The evolution of communication behavior, like that of all traits, is shaped both by external forces of natural and sexual selection and by internal forces of development and physiology. Complexity in both the function and production mechanisms of communication signals makes them a powerful model for understanding evolutionary interactions within and across levels of biological organization (Ryan, 2005).Electrocommunication in weakly electric fish is an outstanding model for integrating mechanistic and historical biology (sensu Autumn et al., 2002) because these behaviors are diverse across species, are easily recorded and analyzed, and are controlled by a well-characterized neural circuit. The family Apteronotidae is particularly well-suited for a comparative approach because it has the highest species diversity among Neotropical electric fish (Crampton and Albert, 2006). Apteronotids continuously emit a quasi-sinusoidal voltage signal or electric organ discharge (EOD) that has two functions. Nearby objects locally distort the electric field generated by the EOD, and by detecting these distortions with their electroreceptors, fish can electrolocate. The fish can also use their EODs to communicate by detecting the interactions of their own EOD with those of other fish. Individual apteronotid fish maintain an extremely stable EOD frequency (EODf) (Bullock, 1970;Moortgat et al., 1998) and waveform (Rasnow and Bower, 1996). In addition to using the baseline EOD frequency and waveform as communication signals, fish also modulate the frequency and amplitude of the EOD during social interactions Electrocommunication signals in electric fish are diverse, easily recorded and have well-characterized neural control. Two signal features, the frequency and waveform of the electric organ discharge (EOD), vary widely across species. Modulations of the EOD (i.e. chirps and gradual frequency rises) also function as active communication signals during social interactions, but they have been studied in relatively few species. We compared the electrocommunication signals of 13 species in the largest gymnotiform family, Apteronotidae. Playback stimuli were used to elicit chirps and rises. We analyzed EOD frequency and waveform and the production and structure of chirps and rises. Species diversity in these signals was characterized with discriminant function analyses, and correlations between signal parameters were tested with phylogenetic comparative methods. Signals varied markedly across species and even between congeners and populations of the same species. Chirps and EODs were particularly evolutionarily labile, whereas rises differed little across species. Although all chirp parameters contributed to species differences in these signals, chirp amplitude modulation, frequency modulation (FM) and duration were particularly diverse. Within this diversity, however, interspecific correlations between chirp parameters suggest that mechanistic trade-offs may shape some aspects of signal evolution. In particular, a consistent trade-of...

Chromobacterium violaceum is one of millions of species of free-living microorganisms that populate the soil and water in the extant areas of tropical biodiversity around the world. Its complete genome sequence reveals (i) extensive alternative pathways for energy generation, (ii) Ϸ500 ORFs for transport-related proteins, (iii) complex and extensive systems for stress adaptation and motility, and (iv) widespread utilization of quorum sensing for control of inducible systems, all of which underpin the versatility and adaptability of the organism. The genome also contains extensive but incomplete arrays of ORFs coding for proteins associated with mammalian pathogenicity, possibly involved in the occasional but often fatal cases of human C. violaceum infection. There is, in addition, a series of previously unknown but important enzymes and secondary metabolites including paraquat-inducible proteins, drug and heavy-metal-resistance proteins, multiple chitinases, and proteins for the detoxification of xenobiotics that may have biotechnological applications.T he genomes of soil-and water-borne free-living bacteria have received relatively little attention thus far in comparison to pathogenic and extremophilic organisms, yet they provide fundamental insights into environmental adaptation strategies and represent a rich source of genes with biotechnological potential and medical utility. A particularly interesting organism of this kind is Chromobacterium violaceum, a Gram-negative ␤-proteobacterium first described at the end of the 19th century (1), which dominates a variety of ecosystems in tropical and subtropical regions. This bacterium has been found to be highly abundant in the water and borders of the Negro river, a major component of the Brazilian Amazon (2) and as a result has been studied in Brazil over the last three decades. These, in general, have focused on the most notable product of the bacterium, the violacein pigment, which has already been introduced as a therapeutic compound for dermatological purposes (3). Violacein also exhibits antimicrobial activity against the important tropical pathogens Mycobacterium tuberculosis (4), Trypanosoma cruzi (5), and Leishmania sp. (6) and is reported to have other bactericidal (2, 7-10), antiviral (11), and anticancer (12, 13) activities.Some other aspects of the biotechnological potential of C. violaceum have also begun to be explored, including the synthesis of poly(3-hydroxyvaleric acid) homopolyester and other shortchain polyhydroxyalkanoates, which might represent alternatives to plastics derived from petrochemicals (14, 15), the hydrolysis of plastic films (16), and the solubilization of gold through a mercury-free process, thereby avoiding environmental contamination (17, 18). These studies, however, have been based on knowledge of only a tiny fraction of the genetic constitution of the organism. In addition, the more basic issues of the mechanisms and strategies underlying the adaptability of C. violaceum, including its observed but infrequent infection of h...

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

We used mitochondrial DNA control region sequences to examine phylogeography and population differentiation of the endangered Amazonian manatee Trichechus inunguis. We observe lack of molecular differentiation among localities and we find weak association between geographical and genetic distances. However, nested clade analysis supports restricted gene flow and/or dispersal with some long-distance dispersal. Although this species has a history of extensive hunting, genetic diversity and effective population sizes are relatively high when compared to the West Indian manatee Trichechus manatus. Patterns of mtDNA haplotype diversity in T. inunguis suggest a genetic disequilibrium most likely explained by demographic expansion resulting from secession of hunting and enforcement of conservation and protective measures. Phylogenetic analysis of T. manatus and T. inunguis haplotypes suggests that T. inunguis is nested within T. manatus, effectively making T. manatus a paraphyletic entity. Paraphyly of T. manatus and recent divergence times of T. inunguis and the three main T. manatus lineages suggest a possible need for a taxonomic re-evaluation of the western Atlantic Trichechus.

According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary-type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non-electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre-existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation. 2001 The Fisheries Society of the British Isles

In this report we generate a partial phylogeny of the mormyriform fishes using mitochondrial DNA sequences from twelve species of mormyriforms belonging to five genera. Electric organs and electric organ discharges are also examined. We have sequenced and aligned 373 bases from the mitochondrial 12S rRNA and 559 bases from the 16s rRNA from fourteen species of the superorder Osteoglossomorpha. Two non-mormyriform genera were used as outgroups. Three phylogenetic methods generated concordant partial phylogenies for these fish. Our analysis focuses on the genus Brienomyrus, which is a heterogeneous clade with at least eleven nominal species. Six morphs from Gabon had distinctive EODs but were morphologically 'cryptic' in that they all had the brachyistius-like body morphology. DNA analysis fully supports the EOD data that the six morphs represent distinct clades. The group from Gabon is monophyletic, while B.brachyistius from West Africa is a separate lineage. B. niger, a second distinct lineage, is a sister group to the six species from Gabon. Petrocephalus is the sister group of all the genera of the subfamily Mormyrinae so far analyzed, thereby confirming previous osteological results. Gymnarchus niloticus is the sister group of the family Mormyridae, also confirming an earlier phylogenetic hypothesis based on morphology. The molecular data adds polarity to electric organ characteristics. Stalkless electrocytes appear to be primitive. Petrocephalus, with non-penetrating stalked electrocytes innervated on the posterior side, represents an ancestral state for the Mormyridae, while Marcusenius, Brienomyrus and Gnathonemus with penetrating-stalked electrocytes, represent the apomorphic condition. Two species with doubly-penetrating electrocytes innervated on the posterior side may represent a transitional stage. At least two species of Brienomyrus appear to have reverted to non-penetrating stalked electrocytes, possibly through paedomorphosis.

The electric communication signals of weakly electric ghost knifefishes (Gymnotiformes: Apteronotidae) provide a valuable model system for understanding the evolution and physiology of behavior. Apteronotids produce continuous wave-type electric organ discharges (EODs) that are used for electrolocation and communication. The frequency and waveform of EODs, as well as the structure of transient EOD modulations (chirps), vary substantially across species. Understanding how these signals have evolved, however, has been hampered by the lack of a well-supported phylogeny for this family. We constructed a molecular phylogeny for the Apteronotidae by using sequence data from three genes (cytochrome c oxidase subunit 1, recombination activating gene 2, and cytochrome oxidase B) in 32 species representing 13 apteronotid genera. This phylogeny and an extensive database of apteronotid signals allowed us to examine signal evolution by using ancestral state reconstruction (ASR) and phylogenetic generalized least squares (PGLS) models. Our molecular phylogeny largely agrees with another recent sequence-based phylogeny and identified five robust apteronotid clades: (i) Sternarchorhamphus + Orthosternarchus, (ii) Adontosternarchus, (iii) Apteronotus + Parapteronotus, (iv) Sternarchorhynchus, and (v) a large clade including Porotergus, ‘Apteronotus’, Compsaraia, Sternarchogiton, Sternarchella, and Magosternarchus. We analyzed novel chirp recordings from two apteronotid species (Orthosternarchus tamandua and Sternarchorhynchus mormyrus), and combined data from these species with that from previously recorded species in our phylogenetic analyses. Some signal parameters in O. tamandua were plesiomorphic (e.g., low frequency EODs and chirps with little frequency modulation that nevertheless interrupt the EOD), suggesting that ultra-high frequency EODs and ‘‘big” chirps evolved after apteronotids diverged from other gymnotiforms. In contrast to previous studies, our PGLS analyses using the new phylogeny indicated the presence of phylogenetic signals in the relationships between some EOD and chirp parameters. The ASR demonstrated that most EOD and chirp parameters are evolutionarily labile and have often diversified even among closely related species.

RESUMOOs efeitos de substâncias genotóxicas sobre o genoma de peixes tem sido objeto de muitos estudos, sobretudo daqueles que buscam estabelecer a resposta dos genes aos estímulos ambientais. O presente trabalho teve como objetivo realizar um estudo sobre mutagenicidade e genotoxicidade em peixes elétricos da espécie Eingenmannia virescens, pela exposição ao benzeno (50ppm), utilizando as técnicas da Freqüência de Micronúcleos (MNs) e o Ensaio do Cometa. Foram coletadas amostras do sangue de dez peixes em diferentes tempos de exposição: T 0 , 24h, 48h, 72h, 96h e 360h (15 dias). Para a análise das lâminas no Teste do MN, foram contadas 1.000 células e estipulada a freqüência de ocorrência de MNs. Para análise do Ensaio do Cometa a contagem foi feita estipulando quatro classes de danos: I -II -III -IV, e para a análise estatística foram atribuídos valores numéricos (ranques) de 0 a 3, respectivamente, verificando diferenças significativas para a soma dos ranques em todos os tempos de exposição em relação ao T 0 . No Teste do Micronúcleo não foi possível detectar efeitos mutagênicos significativos nos eritrócitos analisados. No entanto, para o Ensaio do Cometa os resultados sugerem ação genotóxica do benzeno, devido a um aumento gradual no número de células com maiores classes de danos de acordo com maior tempo de exposição, indicando um efeito tempo-dependente. Estes resultados sugerem maior sensibilidade do Ensaio do Cometa que o Teste do MN. PALAVRAS-CHAVETeste do Micronúcleo; Ensaio do Cometa; peixes elétricos; eritrócitos Eingenmannia virescens, under to benzene exposure (50ppm), utilizing Micronuclei Test (MNs) and Comet Assay techniques. Ten fish blood samples were collected in different times of exposure : T 0 , 24h, 48h, 72h, 96h and 360h (15 days Avaliation of mutagenicity and gentotoxicity in Eigenmannia virescens (Teleostei: Gymnotiformes) exposed to benzene ABSTRACT The effects of genotoxic substances on fishes genome have been object of many studies, especially those which attempt to establish the responses of genes to environmental stimulus. The objective of this study was to evaluate the mutagenicity and genotoxicity in electric fishes of species