Adaptive Radiation in Lake Tanganjika

Central part of evolutionary research is the question of speciation. A common phenomena in speciation is the so called “adaptive radiation” which leads to adaptations to previously isolated or newly formed habitats – like islands or fresh-water seas – and annidations (formation of new ecological niches). Well-known and often cited is this for Darwin’s finches on Galapagos or cichlids in eastern African fresh-water seas. In contrast adaptive radiation in invertebrates is less-known, e.g. the species flocks of fresh-water snails in the central lakes on the Indonesian island Sulawesi or in Lake Tanganyika in east-Africa.

Lake Tanganyika is the greatest and deepest rift lake in Africa. This ancient lake is seen as an evolutionary “hot spot” of speciation since the lake had a stable environment for more than 10 million years providing the unique opportunity for diversification and trophic specialization. The gastropod fauna of this lake had been studied and was morphologically and genetically characterized (e.g. Glaubrecht 2008; Wilson et al. 2004).

Tropical specialization by the radula seems to be an important key factor for adaptive radiation in this and in other gastropod species flocks. This organ for food intake and food processing displays an enormously diverse morphology. The disparity of the radulae is interpreted as phylogenetic heritage or as adaptation to environmental parameters. Especially the function of this organ has only been studied in outlines.

By functional analyses the ecological and biomechanical significance of structures can be evaluated. Evolutionary phenomena like trophic specialization in the range of adaptive radiation can be understood as result of a functional context and hence physical laws.

A functional-morphological analysis of the radula provides deeper insights into the evaluation of morphological characters by an ecological characterization of closely-related species. In this project new and innovative methods of the quantitative form-, material- and functional-analyses are applied to tie onto the basic research of radiation and evolution of organisms.

The morphologically and phylogenetically Paludomidae of Lake Tanganyika are an especially good model system, especially in comparison with the less differentiated members of other radiations (e.g. the Pachychilidae in Sulawesi of the Thiaridae in Australian rivers).

Research on these Paludomid snails in Tanganyika allows formulating hypotheses to the mechanisms of speciation, especially to differentiation and specialization and testing them. This provides a fascinating opportunity to check if single branches of a radiation are an answer to food and substrate in the lake. Hence the phylogenetic-systematic value of distinct morphologies can be separated from the functional context.

In line with this project we engage with annidation driven by shell-heights. New methods like geometric morphometrics are applied (masterthesis). First results were presented at the 17^th GfBS-meeting:

Krings, W. & Glaubrecht, M. (2016): Evolutionary organ pipes in full blast: Do snails dance to the Hutchinson tune?

The following Bachelor- and Masterthesis were already conducted:

References:

Strong, E. E.,Glaubrecht, M. (2002). Evidence for convergent evolution of brooding in an unique gastropod from Lake Tanganyika: anatomy and affinity of Tanganyicia rufofilosa (Caenogastropoda, Cerithioidea, Paludomidae). Zoologica Scripta, 31(2), 167-184.
Strong, E. E., Glaubrecht, M. (2003): Anatomy and systematic affinity of Stanleya neritinoides (Smith, 1880), an enigmatic member of the thalassoid gastropod species flock from Lake Tanganyika, East Africa (Cerithioidea: Paludomidae). Acta Zoologica, 84, 249-265.
Wilson, A. B., Glaubrecht, M., Meyer, A. (2004). Ancient lakes as evolutionary reservoirs: evidence from the thalassoid gastropods of Lake Tanganyika. Proceedings of the Royal Society B: Biological Sciences, 271 (1538), 529–536.
Glaubrecht, M., Strong, E. E. (2004). Spermatophores of thalassoid gastropods (Paludomidae) in Lake Tanganyika, East Africa, with a survey of their occurrence in Cerithioidea: functional and phylogenetic implications. Invertebrate Biology, 123(3), 218-236.
Glaubrecht, M., Strong, E. E. (2007). Ancestry to an endemic radiation in Lake Tanganyika? Evolution of the viviparous gastropod Potadomoides Leloup, 1953 in the Congo River system (Cerithioidea, Paludomidae). Biological Journal of the Linnean Society, 92, 367-401.
Strong, E. E., Glaubrecht, M. (2007). The morphology and independent origin of ovoviviparity in Tiphobia and Lavigeria (Caenogastropoda: Cerithioidea: Paludomidae) from Lake Tanganyika. Org Divers Evol, 7, 81–105.
Glaubrecht, M. (2008). Adaptive radiation of thalassoid gastropods in Lake Tanganyika, East Africa: morphology and systematization of a paludomid species flock in an ancient lake. Zool. Reihe, 84, 71–122.
Strong, E. E., Glaubrecht, M. (2008). Anatomy and systematics of the minute syrnolopsine gastropods from Lake Tanganyika (Caenogastropoda, Cerithioidea, Paludomidae). Acta Zoologica, 89, 289-310.
Strong, E. E., Glaubrecht, M. (2010). Anatomy of the Tiphobiini from Lake Tanganyika (Cerithioidea, Paludomidae). Malacologia, 52 (1), 115-153.
Glaubrecht, M. (2010). The enigmatic Cleopatra broecki Putzeys, 1899 of the Congo River system in Africa – re-transfer from Potadomoides Leloup, 1953 (Caenogastropoda, Cerithioidea, Paludomidae). Zoosystematics and Evolution, 86 (2), 283-293.