A new piece in the puzzle for the riverine slugs of the Acochlidiidae (Gastropoda: Panpulmonata: Acochlidimorpha) helps tracing steps of their freshwater invasion

Gastropods (slugs and snails) are prominent and species-rich faunal elements in marine and terrestrial habitats of the tropics. While several clades of snails inhabit freshwater systems, slugs are extremely rare in freshwater: only the centimeter-sized Acochlidiidae, with currently three genera, contain more than one species and live in the lower reaches of island streams in an area comprising Eastern Indonesia, Fiji, and Palau. Where known, the species of this unique group are specialized predators of other amphidromous snails’ egg capsules (Neritidae) and their reproductive biology and adaptations to life in freshwater are complex. Acochlidiidae are thus of special interest for evolutionary biology and ecology. We here describe a new genus of unusually bluish-green acochlidiid to date known only from a single locality on the island of Ambon, Indonesia. Previous molecular data found this charismatic species to link slender Strubellia slugs with broad and flattened Acochlidium and Palliohedyle. We establish Wallacellia siputbiru n. gen. n. sp., the “blue slug” in Bahasa Indonesia, by using scanning electron microscopy of cuticular elements, light microscopy of serial semithin histological sections of the soft body, and 3D reconstruction of all organ systems based on these sections. Special structures of this seemingly rare endemic species include the enlarged kidney and the huge copulatory organ. Our data now clarify that, in the invasion of freshwater habitats in Acochlidiidae, sexual selection (the anterior three-part copulatory organ) preceded ecological selection (posterior flattened habitus with branched or multiplied internal organs).

Inter-basin water transfers and the expansion of aquatic invasive species

Inter-basin Water Transfers (IBWT) are recognized as one of the major pathways of freshwater invasion. They provide a direct link between previously isolated catchments and may modify the habitat conditions of the receiving waters such that they become more favourable for the establishment of invasive species. Combined, IBWT and invasive species will intensify the stress upon native species and ecosystems. Using the Severn and Thames Rivers-two of the largest river systems in Great Britain—as a case study, here we assess the potential influence of IBWT on the expansion of invasive species and thus their impact on biodiversity conservation. The Thames Valley is subject to extensive water abstraction, and an increasing population means that supplemented flow from the River Severn is being considered. Multi-scale Suitability Models, based on climate and water chemistry respectively, provided novel evidence that there is serious risk for further spread of invasive species in the focus area, particularly of the quagga mussel, a recent invader of the Thames River. Native freshwater mussels are particularly vulnerable to changing environmental conditions, and may suffer the decrease in alkalinity and increase in sedimentation associated with an IBWT from the lower Severn to the upper Thames. Regional models suggest considerable overlap between the areas suitable for three vulnerable native freshwater mussels and the expansion of invasive species that negatively impact upon the native mussels. This study illustrates the use of novel spatially-explicit techniques to help managers make informed decisions about the risks associated with introducing aquatic invasive species under different engineering scenarios. Such information may be especially important under new legislation (e.g. EU Invasive Species Regulation No 1143/2014) which increases the responsibility of water managers to contain and not transfer invasive species into new locations.

Evolutionary history of threespine sticklebacks (Gasterosteus spp.) in British Columbia: insights from a physiological clock

Geologic and allozyme evidence suggests that threespine sticklebacks (Gasterosteus aculeatus complex) in low-lying southwestern British Columbia lakes were founded during two incursions of marine sticklebacks after the retreat of the Pleistocene glaciers (the double-invasion hypothesis). We used the salinity tolerance of embryos, measured as hatchability in salt water, to establish the relative order of freshwater invasion by marine sticklebacks and to test the double-invasion hypothesis. Limnetics and an anadromous population hatched nearly equivalent numbers of young in salt water as in fresh water, whereas benthics and one solitary freshwater population had low hatchability in salt water. We also found that eggs from freshwater populations were larger than those from marine populations and limnetics had smaller eggs than benthics and the solitary population. These results support the double-invasion hypothesis and suggest a trend of increasing egg size with increasing time spent in fresh water.