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postgraduate thesis: Interacting effects of temperature, an insecticide, and an invasive predator on larval amphibians in tropical Hong Kong

TitleInteracting effects of temperature, an insecticide, and an invasive predator on larval amphibians in tropical Hong Kong
Authors
Issue Date2014
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Lau, T. E. [劉特銓]. (2014). Interacting effects of temperature, an insecticide, and an invasive predator on larval amphibians in tropical Hong Kong. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5481873
AbstractExtinction and population declines of amphibian species area pressing global environmental problem. Apart from habitat destruction and diseases, chemical pollution, biological invasion and climate change are widely regarded as major threats causing their declines. In the tropics and subtropics, lowland wetland amphibians are often concurrently exposed to thermal stress, pesticides and invasive predators. However, combined effects of these stressors on wetland amphibians have not been fully elucidated. This study, therefore, aimed to comprehensively investigate the effects of temperature alone and in combination with the presence of a pesticide and an invasive predator on larvae of selected tropical amphibian species. The first part of the study was a meta-analysis of relationships between temperature and chemical toxicity to freshwater ectotherms. Species-and chemical-specific temperature-dependent toxicity were observed. Based on the observed relationships, a model was developed to modify water quality criteria of chemicals (i.e., effect thresholds) for better protection of freshwater ectotherms under various thermal scenarios. The second part focused on the combined effects of temperature, pesticide pollution and an invasive predator on larval amphibians in a local context. Thermal tolerances of larvae of three local, tropical, amphibian species namely Duttaphrynus melanostictus (Bufonidae), Microhyla pulchra (Microhylidae)and Polypedates megacephalus (Rhacophoridae), and their invasive predator, the mosquitofish (Gambusia affinis)were determined. Gambusia affinis was most tolerant oflow temperatures but also least tolerant of high temperatures, but its tolerance was nevertheless high enough to withstand environmentally-relevant temperature fluctuations. An investigation of thermal physiology was conducted on P. megacephalus, whose optimal temperature range (22.0 –25.6°C)was lower than field temperatures during its breeding season, indicating that summer temperatures may be a source of stress. Median lethal concentrations (96 h) of the carbamate insecticide methomyl to the three amphibian species were evaluated at different temperatures. The relationship between temperature and pesticide toxicity generally followed either a “hockey stick” pattern involving a threshold temperature for the interactive response (D. melanostictus and M. pulchra), or a linear pattern (P. megacephalus). Increased toxicity at high temperatures was recorded in both cases. A follow-up investigation on sublethal temperature-pesticide interaction using P. megacephalus as a model species revealed a contrasting temperature-dependent toxicity pattern. Reduction in body mass and length, high occurrences of malformations and decreases in thermal tolerance were recorded at low temperatures, yet these effects were mitigated at high temperatures. Lastly, D. melanostictus and P. megacephalus showed very different responses in an investigation of temperature-pesticide-predator interactions. Duttaphrynus melanostictus was only slightly affected by the combined stressors. In contrast, G. affinis exerted high predation pressure on P. megacephalus, but that was mitigated by the presence of methomyl. However, the presence of a predator alone induced a reduction in growth and changes in energy content of P. megacephalus. Other complex interactions with temperature and pesticide were also observed. This study advances our understanding of interactions between biotic and abiotic factors by demonstrating the complex responses under different combinations of stressors and highlights the need to account for the co-occurrence of multiple stressors in ecotoxicological studies for ecological risk assessment and species conservation.
DegreeDoctor of Philosophy
SubjectAmphibians - Effect of predation on - China - Hong Kong
Amphibians - Effect of temperature on - China - Hong Kong
Amphibians - Effect of pesticides on - China - Hong Kong
Dept/ProgramBiological Sciences
Persistent Identifierhttp://hdl.handle.net/10722/225943

 

DC FieldValueLanguage
dc.contributor.authorLau, Tak-chuen, Edward-
dc.contributor.author劉特銓-
dc.date.accessioned2016-05-27T23:15:52Z-
dc.date.available2016-05-27T23:15:52Z-
dc.date.issued2014-
dc.identifier.citationLau, T. E. [劉特銓]. (2014). Interacting effects of temperature, an insecticide, and an invasive predator on larval amphibians in tropical Hong Kong. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5481873-
dc.identifier.urihttp://hdl.handle.net/10722/225943-
dc.description.abstractExtinction and population declines of amphibian species area pressing global environmental problem. Apart from habitat destruction and diseases, chemical pollution, biological invasion and climate change are widely regarded as major threats causing their declines. In the tropics and subtropics, lowland wetland amphibians are often concurrently exposed to thermal stress, pesticides and invasive predators. However, combined effects of these stressors on wetland amphibians have not been fully elucidated. This study, therefore, aimed to comprehensively investigate the effects of temperature alone and in combination with the presence of a pesticide and an invasive predator on larvae of selected tropical amphibian species. The first part of the study was a meta-analysis of relationships between temperature and chemical toxicity to freshwater ectotherms. Species-and chemical-specific temperature-dependent toxicity were observed. Based on the observed relationships, a model was developed to modify water quality criteria of chemicals (i.e., effect thresholds) for better protection of freshwater ectotherms under various thermal scenarios. The second part focused on the combined effects of temperature, pesticide pollution and an invasive predator on larval amphibians in a local context. Thermal tolerances of larvae of three local, tropical, amphibian species namely Duttaphrynus melanostictus (Bufonidae), Microhyla pulchra (Microhylidae)and Polypedates megacephalus (Rhacophoridae), and their invasive predator, the mosquitofish (Gambusia affinis)were determined. Gambusia affinis was most tolerant oflow temperatures but also least tolerant of high temperatures, but its tolerance was nevertheless high enough to withstand environmentally-relevant temperature fluctuations. An investigation of thermal physiology was conducted on P. megacephalus, whose optimal temperature range (22.0 –25.6°C)was lower than field temperatures during its breeding season, indicating that summer temperatures may be a source of stress. Median lethal concentrations (96 h) of the carbamate insecticide methomyl to the three amphibian species were evaluated at different temperatures. The relationship between temperature and pesticide toxicity generally followed either a “hockey stick” pattern involving a threshold temperature for the interactive response (D. melanostictus and M. pulchra), or a linear pattern (P. megacephalus). Increased toxicity at high temperatures was recorded in both cases. A follow-up investigation on sublethal temperature-pesticide interaction using P. megacephalus as a model species revealed a contrasting temperature-dependent toxicity pattern. Reduction in body mass and length, high occurrences of malformations and decreases in thermal tolerance were recorded at low temperatures, yet these effects were mitigated at high temperatures. Lastly, D. melanostictus and P. megacephalus showed very different responses in an investigation of temperature-pesticide-predator interactions. Duttaphrynus melanostictus was only slightly affected by the combined stressors. In contrast, G. affinis exerted high predation pressure on P. megacephalus, but that was mitigated by the presence of methomyl. However, the presence of a predator alone induced a reduction in growth and changes in energy content of P. megacephalus. Other complex interactions with temperature and pesticide were also observed. This study advances our understanding of interactions between biotic and abiotic factors by demonstrating the complex responses under different combinations of stressors and highlights the need to account for the co-occurrence of multiple stressors in ecotoxicological studies for ecological risk assessment and species conservation.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.subject.lcshAmphibians - Effect of predation on - China - Hong Kong-
dc.subject.lcshAmphibians - Effect of temperature on - China - Hong Kong-
dc.subject.lcshAmphibians - Effect of pesticides on - China - Hong Kong-
dc.titleInteracting effects of temperature, an insecticide, and an invasive predator on larval amphibians in tropical Hong Kong-
dc.typePG_Thesis-
dc.identifier.hkulb5481873-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineBiological Sciences-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b5481873-

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