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.

Notes on Afonsoconus Tucker & Tenorio, 2013 (Gastropoda, Conidae), with description of a new species from the Southwestern Indian Ocean

Although cone snails are among the most studied group of gastropods, new species are still regularly described. Here, we focus on Afonsoconus Tucker & Tenorio, 2013, a lineage that includes only two species from the Indo-Pacific Ocean. The analysis of molecular (partial mitochondrial cox1 gene sequences) and morphological (shell and radular tooth) characters revealed that the samples collected by dredging in deep water during a recent expedition carried out in the Mozambique Channel are different from the samples collected in the Pacific Ocean. We thus introduce here a new species, Afonsoconus crosnieri sp. nov., from the SW Indian Ocean including records from the Mozambique Channel, the Comoros and Glorieuses Islands, Madagascar, South Africa and Reunion Island.

Genus Profundiconus Kuroda, 1956 (Gastropoda, Conoidea): Morphological and molecular studies, with the description of five new species from the Solomon Islands and New Caledonia

The genus Profundiconus Kuroda, 1956 is reviewed. The morphological characters of the shell, radular tooth and internal anatomy of species in Profundiconus are discussed. In particular, we studied Profundiconus material collected by dredging in deep water during different scientific campaigns carried out in the Solomon Islands, Madagascar, Papua New Guinea and New Caledonia. We reconstructed a phylogeny of 55 individuals based on partial mitochondrial cox1 gene sequences. The phylogeny shows several clades containing individuals that do not match any of the known species of Profundiconus based on their shell and radular morphologies, and are introduced here as five new species: Profundiconus maribelae sp. nov. from the Solomon Islands; P. virginiae sp. nov. from Chesterfield Plateau (New Caledonia); P. barazeri sp. nov. from Chesterfield Plateau and the Grand Passage area (New Caledonia); P. puillandrei sp. nov. from Norfolk Ridge (New Caledonia), Kermadec Ridge (New Zealand) and possibly Balut Island (Philippines); and P. neocaledonicus sp. nov. from New Caledonia. Furthermore, Profundiconus teramachii forma neotorquatus (da Motta, 1984) is raised to specific status as P. neotorquatus (da Motta, 1984).

Prey-Capture Strategies of Fish-Hunting Cone Snails: Behavior, Neurobiology and Evolution

The venomous fish-hunting cone snails (Conus) comprise eight distinct lineages evolved from ancestors that preyed on worms. In this article, we attempt to reconstruct events resulting in this shift in food resource by closely examining patterns of behavior, biochemical agents (toxins) that facilitate prey capture and the combinations of toxins present in extant species. The first sections introduce three different hunting behaviors associated with piscivory: ‘taser-and-tether', ‘net-engulfment' and ‘strike-and-stalk'. The first two fish-hunting behaviors are clearly associated with distinct groups of venom components, called cabals, which act in concert to modify the behavior of prey in a specific manner. Derived fish-hunting behavior clearly also correlates with physical features of the radular tooth, the device that injects these biochemical components. Mapping behavior, biochemical components and radular tooth features onto phylogenetic trees shows that fish-hunting behavior emerged at least twice during evolution. The system presented here may be one of the best examples where diversity in structure, physiology and molecular features were initially driven by particular pathways selected through behavior.

Scanning electron microscopical studies of some cephalopod radulae

In an attempt to evaluate the possible uses of scanning electron microscopical (SEM) studies of cephalopod radulae, we examined the radulae of 58 specimens (representing 22 species of nine genera), the majority being from the genera Loligo, Rossia, and Illex. Octopod and decapod radulae have considerable differences and were easily distinguished, as were decapod radulae down to the family level. However, considerable differences in radular tooth form between individuals of a species, not related to size or sex of the animals, were found. Also, similarities between species in a genus, and genera in a family were noted. The advantages of the scanning electron microscopical method of examining radulae are discussed.