Reconstruction of the carbon balance for microsites in a boreal oligotrophic pine fen, Finland

 Carbon dioxide (CO₂) exchange was studied at flark (minerotrophic hollow), lawn and hummock microsites in an oligotrophic boreal pine fen. Statistical response functions were constructed for the microsites in order to reconstruct the annual CO₂ exchange balance from climate data. Carbon accumulation was estimated from the annual net CO₂ exchange, methane (CH₄) emissions and leaching of carbon. Due to high water tables in the year 1993, the average carbon accumulation at the flark, Eriophorum lawn, Carex lawn and hummock microsites was high, 2.91, 6.08, 2.83 and 2.66 mol C m^–2, respectively, and for the whole peatland it was 5.66 mol m^–2 year^–1. During the maximum primary production period in midsummer, hummocks with low water tables emitted less methane than predicted from the average net ecosystem exchange (NEE), while the Carex lawns emitted slightly more. CH₄ release during that period corresponded to 16% of the contemporary NEE. Annual C accumulation rate did not correlate with annual CH₄ release in the microsites studied, but the total community CO₂ release seemed to be related to CH₄ emissions in the wet microsites, again excluding the hummocks. The dependence of CO₂ exchange dynamics on weather events suggests that daily balances in C accumulation are labile and can change from net carbon uptake to net release, primarily in high hummocks on fens under warmer, drier climatic conditions. Received: 16 August 1996 / Accepted: 30 November 1996     

大气甲烷的源和汇与土壤氧化(吸收)甲烷研究进展

甲烷是主要的温室气体之一,对温室效应的贡献仅次于CO2,而每分子甲烷温室增温潜力是CO2的21倍,因此确定全球大气甲烷的源与汇,并与其进行估算,预测已成为目前全球环境变化及温室效应研究的一个热点。本文概述了国内外大气甲烷烷源与汇研究的进展情况,详述了土壤氧化（吸收）大气与内源甲烷机理及其影响因子（如土地利用情况,环境甲烷浓度,土壤温度,湿度,pH值,孔隙状况等）,最后指出,通过在长白山森林垂直分布带开展地带性土壤甲烷氧化（吸收）研究,对估算我国温带至寒带,高山苔原带土壤吸收甲烷含量,乃至全球甲烷汇具有重要意义。     

Tidal impact on planktonic primary and bacterial production in the German Wadden Sea

 Tidal variation of biological parameters was studied at three anchor stations in selected inlet channels of the northern German Wadden Sea in May and July 1994. Concentrations of bacteria, chlorophyll a and suspended matter as well as primary and bacterial production were assessed over a period of 25 h in the surface and in the bottom water. Diurnal variation in primary production was found both under in situ light conditions and under constant illumination. Tidal turbulence caused the introduction of detritus, bacteria and pigments from the sediment into the water column. The impact of sediment resuspension was most evident in the bottom water, leading to tidally oscillating bacterial production rates which were high during high stream velocity and low during the slack times. Estimations of the areal daily phytoplankton production and corresponding bacterial carbon demands were unbalanced. Primary production accounted for only 25–45% of the total bacterial carbon requirement. This discrepancy is due to the shallow euphotic depth in the Wadden Sea, allowing net primary production only in the upper 2–3 m of the water column, while the relatively high levels of bacterial activity do not show a vertical decline. Assuming that the specific biological activities in the water columns over the tidal flats are similar to those found in the inlet channels, it was found that production processes dominate in shallow areas whereas decomposition processes dominate in the deep channels. Moreover, the predominance of heterotrophic processes in the inlet channels means that additional organic carbon sources must contribute to the heterotrophic metabolism in the deep parts of the Wadden Sea, and that the horizontal flux of material is important in this turbid mesotidal ecosystem. Received: 18 April 1998 / Accepted: 12 November 1998     

Seasonal variation in reproductive success and post-nuptial moult of blue tits in southern Europe: an experimental study

Post-nuptial moult and reproductive success were studied in relation to timing of breeding in blue tits, Parus caeruleus, breeding in southern Europe. A group of experimentally delayed pairs was created by removing first clutches, thereby inducing late repeat clutches. Reproductive success and post-nuptial moult of delayed pairs were compared with both control pairs that bred early and unmanipulated late-breeding pairs. Delayed pairs fledged fewer young and with a lower body mass than control pairs. However, the number of fledged young and fledgling mass did not differ between delayed and late-breeding pairs. These results were more consistent with the date hypothesis, and it is concluded that the timing of breeding and reproductive success may be causally related in the blue tit. This study reveals a harmful effect of relaying on female body mass at the end of the nestling period. Therefore, females apparently pay the costs of relaying, since a reduction in body mass during the nestling period may be accompanied by a lowered survival probability. Delayed and late-breeding males often began moulting while still feeding young, but neither control males nor females from the three study groups did so. These results support the view that timing-related energy constraints on breeding may be important causes of a seasonal decline in reproductive success at different latitudes. Received: 15 March 1999 / Accepted: 19 July 1999     

Genetic variation and migration pathways of maritime pine (Pinus pinaster Ait) in the Iberian peninsula

The genetic variability and migration pathways of Pinus pinaster after glaciation in the Iberian peninsula was studied by means of 18 loci from 12 natural populations of the species. The analysis showed the existence of three groups of populations with different levels of diversity and patterns of recolonization. The southern Iberian group displays a high level of diversity, with a stepping-stone model of variation. The presence of rare alleles in this group and their position in the phylogenetic tree suggest the existence of refugia during glaciations in this zone. The eastern Iberian group also has high levels of diversity but is clearly separate from the first group based on their genetic distances. The Atlantic group displays a low level of diversity that could be interpreted as a rapid recolonization of the entire area by the Eastern group that has not yet developed to a divergence in this area. The southern Iberian range is indicated to be the dispersal centre of the species after the last glaciation. Received: 15 February 1999 / Accepted: 30 April 1999     

CH4 production and oxidation processes in a boreal fen ecosystem after long‐term water table drawdown

Fens, which extend over vast areas in the Northern hemisphere, are sources of the greenhouse gas CH₄. Climate change scenarios predict a lowering water table (WT) in mires. To study the effect of WT drawdown on CH₄ dynamics in a fen ecosystem, we took advantage of a WT drawdown gradient near a ground water extraction plant. Methane fluxes and CH₄ production and oxidation potentials were related to microbial communities responsible for the processes in four mire locations (wet, semiwet, semidry, and dry). Principal component analyses performed on the vegetation, pH, CH₄, and WT results clearly separated the four sampling locations in the gradient. Long‐term lowering of WT was associated with decreased coverage of Sphagnum and aerenchymatic plants, decreased CH₄ field emissions and CH₄ production potential. Based on mcrA terminal restriction fragment length polymorphism the methanogen community structure correlated best with the methane production and coverage of aerenchymatic plants along the gradient. Methanosarcinaceae and Methanocellales were found at the pristine wet end of the gradient, whereas the Fen cluster characterized the dry end. The methane‐oxidizing bacterial community consisted exclusively of Methylocystis bacteria, but interestingly of five different alleles (T, S, R, M, and O) of the particulate methane monooxygenase marker gene pmoA. The M allele was dominant in the wet locations, and the occurrence of alleles O, S, and T increased with drainage. The occurrence of the R allele that characterized the upper peat layer correlated with CH₄ oxidation potential. These results advance our understanding of mire dynamics after long‐term WT drawdown and of the microbiological bases of methane emissions from mires.     

The production of two Th2 cytokines, interleukin-4 and interleukin-10, is controlled independently by locus Cypr1 and by loci Cypr2 and Cypr3, respectively

 The strains BALB/cHeA (BALB/c) and STS/A (STS) differ in production of IL-4 and IL-10, two Th2 cytokines, after stimulation of spleen cells with Concanavalin A, STS being a low and BALB/c a high producer. We analyzed the genetic basis of this strain difference using the recombinant congenic (RC) strains of the BALB/c-c-STS/Dem (CcS/Dem) series. This series comprises 20 homozygous strains. Each CcS/Dem strain contains a different, random set of approximately 12.5% genes of the "donor" strain STS and approximately 87.5% of the "background" strain BALB/c. We selected for further analysis the RC strain production intermediate between BALB/c and STS. In (CcS-20×BALB/c)F₂ hybrids we found that different loci control expression of IL-4 and IL-10. Cypr1 (cytokine production 1) on chromosome 16 near D16Mit15 controls IL-4 production, whereas the production of IL-10 is influenced by loci Cypr2 near D1Mit14 and D1Mit227 on chromosome 1 and Cypr3 marked by D5Mit20 on chromosome 5. In addition, the relationship between the level of these two cytokines depends on the genotype of the F₂ hybrids at a locus cora1 (correlation 1) on chromosome 5. This differential genetic regulation may be relevant for the understanding of biological effects of T-helper cells in mice of different genotypes. Received: 2 March 1998 / Revised: 8 June 1998     

Effects of defoliation and symbiosis on polyamine levels in pine and birch

 We report the effect of ectomycorrhizal fungi (Suillus variegatus, Paxillus involutus) and defoliation on polyamine concentrations in pine (Pinus silvestris) and birch (Betula pendula) foliage and roots. Symbiotic root tips showed consistently higher concentrations of putrescine than non-symbiotic roots. Partial defoliation had no effect on the polyamine levels in mycorrhizal pine or birch roots. The foliage of mycorrhizal pine seedlings had lower putrescine concentrations and higher spermidine than foliage of non-mycorrhizal plants, and defoliation reversed this pattern. The response to partial defoliation differed in birch foliage: mycorrhizal status had no effect and all new growth after defoliation had higher spermidine levels than in non-defoliated birch. The potential role of polyamines in mycorrhizal symbiosis is discussed. Accepted: 26 February 1997     

Spatial, temporal and habitat-related variation in the abundance of large predatory fish at One Tree Reef, Australia

 Patterns of abundance of large piscivorous fish (>200 mm TL) were documented at two spatial and four temporal scales within the main lagoon of One Tree Reef on Australia’s Great Barrier Reef. Grouper (Serranidae), snapper (Lutjanidae) and wrasses (Labridae) were the most abundant large piscivores. On a large scale (hundreds of metres), patterns of predator abundance were consistently greater on the inner edge than centre of the lagoon over a range of temporal scales: days, weeks, months and years. On a small spatial scale (tens of metres), the abundance of large predatory fish was patchy. At both spatial scales, fish were consistently aggregated in particular areas and associated with specific structural features of the reef habitat. Predator abundance was high where live corals were predominant and the topography was more complex. Hence, predation pressure and its potential effects on the distribution and abundance of prey populations, both in time and space, may vary greatly within lagoonal environments. Accepted: 25 May 1997     

Spatio-temporal variation in coral recruitment at different scales on Heron Reef, southern Great Barrier Reef

 Recruitment of scleractinian corals on settlement plates at Heron Island, Great Barrier Reef, was examined over four years (September 1991–September 1995) to quantify spatio-temporal patterns at different scales and to assess post settlement mortality. Recruitment was dominated by pocilloporid corals which accounted for 80.1% of the 8627 spat counted, whereas non-isoporan acroporids represented only 16.4%. Poritids, faviids and isoporan acroporids rarely recruited to the plates (3.5%), despite their obvious abundance as adults on the reef. Recruitment patterns on the plates indicate strong space-time interactions as evidenced by patchy recruitment of both pocilloporid and acroporid spat. Interactions were found between space (on the scale of 10² m, i.e. sites within zones, and 10¹ m, i.e. racks within sites) and time (on the scale of years) for pocilloporids and between space (on the scale of 10³ m, i.e. zones, and 10² m) and time (on the scale of years) for acroporids. Post-recruitment mortality of acroporid spat in the period 3–10 months after their major spawning was dependent on their initial recruitment density, but pocilloporid mortality was either independent of initial recruitment density or, more likely, obscured by additional recruitment of pocilloporids to plates between late February and September. High rates of recruitment and growth by other sessile organisms, particularly bryozoans and oysters, appear to result in increased post-recruitment mortality and limit recruitment of scleractinian corals on settlement plates. The work reinforces an emerging picture that coral recruitment patterns are determined by mechanisms that manifest over a large range of spatial scales. Accepted: 1 September 1997     

Phosphate uptake and polyphosphate metabolism of mycorrhizal and nonmycorrhizal roots of pine and of Suillus bovinus at varying external pH measured by in vivo 31P-NMR

 Comparative in vivo ³¹P-NMR analyses of mycorrhizal and nonmycorrhizal roots of Pinus sylvestris and the fungus of Suillus bovinus in pure culture were used to investigate alterations in phosphate metabolism due to changes in external pH in the range 3.5–8.5. All control samples maintained a constant pH in both cytoplasm and vacuole. Mycorrhizal roots and pure fungus, but not nonmycorrhizal roots, transformed accumulated inorganic phosphate into mobile polyphosphate with a medium chain length. Phosphate uptake rates and polyphosphate accumulation responded differently to external pH. In all cases, maximal phosphate uptake occurred at an external pH close to 5.5. At an external pH of 8.5, both roots and fungus showed a distinct lag in phosphate uptake, which was abolished when the external pH was lowered to 7.5. An irreversible effect on phosphate uptake as a consequence of variation in external pH was also observed. The central role of the fungus in regulating mycorrhizal phosphate metabolism is discussed. Accepted: 15 April 1997     

Reduction potentials of blue and purple copper proteins in their unfolded states: a closer look at rack-induced coordination

 Cyclic voltammetry has been used to determine the reduction potentials of blue (Pseudomonas aeruginosa azurin) and purple (Thermus thermophilus Cu_A domain) copper proteins unfolded by guanidine hydrochloride. These Cu(II/I) potentials [456 (azurin); 453 (Cu_A) mV vs., NHE] are higher than those of the folded proteins. The downshift of the potential in the folded state can be accounted for by assuming that rack-induced axial coordination stabilizes Cu(II) relative to Cu(I) in a protein-encapsulated active site. Received: 3 March 1998 / Accepted: 6 April 1998     

Sequence variation at the major histocompatibility complex DRB loci in beluga (Delphinapterus leucas) and narwhal (Monodon monoceros)

 The variation at loci with similarity to DRB class II major histocompatibility complex loci was assessed in 313 beluga collected from 13 sampling locations across North America, and 11 narwhal collected in the Canadian high Arctic. Variation was assessed by amplification of exon 2, which codes for the peptide binding region, via the polymerase chain reaction, followed by either cloning and DNA sequencing or single-stranded conformation polymorphism analysis. Two DRB loci were identified in beluga: DRB1, a polymorphic locus, and, DRB2, a monomorphic locus. Eight alleles representing five distinct lineages (based on sequence similarity) were found at the beluga DRB1 locus. Although the relative number of alleles is low when compared with terrestrial mammals, the amino acid variation found among the lineages is moderate. At the DRB1 locus, the average number of nonsynonymous substitutions per site is greater than the average number of synonymous substitutions per site (0.0806 : 0.0207, respectively;P<0.01). Most of the 31 amino acid substitutions do not conserve the physiochemical properties of the residue, and 21 of these are located at positions implicated as forming pockets responsible for the selective binding of foreign peptide side chains. Only DRB1 variation was examined in 11 narwhal, revealing a low amount of variation. These data are consistent with an important role for the DRB1 locus in the cellular immune response of beluga. In addition, the ratio of nonsynonymous to synonymous substitutions is similar to that among primate alleles, arguing against a reduction in the balancing selection pressure in the marine environment. Two hypotheses may explain the modest amount of Mhc variation when compared with terrestrial mammals: small population sizes at speciation or a reduced neutral substitution rate in cetaceans. Received: 15 July 1997 / Revised: 24 March 1998     

The genetics of stamenoid petal production in oilseed rape (Brassica napus) and equivalent variation in Arabidopsis thaliana

 The agronomic potential of a Brassica napus variant with petalless flowers was compromised by an associated detrimental change in leaf morphology. Genetic analysis demonstrated the cosegregation of genes controlling both morphologies. Two STAP loci controlling the production of flowers with stamenoid petals were mapped to homoeologous locations in the genome of B. napus. The STAP loci were probably duplicate genes because they exhibited an epistatic interaction such that only plants homozygous for recessive stap alleles at both loci expressed the variant phenotype. The CURLY LEAF (CLF) gene of Arabidopsis thaliana pleiotropically influences both flower and leaf morphologies. The cloned CLF gene of Arabidopsis was homologous to a polymorphic B. napus locus coincident with one of the B. napus STAP loci. The possibility that CLF is a candidate gene for STAP suggests that the variant stap alleles of B. napus exert pleiotropic effects over both flower and leaf morphologies. Received: 26 August 1996 / Accepted: 20 September 1996     

Effects of reforestation methods on genetic diversity of lodgepole pine: an assessment using microsatellite and randomly amplified polymorphic DNA markers

 We examined the effects of different methods of forest regeneration on the genetic diversity of lodgepole pine (Pinus contorta var ‘latifolia’) using two different DNA-based molecular markers [randomly amplified polymorphic DNA (RAPDs) and microsatellites or simple sequence repeats (SSRs)]. Genetic diversity was estimated for 30 individuals in each of four populations for the following three stand types: (1) mature lodgepole pine (>100 years); (2) 20- to 30-year-old harvested stands left for natural regeneration; (3) 20- to 30-year-old planted stands (4 stands of each type); and one group of 30 operationally produced seedlings. There was no significant effect of stand type on expected heterozygosity, although allelic richness and diversity were much higher for SSRs than for RAPDs. Expected heterozygosity ranged from 0.39 to 0.47 based on RAPDs and from 0.67 to 0.77 based on SSRs. The number of alleles per locus for SSRs ranged from 3 to 34 (mean 21.0), and there was a significant relationship between sequence repeat length and the number of alleles at a locus. Both marker types showed that over 94% of the variation was contained within the populations and that the naturally regenerated stands sampled had lower (not significant) expected heterozygosity than the planted or unharvested stands. The group of seedlings (assessed by RAPDs only) had expected heterozygosity and allele frequencies similar to those of the unharvested stands. Genetic distance measures were higher than obtained previously in the species using isozyme markers. There was no correlation between the two marker types for pair-wise genetic distances based on populations analyzed by both methods. Pair-wise genetic distance measures and an ordination of allele frequencies for both marker types showed little effect of geographic location or stand type on genetic similarity. Received: 18 August 1998 / Accepted: 17 September 1998     

Population size and structure of giant clams at Rose Atoll, an important refuge in the Samoan Archipelago

Rose Atoll is an important refuge for giant clams (Tridacna maxima) that have been heavily exploited elsewhere in Samoa. During an extensive survey of six islands in the archipelago (50.5?ha surveyed in 420 transects), 97% of a total of 2853 clams were recorded at the atoll (42% of area surveyed). Clam densities were highest in the atoll lagoon, especially around the bases of the pinnacles (mean density=8870?ha^-1). Estimated population size for the small atoll (615?ha) was approximately 27800 clams. Twenty four percent of the population consisted of mature clams (?12?cm), 70% of which occupied the pinnacles and shallow lagoon habitat. Estimated mortality was low (Z=0.3) and primarily due to natural mortality (M=0.3). Maximum recorded size (L _max ) and asymptotic mean size (L _∞) were 25.0?cm and 27.8?cm respectively.     

Seasonal and local spatial patterns in the upper thermal limits of corals on the inshore Central Great Barrier Reef

 Experimental studies of the upper thermal limits of corals from Orpheus Island, an inshore reef in the central Great Barrier Reef, show that Acropora formosa has a 5-day 50%-bleaching threshold of between 31 and 32 °C in summer, only 2 to 3 °C higher than local mean summer temperatures (29 °C). Summer bleaching thresholds for Pocillopora damicornis and A. elseyi were 1 °C higher (between 32 and 33 °C). The winter bleaching threshold of Pocillopora damicornis was 1 °C lower than its summer threshold, indicating that seasonal acclimatisation may take place. This seasonal difference raises the possibility that at least some corals may be capable of short-term thermal acclimatisation. Neither P. damicornis nor A. elseyi showed habitat-specific (reef flat versus reef slope) differences in bleaching thresholds. Further, colonies of P. damicornis collected from sites 3 km apart also showed no difference in bleaching threshold despite populations of this species responding differently at these two sites during a natural bleaching event. The bleaching thresholds determined in this study are best considered as the maximum tolerable temperatures for local populations of these species because they were determined in the absence of additional stressors (e.g. high light) which often co-occur during natural bleaching events. We consider the 5-day 50% bleaching thresholds determined in these experiments to be fair indicators of upper thermal limits, because >50% of a sample population died when allowed to recover in situ. We found a delay of up to a month in the bleaching response of corals following thermal stress, a result that has implications for identifying the timing of stressful conditions in natural bleaching events. Accepted: 26 May 1999     

Seedling disease in an annual legume: consequences for seedling mortality, plant size, and population seed production

The effect of seed and seedling mortality on plant population dynamics depends on the degree to which the growth and reproduction of surviving individuals can compensate for the deaths that occur. To explore this issue, we sowed seeds of the annual Kummerowia stipulacea at three densities in sunken pots in the field, which contained either field soil, microwaved field soil, or microwaved field soil augmented with oospores of three Pythium species. High sowing density reduced seedling establishment and seedling size, but these effects were independent of the soil treatment. In the oospore-augmented soil, seed and seedling survival was low. The surviving plants were initially smaller but, at maturity, average plant size was greatest in the oospore-augmented soil, compared to the other treatments. Total population seed production was unaffected by soil treatment, suggesting that the effect of disease was limited to the seedling stage, with surviving plants released from intraspecific competition. To test the hypothesis that the surviving plants in the oospore-augmented soil were more disease-resistant, seeds from each of the sowing density-soil type treatments were sown in a growth chamber inoculation study. No evidence for selection for resistance was found. A second inoculation experiment revealed that oospore inoculum reduced plant numbers and mass regardless of whether field or microwaved soil was used, suggesting that results from the field experiment were not dependent on the use of microwaved soil. The findings of this study indicate that the ecological effects of disease on individual plants and on plant populations are not necessarily equivalent. Received: 13 January 1999 / Accepted: 21 September 1999     

Genetic variation at chloroplast microsatellites (cpSSRs) in Abies nebrodensis (Lojac.) Mattei and three neighboring Abies species

Abies nebrodensis (Lojac.) Mattei (Sicilian fir) is an endangered species represented by only one population of 29 adult individuals occurring in a limited area of the Madonie Range in northern Sicily (Italy). Taxonomic boundaries between this taxon and the neighboring Abies species are not clear. In this study, we used six chloroplast simple-sequence repeats (cpSSRs) to investigate the population genetic structure and the distribution of chloroplast haplotypic variation in A. nebrodensis and three of the neighboring Abies species: Abies alba (Mill.), Abies numidica (De Lann) and Abies cepha-lonica (Loud.). Our aims were to quantify the level of cpDNA differentiation within the Abies populations and to shed light on the history of A. nebrodensis. Diversity levels based on the haplotype frequency at six cpSSRs were high, especially in A. alba and A. cephalonica. In all, we found 122 haplotypes among the 169 individuals analyzed, and the four species were distinguished from each other by their haplotype composition. The majority of the haplotypes (76%) were detected only once, but in A. nebrodensis seven individuals (41% of the sample population) shared the same haplotype. Moreover, the seven A. nebrodensis individuals with an identical haplotype showed a tendency to be geographically grouped within the population"s limited range. The analysis of molecular variance (AMOVA) showed a significant difference in the level of apportionment of gene diversity between the species A. alba and A. cephalonica (F_ST=0.191 and 0.012, respectively). AMOVA analysis conducted over all populations from the four species showed that 19% of the total cpSSR variation was attributable to differences among species, 6% was due to differences among populations within species, and 74% to differences within populations. The high percentage of unique haplotypes identified confirms the power of cpSSR haplotype analysis for identifying individual trees in individual Abies populations. Our results indicate that A. nebrodensis differs from the other three Abies species investigated and support its classification as an independent taxon. The results also showed a decreased level of variation in A. nebrodensis and suggested that the species has experienced a genetic bottleneck during the last two centuries. Received: 10 April 2000 / Accepted: 13 July 2000     

Organization of an Arabidopsis thaliana gene cluster on chromosome 4 including the RPS2 gene, in the Brassica nigra genome

 Genetic and physical maps, consisting of a large number of DNA markers for Arabidopsis thaliana chromosomes, represent excellent tools to determine the organization of related genomes such as those of Brassica. In this paper we report the chromosomal localization and physical analysis by pulsed-field gel electrophoresis (PFGE) of a well-defined gene complex of A. thaliana in the Brassica nigra genome (B genome n=8). This complex is approximately 30 kb in length in A. thaliana and contains a cluster of six genes including ABI1 (ABA-responsive), RPS2 (resistance against Pseudomonas syringae, a bacterial disease), CK1 (casein kinase I), NAP (nucleosome-assembly protein), X9 and X14 (both of unknown function). The Arabidopsis chromosomal complex was found to be duplicated and conserved in gene number at different levels in the Brassica genome. Linkage group B1 had the most-conserved arrangement carrying all six genes tightly linked. Group B4 had an almost complete complex except for the absence of RPS2. Other partial complexes of fewer members were found on three other chromosomes. Our studies demonstrate that by this approach it is possible to identify ancestrally related chromosome segments in a complex and duplicated genome, such as the genome of B. nigra, permitting one to draw conclusions as to its origin and evolution. Received: 11 July 1997 / Accepted: 9 October 1997