Marine incursion into East Asia: a forgotten driving force of biodiversity

Integrative taxonomy on the rare sky-island Ligidium species from southwest China (Isopoda, Oniscidea, Ligiidae)

Background

The sky-island Ligidium species fauna in southwest China is poorly known. Before this study, six of the seven sky-island species of the genus were known to be endemic to southwest China. In morphology, Ligidium species are often difficult to identify, and an appraisal of integrative taxonomy is needed.

Results

We integrated morphology and molecular analyses to delimit Ligidium species. Molecular species delimitation based on distance- and evolutionary models recovered seven-candidate lineages from five gene markers (COI, 12S rRNA, 18S rRNA, 28S rRNA and NAK). We also estimated that the species divergences of sky-island Ligidium in southwest China started in late Eocene (40.97 Mya) to middle Miocene (15.19 Mya).

Four new species (L. duospinatum Li, sp. nov., L. acuminatum Li, sp. nov., L. rotundum Li, sp. nov. and L. tridentatum Li, sp. nov.) are described. Morphological confusion among L. denticulatum Shen, 1949, L. inerme Nunomura & Xie, 2000 and L. sichuanense Nunomura, 2002 is clarified by integrative taxonomy.

Conclusion

This work confirms that an integrative approach to Ligidium taxonomy is fundamental for objective classification, and deduced the uplift of Qinghai-Tibetan Plateau in the late Eocene and middle Miocene as one of the principal reasons for the species divergences of sky-island Ligidium in southwest China. We also inferred that sky-island mountains have a huge reserve of higher Ligidium species diversity.

Cyphoderia ampulla (Cyphoderiidae: Rhizaria), a tale of freshwater sailors. The causes and consequences of ecological transitions through the salinity barrier in a family of benthic protists

The salinity barrier that separates marine and freshwater biomes is probably the most important division in biodiversity on Earth. Those organisms that successfully performed this transition had access to new ecosystems while undergoing changes in selective pressure, which often led to major shifts in diversification rates. While these transitions have been extensively investigated in animals, the tempo, mode, and outcome of crossing the salinity barrier have been scarcely studied in other eukaryotes. Here, we reconstructed the evolutionary history of the species complex Cyphoderia ampulla (Euglyphida: Cercozoa: Rhizaria) based on DNA sequences from the nuclear SSU rRNA gene and the mitochondrial cytochrome oxidase subunit I gene, obtained from publicly available environmental DNA data (GeneBank, EukBank) and isolated organisms. A tree calibrated with euglyphid fossils showed that four independent transitions towards freshwater systems occurred from the Mid Miocene onwards, coincident with important fluctuations in sea level. Ancestral trait reconstructions indicated that the whole family Cyphoderiidae had a marine origin and suggest that ancestors of the freshwater forms were euryhaline and lived in environments with fluctuating salinity. Diversification rates did not show any obvious increase concomitant with ecological transitions, but morphometric analyses indicated that species increased in size and homogenized their morphology after colonizing the new environments. This suggests adaptation to changes in selective pressure exerted by life in freshwater sediments.

Sea–land transition drove terrestrial amphipod diversification in East Asia, with a description of a new species

Sea–land transition caused by marine incursion and regression is hypothesized to be a major driving force in terrestrial biodiversity, providing opportunities for marine ancestors to colonize terrestrial habitats and driving vicariant speciation in distinct geographical regions. Here, we test this hypothesis in East Asia using amphipods of the Morinoia japonica complex. We constructed a dataset from 269 individuals covering all known ranges of this species complex. Phylogenetic and biogeographic analyses revealed that sea–land transition during the Miocene drove the coastal ancestor to invade terrestrial habitats in East Asia and subsequently split into eight biogeographic lineages in eastern China, Korea, Japan and some Pacific islands. Stepping-stone dispersal resulted in a relatively wide distribution of M. japonica, and long-term geographical isolation led to the diversification of the M. japonica complex. Species delimitation analysis suggests that this complex contains eight species. We describe the geographical group from eastern China as a new species, Morinoia aosen sp. nov., based on genetic and morphological comparisons with other geographical groups. Type specimens are deposited in the Institute of Zoology, Chinese Academy of Sciences (IZCAS) in Beijing, China.

Post-Disturbance Genetic Changes: The Impact of the 2010 Mega-Earthquake and Tsunami on Chilean Sandy Beach Fauna

Earthquake/tsunamis can have profound impacts on species and their genetic patterns. It is expected that the magnitude of this impact might depend on the species and the time since the disturbance occurs, nevertheless these assumptions remain mostly unexplored. Here we studied the genetic responses of the crustacean species Emerita analoga, Excirolana hirsuticauda, and Orchestoidea tuberculata to the 27F mega-earthquake/tsunami that occurred in Chile in February 2010. mtDNA sequence analyses revealed a lower haplotype diversity for E. analoga and E. hirsuticauda in impacted areas one month after the 27F, and the opposite for O. tuberculata. Three years after the 27F we observed a recovery in the genetic diversity of E. analoga and E. hirsuticauda and decrease in the genetic diversity in O. tuberculata in 2/3 of sampled areas. Emerita analoga displayed decrease of genetic differentiation and increase in gene flow explained by long-range population expansion. The other two species revealed slight increase in the number of genetic groups, little change in gene flow and no signal of population expansion associated to adult survival, rapid colonization, and capacity to burrow in the sand. Our results reveal that species response to a same disturbance event could be extremely diverse and depending on life-history traits and the magnitude of the effect.

Persistence of phylogeographic footprints helps to understand cryptic diversity detected in two marine amphipods widespread in the Mediterranean basin

Amphipods of the genus Gammarus are a vital component of macrozoobenthic communities in European inland and coastal, marine and brackish waters of the Mediterranean and the Black Sea. Exceptional levels of cryptic diversity have been revealed for several widespread freshwater Gammarus species in Europe. No comprehensive assessment has yet been made for brackishwater counterparts, such as Gammarus aequicauda and G. insensibilis, which are among the most widely dispersed members of the so-called "G. locusta group" in the Mediterranean and in the Black Sea. Here we probe the diversity of these morphospecies examining the partitioning of mtDNA and nDNA across multiple populations along their distribution range and discuss it within the regional paleogeographic framework. We gathered molecular data from a collection of 166 individuals of G. aequicauda and G. insensibilis from 47 locations along their distribution range in the Mediterranean including the Black Sea. They were amplified for both mitochondrial COI and 16S rRNA as well as the nuclear 28S rRNA. All five MOTU delimitation methods (ABGD, BIN, bPTP, GMYC single and multiple threshold models) applied revealed deep divergence between Black Sea and Mediterranean populations in both G. aequicauda and G. insensibilis. There were eight distinct MOTUs delimited for G. aequicauda (6-18% K2P) and 4 MOTUs for G. insensibilis (4-14% K2P). No sympatric MOTUs were detected throughout their distribution range. Multimarker time-calibrated phylogeny indicated that divergence of both G. aequicauda and G. insensibilis species complexes started already in the late Oligocene/early Miocene with the split between clades inhabiting eastern and western part of the Mediterranean occurring in both species at the similar time. Our results indicate a high cryptic diversity within Mediterranean brackishwater Gammarus, similar to that observed for freshwater counterparts. Moreover, the phylogenetic history combined with the current geographic distribution indicate that the evolution of both studied Gammarus morphogroups has been strongly connected with the geological events in the Mediterranean Basin and it reflect the turbulent history of the area.

Geographic isolation facilitates the evolution of reproductive isolation and morphological divergence

Geographic isolation is known to contribute to divergent evolution, resulting in unique phenotypes. Oftentimes morphologically distinct populations are found to be interfertile while reproductive isolation is found to exist within nominal morphological species revealing the existence of cryptic species. These disparities can be difficult to predict or explain especially when they do not reflect an inferred history of common ancestry which suggests that environmental factors affect the nature of ecological divergence. A series of laboratory experiments and observational studies were used to address what role biogeographic factors may play in the ecological divergence of Hyalella amphipods. It was found that geographic isolation plays a key role in the evolution of reproductive isolation and divergent morphology and that divergence cannot be explained by molecular genetic variation.

Epigean gammarids survived millions of years of severe climatic fluctuations in high latitude refugia throughout the Western Carpathians

Isolated glacial refugia have been documented in Central Europe for a number of taxa, but conclusive evidence for epigean aquatic species has remained elusive. Using molecular data (mitochondrial and nuclear markers), we compared the spatial patterns of lineage diversity of the widely distributed Gammarus fossarum species complex between two adjacent biogeographically and geomorphologically distinct Central European regions: the Bohemian Massif and the Western Carpathians. We investigated if the observed patterns of spatial diversity are more likely to stem from historical or present-day factors. Phylogenetic and phylogeographic analyses revealed eight phylogenetically diverse lineages: two exhibiting local signatures of recent demographic expansion inhabit both regions, while the other six display a relict distributional pattern and are found only in the Western Carpathians. Molecular dating indicates that these lineages are old and probably diverged throughout the Miocene (7-18Ma). Furthermore, their distribution does not seem to be constrained by the present boundaries of river catchments or topography. The contrasting spatial patterns of diversity observed between the two regions thus more likely result from historical rather than contemporaneous or recent factors. Our results indicate that despite the high latitude and proximity to the Pleistocene ice sheets, the Western Carpathians functioned as long-term glacial refugia for permanent freshwater fauna, allowing the uninterrupted survival of ancient lineages through millions of years of drastic climatic fluctuations.