Thesis (bachelor's)--Göteborg University, 1998. / Title from PDF t.p. (viewed on 4/14/08). "April 1998." Includes bibliographical references (p. [6-7]).

Thesis (Ph. D.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 220-243).

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 176-201).

According to Darwin, any inheritable traits that enhance fitness (i.e. survival and reproductive success) would be adaptive in a given environment, and therefore subject to natural selection. Some traits that enhance reproductive success but not necessarily survival may, however, evolve through the process of sexual selection. The importance of sexual selection has been intensively studied in “higher animals” birds, mammals and insects but has largely been neglected in “lower animals” such as gastropods. Using two mangrove snails, Littoraria ardouiniana HEUDE 1885 and L. melanostoma GRAY 1839 (Littorinidae) as model species, this thesis documents their various reproductive traits and the occurrence of sexual selection, in an attempt to understand how these animals optimize their fitness. Being one of a few gastropod families that live closely associated with mangrove habitats, various adaptive reproductive traits are likely to have evolved in the genus Littoraria. The two Littoraria species exhibited several, contrasting, reproductive traits (e.g. reproductive mode; length of reproductive season; seasonal fecundity and egg- or larvae-releasing rate), which may represent species-specific strategies to optimize reproductive success. Both species adopted mucus trail following as a mate-searching strategy; with males being able to discriminate the trails laid by conspecific females and trail orientation during the mating season. Since these two snails mate in the complex habitat of mangrove tree canopies, incorporating some cue into mucus trails to aid mate recognition would increase potential encounter rates and hence reproductive success. 1D proteomic techniques identified two potential pheromones in the trail mucus of female L. ardouiniana, but further investigations are needed to confirm their possible role as sex pheromones. Evidence for sexual selection was found in L. ardouiniana through male mate choice and male-male competition. Large male L. ardouiniana showed a preference for mucus trails laid by large (= more fecund) females, but this preference was not seen in small males, suggesting a size-based male mate preference. Males of this species also mated with larger females for a longer duration and they showed physical aggression (i.e. they pushed each other) when they encountered a female. These sexual selection mechanisms may drive size-assortative mating patterns in littorinid species and in other animals. Conversely, L. melanostoma exhibited no obvious male mate preference or male aggression. Such differences in sexual selection patterns from L. ardouiniana were proposed to be a result of differences in operational sex ratio and variation in female quality. As many gastropods show similar mating behaviour to littorinids (i.e. trail following, shell mounting and copulation), sexual selection may operate in a comparable manner in other gastropods. By revealing the complexity of sex roles of males and females (e.g. the mutual occurrence of male mate choice and male-male competition) and condition-dependent male mate preference in these mangrove snails, this thesis has contributed to a missing link between sexual selection and the “lower animals” and provides new insights into the operation of sexual selection in animals. / HKU 3 Minute Thesis Award, Champion (2012) / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

With the anticipated effects of climate change due to global warming, there is concern over how animals, especially ectotherms, will respond to or tolerate extreme and fluctuating environmental temperature stress. Littorinid snails are intertidal ectotherms that live high on the shore where they experience both extreme and variable conditions of temperature and desiccation stress, and are believed to live close to their tolerance limits. This study investigated the thermal biology of littorinid snails of the genera Afrolittorina, Echinolittorina and Littoraria from temperate, subtropical and tropical regions in South Africa and Brunei Darussalam using thermal tolerance, heart function, and proteome approaches. The effects of conditions, such as rate of change in temperature, acclimation, heat shock, season and starvation were also tested. In addition, the evolutionary relationships and genetic diversity between and within the South African Afrolittorina spp. were investigated using mitochondrial and nuclear markers. Genetic results confirmed that these are two distinct species, with the brown to black A. knysnaensis predominant in the cool-temperate region of South Africa and the pale blue-grey A. africana in the subtropical region. There was low genetic variation and differentiation within each species, suggesting high gene flow among populations as a result of the effects of ocean currents on the dispersal of their planktotrophic larvae. Tests using exposure to high temperatures revealed differences in the thermal tolerances, heart performance and protein profiles of species from different latitudes, regions and zones on the shore. Thermal tolerance conformed to expectations, with clear, statistically significant trends from high tolerance in subtropical species to lower tolerance in temperate species. However, for Afrolittorina spp., there were no significant differences in the thermal tolerances of conspecifics from different regions, though there was a significant difference in thermal tolerance between juveniles and adults. Overall, adults of all species showed higher thermal tolerances than juveniles. Although lethal temperatures for these species were higher in summer than winter, laboratory acclimation had no effect on heat coma temperatures. All species showed some regulation of heart rate, with a degree of independence of heart rate from temperature across mid-range temperatures. The tropical species showed quick induction and good regulation of heart rate followed by the subtropical and temperate species, which displayed mixed responses including regulation, partial regulation and lack of regulation. Overall, tropical Echinolittorina spp. showed good regulation, while the subtropical E. natalensis and Littoraria glabrata exhibited a mixture of partial regulation and regulation. The subtropical/temperate Afrolittorina spp. showed high individual variability, some animals exhibiting regulation, while others did not. These effects seem to be largely phylogenetically determined as there were no differences in the heart rate responses of Afrolittorina spp. from different regions. The temperatures at which heart rate became independent of temperature (thermoneutral zone) were within the range experienced under natural conditions. In addition, there were differences in Arrhenius breakpoint and endpoint temperatures, showing a trend from higher in tropical animals to lower for temperate animals. Conditions such as acclimation, heat shock and starvation had little or no effect on heart performance. However, a slow increase in temperature induced good regulation of heart rate with noticeable shifts of breakpoints and endpoints for Afrolittorina spp. Lastly, there were differences in the proteome responses between and within Afrolittorina spp. as a function of species, size and treatment. Although both large and small A. knysnaensis had a greater number of protein spots in their proteome than A. africana (though the difference was not significant), the later showed significantly higher differential expression of certain proteins following heat stress. In addition, juveniles of both species displayed greater numbers of protein spots in their proteome than adults. The results indicate a difference in the physiological and biochemical responses (i.e. adaptations) of these snails to temperature, and this seems to relate to differences in biogeography, phylogeny, species identity and ecology. The ability to regulate heart rate is phylogenetically determined, while thresholds and lethal limits correspond to biogeography and species ecology. The proteome seems to correspond to species ecology. The results also indicate that these littorinids can tolerate high temperature stress and in this respect they are well suited to life in the intertidal zones or habitats where temperature and other stresses or conditions are extreme and can change abruptly. However, the limited ability of these snails to acclimate to different temperatures suggests that they are already living close to their tolerance limits with small safety margins or narrow thermal windows and so may be vulnerable to small rises in substratum temperature and/or solar radiation.

Intertidal rocky shores represent an extremely stressful physical environment dictated by the rise and fall of the tides. One of the major environmental stresses over this gradient is temperature, especially towards the upper reaches of the shore where species spend long periods out of water exposed to hot, desiccating conditions. As a result, the thermal tolerance of intertidal species is often positively correlated with their vertical distributions, and the physiological and molecular limits that drive such patterns have been the subject of recent research. Understanding these tolerance limits, from small (e.g. vertical distribution) to large (e.g. latitudinal) spatial scales, may provide information to predict species’ success under future climate change scenarios, and thus possible changes in community structure. Given their abundance in the high shore, and well resolved taxonomy and phylogeography, the littorinids Echinolittorina malaccana, E. radiata and E. vidua are excellent models to investigate the relationship between thermal tolerance and spatial distribution patterns. These littorinids are widely distributed on Hong Kong shores and exhibit a distinct and consistent vertical distribution that ranges from temperate to tropical regions along the western Pacific coast. Field surveys in summer and winter at two moderately exposed shores (Stanley and South Bay, Hong Kong) showed that E. malaccana was distributed highest on the shore, followed by E. radiata and E. vidua respectively, and all the three species were found ~ 0.25m lower on the shore in summer than winter. Laboratory experiments, including determination of survival limits (LT50), Arrhenius breakpoint temperature of heart rate (ABT of HR) and activities of metabolic enzymes (MDH and LDH), were used to establish if the physiological attributes of the three species were related to their distribution patterns. The LT50 of E. malaccana were the highest of the three species (56.47oC), followed by E. radiata (55.5oC), and finally the lower shore species E. vidua (53.7oC); while ABT of HR in E. malaccana (48.2oC) was also higher than E. radiata (46.5oC) and E. vidua (46.6oC). The enzyme activities did not show any clear patterns. In terms of seasonal variation, LT50 and ABT of HR of all three Echinolittorina species were higher in summer than winter, which showed the potential for the littorinids to acclimate when environmental conditions become more severe. The present study provided a fundamental understanding of how physiological, temperature tolerance may determine the spatial and temporal distribution patterns of Echinolittorina species at a local scale where strong environmental gradients vary vertically and also between seasons. Information on the tolerance limits of physiological traits such as LT50, heart rates and enzyme functioning may direct further investigations to identify the underlying causes of the survival limits of these species to temperature variation, and whether this tolerance is genetically or environmentally determined, for example through acclimation. Such studies will provide insights into how a species' physiology may limit their present-day distributions at multiple scales from local to biogeographical, but also enable predictions of how species may respond to changing temperature regimes. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--Stanford University, 2008. / Submitted to the Department of Biology. Copyright by the author. Includes bibliographical references (p. 183-205). Also available online.

Foi estudada a morfologia de Echinolittorina lineolata, Echinolittorina ziczac e Echinolittorina vermeiji, pertencentes ao \"complexo E. ziczac\", das quais resultaram duas novas espécies, todas procedentes da costa oeste do Atlântico. Foi possível averiguar características morfológicas que diferenciam todas as espécies entre si. Diferenças foram encontradas principalmente nas seguintes estruturas: concha, com variação interespecífica; rádula, que apresentou diferenças entre as cinco espécies com destaque para a forma geral do dente raquidiano; pênis, com variações na glândula acessória e corpo peniano; osfrádio, destacando-se suas proporções e a presença ou ausência de pregas satélites; músculo columelar com comprimento muito variável e tentáculos, em relação à sua forma e tamanho. Ao se associar às conchas as características da morfologia interna, principalmente rádula e pênis, encontra-se um conjunto diagnóstico eficiente na determinação dessas espécies em Littorinidae. / The morphology of Echinolittorina lineolata, Echinolittorina ziczac and Echinolittorina vermeiji, all belonging to the \"E. ziczac complex\", is analyzed. The analysis resulted in two new species, all of them from the Atlantic west coast. It was possible to determine morphological characteristics that distinguish each species from eachother. Differences were mainly found in the following structures: shell, with interspecific variation; radula, which showed differences between the five species with emphasis on the general shape of the rachidian tooth; penis, with variations in the accessory gland and penile body; osphradium, highlighting its proportions and the presence or absence of secondary folds; columellar muscle with varied length and tentacles in relation to their size and shape. By associating shell features with internal morphology, especially the radula and penis, an efficient diagnostic set in the determination of these species in Littorinidae can be attained.