No description available.

Most organisms maintain a nearly 24-hour circadian rhythm which allows them to anticipate daily events in the Earth’s solar day. Circadian clocks can be regulated by external time cues such as light/dark (LD) cycles, allowing nocturnal organisms to synchronize their rhythms around dusk in a process known as entrainment. In the absence of external time cues, these rhythms persist, revealing the period of the organism’s internal clock. In nature, day-night cycles have gradual transitions at dawn and dusk, yet these transitions often are not reflected in laboratory studies. Most utilize instantaneous transitions from light to dark, including previous work on spider circadian behavior. To mimic natural conditions, the next logical step is to evaluate how a gradual, dusk transition affects activity patterns and entrainment in nocturnal spiders. Two spider species were used: Pholcus phalangioides and Metazygia wittfeldae. Three hypotheses were identified: 1) spider circadian behavior is unaffected by the type of dusk transition; 2) spider activity entrains to a proportional decrease in light intensity; and 3) spider activity entrains to a specific dimness threshold. Spiders were placed in activity monitors and exposed to 12:12 LD cycles with high (8934 lux) and low (2918 lux) light intensities. There were two groups within each light intensity: one with instantaneous, dusk transitions and one with linear 4-hour transitions. In all experiments, spiders were switched to constant darkness after 5 days of LD cycles to identify the phasing of the circadian clock. In P. phalangioides, there were no significant differences among onsets of activity for high and low light intensities with ramped transitions, nor high and low intensities with instantaneous transitions. The average onset of activity was 0.2 ± 0.1 hours after absolute darkness. For M. wittfeldae, onsets of activity were significantly earlier in ramped than instantaneous LD cycles. However, there was no observable difference in activity onset associated with absolute light intensity for either transition type. The average onset of activity for ramped transitions was 1.9 ± 0.5 hours before complete darkness, while the average onset for instantaneous transitions was 0.5 ± 0.1 hours after complete darkness. Pholcus phalangioides requires complete darkness before activity begins, supporting the hypotheses that either the activity onset is unaffected by the type of dusk transition or requires a very low threshold of light. However, M. wittfeldae began activity about 2 hours earlier or around when light decreases by 50%, supporting the hypothesis that this species entrains to a proportional decrease in light intensity. These activity patterns match their ecologies, as P. phalangioides typically sits and waits in a permanent web while the orbweaver M. wittfeldae begins building a new web during the dusk transition. Overall, these results suggest that ramping light cycles should be considered when circadian rhythms are evaluated in the lab.

No description available.

No description available.

No description available.

No description available.

Ctenus fasciatus e Enoploctenus cyclothorax (Araneae: Ctenidae) foram estudadas em cavernas da área cárstica do Alto Ribeira, município de Iporanga, sul de São Paulo, abordando a distribuição no meio subterrâneo, ecologia populacional, deslocamentos, alimentação e reprodução e crescimento. A primeira espécie foi estudada na Gruta da Lage Branca, localizada no Parque Estadual Turístico do Alto Ribeira (PETAR), e em quatro cavernas do Parque Estadual Intervales (Grutas da Barra Bonita, do Tatu, do Fóssil Desconhecido e Toca Detrás), enquanto que E. cyclothorax foi estudada apenas nas cavernas mencionadas do PEI. Utilizou-se o método de marcação e recaptura em viagens mensais e os dados obtidos foram analisados pelo método de Jolly-Seber para se estimar o tamanho das populações. Observou-se que as populações são sazonais, com pico no número de exemplares encontrados coincidindo com o período reprodutivo, que ocorre no verão (novembro a março) para C. fasciatus e no inverno (maio a outubro), para E. cyclothorax. A população de C. fasciatus estudada na Lage Branca apresentou uma acentuada queda de um ano para o outro, o que foi atribuído às constantes enxurradas que ocorreram no período de estudo e às atividades turísticas descontroladas. Também houve queda populacional para essa espécie no conjunto das cavernas do PEI, entretanto em menor escala, a qual foi interpretada como flutuação natural das populações. No caso de E. cyclothorax, o estudo populacional no PEI sugere que a população de exemplares adultos se renova anualmente, com indivíduos machos mais errantes e fêmeas sedentárias. Concluiu-se que estas últimas são trogloxenas não obrigatórias, enquanto aranhas C. fasciatus são troglófilas, distribuídas por todo o interior das cavernas e raramente encontradas no meio epígeo. Estas últimas são caracteristicamente errantes, observando-se deslocamentos de até 140 m em períodos máximos de 4 e 5 meses. Exemplares das duas espécies foram transportados ao laboratório, em sala climatizada no Departamento de Zoologia da USP, onde foram mantidos para acompanhamento do comportamento reprodutivo e desenvolvimento pós-embrionário. Aranhas de uma outra espécie da mesma família (Isoctenus sp.), coletada na Lapa do Angélica, situada no Parque de Terra Ronca (PETER), município de São Domingos (GO), reproduziram-se em laboratório e também foram acompanhadas com relação ao desenvolvimento pós-embrionário. O desenvolvimento tanto de C. fasciatus como de Isoctenus sp. é longo (três a quatro anos), e essas aranhas só atingem a vida adulta após 17 ou 18 mudas. Não foi possível acompanhar o desenvolvimento pós-embrionário de E. cyclothorax, pois os exemplares jovens não suportaram as condições de laboratório. Após a cópula, as fêmeas de C. fasciatus sempre se alimentam dos machos para suportar longos períodos sem alimentação até o nascimento e dispersão dos filhotes. E. cyclothorax pode alimentar-se dos machos ou não, já que elas abandonam suas posturas periodicamente para buscar alimento. As ootecas das três espécies são fixas ao substrato rochoso, em superfícies verticais, e nascem aproximadamente 400 a 500 aranhiços de cada ooteca. / Ctenus fasciatus e Enoploctenus cyclothorax (Araneae: Ctenidae) from caves in the Alto Ribeira karst area, Iporanga Co., southern State of São Paulo, were studied with focus on their distribution in the subterranean habitat, population ecology, movements, feeding, and reproduction and growth. The populations of C. fasciatus from Lage Branca Cave, in the Parque Estadual Turístico do Alto Ribeira (PETAR), and from four caves in the Parque Estadual Intervales (Barra Bonita, do Tatu, do Fóssil Desconhecido e Toca Detrás), as well as those of E. cyclothorax found in the latter, were investigated using mark-recapture techniques. These populations are seasonal, with a peak in the number of observed specimens coincident with the reproductive season, which occurs in the summer (November to March) for C. fasciatus and in the winter for E. cyclothorax. There was an accentuated decrease in the population of C. fasciatus in the Lage Branca Cave from the first to the second study year (2001 to 2002), possibly due to floodings and/or poorly controlled touristic visitation. A less accentuated population decrease was also observed for C. fasciatus in caves from the PEI, possibly representing a natural fluctuation. For E. cyclothorax, the study in the PEI indicates that the males are errant and the females tend to be sedentary, and that the adult population renews every year. Females of E. cyclothorax are non-obligatory trogloxenes (aparently males do not use the hypogean habitat), whereas C. fasciatus is a typical troglophile rarely found in the epigean environment. The latter is found throughout the caves, in different substrata (walking on the floor, on rocky walls, hidden in crevices or log); 140 m long movements within 4-5 months were observed for two individuals. Individuals of both species, as well as Isoctenus sp. from a cave in São Domingos karst area, State of Goiás, Central Brazil, were kept in laboratory for study of reproduction and postembryonic development. Development in C. fasciatus and Isoctenus sp. Takes a long time (three to four years till the sexual maturity) and a relatively high numbers of moults (at least 17-18). It was not possibly to describe the postembryonic development in E. cyclothorax because the spiderlings did not survive in laboratory. C. fasciatus females usually eat the male after copulating, probably as an adaptation to survive the long time of parental care without leaving the egg sac to feed. Females of E. cyclothorax may or may not eat the males, and may leave temporarily the egg sac to eat.

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Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Title from second page of PDF document. Includes bibliographical references.