Population structure and reproductive biology of Loricariichthys melanocheilus Reis & Pereira, 2000 (Siluriformes: Loricariidae) in the rio Ibicuí, Brazil

The objective of this study was to analyze population structure (spatial distribution, seasonal distribution and distribution by length classes, sex ratio and length-weight relationship) and aspects of the reproductive biology of Loricariichthys melanocheilus. Fish were sampled bimonthly using gillnets and trammel nets in lentic and lotic environments in the rio Ibicuí, between the years 2000 and 2001. Were collected 410 specimens: 230 females, 164 males and 16 specimens whose sex could not be determined. A greater number of specimens were collected in October/November and December/January and in lentic environments. The greater length classes had a higher amount of females (p < 0.05) and the sex ratio in all sampling periods was 1.38 females per male. Both males and females showed positive allometric growth (b = 3.299 and b =3.487, respectively). The highest values for gonadosomatic index (GSI) and gonadal condition factor (K) were observed from August/September and peaked in October/November, just like the highest frequencies of females at maturity stage C (mature), which is indicative that the breeding season occurs at this time.

Período reprodutivo de Ucides cordatus (Linnaeus) (Brachyura, Ocypodidae) na Baía das Laranjeiras, sul do Brasil

Análises macroscópica e microscópica das gônadas de Ucides cordatus foram realizadas mensalmente, durante um ano, visando determinar o período reprodutivo da espécie. A coleta dos espécimes foi realizada em duas ilhas no Sul do país, que apresentaram salinidades diferentes. Os dados obtidos apresentaram consonância com as informações existentes para a espécie no Nordeste brasileiro, possibilitando inferir que variações geográficas e em salinidade parecem não influenciar o período reprodutivo de U. cordatus. Para as fêmeas, foram identificados três estágios de desenvolvimento gonadal: em maturação, maturo e desovado. Fêmeas em maturação foram registradas de agosto a setembro, enquanto as maturas ocorreram de outubro a abril e as desovadas de dezembro a agosto. Os machos foram classificados em duas categorias: gônadas cheias, encontradas durante todo o período de estudo; e gônadas vazias, registradas de dezembro a abril. O contraste da condição gonadal dos machos e das fêmeas possibilitou a determinação do período reprodutivo da espécie na Baía das Laranjeiras, que ocorreu de dezembro a abril. Reproductive period of Ucides cordatus (Linnaeus) (Brachyura, Ocypodidae) in Laranjeiras Bay, southern Brazil Abstract Histological and macroscopic analyses of the gonads of Ucides cordatus were used to determine the reproductive period of the species. The specimens were collected monthly, during one year, in two islands located in the Laranjeiras Bay, Southern Brazil. The obtained data were similar for the two islands and they showed consonance with the information for the species in the Brazilian Northeast. Three stages of gonadal development were identified for the females: in maturation (registered from August to September), mature (registered from October to April) and spawned (registered from December to August). The males were classified in two categories: full gonads, found during the whole study period; and empty gonads, registered from December to April. The contrast of the gonadal condition between males and females allows to determine the reproductive period, which occurs from December to April in Laranjeiras Bay. Résumé Des analyses macroscopiques et microscopiques de Ucides cordatus ont été réalisées mensuellement pendant une année, em envisageant déterminer la période reproductive de l’espèce. La collecte des espècemenes a été réalisée em deux îles (Peças et Pavoçá) qui présentaient des salinités différentes. Les données obtenues ont presente consonance aux renseignements existants pour l’espéce du Nort-est brésilien em rendant possible infere que les variations geographiques et em salinité semblent ne pás influencer la ériode reproductive de U. cordatus. Pour lês femelles, ont été identifiés trois stages de développement dês gonades: en maturation, mature et frayé. Des femelles en maturation ont été enregistrées d’août à septembre, tandis que celles matures l’ont été d’octobre à avril et celles frayées de décembre à août. Les mâles ont été classés em deux catégories: gonades pleines trovées pendant toute la période d’étude,, et gonades vides, enregistrées de décembre à avril. Le contraste de la condition dês gonades des mâles et des femelles a rendu possible la détermination de la période reproductive de l’espèce dans la Baia das Laranjeiras, qui a eu lieu entre décembre et avril.

A test of absolute photorefractoriness and photo-induced neural plasticity of song-control regions in black-capped chickadees (Poecile atricapillus)

We tested whether male and female black-capped chickadees, Poecile atricapillus (L., 1766), were absolutely photorefractory according to Hamner's (1968) criteria of (i) spontaneous regression of gonads during prolonged long-day exposure and (ii) no subsequent recrudescence of gonads in response to constant light. We initially exposed black-capped chickadees to constant long-day photoperiods. Gonads regressed spontaneously, demonstrating that the birds met Hamner's first criterion for absolute photorefractoriness. Once their gonads fully regressed and the birds were in advanced prebasic moult, we exposed them to one of three photoperiods for an additional 2 weeks: constant light (24 h L), short days (8 h L), and controls (15 h L). Constant light challenge had no effect on gonadal condition or rate of moult, confirming that the birds met Hamner's second criterion for absolute refractoriness. We also compared volumes of song-control nuclei in the three groups and found that males overall had larger HVC, robust nucleus of arcopallium, and area X than females, but that longer days (24 h L) did not increase volumes and that shorter days (8 h L) did not decrease volumes compared with controls (15 h L). These data support the inference that black-capped chickadees do indeed become absolutely photorefractory, and that photorefractoriness precludes photo-induced plasticity of the song-control system.