Taxonomic diversity and biogeography of Chironomidae (Insecta: Diptera) in lakes of tropical West Africa using subfossil remains extracted from surface sediments

Abstract

AbstractAim This paper assesses whether chironomid (Insecta: Diptera) faunas of lakes in tropical West Africa and the central Sahara are biogeographically and ecologically sufficiently compatible with those of East African lakes to allow treating them as being derived from a single continent‐wide species pool, and to justify merging regional palaeoenvironmental data sets relating species distributions to abiotic environmental factors and microhabitats into a pan‐African data set.Location Tropical West Africa (Cameroon and Gabon), central Sahara (Chad) and East Africa (Uganda, Kenya, Ethiopia).Methods We employ three main approaches herein. First, we analyse the taxonomic diversity and distribution of larval Chironomidae in 12 regional study lakes using death assemblages of recently buried remains extracted from surface sediments. Secondly, we make taxonomic comparison with a similar analysis conducted in 73 East African lakes, and with checklists of Chironomidae species distribution in Africa. Thirdly, we present descriptions and illustrations of 21 West African morphotypes not previously encountered in surveys of East African Chironomidae based on subfossil larval remains.Results This study involves 84 morphospecies or higher taxa, comprising 17 Tanypodinae, 14 Orthocladiinae, and 53 Chironominae (43 Chironomini; 10 Tanytarsini). As represented in our subfossil collections, the West African chironomid fauna shares at least 59 taxa (or 70.2% of faunal diversity) with the East African fauna, and a literature study also indicates that the majority of West African chironomid species are shared by the drier regions of North, East and Southern Africa. Freshwater lakes in tropical West Africa display a greater average taxon richness and diversity than freshwater lakes in East Africa, partly because Plio‐Pleistocene climate variation in West Africa was more favourable to species survival and accumulation (promoting beta‐diversity), and partly because current climatic and hydrological conditions in the region permit narrow niche differentiation and hence a more complex community structure (promoting alpha‐diversity). Freshwater lakes in East Africa, especially those located in the semi‐arid eastern Rift valleys of Kenya and Ethiopia, experience fluctuating hydrological regimes, which select for species able to tolerate a wide range of environmental conditions.Conclusion Considerable species overlap between the larval chironomid faunas of the West and East African study lakes suggests that palaeoenvironmental calibration data sets from these two regions can be merged.