Thesis (M. Sc. (Zoology and Entomology))--Rhodes University, 2006.

The population structure and feeding dynamics of the hyperiid amphipod, Themisto gaudichaudii, was investigated during two cruises of the South African National Antarctic Programme conducted in the Indian sector of the Polar Frontal Zone during austral autumn (April) 2004 and 2005. During the 2004 cruise the frontal features that delimit the PFZ converged to form a single distinctive feature. In 2005, the research cruise was conducted in the vicinity of a cold-core eddy which was spawned from the Antarctic Polar Front. Total mesozooplankton abundance and biomass during the 2004 study ranged from 55.19 to 860.57 ind. m⁻³, and from 2.60 to 38.42 mg dwt m⁻³, respectively. In 2005 the abundance and biomass ranged from 23.1 to 2160.64 ind. m⁻³, and from 0.76 to 35.16 mg dwt m⁻³, respectively. The mesozooplankton community was numerically dominated by copepods, pteropods, and ostracods during both surveys. The abundance and biomass of Themisto gaudichaudii in the region of investigation was < 0.2 ind. m⁻³ (range 0.01 to 0.15 ind. m⁻³) and < 0.06 mg dwt m⁻³ (range 0.02 to 0.06 mg dwt m⁻³) during 2004, while in 2005 the abundance and biomass of the amphipod ranged from < 0.01 to 0.2 ind. m⁻³ and < 0.01 to 0.04 mg dwt m⁻³, respectively. These values correspond to < 1% of the total mesozooplankton abundance and biomass during both surveys. T. gaudichaudii exhibited no significant spatial patterns in abundance, biomass and total length during both 2004 and 2005 (p > 0.05 in all cases). A key feature of the two investigations was the virtual absence of juveniles (total length < 15 mm) among the amphipod population, supporting the suggestion that they exhibit strong seasonal patterns in reproduction. Gut content analysis during both years indicated that for both the male and female amphipods’, copepods were the most prevalent prey species found in stomachs, followed by chaetognaths and pteropods. Results of electivity studies indicate that T. gaudichaudii is an opportunistic predator, generally feeding on the most abundant mesozooplankton prey. Results of in vitro incubations indicated that the total daily feeding rate of T. gaudichaudii during 2004 ranged from 11.45 to 20.90 ind. m⁻³ d⁻¹, which corresponds to between 0.12 and 1.64% of the total mesozooplankton standing stock. In 2005, the feeding rate ranged between 0.1 and 1.73% of the total mesozooplankton standing stock. The low predation impact of T. gaudichaudii during this study can be related to their low abundances and high interannual variability throughout the region of investigation.

Orientador: Jose Roberto Trigo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-10T19:03:33Z (GMT). No. of bitstreams: 1 Massuda_KamilaFerreira_M.pdf: 3824014 bytes, checksum: d4db5cb4afb22e7d40b4afc3d0677236 (MD5) Previous issue date: 2008 / Resumo: As defesas químicas em lepidópteros compreendem mecanismos que vão desde o seqüestro de compostos do metabolismo secundário de plantas até a biossíntese de novo de compostos que podem torná-los tóxicos ou impalatáveis. As larvas da borboleta Methona themisto (Nymphalidae: Ithomiinae), que apresentam coloração conspícua e se alimentam apenas da solanácea Brunfelsia uniflora, rica em compostos do metabolismo secundário, foram analisadas sob vários aspectos, para verificar se são quimicamente defendidas. O acompanhamento da sobrevivência das larvas indicou que a predação afeta significativamente a sobrevivência em seu ambiente natural. As defesas químicas dessas larvas são aparentemente ineficazes contra predadores invertebrados, como a aranha Lycosa erythrognatha e a formiga Camponotus crassus (100% dos indivíduos testados predaram as larvas), mas parecem ser eficazes contra os mantídeos Oxyopsis saussuurei (redução no tempo de manipulação da presa e predação em um segundo contato). Para predadores vertebrados como o lagarto Tropidurus itambere e a ave Gallus gallus, a defesa parece atuar em relação à palatabilidade e à coloração conspícua. Gallus gallus apresentou maior predação de larvas de 1o ínstar, sugerindo que há um incremento na impalatabilidade da larva no decorrer de seu desenvolvimento. Os testes de aprendizagem dos pintinhos demonstraram que com poucos contatos com a presa impalatável já se obtém uma resposta de rejeição visual. O emprego de uma larva de coloração semelhante a da Methona themisto indica que os pintinhos são capazes de relacionar a cor com o gosto desagradável, rejeitando assim uma presa palatável. Apenas extratos diclorometânicos das larvas testados com Gallus gallus foram significativamente rejeitados em relação a seus controles. Dessa forma, esses dados comprovam que as defesas químicas das larvas de Methona themisto atuam principalmente contra predadores vertebrados visualmente orientados / Abstract: Chemical defense in Lepidoptera involves several mechanisms such as sequestration of secondary metabolismcompounds of host plants and de novo synthesis of compounds that can provide some unpalatability or toxicity. The larvae of the butterfly Methona themisto (Nymphalidae: Ithomiinae) have a conspicuous coloration and feed exclusively on Brunfelsia uniflora (Solanaceae), that is rich in compounds of the secondary metabolismo These larvae were analyzed under several aspects to confirm if they are chemically defended. Survivorship data showed predation significantly affecting larval survival in natural habitat. Larvae chemical defenses are inefficient against invertebrate predators, such as the spider Lycosa erythr-ognatha and the ant Campónotus crassus (100% of predation), but it seems to be efficient against the mantid Oxyopsis saussuurei (reduction of prey manipulation time and predation in a second contact). To vertebrate predators, like the lizard Tropidurus itambere and the chick Gallus gallus, defense acts through conspicuous coloration and palatability. Predation by Gallus gallus was highest upon 1st ínstar larvae, suggesting an increase of unpalatability throughout development. Learning avoidance tests with Gallus gallus demonstrated that few contacts with distasteful and warning colored prey could make the predator reject visually Methona themisto larvae. Chicks visually rejected palatable larvae painted in the same color pattem of Methona themisto larvae confirming their ability to associate taste and color. Only dichloromethanic extracts tested with chicks showed significant rejection in relation to controls. These results confirm that Methona themisto larvae are chemical defended against visually oriented vertebrate predators / Mestrado / Mestre em Ecologia