First-generation Hybrids Research Articles

Hybrid origin of the arctic � Pucciphippsia vacillans (Poaceae): evidence from Svalbard plants

The hypothesised hybrid origin of the High Arctic grass × Pucciphippsia vacillans from the putative parents Puccinelliavahliana, Phippsia algida or Phippsia concinna was investigated by analyses of morphological, cytological, and enzymatic data. Chromosome counts showed that × P. vacillans from Svalbard is triploid (2n = 21) and sterile, supporting the hypothesis of a hybrid origin. Enzymatic investigations showed that × P. vacillans is identical to Phippsia in most enzyme markers and furthermore that all four taxa are closely related. Additive banding pattern in one enzyme system (6-PGD) as well as some morphological traits indicated that × P. vacillans is a Puccinellia × Phippsia hybrid. × Pucciphippsia vacillans is morphologically intermediate between Phippsia algida and Puccinellia vahliana in several individual characters as well as in a multivariate analysis, indicating that Phippsia algida is the more probable Phippsia parent. Mature seeds have never been observed in × P. vacillans and the taxon has no known mode of vegetative reproduction. This investigation suggests that it might be a sterile first-generation hybrid wherever it occurs in Svalbard. The close genetic relationship between × Pucciphippsia, Phippsia, and Puccinellia vahliana has implications for their generic delimitation and might suggest that only one genus is involved.

B6D2F1 Mouse

This document contains a summary of the biological characteristics of the B6D2F1 mouse, a first-generation (F 1 ) hybrid from a cross of a C57BL/6 female with a DBA/2 male. Included are longevity statistics calculated from data provided by the National Center for Toxicological Research.

CB6F1 Mouse

This document contains a summary of the biological characteristics of the CB6F1 mouse, which is a first-generation hybrid strain produced by crossing BALB/c females and C57BL/6 males.

Conservation genetics and evolutionary history of Gleditsia caspica: Inferences from allozyme diversity in populations from Azerbaijan

Gleditsia caspica is an endemic treespecies found in the endangered lowlandHyrcanian forests near the Caspian Sea insoutheastern Azerbaijan and northwestern Iran. Phylogenetic analyses show that G.caspica is a derivative of G. japonica,a widely distributed species of eastern Asia. Using allozyme markers to investigate geneticdiversity within two populations fromAzerbaijan, we discovered that a populationfrom a protected nature reserve was composedlargely of first-generation hybrids betweenG. caspica and G. triacanthos,which is native to eastern North America but isplanted as an ornamental shade tree inAzerbaijan. Hybrids exhibited higher levels ofself-fertilization and lower seed productionthan either parental species. In the secondpopulation, composed of pure G. caspica,11 of 31 loci scored were polymorphic, theaverage number of alleles per locus was 1.39,and gene diversity was 0.105. All diversityestimates were substantially lower than thosewe obtained from a small sample of G.japonica from South Korea and than estimatesfrom more extensive samples of South KoreanG. japonica and North American G.triacanthos published by other workers. Weconclude that (i) in addition to ongoingthreats from habitat conversion andfragmentation, G. caspica may also bethreatened in Azerbaijan by hybridization withG. triacanthos; and (ii) low variabilityin G. caspica populations is most likelynot a consequence of recent habitat loss andreductions in population size, but insteadreflects a long history of range contractionand endemism following isolation from G.japonica during the Pliocene or Pleistocene.

B6C3F1 Mouse

This document contains a summary of the biological characteristics of the B6C3F1 mouse, which is a first-generation hybrid strain produced by crossing C57BL/6 females and C3H males.

Retrotransposons and genomic stability in populations of the young allopolyploid species Spartina anglica C.E. Hubbard (Poaceae).

Spartina x townsendii arose during the end of the 19th century in England by hybridization between the indigenous Spartina maritima and the introduced Spartina alterniflora, native to the eastern seaboard of North America. Duplication of the hybrid genome gave rise to Spartina anglica, a vigorous allopolyploid involved in natural and artificial invasions on several continents. This system allows investigation of the early evolutionary changes that accompany stabilization of new allopolyploid species. Because allopolyploidy may be a genomic shock, eliciting retroelement insertional activity, we examined whether retrotransposons present in the parental species have been activated in the genome of S. anglica. For this purpose we used inter-retrotransposon amplified polymorphism (IRAP) and retrotransposons-microsatellite amplified polymorphism (REMAP) markers, which are multilocus PCR-based methods detecting retrotransposon integration events in the genome. IRAP and REMAP allowed the screening of insertional polymorphisms in populations of S. anglica. The populations are composed mainly of one major multilocus genotype, identical to the first-generation hybrid S. x townsendii. Few new integration sites were encountered in the young allopolyploid genome. We also found strict additivity of the parental subgenomes in the allopolyploid. Both these findings indicate that the genome of S. anglica has not undergone extensive changes since its formation. This contrasts with previous results from the literature, which report rapid structural changes in experimentally resynthesized allopolyploids.

Evidence of Introgressive Hybridization between Bull Trout and Brook Trout

Abstract Hybridization between native bull trout Salvelinus confluentus and introduced brook trout S. fontinalis occurs over a wide geographic area in the western United States. We described the extent to which introgressive hybridization has occurred between these species using biochemical and molecular genetic techniques in samples collected from five streams in western Montana. We found that about three-quarters of the hybrids detected were male, first-generation (F1) hybrids. Most of the rest were backcrosses to the parental species, indicating that F1 hybrids can reproduce. We found no evidence of hybrid swarms in which all individuals were of hybrid origin. Our results suggest that both the reduced fertility of F1 hybrids and the reduced survival of their progeny prevents these species from forming such hybrid swarms. We also found that hybridization between bull and brook trout tends to occur predominantly between female bull trout and male brook trout, indicating that hybridization represents grea...

Molecular investigations in populations of Spartina anglica C.E. Hubbard (Poaceae) invading coastal Brittany (France).

Spartina anglica is a classical example of recent alloploid speciation. It arose during the end of the nineteenth century in England by hybridization between the indigenous Spartina maritima and the introduced East-American Spartina alterniflora. Duplication of the hybrid genome (Spartina x townsendii) gave rise to a vigorous allopolyploid involved in natural and artificial invasions on different continents. Spartina anglica was first recorded in France in 1906, and since then, it has spread all along the western French coast. Earlier studies revealed that native British populations display consistent morphological plasticity and lack of isozyme variation. In this paper, we use different molecular markers (randomly amplified polymorphic DNA, intersimple sequence repeats and restriction patterns from nuclear and chloroplast DNA sequences) to analyse the genetic patterns of the French populations of S. anglica. Our results show that French populations are mainly composed of one "major" multilocus genotype. This genotype is identical to the first-generation hybrid S. x townsendii from England. Losses of few markers from this genotype are observed but are restricted to a few populations from Brittany; it is likely that they appeared independently, subsequent to their introduction. In southern Brittany, no hybrids between S. anglica and S. maritima have been found where the two species co-occur. All French populations of S. anglica display the same chloroplast DNA sequences as S. alterniflora, the maternal genome donor. These findings are consistent with a severe genetic bottleneck at the time of the species formation, as a consequence of a unique origin of the species. Both parental nuclear sequences are present in the allopolyploid populations, revealing that for the markers investigated, no extensive changes have occurred in this young species.

Absence of conspecific pollen advantage in the dynamics of anIpomopsis(Polemoniaceae) hybrid zone

The frequency of hybrid formation in angiosperms depends on how often heterospecific pollen is transferred to the stigma and on the success of that heterospecific pollen at fertilizing ovules. Even if heterospecific pollen is capable of effecting fertilization it may perform poorly when conspecific pollen is also available on the stigma. We applied pollen mixtures to stigmas to determine how pollen interactions affect siring success and the frequency of hybrid formation between two species of Ipomopsis (Polemoniaceae) in Colorado. Plants of both parental species and natural hybrids were pollinated with I. aggregata and I. tenuituba pollen in ratios of 100:0, 80:20, 50:50, 20:80, and 0:100 by mass. Plants were homozygous for different alleles at an isozyme marker, allowing us to distinguish the type of pollen parent for 2166 viable seeds from 273 fruits. In contrast to studies of many other hybridizing taxa, there was no evidence of an advantage to conspecific pollen, nor did composition of the stigmatic pollen load affect seed set. Instead, the frequency of seeds sired by a given species was proportional to its representation in the pollen load. In this hybrid zone, both the frequency of first-generation hybrid formation and the relative male fitness of the two parental species should be predictable from the rates of pollen transfer to stigmas.

Comparison of Two Tests for Detecting Carcinogenic HPV in Women with Papanicolaou Smear Reports of ASCUS and LSIL

Background The detection of cancer-associated types of human papillomavirus (HPV) in cervical specimens predicts the presence and future development of cervical intraepithelial neoplasia (CIN). The purposes of this study were (1) to determine the efficacy of a second-generation assay by hybrid capture (HC II) to detect carcinogenic HPV from residual cervical cells of a liquid-based cervical cytologic specimen, and (2) to compare the performance of this second-generation test with the first-generation hybrid capture (HCT) HPV test of material from direct cervical sampling to detect CIN in women with atypical squamous cells of undetermined significance (ASCUS) and low-grade squamous intraepithelial lesion (LSIL) Papanicolaou (Pap) smear reports. Methods Women with a recent Pap smear report of ASCUS or LSIL had a sampling of the cervix using either an Ayre's spatula and cytobrush or an Accellon device sampling for liquid-based cytologic system HC II HPV testing, followed by a Dacron swab sampling of the cervix for standard HCT HPV testing of the paired specimens. All women received colposcopy examinations including cervical biopsy and endocervical curettage, when indicated, to determine criterion standards for comparison. Results Paired swabs and liquid-based cervical specimens from 242 women were available for testing by standard HCT and the newer HC II HPV DNA assays. The sensitivity, specificity, and positive and negative predictive values for detecting CIN grade 2 or 3 (CIN 2/3) were 61.9%, 57.0%, 12.0%, and 94.0%, respectively, for the HCT test, and 90.5%, 29.4%, 10.9%, and 97.0%, respectively, for the liquid-based cytology HC II assay. When only women with an initial ASCUS Pap smear report were considered, the HC II test results were 88.9%, 40.3%, 9.1%, and 98.2%, respectively. Conclusions Testing for lower genital tract carcinogenic HPV DNA using a cervical cytology liquid transport media residual sample is clinically feasible. The new HC II microplate HPV test achieved a greater test sensitivity for detecting carcinogenic HPV and correspondingly of CIN 2/3 compared with the currently available first-generation HC HPV test. Use of a liquid-based cervical cytology system combined with intermediate triage by HC II testing of residual cells for carcinogenic HPV alone may help to efficiently identify CIN 2/3 in women who have a prior screening Pap smear report of ASCUS.

Interspecific mating in the Piriqueta caroliniana (turneraceae) complex: effects of pollen load size and composition

Two taxa of Piriqueta (P. caroliniana and P. viridis) form a broad hybrid zone that extends over much of the central Florida peninsula. We used genetic markers to examine the strength of the isolation barriers between these taxa and the patterns of mating at the initial stages of hybridization. Regression models were employed to analyze the effects of pollen load size and the proportions of intra- and interspecific pollen on the frequency of first-generation (F1) hybrid formation. Overall, the postpollination mating barriers between these two taxa were relatively weak. However, there were significant effects of pollen load composition and size on the patterns of hybridization in both taxa with frequency-dependent responses to composition in both taxa. The frequency of F1 hybrid formation was generally lower than expected based on the frequency of each pollen type on the stigma for P. caroliniana recipients. The lower frequencies of F1 seeds in this taxon were apparently due to a greater competitive ability for intraspecific pollen, since hybrid seed formation decreased with increasing pollen load size. Pollen from P. caroliniana donors was also competitively superior on P. viridis recipients, leading to higher than expected frequencies of hybrid seed formation. Pollen from P. caroliniana did suffer higher rates of pollen-tube attrition than intraspecific pollen on P. viridis recipients, so the frequency of hybrid seed formation would be lower when pellen load sizes were small. In general, reproductive isolation mechanisms were stronger in P. caroliniana, suggesting that introgression should occur into P. viridis when these taxa come into close contact. Comparison of these expected patterns of mating to the distribution of hybrid genotypes in Florida provides insights into the relative roles of mating and selection in the evolution of hybrid populations of Piriqueta.

Relaxation of insulin-like growth factor-2 imprinting in rat cultured cells

The parental-specific expression of the insulin-like growth factor-2 ( Igf-2) and H19 genes was studied in rat fibroblast cells derived from a 3 day-old first-generation hybrid animal obtained by crossing Fisher and Wistar strains (F×W cells). Results showed that the reciprocal imprinting of the Igf-2 and H19 genes was conserved in the rat tissues and in the derived F×W cells when cultured with frequent transfer. Igf-2 and H19 gene expression was coordinately up-regulated upon reaching confluence, but Igf-2 RNA levels were further increased in a time-dependent manner and the repressed state of the maternal Igf-2 allele was progressively relaxed in cultures held in the confluent state and in the presence of low serum for more than 3 days. The active expression and relaxed imprinting status of the Igf-2 gene persisted over cell generations when the growth-constraining conditions were released by trypsinization and dilution. On the contrary, the imprinting of the H19 gene appeared to be unaffected by changes in growth conditions and its expression was down-regulated when the confluent cells were passaged. Methylation of the H19 promoter and Igf-2 coding regions was increased in the F×W cells extensively held under confluence and in the derived ‘post-confluent’ cultures. The heritable changes in the expression, and imprinting status of the Igf-2 and H19 genes observed in the F×W cells closely resembles events described in human embryonal cancers and cancer-predisposing syndromes. The occurrence of imprinting relaxation under strong growth-inhibitory conditions supports the hypothesis that it is an epigenetic change.

Performance of Imazethapyr-Resistant Corn (Zea mays) Compared with Susceptible Near-Isogenic and Commercial Hybrids

Farmers need information on herbicide technology and crop performance to assess the profitability of new herbicide-resistant crop technologies. First-generation imazethapyr-resistant corn hybrids evaluated at the University of Wisconsin yielded less than other commercial hybrids. To determine if this resistance trait affected yield or agronomic traits, 10 near-isogenic pairs of imazethapyr-resistant and -susceptible corn hybrids were compared. Whether treated with imazethapyr or not, imazethapyr-resistant hybrids yielded the same when averaged across hybrids, although yield varied among a few individual hybrids within single experiments. Seven of the imazethaypr-resistant hybrids yielded the same, two yield more, and one yielded less than their susceptible near-isogenic counterpart during eight site-years. Grain moisture was not affected, but imazethapyr-resistant hybrids had fewer broken stalks than did susceptible hybrids. The imazethapyr resistance trait does not appear to affect yield potential, but the backcrossing procedure may have caused early resistant hybrids to lag behind in yield compared to other new hybrids.

Angling vulnerability of black crappies, white crappies, and their naturally produced hybrid in Weiss Reservoir, Alabama, USA

We examined differences in angling vulnerability among black crappies Pomoxis nigromaculatus, white crappies Pomoxis annularis, and their naturally produced hybrid offspring in Weiss Reservoir, Alabama, USA, during spring and fall of 1992 and 1993. Proportions of crappie phenotypes (determined by starch-gel electrophoresis) in the reservoir were estimated from trapnet and electrofishing collections. We collected angled crappies from local resort owners and crappie tournaments during spring and fall 1992 and 1993 to determine relative proportions of crappie phenotypes in angler catch. The proportion of black crappies caught by anglers was higher ( P < 0.05) and the proportion of white crappies caught by anglers was lower ( P < 0.05) compared to their proportions in trapnet and electrofishing catches from the reservoir. Although first-generation (F 1) hybrids recruited to the minimum harvestable size (254 mm total length) earlier than either parental, these fish were not overly abundant in angler catches compared to their abundances in the reservoir. In fact, we found that in the fall of 1992 F 1 hybrid crappies were less abundant in angler catches compared with their abundances in the reservoir. Black crappies were more vulnerable to angling than the other phenotypes, yet the proportion of this species did not decrease over time, likely because of moderate rates of crappie exploitation in Weiss Reservoir. Results of this study suggest that stocking of hybrid crappies for sport fishing purposes may not be as beneficial as once thought because they do not always contribute to the sport fishery relative to their abundance.

Hatching Time and Early Growth of Age-0 Black Crappies, White Crappies, and Their Naturally Produced F1Hybrids in Weiss Lake, Alabama

Abstract Extensive natural hybridization occurs between black crappie Pomoxis nigromaculatus and white crappie P. annularis in Weiss Lake, Alabama. First-generation (F1) hybrids have faster annual growth than black crappies and white crappies in this reservoir. However, no information exists on hatching date and early growth differences among black crappies, white crappies, and F1 hybrid offspring. We collected age-0 crappies in early August 1992–1994 from Weiss Lake and identified species and their hybrids with starch gel electrophoresis. Hatching date and early growth were determined from otoliths. Swim-up dates of F1 hybrids peaked about a week earlier than those of parental species. The growth rate of F1 hybrids (0.86 mm/d) was significantly higher than those of black crappies (0.67 mm/d) and white crappies (0.72 mm/d). Back-calculated lengths at ages 10, 20, and 30 d were higher for F1 hybrids compared with black crappies. Thus, the faster growth of F1 hybrids starts just after hatching and continues...

Long-Term Effects of Prenatal Exposure to Low Levels of Gamma Rays on Open-Field Activity in Male Mice

The open-field activity of first-generation (F1) hybrid male C57BL/6 x C3H mice irradiated with gamma rays on day 14 of gestation was studied at the following ages: 6-7 months (young), 12-13 months (adult) and 19-20 months (old). Doses were 0.5 Gy or 1.0 Gy. Open-field activity was recorded with a camera. The camera output signal was recorded every second through an A/D converter to a personal computer. The field was divided into 25 8-cm2 units. All recordings were continuous for 60 min. The walking speed of the 1.0-Gy group recorded at 19-20 months was higher than that for the comparably aged control group. The time which the irradiated group, recorded at 19-20 months, spent in the corner fields was high in comparison with the control group at the same age. Conversely, the time spent by the irradiated group in the middle fields when recorded at 19-20 months was shorter than in the comparably aged control group. No effect of radiation was shown for any of the behaviors observed and recorded at 6-7 and 12-13 months. The results demonstrate that such exposure to gamma rays on day 14 of gestation results in behavioral changes which occur at 19-20 months but not at 6-7 or 12-13 months.

INTELLECTUAL PROPERTY RIGHTS UPDATE: PLANT VARIETY PROTECTION ACT AMENDMENTS

The Plant Variety Protection (PVP) Act provides intellectual property rights to new varieties of seed-reproduced plants. Eligible varieties must demonstrate that they are uniform, stable, and distinct from all other varieties. In 1991 the International Union for the Protection of New Varieties of Plants (UPOV) adopted a new Convention. As a member of UPOV, the United States needed to amend the PVP Act to conform to the 1991 UPOV Convention. Amendments to the PVP Act were signed by President Clinton on 6 Oct. 1994, and will become effective on 4 Apr. 1995. Among other changes, these amendments will provide protection to tuber-propagated varieties and first-generation hybrids. An overview of the amendments and a comparison of rights granted under PVP and plant patents will be presented.

Failure of Quantitative Phenotypic Characteristics to Distinguish Black Crappie, White Crappie, and Their First-Generation Hybrid

Abstract Commonly used quantitative phenotypic characteristics, including dorsal hard spine count and a nape measure (the ratio of the dorsal fin base length to the distance of the fin origin to the eye) failed to consistently distinguish between black crappie Ponioxis nigromaculatus and white crappie P. annularis in Alabama reservoirs. A high percentage (67%) of first-generation (F1) hybrid crappies were correctly identified with an alternate combination of these two characteristics, but this combination could not discriminate F1 hybrids from parentals. Correct identification of crappie parentals and their F1 hybrids was verified by examination of allozymes. In Lake Weiss, 43% of the crappies were misidentified when both characteristics were used. In Jones Bluff and Gainesville lakes, 13 and 11%, respectively, were misidentified by dorsal spine counts. Our results suggested that spine counts and nape measures are not entirely reliable for distinguishing crappie species or their hybrids in Alabama reservo...

Hybridization in the Catalina Island Mountain Mahogany (Cercocarpus traskiae): RAPD Evidence

The Catalina Island mountain mahogany is one of 10 species of shrubs and small trees (Lis 1992) comprising the genus Cercocarpus H. B. K (Rosaceae). Species in the genus are widely distributed throughout western North America and are delimited primarily on the basis of leaf characteristics (Mortenson 1973; Lis 1992). The Catalina Island mountain mahogany (C. traskiae Eastwood) is one of the most distinctive species in the genus due to its thick, coriaceous leaves and woolly pubescence on the leaf undersurface. The species is extremely rare, restricted to Wild Boar Gully on the southwest side of Santa Catalina Island in the Channel Islands off the coast of California (Fig. 1). When the population was first discovered in 1897, it consisted of over 40 individuals (Thorne 1967). Due to overgrazing by introduced mammalian herbivores (Coblentz 1980; Hobbs 1980), however, the population has been greatly reduced (Rieseberg et al. 1989). Cercocarpus traskiae is listed as endangered by the state of California and thus is afforded protection by California law (Smith & Berg 1988). Inexplicably, the species is not listed as endangered or threatened by the U.S. Fish and Wildlife Service, although it is under consideration for listing. In the late 1970s a detailed inventory of the Wild Boar Gully population was undertaken, and a total of eight Cercocarpus trees were discovered and tagged (Martin 1984). In addition, two of the trees (A, B; Fig. 1) were fenced to protect them from herbivores, and in 1985 the Catalina Conservancy constructed a larger fence around an area that included both trees, as well as about an acre of good habitat. The fencing effort was extremely successful, and by 1988 approximately 70 seedlings were observed within the fenced area (Rieseberg et al. 1989). Unfortunately, several of the adult plants resembled the island mountain mahogany, Cercocarpus betuloides Torrey & A. Gray var. blancbeae (C. Schneider) Little, in key morphological features such as leaf pubescence and leaf thickness or were immediate for these characters (descriptions of both species are given by R. Lis in Hickman [1993]). Cercocarpus betuloides var. blancbeae is only slightly more widespread than C traskiae, occurring on all of the Channel Islands except San Clemente. But the species is much more abundant than C traskiae on Santa Catalina and is known to occur in adjacent canyons, so the possibility of hybridization between the two species could not be dismissed. Furthermore, it is suspected that some of the seedlings might be of hybrid origin (T. Martin, personal communication). In an attempt to clarify the identity of morphologically ambiguous individuals, Rieseberg et al. (1989) undertook a study of allozymic variation and leaf anatomy of all the adult mahogany trees discovered in Wild Boar Gully. Of the eight adult trees in the Gully, three were anatomically intermediate between C. traskiae and C betuloides var. blancbeae, suggestive of hybridization. Analysis of 17 isozyme loci in C traskiae, as well as a nearby population of C betuloides var. blancbeae (Fig. 1), revealed one diagnostic isozyme polymorphism differentiating the two species. Based on this single isozyme polymorphism, five of the eight trees were diagnosed as C traskiae, one as C betuloides var. blancbeae, and two as hybrids. However, isozyme analyses of the 28 seedlings large enough to survive the loss of a single leaf revealed all to be pure C traskiae. The results from this study were not entirely satisfactory, however, because the classification of individuals as parental versus hybrid was based on a single locus. The use of a single diagnostic locus can ensure the correct identification of first-generation hybrids, but F2or later-generation hybrid or backcross progeny could easily be misdiagnosed as belonging to one of the parental classes. Thus, it was not surprising that two of the plants lacking a hybrid enzyme genotype were anatomically Paper submitted April 1994; revised manuscript accepted July 15, 1994.

Natural hybridization between Murray cod, Maccullochella peelii peelii (Mitchell) and trout cod, Maccullochella macquariensis (Cuvier) (Percichthyidae) in the Murray River, Australia

Hybridization is confirmed between two wild, naturally sympatric populations of Murray cod, Maccullochella peelii peelii, and trout cod, M. macquariensis, from the Murray River, Australia. Electrophoretic comparisons of proteins in muscle and liver tissues from trout cod, Murray cod, an artificially produced hybrid of Murray cod and trout cod, and putative wild hybrids from the Murray River indicated that the last group were first-generation interspecific hybrids. This is the first record of hybridization between naturally occumng populations of these two species. Naturally occurring wild populations of both trout cod and Murray cod are nonetheless genetically distinct and there is no evidence of introgression between the species. These findings have some implications for management policies and practices in relation to both species, and these are discussed.