Yaron Tikochinski

The change in genetic diversity down the core-edge gradient in the eastern spadefoot toad (Pelobates syriacus)

Several hypotheses are available to predict change in genetic diversity when approaching peripheral populations. We used the eastern spadefoot toad in Israel as a model system to examine these hypotheses using population genetics analyses and network theory. Our results contradicted most of the predictions from the ‘abundant centre’ model, that edge populations should have lower density and lower genetic diversity than core populations. Furthermore, dispersal rate between core and peripheral populations is expected to be asymmetric, mostly directed outwards from the core population, but we did not detect such a trend. Our data did not support the hypothesis of no change or a non‐linear change in genetic diversity towards the range edge. However, our results did fit the Fisher (The Genetical Theory of Natural Selection, Clarendon Press, Oxford, 1930) hypothesis, which predicts increase in genetic variability from core to edge of distribution. We attributed this finding to the much harsher climatic and abiotic conditions at the edge, which must be tolerated over generations by both tadpoles and post‐metamorphic individuals in this region. Finally, our results have significant conservation implications for the survival of this species in Israel, where it is critically endangered. We identified two distinct communities, which are genetically linked through two specific rain pools in the Upper Galilee. Details on the spatial subdivision of this species are cardinal for future management and restoration of temporary wetlands in Israel.

Saurida lessepsianus a new species of lizardfish (Pisces: Synodontidae) from the Red Sea and Mediterranean Sea, with a key to Saurida species in the Red Sea

Saurida lessepsianus n. sp., a lizardfish (Aulopiformes: Synodontidae) from the Red Sea and Mediterranean Sea, previously misidentified as S. undosquamis (Richardson) and more recently as S. macrolepis Tanaka, is described as a new species. It is characterised by the following combination of characters: dorsal fin with 11-12 rays; pectoral fins with 13-15 rays; lateral-line scales 47-51; transverse scale rows above lateral line 4½, below lateral line 5½; pectoral fins moderately long (extending to between just before or just beyond a line from origin of pelvic fins to origin of dorsal fin); 2 rows of teeth on outer palatines; 0-2 teeth on vomer; tongue with 3-6 rows of teeth posteriorly; caudal peduncle slightly compressed (depth a little more than width); upper margin of caudal fin with row of 3-8 (usually 6 or 7) small black spots; stomach pale grey to blackish anteriorly; intestine whitish. The species is common in the Red Sea and as a result of Lessepsian migration through the Suez Canal, it is now widely distributed in the eastern Mediterranean. The taxonomic status of two other Red Sea nominal species, Saurus badimottah Rüppell [= Saurida tumbil (Bloch)] and Saurida sinaitica Dollfus in Gruvel (a nomen nudum), is clarified. A key is provided for the species of Saurida in the Red Sea.

Preliminary data on the genetic structure of a highly successful invading population of oyster suggesting its establishment dynamics in the Levant

Abstract Biological invasions in the marine environment are a worldwide threat to native communities. The opening of the Suez Canal, which connects the Red Sea with the Mediterranean, resulted in the most invaded marine system in the world, causing dramatic ecological changes to the East Mediterranean Sea. One of the most prominent rocky benthos invertebrate invaders is the Indo-Pacific oyster Spondylus spinosus (family Spondylidae), first recorded along the Israeli coast in 1988. The biology and ecology of S. spinosus have not been studied in its native range or in the newly invaded one. We used field surveys to uncover the invasive oysters current status and molecular tools to characterize some aspects of its genetic population structure, in search of clues to its invasion dynamics. We found that S. spinosus forms dense populations along the Israeli Mediterranean coast and reaches large shell sizes. Using two mitochondrial DNA markers, we confirmed that the invading species is identical to that found in the Red Sea. The genetic structure of the population at five sites along the coast reveals a total of seven haplotypes. The most common haplotype was the only one found in the northern Red Sea population, whereas one Mediterranean site (Sdot Yam) was particularly variable (five haplotypes). We conclude that S. spinosus has become well established in the Mediterranean following more than two decades since its first record there. We suggest that the Sdot Yam site is where the oyster was first established and where repeated introductions may since have occurred.

Sillago suezensis, a new whiting from the northern Red Sea, and status of Sillago erythraea Cuvier (Teleostei: Sillaginidae)

The status of Sillago erythraea Cuvier in Cuvier and Valenciennes 1829 is re-examined. A lectotype designation by McKay in 1985 fixes it as a junior synonym of Sillago sihama (Forsskål in Niebuhr, 1775), which is restricted to the southern Red Sea. Northern Red Sea populations previously assigned to S. sihama or S. erythraea, are here described as Sillago suezensis sp. nov. Sillago suezensis is also distributed in the eastern Mediterranean Sea due to Lessepsian immigration through the Suez Canal. The new species is characterized within the Sillago sihama group, which has the swimbladder divided posteriorly into two tapering extensions projecting below the vertebral column extending into the tail musculature, by the absence of scales on the preopercle and on most of the opercle, a total number of 34 vertebrae, the swimbladder with lateral extensions each spreading a blind tubule anterolaterally, and a low position of the nostril. http://www.zoobank.org/urn:lsid:zoobank.org:act:B289CDF4-AE82-44D3-9AE1-4A2B514AD348

Genetic evidence for an undescribed species previously considered as Sillago sihama from the northern Red Sea

Abstract The augmentation of traditional taxonomy by the addition of genetic methods, particularly DNA analysis, has revealed that many species that appeared identical morphologically throughout their distribution range are actually divided into two or more genetically distinct species. The whiting, Sillago sihama, is a fish that was considered to be of a wide Indo-Pacific distribution. Not long ago, what was considered to be S. sihama invaded the Mediterranean from the Red Sea via the Suez Canal. In our study we sequenced a 655-bp region of the mitochondrial cytochrome c oxidase subunit I gene (COI) from Hong Kong, southern Red Sea and Mediterranean populations of Sillago. We discovered that the first two (HK and southern Red Sea) are genetically similar while the sequencing of the Mediterranean population shows a significant divergence, confirming the existence of two distinct species. We further sequenced a segment of 178 bp (of the 655 bp) from a formaldehyde-fixed specimen from the northern Red Sea (Gulf of Suez) and found it to be identical to that of the Mediterranean population. We were thus able to confirm that the northern Red Sea population is the source for the invading population. The mitochondrial control region (D-loop) analysis of the Mediterranean population revealed that all 38 specimens have a single mitochondrial haplotype.

Variation in repeat length and heteroplasmy of the mitochondrial DNA control region along a core–edge gradient in the eastern spadefoot toad (Pelobates syriacus)

Peripheral populations are those situated at the distribution margins of a species and are often subjected to more extreme abiotic and biotic conditions than those at the core. Here, we hypothesized that shorter repeat length and fewer heteroplasmic mitochondrial DNA (mtDNA) copies, which are associated with more efficient mitochondrial function, may be related to improved survival under extreme environmental conditions. We sampled eastern spadefoot toads (mostly as tadpoles) from 43 rain pools distributed along a 300‐km gradient from core to edge of the species’ distribution. We show that mean pool tandem repeat length and heteroplasmy increase from edge to core, even after controlling for body size. We evaluate several alternative hypotheses and propose the Fisher hypothesis as the most likely explanation. However, additional sequential sampling and experimental studies are required to determine whether selection under extreme conditions, or alternative mechanisms, could account for the gradient in heteroplasmy and repeat length in the mtDNA control region.

Surface properties of SAR11 bacteria facilitate grazing avoidance

Oceanic ecosystems are dominated by minute microorganisms that play a major role in food webs and biogeochemical cycles1. Many microorganisms thrive in the dilute environment due to their capacity to locate, attach to, and use patches of nutrients and organic matter2,3. We propose that some free-living planktonic bacteria have traded their ability to stick to nutrient-rich organic particles for a non-stick cell surface that helps them evade predation by mucous filter feeders. We used a combination of in situ sampling techniques and next-generation sequencing to study the biological filtration of microorganisms at the phylotype level. Our data indicate that some marine bacteria, most notably the highly abundant Pelagibacter ubique and most other members of the SAR 11 clade of the Alphaproteobacteria, can evade filtration by slipping through the mucous nets of both pelagic and benthic tunicates. While 0.3 µm polystyrene beads and other similarly-sized bacteria were efficiently filtered, SAR11 members were not captured. Reversed-phase chromatography revealed that most SAR11 bacteria have a much less hydrophobic cell surface than that of other planktonic bacteria. Our data call for a reconsideration of the role of surface properties in biological filtration and predator-prey interactions in aquatic systems.In situ sampling reveals that members of the SAR11 clade show significantly lower retention by mucous filter feeders, and that this is probably due to their reduced hydrophobic cell surface, suggesting that cell surface properties are important factors in predator–prey interactions.

Molecular comparison of geographically extreme populations of fish species of wide Indo-Pacific distribution

A total of six Red Sea inshore fish species with wide Indo-Pacific distribution, including Lessepsian migrants that reached the Mediterranean Sea via the Suez Canal, were studied and compared genetically to conspecific populations from Japan and the Seychelles. Examination of the cytochrome c oxidase 1 (COI) gene of Apogon cyanosoma, Sargocentron rubrum, Upeneus moluccensis, Spratelloide sdelicatulus, Gerres oyena and Terapon jarbua from Japan, the Red Sea, the Seychelles and the Mediterranean revealed that in five out of six fish species, a difference greater than 4% was found. These results indicate the importance of DNA genetic analysis in revealing possible cryptic species and supplementing classic taxonomic studies, as well as contributing to a reappraisal of the zoogeography and evolution of Indo-Pacific ichthyofauna and enhancing our understanding of fish biodiversity.

Author Correction: Surface properties of SAR11 bacteria facilitate grazing avoidance

In the version of this Letter originally published, the authors incorrectly stated that primers 28F-519R were reported in ref. 54 to underestimate the abundance of SAR11 in the ocean. This statement has now been amended in all versions of the Letter.