Sympatric Occurrence Research Articles

Mapping a floral trait in Shepherds purse – ‘Stamenoid petals’ in natural populations of Capsella bursa-pastoris (L.) Medik

Striking feature of angiosperm diversity is the huge number of variations in corolla morphology including complex innovations like variations in symmetry or the identity and number of floral organs. Throughout the Brassicaceae, the disymmetric flower structure is highly conserved. Still, quite a few floral alterations occur like a variant of Common Shepherds purse (Capsella bursa-pastoris), in which all petals have been transformed into additional stamens. This “decandric” phenotype has been reported for the first time about 200 years ago. In some of the original locations the variant has been recovered recently. The long term persistence indicates the establishment of an evolutionary novelty in wild populations in sympatric occurrence with wild-type plants. Due to this fact the floral variant has become an interesting model for evolutionary studies. The phenotype is heritable and just a single locus, termed “Stamenoid petals” (Spe), is assumed to be involved in the molecular origin. To unravel the chromosomal localization of this locus, a linkage map analysis was carried out using molecular markers (AFLPs, RAPDs). The final map includes 15 linkage groups and the floral trait was integrated on linkage group 12 (CBP12) including six AFLP markers. Out of these, five markers were successfully sequenced and revealed sequence identities with chromosome IV of the A. thaliana genome. Interestingly, AGAMOUS is located on this chromosome, the only class C floral organ identity gene in the A. thaliana genome, which is compatible with the assumption that Spe is an allele of AGAMOUS rather than a regulator of that gene.

Relative abundance of two dreissenid species, Dreissena polymorpha and Dreissena rostriformis bugensis in the Lower Don River system, Russia

Relative abundance of two dreissenid species, Dreissena rostriformis bugensis and Dreissena polymorpha, in the total dreissenid community was calculated for 15 sites in the lower Don River system, Russia, between 1977 and 2010 to determine relative trends in their sympatric occurrence. The proportion of D. r. bugensis first increased at most stations reaching a maximum by 1999. However, after 1999, this species consistently decreased at 14 of the 15 sites. Degree of decline seems to correlate strongly to calcium content and total mineral content of the water. At sites in the Manych River with a higher Ca 2+ and total mineral content, the proportion of D. r. bugensis in the total dreissenid population declined from 65–75% in 1999 to 14–22% by 2009–2010, whereas at sites in the Don River with lower Ca 2+ and total mineral content its proportion declined from 25–50% to only 1 %. However, Ca 2+ and total mineral content cannot explain the synchronous and consistent long-term decrease in relative numbers as observed. D. r. bugensis normally displaces D. polymorpha over time due to superior physiological characteristics. Reasons for the decline of D. r. bugensis in the total dreissenid community are unclear, but given its synchronicity despite different times of invasion and hence species interactions we assume a macroregional factor affecting all the populations examined.

Habitat alteration enables hybridisation between Lesser Spotted and Greater Spotted Eagles in north-east Poland

SummaryWetlands in the Biebrza Valley, north-east Poland, are inhabited by two closely related Aquila species: the more numerous Lesser Spotted Eagle A. pomarina prefers human-transformed landscapes, whereas the very rare Greater Spotted Eagle A. clanga is associated with natural marshy landscapes. At least since the last decade of the 20th century, these two species have been known to hybridise in the broad zone of their sympatric occurrence in Europe. The aim of the present study was to compare habitat preferences of both spotted eagle species in order to detect which environmental factors could increase the probability of hybridisation. We analysed nesting and hunting habitats for 148 breeding territories (61 of A. pomarina, 56 of A. clanga and 31 of mixed pairs). As expected, the presence of breeding Greater Spotted Eagles was associated with non-transformed marshy landscapes, whereas Lesser Spotted Eagles clearly preferred human-transformed areas. We hypothesised that mixed pairs should occur in intermediate habitat, confirming this assumption by analysing several variables: distance to human settlements, distance to open areas, and proportion of wetlands, shrublands, grasslands, agricultural mosaic and arable land. Results of this study suggest that some landscape changes can enable two species with different habitat requirements to inhabit the same area and hybridise. This scenario has potential conservation implications for the rarer species, Greater Spotted Eagle, which has narrower habitat preferences.

Remotely sensed forest structural complexity predicts multi species occurrence at the landscape scale

Along with plant species composition forest structural complexity is an important determinant of forest biodiversity, but difficult to predict in space from field data. We analyzed forest structural complexity based on a comprehensive set of variables derived from nationally available, area-wide remote sensing, particularly LiDAR data. We generated variables related to vertical and horizontal structural heterogeneity, as well as site factors potentially indicating the abundance of weakened trees or snags. We used them to predict the occurrence of four bird species with narrow and complementary structural habitat requirements, together being indicative of structurally diverse forests. Presence/absence data of Capercaillie (Tetrao urogallus), Hazel Grouse (Bonasa bonasia), Three-toed Woodpecker (Picoides tridactylus) and Pygmy Owl (Glaucidium passerinum) from three biogeographic mountain regions in Switzerland were used to calibrate species distribution models (boosted regression trees BRT) for each species individually, as well as for the sympatric occurrence of at least three of the four target species. The predictive deviances explained (D2) and the AUC values obtained from cross-validation ranged from 15.5% to 63.1% and 0.77% to 0.97% respectively. Sympatric species occurrence reflecting overall forest structural complexity was predicted best, with an outstanding accuracy. To support management and monitoring schemes we identified variable threshold effects based on partial dependence plots. Variables related to vertical foliage distributions were most important, followed by horizontal structural attributes such as canopy height variations, forest edges and gaps. Site factors such as topographic position improved all models and were most important for the species depending on weakened trees and dead wood. We conclude that recent advances in remote sensing allow for large-scale determination of forest structural characteristics suitable for developing species and habitat distribution models of considerable generality, while keeping an unprecedented level of detail. Our approach allows forest managers to amend regional and countrywide management plans with reliable maps depicting areas of high forest structural complexity and habitat quality, which will facilitate the integration of conservation-relevant information into multifunctional forestry.

Habitat use in an assemblage of Central American wandering spiders

The sympatric occurrence of species is thought to be based mainly on the differences in their use of habitat and of limiting resources. Segregating parameters may be of spatial or temporal character and may include behavioral differences. We hypothesized that species of large hunting spider living sympatrically in a Costa Rican lowland rain forest should differ in their habitat and/or hunting microhabitat preferences, in daily activity pattern, and, as an adaptation to the preferred hunting microhabitat, in their specific ability to adhere to smooth surfaces. We found an assemblage of eight large species of the families Ctenidae and Trechaleidae, consisting of three subguilds: 1) two semi-aquatic species with low adhesion ability, 2) three forest-floor dwelling species with good adhesion ability, and 3) three vegetation dwelling species showing very good adhesion ability. The species were partially segregated by habitat type, with two of the vegetation dwelling species preferring the treeless area of a temporary swamp. We found no species-specific differences in daily activity patterns. The similarity in community structure between this Costa Rican and a central Amazonian assemblage suggests the existence of similar structuring mechanisms in wandering spider assemblages in climatically similar biomes.

Freshwater habitat associations between pink (Oncorhynchus gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in a watershed dominated by sockeye salmon (O. nerka) abundance

AbstractTo understand the interplay between habitat use and contemporary anadromous Pacific salmon, Oncorhynchus spp., distributions we explored the habitat associations of three species, pink (O. gorbuscha), chum (O. keta) and Chinook salmon (O. tshawytscha) in streams of the Wood River system of Bristol Bay, Alaska, where sockeye salmon (O. nerka) are numerically dominant. We developed models to investigate the occurrence of nondominant salmon in relation to habitat characteristics and sockeye salmon density, using four decades of salmon presence and abundance data. The frequency of occurrence and abundance of nondominant species increased with watershed drainage area and stream depth and decreased with sockeye salmon density. The range of occurrence varied from nonexistent to perennial for the other species in sockeye‐dominated streams. Increasing watershed area resulted in larger stream habitat area and deeper habitats, allowing for the sympatric occurrence and persistence of all salmon species. The relationships between habitat and the presence of these Pacific salmon help define their requirements but also remind us that the patterns of presence and absence, within the overall ranges of salmon species, have yet to be fully understood.

Environmental Factors Affecting the Differential use of Foraging Habitat by Three Sympatric Species ofPipistrellus

We identified several ecological parameters that may promote the foraging habitat differentiation by sympatric bat species. The exploitation of discrete habitats was shown to facilitate the coexistence of morphologically similar species. Bats represent a model species group, where many morphologically similar species exploit similar resources, e.g. insects as prey organisms. We studied three closely related species of bats in a Central European region of sympatric occurrence — the common pipistrelle (Pipistrellus pipistrellus), Nathusius’ pipistrelle (P. nathusii), and the soprano pipistrelle (P. pygmaeus). We employed point locality data and niche-based species distribution modelling (maximum entropy modelling, ‘MaxEnt’) to model the habitat use by these species. A restricted distribution of P. pygmaeus and P. nathusii compared to P. pipistrellus was observed that may indicate a stronger habitat specialization of these two species compared to P. pipistrellus. Land cover, as well as several climatic varia...

Crocodylian diversity peak and extinction in the late Cenozoic of the northern Neotropics

Northern South America and South East Asia are today's hotspots of crocodylian diversity with up to six (mainly alligatorid) and four (mainly crocodylid) living species respectively, of which usually no more than two or three occur sympatrically. In contrast, during the late Miocene, 14 species existed in South America. Here we show a diversity peak in sympatric occurrence of at least seven species, based on detailed stratigraphic sequence sampling and correlation, involving four geological formations from the middle Miocene to the Pliocene, and on the discovery of two new species and a new occurrence. This degree of crocodylian sympatry is unique in the world and shows that at least several members of Alligatoroidea and Gavialoidea coexisted. By the Pliocene, all these species became extinct, and their extinction was probably related to hydrographic changes linked to the Andean uplift. The extant fauna is first recorded with the oldest Crocodylus species from South America.

The early Turolian (late Miocene) Cervidae (Artiodactyla, Mammalia) from the fossil site of Dorn-Dürkheim 1 (Germany) and implications on the origin of crown cervids

Dental and cranial appendage remains of Cervidae from the fossil site of Dorn-Durkheim are studied in detail. The material mainly includes isolated teeth, isolated pedicles and antler pieces. Neither tooth rows nor complete appendages are recorded. Comparative morphology and statistics of morphometrics (principal component analysis and discriminant analysis) allow for the classification of small and large dentitions, small cranial appendages, two morphotypes of large pedicles and two morphotypes of large antlers. Possible combinations of the classified units document the sympatric occurrence of three species, namely, Procapreolus sp., Muntiacinae gen. and sp. indet., cf. Cervavitulus mimus, but the fragmentary condition of the material leads to ambiguity regarding their composition and, consequently, to a certain extent regarding the taxonomic identification. However, these remains indicate the contemporaneous occurrence of early Turolian members of the crown cervids Muntiacinae and Capreolinae and close a previous spatiotemporal gap in the European cervid record. In addition, their presence proves the progressive turnover from dichotomous-antlered muntiacines to early monopodial-antlered crown cervids from NE to SW Europe in the late Miocene. The taxonomical assignment challenges the recent hypothesis on the origin of crown Cervidae around the middle/late Miocene border since Dorn-Durkheim cervids provide further evidence for the successive achievement of derived characters in cranial appendages of crown cervids (mediopostorbital position and backwards orientation of pedicles, coronet development, shaft development/elongation, beam development and increase in number of antler tines) in the lineage of crown cervids, which originated during the middle Miocene.

Diversity of Culex torrentium Martini, 1925 — a potential vector of arboviruses and filaria in Europe

Culex torrentium is one of the most common mosquito species in Germany. Due to its sympatric occurrence as well as its similar morphological and ecological characteristics, it has often been confused with another common species, Culex pipiens. Both species are known to be potential vectors for different arboviruses (not only in Germany) with C. torrentium being a possible vector for Sindbis or Ockelbo virus. In our study, we analyzed the genetic variability in a 658 bp fragment of the cytochrome c oxidase subunit I gene (coxI) of C. torrentium, from nine localities in the Frankfurt/Rhine-Main Metropolitan Region. The results of our genetic survey indicate a higher genetic diversity in this gene region for C. torrentium than for the morphologically similar C. pipiens. Our findings may explain the difficulties in the past to find morphological characteristics that apply to all populations of C. torrentium, when attempting to separate them clearly from C. pipiens, by any other criteria than male genitalia. Being ornithophilic, possible hybrids between C. torrentium and the humanophilic C. pipiens biotype molestus, could potentially serve as important vectors for zoonotic diseases. Therefore, we recommend that greater emphasis is placed on the ecological characteristics, population structure, and the taxonomy of this often neglected species, in the future.

Polyploidy and invasion of English ivy (Hedera spp., Araliaceae) in North American forests

Polyploidy is a common feature of agricultural weeds and natural area invaders. There are few studies comparing related diploid and polyploid exotics, however, and it is unclear what ecological and genetic factors favor the establishment of weedy polyploids. This research characterizes the geographic distribution and phenotypic characteristics of diploid Hedera helix and tetraploid Hedera hibernica, European species that are invading North American forests. To confirm the taxonomic affinity of invasive plants, we sequenced five non-coding cpDNA regions for 108 individuals (105 populations) as well as reference samples representing all species in the genus Hedera. Because diploid H. helix and tetraploid H. hibernica are poorly distinguished by morphology and DNA sequence, we used flow cytometry to determine their distribution (585 individuals). More than 90 % of sampled plants had cpDNA sequences identical or similar to H. helix sensu lato and H. hibernica. Diploid H. helix was dominant on the U.S. east coast (78.5 % of sampled plants) while tetraploid H. hibernica was dominant on the U.S. west coast (72.2 % of sampled plants), mirroring the species’ occurrence in maritime versus continental climates of Europe. Moreover, for sympatric occurrences in the Pacific Northwest, H. hibernica was larger and more frequently reproductive than H. helix. In a 2-year garden experiment, tetraploid H. hibernica had substantial architectural differences compared to diploid H. helix, including larger (but less numerous) leaves and thicker (but less branched) stems. Field experiments are needed to evaluate “pre-adaptation” (directional ecological filtering) and other factors mediating the invasion of H. helix and H. hibernica.

Redescription of Astyanax multidensEigenmann, 1908 (Characiformes: Characidae), a small characid of the Brazilian Amazon

Astyanax multidensis redescribed based on syntypes and additional specimens from the rio Amazonas at Silves, Amazonas State and Óbidos, Pará State, and the rios Trombetas, Tapajós, Xingú, and Araguaia.Astyanax multidensis distinguished from congeners by the unique combination of five to seven maxillary teeth, 31 to 34 pored lateral-line scales, 20 to 23 branched anal-fin rays, and a dark triangular blotch restricted to the middle caudal-fin rays. Astyanax multidens was collected syntopically with Jupiaba paranatinga in the rio Tapajós basin and with Jupiabacf. essequibensis in the rio Xingu basin, which have paired anteriorly oriented pelvic-fin spines, a antipredatory mechanism. Based on the external morphological similarity betweenAstyanax multidens and the two species ofJupiaba, their sympatric occurrence, and their distinct phylogenetic position, we interpret this a case of Batesian mimicry.

Molecular discrimination of toxic and non-toxic Alexandrium species (Dinophyta) in natural phytoplankton assemblages from the Scottish coast of the North Sea

Molecular methods provide promising tools for routine detection and quantification of toxic microalgae in plankton samples. To this end, novel TaqMan minor groove binding probes and primers targeting the small (SSU) or large (LSU) ribosomal subunit (rRNA) were developed for two species of the marine dinoflagellate genus Alexandrium (A. minutum, A. tamutum) and for three groups/ribotypes of the A. tamarense species complex: Group I/North American (NA), Group II/Mediterranean (ME) and Group III/Western European (WE). Primers and probes for real-time quantitative PCR (qPCR) were species-specific and highly efficient when tested in qPCR assays for cross-validation with pure DNA from cultured Alexandrium strains. Suitability of the qPCR assays as molecular tools for the detection and estimation of relative cell abundances of Alexandrium species and groups was evaluated from samples of natural plankton assemblages along the Scottish east coast. The results were compared with inverted microscope cell counts (Utermöhl technique) of Alexandrium spp. and associated paralytic shellfish poisoning (PSP) toxin concentrations. The qPCR assays indicated that A. tamarense (Group I) and A. tamutum were the most abundant Alexandrium taxa and both were highly positively correlated with PSP toxin content of plankton samples. Cells of A. tamarense (Group III) were present at nearly all stations but in low abundance. Alexandrium minutum and A. tamarense (Group II) cells were not detected in any of the samples, thereby arguing for their absence from the specific North Sea region, at least at the time of the survey. The sympatric occurrence of A. tamarense Group I and Group III gives further support to the hypothesis that the groups/ribotypes of the A. tamarense species complex are cryptic species rather than variants belonging to the same species.

Three new species of Callulops (Anura: Microhylidae) from western New Guinea

Various works in recent years have shown that the microhylid genus Callulops is not a monophyletic group, and that the „central species“ Callulops robustus is not, as previously assumed, distributed over the entire island of New Guinea. Further, Callulops robustus apparently does not occur in the northwestern part of the island. This species is there replaced by a number of other species, and at present no sympatric occurrence of species in the C. robustus-group are known. On the basis of our own collections in the Wondiwoi Mountains at the base of the Wandammen Peninsula as well as on the islands of Yapen and Biak (Cenderawasih Bay) in the years 1998 to 2003, we here describe three new species in the Callulops robustus-group.

The Culex pipiens Complex in Continental Portugal: Distribution and Genetic Structure

Portugal is a southern European country that displays favorable ecological conditions for the establishment of West Nile virus (WNV) transmission cycles. Competent mosquito vector species are present throughout the country. Among the species with reported cases of WNV isolation in Portugal, Culex pipiens is the most ubiquitous and abundant mosquito. This species exhibits two biological forms with differences in host preferences. The molestus form has a greater tendency to feed upon humans and other mammals whereas the pipiens form prefers avian hosts. In northern latitudes, both forms are physically separated, with molestus occupying underground habitats and pipiens being found aboveground. However, the warmer climatic conditions of southern regions such as Portugal may favor the sympatric occurrence of both forms hence promoting interform hybridization. Genetic introgression between molestus and pipiens forms may result in a higher propensity for admixed populations to serve as bridge-vectors of WNV between humans and birds. Here we revise our present knowledge on the distribution, role in WNV transmission and genetic structure of the Cx. pipiens complex in continental Portugal. We focus on recent findings of sympatric molestus and pipiens populations that display considerable levels of hybridization and discuss the epidemiological repercussions of this occurrence.

Lack of taxonomic information from parietal spine size invalidates subspecies in the Atlantic hookear sculpin Artediellus atlanticus

An analysis of 107 individuals of Atlantic hookear sculpin Artediellus atlanticus from the Barents Sea-Svalbard region and from north-east Greenland shows that the state of the parietal spines, although not randomly distributed geographically, occurs sympatrically. They do not diagnostically describe populations. They are therefore inept for subspecies delimitation into Artediellus atlanticus atlanticus, Artediellus atlanticus corniger and Artediellus atlanticus europaeus. Sympatric occurrence of parietal spine states called for a molecular approach to look for differences at a species level. Sequencing the mitochondrial genes, cytochrome oxidase c subunit I (coI) and cytochrome b (cytb), shows no difference between individuals with different parietal spine size. Thus, there is no evidence of the spine states representing species-level variation. The study shows that parietal spine size has no taxonomic information for this species. The patterns of variation in parietal spine size differ to some degree between the sexes.

Convergent Evolution within an Adaptive Radiation of Cichlid Fishes

The recurrent evolution of convergent forms is a widespread phenomenon in adaptive radiations (e.g., [1-9]). For example, similar ecotypes of anoles lizards have evolved on different islands of the Caribbean, benthic-limnetic species pairs of stickleback fish emerged repeatedly in postglacial lakes, equivalent sets of spider ecomorphs have arisen on Hawaiian islands, and a whole set of convergent species pairs of cichlid fishes evolved in East African Lakes Malawi and Tanganyika. In all these cases, convergent phenotypes originated in geographic isolation from each other. Recent theoretical models, however, predict that convergence should be common within species-rich communities, such as species assemblages resulting from adaptive radiations. Here, we present the most extensive quantitative analysis to date of an adaptive radiation of cichlid fishes, discovering multiple instances of convergence in body and trophic morphology. Moreover, we show that convergent morphologies are associated with adaptations to specific habitats and resources and that Lake Tanganyika's cichlid communities are characterized by the sympatric occurrence of convergent forms. This prevalent coexistence of distantly related yet ecomorphologically similar species offers an explanation for the greatly elevated species numbers in cichlid species flocks.

Habitat Preferences of the Sympatric Barred Warbler (Sylvia nisoria) and the Red-Backed Shrike (Lanius collurio) Breeding in Central Poland

The phenomenon of creating a breeding association by the barred warbler (Sylvia nisoria) and the red-backed shrike (Lanius collurio) was documented relatively long ago by several researchers. Some of the authors suggest that this phenomenon is a result of similar habitat requirements rather than a product of active selection. The main goal of this study was a quantitative analysis of differences and similarities in selection of breeding habitats by both species in the area of their sympatric occurrence. Research was carried out in the years 2009–2011 in the study plot located in the Middle Vistula Valley (central Poland). The red-backed shrike preferred shrubs and open areas, however, it avoided woods and waters. The only habitat strongly preferred by the barred warbler was bushes, and this species avoided waters, woods and open areas. Neither species nested in places with a thick tree concentration. Because of differences in their feeding strategy, as opposed to barred warblers, red-backed shrikes prefer...

Cryptic species inIphisa elegansGray, 1851 (Squamata: Gymnophthalmidae) revealed by hemipenial morphology and molecular data

Iphisa elegans Gray, 1851 is a ground-dwelling lizard widespread over Amazonia that displays a broadly conserved external morphology over its range. This wide geographical distribution and conservation of body form contrasts with the expected poor dispersal ability of the species, the tumultuous past of Amazonia, and the previously documented prevalence of cryptic species in widespread terrestrial organisms in this region. Here we investigate this homogeneity by examining hemipenial morphology and conducting phylogenetic analyses of mitochondrial (CYTB) and nuclear (C-MOS) DNA sequence data from 49 individuals sampled across Amazonia. We detected remarkable variation in hemipenial morphology within this species, with multiple cases of sympatric occurrence of distinct hemipenial morphotypes. Phylogenetic analyses revealed highly divergent lineages corroborating the patterns suggested by the hemipenial morphotypes, including co-occurrence of different lineages. The degrees of genetic and morphological distinctness, as well as instances of sympatry among mtDNA lineages/morphotypes without nuDNA allele sharing, suggest that I. elegans is a complex of cryptic species. An extensive and integrative taxonomic revision of the I. elegans complex throughout its wide geographical range is needed. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 361–376.

Salt tolerance of halophytes, research questions reviewed in the perspective of saline agriculture

Halophytes of the lower coastal salt marsh show increased salt tolerance, and under high salinity they grow faster than upper marsh species. We could not show reduced growth rate of halophytes compared with glycophytes when grown under non-saline conditions. This indicates limited energy costs associated with high-salt tolerance in plants of genera such as Salicornia, providing a good perspective of saline agriculture cultivating Salicornia as a vegetable crop.We show that halophytes do not occur on non-saline or inland sites because of a reduced growth rate at low soil salinity, but probably due to other ecological traits of glycophytic upper marsh species. These traits provide competitive advantage over lower salt marsh halophytes, such as earlier germination and increased growing season length.Some halophytic Amaranthaceae (Salicornioideae, Chenopodioideae and Suaedoideae) are not just highly salt tolerant, their growth rate is stimulated at a salinity range of 150–300mM NaCl. Alternatively this may be described as depressed growth at low salinity.Selective pressure for such high-salt tolerance and salt stimulated growth likely occurred with prevailing arid climate and saline soil conditions. Under such conditions highly-salt tolerant succulent Salicornioideae, Chenopodioidea and Suaedoideae may have evolved about 65Mya. In the context of evolution and diversication of land plants this origin of highly-salt tolerant succulent plants is relatively recent.Such high-salt tolerance might be characterized as constitutive in comparison with inducible (lower) salt tolerance of other dicotyledonae and monocotyledonae (Poaceae) species. Levels of salt tolerance of the latter type span a large range of low, intermediate to high-salt tolerance, but do not include salt stimulated growth. Salt tolerant traits of the latter inducible type appear to have evolved repeatedly and independently.Early highly-salt tolerant succulent Salicornioideae, Chenopodioidea and Suaedoideae were perennial and frost sensitive and occurred in warm temperate and Mediterranean regions. A shift from the perennial Sarcocornia to an annual life form has been phylogenetically dated circa 9.4–4.2Mya and enabled evolution of annual hygrohalophytes in more northern coastal locations up to boreal and subarctic coastal sites avoiding damage of winter frost. Diversification of such hygrohalophytes was facilitated by polyploidization (e.g. occurrence of tetraploid and diploid Salicornia species), and a high degree of inbreeding allowing sympatric occurrence of Salicornia species in coastal salt marshes.High-level salt tolerance is probably a very complex polygenic trait. It is unlikely that glycophytes would accommodate the appropriate allelic variants at all the loci involved in halophyte salt tolerance. This might explain why attempts to improve crop salt tolerance through conventional breeding and selection have been unsuccessful to date.Genetic engineering provides a viable alternative, but the choice for the appropriate transgenes is hampered by a fundamental lack of knowledge of the mechanisms of salt tolerance in halophytes. The chances to identify the determinant genes through QTL analyses, or comparisons among near isogenic lines (NILS) are limited. Salt-tolerance is usually a species-wide trait in halophytes, and intra-specific divergence in salt tolerance in facultative halophytes seems to be often associated with chromosomal incompatibility.A variety of candidate salt tolerance genes been identified in Arabidopsis thaliana, among which genes encoding Na+ and K+ transporters, and genes involved in the general stress or anti-oxidant response, or in compatible solute metabolism. Many of these genes have been over-expressed in different glycophytic hosts, which usually appeared to alleviate, to some degree, the response to high salinity levels. However, with few exceptions, there are no indications that the same genes would be responsible for the superior salt tolerance in (eu)halophytes. Comparisons of gene expression and gene promoter activity patterns between halophytes and glycophytes are, with few exceptions, virtually lacking, which is a major omission in current day salt tolerance research.Full-genome transcriptomic comparisons between halophytes and related glycophytes through deep sequencing seem to be the most promising strategy to identify candidate genetic determinants of the difference in salt tolerance between halophytes and glycophytes.The most reliable validation of any candidate gene is through silencing the gene in the halophytic genetic background, preferably down to the level at which it is expressed in the glycophyte reference species. This requires genetically accessible halophyte models, which are not available to date, with the exception of Thellungiella halophila. However, more models are required, particularly because T. halophila is not a typical halophyte. Eventually, the pyramiding of validated salt tolerance genes under suitable promoters may be expected to be a viable strategy for crop salt tolerance improvement.