Seasonal succession of the travertine‐forming desmid Oocardium stratum

The calcifying Conjugatophyte Oocardium stratum occurs exclusively in spring‐associated limestones (SAL) with active meteogene limestone deposition. The macroscopic colonies of Oocardium stratum form hemispherical, pinhead‐like structures with a diameter of 0.5–2.0 mm. As its autecology is still poorly understood, we focused on the seasonal development of Oocardium stratum and linked environmental factors to its abundance. The study was conducted in a rivulet in Lunz/See (Austria) for 16 months on a weekly (growing season) to monthly (winter season) basis. Oocardium colonies were found throughout the whole year, with maximum abundance during the mid‐summer months July and August. Repeated macro‐mapping of three SAL sites measuring 750 cm² each showed a maximum Oocardium cover of around 30% in August; two smaller peaks developed in early summer and late autumn with ~10% cover. Diatom mats dominated by Cymbella excisiformis occurred in spring, autumn and winter, with more than 75% cover. The seasonal change between Oocardium and diatoms in limestone‐precipitating springs causes a typical sequence pattern of limestone layers. Redundancy analysis revealed water temperature and bicarbonate content as the main structuring factors; these control the occurrence and growth of Oocardium, reflecting season as a background variable. Optimum growth conditions for Oocardium were an alkalinity around 4.7 meq · L^?1 and a water temperature around 13°C. Site openness, nitrate and dissolved carbon dioxide were inversely related to Oocardium biomass, the opposite for diatoms. Other environmental factors such as total ions or soluble reactive phosphorus had no significant influence on Oocardium stratum abundance.     

The Early Holocene treeline in the southern French Alps: new evidence from travertine formations

Aims The present paper concerns the analysis of macro‐remains (plant imprints) from high altitude travertine deposits dating back to the early Holocene (9800 BP ). Our results allow us to discuss treeline location and ecology, and to supplement previous data based on pollen from natural sediments and charcoal from natural soil. Location The travertine under study is located in the Queyras massif, in the southern French Alps, along the Italian border. The site is situated on a south‐facing slope. Methods The travertine deposit has been dated by ²³⁰Th/²³⁴U. Taxonomic identification of plant imprints was achieved by comparison of the morphology of fossil specimens with extant material. Results Imprints of Pinus uncinata (cones and needles), broad‐leaved trees (Betula cf. pubescens, Populus tremula and Salix spp.), and unidentified trunks have been found. The plant assemblage records the existence at a high altitude (2200 m) of shade‐intolerant vegetation at around 9800 BP. Our data indicate that the treeline limit was at least 100 m higher than previously thought. The morphological features of the travertine, the plant assemblage and trunk diameters indicate that during the travertinization process, vegetation around the site was probably dense with tall upright trees. Main conclusions Our data show that Pinus uncinata and broad‐leaved trees developed at 2200 m, while regional pollen analyses locate the treeline at lower altitudes. Different research methods appear to provide different results. Around 9800 BP tree regeneration and growth were made possible up to at least 2200 m a.s.l., probably as a result of warmer and wetter summers. Warmer conditions are inferred from the predicted increase in incoming solar radiation based on calculated orbital variations, and wetter conditions are inferred from the build‐up of the travertine.     

Increase in calmodulin level in the early phases of radish seed (Raphanus sativus) germination

Abstract Calmodulin (Cam), the heat-stable, ubiquitous, Ca²⁺-dependent regulator protein, has been purified to apparent homogeneity from germinating radish seeds (Raphanus sativus). The characteristics of radish Cam-molecular weight, absorption spectrum, Ca²⁺-dependent activation of brain phosphodiesterase (PDE)-are very similar to those described for Cam from other plant materials. Radish Cam, like other plant Cam, shows some differences to Cam of calf brain. The total amount of Cam in radish embryos at 24 h of germination is ca. 37 μg g⁻¹ fresh weight. Approximately 95% of the total amount of Cam is present in the soluble fraction (supernatant at 100,000 g). The level in the embryo axis strongly increases in the first 24 h of germination (+540%); this increase is strongly reduced when the germination is inhibited by abscisic acid (ABA). In the presence of Ca²⁺, no ‘free’ Cam (i.e. not bound to other structures) is present in the soluble fraction, suggesting that, during early germination, Cam level is a limiting factor for the activities of Ca²⁺ -Cam-dependent systems. These studies suggest that Cam plays an important role in the early phases of seed germination. An inhibitor of the Ca²⁺-Cam-dependent phosphodiesterase is present in the soluble fraction from radish embryos; this substance decreases during germination. A possible role of this inhibitor during the early germination phases is hypothesized.     

Significance of the biomineralizing microniche in a lyngbya (cyanobacterium) travertine

Observations of the spatial arrangement of Lyngbya (Phormidium) incrustatum tri‐chomes in a travertine crust allowed prediction of the frequency of four types of microniche favorable for photosynthetically induced calcification. The most frequent type of microniche occurred at “cross‐over”; points where two trichomes made contact at a single point. Such points occurred very frequently (～6000/mm² travertine). Microniches more favorable to photocalcification consist of groups of three or more trichomes lying side by side, enclosing narrow tubes of interstitial water. These configurations were far less frequent and their effects would be negligible in Lyngbya travertines. In the calcified cyanobacteria Rivularia and Schizothrix such configurations may be much more common. The existence of such microniches demonstrated that regions favorable for photocalcification occur in travertine‐encrusted cyanobac‐terial mats and may initiate carbonate precipitation. However, the bulk of the carbonate precipitated in such travertines is known to be formed through inorganic processes.     

Surprisingly high orchid diversity in travertine and forest areas in the Huanglong valley, China, and implications for conservation

The presence of such a large number of terrestrial orchid species in a small area (ca. 1 km²) of the Huanglong valley in southwestern China is uncommon for this country. Studying the relationship between the distribution patterns of these orchid species and their microenvironments may help us understand this uncommon phenomenon. We established 662 1 m × 1 m plots, measured the cover of each species and found that there were 33 orchid species distributed mainly in two different habitats, i.e. travertine areas and forest. In the travertine areas, 30 orchid species were found; the six most common ones being Cypripedium bardolphianum, Cypripedium flavum, Cypripedium tibeticum, Galearis diantha, Ponerorchis chusua and Phaius delavayi. However in the forested habitat, we found 21 orchid species; the most common ones being Tipularia szechuanica and Goodyera repens. Travertine areas had a higher number of orchid species as well as higher numbers of orchid species per plot as compared to forest. Light availability seems critical to the performance and distribution of orchid species. Stream flow through the travertine area during the orchids growing season appears to be an important factor in shaping and maintaining stable microenvironments favorable to the growth and reproduction of orchids. The results presented in this study suggest that some orchid species in the travertine area might be threatened if the travertine stream flows were to change or be disrupted.     

A freshwater analog for the production of Epiphyton‐like microfossils

Calcified microbial microfossils—often interpreted as cyanobacteria—were important components of Precambrian and Paleozoic limestones, but their paucity in modern marine environments complicates our ability to make conclusive interpretations about their taxonomic affinity and geologic significance. Freshwater spring‐associated limestones (e.g., travertine and tufa) serve as terrestrial analogs to investigate mineralization in and around aquatic biofilms on observable timescales. We document the diagenesis of calcite fabrics associated with the freshwater algae Oocardium stratum, an epiphytic colonial green algae (desmid) known for producing stalks of extracellular polymeric substances (EPS) and passively producing a bifurcating tubular calcite monocrystal. Bifurcating EPS stalks produced by Oocardium colonies can become calcified and preserved in ancient carbonate deposits. Calcified micritic EPS stalks have a filamentous morphology, show evidence of branching, and maintain uniformity in diameter thickness throughout the mm‐scale colony, much like the enigmatic calcimicrobe Epiphyton. We provide a mechanism by which calcification associated with a colonial semispherical micro‐organism produces microfossils that deceptively resemble filamentous forms. These findings have implications for the use of morphological traits when assigning taxonomic affinities to extinct microfossil groups and highlight the utility of calcifying freshwater modern environments to investigate microbial taphonomy.     

The populations of fish in tributaries of the River Eden on the Moor House National Nature Reserve,northern England

The population dynamics of trout (Salmo trutta L.) were studied in two high-altitude streams flowing westwards into the River Eden in northern England. The results from one (Knock Ore Gill), which is accessible to spawners from downstream, were compared with published data from an isolated population in a nearby stream which flows eastward into the River Tees. The Knock Ore Gill trout had a population density of 0.4–0.9 fish m^–2, a biomass of 12.4 g m^–2, annual production of 12–14 g m^–2 year^–1 and an instantaneous mortality rate of 0.97 year^–1. Comparable values from the Tees tributary were 0.2, 3.3, 2.3 and 0.66 respectively. The Knock Ore Gill population also contrasted with that of the Tees tributary in having reliable recruitment from year to year. These differences were related to differences in the chemistry and spate characteristics of the two streams and to the fact that immigrants from downstream were responsible for over 30% of the annual oviposition in Knock Ore Gill.     

Cell morphology, ultrastructure, and calcification pattern of Oocardium stratum, a peculiar lotic desmid

Cell morphology and ultrastructure of the desmid Oocardium stratum and its habitat conditions in two limestone-precipitating spring habitats in the Alps were studied. In spite of specific cell geometry, we found ultrastructural features (nucleus with nucleolus, Golgi apparatus, chloroplast structure, lipid bodies, cell wall texture) closely related to other desmids. The type of the mucilage pore apparatus perforating in high densities extended areas of the cell wall of Oocardium is of the Cosmarium type. Oocardium contrasts to Cosmarium by a peculiar bilateral cell geometry (lateral sphenoid shape) which is combined with a dislocated nucleus. Although the cell features of Oocardium did not differ between the two habitats, different calcification types (rhombohedral calcite versus fascicular-fibrous calcite) and calcification intensities were recorded. The spatial positioning and extension of the Oocardium niches differed considerably between the two springs in spite of high CO₂ oversaturation at both sites.     

The development of gill arches and gill blood vessels of the rainbow trout,Salmo gairdneri

Gill development begins on the sixth day of incubation at 10^°C and is complete by 31 days (hatching). Gill arches are formed by fusion and perforation of ectoderm and endoderm across the pharyngeal wall. A primary branchial artery forms within each arch and a second branchial artery forms as a branch from its ventral end. A series of filament loop vessels forms connecting the two arteries and when several are patent a unidirectional blood flow is established via afferent (second) branchial artery, filament loop vessels to efferent (primary) branchial artery. Part of the efferent branchial artery just above its junction with the afferent branchial artery constricts and occludes. It is suggested that this change in the pattern of blood flow is dependent on differences in resistance of the two branchial arteries. A later extension of the gill ventrally is thought not to be homologous with similar regions in elasmobranchs and Acipenser.     

Changes in the Levels of Calmodulin and of a Calmodulin Inhibitor in the Early Phases of Radish (Raphanus sativus L.) Seed Germination: Effects of Aba and Fusicoccin

An inhibitor of Ca²⁺-calmodulin (Cam)-dependent brain phosphodiesterase was present in the soluble fraction of embryo axes from ungerminated radish (Raphanus sativus L.) seeds. This inhibitor is a Ca²⁺-dependent, Cam-binding protein; in fact: (a) its effect was strongly reduced by treatment with proteases; (b) the inhibition was counteracted by Cam but not by Ca²⁺; (c) on gel filtration in the presence of Ca²⁺, Cam co-chromatographed with the inhibitor. The inhibitor is heat stable and positively charged at pH 7.5. During early phases of germination, the fresh weight and the levels of DNA and RNA of embryo axes increased, the level of the inhibitor decreased, and the level of Cam increased. Abscisic acid (ABA) inhibited germination, the decrease of inhibitor, and the increase of Cam. Fusicoccin (FC) stimulated the increase in fresh weight but not the increase in the RNA and DNA levels; in this condition, the inhibitor level decreased and the increase in Cam level was higher than in the control. In the presence of both ABA and FC, there was an increase in fresh weight not accompanied by an increase in DNA and RNA levels; Cam increased and, on a fresh weight basis, reached the value of the control. These results indicate that the Ca²⁺-Cam system was activated in early germination of radish seeds by an increase in Cam and a decrease in the inhibitor levels, that FC, probably through the activation of membrane functions, increased Cam level, and that the ABA inhibition on germination was not mediated by the Ca²⁺-Cam system.     

Datation des travertins de Kocabaş par la méthode des nucléides cosmogéniques Al/Be

The archaic Homo erectus Kocaba? skullcap was discovered at Kocaba?, Denizli, Turkey in travertine formations over- and underlain by conglomerate formations. These units dated by the ²⁶Al/¹⁰Be cosmogenic nuclide method constrained the skullcap age between 1.0 and 1.6 Ma.     

Preliminary results on sperm motility and testicular histology of two feral fish species, Oreochromis mossambicus and Clarias gariepinus, from a currently DDT-sprayed area, South Africa

The effects of DDT and its metabolites on the reproductive health of two fish species (Clarias gariepinus and Oreochromis mossambicus) were studied using the gonadosomatic index (GSI), gonadal histology and computer assisted sperm analysis (CASA). DDT and its metabolites, DDE and DDD are endocrine disrupting chemicals posing estrogenic and anti‐androgenic properties, which have detrimental effects on growth and reproduction. Although DDT was banned internationally, it is still used for Malaria vector control in areas of South Africa. Both species were sampled at a reference site, Albasini dam (AD), (outside the DDT‐sprayed area, <0.01 μg L^?1 of DDT) and at an exposed site, Xikundu weir (XW), in the same river ± 70 km within the DDT‐sprayed area, <0.01 μg L^?1 of DDT. Gill nets were used to acquire a sample size of 10 male fish per site for each species. Both testes were dissected out and the GSI calculated. Uncontaminated milt was collected and analyzed using a novel CASA system based on open source software for characterization of sperm motility parameters. Testis tissue sampled for histology was fixed in Bouins and processed according to standard methods. The sample size obtained at the reference site (AD) was O. mossambicus n = 6, C. gariepinus n = 9; and at the exposed site (XW) was O. mossambicus n = 10, C. gariepinus n = 3. The GSI results showed a lower value for O. mossambicus at XW (0.06) (n = 13) than AD (0.12) (n = 6); U = 16.0, P = 0.044. However the opposite was true for C. gariepinus. Exposure to various environmental toxicants can result in gonadal changes such as decreased GSI, morphological alterations or both. Histological assessment showed histopathological alterations to testes tissue including intersex (only in O. mossambicus) and detachment of basal membranes. The CASA results showed a decrease in parameters from the reference site (AD) to the exposed site (XW) for both species. The decrease in percent motility (% MOT) for O. mossambicus from the reference site (AD) (n = 6) to the exposed site (XW) (n = 13) was statistically significant; U = 13.0, P = 0.023. C. gariepinus from the exposed site (XW) was most affected in terms of percent motility (10.00%) and velocity (67.94 μm s^?1). Detailed assessment of the environmental effects of DDT in this area seems crucial before population impacts become evident.     

Processes Forming Daily Lamination in a Microbe-Rich Travertine Under Low Flow Condition at the Nagano-yu Hot Spring,Southwestern Japan

A daily rhythm of microbial processes, in terms of sub-mm order lamination, was identified for a microbe-rich aragonite travertine formed at a low-flow site of the Nagano-yu Hot Spring in Southwestern Japan. Continuous observation and sampling clearly showed that the lamination consisted of diurnal microbe-rich layers (M-layers) and nocturnal crystalline layers (C-layers). The M-layers originated from biofilm formed by growth and upward migration of filamentous cyanobacteria related to Microcoleus sp., which can rapidly glide and secrete extracellular polymeric substances (EPS). During the daytime, cyanobacterial biofilm development inhibited aragonite precipitation on the travertine surface due to the calcium-binding ability of EPS. After sunset, aragonite precipitation started on the surface where aerobic heterotrophic bacteria decomposed EPS, which induced precipitation of micritic crystals. This early stage of C-layer formation was followed by abiotic precipitation of fan-shaped aragonite aggregates. Despite their major role in lamina formation, the cyanobacteria were readily degraded within 6–10 days after embedding, and the remaining open spaces in the M-layers were sparsely filled with crystal clots. These lamina-forming processes were different from those observed in a high-flow site where the travertine has a dense texture of aragonite crystals. The microbial travertine at Nagano-yu is similar to some Precambrian stromatolites in terms of in situ mineral precipitation, regular sub-mm order lamination, and arrangement of filamentous microbes; therefore, the lamination of these stromatolites possibly occur with a daily rhythm. The microbial processes demonstrated in this study may revise the interpretation of ancient stromatolite formation.     

Reciprocal fluxes of stream and riparian invertebrates in a coastal California basin with Mediterranean climate

Stream and riparian food webs are connected by reciprocal fluxes of invertebrates, and a growing number of studies demonstrate strong effects of these subsidies on consumers and food webs in both habitats. However, despite its importance in understanding energy flow between these habitats, seasonality of reciprocal subsidies has been examined only in a single temperate system in Japan. We measured input of terrestrial invertebrates and emergence of adult aquatic insects for 14?months in two adjacent streams in a coastal Mediterranean basin in California to assess seasonal patterns, annual fluxes, and local variation. Fluxes of terrestrial and aquatic invertebrates fluctuated seasonally and were relatively synchronous, although in the fall of 2004, terrestrial inputs peaked 1?C2?months earlier than emergence. Terrestrial inputs were similar in the two streams with annual flux of 7.9?C8.6?g dry mass?m^?2?year^?1. Emergence differed between the streams: annual emergence was 7.8?g?m^?2?year^?1 (similar to terrestrial flux) in one reach but 5.3?g?m^?2?year^?1 from the other. The presence of streambed travertine in the reach with lower emergence was the primary difference in habitat between the streams, suggesting that travertine may reduce emergence and alter net reciprocal flux. Comparison of our results with those from Japan suggests that seasonality and net annual flux of reciprocal stream-riparian subsidies vary among biomes due to differences in climate, vegetation, and geography. Our results also indicate that local factors, such as travertine, may cause reciprocal fluxes to vary at finer spatial scales.     

Absolute dating of sedimentation on Lake Torrens with spring deposits,South Australia

The travertine structure containing Mountford Spring is in the only surface accumulation of CaCO₃ on Lake Torrens, a playa in South Australia. Here the first ¹⁴C data on Lake Torrens is presented. ¹⁴C ages for travertine samples surrounding Mountford Spring, range from 13 770 ± 130 years BP to 22 700 ± 290 years BP, giving a time frame for lacustrine sediments wedged in between. In the absence of recent tectonic movements, the old travertine (22 700 ± 130 years) on the clifftop, surrounded by younger spring deposits (13770 ± 130 years) at a lower level, prove a deflation event at this playa.     

Molecular analysis of the gene for the human vitamin-D-binding protein (group-specific component): allelic differences of the common genetic GC types

Summary DNA sequence analysis of the polymerase chain reaction products, including the coding region for amino acids 416 and 420, of the vitamin-D-binding protein (DBP, group-specific component, GC) shows allelespecific differences. The GC2 and GC1F phenotypes have an aspartic acid residue at amino acid position 416, whereas the GC1S phenotype has a glutamic acid at this position. In the GC2 phenotype, amino acid 420 is a lysine residue, and in the both common GC1 phenotypes, it is a threonine residue. The nucleotide exchanges involve a HaeIII (position 416) and a StyI (position 420) restriction site: the HaeIII restriction site is specific for the GC^*1S allele and the StyI restriction site is specific for the GC^*2 allele. We have tested 140 individual genomic DNA samples for the HaeIII site and 148 samples for the StyI site by restriction fragment length polymorphism (RFLP) analysis with a DBP-specific direct genomic DNA probe, and have compared these findings with the GC phenotype classification, by isoelectric focusing (IEF) of the corresponding plasma. The results of the HaeIII RFLP analysis and the IEF typing were in complete agreement. By using our DNA probe, we could disclose, in addition to the StyI site at amino acid position 420, two further StyI site downstream: one was specific for the GC^*1S allele and another for the GC^*1F allele. In 147 samples, there was agreement between the IEF GC typing and the analysis of the StyI restriction sites. In a single case, the observed result of the StyI-digest differed from the result expected after IEF classification: homozygous GC 1F-1F by IEF and heterozygous by StyI RFLP analysis. We discuss this finding as a recombination event or a possible silent allele in IEF typing. The GC polymorphism revealed by Southern blot analysis of StyI-digests provides an informative DNA marker system for chromosome 4q11–q13.     

Community–habitat relationships in coastal streams in Big Sur, California, USA: travertine influences macroinvertebrate abundance and community structure

Travertine deposition occurs in streams worldwide but its effects on stream communities are poorly understood. I sampled benthic macroinvertebrates, periphyton, and reach-scale environmental variables in coastal streams in Big Sur, central California, USA, to determine the specific effects of travertine that occurred at some sites as well as to provide a broader assessment of community–habitat relationships. Total density and biomass of macroinvertebrates varied 6- and 9-fold across sites, respectively, and chlorophyll a concentrations varied 10-fold, but invertebrate and periphyton abundances were not correlated. Baetis tricaudatus (Ephemeroptera), Simuliidae (Diptera), and Chironomidae (Diptera) dominated macroinvertebrate communities across all sites, although differences in the relative abundances of these and other taxa produced moderate variation in community structure among sites (Bray-Curtis similarity coefficients of 47–84). Variation in community structure was related to a number of habitat features, notably travertine but also including variables reflecting channel morphology, flow, substrate size, and riparian tree type. Median density and biomass of macroinvertebrates were more than twice as high at sites without travertine than sites with travertine. Taxa richness also was higher at sites without travertine, and community structure differed moderately between sites with and without travertine, although there were no particular assemblages associated with either group. Non-metric multidimensional scaling (MDS) and cluster analysis of similarities in community structure appeared to separate sites with either travertine or high fines from sites without those conditions. These results demonstrate that travertine can have strong effects on stream communities, and additional studies are needed to identify the full range of effects on ecosystems and to evaluate the potential consequences of travertine for conservation efforts such as biomonitoring programs and threatened species management. Handling editor: R. Bailey     

Two new Gaucher disease mutations

Recently, a mutation at nucleotide 1193 of the glucocerebrosidase gene was described in a patient with type 1 Gaucher disease. This mutation destroys a TaqI site in a polymerase chain reaction (PCR)-amplified fragment. We used digestion with this enzyme to screen DNA samples from Gaucher disease patients representing 23 previously unidentified alleles and discovered that this site had been destroyed in three samples. However, the mutation that caused this change proved to be a CT substitution at cDNA nucleotide 1192 (Genomic 5408; ³⁵⁹ArgEnd). Fortuitously, another TaqI site was destroyed by a different mutation, a GA mutation at nt 1312 (Genomic 5927; ³⁹⁹AspAsn). Both of these mutations were functionally severe in that they were associated with type 2 (acute neuronopathic) Gaucher disease.     

How Phosphorus Availability Affects the Impact of Nitrogen Deposition on <Emphasis Type="Italic">Sphagnum</Emphasis> and Vascular Plants in Bogs

To elucidate the impact of high nitrogen (N) deposition on intact bog vegetation, as affected by phosphorus (P) availability, we conducted a 4-year fertilization experiment with N and P at six sites, one with moderate N deposition and five with high N deposition. During the growing season, N (40 kg ha^–1 ya^–1), P (3 kg ha^–1 y^–1), or a combination of both elements was applied to the vegetation. The fertilization effects turned out to be additive in nature. Adding P decreased the inorganic N concentration and increased the P concentration in the rhizosphere at two sites. Furthermore, P stimulated Sphagnum growth and Sphagnum net primary productivity (NPP) at two sites; it also seemed to encourage growth at two other sites including the moderate-deposition site. Vascular plant growth remained largely unaffected but was depressed at one high-deposition site. Adding N increased the concentration of inorganic N in the rhizosphere at the moderate-deposition site and at two of the three high-deposition sites; vascular plant growth and litter production were encouraged at three high-deposition sites. The addition of N depressed Sphagnum height increment at four high deposition sites and reduced Sphagnum NPP at two sites. Shading by vascular plants was of minor importance in explaining the negative effects of N on Sphagnum. We conclude that because P alleviates the negative impact N has on Sphagnum by enhancing its capability to assimilate the deposited N, P availability is a major factor determining the impact of N deposition on Sphagnum production and thus on carbon sequestration in bogs.     

Close linkage between mouse genes determining the two forms of complement component C6 and component C7, and cis action of a C6 Regulatory Gene

Two forms of mouse complement component C6, with molecular weights (M _rs) of 90 and 100 kilodaltons (kd), are present in the sera from certain inbred strains such as the CBA strain; other strains, such as the BALB/c and DBA/2 strains, have only the 90 kd C6A form. The present work was undertaken to determine whether the two M _r forms were the products of genes coding at separate loci. We screened sera from mice from a number of inbred strains by isoelectric focusing and found one strain, AKR, exhibiting allotypic structural variations of C6 forms. To distinguish the various types, we designated the 90 kd types from CBA and AKR mice C6A1 and C6A2, respectively, and the corresponding 100 kd types C6B 1 and C6B2, respectively. Mice possessing only one M _r form were all typed as C6A1. Results of breeding experiments strongly suggested that the two M _r forms of C6 are coded for at two closely linked loci. Sera from a number of inbred strains were also screened for a complement C7 polymorphism by means of isoelectric focusing and functional overlay. C7 from all strains, excepting the AKR strain, produced identical C7 band patterns. AKR C7 produced a unique band pattern, and results of breeding experiments with AKR and BALB/c mice showed the C6 and C7 loci to be closely linked. In addition, we identified a regulatory gene for C6 production. The gene apparently requires androgen to facilitate C6 production in the majority of strains. In these strains C6 activity is virtually absent from female sera. However, we observed moderate levels of C6 activity in sera from IS/Cam females, indicating that, in this strain, male physiological androgen levels are not necessary for C6 production. IS/Cam possess one form of circulating C6 which appears identical with BALB/c C6A1, and therefore IS/Cam mice differ from AKR mice at both the C6 structural and regulatory loci. These two strains were thus suitable for use in breeding experiments to determine the manner of action of the regulatory gene. Results showed that it acted in a cis manner.Abbreviations used in this paper M _r molecular weight - kd kilodaltons - SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - IEF isoelectric focusing - Slp sex-limited protein - MHC major histocompatibility complex