The Aegagropila-clade is a unique lineage of algae within the large order Cladophorales and consists of poorly known taxa that mainly occur in brackish and freshwater environments. The clade is... Show moreThe Aegagropila-clade is a unique lineage of algae within the large order Cladophorales and consists of poorly known taxa that mainly occur in brackish and freshwater environments. The clade is sister to the species-rich, primarily marine Cladophora- and Siphonocladus-lineages. Most of its members occur in narrow niches such as on the carapaces of freshwater turtles (some members of Basicladia), on freshwater snails and bivalves (monotypic Arnoldiella and several Basicladia species), on and endophytically in saltmarsh plants and mangrove pneumatophores (some members of Wittrockiella), or on marine intertidal snails (Cladophora conchopheria). Aegagropila linnaei is the best known representative of the lineage and has gained considerable scientific, cultural and economic fame due to the peculiar lake balls formed under specific conditions. The confused taxonomy of the Aegagropila-clade was clarified using methods of molecular phylogenetic inference, resulting in the re-instatement of the Pithophoraceae, descriptions of two new genera and several nomenclatural changes. Phylogenetic analyses led to an understanding of the evolution of the heterotrichous habit as an adaptation to changeable environmental conditions. In selected taxa, topics such as phylogeography and dispersal abilities, historical biogeography and glacial refugia, and ecology and declining populations were studied in detail. Show less
Africa has a large and almost uninterrupted land surface that is isolated from surrounding continents. In the last 20 million years Africa had a variable and increasingly dry climate. As a result... Show moreAfrica has a large and almost uninterrupted land surface that is isolated from surrounding continents. In the last 20 million years Africa had a variable and increasingly dry climate. As a result the Afrotropics have only half as many odonate species as tropical America or Asia. __Relict__ families are scarce and concentrated in five isolated, climatically stable areas: (1) the Cameroon highlands, (2) locally in East Africa, (3) the Cape region, (4) the granitic Seychelles, and especially (5) Madagascar. Most African odonate species, about two-fifths, are restricted to the Central and West African forests. The remainder is found, in three fairly equal parts, in (1) the highlands from Arabia to the Cape, (2) Madagascar and surrounding archipelagos, and (3) open habitats throughout the region. Most mainland species appear related to the relatively diverse fauna of tropical Asia, but have few relatives on Madagascar, suggesting that the modern continental fauna mostly diversified after the arrival of Asian ancestors. Being best adapted to change, Coenagrionidae and Libellulidae are the largest odonate families on Earth. Only in temperate regions, impacted strongly by the ice ages, is their dominance comparable to that in changeable Africa. The climatic influence is further seen in forest species __stranded__ in highlands by forest reduction, savanna species __trapped__ by forest expansion, and overseas colonisation of East Africa by island species. Traditional theory is that speciation took place in habitat fragments created by climatic change, especially in forest refuges, but such refuges seem to conserve old species rather than generate new ones. Abrupt habitat gradients in heterogeneous landscapes may be more important in speciation, especially close to areas where potential ancestors are conserved. The habitat mosaic on the Congo-Zambezi watershed is the best modern example of such an area. Phylogenetic research of various African plants and animals indicate that environmental and dispersal barriers are easily straddled, with savanna species radiating from a forest ancestors and vice versa. Species were eliminated with climatic change, but new ecological space was also constantly created. Such processes must also have lead to the __demise__ of most of Africa__s old odonate diversity and the __rise__ of a rich new fauna. Show less
