Luiz Roberto Malabarba

Reproductive Biology of the Inseminating Glandulocaudine Diapoma speculiferum Cope (Teleostei: Characidae)

Abstract The reproductive period of the inseminating glandulocaudine Diapoma speculiferum was determined through the analysis of 133 males and 158 females obtained from monthly collections in Rio Grande do Sul, Brazil. The reproductive period is highly seasonal, occurring from September to February, which corresponds to the Austral spring and summer. Both male and female gonadosomatic indices were highly correlated with changes in water temperature and day length and, to a lesser extent, food availability. No correlation with rainfall was found. Absolute fecundity (mean 491.1 ± 159.5 oocytes per female) was similar to those found in two externally fertilizing cheirodontine characids but lower than that found in the inseminating glandulocaudine Pseudocorynopoma doriae. Relative fecundities (oocyte number per milligram total body weight) of the inseminating D. speculiferum and P. doriae were found to be lower than that of two externally fertilizing cheirodontines, suggesting that inseminating species may expend a smaller amount of energy in egg production, perhaps as a result of a higher efficiency in fertilization. Gonad histology showed the presence of spermatozoa in ovaries of maturing females, indicating that courtship and insemination take place before the ovaries are mature. Fertilized eggs were not found in the ovaries, suggesting that fertilization may be a very rapid event once oocytes are ovulated. O período reprodutivo do glandulocaudíneo com inseminação, Diapoma speculiferum, foi determinado pela análise de 133 machos e 158 fêmeas obtidos em coletas mensais no Rio Grande do Sul, Brasil. Seu ciclo reprodutivo é sazonal ocorrendo de setembro a fevereiro, correspondendo á primavera e verão na região Austral. Para machos e fêmeas o índice gonadossomático foi altamente correlacionado com as mudanças na temperatura da água e fotoperíodo e, em menor extensão, com a disponibilidade de alimento. Quanto ao índice pluviométrico, não foi verificada nenhuma correlação. A média da fecundidade absoluta (491,1 ± 159,5 ovócitos por fêmea) foi semelhante a observada em dois queirodontíneos de fecundação externa, e menor do que o glandulocaudíneo com inseminação Pseudocorynopoma doriae. A fecundidade relativa (número de ovócitos por miligrama de peso total) dos glandulocaudíneos com inseminação D. speculiferum e P. doriae foi menor do que nos queirodontíneos com fertilização externa, sugerindo que espécies com inseminação tem um menor gasto energético na produção dos ovócitos, talvez como resultado de uma maior eficiência na fertilização. A histologia das gônadas demonstrou a presença de espermatozóides em ovários de fêmeas em maturação, indicando que a corte e inseminação iniciam antes dos ovários estarem maduros. Não foram encontrados ovos fertilizados nos ovários, sugerindo que a fertilização ocorra durante a ovulação.

Revision of the neotropical cichlid genus Gymnogeophagus Ribeiro, 1918, with descriptions of two new species (Pisces, Perciformes)

The Neotropical cichlid genus Gymnogeophagus Ribeiro, 1918 is revised. The following species are considered valid and are redescribed: G. rhabdotus (Hensel, 1870), G. gymnogenys (Hensel, 1870), G. labiatus (Hensel, 1870), G. balzanii (Perugia, 1891) and G. australis (Eigenmann, 1907). In addition, two new species are described: G. lacustris, sp. n., from the coastal region of southern Brazil and G. meridionalis, sp. n., from the lower Rio Parana and Rio Uruguay systems. Lectotypes are designated for Geophagus bucephalus Hensel, 1870 (= G. labiatus) and Geophagus scymnophilus Hensel, 1870 (= G. labiatus) and the phylogenetic relationships among the species are analyzed. An osteological description based mainly on G. meridionalis is presented. A map of species distribution and a key to the species are provided.

Molecular phylogeny of the subfamily Stevardiinae Gill, 1858 (Characiformes: Characidae): classification and the evolution of reproductive traits

BackgroundThe subfamily Stevardiinae is a diverse and widely distributed clade of freshwater fishes from South and Central America, commonly known as “tetras” (Characidae). The group was named “clade A” when first proposed as a monophyletic unit of Characidae and later designated as a subfamily. Stevardiinae includes 48 genera and around 310 valid species with many species presenting inseminating reproductive strategy. No global hypothesis of relationships is available for this group and currently many genera are listed as incertae sedis or are suspected to be non-monophyletic.ResultsWe present a molecular phylogeny with the largest number of stevardiine species analyzed so far, including 355 samples representing 153 putative species distributed in 32 genera, to test the group’s monophyly and internal relationships. The phylogeny was inferred using DNA sequence data from seven gene fragments (mtDNA: 12S, 16S and COI; nuclear: RAG1, RAG2, MYH6 and PTR). The results support the Stevardiinae as a monophyletic group and a detailed hypothesis of the internal relationships for this subfamily.ConclusionsA revised classification based on the molecular phylogeny is proposed that includes seven tribes and also defines monophyletic genera, including a resurrected genus Eretmobrycon, and new definitions for Diapoma, Hemibrycon, Bryconamericus sensu stricto, and Knodus sensu stricto, placing some small genera as junior synonyms. Inseminating species are distributed in several clades suggesting that reproductive strategy is evolutionarily labile in this group of fishes.

Sperm and Spermatozeugma Ultrastructure in the Inseminating Catfish, Trachelyopterus lucenai (Ostariophysi: Siluriformes: Auchenipteridae)

Abstract This study presents details of the ultrastructure of the spermatozeugmata and spermatozoa of the South American catfish, Trachelyopterus lucenai, an inseminating species. Spermatozoa are tightly packaged into unencapsulated bundles, spermatozeugmata, with as many as 130 cells comprising a single packet. Within an individual spermatozeugma, cells are aligned side by side such that the anterior region of the bundle is comprised of nuclei, the middle region midpieces, and the posterior region flagella. Integrity of the packet appears to be maintained by specialized junctions between adjacent cells along their entire lengths. Each spermatozoon is characterized by an elongate nucleus containing condensed chromatin and a fossa at the posterior end. The elongate midpiece contains multiple mitochondria, abundant glycogen deposits, and accessory microtubules that run along the length of the midpiece. The ultrastructural modifications of the spermatozoa are discussed as possible adaptations associated with the reproductive mode of insemination.

Gymnogeophagus eocenicus, n. sp. (Perciformes: Cichlidae), an Eocene Cichlid from the Lumbrera Formation in Argentina

ABSTRACT A new cichlid referable to the extant genus Gymnogeophagus is described from the Eocene Lumbrera Formation of the Salta Group, northwestern Argentina. †Gymnogeophagus eocenicus, n. sp., presents the synapomorphies that support the genus: absence of supraneurals and a presence of a forward spine in the first dorsal pterygiophore. The existence of an early to middle Eocene—aged species presenting the synapomorphies and the appearance of a modern genus requires the acceptance of an extensive differentiation from the basal cichlid lineages. Extant Gymnogeophagus species are restricted to the La Plata drainage and a few coastal drainages of southern Brazil and Uruguay. The occurrence of an Eocene fossil in the geographical area corresponding to the present distribution of the genus suggests the patterns of distribution and endemism of the Neotropical fish fauna have a very old history in the continent.

Spermiogenesis and spermatozoa ultrastructure in five species of the Curimatidae with some considerations on spermatozoal ultrastructure in the Characiformes

Spermiogenesis in the curimatid species, Steindachnerina insculpta, Cyphocharax gillii, C. modestus, C. spilotus, and Potamorhina altamazonica, is characterized by lateral development of the flagellum, nuclear rotation, eccentric nuclear fossa formation, and chromatin compacted into thick fibers. These spermatozoa exhibit a spherical head containing a nucleus with the chromatin highly condensed into thick fibers with small electron-lucent areas, and no acrosome. The nuclear fossa is of the moderate type and eccentric and penetrated by the centriolar complex. The midpiece is small, has many elongate vesicles, and a short cytoplasmic channel. Mitochondria may be elongate, branched or C-shaped, and are separated from the initial segment of the axoneme by the cytoplasmic channel. The flagellum contains the classical axoneme structure (9+2) and has a membranous compartment in the initial region; it does not have lateral fins. Only small differences were observed among the analyzed species and genera of the Curimatidae. Spermiogenesis and spermatozoa in the Curimatidae have many of the characteristics found in almost all other characiform species. On the other hand, the presence of a membranous compartment in the initial region of curimatid flagella, a structure common in many Cypriniformes spermatozoa, is unknown in other characiforms. Spermiogenesis and the spermatozoa of the Characiformes are discussed.

A new species of Hyphessobrycon (Teleostei: Characidae) from the upper rio Tocantins drainage, with bony hooks on fins

A new species of characid, Hyphessobrycon hamatus, is described from the upper rio Tocantins, Goias, Brazil. The new species is distinguished from all other Hyphessobrycon species by the presence of bony hooks on dorsal, anal, pelvic, and pectoral fins of males, the two black humeral spots, the 4 or 5 teeth in the inner series of the premaxilla, a maxilla with 2-3 teeth, the iii-v, 16-18 anal-fin rays, and a lateral line with 10-32 perforated scales and 33-35 scales in a longitudinal series.

Phylogenetic relationships of Paleotetra, a new characiform fish (Ostariophysi) with two new species from the Eocene-Oligocene of south-eastern Brazil

Paleotetra, a new characiform genus with two new species (P. entrecorregos and P. aiuruoca) from Palaeogene deposits of south-eastern Brazil is described. The fossil material is made up of two articulated specimens preserved as impressions in lateral view and including some bones and teeth. The new genus is hypothesized to be deeply inserted within the Characidae based on the apomorphic lack of a supraorbital bone, the low number of vertebrae (35), and the presence of four teeth in the inner series of the premaxilla; however, the new species cannot be assigned to any modern genus. Relationships of the two new species are further tested in a phylogenetic analysis along with 160 other characiform species using 360 morphological characters (150 coded for Paleotetra entrecorregos and 123 for P. aiuruoca), further supporting their recognition as characid characiforms. These results document the evolution of these characid lineages as early as the Eocene-Oligocene.

Reproductive period, fecundity and histology of gonads of two cheirodontines (Ostariophysi: Characidae) with different reproductive strategies - insemination and external fertilization

The reproductive period and fecundity of the inseminating cheirodontine Compsura heterura and of the externally fertilizing cheirodontine Odontostilbe pequira, from tropical and subtropical regions of Brazil, respectively, are described. The reproductive period of C. heterura lasted from January to April 2002, while O. pequira showed two reproductive periods, the first during September and October 2001 (spring), and the second between January and February 2002 (summer). Smaller classes of SL of females of O. pequira predominated in the second reproductive period, suggesting individuals born in the first period become shortly sexually mature, participating in the second reproductive period. In C. heterura, from a tropical region, temperature showed significant correlations with the variation in the gonadosomatic index (GSI) for both sexes, and rainfall showed significant correlation with the variation in the GSI only for females. In O. pequira, from a subtropical region, photoperiod was the only factor that showed significant correlations with the GSI variation in both sexes. The mean relative fecundity of C. heterura was 0.55 oocytes per milligram of total weight, similar to that of other cheirodontines with external fertilization, refuting the hypothesis, at least in Cheirodontinae, that insemination provides diminishing energy expenditure for the production of oocytes, due to a greater probability of fertilization. The mean relative fecundity of O. pequira was 0.8 oocytes per milligram of total weight, the largest known among cheirodontines. Spermatozoa were found inside the ovaries of maturating, mature and semi-spent females of C. heterura supporting the hypothesis of temporal separation between courtship and spawning. The largest relative weight of testis and the presence of sperm in maturing ovaries outside the reproductive period in C. heterura support the hypothesis that males of inseminating species make a greater investment in gonadal development than those externally fertilized.

Reproductive biology and development of gill glands in the inseminating characid, Macropsobrycon uruguayanae Eigenmann, 1915 (Cheirodontinae: Compsurini)

The reproductive biology and development of the gill gland are described for Macropsobrycon uruguayanae, an inseminating characid species of the tribe Compsurini, subfamily Cheirodontinae. Between April 2001 and March 2002, 117 males and 143 females of this species were collected in the rio Ibicui, Uruguay basin in the State of Rio Grande do Sul, Brazil. Reproductively active individuals were present during most months sampled, indicating lack of a well-defined seasonal reproductive period. Several maturing females were found to be inseminated before completing full maturation. Histological analyses demonstrated spermatozoa within the ovaries of females in different stages of gonadal maturation collected during most months. No immature females had inseminated ovaries. Standard length at first gonadal maturation was estimated to be 24 mm for both males and females. Mean absolute fecundity was 191.08 (± 48.83 SD) oocytes per female, one of the lowest among characids. Relative fecundity was 0.539 (± 0.069 SD) oocytes per mg weight of the female, a value similar to that found for the majority of species of Cheirodontinae. The presence of two cohorts of oocytes within ovaries of M. uruguayanae indicates synchronous development, with total spawning. The mean diameter of mature oocytes was 0.6711 (± 0.1252 SD) mm, smaller than that found for the majority of species of Characidae. Gill glands occurred in all mature males, as well as in males undergoing advanced maturation. In the latter case, fewer gill filaments comprised the glands. Gill glands were not observed in immature males, males undergoing the initial stages of maturation, or in any female. A given gill gland may comprise as many as 24 filaments of the lateral hemibranch of the first gill arch. Secondary lamellae within most of the gill gland are greatly reduced, with columnar cells being present between them. These columnar cells contain abundant vesicles, suggesting secretory activity. The morphology of the gill gland of M. uruguayanae resembles that found in the majority of characid species that possess this structure.