Occurrence Of Natural Hybridization Research Articles

Living in Temporary Ponds Loading Giant Genomes: The Neotropical Annual Killifish Genus Austrolebias as New Outstanding Evolutionary Model.

The term Annual killifish describes a short-lived and amazing group of vertebrates inhabiting temporary ponds exposed to an extremely variable environment during its short lifespan in South America and Africa, leading to the death of the entire adult population during the dry season. Austrolebias is a specious genus of the family Rivulidae, with ∼58 currently recognized species, extensively distributed in the temperate Neotropical region. Herein, we reviewed different aspects of the evolutionary biology with emphasis on the genome dynamic linked to the burst speciation process in this genus. Austrolebias constitutes an excellent model to study the genomic evolutionary processes underlying speciation events, since all the species of this genus analyzed so far share an unusually large genome size, with an average DNA content of 5.95 ± 0.45 picograms per diploid cell (mean C-value of about 2.98 pg). The drastic nuclear DNA–increasing would be associated with a considerable proportion of transposable elements (TEs) found in the Austrolebias genomes. The genomic proportion of the moderately repetitive DNA in the A. charrua genome represents approximately twice (45%) the amount of the repetitive components of the highly related sympatric and syntopic rivulinae taxon Cynopoecilus melanotaenia (25%), as well as from other rivulids and actinopterygian fish. These events could explain the great genome instability, the high genetic diversity, chromosome variability, as well as the morphological diversity in species of Austrolebias. Thus, species of this genus represent new model systems linking different evolutionary processes: drastic genome increase, massive TEs genomic representation, high chromosome instability, occurrence of natural hybridization between sister species, and burst speciation events.

RADseq Data Suggest Occasional Hybridization between Microcebus murinus and M. ravelobensis in Northwestern Madagascar.

The occurrence of natural hybridization has been reported in a wide range of organisms, including primates. The present study focuses on the endemic lemurs of Madagascar, primates for which only a few species occur in sympatry or parapatry with congeners, thereby creating limited opportunity for natural hybridization. This study examines RADseq data from 480 individuals to investigate whether the recent expansion of Microcebus murinus towards the northwest and subsequent secondary contact with Microcebus ravelobensis has resulted in the occurrence of hybridization between the two species. Admixture analysis identified one individual with 26% of nuclear admixture, which may correspond to an F2- or F3-hybrid. A composite-likelihood approach was subsequently used to test the fit of alternative phylogeographic scenarios to the genomic data and to date introgression. The simulations yielded support for low levels of gene flow (2Nm0 = 0.063) between the two species starting before the Last Glacial Maximum (between 54 and 142 kyr). Since M. murinus most likely colonized northwestern Madagascar during the Late Pleistocene, the rather recent secondary contact with M. ravelobensis has likely created the opportunity for occasional hybridization. Although reproductive isolation between these distantly related congeners is not complete, it is effective in maintaining species boundaries.

The natural hybridization between species Ligularia nelumbifolia and Cremanthodium stenoglossum (Senecioneae, Asteraceae) suggests underdeveloped reproductive isolation and ambiguous intergeneric boundary.

Natural hybridization is frequent in plants and is considered an important factor facilitating speciation. The natural intergeneric hybridization between Ligularia and Cremanthodium was previously confirmed using a couple of DNA markers. However, the mechanism of this intergeneric hybridization and the role of reproductive isolation in the process of hybridization remain unclear. Here we used double-digest restriction site-associated DNA sequencing (ddRAD-seq) to further quantify the occurrence of hybridization, the genetic structure of the hybrid population and the role of reproductive isolation between Ligularia nelumbifolia and Cremanthodium stenoglossum. The results based on the ddRAD-seq SNP data sets indicated that hybridization between L. nelumbifolia and C. stenoglossum was restricted to F1s, and no gene introgression was identified between these two species. STRUCTURE analysis and maximum likelihood (ML) tree results showed a slightly larger genetic contribution of L. nelumbifolia to putative hybrid F1s. We deduced that the reproductive isolation between these two parent species is not well-developed but still strong enough to maintain the genetic integrity of the species, and that their F1s are sterile or with low fertility. Given the poorly resolved phylogenetic relationship between Ligularia and Cremanthodium, the occurrence of natural hybridization between L. nelumbifolia and C. stenoglossum may provide new insights into the re-circumscription and re-delimitation of these two genera.

Molecular evidence for natural hybridization betweenLigularia nelumbifoliaandCremanthodium stenoglossum(Asteraceae, Senecioneae)

Natural hybridization occurred frequently in the sunflower family. To date, however, no study on natural hybridization involving in Ligularia and Cremanthodium has been reported. Here, we presented the molecular evidence for natural hybridization between Ligularia nelumbifolia (Bureau & Franch.) Hand.-Mazz. and Cremanthodium stenoglossum Ling & S.W.Liu. Four nuclear DNA regions were sequenced to test the natural hybridization hypothesis, and three chloroplast DNA regions were sequenced to determine the direction of hybridization. Analyses of the investigated DNA data suggested that all of the putative hybrid individuals were derived from hybridization between L. nelumbifolia and C. stenoglossum and that bidirectional hybridization occurred. Moreover, sympatric Ligularia tsangchanensis (Franch.) Hand.-Mazz. and Ligularia virgaurea (Maxim.) Mattf. ex Rehder & Kobuski were not apparently involved in the hybridization. Although NewHybrids analysis showed that all the putative hybrid individuals were F1class, a low frequency of backcrossing to C. stenoglossum might exist in the hybrid swarm. In such a case, hybrids might serve as a bridge facilitating gene flow between L. nelumbifolia and C. stenoglossum, and hybrid speciation is unlikely to happen for these hybrid individuals without asexual reproduction. Given the poorly resolved phylogenetic relationship between Ligularia and Cremanthodium, the occurrence of natural hybridization between L. nelumbifolia and C. stenoglossum might provide new insights into the recircumscription and redelimitation of these two genera.

Evidence for interspecific hybridization between exotic ‘Dam manel’ (<em>Nymphaea</em> × <em>erangae</em)) and native ‘Nil manel’ (<em>Nymphaea nouchali</em> Burm. f.) in Sri Lanka

Biological invasions are considered a serious threat to the biodiversity, and second only to habitat loss, but predicted to soon become the key cause of environmental degradation globally. In addition to competing with natives in natural habitats, another serious threat possessed by Invasive Alien Species (IAS) is their ability to hybridize with natives. The exotic violet flowered Nymphaea × erangae has been introduced to the country for ornamental purposes where it has got naturalized. Now it is recognized as a silent invader in wetlands of the country. The revealing of Nymphaea populations with intermediate characters, both of the native N. nouchali and Nymphaea × erangae in the wetlands of the island raised the question of the occurrence of natural hybridization. The present study was carried out to investigate the event of natural hybridization between the native and the exotic using morphological data. Data collected from putative hybrids and pure populations of the two parents were subjected to multivariate statistical analyses. The results confirmed the identity of the populations with intermediate characters as hybrids between the native N. nouchali and Nymphaea × erangae, highlighting the importance of conserving the natural populations of the native, as hybridization with the exotic pose a threat to its genetic purity.

ドロクイ属2 種の分布および生息環境： 近年の沿岸域の改変と交雑個体の出現の関係

ドロクイ属2 種の分布および生息環境： 近年の沿岸域の改変と交雑個体の出現の関係

Phylogenetic analysis of Saccharum s.l. (Poaceae; Andropogoneae), with emphasis on the circumscription of the South American species.

Polyploidy and reticulate evolution are often a complication for discovering phylogenetic relationships between genera and species. Despite the huge economic importance of sugarcane (Saccharum officinarum-Poaceae, Andropogoneae), the limits of the genus Saccharum and its species are complex and largely unresolved, involving both polyploidy and reticulate evolution. This study aimed to assess the phylogenetic relationships of Saccharum s.l., including Erianthus and Tripidium, as well as investigate the taxonomic circumscription of the South American species of the genus. Molecular cloning and sequencing of five regions of four low-copy nuclear loci were performed, including Aberrant panicle organization1 (apo1), Dwarf8 (d8), two exons of Erect panicle2 (ep2-ex7 and ep2-ex8), and Retarded palea1 (rep1). Concatenated trees were reconstructed using Maximum Parsimony, Maximum Likelihood, and Bayesian Inference analyses. The allopolyploid origin of Saccharum was demonstrated using evidence from nuclear genes. The samples of Saccharum s.l. grouped in two distinct clades, with S. arundinaceum and S. ravennae (= Tripidium, or Erianthus sect. Ripidium) apart from all other species analyzed of the genus. Saccharum angustifolium, S. asperum, and S. villosum correspond to distinct clades (different species). The plants with intermediate morphology between S. angustifolium and S. villosum presented a pattern of paralogues consistent with a hybrid origin. Saccharum s.l. is polyphyletic and Tripidium should be recognized as a distinct genus. However, no strong evidence was found to support the segregation of Erianthus. The taxonomic circumscription of the South American species of the genus was resolved and the occurrence of natural hybrids was documented. Better understanding of the phylogenetic relationships of Saccharum and relatives may be useful for sugarcane breeders to identify potential taxa for interspecific and intergeneric crosses in the genetic improvement of sugarcane.

長崎市におけるアカイエカとチカイエカの交雑

The occurrence of natural hybridization between the mosquitoes Culex pipiens pallens and Cx. pipiens f. molestus in Northwestern Kyushu, Japan, was confirmed based on morphology and molecular methods. In order to assess the morphological difference in male genitalia of the two forms on the basis of the dorsal/ventral (D/V) ratio, mosquito egg rafts were collected in Nagasaki City using oviposition traps. The morphological parameters of male genitalia from Cx. pipiens f. molestus were discontinuous with those from Cx. pipiens pallens, while intermediate individuals could be found in a single egg raft. These individuals were identified as hybrids using a polymerase chain reaction (PCR)-based assay. The fitness of the family descended from hybrids was lower than that from typical pallens and molestus families, as measured by egg raft size and egg hatchability. The reduced fitness of the hybrids suggested that the genetic introgression between the two forms could be restricted.

Genetic and morphometric markers are able to differentiate three morphotypes belonging to Section Algarobia of genus Prosopis (Leguminosae, Mimosoideae)

The section Algarobia of genus Prosopis includes promising species for reforestation and afforestation programmes in arid and semiarid regions, mainly of the Americas. Many interspecific natural hybrid combinations have been described in this group. In this paper we analysed a hybrid zone in Chaco biogeographical province in Argentina, where P. ruscifolia and P. alba overlap and hybridise producing intermediate fertile hybrid forms. Eleven morphological traits and 76 loci RAPD were analysed to determine the effect of hybridization between these species. The comparison of morphological traits among groups yielded significant or highly significant differences for all traits. Estimates of H e in P. alba and P. ruscifolia did not differ from each other, but both showed significantly lower values than the hybrid group. The analysis of correlations between shared phenotypes and pair-wise relationships estimated from RAPD gave also strong support to the hypothesis that most of the phenotypic traits analysed have significant heritability. The analyses of population structure and clustering based on morphological and molecular data by DAPC and STRUCTURE were rather consistent and indicated that the three morphotypes studied here are differentiated with low overlapping. All results indicated that despite the occurrence of natural hybridization and introgression, interspecific gene flow would be limited by hybrid breakdown or natural selection favouring the maintenance of species integrity.

Biological traits of naturally induced hybrid individuals of two gizzard shads, Nematalosa come and N. japonica, in coastal waters around Okinawa Island, Ryukyu Archipelago, southwestern Japan

The age, growth, reproductive condition, and occurrence of natural hybrids of two Nematalosa species around Okinawa Island were examined using 128 specimens obtained from April 2003 to June 2004. Standard length (SL) reached approximately 150–210 mm within the first 2 years, and then remained stagnant. The maximum age for both sexes was ca. 5 years old. Maturity sizes and ages were estimated to be at least 173.2 mm SL and 2 years old for females and 192.6 mm SL and 3 years old for males. Spawnable individuals were mainly observed from January to March based on histological observations of gonads. Natural hybrids appeared at all sampling sites except for the Haneji Inlet and were dominant at Makiminato (in south-central Okinawa Island). Their incidence was also quite high (66.9%) in the Makiminato population, when compared with records for other marine fishes around Japan. In Okinawa Island, these shallow areas are rapidly decreasing in size because of recent reclamation and land exploitation. Hybrid production may be caused by not only the reproductive biology and sympatric distributions of the parent species but also recent environmental changes.

When interspecific prezygotic barriers break down: hybridization between two Potamogeton species (P. wrightii and P. perfoliatus) and comparison of the artificial and natural hybrids

Interspecific hybridization played an important role in speciation and evolution of angiosperms. Although the widespread occurrence of natural hybrids in the genus Potamogeton has been studied intensively, few successful experimental hybridization studies have been reported in this genus. In the present study, critical experimental hybridization was conducted using Potamogeton × intortusifolius, a natural hybrid widely distributed in China, and its parents (P. perfoliatus and P. wrightii). The absence of prezygotic barriers between P. wrightii and P. perfoliatus was observed, which contributes to the frequent hybridization of these species in nature. The pollen tube growth rates of P. perfoliatus were much faster than those of P. wrightii in the style of that species. However, the conspecific pollen tubes were competitively advantageous in P. perfoliatus styles. The interspecific hybridization could be applied bidirectionally, and 28 F1 hybrid individuals were successfully obtained from P. wrightii × P. perfoliatus, despite the low germination possibility of the hybrid seeds. Both the artificial and natural hybrids exhibited intermediate morphological characters but presented much lower fertility. The sterility of P. × intortusifolius is mainly due to its low female fitness. However, the offspring from P. wrightii × P. × intortusifolius indicated the potential for backcrossing in nature. This is the most successful attempt at artificial hybridization in this genus so far. The possible route for restoration of fertility and the fitness of the hybrids are also discussed in this paper.

Hybridization and polymorphic microsatellite markers for two lagomorph species (Genus Sylvilagus): implications for conservation

Eastern cottontails (Sylvilagus floridanus) are a prolific and popular game species in North America but have declined within the core of their range. Swamp rabbits (S. aquaticus) are sympatric with eastern cottontails and are a species of concern at the northern fringe of their range in Illinois. Although hybridization between these species may be a potential factor affecting their declines, no studies have yet been conducted to address this issue. We examined the potential for hybridization between sympatric eastern cottontails and swamp rabbits in Illinois by sequencing a portion of the mitochondrial 12S gene in 17 individuals of each species. Additionally, we developed six microsatellite markers for the eastern cottontail (7–13 alleles/locus) that also amplify in swamp rabbits (3–5 alleles/locus). We found fixed differences between species with haplotypes forming well-differentiated clades indicating a lack of hybridization. Hybridization between eastern cottontails and swamp rabbits does not appear to be affecting their declines. Misidentification due to ambiguous morphological characteristics of the two species occurred in an earlier study and in our own. We suggest the mitochondrial 12S gene may be a convenient molecular marker for the resolution of species identity questions. Information on microsatellites, occurrence of natural hybridization, and a molecular marker for species resolution will be useful for developing management plans for lagomorphs and focusing further research on factors affecting population status.

Detection of haplotypic variation and natural hybridization in halepensis‐complex pine species using chloroplast simple sequence repeat (SSR) markers

In this investigation, nine chloroplast, paternally inherited simple‐sequence repeat (cpSSR) markers were used to describe genetic variation of three closely related species belonging to the halepensis complex (Pinus halepensis Ait., P. brutia Mill. and P. eldarica Medwed.). Both the infinite allele model (IAM) and stepwise‐mutation model (SMM) have been applied to the analysis of the genetic structure of natural populations and the geographical distribution of haplotypic variation. SMM‐based estimators performed better than IAM‐based estimators for large values of within‐population diversity and divergence between population pairs. Overall, large haplotypic variation and high genetic divergence were detected for both P. halepensis and P. brutia. The genetic structures of the three species are discussed with consideration to the evolutionary and ecological characteristics of these species. Three highly informative markers showing size variants distinguishing P. halepensis from the other two species were used to provide more information on the occurrence of natural hybridization in a Turkish sympatric population of P. halepensis and P. brutia. Strong evidence of introgression of ‘halepensis’ chloroplast haplotypes into P. brutia seeds (but not vice versa) was detected. According to previous evidence from controlled crossings, matings between the above species seem to be successful only when P. halepensis is the pollen donor and P. brutia is the female parent (but not reciprocally). The existence of unidirectional gene flow in sympatric populations confirms previous evidence about partial reproductive barriers between P. halepensis and P. brutia. Implications of the above evidence for the evolutionary history of these species are discussed.

Inter-Specific Host Hybrids and Phalacrid Beetles Implicated in the Local Survival of Smut Pathogens

In populations of the sedges Carex canescens and Carex mackenziei, the incidence and severity of a non-systemic floral smut fungus, Anthracoidea fischeri, was strongly associated with the occurrence of natural hybrids. Data from 23 localities showed that in the presence of the hybrid (13 localities), both parents sustained infection while in its absence (10 localities), both were disease-free. Furthermore, in mixed populations of parental and hybrid plants, the incidence and severity of disease was always much greater on hybrid than parental plants (5 to 9 and 30 to 80-fold, respectively), and parental plants were more often diseased when growing close to hybrid plants. Hybrids were earlier regarded as completely sterile, however, we obtained successful germination of hybrid seeds from two localities (...)

Early Occurrence of Natural Hybridization within Morone (Perciformes)

Early Occurrence of Natural Hybridization within Morone (Perciformes)

Occurrence of Natural Hybrid between Pufferfishes, Takifugu xanthopterus and T. vermicularis, in Ariake Bay, Kyushu, Japan.

Six unidentifiable pufferfishes of the genus Takifugu collected in Ariake Bay, Kyushu, Japan in 1985 and 1986, were examined enzyme electrophoretically and morphologically. Electrophoretic analysis showed these specimens to be natural F1 hybrids between T. xanthopterus and T. vermicularis, since they were heterozygous of having one allele from T. xanthopterus and another from T. vermicularis at all the eight diagnostic loci. Morphological examinations showed intermediacy of the hybrid specimens, and supported the findings of the electrophoretic analysis: (a) mean values of five meristic characters of the hybrids fell between those of the parental species, hybrid indices ranging from 16.7 to 73.3, with a mean of 44.4; (b) the first principal component (PC1) extracted from the values for three meristics and seven morphometrics clearly separated T. vermicularis from T. xanthopterus, with the hybrids situated between them; and (c) coloration and body prickles of the hybrids were intermediate between those of the parent species. The incidence of hybridiza-tion was quite low (0.4%), as recorded for some other marine fishes.

Delimitation ofPelargonium sect.Glaucophyllum (Geraniaceae)

Pelargonium otaviense Knuth andP. spinosum Willd. are excluded from sect.Glaucophyllum, whileP. grandiflorum (Andr.)Willd.,P. patulum Jacq. andP. tabulare (Burm. f.)L'Herit. of sect.Eumorpha are included. Sect.Glaucophyllum is characterized by green to glaucous vegetative organs and zygomorphic white to pink corolla with five narrow petals. All the species have an identical pollen and chromosome morphology, the same basic chromosome number (x = 11) and similar flavonoid patterns. A close relationship between sect.Glaucophyllum and sect.Pelargonium is indicated by the occurrence of natural hybrids and concordant characters. Isorhamnetin and luteolin have been detected in the genus for the first time.

Occurrence of Natural Hybrids between Etheostoma and percina (Pisces: Percidae)

Occurrence of Natural Hybrids between Etheostoma and percina (Pisces: Percidae)

Allotriploidy in Natural Hybrid Frogs, Rana chiricahuensis X R. pipiens, from Arizona: Chromosomes and Electrophoretic Evidence

-In samples totalling 16 leopard frogs, R. chiricahuensis and R. pipiens, two triploid hybrids were found, both from a collection of four frogs from a sympatric locality. Analysis of the normal karyotype of R. chiricahuensis shows it to be extremely similar to that of R. pipiens. It was thus not possible to identify the three chromosome sets in the triploids cytologically. C-banding was weak, indicating that little heterochromatin was present. Electrophoretic evidence based on 21 isozyme loci indicates one hybrid to be 2 chiricahuensis, 1 pipiens and the other to be 1 chiricahuensis, 2 pipiens. The unexpectedly high occurrence of triploid hybrids may be due to higher viability of triploids relative to diploid hybrids. The many species of frogs of the Rana pipiens complex of North America are known to hybridize to varying degrees (Sage and Selander, 1979; Frost and Platz, 1983). Four species of this complex inhabit southern Arizona: R. pipiens, R. blairi, R. chiricahuensis and R. yavapiensis (Platz, 1976; Frost and Bagnara, 1977; Platz and Mecham, 1979; Platz and Frost, 1984). R. chiricahuensis, perhaps the most distinctive of these four leopard frog species in southern Arizona (Hillis et al., 1983), occurs sympatrically with R. pipiens, R. blairi and R. yavapaiensis, whose ranges are for the most part mutually allopatric. Frost and Platz (1983) have reported about 9% occurrence of natural hybrids between sympatric R. chiricahuensis and R. pipiens, with little or no backcrossing. In appearance, R. chiricahuensis is a more robust looking frog than R. pipiens, with a noticeably wider head and shorter legs and cream-colored spots on the poste3 Present address: Department of Biology, University of Windsor, Windsor, Ontario N9B 3P4, Canada. 4 Present address: Division of Hematology-Oncology, New England Medical Center, 171 Harrison Ave., Box 841, Boston, Massachusetts, USA 02111. rior thigh; it also has a different mating call (Platz and Mecham, 1979). In a collection of 16 frogs from three sites in Arizona (sympatric and allopatric R. chiricahuensis and R. pipiens), we found one triploid individual through an initial survey of karyotypes and noted that it had what appeared to be an intermediate, hybrid morphology. A ubsequent electrophoretic examination of all the specimens was undert ken to verify its suspected genotype and revealed, in addition, that another specimen we had earlier referred to R. pipiens was also a hybrid with an electrophoretic pattern again suggesting polyploidy. We report here on these findings and, with an analysis of the normal karyotype of R. chiricahuensis, discuss the possible significance of polyploidy in these wild-caught, hybrid individuals. MATERIALS AND METHODS All specimens were obtained from sites in Coconino National Forest, Coconino Co., Arizona in 1981 as follows: six allopatric R. pipiens from Fuller Tank (34040' x 111?20'), six allopatric R. chiricahuensis from New Tank (34032' x 111? 29') and three R. chiricahuensis (one later confirmed as a hybrid) and one R. pipThis content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 05:06:31 UTC All use subject to http://about.jstor.org/terms D. M. GREEN AND D. M. DELISLE 41iil( ai a 4 t xx xx ..x xx A.X x 1 2 3 4 5 6 7 8 9 10 11 12 13 FIG. 1. Normal karyotype of Rana chiricahuensis (MVZ No. 176678), Baker Lake, Arizona. iens (later confirmed as a hybrid) from the sympatric locality Baker Lake (34? 27' x 111?23'). The specimens have been deposited in the Museum of Vertebrate Zoology (MVZ 176676-92). Chromosome preparations were obtained from squashes of corneal epithelium, using Bogart's (1973, 1981) methods, and of gut and testis, using the methods of Kezer and Sessions (1979). C-banding of chromosomes was attempted using Schmid's (1978) methods. Numerical analyses of karyotypes was done using the CHROMPAC system (Green et al., 1980, 1984). Starch gel electrophoresis employed methods described by Selander et al. (1971) and Clayton and Tretiak (1972).

Hybridization Between Eucalyptus obliqua L'hérit. And E. pulchella Desf

The present study provides the first evidence for the occurrence of natural hybrids between the wide- ranging species E. obliqua (series Obliquae) and the restricted Tasmanian endemic E. pulchella (series Piperitae). The progeny from one putative hybrid is shown to be intermediate between the progeny from the two parental species for virtually all characters examined. Principal component and likelihood analyses support this intermediacy of the hybrid progeny and suggest that no other species are involved in this hybrid system. The hybrid progeny shows greater variability than progeny from either parental species. Further, the hybrid tree has a lower seed output per capsule than trees of either parental species and therefore the hybrid tree appears to be at an evolutionary disadvantage. The two adult hybrids were found on the edge of shallow gullies on E. pulchella-dominated, north- facing slopes away from pure stands of E. obliqua. Some natural saplings outside the phenotypic range of either species were also found in the gullies. These results are most easily interpreted as suggesting that the intermediate trees examined originated from recent hybridization (possibly F1) following the migration of E. obliqua pollen into the range of E. pulchella. It is suggested that long-distance pollen migration of this type may be of evolutionary importance in allowing the colonization of suitable sites (in this case, small gullies) by advantageous genes or gene combinations from a distant species. The gene combinations of the pollen parent may be reselected from a segregating hybrid swarm.