Sub-fossil Chironomidae from East Africa. 1. Tanypodinae and Orthocladiinae

Abstract

This paper and a companion article present illustrated guides to the identification of sub-fossil chironomid larvae (Insecta: Diptera: Chironomidae) preserved in the sediments of low- and mid-elevation lakes in East Africa. They are based on analysis of surface-sediment death assemblages from 61 lakes located in the humid to semi-arid environments of equatorial East Africa (Uganda, Kenya, Tanzania), supplemented with similar surface-sediment samples from 12 lakes in the Horn of Africa (Ethiopia), and sub-recent core samples from six lakes in Kenya and two in Uganda. We analyzed about 11,000 specimens and identified 98.4% of these to species, species group, genus, or tribe level depending on current α -taxonomic knowledge of the various genera considered and the taxonomic resolution of preserved diagnostic features. We distinguished 90 different sub-fossil morphotypes, of which 16 are Tanypodinae, 19 are Orthocladiinae, and 55 are Chironominae. Diagnostic characters distinguishing these morphotypes from each other resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our morphotypes equivalent to morphological species or groups of closely related species. In this paper we focus on the Tanypodinae and Orthocladiinae, with special attention to the high taxon richness among the Pentaneurini. Patterns of cephalic setation were found to facilitate identification of Tanypodinae both at the genus and species level, and contributed to improved taxonomic resolution in sub-fossil East African material. High taxon richness and numerical abundance of the Orthocladiinae in our study lakes indicates that a considerable number of African Orthocladiinae is adapted to warm standing-water environments.