Testate amoebae and the fossil record: issues in biodiversity

Abstract

SummaryBiodiversity assessment is broadly divided into a consideration of species diversity, genetic diversity and ecosystem diversity. Individual species are readily defined for many groups of organisms and their relationship with fossil taxa found in the Late Quaternary is clear. Testate amoebae are a group of protozoa which form external tests that are preserved in peat and lake sediments. The higher taxa levels are defined by the morphology of the soft pseudopodia which are not preserved in fossil specimens but many lower taxa can be recognized by test characteristics. Two sets of problems occur in the assessment of fossil testate amoebae biodiversity, related to species definitions based on morphological criteria in living specimens, and the preservation and study of fossil tests. The biological species concept cannot be readily applied to testate amoebae and morphospecies are therefore defined on the basis of the characteristics of pseudopodia and tests. However, the accepted degree of intraspecific morphological variation appears to be variable between authorities and the number of described species is therefore poorly defined. In addition, there is likely to be no straightforward relationship between species diversity and genetic diversity. Further problems of species differentiation are encountered in fossil specimens so that the assessment of biodiversity in fossil populations is even more problematic. The variable results which can be obtained by the adoption of different sets of species definitions are illustrated with respect to fossil faunas from peat profiles in Canada and the UK. The biodiversity of living testate amoebae and other groups of lower organisms is poorly known and further consideration needs to be given to the definition and description of both living and fossil specimens if these problems are to be resolved. The assessment of complete ecosystem biodiversity is not possible without this and investigations which consider the role of diversity in ecosystem functioning cannot even begin.