Jiří Macháček

Daphnia hybridization along ecological gradients in pelagic environments: the potential for the presence of hybrid zones in plankton.

The relative homogeneity of pelagic environments has been regarded as the reason for the absence of hybrid zones for hybridizing planktonic Daphnia (Crustacea: Cladocera); occasional dominance of interspecific hybrids over parental species was explained by their temporal superiority in fluctuating environments. However, water bodies with spatially varying environmental conditions might facilitate the formation of hybrid zones in plankton. We studied the distribution of species and hybrids of the Daphnia longispina complex in 11 canyon-shaped reservoirs, localities characterized by horizontal environmental gradients (particularly of food supply and size-selective predation); we also analysed patterns of carapace size and fecundity among coexisting taxa. Spatial distribution of taxa agreed with their ecological characteristics; those showing different affinities along longitudinal reservoir profiles differed in size according to the presumed fish predation gradient. Only hybrids of Daphnia galeata with Daphnia cucullata and D. longispina (=hyalina) were recorded. The latter two species preferred opposite ends of gradients, such spatial segregation probably explaining the absence of their hybrids. Distributional patterns were relatively stable in two consecutive summers, apart from a substantial decline of D. galeata×cucullata in the second year. The observed pattern of a hybrid-dominated zone in intermediate conditions suggests that local Daphnia hybrid zones may indeed form within reservoirs.

Alkoxohydridoaluminates: multinuclear NMR study of sodium hydrido-(2-methoxyethoxo) aluminates

Abstract 23 Na, 27 Al, and 1 H NMR spectra were obtained on benzene solutions of varying sodium alkoxohydridoaluminate compositions, Na + H x Al − (OR) 4− x , where x = 2 to 0, and OR = OCH 2 CH 2 OCH 3 . An extensive series was prepared by titration of initial Na + H 2 Al(OR) 2 − , (SDMA), x = 2, by 2-methoxyethanol, HOCH 2 CH 2 OCH 3 . The NMR data presented enabled the refinement of the structure of SDMA, sodium dihydrido-bis(2-methoxyethoxo)aluminate, proposed formerly as an individual compound. The preparation of the analogous ‘mono-hydrido aluminate’, Na + HAl − (OR) 3 , x = 1, as an individual compound, for reason of excellent selective reducing ability, failed. NMR data revealed that alcoholysis of the SDMA by 2-methoxyethanol (in molar ratio Na + H 2 Al − (OR) 2 : HOCH 2 CH 2 OCH 3 = 1:1) does not result in in the desired individual Na + HAl − (OR) 3 , but in an equilibrium mixture of the Na + salt of H 2 Al − (OR) 2 , HAl − (OR) 3 and Al − (OR) 4 aluminate anions. The inherently ionic sodium alkoxohydridoaluminate are stabilized in solvents of low dielectric constant and low donation strength—in benzene—via different types of aggregate: SDMA via higher, weaker ionic aggregates, and mixture of Na + salt of HAl − (OR) 3 , HAl − (OR) 3 and Al − (OR) 4 aluminate anions via ion-paired predominantly trimeric aggregates. These different types of aggregation were recognized on the basis of apparent molecular weight and conductivity measurements on the system. Multinuclear NMR data were used for discussion of these different types of aggregate in more detail.

71Ga NMR studies of mixtures of gallium trichloride and trimethylgallium

Abstract 71 Ga NMR spectra of solutions of GaCl 3 and Me 3 Ga, and of binary mixtures of GaCl 3 Me 3 Ga, in n-heptane have been recorded. The resonance signals for both Me 3 Ga and GaCl 3 are unchanged on dilution over the temperature range 20–100°C. Mixtures of GaCl 3 and Me 3 Ga show only one resonance signal, whose chemical shift is determined predominantly by the nature of the coordination at gallium, indicating rapid chemical exchange of the species involved. The results of studies of methanolysis and hydrolysis, and of adduct formation, are also discussed. The 71 Ga resonances of several possible external standards in the temperature range 20–100°C are also reported. The 71 Ga NMR signal of a solution of GaCl 4 − in 6 M aqueous hydrochloric acid, for which δ( 71 Ga) = 250 ± 0.5 ppm downfield from the signal of a 1 M solution of [Ga(H 2 O) 6 ] 3+ [ClO 4 ] 3 − in 1 M HClO 4 , is recommended as a temperature-independent external standard for gallium NMR studies.

71Ga NMR spectroscopy of solutions of gallium tribromide in aromatic solvents

Abstract The 71 Ga NMR spectra of solutions of gallium tribromide in different aromatic solvents have been recorded, and dependences of chemical shift on concentration, temperature and solvent observed. Such effects are absent in the corresponding solutions of Me 3 Ga. The 71 Ga chemical shift changes are consistent with the dissociation of the dimeric form of gallium tribromide to the monomer, as observed in the gas phase, but a study of effect of added H 2 O or Et 2 O indicates that solutions of gallium tribromide contain no monomeric species and the changes are best accounted for in terms of rapid chemical exchange between two different dimeric forms of gallium tribromide, one closed and the other half-open. With increasing solvating power of the aromatic solvent, the equilibrium between these dimeric structures favours the half-open solvated species.

Sexual reproduction of Daphnia in a deep temperate reservoir: the phenology and genetics of male formation

Long-term persistence of a Daphnia population is allowed by the production of dormant stages, produced mostly through sexual reproduction. We investigated the spatio-temporal dynamics of male production in a spring population of Daphnia galeata in the reservoir, and compared the genetic structure of three groups within this population: male-, female-producing females, and adult males. With a fine resolution sampling design and the use of highly variable microsatellite markers we revealed that: (1) the spring period of male offspring production was delimited in time with minimum interannual variation to about 3 weeks, and in space to the upper 5-m water layer; (2) there were no remarkable changes in the clonal composition of male-producing females within the period of male production; (3) overall certain clones exhibited a higher tendency to produce male offspring and therefore the clonal structure of male-producing lineages was significantly different from that of female-producing lineages; and (4) the clonal structure of male-producing females was not significantly different from that of adult males occurring later in the reservoir. This suggests that males were not subjected to any significant selective forces till maturity and the male-producing females confer a long-term fitness advantage over female-producing females.

Intraspecific spatial genetic differentiation of a Daphnia species within a long narrow reservoir

Environmental gradients influence the distribution and taxonomic composition of planktonic taxa, including Daphnia. In canyon-shaped reservoirs with pronounced horizontal gradients of food supply, predation pressure and other factors, not only species and interspecific hybrids but also clones within these taxa are non-randomly distributed. Using a long-term data set from a reservoir mostly dominated by a single Daphnia species, we evaluated whether intraspecific genetic differentiation can be frequently detected between upstream and downstream reservoir regions with different environmental conditions. We analysed variation at four allozyme loci (two species-specific and two polymorphic) to assess the taxonomic composition and intraspecific variation of Daphnia collected in different years (between 1995 and 2005) and periods of the growing season. D. galeata dominated in all samples, although other species and hybrids with D. galeata were also occasionally detected. Despite limited variation at the analysed loci, D. galeata from upstream and downstream regions were significantly genetically differentiated on seven out of twelve sampling dates. Although genetic drift in geographically distant subpopulations may contribute to differentiation, we presume that the observed patterns are primarily due to different selection regimes. We predict that a significant genetic differentiation within planktonic populations also occurs more frequently in natural water bodies.