Lacustrine Mollusc Radiations in the Malawi Basin: Experiments in Alaboratory Natural for Evolution D

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussions Biogeosciences clade in Lake Tanganyika Lavigeria ciently important to trigger a vast radiation. All 18520 18519 ffi ecting the malacofauna of all East African lakes. All lacustrine endemic fau- ff This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. This view is partly applicable even to the unique malacofauna of Lake Tanganyika. The The hypothesis that thethat large their African diversified lakes molluscan arecesses fauna “natural of are laboratories in-lake prime of evolution examples evolution” (Michelrecent of and and et intense fossil al., and malacofauna 1991) of ancientall has Lake pro- actual Malawi become molecular does generally and not accepted. paleontological corroboratecontrary, investigations The this namely provide theory. evidence In that pointing fact, in tomolluscan the Lake in-lake Malawi, divergence as is surprisingly well modest as and in young other geologically past speaking. and present rift lakes, African endemic lacustrine molluscanare clades hence that geologically are young, the(ca. including 43 result species). the of vast in-lake divergence 1 Introduction est. The lacustrine ChiwondoThe fauna Modern went Lake extinct Malawi atEast malacofauna African the taxa is beginning and poor of somethe Malawi and the Basin Late Pleistocene. descends endemics Pleistocene that from invaded mega-droughts. ubiquistic thechanges, The a present South- lake Pleistocene after ariditynas crises that caused had dramatic evolved in theextinct. Pliocene In rift Lake lakes, Tanganyika, such thebut as freshwater the palaeo-lake ecosystem environmental Chiwondo, did changes became were not su crash as in other lakes, In Terminal Pliocene-Early Pleistoceneby times, part palaeo-lake of Chiwondo. the Molluscanther Malawi biostratigraphy in Basin situates the was this East occupied divergent freshwater African evolution lake wet remained phase ei- restricted between 2.7–2.4 to Ma a or few that molluscan of 2.0–1.8 taxa Ma. and In-lake was very mod- Abstract Biogeosciences Discuss., 9, 18519–18544, 2012 www.biogeosciences-discuss.net/9/18519/2012/ doi:10.5194/bgd-9-18519-2012 © Author(s) 2012. CC Attribution 3.0 License. Lacustrine mollusc radiations in the Malawi Basin: experiments in alaboratory natural for evolution D. Van Damme and A. Gautier Paleontological Research Unit, Ghent University, Krijgslaan 281, 9000,Received: Gent, 17 Belgium July 2012 – Accepted: 26Correspondence November to: 2012 D. – Van Published: Damme 18 ([email protected]) December 2012 Published by Copernicus Publications on behalf of the European Geosciences Union. 5 20 25 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 2 (Fig. 1). Melania Sørensen , the num- ff “the dawn of cient sampling in ffi and the rest belonging Nyassomelania and ) have not yet been fully resolved M. tuberculata -complex”, considered to be a poly- or 18522 18521 Ampullariidae ( (Brown, 1994; Darwall et al., 2005), but the number Lanistes Nyassia, Nyassella, Micronyassia ) and Melanoides polymorpha Melanoides endemics is still unresolved. Eldblom and Kristensen (2003) retain ) no such a diversified thalassoid fauna was found, for according 2 ) represented only by the ubiquistic Viviparidae ( Melanoides from speciose 19th century LakeMalawi Nyasa to species-poor 21th century Lake Melanoides Questions on the morphological distinctiveness and the number of the endemic In the middle of the 20th Century, during what Michel et al. (2003) call The present paper is essentially a critical review of the fossil material cited above = Bellamya only 16 gastropods areeight presently considered are to endemic liveof in the the lake sensuthree stricto endemics of only which inogists the speak last of revisionparaphyletic the based group on “ morphology. of Whileet clones molecular al., (Genner 2005). biol- This et led“standard” Michel al., species, et 2004, i.e. al. as (2008) 2007b; defined to according raise Von to a Gersdor question the about Biological their Species equivalence Concept to (BSC). the at the time virtually unexplored lake. Mayrian optimism for the practicalityber of a of single “biological” molluscan species speciesMalawi concept” none in of all the endemic African thiarid lakes genera survived was this taxonomically taxonomic decimated. lumping event In and Lake The comparatively unspectacular molluscswas of known, Lake saddled Nyasa, them(area: as with 29 600 Lake the km Malawi subsidiaryto formerly question Bourguignat why in (1889)This this only author, equally recognizing the about vast Nyasan 40 lake ( thiarid thiarids species, divided did them possess into five the thalassoid genera: endemic characters. genera He believed that the relatively low species richness was due to insu The spectacular thalassoid or marine-like faunagreatly of puzzled Lake Tanganyika (area: 19th 32 900 Century km scientists and led to heated debate as to their origin. 3 The evolution of taxonomic concepts about the Modern Malawi malacofauna: (2010). and the publishedthe literature light on of themolluscs modern our of vastly and the improved fossil Africanlake knowledge Lake Great basins. The Lakes on Malawi published and malacofauna phylogeny literature offossil in in and which the molluscs provisional palaeontology palaeolimnological or species evolution of lists partIt of of the of the these includes them Chiwondo Pain are inVan provided Damme Coryndon is (1984, (1966), quite 1988),Gorthner Gautier extensive Van et Damme and in al. and widely (1992), Clark Schrenk Pickford scattered. et (1999, et al. 2003), (1995), al. Schultheiß Gorthner (1966), et (1994), al. Gautier (2009) and (1970), Van Bocxlaer taxonomy of the Desmondlished manuscript, Clark 1975) collection and was taxonomyGorthner and studied (unpublished biostratigraphy manuscript, by of 1995). the GautierPaleontological HCRP-collection Copies (Gautier, Research by of Unit unpub- both Ghent manuscripts as are part kept of at the the collection. This study isluscs based collected in on the Chiwondo the region1960’ths collections (NW during margin of the of Lake Desmond Terminal Malawi),1990’ths Clark respectively Pliocene/Early during Palaeo-Antropological in the Investigation Pleistocene the and Hominid mol- inFriedemann Corridor 1980– Schrenk. Research Project Albrecht led Gorthner,Holocene by assemblages the Timothy near HCRP Bromage the and malacologist,was Shire recently also River continued sampled outlet (Van the fossil and Bocxlaer, material this 2004; preliminary collected Van Bocxlaer investigation inlogical et the Research al., Malawi Unit, 2012). Basin Ghent All is University, relevant awaiting provisionally formal stored taxonomic at description. the The Paleonto- increasing climate destabilisation in East Africa since the Late Pliocene. 2 The fossil record present study links the late origin of the malacofaunas of the present Rift lakes to the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | natural L. nasutus or wide as in , can only partially L. nasutus Melanoides 4 to ca. 3.75 Ma). Lacustrine limestone and 5 to ca. 4.0 Ma). Exclusively fluvial deposits, ≥ > 18524 18523 (Fig. 2), possessing morphological adaptations lineages endemic to lake Malawi are not the result Malawi gastropod classification is in a continuing state ” is still painfully actual. Certain is that the recent genetic erent times, is considered a possible scenario in view of their ff ”. The largest Malawi group, that of Bellamya ecclesi ). At the top of the unit the facies changes to littoral marlstones Melanoides and Bellamya . Such morphological features increase buoyancy and permit the extension lake – Chiwondo Beds, Unit 1 (time range: – Chiwondo beds, Unit 2 (time range: According to the authors cited, five limnological stages can be discerned in the Chi- Diversification is not spectacular and hence niche partitioning and occupation are Dudley’s (2000) remark that “ shells. silt- to sandstone deposits formedpod in fossils littoral ( and margin environmentswith with abundant rare gastropods gastro- and rareconsolidated bivalves. shell The beds molluscan cropping assemblages out areand as found extending benches in over with several a hundred thicknesscoarse meters up sandstone (Schrenk to is et several meters poor al., 1995). withmarl- Preservation inner and in casts limestones the and fossilization partly is dissolved slightly outer casts. better, In consisting the of rare recrystallized calcitic on stratigraphic correlations with nearby exposures yielding mammals. wondo region ranging from Terminal Miocene to Late Pleistocene times: no molluscs. 4 The palaeontological data reviewed: the end of Lake Malawi asThe an palaeolimnological, ancient pre-Holoceneand evidence localized. in Plio-Pleistocene deposits, the describedBeds, as Malawi the are Basin Chiwondo exposed and is at theFor Chitimwe the fragmentary detailed NW stratigraphic fringe information of(2008). we Lake Age refer Malawi estimates to nearfossils its Sandrock are are satellite et found based lake at al. on the Chiwondo. (2007) mollusc suid and bearing sites, biochronostratigraphy. Kullmer their Since age was no based, mammal as well as possible, of a large foot,tures adaptions are mentioned for in life(Mandahl-Barth, literature in 1972; except or Berthold, for 1990). on strongly elongated fluid tentacles sediment. in No special anatomical fea- B. ecclesi and width of the animal, either being strongly elongated as in neither. Most Malawisubstrate species (above are 20 m) restrictedand and to 80 only m. the But a at few shallowLanistes such nasutus are depths littoral found their zone in occurrencefor is with the life sporadical deep sandy and at sublittoral the greatertions only between depths, (Brown, two 40 are 1994). species, The represented specificsistence by shells of a adaptations essentially in few neotenous both rare traits, speciesinflated namely and consist body a whorl of highly thin, and the rapidly localized a per- growing mouth popula- shell, aperture a that strongly is very large compared to the total length research on Lakeof Malawi “spectacular” molluscs species does diversification/radiationlaboratory not in of this evolution lend supposedly support long-livedresult to “ from an the in-lake radiation ingrained anddiversified. the concept two other “clades” are small and genetically little are going onbility in that the the viviparid clonal of flock an (Schultheiß in-lake et radiationnized Lake either, al., Malawi but 2011). at that di Inpara/polyphyly they (Genner addition, et are al., the allopatric 2007b). palaeo-endemics possi- that colo- of revision and that itfor will the be groups some of time higher before a rank system comes to be generally agreed considered to have diverged withinclusively the of in-lake lake, endemics, revealed as that wasstricto both formerly plus groups assumed, one consist or but two of not paludal/fluvial in-lakei.e. ex- species endemics basin endemic sensu to endemics the (Sengupta whole etMalawi of species the al., groups Malawi 2009; are Basin, monophyletic, Schultheiß young et and the al., speciation 2009, processes still 2011). likely Both these either. Recent molecular investigations of these two other prosobranch “species flocks”, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Bel- Buli- (2–3 (1 sp.; ) (Graf ), Union- Corbicula ) widespread (1 sp.; and (Fig. 2.), which Gabbiella appears for the Thiaridae Corbicula ), Bellamy, Gabbiella, Lanistes, Gabbiella, cult to accept, not pri- ) and ffi (2 sp.; Bellamya . In the two other basins Corbicula is dominant, all others are Pseudobovaria Viviparidae ” auctores) is represented by Pseudobovaria 20 ka). Deposits of eolian sands , the morphological divergence Chambardia nyassaensis ), Etheriidae > Melanoides (4 sp.; ), . All appear to have been formed in the B. capillata Pseudobovaria (1 sp.; Unionidae Melanoides . The presence of fossils of this Asian clam Bellamya 18526 18525 Bellamya capillata Bellamya Etheria ), erences suggest a para- or polyphyletic origin of (2 sp.; 20 ka). Alluvial fan deposits indicate a phase of ff ), Paludomidae ≤ date of 2.6–2.5 Ma for African assemblages. Well- Corbicula , resembling the Modern Lake Victoria endemic and (3) (1 sp.; Iridinidae erences between Terminal Pliocene-Early Pleistocene and Coelatura ff for the likeness with the Modern Lake Mweru species, (2) a Ampullariidae ), -group. That these Chiwondo lacustrine endemics are ancestral trochlearis (1 sp.; cf. Cleopatra , which is morphologically quite similar to the present day Lake Malawi B. ), Bellamya but smaller. The unornamented ). Many assemblages are species poor with mainly or monospecific with only terminus ante quem Planorbidae pagodiformis (2–3 species; cf. Chambardia robertsoni (1 sp.; ), Bithyniidae cf. That the Chiwondo malacofauna dates from the Early Pliocene, that is from 4–3.8 Ma Generally the Chiwondo littoral malacofauna is surprisingly similar in diversity and Most Chiwondo species, i.e. those belonging to the genera A marked diversification can be observed only in the genus – Chitimwe Beds (time range: The known Chiwondo malacofauna comprises species belonging to the genera – Chiwondo Beds, Unit 3 (time range: ca. 3.75 to 2.0 Ma for Subunit 3A and ca. 2.0 – Chiwondo Beds, Unit 4 (time range: ca. 1.5 Ma to calibrated evidence comes from the Turkana Basin where in the Chiwondo assemblagesmentioned, is Pliocene fauna the elements unionid remain dominant1.2 Ma until (see the period further). ca. 1.8 Ma to ca. as proposed by Sandrock et al.marily (2007) because and that Kullmer would (2008), ismillions infer di that of the years Malawi earlier faunapresence had than of reached those the its of Asiatic modernprovides bivalve other aspect a East African basins, but because of the Holocene-Modern faunas in palaeo-lakes ofsafe the to Turkana and conclude the that Albertine duringconsist basins. Late for It Pliocene an is times important the partin Chiwondo of the lake the fauna present same did lake ubiquisticwas already and and in basin that many endemic the aspects taxa already composition occurring “modern”. of The the only Late “ancient” Pliocene taxon faunal present, community be it rare, and salinity peaks duringPleistocene the Pleistocene events). (see As palaeoenvironmental toand reconstruction a dwarfism of continuity observed in in wondo the assemblages, Modern where Malawi the representatives taxondistinct is is correlations not represented to found by the in two Modern the large clade Chi- sized (see forms also with further). no composition to the Early-Middle Holoceneparison fauna (Van to Boxclaer, 2004), the at marked least di in com- B. B. robertsoni relatively rare. The morphological di the Chiwondo to the present ones is highly unlikely, considering the evidence for intermittent aridity carinated form, lamya Melanoides, Bulinus, Coelatura, Pseudobovaria,are Chambardia, morphologically similar Etheria to species thatin are East or Africa were or (i.e. are endemicand to Cummings, the 2007) Malawi and Basin do (e.g. not show lacustrine adaptations. apart from an unornamented(1) morph a (“ form with sloping,published flattened manuscript, whorls and 1968) a and basal carina, cited described in by Van Gautier (un- Damme and Pickford (1999) as nus idae Corbiculidae Melanoides littoral storm wave zone and the higher part of the littoral. indicate periods of marked aridity but(no a molluscs). brief lacustrine transgressive phase is recorded lacustrine regression. Holocene lacustrineMalawi region. deposits are not present in theLanistes NW Lake sp.; to ca. 1.5 Ma forunit, Subunit 3b separated on from the the basisreturn earlier of of suid deposits deltaic/fluvial biochronostratigraphy). by The conditions.2.3–2.0 an overlying Ma Pronounced and unconformity, 1.6–1.5 lake is Ma. regressions characterized No molluscan took by assemblages. the place between 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , ) 1 − Etheria morph is Bellamya Corbicula Ar analytical (Fig. 2) does ) and 39 Ar/ 40 robertsoni Iridinidae robertsoni ( cf. B. Pleiodon and (Van Damme and Pickford, 2010). The ) and equally sensitive bivalves such as Complex in the Hadar Formation are dated at Mutela 18528 18527 ff still present but dwarfed (Van Damme, 1976; ), without freshwater prosobranchs or bivalves and and Plio-Pleistocene 1 − Pseudobovaria Paludomidae ( date based on the molluscs is 1.5 to 1.2 Ma, i.e. the last Gabbiella Unionidae erences among the assemblages, be considered as being ( 0.06 Ma (Feibel et al., 1989; McDougall and Brown, 2008). ff ± erent basins during the time segment. Palaeo-lake Chiwondo and ff Cleopatra from the Kada Me’e Tu Nyassunio Bellamya robertsoni ) and ) could survive these intermittent aridity/hyper-aridity peaks in the restricted and Melanoides , dated to 2.68 ff terminus post quem Corbicula The chances that populations of oligohaline taxa such as the gastropod From Pleistocene times only a single, brief high lake level stand of unknown age, As in other parts of East Africa, periods of increasingly aridification and climatic in- The Viviparidae Etheriidae ( Coelatura ( and endorheic Malawi Basin, i.e. priorRiver Shire, to were the nil. connection These with groups theronmental must Zambezi conditions have Basin improved re-invaded in the via the Malawi the Basin, Latetween when Pleistocene. Modern envi- The morphological likeness be- therefore not imply direct parentage, in particular since the Modern fluctuated between a Lake Baringo–Lakeity Naivasha in type excess of of lake,a 4000–4500 µScm i.e. Lake with Turkana–Lake a Langano conductiv- with type only with aBrown, conductivity 1994). around 2200–2300 µScm younger than 1.5 Ma, and withoutmay fossils possibly is recorded fall (Sandrock within et the al.,sition, late 2007). situated This Early at event Pleistocene 1.1 periodevents. to The of 0.9 absence Ma major of by global macrofossils Thraut climaticsation, may et tran- be but al. due more to (2007), likely unfavourable or indicatesalkalinity). conditions the it for For absence results fossili- the of from macroscopic local wholeMalawi life Basin climatic of is (hyper-salinity/hyper- hence the missing. The Pleistocene, lacustrine information ecosystem during about that molluscan epoch must life have in the treme periods of ariditythe during freshwater the lacustrine ecosystem Late hasciplinary Pleistocene been study and reconstructed of the in Malawi dramatic detail lakeperiod degradation via between cores 135 of the (Cohen to multidis- et 90 al.,tic ka, 2007). when and the saline, Hyper-aridity strongly surrounded is constricted by noted semi-desert. lake in was the shallow, holomic- Pleistocene (Sandrock et al., 2007). The intermittent occurrence of discrete but ex- sands equally indicate phases of hyper-aridity during the rest of the Early and Middle same period as palaeo-lake Lorenyangterminal (ca. stages 2.0–1.8 Ma) of in both(Van the Damme aforementioned Turkana and lakes Basin Van Bocxlaer, in and 2009; the Van thean Damme equally Albertine and Pickford, wide Basin 2010), spread present (ca. East during the 2.0–1.8 African Pliocene Ma) wet fauna-elements phase in the (Traut et two al., basins 2010). were In disappearing the also. stability latter are recorded period in the Malawiextremely Basin low throughout lake the whole levels Pleistocene betweenPleistocene period 2.3–2.0 times, with Ma and in between Unit 1.6–1.5 Ma 3b during of Lower the Chiwondo Beds. In the overlying Unit 4, eolian (Van Damme and Pickford, 2003,connections 2010) among indicate di a significantmay hence increase have of existed hydrological synchronously withTurkana palaeo-lake Basin Lokeridede and (ca. with 2.5 Ma) the of(ca. earlier the 2.5 stages Ma) of of palaeo-lake the Kaiso Albertine and Basin. palaeo-lake An Lusso alternative possibility is that it existed during the records of the extinctage unionid of all molluscanmarked Chiwondo morphologically assemblages di should, consideringbroadly the similar, hence absence deposited of either any the around 2.7–2.4 2.5 Ma Ma or interval around appearshistory 1.9 to Ma. of In be the East a Ethiopian, Africa 2010; major Kenyan Tiercelin lake and et period Tanzanian al., rift suggestedsynchronously 2010). by basins in Important the (Trauth the et Turkana incursions moisture Basin al., of (Van Bocxlaer 2005, invasive et species 2007, al., 2008) (e.g. and the Albertine Basin Burgi Tu Fossil ca. 3.4 Ma, but thisdata in and an considered as estimate unreliable obtained (Campisano, by 2007; interpolation Campisano of and Feibel, six 2008). first time in deposits of the short-lived palaeo-lake Lokeridede directly overlying the 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , was Lanistes Chambardia -group should Melanoides Gabbiella stanleyi ) and ) tolerate relatively , , the case is more com- erent from that of the other , or significant increases in ff M. polymorpha Bithyniidae ( Ampullariidae ( Melanoides Lanistes ellipticus species-group, occurring in the south- Gabbiella Lanistes 18530 18529 ) and M. anomala - Chambardia nyassaensis , a Modern Lake Malawi endemic, by Gautier (unpub- may derive from basin endemics already present during , also were gone after ca. 1.3 to 1.2 Ma. Thiaridae ( M. mweruensis polymorpha - Melanoides cf. M. Gabbiella stanleyi ) are able to aestivate during extended dry periods (Van Damme, 1984). Chambardia nyassaensis M. polymorpha and major evolutionary radiations in the molluscs of the African Rift lakes? The palaeo-environmental data for the Malawi Basin we possess, indicate the in- In all larger East African basins, where according to the fossil evidence an en- After that period, possibly from ca. 1.8 Ma and definitely after 1.5 Ma, the old Pliocene For the modern representatives of the genus Taxa such as Iridinidae trine endemics and many basin endemics appear to have become extinct during the stauration of hyper-arid phases possiblychronostratigraphy of already Sandrock from et about al. 2.3Malawi Ma, (2007) Basin if is all the followed. It mammalian molluscanand can lake that be endemics most assumed of must that the have inextended basin the become endemics, periods possibly extinct of except prior those aridity,salinity, with to e.g. e.g. adaptations 1.8 to Ma survive demic lake fauna developed during Late Miocene-Pliocene times, all Pliocene lacus- by an impoverished eurytopicand fauna Pickford, of 1999, the 2003, “Nilotic”elements 2010). type In are around the definitely 1.8 Turkana Ma gonearound Basin (Van ca. virtually after Damme 1.4 all Ma ca. at old 1.32008). the Pliocene base to basin of 1.2 Member Ma, L, i.e. Shungura Formation after (Van Bocxlaer the et brief al., lake interval ing Late Pliocene times. Itready contained a lacustrine distinct endemics south-eastern and Africanbasins definitely mentioned. character, possessed The clearly age al- di of thisis palaeo-lake not Chiwondo fauna older is than uncertain.wet It 2.7–2.6 Ma phase certainly at but 2.0–1.9 it Ma. could be younger, i.e.malacofauna dating in from the the East Turkanation. and African In Albertine the basins Albertine shows Basin signs the of Mio-Pliocene a Congolian severe faunal deteriora- elements are replaced The reconstruction of thetary, malacological history shows of that theTurkana as Malawi and Basin, in Lake though Albert the fragmen- Basin, two a diversified other lacustrine East fauna existed African in the basins basin with dur- a fossil record, Lake 5 Is the Pleistocene climatic destabilization responsible for major extinctions to provide a specific attribution.the Presently it seems besteastern to African consider region (Van them Bocxlaer, to 2010).the belong Using molecular these to clock Chiwondo in fossils calculatingbe to the avoided calibrate (Genner age et of al., the 2007b). Modern scended from populations already present inet the al., basin during 2007b) Chiwondo cannot timesidentified be (Genner as ascertained. The dominantlished fossil manuscript, Chiwondo 1968), cited(2003), in but this Van identification Damme is incorrect. (1984) The and Chiwondo shells Van are Damme too poorly and preserved Pickford representatives in the basin or inand the lake such as Chiwondo times. However, theindicates molecular that evidence the concerning formationet the of al., 2009). this Malawi group is young (Middle Pleistocene?)plex. (Schultheiß They are notoriginated yet during present Pleistocene times in in Chiwondo the times saline and lakes, but may that be these dwarfed morphs morphs are that de- Van Bocxlaer and Van Damme, 2009). high salinity concentrations and taxa such( as Populations of these taxa may have survived the Pleistocene salinity crises and Modern not yet clearly discernible in the Late Holocene Malawi deposits (Van Bocxlaer, 2004; 5 5 25 15 20 10 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Lav- and oth- , that be- catfish and Lavigeria Neothauma clade of Lake Malawi, Synodontis radiation certainly is the . The lacustrine ecosystem Lanistes in Lake Rukwa, when this lake Lavigeria is still an ongoing process. On-going Lavigeria 18532 18531 Lavigeria may be quite young. ” stable systems but which are, viewed on a geological time Lavigeria seemingly “have regularly proved to be remarkably old” , the latest estimate of this clade being ca. 43 species (Ngereza, 2010). This In all East African lakes the current molluscan radiations are recent events, post- Convincing arguments that abiotic changes did have a severe impact on Lake Tan- We fail to see why the lacustrine malacofaunas in the Lake Malawi Basin should In their study on the evolution of the modern endemic same time-segment as the extinction-events in the other lakes. That the genus is an dating the Plio-Pleistocene aridityinvolved crises. in the Lake modest Tanganyika Modern excepted,ing radiation the older events populations belong Pliocene to in-lake lineages Pleistoceneenvironmental that invaders stress replac- went triggered extinct. In a Lakeigeria spectacular Tanganyika the radiation increased but only inmarked a radiation single in taxon, Lakeavailable Tanganyika due may to also the indicate extinctionresult that of of much other an ecospace in-lake groups. became process, The but the onset of this divergence-event probably falls in the 1992), must also dateThe from quite Late impressive Pliocene Holocenewas or radiation joined Early of with Pleistocene Lakethe times Tanganyika evolutionary at (Cox, divergence the process 1939; in earliest. divergence Cohen is et also al., suggested for 2010) the may plathytelphusid crabs indicate (Marijnissen that et al., 2008). ganyika’s fauna have recently beenmolluscivorous found by plathytelphusid molecular crabs, phylogenetic limnochromine research,mastacembelid cichlids, e.g. eels. on The studiesologically indicate recent that events the (Late radiationsMarijnissen Pliocene-Early in et these al., Pleistocene; groups 2006, Cumberlidgeet are 2008; al., et ge- Duftner 2010). al., Since et speaking 1999; al.,evolved in 2005; only geological Day terms, recently, and the the specializeders, Wilkinson, onset molluscivorous considered 2006; crabs of to Brown result the from radiation an in arms-race between the crabs thalassoid and their prey (West et al., acted as a refugecame for extinct a in number the ofThe Albertine taxa, molluscan Basin e.g. in-lake the around diversification viviparid 1.8 processespaludomid Ma genus observed tribes (Van in such Damme some as and of Pickford, the 1999). Tanganyikan McGlue et al., 2008), the Tanganyikan freshwater system did not crash, and the lake Pleistocene (ca. 435 m level drop during the Early Late Pleistocene mega-drought, be given this specialdepth status. and The size, data all advanced Africancrashed in freshwater systems, this during that paper in the indicate theextinct. Pleistocene that Lake The Malawi regardless and Basin only included, that exceptionmalacofauna their survived is in endemic Lake that lake, Tanganyika. intra-lacustrine there However,luscan are faunas while radiations no went in indications part that it of the areendemics, intra-lacustrine the remarkably not mol- neo-endemics, old. Pliocene as Most shown Tanganyikan2003, mollusc by paleontological taxa 2010), (Van are Damme molecular palaeo- andevidence. (Wilson Pickford, Though et significant al., lake 2004) level drops and did morphological occur (Glaubrecht, during the 2008) Late Pliocene and the Lake Tanganyika ecosystem characterizedting. by long-term The stability authors of claim theor that abiotic Lake the Baikal set- endemic radiationsin within the lakes Malawi like Basin is Lake considered Tanganyika by them as an intermediate. in molluscs to alltems large based on African the lakes. criteriondetermined They that by discern tempo the three and mode degree typesend of they of of molluscan place lacustrine ecosystem evolution “ are ecosys- stabilityscale, primarily instable on and a intermittently cease geological toan exist time example, as scale. they large standing cite At freshwatertype Lake bodies. one of As Victoria, lake that radiation driedthere events out may is in be no Late triggered continuity in Pleistocene during the times. renewed molluscan freshwater In lineages phases such involved. but On the other end they place and Ethiopian rift, fossil molluscknown, assemblages but from intense Pliocene level freshwater fluctuations,short lakes are endorheism lived also incursions and of volcanic eurytopic activity species only and permitted no evolutionSchultheiß (Van Damme, et 1984). al. (2009) extend the debate concerning possible evolutionary patterns hyper-arid Early Pleistocene times. In all smaller basins such as those in the Gregory 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and Pota- . Ampullari- Lavigeria Chambardia nyassaen- Lanistes, Gabbiella and species flock. A new model to un- ` ese and Teugels, 2001), Mbuna and (Agn 18534 18533 Gabbiella stanleyi Bathyclarias-Clarias Clariidae , Bathyclarias The first author likes to thank Christian Albrecht, Department of Animal . In the palaeo-lake that formed subsequently in this basin during an East ) occurs in the Malagarasi and Luapula (Brown, 1994) and an invasion or (Mollusca, Gastropoda) endemic to Lake Malawi, Africa, Abhandlungen des Naturwis- cient to cause the freshwater ecosystem to crash, but it nevertheless altered the ` ese, J. F. and Teugels, G. G.: The . The fact that in Modern Lake Malawi the colonization of the lacustrine environment ffi idae senschaftlichen Vereins Hamburg, 31/32, 85–118, 1990. derstand rapid speciation in African great lakes, C. R.distributions? Acad. The Sci. Nyanza III, Project 324, 2003, 683–688, Annual 2001. Report, University of Arizona, 2003. The Terminal Pliocene-Early Pleistocene aridity crises had continent-wide impact on Berthold, T.: Phylogenetic relationships, adaptations and biogeographic origin of the Barrett, M., Bishobibiri, A., and Catron, J.: Why do Lake Tanganyika gastropods have patchy Agn References i.e. late Early Pleistocenethis at the coincides beginning with of aAfrica the time Calabrian (Trauth et of Stage, al., major isLate 2005, proposed, molluscan Pleistocene since 2007, extinctions date is 2010). and also A consistent extremeof with late aridity Modern molecular Early clock Lake in divergence Malawi Pleistocene time East molluscs estimates orModern (Genner Lake even et al., Malawi a 2007b; Middle Schultheißnon-Mbuna to et cichlids al., (Won 2009, et 2011), al.,gadi 2005, and in 2006) Modern and L. of Victoria cichlids (Genner in etAcknowledgements. palaeo-lake al., Makgadik- 2007a). Ecology and Systematics, Justushis Liebig patience University, for and invitingare him support. thanked to The for write two their thisResearch anonymous constructive article Unit Paleontoloy, comments. referees and Ghent University Both for and for authors financial the wish and editor, logistic to Roland support. thanks Schultheiß, Jacques Verniers, phylogeny instead of estimates of thein age any suggested for given the rift earliestgency formation basin. estimates of This a for lake proposal severalsome Tanganyikan is non-molluscan of consistent groups these with estimates (see recentGelasian place higher), Stage, molecular this i.e. though between event clock ca. around 3–2 diver- Ma. the Here very a slightly onset younger of age of the ca. Pleistocene 1.8–1.6 Ma, or used as a reference point in calibrating molecular clocks for African freshwater mollusc the African malacofauna and thisas geological well abrupt as event radiations. did initiate Therefore major we extinctions propose that the beginning of the Pleistocene is regardless of their size andthat depth. seems The only to exception have appearscofauna acted to primarily during be Lake as Pleistocene Tanganyika, a mega-droughtsApparently refugium and in for not part Lake as Tanganyika ofsu the the a Pleistocene older center Pliocene climatological of mala- limnological destabilization in-lake environment was so evolution. in- drastically thate.g. spectacular in divergence plathythelphusid processes crabs started, and in one thallasoid molluscan taxon, sis remains mainly restricted to sandynow, bottoms during of the the upper present epilimnionniches freshwater suggests is that optimum, suboptimal. even The exploitation cycleluscs of of seems the extinction to and available have incipient space been radiation the and in norm the in Malawi the mol- African rift lakes since Late Pliocene times 6 Conclusions The available data indicate thatbasin probably endemism already had during developed Late in Pliocene theChambardia times Malawi malacofauna, a in marked African Late Pliocene wetbut phase, ended intra-lacustrine abruptly divergence due processes torect were increasing relation initiated aridity with crises. the Theresistant Late species, Modern such Pliocene lake as, one, fauna respectively has possibly no except di- for some salinity or drought domoides multiple invasions could havePleistocene occurred times. during transgressive periods throughout Plio- ancient occupant of the lake is not even certain since a closely related taxon ( 5 5 25 20 10 15 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) in Thiaridae (Gastropoda: doi:10.1186/1471-2148-10- catfish species flock from Lake Melanoides Synodontis 18536 18535 ´ e, J.-C.: The status and distribution of freshwater biodi- ´ erie in-8o. 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S.: Gradual versus punctuated equilibrium Van Bocxlaer, B. and Van Damme, D.: Illuminating the black box of punctuated equilibrium Van Bocxlaer, B.: Palaeobiology and evolution of the late Cenozoic freshwater molluscs of the Van Bocxlaer, B.: Morfologische veranderingen in de malacofauna van het Malawimeer 5 5 10 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | er ge- ff , but more Cl. smithi/Cl. , equally found in er genetically and Valvata ff , widespread in the Congo tuberculata M. pergracilis L. ellipticus by Van Damme and Pickford (2004) C. briarti . Present in Holocene deposits by Eldblom and Kristensen (2003) Bgt, a basin endemic, has preference nodicincta cf. species, related to the above. Lake endemic? C. hypsiprymna M. nodicincta M. Ancey, a basin endemic, hence has preference. does presently not occur anymore in the Malawi Basin Bellamya simonsi Assiminaeidae , resembling Modern Gabbiella Etheria group from Zambia. Genus presently absent in the Malawi Basin. Coelatura Lanistes ingens 18542 18541 likely belonging to the Remarks Basin the L. Turkana and Albert Basin, where it is restricted to Early Pleistocene strata. mweruensis Remarks netically and the name the name Modern Lake Malawi Modern Lake Malawi X Modern lake endemic, absent in Early Holocene L. Malawi deposits –––X X X X – Lake endemic very– close to Basin endemic, alsoX in Modern Widespread L. south-eastern Malombe African and– species in Probably Holocene identical L. to Malawi– the deposits Modern species XX X X XX Widespread Ranging from L. – Rukwa– (Tanganyikan Basin) Widespread to L.– Malombe (Malawi In Basin) L. Malawi, Shire X R., L. Malombe and in Malagarasi R. The (Tanganyikan Basin) river oyster X X Widespread Oriental species Widespread Widespread Lake Chiwondo –––– X X– X X Clonal– dwarfed form, endemic to Clonal L.– dwarfed Malawi form, endemic to Clonal L.– dwarfed Malawi form, X endemic to Considered L.– distinctive Malawi from X X– X– Widespread pulmonate X– X – Ubiquistic. S. America genus that X Widespread invaded Africa probably in X Widespread Pleistocene times X Widespread Species-level identification requires anatomical characters Modern Lake Malawi endemic, also Modern present Lake in Malawi Early endemic Holocene Widespread deposits – X Invasive Oriental species in Modern L. Malawi (Eldblom and Kristensen, 2003) X – Extinct genus en species represented by the subsp. ––– X X X Clonal dwarfed form, endemic to Clonal L. dwarfed Malawi form, endemic to Modern L. Lake Malawi Malawi endemic. Extremely polymorphic species X–?–– X X– –X X Basin X endemic, not found in Lake the Malawi lake endemic proper (?) nearly Only indistinct a from X few badly preserved Modern specimens Lake – possibly Malawi belong endemic, to not Modern this found Lake in species Malawi Early deep Holocene water deposits species, only known from a dozen Mainly specimens in vegetation in Lake Morphological Malawi identical shallows, to probably Modern basin species, endemic probably basinX endemic ––X X X XX – Widespread Oriental species Clone, endemic to Modern L. Clone, Malawi endemic to Modern – L. Very Malawi slender form, ca. twice the size of Modern Erroneously mentioned as Lake Chiwondo –X–X XX – X – Modern lake endemic, absent – in Early Holocene L. Malawi Lake deposits endemic. Morphological convergence with Modern Modern lake species endemic from known L. only Lake Malawi from endemic. deeper Morphological water convergence in with Lake southern Modern endemic. L. species Morphological Malawi from convergence L. with Mweru Modern species from L. Victoria Brown X X Wide spread SE-African species, but Modern Malawi Basin populations di Brown X X Widespread in Africa but Modern Malawi Basin populations di eri ff polymorpha pergracilis mossambicensis stanley reysi robertsoni pagodiformis trochlearis cf. cf. solidus ff globosus cf. sp. X – Very large sp. X – Basin endemic with modest carinae, probably belonging to the cf. sp. X – Exceptionally large cf. cf. cf. sp. X – Costulate ovate species, identified by Van Damme (1976) as cf. cf. Continued. Freshwater molluscs from Terminal Pliocene-Early Pleistocene Palaeo-Lake Chiwondo Valvata Coelatura Pseudobovaria mawayana tuberculata Lanistes ellipticus Lanistes Lanistes solidus Lanistes nyassanus Lanistes nasutus Gabbiella BIVALVIA Unionidae Nyassunio nyassaensis Coelatura hypsiprymna Coelatura mossambicensis Coelatura Iridinidae Aspatharia subreniformis Chambardia nyassaensis Chambardia wahlbergi Mutela alata Etheriidae Etheria elliptica Corbiculidae Corbicula fluminalis Sphaeriidae Pisidium pirothi Pisidium reticulatum TaxonMelanoides nyassana Melanoides truncatelliformis Melanoides magnifica Melanoides simonsi Lymnaeidae Lymnaea natalensis Palaeo- Planorbidae Biomphalaria pfei Ceratophallus natalensis Gyraulus costulatus Bulinus globosus Bulinus Bulinus nyassanus Bulinus succinoides Bulinus forskalii Melanoides virgulata Melanoides pupiformis Melanoides turritispira Melanoides polymorpha Melanoides Bithyniidae Gabbiella stanley Gabbiella ?Valvatidae ? Paludomidae Cleopatra Thiaridae Melanoides tuberculata Melanoides nodicincta Melanoides pergracilis Melanoides TaxonGASTROPODA Viviparidae Bellamya capillata fide Palaeo- Ampullariidae Lanistes ovum fide Bellamya je Bellamya robertsoni Bellamya Bellamya ecclesi Bellamya Bellamya Table 1. Table 1. and Modern Lake Malawi. Taxonomyand and Graf range and of Cummings Modern (2007) species except according when to mentioned Brown otherwise. (1994)

Micronyassia epresentatives epresentatives of the ﬃ B. je R

Nyassia ma (4)

Two gro -

(5) trochlearis 1

, and : to be parthenogenetic clones cf cf

pagodiformis B. cf. he second group, consisting of consisting group, second he (2) (2) the the Malawi basin B.

). Melanoides Melanoides truncatelliformis (1) Micronyassia Micronyassia singularis Lake Lake Malawi in present Lake Malawi.

- s Melanoides polymorpha (e.g., (e.g., 4 lakes of c to

Bellamya ecclesi cially” considered as distinct endemic occur and ome ome pagodiformis , ﬃ (4) by by molecular research

. . S endemi ) that evolved in lakes of the Malawi Basin

. cf. (Scale bar: 10mm bar: (Scale

B evolved evolved in shown

(1) robertsoni

18544 18543 complex’ that that - species B.

) are still “o o during Late Pliocene times. T times. Pliocene Late during o Nyassomelania truncatelliformis

. splitting splitting in Modern Lake Malawi molluscs. Viviparidae - a a truncatelliformis (3) have have been ; , lived in palaeo-lake Chiwondo during Late Pliocene-Early and and (6) endemic ke Chiwond ke species ( la - eo ted ted by Bourguignat (1889), robertsoni Nyassomelani a

B. B. jeffreysi - (Scale bar: 10mm) bar: (Scale species species (Viviparidae)

cf.

Melanoides Melanoides polymorpha (5) (5) ; ‘

Bellamya B. , he he first group, consisting of ra Nyassella pulchra h , occurs in present Lake Malawi. Both groups are not directly a (3) genera genera crea lived in pal lived considered as distinct as considered (2)

Bellamya aptions aptions , ecclesi Example Example of partly repeated convergent evolution in the Malawi Basin. ’ Example Example of taxonomic hyper ;

Melanoides truncatelliformis la la pulc l , and . All ca. 40 thiarid species recognized by Bourguignat have been shown by molecular thiarid nging nging to the

Example of partly repeated convergent evolution in the Malawi Basin. Two groups of Example of taxonomic hyper-splitting in Modern Lake Malawi molluscs. Representatives officially lacustrine million years. T robertsoni Bellamya affiliated notdirectly c Figures’ Figure 1. four Nyasse species recognized by Bourguignat belo ‘ Figure 2.

B. robertsoni endemic lacustrine Fig. 2. separated by ca. 2 million years. The ﬁrst group, consisting of trochlearis Pleistocene times. The second(6) group, consisting of bar: 10 mm). Fig. 1. of the four thiarid genera created by Bourguignat (1889), endemic to Lake Malawi: species (Scale bar: 10 mm). sia magniﬁca singularis research to beSome parthenogenetic (e.g. clones belonging to the “