Lacustrine mollusc radiations in the Lake Malawi Basin: experiments in a natural laboratory for evolution

Abstract

In terminal Pliocene–early Pleistocene times, part of the Malawi Basin was occupied by paleo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7–2.4 Ma or that of 2.0–1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The modern Lake Malawi malacofauna is depauperate and descends from ubiquistic southeast African taxa and some Malawi basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as paleo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast <i>Lavigeria</i> clade in Lake Tanganyika (ca. 43 species)

Phylogeography of Bellamya (Mollusca: Gastropoda: Viviparidae) snails on different continents: contrasting patterns of diversification in China and East Africa

“…The lake regression created empty ecological niches allowing for a secondary species radiations when the climate became favorable again [25]. The divergence time of the Lake Malawi lineage was dated at around 0.68 Ma, consistent with the refilling of the basin [72] and the radiation of another gastropod Lanistes in the lake [91].…”

Role of ancient lakes in genetic and phenotypic diversification of freshwater snails

“…Based on the phylogenetic relationships of the present study and previous studies, we decided how viviparid species belonged to each clade (Gu et al, ; Sengupta et al, ; Van Bocxlaer et al, ; Zhang et al, ). In the fossil species, we mainly focused on presumably lake endemic species (Japan: Igapaludina in the late Pliocene, and Tulotomoides in the late Pliocene‐early Pleistocene [Matsuoka, ]; Heterogen in the early Pleistocene‐present [Matsuoka & Nakamura, ; Matsuoka, ]; China: Margarya and Macromargarya in the early Oligocene [Ying, Fürsich, & Schneider, ]; Africa: Bellamya in the late Pliocene‐early Pleistocene [Van Damme & Gautier, ]), which inhabited the same/close regions to the distribution areas of extant lake endemic species. In addition, we also used a fossil specimen of H. japonica (0.5 Ma: Matsuoka & Nakamura, ).…”

“…First, we took a photograph of the shell of each specimen obtained from the field and museum (Table S6). For the quantitative evaluation of the entire shell shape, we generated elliptic Fourier descriptors (EFDs; Kuhl & Giardina, 1982) using the same digital images we had taken and obtained images from the figures indicated (Gu et al, 2019;Matsuoka, 1985Matsuoka, , 1986Matsuoka & Nakamura, 1981;Prozorova, Makarenko, & Balan, 2014;Sengupta et al, 2009;Van Bocxlaer et al, 2018;Van Damme & Gautier, 2013;Ying et al, 2013;Zhang et al, 2015). We used adult shells with strongly thickened outer lips.…”

Transcriptome‐based phylogeny of endemic Lake Baikal amphipod species flock: fast speciation accompanied by frequent episodes of positive selection

“…), lakes Tanganyika and Malawi gastropods (Genner et al . ; Van Damme & Gautier ), Lake Tanganyika crabs (Marijnissen et al . ), shrimps (von Rintelen et al .…”

“…The endemic species flocks of cichlid fishes from lakes Tanganyika, Malawi and Victoria in the African Rift valley (Meyer 1993;Allender et al 2003;Kocher 2004;Keller et al 2013;Brawand et al 2014;Fan & Meyer 2014) and of amphipod crustaceans in Lake Baikal in Siberia, Russia (Sherbakov et al 1998;Kamaltynov 1999;Takhteev 2000a, b;MacDonald et al 2005), are among the most species rich and best studied. However, other examples are diverse and abundant (Martens 1997;Cristescu et al 2010) and include Lake Titicaca amphipods (Pyle & Adamowicz 2015) and gastropods (Kroll et al 2012), Lake Ohrid amphipods and gastropods (Albrecht et al 2008;Wysocka et al 2014;Foeller et al 2015), lakes Tanganyika and Malawi gastropods (Genner et al 2007;Van Damme & Gautier 2013), Lake Tanganyika crabs (Marijnissen et al 2006), shrimps (von Rintelen et al 2010) and bivalves (von Rintelen & Glaubrecht 2006) from several lakes in Sulawesi, as well as several species flocks present in Lake Baikal (Sherbakov 1999), such as sponges (Meixner et al 2007), three independent gastropod radiations (Sitnikova 1994(Sitnikova , 2006Hausdorf et al 2003), planarians (Novikova et al 2006) and sculpins (Hunt et al 1997), among others. Several common features have been identified that are shared by ancient lakes species flocks (as well as by similar radiations in terrestrial, often insular, habitats, such as those of Galapagos Darwin's finches, Hawaiian Drosophila, Hawaiian silverswords, Hawaiian honeycreepers or Greater Antilles anoles).…”