Diversity of the genus Seira (Collembola: Entomobryidae: Seirinae) in the Fynbos and Southern Afrotemperate forest

[摘要] ENGLISH ABSTRACT: Soil is one of the most complex and understudied terrestrial habitats, and it comprises a widerange of organisms that affect the functioning of terrestrial ecosystems. Despite the importanceof these below-ground fauna, our understanding of this diversity remains limited, especially in theCape Floristic Region (CFR), where higher plants and other more conspicuous invertebrates havebeen better represented in the literatures. The main aim of this thesis is to provide the first insightsinto the taxonomic, cryptic and spatial diversity of one of the more diverse Collembola genera,Seira (Collembola: Entomobryidae: Seirinae), in the Fynbos and Southern Afrotemperate foresthabitats of the CFR. Collembola constitute an important component of terrestrial biodiversity andare essential for ecosystem functioning.The thesis is divided into two data chapters. The first data chapter examines the mitochondrialbarcoding COI (Cytochrome-c oxidase subunit I) gene of 496 Seira specimens from 41 Fynbosand forest sites. Discrete Molecular Operational Taxonomic Units (MOTUs) are identified withinSeira. Furthermore, divergence times are estimated and tentatively used to propose historicaltriggers for the diversification of Seira. Habitat specificity of Seira is assessed throughphylogenetic reconstruction using Parsimony and Bayesian analyses based on the nucleotideand amino acid sequences. Genetic divergence indicates that Seira is composed of at least 91MOTUs, suggesting that morphological taxonomy has vastly under-estimated the richness of thisgenus by at least four folds. Most of the MOTUs are highly habitat specific and geographicallylocalised. The reconstruction of an evolutionary time frame of these lineages reveals several deepdiversifications in the Miocene and a spate of more recent radiations in the Pleistocene andHolocene. Palaeo-environmental fluctuations and vegetation composition shifts are hypothesisedas having increased the environmental complexity of the region and this may have influenced thediversification patterns of Seira.In the second data chapter, the spatial variation of Seira diversity is examined and comparedbetween and within two major habitat types, Fynbos and forest, across nine study sites. Abioticvariables were recorded and compared for the investigation of environmental differences amonghabitat types. The habitat specificity of Seira is assessed, as well as the relative effects of habitattypes and study sites on assemblage structure. Species richness of Seira is higher in Fynbos thanin forest, and this could be due to the high heterogeneity of niches and resources created by thesteep environmental and floristic gradients in the Fynbos habitats. Perhaps one of the most striking results is the high levels of beta diversity exhibited by Seira. The spatial turnover of theSeira assemblage is complete or nearly complete among and within habitat types across studysites within the CFR. Low dispersal abilities and consequently isolated evolutionary histories mayaccount for the strong assemblage differences within the same habitat type of different studysites. However, the substantial differences in assemblage composition between adjacent habitattypes in the same site are likely to be the result of the contrasting abiotic conditions exhibited bythe Fynbos and forest habitats, as found by this study.Overall, the results of this thesis suggest that Seira species richness is much greater thanpreviously thought. It follows similar diversity patterns to the well-described and hyper-diverseplant communities of the CFR. Here, for both CFR plants and Seira, the spectacular regionaldiversity displayed is not the result of high alpha diversity, but rather of substantial beta diversity.Because of the high beta diversity and the fact that only two CFR vegetation types were sampledfrom a limited number of study sites, I predict that the Seira species richness presented here isbut the tip of the iceberg.

[发布机构] Stellenbosch University