Sub-fossil Chironomidae from East Africa. 2. Chironominae (Chironomini and Tanytarsini)

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 in 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 considered genera 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. In this paper we focus on the subfamily Chironominae (tribes Chironomini and Tanytarsini). The 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. Given that core samples yielded only seven morphotypes not also found in the surface-sediment samples, the current inventory of 90 taxa likely represents the large majority of distinct sub-fossil chironomid larval types to be found in East African lakes, excluding the few very large Rift lakes, cold-water lakes above treeline, and special standing-water environments such as fens and bogs. Consistent use of a single set of morphological characters to identify both fossil and living chironomid larvae would ensure exchangeability of information between modem and paleoenvironmental studies on aquatic invertebrate communities in African lakes, and increase the relevance of paleoenvironmental reconstructions to water-quality evaluations aimed at sustainable management of scarce, fluctuating surface-water resources in tropical East Africa.