Old fossils–young species: evolutionary history of an endemic gastropod assemblage in Lake Malawi

Abstract

Studies on environmental changes provide important insights into modes of speciation, into the (adaptive) reoccupation of ecological niches and into species turnover. Against this background, we here examine the history of the gastropod genus Lanistes in the African Rift Lake Malawi, guided by four general evolutionary scenarios, and compare it with patterns reported from other endemic Malawian rift taxa. Based on an integrated approach using a mitochondrial DNA phylogeny and a trait-specific molecular clock in combination with insights from the fossil record and palaeoenvironmental data, we demonstrate that the accumulation of extant molecular diversity in the endemic group did not start before approximately 600 000 years ago from a single lineage. Fossils of the genus from the Malawi Rift, however, are over one million years older. We argue that severe drops in the lake level of Lake Malawi in the Pleistocene offer a potential explanation for this pattern. Our results also challenge previously established phylogenetic relationships within the genus by revealing parallel evolution and providing evidence that the endemic Lanistes species are not restricted to the lake proper but are present throughout the Malawi Rift.

Constant diversification rates of endemic gastropods in ancient Lake Ohrid: ecosystem resilience likely buffers environmental fluctuations

“…Preliminary data of the SCOPSCO deep-drilling program based on core catcher data for the last 1.2 My and high-resolution data for the last 640 thousand years (ky) so far do not indicate the occurrence of catastrophic environmental events Wagner et al, 2014), i.e., events that lead to sudden drastic regime shifts (sensu Scheffer and Carpenter, 2003;Scheffer et al, 2001) and thus potentially to mass extinction. By comparison, such events have been observed in other ancient lakes, including Lake Titicaca (Kroll et al, 2012;Lavenu, 1992) and Lake Malawi Schultheiß et al, 2009Schultheiß et al, , 2011. We do, however, see signatures of severe environmental/climatic perturbations in Lake Ohrid, including significant lake-level drops (Lindhorst et al, 2010), volcanic ash deposits Wagner et al, 2014), and glacial-interglacial cycles (Lézine et al, 2010;Reed et al, 2010;Wagner et al, 2014).…”

“…Some lakes, despite being old, have gone through a series of major environmental events, and the respective endemic species are often comparable young, as observed in Lake Malawi (e.g., Schultheiß et al, 2009Schultheiß et al, , 2011 and Lake Titicaca (Kroll et al, 2012). Other lakes such as Lake Baikal (e.g., Ivanov et al, 2013) and Lake Tanganyika (e.g., Salzburger et al, 2014; might be sufficiently old but lack a continuous paleo-limnological record.…”

Fifty years after the ‘‘Homage to Santa Rosalia’’: Old and new paradigms on biodiversity in aquatic ecosystems

“…The permanence of water bodies is clearly of great significance in allowing for the continued development of gastropod diversity (e.g., Genner et al, 2007;Schultheiss et al, 2009). The longer an inland aquatic habitat can persist, the greater the chances are for the number of gastropod species to increase by colonization and, possibly by speciation.…”

“…The longer an inland aquatic habitat can persist, the greater the chances are for the number of gastropod species to increase by colonization and, possibly by speciation. The shoreline habitats of several tropical and sub-tropical rivers and lakes are known to have shifted in location in response to extreme climatic changes over millennia (e.g., Cohen et al, 1997Cohen et al, , 2005Curtis et al, 1998;Felton et al, 2007;Genner et al, 2007;Schultheiss et al, 2009). As discussed below, these changes in lake level can create habitats where impacts of different types of invertebrate and vertebrate predators can alter which gastropods dominate the assemblages.…”

“…Prolonged dry periods in generally wet basins are known to have occurred in ancient lakes such as Tanganyika (Cohen et al, 1997), Lake Malawi (Genner et al, 2007;Schultheiss et al, 2009), and the Malili lakes on Sulawesi island (von Rintelen et al, 2004;Glaubrecht & von Rintelen, 2008). In those ecosystems where the water chemistry is enriched in calcium, especially during drier periods when evaporation is high, the diversities of gastropods are likely to be high if they persist over millennia.…”