic stochasticity. Smaller populations, which can be typical of endangered species, are especially vulnerable to loss of variation through stochastic events. For 10 populations of Platanthera leucophaea (Nuttall) Lindley (Orchidaceae), a threatened species, genetic variation at allozyme and random amplified polymorphic DNA (RAPD) loci was measured to assess the potential effects of fragmentation and reduced population size on the future viability of populations. Allozymes revealed very low levels of diversity (AP = 1.18; PP = 12%; HO = 0.008) and high levels of population differentiation (FST = 0.75). Additionally, inbreeding coefficients were very high in five of the 10 populations surveyed, due largely to the fixation of alternative alleles at two loci in different populations. In contrast, every individual displayed a unique RAPD fingerprint, yielding higher levels of polymorphism (PP = 45%) and gene diversity (Nei's H = 0.159). Estimates of population differentiation based on RAPD are moderate as measured by amova (ΦST = 0.21), Wright's F‐statistics (GST = 0.26), or Shannon's information index (Hamong = 0.30). However, genetic and geographic distances are not significantly correlated, suggesting a lack of interpopulation gene flow and/or genetic drift within populations. Population size is not a good predictor of genetic variation in the present study, and it is hypothesized that plant dormancy patterns and chaotic fluctuations in population size from year to year may buffer against stochastic events, especially in small populations.

Acrocomia emensis (Arecaceae) genetic structure and diversity using SSR molecular markers

“…However, conservation strategies may not be performed based only on results of the fine scale genetic structure. It is also important to consider knowledge on the levels of diversity within and among populations, which provide a historical perspective of evolutionary changes that characterize a species, allowing prediction of the behavior of populations when subjected to future events of natural and artificial origin (Wallace, 2002).…”

Molecular diversity and population structure of the forage grass Hemarthria compressa (Poaceae) in south China based on SRAP markers

“…The levels of gene flow calculated here are of insufficient magnitude to counter-balance genetic drift, which may also play a role in the population differentiation observed. Lack of effective mechanisms for longdistance dispersal of genetic materials may also play an important role in shaping the genetic structure observed (Wallace, 2002). Furthermore, habitat fragment caused by human action also contributes to genetic differentiation.…”

Population genetic structure of the tropical tree species Aegiphila sellowiana (Lamiaceae)

“…A historic perspective of the evolutionary changes that characterize a species will also allow us to predict how populations will respond to future events of natural and artificial origin (Wallace, 2002).…”

“…Successful management strategies and the preservation of forest tree species are therefore dependent on an accurate assessment of their genetic diversity to address questions regarding the genetic relationships among individuals as well as the levels and structures of their genetic variation. Knowledge of a particular plant population structure also provides a historical perspective of the evolutionary changes that characterize a species and allows researchers to more accurately predict how populations of plants will respond to future events of both natural and artificial origin (Wallace, 2002).…”