Summary. Pollimyrus isidori's electric organ discharge (EOD) is of the pulse type. Patterns of EOD intervals were investigated prior to, during and following spawning behaviors as related with overt behaviors, and with the sound production by the nestbuilding male. Prior to the time of reproduction, isolated and socially interacting fish (n = 15) showed characteristic discharge interval patterns for resting, swimming, probing, hovering and hiding activities. Males (n = 8) and females (n = 6) did not differ in their mean EOD repetition rates during resting (11.6+2.5 Hz), nor Short Bursts/rain (less than 20 intervals of 8-13 ms). In interacting fish Long Bursts (greater than 20 intervals of 8-13 ms, lasting for more than 300 ms) were observed only during the attack and bite sequence.

Water is known to play a significant role in the formation of protein-ligand complexes. In this paper, we focus on the influence of water molecules on the structure of protein-ligand complexes. We present an algorithmic approach,

Allopatric differentiation in the AbstractWe critically compared local populations of the bulldog fish, Marcusenius macrolepidotus (Peters 1852), from different watersheds, from the furthest south (28u South, South Africa) to the Equator in Kenya. We ascertained allopatric differentiation from topotypical M. macrolepidotus from the Lower Zambezi River (Mozambique) in morphology, electric organ discharges, and molecular genetics for: (1) samples from the Okavango and Upper Zambezi Systems (Botswana and Namibia), (2) samples from South Africa's rivers draining into the Indian Ocean, and (3) samples from the East African Tana River (Kenya). Significant genetic distances in the mitochondrial cytochrome b gene and differing ISSR-PCR profiles corroborate differentiation between the four taxa. We resurrect M. pongolensis (Fowler, 1934) for South Africa (sample 2), and M. angolensis (Boulenger, 1905) for the Quanza River/Angola. We recognize M. altisambesi sp. n. for the Upper Zambezi/Okavango specimens (sample 1), and M. devosi sp. n. for those from Kenya (sample 3).

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CD spectra of bovine pancreatic ribonuclease A (RNase A) and its subtilisin-modified from (RNase S) have been calculated, based upon high-resolution structures from x-ray diffraction. All known transitions in the peptide and side-chain groups, especially the aromatic and disulfide groups, have been included. Calculations have been performed with both the matrix method and with first-order perturbation theory. A newly developed method for treating the electrostatic interactions among transition charge densities and between static charge distributions and transition charge densities is used. The effects of local electrostatic fields upon the group transition energies are included for all transitions. Rotational strengths generated by the matrix method were combined with Gaussian band shapes to generate theoretical CD spectra. The calculated spectra reproduce the signs and approximate magnitudes of the near-uv CD bands of both RNase A and S. Agreement is most satisfactory for the negative 275 nm band, dominated by tyrosine contributions. In agreement with two previous studies by other workers, coupling between Tyr 73 and Tyr 115 is the single most important factor in this band. The positive band observed near 240 nm is dominated by disulfide contributions, according to our results. The far-uv CD spectrum is poorly reproduced by the calculations. The observed 208 nm band, characteristic of alpha-helices, is absent from the calculated spectrum, probably because the helices in RNase are short. A strong positive couplet centered near 190 nm is predicted but not observed. Possible reasons for these incorrect predictions of the current theoretical model in the far-uv are discussed.

1 Kramer, B., Van der Bank, & H., Wink, M. (2004) Hippopotamyrus ansorgii species complex in the Upper Zambezi River System with a description of a new species, H. szaboi (Mormyridae).-Zoologica Scripta, 33 , 1 -18. Specimens referable to Hippopotamyrus ansorgii sampled from the Upper Zambezi River System within Caprivi (Namibia) represent a complex of three species, two of which coexist in the Upper Zambezi River, and a third that inhabits a nearby river, the Kwando, with which the Zambezi has been connected during periods of flooding. All three are indistinguishable in terms of their general appearance, but differ consistently in electric organ discharges (EOD), morphology, and molecular genetic characters. All phenotypes display a monopolar, headpositive EOD pulse with specific post-or prepotentials. For H. ansorgii from the Zambezi River (HaZ), pulse duration is less than 0.5 ms (down to 0.205 ms; N = 34); for the syntopic H. szaboi sp. n., it is greater than 0.6 ms (up to 1.8 ms at 10% peak amplitude; N = 19). The parapatric phenotype of H. ansorgii from the Kwando River (HaK) has pulses shorter than 0.215 ms (down to 0.105 ms; N = 36). All three members of the species complex may be distinguished from each other by 7 − 9 anatomical characters, analysed by MANOVA . Based on 22 enzymes and proteins studied, the moderate to high Wright's fixation index and the significant ( P < 0.05) allele differentiation between EOD phenotypes provide additional evidence for incipient speciation. Pairwise analyses of the three different phenotypes showed the two parapatric species of H. ansorgii grouped together, and distinguishable from individuals of H. szaboi . Analyses of the mitochondrial cytochrome b gene revealed that all specimens which were attributed to H. szaboi form a well-supported monophyletic basal clade (bootstrap support 73% or 82%). The genetic distances (uncorrected p distances) between H. szaboi and the two species of H. ansorgii are between 0.6% and 1.7%. Within the derived H. ansorgii clade some phylogeographical differentiation can be seen for fishes from the Zambezi and Kwando Rivers, but the respective groups are not consistent or supported by significant bootstrap values. The question of which of the two parapatric morphological and EOD phenotypes of H. ansorgii recognized in the present paper represents H. ansorgii (Boulenger, 1905) cannot be resolved at present because of the paucity and unclear origin of the historical type material.

Previous work has revealed that Hippopotamyrus ansorgii (Boulenger, 1905) is a species complex, with specimens from the Upper Zambezi system (Caprivi Strip in Namibia) that are well differentiated from the Angolan type specimens. Here, we sampled the Cunene River, one of several possible type rivers for H. ansorgii, on the border between Namibia and Angola. The specimens are morphologically differentiated from the six other known morphs within the H. ansorgii species complex, including the types and H. szaboi. The electric organ discharge of the Cunene specimens has a different pulse waveform and associated amplitude spectra to that of the three Upper Zambezi system morphs of the species complex. The Cunene specimens are genetically distinct, but relatively closely related to other taxa of the H. ansorgii complex, such as the Upper Zambezi system morphs. We recognize the Lower Cunene morph as the new species, Hippopotamyrus longilateralis sp. nov.

Summary. 1. Agonistic motor behaviour and concurrent electric signalling were studied in individually held, residential Gnathonemus petersii. Aggressive behaviour was elicited by presenting a specimen of a closely related species, Mormyrus rume, for 3 min a day.2. The principal agonistic motor patterns are described (Fig. 2). Among them head butt, approach and lateral display were further analysed.3. The electrical activity displayed during agonistic behaviour was found to differ fundamentally both from isolated resting and swimming conditions. The mean discharge rate recorded during aggressive behaviour (31 Hz, Fig. 3 c) is approximately twice the rate observed in an isolated swimming fish (Fig. 3b) and three times the rate displayed by a resting animal (Fig. 3a). An attacking G. petersii exhibits a much greater range of electric organ discharge (EOD) intervals than isolated swimming or resting individuals. EOD-intervat histograms recorded from attacking fish show two sharp modes at high discharge rate; there are no intermediate intervals.4. During the course of an attack, the initially low and variable discharge rate increases fairly linearly as the distance from the attacked fish diminishes (Fig. 9). The EOD rate associated with physical contact (head butt) comprises between 60 and 80 Hz in 24 of 28 attacks analysed; the dominant mode of the distribution is 61 Hz (Fig. 8).5. During subsequent lateral display, G. petersii emits a high discharge rate pattern consisting of two types of "steady-state" activities which may last up to a few seconds: the first is a fairly regular alternation of approx. 16 and 8 ms intervals (paired pulses); this pattern gives rise to the two peaks of high discharge rate in the interval histogram (Fig. 3 c). The second is a regular sequence of either 16 or 8 ms intervals (Fig. 4A). The only female among the animals used in our study showed the same display but did not exhibit the highest possible discharge rate (i.e. a regular sequence