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21.
F. MONTEALEGRE‐Z 《Journal of evolutionary biology》2009,22(2):355-366
Male katydids (Orthoptera: Tettigoniidae) produce mating calls by rubbing the wings together, using specialized structures in their forewings (stridulatory file, scraper and mirror). A large proportion of species (ca. 66%) reported in the literature produces ultrasonic signals as principal output. Relationships among body size, generator structures and the acoustic parameters carrier frequency (fc) and pulse duration (pd), were studied in 58 tropical species that use pure‐tone signals. A comparative analysis, based on the only available katydid phylogeny, shows how changes in sound generator form are related to changes in fc and pd. Anatomical changes of the sound generator that might have been selected via fc and pd are mirror size, file length and number of file teeth. Selection for structures of the stridulatory apparatus that enhance wing mechanics via file‐teeth and scraper morphology was crucial in the evolution of ultrasonic signals in the family Tettigoniidae. 相似文献
22.
23.
We present a single-step procedure for the specific mass labeling of unblocked protein N termini. We show that the dye fluorescamine, which is commonly assumed to require mildly alkaline conditions for undergoing a nonspecific reaction with α- and ε-amino groups associated with amino acids, in fact shows a specific reaction only with α-amino groups present at protein N termini when mildly acidic conditions are used. We use this finding to label, identify, and sequence the trypsinolysis-derived N-terminal peptide of lysozyme, using only mass spectrometry, to illustrate how this method could be used with other proteins. 相似文献
24.
The ‘benefits of philopatry’ hypothesis states that helpers in cooperatively breeding species derive higher benefits from
remaining home, instead of dispersing and attempting to breed independently. We tested experimentally whether dispersal options
influence dispersal propensity in the cooperatively breeding Lake Tanganyika cichlids Neolamprologus pulcher and N. savoryi. Cooperative groups of these fishes breed in densely packed colonies, surrounded by unoccupied, but apparently suitable breeding
habitat. Breeding inside colonies and living in groups seems to benefit individuals, for example by early detection and deterrence
of predators. We show that despite a slight preference of both species for habitat with a higher stone cover, 40% of the preferred
habitat remained unoccupied. On average, the colonies contained a higher number of (1) predators of adults, juveniles and
eggs, (2) shelter competitors, and (3) other species including potential food competitors, compared to the outside colony
habitat. Apparently, habitat differences cannot explain why these cichlids breed in colonies. Accordingly, dispersal may not
be limited by a lack of suitable breeding shelters, but by the relatively higher risk of establishing an outside- compared
to a within-colony breeding territory. To test whether cichlids prefer within- to outside-colony breeding territories, we
provided breeding shelters inside the colony and at the colony edge and studied helper dispersal. As expected, significantly
more shelters were occupied within the colony compared to the edge. New breeding pairs with several helpers occupied these
shelters. We conclude that although breeding habitat is plentiful outside the colonies, helpers delay dispersal to obtain
a higher quality breeding position within the group or colony eventually, or they disperse in groups. Our results suggest
that (1) group augmentation and Allee effects are generally important for dispersal decisions in cooperatively breeding cichlids,
consistent with the ‘benefits of philopatry hypothesis’, and (2) habitat saturation cannot fully explain delayed dispersal
in these species. 相似文献
25.
Archaeal genes for ammonia oxidation are widespread in the marine environment, but direct physiological evidence for ammonia oxidation by marine archaea is limited. We report the enrichment and characterization of three strains of pelagic ammonia-oxidizing archaea (AOA) from the North Pacific Ocean that have been maintained in laboratory culture for over 3 years. Phylogenetic analyses indicate the three strains belong to a previously identified clade of water column-associated AOA and possess 16S ribosomal RNA genes and ammonia monooxygenase subunit a (amoA) genes highly similar (98–99% identity) to those recovered in DNA and complementary DNA clone libraries from the open ocean. The strains grow in natural seawater-based liquid medium while stoichiometrically converting ammonia (NH3) to nitrite (NO2−). Ammonia oxidation by the enrichments is only partially inhibited by allylthiourea at concentrations known to completely inhibit cultivated ammonia-oxidizing bacteria. The three strains were used to determine the nitrogen stable isotope effect (15ɛNH3) during archaeal ammonia oxidation, an important parameter for interpreting stable isotope ratios in the environment. Archaeal 15ɛNH3 ranged from 13‰ to 41‰, within the range of that previously reported for ammonia-oxidizing bacteria. Despite low amino acid identity between the archaeal and bacterial Amo proteins, their functional diversity as captured by 15ɛNH3 is similar. 相似文献
26.
BRUCE S. PERLMAN 《The Journal of eukaryotic microbiology》1973,20(1):106-107
Cells of Tetrahymena pyriformis syngen 1 grown at 30 C after conjugation achieve sexual maturity more quickly than do cells grown at 19 C, whether time is measured in numbers of cell divisions or in terms of absolute time. This result is achieved regardless of the temperature at which conjugation and nuclear reorganization occur. These observations differ from those of other workers investigating Paramecium, and suggest that the long term “chronometer” is more tightly coupled to cell division in Paramecium multimicronucleatum and Paramecium caudatum than in Tetrahymena pyriformis. 相似文献
27.
Kuntz and Kauzmann have argued that dehydrating a protein results in conformational changes. In contrast, Rupleyet al. have developed a hydration model which involves no significant change in conformation; the onset of enzyme activity in hen
egg-white lysozyme at hydration values of about 0.2 g water/g protein they ascribe rather to a solvation effect. Using a direct
difference infra-red technique we can follow specific hydration events as water is added to a dry protein. Conformational
studies of lysozyme using laser Raman spectroscopy indicate changes in conformation with hydration that are complete just
before measurable activity is found. Parallel nuclear magnetic resonance measurements of exchangeability of the main chain
amide hydrogens, as a function of hydration from near dryness, suggest a hydration-related increase in conformational flexibility
which occurs before-and is probably necessary for-the Raman-detected conformational changes. Very recent inelastic neutron
scattering measurements provides direct evidence of a flexibility change induced by hydration, which is apparently necessary
before the enzyme can achieve adequate flexibility for it to begin to function. 相似文献
28.
Hellmuth Broda Doug Brugge Keiichi Homma J. Woodland Hastings 《Cell biochemistry and biophysics》1986,8(1):47-67
Populations ofGonyaulax polyedra, in two different phases, about 11 h apart, were mixed, and the intensity of their spontaneous bioluminescence glow recorded
for about 2 wk under conditions of constant dim (35±3 μE/m2/s) white light and constant temperature (19.0±0.3°C). The phases and amplitudes of glow signals recorded from mixed cultures
were compared with those obtained from the arithmetic sum of the intensity data from two control vials. Peaks in control cultures
generally remained separate, but there was a spontaneous increase in the period beginning 6–11 d after the onset of constant
conditions. This did not occur in cultures in which the medium was exchanged with fresh medium every 2 d. In the actual mixes
of two cultures there was a merging of the two subpeaks in the signal, which did not occur when the medium was exchanged.
The results indicate that conditioning of the medium by cells may affect the period of the circadian rhythm and that this
might result in a type of communication.
Supported by the Deutsche Forschungsgemeinschaft; present address 相似文献
29.
30.
Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm−1 ). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required. 相似文献