Osteo-pathological analysis provides evidence for a survived historical ship strike in a Southern Hemisphere fin whale (Balaenoptera physalus).

The life history of a fin whale (Balaenoptera physalus) caught during whaling operations in the 1950s was partly reconstructed. 3D surface models of the bones of the skeleton curated at the Zoological Museum of Hamburg were used for an osteopathological analysis. The skeleton revealed multiple healed fractures of ribs and a scapula. Moreover, the processus spinosi of several vertebrae were deformed and arthrosis was found. Together, the pathological findings provide evidence for large blunt trauma and secondary effects arising from it. Reconstruction of the likely cause of events suggests collision with a ship inflicting the fractures and leading to post traumatic posture damage as indicated by skeletal deformations. The injured bones had fully healed before the fin whale was killed by a whaler in the South Atlantic in 1952. This study is the first in-detail reconstruction of a historical whale-ship collision in the Southern Hemisphere, dating back to the 1940s, and the first documentation of a healed scapula fracture in a fin whale. The skeleton provides evidence for survival of a ship strike by a fin whale with severe injuries causing long-term impairment.

Incorporating palaeogeography into ancestral area estimation can explain the disjunct distribution of land snails in Macaronesia and the Balearic Islands (Helicidae: Allognathini).

The systematics and biogeographical history of the Eastern Mediterranean and Macaronesian land snail tribe Allognathini (Helicidae: Helicinae) is investigated based on mitochondrial and nuclear DNA sequence data. Our molecular phylogenetic analyses indicate that the genus-group systematics of the tribe needs to be revised. We show for the first time that the narrow-range endemics Lampadia and Idiomela from the Madeira Archipelago belong to Allognathini and represent together the sister group of the diverse Canary Island Hemicycla radiation. We therefore suggest synonymising Lampadiini with Allognathini. Sister to these Macaronesian genera was the Balearic Island Allognathus radiation. Pseudotachea was not recovered as a monophyletic group and the two currently recognised species clustered in Iberus. Similarly, Adiverticula was not recovered as a monophyletic group and clustered in Hemicycla. We therefore suggest synonymising Pseudotachea with Iberus and Adiverticula with Hemicycla. The six genera in Allognathini, which we distinguish here (Cepaea, Iberus, Allognathus, Hemicycla, Idiomela and Lampadia), originated in Western to South-western Europe according to our ancestral area estimation and the fossil record. The disjunct distribution of the Balearic Islands and Macaronesian sister clades and the mainly Iberian Iberus clade that separated earlier can be explained by the separation of the Betic-Rif System from the Iberian Peninsula during the late Oligocene to early Miocene, along with independent Miocene dispersals to the Balearic Islands and Macaronesia from the Iberian Peninsula, where the ancestral lineage became extinct.

Trophic specialisation reflected by radular tooth material properties in an "ancient" Lake Tanganyikan gastropod species flock.

BACKGROUND: Lake Tanganyika belongs to the East African Great Lakes and is well known for harbouring a high proportion of endemic and morphologically distinct genera, in cichlids but also in paludomid gastropods. With about 50 species these snails form a flock of high interest because of its diversity, the question of its origin and the evolutionary processes that might have resulted in its elevated amount of taxa. While earlier debates centred on these paludomids to be a result of an intralacustrine adaptive radiation, there are strong indications for the existence of several lineages before the lake formation. To evaluate hypotheses on the evolution and radiation the detection of actual adaptations is however crucial. Since the Tanganyikan gastropods show distinct radular tooth morphologies hypotheses about potential trophic specializations are at hand. RESULTS: Here, based on a phylogenetic tree of the paludomid species from Lake Tanganyika and adjacent river systems, the mechanical properties of their teeth were evaluated by nanoindentation, a method measuring the hardness and elasticity of a structure, and related with the gastropods' specific feeding substrate (soft, solid, mixed). Results identify mechanical adaptations in the tooth cusps to the substrate and, with reference to the tooth morphology, assign distinct functions (scratching or gathering) to tooth types. Analysing pure tooth morphology does not consistently reflect ecological specializations, but the mechanical properties allow the determination of eco-morphotypes. CONCLUSION: In almost every lineage we discovered adaptations to different substrates, leading to the hypothesis that one main engine of the flock's evolution is trophic specialization, establishing distinct ecological niches and allowing the coexistence of taxa.

One, two or three? Integrative species delimitation of short-range endemic Hemicycla species (Gastropoda: Helicidae) from the Canary Islands based on morphology, barcoding, AFLP and ddRADseq data.

Hemicycla mascaensis and H. diegoi are short-range endemics that occur allopatrically in small areas in the Teno Mountains in the western part of Tenerife (Canary Islands). Both taxa have been recognised as distinct species based on differences in shell morphology and genital anatomy. Preliminary molecular analyses using mitochondrial markers suggested a potential paraphyly of H. diegoi with regard to H. mascaensis. We here use multilocus AFLP data and ddRADseq data as well as distribution data, data on shell morphology and genital anatomy to assess the status of these taxa using phylogenetic analyses, species tree reconstruction and molecular species delimitation based on the multispecies coalescent as implemented in BFD* and BPP in an integrative approach. Our analyses show that, based on the analysis of multilocus data, the two taxa are reciprocally monophyletic. Species delimitation methods, however, tend to recognise all investigated populations as distinct species, albeit neither lending unambiguous support to any of the species hypotheses. The comparison of the anatomy of distal genital organs further suggests differentiation within H. mascaensis. This highlights the need for a balanced weighting of arguments from different lines of evidence to determine species status and calls for cautious interpretations of the results of molecular species delimitation analyses, especially in organisms with low active dispersal capacities and expected distinct population structuring such as land snails. Taking all available evidence into account, we favour to recognise H. mascaensis and H. diegoi as distinct species, acknowledging, though, that the recognition of both taxa as subspecies (with possibly a third yet undescribed) would also be an option as morphological differentiation is within the limits of other land snail species that are traditionally subdivided into subspecies.

Not just scratching the surface: distinct radular motion patterns in Mollusca.

The radula is the organ for mechanical food processing and an important autapomorphy of Mollusca. Its chitinous membrane, embedding small radular teeth, is moved by the set of muscles resulting in an interaction with the ingesta, tearing it and collecting loosened particles. Radulae and their teeth can be quite distinct in their morphology and had been of high research interest, but only a few studies have examined the basic functional principles of this organ, the movement and motion during feeding action. Here, the radular motion of 20 representative species, belonging to four major gastropod lineages (Vetigastropoda, Neritimorpha, Caenogastropoda and Heterobranchia) and Polyplacophora, were recorded and classified. Comparisons of the video footage with the scanning electron microscope (SEM) images of the radula resulted in the recognition of functional tooth rows and the correct position of the teeth during feeding. We identified six different types of radular movements, including rotations and bending of the radula itself. In each movement type, different structures act as counter bearings enabling the animals to grab and tear food.

Finite element analysis of individual taenioglossan radular teeth (Mollusca).

Molluscs are a highly successful group of invertebrates characterised by a specialised feeding organ called the radula. The diversity of this structure is associated with distinct feeding strategies and ecological niches. However, the precise function of the radula (each tooth type and their arrangement) remains poorly understood. Here for the first time, we use a quantitative approach, Finite-Element-Analysis (FEA), to test hypotheses regarding the function of particular taenioglossan tooth types. Taenioglossan radulae are of special interest, because they are comprised of multiple teeth that are regionally distinct in their morphology. For this study we choose the freshwater gastropod species Spekia zonata, endemic to Lake Tanganyika, inhabiting and feeding on algae attached to rocks. As a member of the African paludomid species flock, the enigmatic origin and evolutionary relationships of this species has received much attention. Its chitinous radula comprises several tooth types with distinctly different shapes. We characterise the tooth's position, material properties and attachment to the radular membrane and use this data to evaluate 18 possible FEA scenarios differing in the above parameters. Our estimations of stress and strain indicate different functional loads for different teeth. We posit that the central and lateral teeth are best suitable for scratching substrate loosening ingesta, whereas the marginals are best suited for gathering food particles. Our successful approach and workflow are readily applicable to other mollusc species.

One species, two developmental modes: a case of geographic poecilogony in marine gastropods.

BACKGROUND: Poecilogony, the presence of two developmental modes in the same animal species, is a rare phenomenon. Few cases of poecilogony have been suggested for marine invertebrates including molluscs and even less stood extensive testing, mostly revealing a species pair with differing developmental modes. We studied a textbook example of poecilogony in the viviparous snail Planaxis sulcatus (Gastropoda: Planaxidae), for the first time throughout its entire distribution range. RESULTS: In the Western Indian Ocean and Red Sea this intertidal species is observed to have large, shelled juveniles, whereas in the Indo-West Pacific planktotrophic veliger larvae are released from a subhaemocoelic brood pouch. We uncovered a shift in developmental modes across its range: from west to east successively earlier developmental stages are released. Furthermore, genetic data based on mitochondrial DNA suggests to recognize P. sulcatus as a single species rather than a group of cryptic species. A reconstruction of the ancestral area of P. sulcatus based on molecular data outlines the Western Indian Ocean and the Indo-West Pacific as area of origin. CONCLUSION: The findings supporting Planaxis sulcatus as a single widespread species and the geographical shift from one reproductive mode to another suggest for this species to truly represent a case of geographic poecilogony, i.e. differing developmental modes between populations of the same species. Furthermore, the results of our ancestral range estimation imply the release of planktotrophic larvae as the ancestral developmental mode.

Molecular phylogeny and trait evolution of Madeiran land snails: radiation of the Geomitrini (Stylommatophora: Helicoidea: Geomitridae).

The Geomitrini is the most species-rich group of land snails in the Madeiran Archipelago. The phylogeny of the group is reconstructed based on mitochondrial and nuclear genetic markers. The timing of diversification, the colonisation history of the islands of the Madeiran Archipelago and the evolution of characters of the dart apparatus are studied. The results of the phylogenetic analyses confirm the sister group relationship of Geomitrini and Cochlicellini, but also show that several previously accepted genus-group taxa are not monophyletic. A new classification for the Geomitrini is proposed, including the description of two new genera, Domunculifex Brozzo, De Mattia, Harl & Neiber, n. gen. and Testudodiscula Brozzo, De Mattia, Harl & Neiber, n. gen. The onset of diversification of Geomitrini was dated in our analysis at 13 Ma, which largely coincides with the emergence of the present-day islands. The ancestral state estimation recovered the presence of two appendiculae in the reproductive system as the ancestral state in Geomitrini. One appendicula was lost three times independently within the tribe and is even missing completely in one group. The ancestral area estimation suggests recurrent colonisations of Madeira (and the Ilhas Desertas) from the older island Porto Santo.

Adding the West-African riverine component: Revision of the Recent freshwater snails belonging to Pseudocleopatra Thiele, 1928 (Caenogastropoda, Cerithioidea, Paludomidae).

While Africa's lacustrine gastropod fauna, in particular of Lake Tanganyika, has received much attention, the continent's riverine malacofauna has long been neglected. Pseudocleopatra is a relatively poorly known paludomid gastropod genus with species found throughout the lower reaches of the West African Volta and Congo rivers. In the course of ongoing systematic revisions of African paludomids, we present here a morphometric analysis and revision of the recent species assigned to the genus, i.e., P. togoensis, P. voltana, P. dartevellei and P. bennikei, to improve taxonomic acuity for this group. We use available museum material for geometric morphometrics, multivariate ratio analysis and comparisons of radular and opercular characters. Our results demonstrate that the four recent species of Pseudocleopatra are clearly distinguishable on the basis of ratios of shell measurements as well as radular and opercular characters. Pseudocleopatra has generic-level synapomorphies including: concentric opercula with relatively large paucispiral nuclei, and rachidian radular teeth with usually 13-20 cusps. On the basis of this characterisation, the nominal species Cleopatra broecki is transferred to Pseudocleopatra. Additionally, the nominal taxon P. bennikei is synonymized with P. broecki n. comb. The phylogenetic relationships of Pseudocleopatra are currently unknown, but the observed tendency of some fossil taxa assigned to Pseudocleopatra towards thalassoidism, i.e., the resemblance to marine gastropods, has led to the hypothesis that some of the thalassoid endemics in Lake Tanganyika may have originated from or be related to Pseudocleopatra. Should this hypothesis be correct, which is in need of testing by molecular genetic methods when suitable samples become available, Pseudocleopatra may play a crucial role in understanding of the evolution of thalassoidism in African Paludomidae.

Differences in the Young modulus and hardness reflect different functions of teeth within the taenioglossan radula of gastropods.

One important autapomorphy of molluscs is the radula, which is the anatomical structure used for feeding in most species of Mollusca. As this phylum represents the second species-richest animal group inhabiting very diverse environments, it is not surprising that the morphology of the radula and its teeth is also very diverse between taxa. However, the taenioglossan radulae are remarkable because its tooth types (central, lateral, and marginal teeth) are highly distinct in their morphology within the same radula. There are several hypotheses attempting to explain this tooth diversity by their functional specialisations. Here, for the first time, the functional morphology of taenioglossan radular teeth from one single species was analysed and their material properties (hardness and elasticity modulus) were characterised by nanoindentation. Spekia zonata Bourguignat, 1879 belongs to the Paludomidae inhabiting and feeding on solid substrates in Lake Tanganyika. All tooth types show gradual and significant differences in their stiffness and hardness: from the basis, as the softest and most flexible area, to the stylus and the cusps as the stiffest and hardest areas. The flexibility of the stylus allows the teeth to act as one single feeding organ: the central and lateral teeth can stabilize each other during feeding by the rear teeth providing support to the next row. Tooth types also differ significantly in their stiffness and hardness: the central teeth consist of the hardest and stiffest material, followed by the lateral teeth and finally marginal teeth. This can be explained by different functional loads of teeth: central and lateral ones are used for scratching over the substrate while the marginals serve mainly as brooms collecting food particles.

In slow motion: radula motion pattern and forces exerted to the substrate in the land snail Cornu aspersum (Mollusca, Gastropoda) during feeding.

The radula is the anatomical structure used for feeding in most species of Mollusca. Previous studies have revealed that radulae can be adapted to the food or the substrate the food lies on, but the real, in vivo forces exerted by this organ on substrates and the stresses that are transmitted by the teeth are unknown. Here, we relate physical properties of the radular teeth of Cornu aspersum (Müller. 1774 Vermium terrestrium et fluviatilium, seu animalium infusoriorum, helminthicorum, et testaceorum, non marinorum, succincta historia. Volumen alterum. Heineck & Faber, Havniæ & Lipsiæ.), a large land snail, with experiments revealing their radula scratching force. The radula motion was recorded with high-speed video, and the contact area between tooth cusps and the substrate was calculated. Forces were measured in all directions; highest forces (106.91 mN) were exerted while scratching, second highest forces while pulling the radula upwards and pressing the food against its counter bearing, the jaw, because the main ingesta disaggregation takes place during those two processes. Nanoindentation revealed that the tooth hardness and elasticity in this species are comparable to wood. The teeth are softer than some of their ingesta, but since the small contact area of the tooth cusps (227 µm2) transmits high local pressure (4698.7 bar) on the ingesta surface, harder material can still be cut or pierced with abrasion. This method measuring the forces produced by the radula during feeding could be used in further experiments on gastropods for better understanding functions and adaptations of radulae to ingesta or substrate, and hence, gastropods speciation and evolution.

Annotated nomenclator of extant and fossil taxa of the Paludomidae (Caenogastropoda, Cerithioidea).

This nomenclator provides bibliographic details on all names in the family-, genus-, and species-group of the the family Paludomidae. All nomenclaturally available names are discussed including junior homonyms and objective junior synonyms as well as unavailable names such as nomina nuda, infrasubspecific names and, to some extent, also incorrect subsequent spellings. In the family-group a total of 28 names are included in the nomenclator, of which 21 are available and seven unavailable names. Of the available names in the family-group, six are invalid for nomenclatural reasons. In the genus-group a total of 57 names are included in the catalogue. Of the available names in the genus-group, 11 are invalid for nomenclatural reasons. In the species-group a total of 499 names are included, of which 463 are available, but 21 are invalid for nomenclatural reasons. All names are given in their original combination and spelling (mandatory changes are discussed and corrected spellings are provided), along with the reference to the original publication. For each family- and genus-group name, the original classification and the type genus or type species, respectively, are given. For species-group taxa the type locality and type horizon (for fossil taxa) are provided, usually as given in the original publication. A new name, Cleopatraadami nom. nov., is proposed for the fossil Cleopatracylindrica (Adam, 1957), which is a homonym of Cleopatracridlandicylindrica Mandahl-Barth, 1954, and a lectotype for Cleopatradubia Adam, 1959 is designated. A new replacement name Leloupiella nom. nov. is proposed for Stormsia Leloup, 1953 which is a homonym of Stormsia Bourguignat, 1891.

Unparalleled disjunction or unexpected relationships? Molecular phylogeny and biogeography of Melanopsidae (Caenogastropoda: Cerithioidea), with the description of a new family and a new genus from the ancient continent Zealandia.

Melanopsidae are an important component of the freshwater fauna of the subtropical to temperate regions of the Western Palaearctic and also are reported from Zealandia, representing an unparalleled disjunction among a group of freshwater animals. We sequenced markers for species of all constituent genera covering the entire range of the group. Our phylogenetic analyses indicate that Melanopsidae are only monophyletic when excluding Holandriana from the Balkans, which was found to be more closely related to Pleuroceridae (eastern North America) and Semisuclospiridae (western North America and eastern Asia) than to the remaining melanopsids. It is, therefore, placed in the previously proposed family Amphimelaniidae. Zemelanopsis from New Zealand and Caledomelanella gen.n. from New Caledonia were recovered as a deeply divergent clade, here suggested to represent Zemelanopsidae fam.n. as the sister group of Melanopsidae s.s. The genus Microcolpia, including M. daudebartii and the extinct M. parreyssii, was recovered as a moderately well-supported sister group of Melanopsis s.s., which comprises three distinct lineages: one from the western Mediterranean region, a second from the eastern Mediterranean region and the Near to Middle East, and a third from thermal springs in Tuscany. Although the Italian populations show little variability, both the eastern and western Melanopsis clades exhibit a high degree of variation in shell form and/or sculpture. Whether this is indicative of more than a species pair each (M. praemorsa/cariosa and M. buccinoidea/costata) within the eastern and western clade, respectively, or the result of parallel evolution currently cannot be answered with certainty. Distinct populations were not recovered as monophyletic clades in some cases, which may indicate incomplete reproductive isolation. We compare the timeframe for the evolution of major "melanopsid" lineages with geological events, and elucidate scenarios that may have shaped the distribution patterns observed today.

A snail perspective on the biogeography of Sulawesi, Indonesia: origin and intra-island dispersal of the viviparous freshwater gastropod Tylomelania.

The complex geological history of the Indonesian island Sulawesi has shaped the origin and subsequent diversification of its taxa. For the endemic freshwater snail Tylomelania a vicariant origin from the Australian margin has been hypothesized. Divergence time estimates from a mtDNA phylogeny based on a comprehensive island-wide sampling of Tylomelania fit regional tectonic constraints and support the 'out-of-Australia' vicariance hypothesis. The Banggai-Sula region of the Sula Spur, the Australian promontory colliding with West Sulawesi during the Miocene, is identified as a possible source area for the colonization of Sulawesi by the ancestor of Tylomelania. The molecular phylogeny also shows a rapid diversification of Tylomelania into eight major lineages with very little overlap in their distribution on the island. Haplotype networks provide further evidence for a strong spatial structure of genetic diversity in Tylomelania. Distribution boundaries of the major lineages do at best partially coincide with previously identified contact zones for other endemic species groups on Sulawesi. This pattern has likely been influenced by the poor dispersal capabilities and altitudinal distribution limits of this strict freshwater inhabitant. We suggest that late Miocene and Pliocene orogeny in large parts of Sulawesi has been the vicariant event driving primary diversification in Tylomelania.

Rare gene capture in predominantly androgenetic species.

The long-term persistence of completely asexual species is unexpected. Although asexuality has short-term evolutionary advantages, a lack of genetic recombination leads to the accumulation over time of deleterious mutations. The loss of individual fitness as a result of accumulated deleterious mutations is expected to lead to reduced population fitness and possible lineage extinction. Persistent lineages of asexual, all-female clones (parthenogenetic and gynogenetic species) avoid the negative effects of asexual reproduction through the production of rare males, or otherwise exhibit some degree of genetic recombination. Another form of asexuality, known as androgenesis, results in offspring that are clones of the male parent. Several species of the Asian clam genus Corbicula reproduce via androgenesis. We compared gene trees of mitochondrial and nuclear loci from multiple sexual and androgenetic species across the global distribution of Corbicula to test the hypothesis of long-term clonality of the androgenetic species. Our results indicate that low levels of genetic capture of maternal nuclear DNA from other species occur within otherwise androgenetic lineages of Corbicula. The rare capture of genetic material from other species may allow androgenetic lineages of Corbicula to mitigate the effects of deleterious mutation accumulation and increase potentially adaptive variation. Models comparing the relative advantages and disadvantages of sexual and asexual reproduction should consider the possibility of rare genetic recombination, because such events seem to be nearly ubiquitous among otherwise asexual species.

Adaptive radiation and ecological diversification of Sulawesi's ancient lake shrimps.

Ancient lakes are natural laboratories for the study of adaptive radiation. Recently, two lake systems on the Indonesian island Sulawesi have emerged as promising new model systems. A species flock of atyid freshwater shrimps in the Malili lake system comprises 15 colorful endemic taxa. Mitochondrial DNA data suggest two independent colonizations by riverine ancestors. Only one colonization event led to subsequent radiation into 14 species, while the second clade comprises just one species. The vast majority of species (n= 12) are habitat specialists, which are confined to the larger Malili clade and include all taxa with species-specific color patterns and a restricted distribution within the five connected Malili lakes. Morphological, genetic, and ecological data are consistent with the existence of an adaptive radiation in the Malili lakes, involving the habitat-specific diversification of trophic morphology. In addition to testing criteria for the recognition of an adaptive radiation, an ancestral state reconstruction reveals an equal probability for either a riverine generalist or a lacustrine specialist as ancestor of the large Malili clade, which is interpreted as indicative of an early stage of habitat specialization within this radiation. Finally, our results suggest that species diversification may have been primarily driven by ecological specialization and allopatric speciation.

Molecular phylogeny and diversification of freshwater shrimps (Decapoda, Atyidae, Caridina) from ancient Lake Poso (Sulawesi, Indonesia)--the importance of being colourful.

Ancient Lake Poso on the Indonesian island Sulawesi hosts a highly diverse endemic fauna, including a small species flock of atyid Caridina shrimps, which are characterized by conspicuous colour patterns. We used a mtDNA based molecular phylogeny to test the assumption of a monophyletic origin and intralacustrine radiation of the species flock and to assess the species specificity of some colour morphs. Our data reveal a rapid radiation of Caridina in the entire Poso drainage system, but provide no strong evidence for a monophyletic radiation of the lake species. Nevertheless each lacustrine species shows a varying degree of substrate or trophic specialization, usually considered a hallmark of adaptive radiation. Two distinct colour forms previously attributed to a single species, C. ensifera, lack distinguishing qualitative morphological characters, but are shown to be two different species. In contrast, morphologically rather distinct lake species lacking specific colour patterns may be hybridizing with riverine taxa. These results suggest that colour may play a similar role in species recognition and possibly speciation in ancient lake Caridina as hypothesized, e.g. for some African cichlids.

Freshwater shrimp-sponge association from an ancient lake.

Shrimp-sponge associations occur frequently in marine ecosystems, serving as model systems for the evolution of eusociality. Here, we describe the first known instance of such association in freshwater from an ancient lake in Indonesia. The shrimp Caridina spongicola forms an exclusive and probably commensal association with a yet undescribed spongillinid sponge. Phylogenetic and ecological data suggest a comparatively recent origin of both taxa. Climatic fluctuations may have facilitated speciation and occasional hybridization of the shrimp species, which is derived from a rock-dwelling ancestor. Their extremely localized occurrence in an increasingly disturbed area makes both taxa a conservation priority.

Rapid evolution of sessility in an endemic species flock of the freshwater bivalve Corbicula from ancient lakes on Sulawesi, Indonesia.

The fauna of ancient lakes frequently contains taxa with highly derived morphologies that resulted from in situ radiation of lacustrine lineages with high antiquity. We employed a molecular mtDNA phylogeny to investigate this claim for corbiculid freshwater bivalves in two ancient lake systems on the Indonesian island Sulawesi. Among the otherwise mobile corbiculid species flock, only one taxon, Posostrea anomioides, in the ancient Lake Poso exhibits a unique habit, i.e. cementing one valve to the substrate. Our data show that Corbicula on Sulawesi is polyphyletic, with the endemic riverine taxa in terminal position, and the lacustrine species flock being paraphyletic. Surprisingly, Posostrea is not confirmed as a genus distinct from Corbicula and genetic distances suggest a rather recent origin from the only other corbiculid species endemic to Lake Poso, the non-cementing Corbicula possoensis. While the cementing anomioides, despite its unique behavioural and morphological characteristics, clusters together with non-sessile Corbicula species, the latter exhibit strong genetic distances in the absence of morphological disparity and fall into several genetically rather distinct clades. These findings suggest that developmental plasticity of animals in ancient lakes rather than the antiquity of lineages might account for the unique morphology of some species.

Escalation and trophic specialization drive adaptive radiation of freshwater gastropods in ancient lakes on Sulawesi, Indonesia.

Species flocks in ancient lakes have long been appreciated as ideal model systems for the study of speciation and adaptive processes. We here present data from a new invertebrate model system with intrinsic parameters distinct from those of other documented radiations. The ancient lakes on Sulawesi harbour an endemic species flock of at least 33 species of viviparous snails. Molecular data reveal multiple independent colonizations of the lakes by riverine ancestors. In each colonizing clade, parallel evolution of conspicuous shell morphologies, followed by a differentiation of trophic morphology and the development of habitat specificity can be observed. Extensive shell crushing experiments and strong dentition of the chelae observed in some lacustrine crab species suggest that coevolution with crabs, i.e. escalation, is the most likely cause of initial shell divergence. By contrast, repeated parallel evolution in radula morphology indicates that speciation within lineages is driven by divergent adaptation to different resources among sympatric taxa. The inclusion of coevolutionary processes is unique in this system compared with diversification models developed for vertebrate radiations.