Reproductive biology, ecology and historic biogeography of selected rare and endagered Oxalis L. (Oxalidaceae) species

[摘要] ENGLISH ABSTRACT: Twenty five percent of all southern African Oxalis species are rare/endangered and highlylocalized, making them especially vulnerable to threats of extinction (inbreeding, low geneticvariation, disrupted biological interactions) associated with small, isolated populations. In addition,Oxalis also displays tristyly, a restrictive breeding system that includes a strong self-incompatibilitycomponent that promotes out-crossing within populations. As it requires equal availability of threedifferent floral morph types as well as effective pollinators for seed production, this breedingsystem can be a further threat to small, isolated populations when it is fully expressed. Breakdownhas been recorded in terms of all the components of this complex breeding system, but usuallycomprises a relaxation in the expression of self-incompatibility. This may significantly alterreproductive assurance regardless of the availability of pollinators and morph types, with positiveconsequences for at least the short-term future survival of rare species.Potential factors that may contribute towards rarity in Oxalis were investigated by focusing on thereproductive biology and ecology of two widespread and eight rare/highly localized Oxalis species.The expression of tristyly, levels of natural seed production and vegetative reproduction wereinvestigated to identify possible limitations to reproductive success. Several ecological attributes,including habitat type and specificity, population size and density, rainfall patterns, potentialpollinators, potential threats, etc. were investigated for the studied populations and compared to thereproductive biological expression in each case. In addition, phylogeographic patterns wereassessed by investigating the degree of genetic variation within and among populations of a wellsupportedmonophyletic clade including two rare and highly localized species and one widespreadspecies.Comparisons of results of different rare species together with comparisons between rare and relatedcommon species are presented to reveal the most likely threats to specific populations. Tristylyexpression was unstable and extremely variable among the populations studied. In addition tolimited reproductive success, most rare species are restricted by their highly specific habitatrequirements and are particularly vulnerable to variation in rainfall patterns. Low genetic variationwithin rare species may also prevent the colonisation of new habitats or the adaptation to achanging environment.

[发布机构] Stellenbosch University