First data on testate amoebae associated with the endemic cave bivalve Congeria jalzici Morton & Bilandžija, 2013 with a description of Psammonobiotus dinarica sp. nov

Testate amoebae are phylogenetically a very diverse group of eukaryotic microorganisms. They can be found in marine and freshwater habitats and in soil. Some of these single-celled organisms inhabit both surface and cave habitats, but their diversity in caves has barely been explored. Recent studies in the Dinaric region imply that testate amoebae in caves show a high diversity. The aim of this study was to identify the alpha diversity of testate amoebae in the Lika region (Dinaric karst, Croatia) and to compare the habitats of different caves based on testate amoebae assemblages. In eight caves we found more than 40 testate amoebae taxa, including a new testate amoeba species, Psammonobiotus dinaricasp. nov. The greatest diversity of testate amoebae was found in Markov ponor (27 taxa). The Bray-Curtis Similarity Index showed that testate amoebae assemblages in caves inhabited by the endemic and endangered cave bivalve Congeria jalzici (Markov ponor, Dankov ponor and Dražice ponor) differ from caves not inhabited by this species. This differentiation is attributed to the impact of the sinking Lika river, which occasionally completely submerges these caves, creating specific habitats for eukaryotic microorganisms. This study contributes to our understanding of the diversity, biogeography and ecology of testate amoebae in caves, as well as providing further insight into the conditions that sustain populations of C. jalzici.

Longevity in Cave Animals

An extraordinary longevity has been observed in some cave species, and this raised the hypothesis that a longer lifespan may be considered one of the characteristic traits of these animals. However, only a few cave species have been studied thus far, and a firm conclusion remains to be drawn. Here we review the available knowledge on the longevity of subterranean species, point out the limitations of previous studies, and provide suggestions for future studies to answer important questions regarding the longevity in cave animals, its adaptive value and the related promoting factors. We also argue that studying the longevity in cave animals will contribute to the field of aging, especially to understanding the evolution of this phenomenon.

Predatory marine bivalves: A review

Most bivalves are suspension feeders. On the deep sea floor, however, some are predators, typically of meiobenthic crustaceans: copepods, cumaceans and ostracods. Propeamusiid scallops are one such group of predators. The largest numbers of predators, however, belong to the bivalve subclass Anomalodesmata and constitute, as currently recognised, some 500 species belonging principally to the Verticordioidea (120), Poromyoidea (75) and Cuspidarioidea (304) with four, two and four constituent families, respectively. A further family, the Parilimyidae, is considered to be derived from the Pholadomyoidea-the anomalodesmatan ancestor. These, generally small (<60mm shell length), nacreous and thin-shelled predators share many anatomical features that formerly allowed them to be collectively classified as the Septibranchia. Although this name is now rarely used, it refers to their possession of a ctenidially-derived septum in the mantle cavity and functioning in prey capture. Generally, there is a trend, possibly evolutionary, from a typical bivalve ctenidium (Parilimyidae and some Verticordioidea) to a complete septum (other Verticordioidea, Poromyoidea and Cuspidarioidea). In addition, the inhalant siphon, foot, labial palps, mouth and its lips play a role in prey capture, and ingestion. Similarly, the stomach is modified to digest such, typically chitinous, ingested prey. Most septibranchs are either consecutive or simultaneous hermaphrodites with self-fertilisation possibly usual and with some evidence in a few of larval brooding. Notwithstanding, the deep sea septibranch species are poorly studied with virtually nothing being known about their wider distributions, ecology, detailed reproductive strategies and life history traits.

Multilocus phylogeny of the zebra mussel family Dreissenidae (Mollusca: Bivalvia) reveals a fourth Neotropical genus sister to all other genera

Dreissenidae is one of the most economically and ecologically important families of freshwater and estuarine mollusks. Fourteen extant species and three genera are currently recognized: Congeria contains three species from karst caves along the eastern Adriatic coast and one from the Orinoco River of Venezuela, Dreissena contains six species native to Eastern European rivers and estuaries, and Mytilopsis contains three species from the Gulf of Mexico, Caribbean, and northwestern coast of South America and one from the Tocantins River of Brazil. Previous molecular phylogenetic studies have examined all species except those from South American rivers, and found each genus to be monophyletic with Congeria and Mytilopsis forming a clade sister to Dreissena. We present the first multilocus phylogeny of Dreissenidae inclusive of South American riverine species. Bayesian and maximum likelihood analyses of a 3085 bp alignment consisting of mitochondrial (COI and 16S) and nuclear (18S and 28S) gene regions found Neotropical species to be consistently and strongly supported as sister to all other dreissenids, although incomplete sequencing of the single Orinoco specimen obscured Neotropical monophyly. Our intergeneric relationships are inconsistent with an extensive fossil record suggesting that dreissenids originated in Europe approximately 30 My before dispersing to the Western Hemisphere. Fossil-calibrated analyses indicated that Neotropical dreissenids diverged from European lineages in the mid to late Eocene (∼39.3 Ma), and Brazilian and Guiana shield populations diversified during the Oligocene to Miocene. We erect the new genus Rheodreissena for all Neotropical freshwater dreissenids and present haplotype data indicative of at least three species. Widespread anthropogenic alteration of the middle Xingu River and lower Amazon threatens the persistence of these endemic, poorly studied mussels and may facilitate introduction beyond their native range.

Evolutionary history of relict Congeria (Bivalvia: Dreissenidae): unearthing the subterranean biodiversity of the Dinaric Karst

Background

Patterns of biodiversity in the subterranean realm are typically different from those encountered on the Earth’s surface. The Dinaric karst of Croatia, Slovenia and Bosnia and Herzegovina is a global hotspot of subterranean biodiversity. How this was achieved and why this is so remain largely unresolved despite a long tradition of research. To obtain insights into the colonisation of the Dinaric Karst and the effects of the subterranean realm on its inhabitants, we studied the tertiary relict Congeria, a unique cave-dwelling bivalve (Dreissenidae), using a combination of biogeographical, molecular, morphological, and paleontological information.

Results

Phylogenetic and molecular clock analyses using both nuclear and mitochondrial markers have shown that the surviving Congeria lineage has actually split into three distinct species, i.e., C. kusceri, C. jalzici sp. nov. and C. mulaomerovici sp. nov., by vicariant processes in the late Miocene and Pliocene. Despite millions of years of independent evolution, analyses have demonstrated a great deal of shell similarity between modern Congeria species, although slight differences in hinge plate structure have enabled the description of the two new species. Ancestral plesiomorphic shell forms seem to have been conserved during the processes of cave colonisation and subsequent lineage isolation. In contrast, shell morphology is divergent within one of the lineages, probably due to microhabitat differences.

Conclusions

Following the turbulent evolution of the Dreissenidae during the Tertiary and major radiations in Lake Pannon, species of Congeria went extinct. One lineage survived, however, by adopting a unique life history strategy that suited it to the underground environment. In light of our new data, an alternative scenario for its colonisation of the karst is proposed. The extant Congeria comprises three sister species that, to date, have only been found to live in 15 caves in the Dinaric karst. Inter-specific morphological stasis and intra-specific ecophenotypic plasticity of the congerid shell demonstrate the contrasting ways in which evolution in the underground environments shapes its inhabitants.