Natural Interspecific Hybrids Research Articles

Extant interspecific hybridization among trematodes within the Schistosoma haematobium species complex in Nigeria.

Natural interspecific hybridization between the human parasite (Schistosoma haematobium [Sh]) and bovine parasites (Schistosoma bovis [Sb], Schistosoma curassoni [Sc]) is increasingly reported in Africa. We developed a multi-locus PCR DNA-Seq strategy that amplifies two unlinked nuclear (transITS, BF) and two linked organellar genome markers (CO1, ND5) to genotype S. haematobium eggs collected from infected people in Ile Oluji/Oke Igbo, Ondo State (an agrarian community) and Kachi, Jigawa State (a pastoral community) in Southwestern and Northern Nigeria, respectively. Out of a total of 219 urine samples collected, 57 were positive for schistosomes. All patients from Jigawa state possessed an Sh mitochondrial genome and were infected with a genetic profile consistent with an Sh x Sb hybrid based on sequences obtained at CO1, ND5, transITS and BF nuclear markers. Whereas samples collected from Ondo state were more varied. Mitonuclear discordance was observed in all 17 patients, worms possessed an Sb mitochondrial genome but one of four different genetic profiles at the nuclear markers, either admixed (heterozygous between Sh x Sc or Sh x Sb) at both markers (n = 10), Sh at BF and admixed at transITS (Sh x Sc) (n = 5), admixed (Sh x Sc) at BF and homozygous Sc at transITS (n = 1) or homozygous Sh at BF and homozygous Sc at transITS (n = 1). Previous work suggested that zoonotic transmission of S. bovis in pastoral communities, where humans and animals share a common water source, is a driving factor facilitating interspecific hybridization. However, our data showed that all samples were hybrids, with greater diversity identified in Southwestern Nigeria, a non-pastoral site. Further, one patient possessed an S. bovis mitochondrial genome but was homozygous for S. haematobium at BF and homozygous for S. curassoni at transITS supporting at least two separate backcrosses in its origin, suggesting that interspecific hybridization may be an ongoing process.

Genomic analyses indicate two blue swimmer crab species in Australia, evidence for natural interspecific hybridization and genetic structure within species with implications for fisheries management and stock enhancement

Blue swimmer crab species are widely distributed in Indian and west Pacific Oceans including the coastline around Australia and have been identified as potential candidates for stock enhancement. A recent taxonomic review revealed the presence of two blue swimmer crab species in Australia, namely Portunus armatus which is found around most of the Australian coastline, and Portunus pelagicus which is found in the northern coast where it is sympatric with P. armatus. It is important to understand population structure and genetic diversity of Portunus spp. to efficiently manage stocks. In the present study we investigated species classification and population structure of Portunus spp. in Australia using full and partial genomic information, namely mitochondrial COX1 gene sequences derived from whole genome sequencing and single nucleotide polymorphic (SNP) markers developed from partial genome sequencing. Blue swimmer crab samples were collected from the western (n = 52), northern (n = 17) and eastern (n = 110) coasts of Australia. Genetic diversity and population genetic structure were assessed for within and between region variation. Our genomic results indicated the presence of two blue swimmer crab species in Australia. One, namely, P. pelagicus was found only in Northern Territory (Darwin), and other, namely P. armatus was found around Australia. There was evidence of natural hybridisation between two species in Northern Territory (Darwin) where they were sympatric. P. armatus populations from the western, northern and eastern regions were genetically different although there were no significant genetic differences observed between the Queensland and New South Wales populations nor between the two neighbouring populations in Western Australia. Results found in the present study supports the view that the P. armatus populations in western, northern and eastern regions of Australia should be treated as at least three different stocks. A lack of genetic structuring along the eastern coast suggests blue swimmer crabs can be considered as a single stock along the sampled range at least in relation to fisheries enhancement, release programs and broodstock management.

Evidence of a Natural Hybrid Oomycete Isolated from Ornamental Nursery Stock

The oomycete genus Phytophthora includes many plant pathogens important in agricultural and environmental systems. Natural interspecific hybridization has been reported several times in Phytophthora, and although the fundamental processes of interspecific hybridization and the consequences of subsequent ecological distribution are poorly understood, reports suggest some hybrids can infect a broader host range and display enhanced virulence compared to the putative parental species. During a survey carried out at the University of Aberdeen in 2014–2015, of oomycetes present in ornamental plants purchased via the internet, a batch of oomycete isolates remained unidentified, showing, in some isolates, features generally related to hybridization. The aim of this study was to determine whether hybridization events had occurred between endemic and introduced oomycetes, probably/possibly facilitated through the international plant trade. The list of isolates examined included a putative hybrid closely related to Phytophthora cryptogea. The putative hybrid isolate was further characterized, and pathogenicity were tests carried out on Eucalyptus globulus, using an isolate of P. cryptogea as a positive control. Cloning of ITS, COXI and β-tubulin genes resulted in different sequence versions of the putative hybrid isolate; after mapping and a polymorphism position comparison, it was concluded that the studied isolate contained genetic information from P. cryptogea, P. erythroseptica, P. kelmanii, P. sansomeana and Phytopythium chamaehyphon. A PCR-RFLP assay, a NEBcutter analysis and flow cytometry analysis (genomes ranged between 0.168 to 0.269 pg/2C) added further evidence of the hybrid nature of this isolate. The putative hybrid presented complex growing patterns ranging from rosaceous to chrysanthemum-like and had an optimum growth temperature of 25 °C. Although the putative hybrid produced visible symptoms of disease on E. globulus seedlings, assessment of the relative susceptibility of E. globulus to P. cryptogea and the putative hybrid indicated that P. cryptogea was significantly more virulent than the putative hybrid, based on mortality, disease severity and foliar symptoms.

Comparative transmission genetics of introgressed chromatin in reciprocal advanced backcross populations in Gossypium (cotton) polyploids.

Introgression is a potential source of valuable genetic variation and interspecific introgression lines are important resources for plant breeders to access novel alleles. Experimental advanced-generation backcross populations contain individuals with genomic compositions similar to those resulting from natural interspecific hybridization and provide opportunities to study the nature and transmission pattern of donor chromatin in recipient genomes. Here, we analyze transmission of donor chromatin in reciprocal backcrosses between G. hirsutum and G. barbadense. Across the genome, recurrent backcrossing in both backgrounds yielded donor chromatin at slightly higher frequencies than the Mendelian expectation in BC5F1 plants, while the average frequency of donor alleles in BC5F2 segregating families was less than expected. In the two subgenomes of polyploid cotton, the rate of donor chromatin introgression was similar. Although donor chromatin was tolerated over much of the recipient genomes, 21 regions recalcitrant to donor alleles were identified. Only limited correspondence is observed between the recalcitrant regions in the two backgrounds, suggesting the effect of species background on introgression of donor segments. Genetic breakdown was progressive, with floral abscission and seed inviability ongoing during backcrossing cycles. Regions of either high or low introgression tended to be in terminal chromosomal regions that are generally rich in both genes and crossover events, with long stretches around the centromere having limited crossover activity resulting in relatively constant low introgression frequencies. Constraints on fixation and selection of donor alleles highlights the challenges of utilizing introgression breeding in crop improvement.

Phylogeography of the endangered "eyed" turtles (genus Sacalia) and the discovery of a lineage derived from natural interspecific hybridization.

The herpetofauna of the Indomalayan bioregion of Asia suffers from severe habitat loss, unsustainable harvesting, and lack of research and conservation. Here, we investigated the range-wide phylogeography of the endangered "eyed" turtles (genus Sacalia, including the Beale's Eyed Turtle S. bealei and the Four-eyed Turtle S. quadriocellata) and discovered a natural interspecific hybrid turtle population in China. Based on phylogeny of the mitochondrial Cytochrome b gene of 101 samples in this study and public data, three major clades and six subclades were identified: S. bealei (SBE) in eastern-southern China, east S. quadriocellata in South China (northern east [SQUen] and southern east [SQUes] subclades), and west S. quadriocellata mainly in Vietnam (northern west [SQUwn], central west [SQUwc], and southern west [SQUws] subclades). We sequenced 16 nuclear DNA loci of 87 samples from SBE, SQUen, SQUes, and SQUwn subclades. Population genetic clustering analysis suggested a structure similar to the mitochondrial phylogeny, where most samples were classified into four genetic clusters corresponding to the four mtDNAsubclades. However, a proportion of samples carrying SQUen mtDNAhaplotypes formed an additional distinct cluster SHY. Those samples are found in the contact zone of the two species bearing mosaic and intermediate morphological characteristics. We detected an admixed ancestry in SHY from SBE and SQUen that conformed to an intrapopulation breeding scenario for at least hundreds of generations after the initial hybrid event, leading to a conclusion that SHY is a distinct and near-panmictic population derived from natural interspecific hybridization. In addition, SQUes (Hainan Island endemic) is of special concern due to significant isolation and low genetic diversity. We suggest that seven evolutionarily significant units should be recognized to facilitate appropriate conservation actions. These findings also highlight the urgent need for further herpetological research and conservation in this region.

Development of morphological marker on natural interspecific hybrid seedling of Acacia (Acacia mangium × Acacia auriculiformis) verified by molecular marker

Development of the hybridization between two different species of Acacia mangium and Acacia auriculiformis in Indonesia started in 2009 by establishing an open-pollinated orchard to produce the natural Acacia hybrid seed in Wonogiri District, Central Java Province. The design of the orchard was an alternate row between A. mangium and A. auriculiformis with a spacing of 5 × 5 meters. The orchard produced putative Acacia hybrid seeds firstly in 2013. Based on flowering synchronization between the two species, seeds from 38 sample trees of A. mangium were taken to identify their character seedling morphology to obtain the Acacia putative hybrid. The seedling morphological characteristics observed were leaf development patterns from the emergence of a true leaf (pinnate) until the pseudo leaf (phyllode) emerged. Acacia putative hybrid was then verified using a Simple Sequence Repeat (SSR) marker and Sequence Characterized Amplified Region (SCAR) to obtain the hybrid of A. mangium × A. auriculiformis. The result showed that the presence of 4-pinnate on the seedling development pattern was verified as 100% pure species of A. mangium and the opposite was 100% hybrid. In comparison, the presence of a true leaf of phyllode + 4-pinnate was verified as a 40% hybrid. The final estimation of Acacia hybrid seed production at the hybrid seed orchard on the first flowering was about 3.1% approximately based on the seedling leaf development pattern.

Genomic insights into the origin, domestication and diversification of Brassica juncea

Despite early domestication around 3000 BC, the evolutionary history of the ancient allotetraploid species Brassica juncea (L.) Czern & Coss remains uncertain. Here, we report a chromosome-scale de novo assembly of a yellow-seeded B. juncea genome by integrating long-read and short-read sequencing, optical mapping and Hi-C technologies. Nuclear and organelle phylogenies of 480 accessions worldwide supported that B. juncea is most likely a single origin in West Asia, 8,000–14,000 years ago, via natural interspecific hybridization. Subsequently, new crop types evolved through spontaneous gene mutations and introgressions along three independent routes of eastward expansion. Selective sweeps, genome-wide trait associations and tissue-specific RNA-sequencing analysis shed light on the domestication history of flowering time and seed weight, and on human selection for morphological diversification in this versatile species. Our data provide a comprehensive insight into the origin and domestication and a foundation for genomics-based breeding of B. juncea.

DNA barcoding supports existence of morphospecies complex in endemic bamboo genus Ochlandra Thwaites of the Western Ghats, India

Ochlandra Thwaites, an economically exploited bamboo genus of the Western Ghats of India is severely affected by unsustainable extraction, natural habitat destruction and endangerment of species resources. This taxonomically challenging genus consists of a genetic mixture of 10 related polyploid species that are difficult to define and classify using traditional morphology. The present study investigated the probability of DNA barcoding using seven standard barcode regions recommended by CBOL as a supplementary tool to define true species boundaries. Distance (MEGA v.6.0) and sequence similarity (TaxonDNA) based approaches highlighted the discriminatory power of psbA-trnH intergenic spacer barcode region, but did not support true species entities. Neighbour-joining and Bayesian inference trees supported the existence of morphospecies complex in seven species of the genus owing to weak reproductive barriers amongnaturally coexisting species. Morphological affinities existing within genus might have stemmed from natural interspecific hybridization events and consequent reticulate evolution in morphospecies complex of genus Ochlandra.

Preferential Disomic Segregation and C. micrantha/C. medica Interspecific Recombination in Tetraploid 'Giant Key' Lime; Outlook for Triploid Lime Breeding.

The triploid ‘Tahiti’ lime (C. x latifolia (Yu. Tanaka) Tanaka) naturally originated from a merger between a haploid ovule of lemon (C. x limon (L.) Burm) and a diploid pollen from a ‘Mexican’ lime (C. x aurantiifolia (Christm.) Swing). The very limited natural inter-varietal diversity and gametic sterility of C. latifolia requires a phylogenomic based reconstruction breeding strategy to insure its diversification. We developed a strategy based on interploid hybridization between diploid lemon and the doubled diploid ‘Giant Key’ lime. This lime is a doubled diploid of ‘Mexican’ lime, itself a natural interspecific F1 hybrid between C. medica L. and C. micrantha Wester. For an optimized breeding program, we analyzed the meiotic behavior of the allotetraploid lime, the genetic structure of its diploid gametes, the interspecific recombination between C. medica and C. micrantha, and constructed its genetic map. A population of 272 triploid hybrids was generated using ‘Giant Key’ lime as pollinator. One hundred fifty-eight SNPs diagnostic of C. micrantha, regularly distributed throughout the citrus genome were successfully developed and applied. The genetic structure of the diploid gametes was examined based on C. micrantha doses along the genome. The diploid gametes transmitted in average 91.17% of the parental interspecific C. medica/C. micrantha heterozygosity. Three chromosomes (2, 8, and 9) showed disomic segregation with high preferential pairing values, while the remaining chromosomes showed an intermediate inheritance with a preferential disomic trend. A total of 131 SNPs were assigned to nine linkage groups to construct the genetic map. It spanned 272.8 cM with a low average recombination rate (0.99 cM Mb-1) and high synteny and colinearity with the reference clementine genome. Our results confirmed that an efficient reconstruction breeding strategy for ‘Tahiti’ lime is possible, based on interploid hybridization using a doubled diploid of C. aurantiifolia. The tetraploid parent should be selected for favorable agronomic traits and its genetic value should be efficiently inherited by the progeny thanks to transmission of the high level of parental heterozygosity. However, it would require developing numerous progeny to overcome the linkage drag caused by the limited interspecific recombination associated with the predominant disomic inheritance.

Species boundary and extensive hybridization and introgression in Petunia

ABSTRACT Studying the role of hybridization in the speciation of plants is one of the most thrilling areas of evolutionary biology. Hybridization in natural populations can act in opposition to divergence, contribute to adaptation through introgression or foster the emergence of new lineages via hybrid speciation. Species of the plant genus Petunia grow in open areas in southern South America. Some natural interspecific hybrid events have been described for the genus, such as between the endemic P. exserta and the widespread P. axillaris. Both species occur in sympatry in Serra do Sudeste (Brazil), where they occur in diverse habitats and exhibit floral divergence, which has been related to the attraction of different primary pollinators. The present study evaluates the maintenance of the species boundaries front of hybridization and introgression. Direct and indirect methods of estimating gene exchange employed genotyping 720 reproductive plants and 611 progenies of both species with eight microsatellite loci. Gene exchange was found to be frequent and bidirectional between the species, indicating that introgression changes their genetic constitution in areas of sympatry. Limits of the studied species are being maintained because of the high level of inbreeding and backcrosses that are habitat-dependent.

Homoploid hybridization of plants in the Hengduan mountains region.

The Hengduan Mountains Region (HMR) is a major global biodiversity hotspot. Complex tectonic and historical climatic conditions created opportunities for natural interspecific hybridization. Likewise, anthropogenic disturbance potentially raises the frequency of hybridization. Among species studies to date, the frequency of homoploid hybridization appears in the HMR. Of nine taxa in which natural hybridization has been detected, three groups are involved in homoploid hybrid speciation, and species pairs from the remaining six genera suggest that continuous gene flow occurs in hybrid zones. Reproductive isolation may greatly affect the dynamic and architecture of hybrid zones in the HMR. Asymmetrical hybridization and introgression can primarily be attributed to both prezygotic and postzygotic barriers. The frequent observation of such asymmetry may imply that reproductive barrier contributes to maintaining species boundaries in the alpine region. Ecological isolations with environmental disturbance may promote breeding barriers between parental species and hybrids. Hybrid zones may be an important phase for homoploid hybrid speciation. Hybrid zones potentially provided abundant genetic resources for the diversification of the HMR flora. The ecological and molecular mechanisms of control and mediation for natural hybridization will help biologists to understand the formation of biodiversity in the HMR. More researches from ecological and molecular aspects were required in future studies.

THE CHEMICAL COMPOSITION OF THE BERRIES OF SPECIES AND INTERSPECIFIC HYBRIDS OF RED CUR-RANT IN CULTURE

Red currant is a valuable food and medicinal plant widely used in industrial and amateur gardening. 
 The aim of this article is a summary of results of a multi-year research of the chemical composition of fruits of red currant wild-growing species and natural interspecific hybrids of different geographical origin and assessment of a possibility of use of the selections to produce interspecific hybrids.
 Biochemical study of dry substance, ascorbic acid, sugars, acids, anthocyans, catechins, pectins and protopectins in red currant berries was carried out. The analyses of the chemical composition were performed by the universally accepted procedures.
 The levels of variability of 8 biochemical characters of red berry fruits depending on conditions of a year were established. It was shown that the most stable biochemical character was content of dry substance in berries and the most variable one – content of catechins. More ascorbic acid accumulates in berries of Ribes atropurpureum from the Salair Ridge in comparison with the amount in berries of R. atropurpureum from the Altai Mountains. By the complex of biochemical characters of prime interest are R. atropurpureum and hybrid R. atropurpureum × R. altissimum, and by the content of dry substance, sugars and catechins – hybrid R. atropurpureum × R. vulgare. The selections are a source of 1-5 outstanding biochemical characters and promising for the use in breeding. The interspecific hybrids of red currant obtained in CSBG by the use of selections testify to the possibility of production of high yield, large-fruited cultivars with a high content of biologically active substances in berries.

Epigenetic consequences of interploidal hybridisation in synthetic and natural interspecific potato hybrids.

Interploidal hybridisation can generate changes in plant chromosome numbers, which might exert effects additional to the expected due to genome merger per se (that is genetic, epigenetic and phenotypic novelties). Wild potatoes are suitable to address this question in an evolutionary context. To this end, we performed genetic (AFLP and single sequence repeart (SSR)), epigenetic (MSAP), and cytological comparisons in: (1) natural populations of the diploid cytotype of the hybrid taxonomic species Solanum×rechei (2n=2×, 3×) and its parental species, the triploid cytotype of Solanum microdontum (2n=2×, 3×) and Solanum kurtzianum (2n=2×); and (2) newly synthesised intraploidal (2××2×) and interploidal (3××2×) S.microdontum×S.kurtzianum hybrids. Aneuploidy was detected in S.×rechei and the synthetic interploidal progeny; this phenomenon might have originated the significantly higher number of methylation changes observed in the interploidal vs the intraploidal hybrids. The wide epigenetic variability induced by interploidal hybridisation is consistent with the novel epigenetic pattern established in S.×rechei compared to its parental species in nature. These results suggest that aneuploid potato lineages can persist throughout the short term, and possibly medium term, and that differences in parental ploidy resulting in aneuploidy are an additional source of epigenetic variation.

Whole-genome sequence of the bovine blood fluke Schistosoma bovis supports interspecific hybridization with S. haematobium.

Mesenteric infection by the parasitic blood fluke Schistosoma bovis is a common veterinary problem in Africa and the Middle East and occasionally in the Mediterranean Region. The species also has the ability to form interspecific hybrids with the human parasite S. haematobium with natural hybridisation observed in West Africa, presenting possible zoonotic transmission. Additionally, this exchange of alleles between species may dramatically influence disease dynamics and parasite evolution. We have generated a 374 Mb assembly of the S. bovis genome using Illumina and PacBio-based technologies. Despite infecting different hosts and organs, the genome sequences of S. bovis and S. haematobium appeared strikingly similar with 97% sequence identity. The two species share 98% of protein-coding genes, with an average sequence identity of 97.3% at the amino acid level. Genome comparison identified large continuous parts of the genome (up to several 100 kb) showing almost 100% sequence identity between S. bovis and S. haematobium. It is unlikely that this is a result of genome conservation and provides further evidence of natural interspecific hybridization between S. bovis and S. haematobium. Our results suggest that foreign DNA obtained by interspecific hybridization was maintained in the population through multiple meiosis cycles and that hybrids were sexually reproductive, producing viable offspring. The S. bovis genome assembly forms a highly valuable resource for studying schistosome evolution and exploring genetic regions that are associated with species-specific phenotypic traits.

Molecular and physiological characterization of a natural interspecific coffee hybrid

Natural hybridization is a common phenomenon in plants and considered to be a driving force of biodiversity and evolution. In coffee spontaneous hybridization between two different species is earlier documented. Here we investigated the morphological, molecular and physiological characteristics of a natural tetraploid interspecific coffee hybrid involving allopolyploid Coffea arabica and diploid C. excelsa species. The formation of the tetraploid hybrid was postulated on account of the production of unreduced female gametes in C. excelsa. In our findings, most morphological characters of the interspecific hybrid were found to be intermediate between the putative parental species, but the young leaf colour was found to be distinctively transgressive. Sequence-related amplified polymorphism marker analysis unequivocally supported the involvement of C. excelsa and C. arabica in hybrid formation. The gas exchange parameters, chlorophyll fluorescence parameters were compared between the hybrid and parents which revealed that the interspecific hybrid had the significantly higher substomatal CO2 concentration and non-photochemical quenching compared to parents. This tetraploid interspecific hybrid encompassing the genome of two divergent species could be of ascertainable importance in arabica coffee breeding program.

Evidence of introgressive hybridization between Stenella coeruleoalba and Delphinus delphis in the Greek Seas

Natural interspecific hybridization might be more important for the evolutionary history and speciation of animals than previously thought, considering several demographic and life history traits as well as habitat disturbance as factors that promote it. In this aspect, cetaceans comprise an interesting case in which the occurrence of sympatric species in mixed associations provides excellent opportunities for interspecific sexual interaction and the potential for hybridization. Here, we present evidence of natural hybridization for two cetacean species commonly occurring in the Greek Seas (Stenella coeruleoalba and Delphinus delphis), which naturally overlap in the Gulf of Corinth by analyzing highly resolving microsatellite DNA markers and mitochondrial DNA sequences in skin samples from 45 individuals of S. coeruleoalba, 12 D. delphis and three intermediate morphs. Employing several phylogenetic and population genetic approaches, we found 15 individuals that are potential hybrids including the three intermediate morphs, verifying the occurrence of natural hybridization between species of different genera. Their hybrids are fertile and able to reproduce not only with the other hybrids but also with each of the two-parental species. However, current evidence does not allow firm conclusions whether hybridization might constitute a step towards the generation of a new species and/or the swan song of an already existing species (i.e., D. delphis). Given that the focal species form mixed pods in several areas of Mediterranean, this study is an excellent opportunity to understand the mechanisms leading to hybridization in the context of gene flow and urges for the evaluation of the genetic status of common dolphins in the Mediterranean.

Origin of C. latifolia and C. aurantiifolia triploid limes: the preferential disomic inheritance of doubled-diploid 'Mexican' lime is consistent with an interploid hybridization hypothesis.

Two main types of triploid limes are produced worldwide. The 'Tahiti' lime type (Citrus latifolia) is predominant, while the 'Tanepao' type (C. aurantiifolia) is produced to a lesser extent. Both types result from natural interspecific hybridization involving a diploid gamete of C. aurantiifolia 'Mexican' lime type (itself a direct interspecific C. micrantha × C. medica hybrid). The meiotic behaviour of a doubled-diploid 'Mexican' lime, the interspecific micrantha/medica recombination and the resulting diploid gamete structures were analysed to investigate the possibility that 'Tahiti' and 'Tanepao' varieties are derived from natural interploid hybridization. A population of 85 tetraploid hybrids was established between a doubled-diploid clementine and a doubled-diploid 'Mexican' lime and used to infer the genotypes of 'Mexican' lime diploid gametes. Meiotic behaviour was studied through combined segregation analysis of 35 simple sequenbce repeat (SSR) and single nucleotide polymorphismn (SNP) markers covering the nine citrus chromosomes and cytogenetic studies. It was supplemented by pollen viability assessment. Pollen viability of the doubled-diploid Mexican lime (64 %) was much higher than that of the diploid. On average, 65 % of the chromosomes paired as bivalents and 31.4 % as tetravalents. Parental heterozygosity restitution ranged from 83 to 99 %. Disomic inheritance with high preferential pairing values was deduced for three chromosomes. Intermediate inheritances, with disomic trend, were found for five chromosomes, and an intermediate inheritance was observed for one chromosome. The average effective interspecific recombination rate was low (1.2 cM Mb-1). The doubled-diploid 'Mexican' lime had predominantly disomic segregation, producing interspecific diploid gamete structures with high C. medica/C. micrantha heterozygosity, compatible with the phylogenomic structures of triploid C. latifolia and C. aurantiifolia varieties. This disomic trend limits effective interspecific recombination and diversity of the diploid gamete population. Interploid reconstruction breeding using doubled-diploid lime as one parent is a promising approach for triploid lime diversification.

The genetic relationship and structure of some natural interspecific hybrids in Prunus subgenus Prunophora, based on nuclear and chloroplast simple sequence repeats

In the subgenus Prunophora of the genus Prunus, many transitional traits presented in interspecific hybrids, the so-called ‘new species’, were frequently named due to the complicated botanical classification system. In this study, we used 16 nuclear simple sequence repeats (nSSRs) and 10 chloroplast simple sequence repeats (cpSSRs) to evaluate genetic relationships among 42 accessions, which included 15 putative interspecific hybrids, and then to reveal the speciation and differentiation in the subgenus Prunophora. In total, 231 and 27 alleles were observed in nSSRs and cpSSRs respectively; and with cpSSRs 20 haplotypes were revealed among the accessions. Furthermore, the haplotype and genetic structure analysis implied that (1) Prunus simonii Carr. might be a subspecies or a forma of Prunus salicina L., rather than an interspecific hybrid between P. salicina and Prunus armeniaca L., (2) Prunus limeixing Zhang et Wang was derived from a natural hybrid with P. salicina as its maternal progenitor and P. armeniaca as the female parent, and (3) Prunus cathayana Fu et al. (or kernel-using apricot) was an interspecific hybridization species of P. armeniaca (maternal parent) and Prunus sibirica L. (female parent). These results will be useful for clarifying the problems in the botanical classification, and facilitate the conservation and management of plum and apricot genetic resources in the Chinese National Germplasm Repository for Plums and Apricots.

Reproductive behaviour of two tilapia species (Oreochromis niloticus, Linné, 1758; Sarotherodon melanotheron, Rüppel, 1852) in freshwater intra and interspecific pairing context

Nile tilapia Oreochromis niloticus (NT) and Black-chinned tilapia Sarotherodon melanotheron (BCT) are respectively characterized by fast growth and water salinity tolerance which attract the farmers who could take advantage of both species characteristics by producing hybrids reared in brackish or marine waters. Little information is however available about social interactions between the two species which are distinct by their mode of parental care (oral incubation). The objective of this study was to determine the behaviour of the two species, NT and BCT placed in freshwater intraspecific and interspecific pairing contexts. Females of both species (n=20 per species) were first isolated for 90days in a 60L aquarium to determine the average duration between spawning in the absence of males. With the approach of 4th spawning or after 90days of isolation, intra and interspecific pairing (fish average weight 200.4±5.1g) were made 10 times by pairing mode in a 350L aquarium. The day after fish pairing, 15min videos were recorded at one hour intervals from 8:00h to 17:00h, and courtship and aggressiveness behaviour were quantified. The results showed that isolated NT females had an average duration between two spawning of 15.9days. No spawning was observed in BCT females. Spawning events were observed in the NT intraspecific pairs, with strictly maternal oral egg incubations. Behavioural differences and some similarities were noted between the two species. NT male was the most dominant in front of females of both species and NT females showed dominance on BCT males. No clear hierarchy was observed in BCT pairs. Courtship behaviours were observed in all pairings with longer durations in NT pairs. Nest building was observed from 8:00h to 17:00h in both sexes of BCT and male NT. NT females built nests from 11:00h with longer durations when paired with males BCT than when paired with their conspecific males. These first results, reflecting behavioural plasticity in both species suggested that other breeding conditions favouring less aggressive behaviour could lead to a natural interspecific hybridization between NT and BCT.

The Pacific yam (Dioscorea nummularia Lam.), an under-exploited tuber crop from Melanesia

This study aims to explore the potential of Dioscorea nummularia Lam. and to gather information as a prelude to its improvement by plant breeding. After a taxonomic clarification and a review of the botanical data, its geographical areas of origin and distribution are determined. A germplasm survey conducted on nine islands of Vanuatu enabled the collection of 110 accessions corresponding to 84 cultivars. These were grouped into: (1) wild forms under domestication, (2) annual types, (3) perennial-type cultivars of D. nummularia and (4) natural interspecific hybrids with D. alata L. Within each group, remarkable morphological variation exists for stem spininess, leaf shape, emerging leaf colour, tuber shape and tuber flesh colour. Selected accessions examined for ploidy had chromosome numbers ranging from 2n = 3x = 60 to 2n = 6x = 120. Chloroplast counts conducted on stomatal guard cells confirmed the variation in ploidy levels. Eight different male cultivars were studied for pollen fertility, but <5% of the pollen grains appeared to be fertile when stained with acetocarmine. However, profuse flowering and synchrony favour pollination and result in fruit set. All accessions are resistant to anthracnose. Viruses were detected but are morphologically not discernible, with no incidence on yield. Physicochemical analyses of tubers from 16 accessions revealed that D. nummularia and interspecific hybrids have high percentages of dry matter (mean of 33.11%) and starch (82.81%). The Pacific yam could be improved through conventional hybridisation or used for interspecific crosses with related economically important species. Recommendations are made for further research.