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Interactions between multiple anthropogenic stressors can have unexpected synergistic or antagonistic effects, making it difficult to predict their combined effect using single stressor studies. The interaction between invasive consumers and nutrient enrichment is particularly important as both of these stressors frequently co-occur and their respective bottom-up and top-down effects have the potential to interact across multiple trophic levels. We conducted a mesocosm experiment that crossed an increasing nutrient addition gradient against an increasing zebra mussel invasion gradient. Native zooplankton communities were added to the mesocosms, and after three months we examined how the single stressor effects on available resources and the zooplankton community were altered by their multiple stressor interaction. Added nutrients had no effect on primary producer abundance, but increased the abundance and dominance of the top consumer, which likely increased predation pressure on the producers and so prevented their response to increased nutrients. Zebra mussels reduced total phytoplankton abundance by ~75%, rotifer abundance by ~80%, and shifted communities towards dominance of cladocerans and adult/juvenile copepods. When combined, the top-down control exerted by the mussels interacted antagonistically to prevent any bottom-up influence of nutrient enrichment on the zooplankton community. These results provide insight into the potential outcomes of nutrient and invasive consumer stressor interactions, and illustrate the need for researchers to consider single stressor problems in a multiple stressor context. / Thesis (Master, Biology) -- Queen's University, 2014-01-31 15:20:15.387

It is well established in mammals that chronic, long-term elevations in sex steroids are associated with improvements in spatial cognition. It is less clear the extent to which short to medium term elevations in sex steroids improve spatial cognition and change hippocampal morphology, particularly in birds. The avian hippocampus expresses both androgen receptors (AR) and oestrogen receptor alpha (ERα) and high levels of the enzyme aromatase that converts testosterone to oestrogen. I began by comparing spatial cognition, hippocampal sex steroid receptor and aromatase expression between males and females. There were no differences in spatial or visual cognition or in hippocampal sex steroid receptor expression between the sexes, although hippocampal aromatase mRNA expression was higher in males. I then addressed the effects of acute and medium-term sex steroid treatment on spatial cognition and hippocampal aromatase and sex steroid receptor expression. A single treatment of testosterone 30 minutes or four hours prior to cognitive testing improved spatial performance. Additionally, when testosterone and oestrogen were given daily for five days spatial cognition in both sexes was improved. The testosterone-induced improvement was blocked when testosterone was administered in conjunction with the aromatase inhibitor fadrozole but not when administered with saline. These findings suggest that spatial cognition is improved by an oestrogenic effect. Thirty minutes following acute testosterone treatment, plasma testosterone levels, hippocampal AR and ERα mRNA expression all increased. Five days of oestrogen treatment increased plasma oestrogen levels, hippocampal ERα mRNA and Nmethyl- D-aspartate (NMDA) receptor levels in males and females; all were positively correlated with enhanced spatial cognition on day five of treatment. Finally, I determined which genes were differentially expressed as a result of five days of oestrogen treatment. Nineteen genes, identified as being involved in learning and memory were differentially expressed in the hippocampus, eleven of which were up-regulated and eight were down-regulated. Taken together these results demonstrate that oestrogen can improve spatial cognition in birds. It is plausible that oestrogen acts to improve spatial memory in the hippocampus through upregulation of genes that control neurotransmitter release, reuptake and receptor levels.

In the zebra finch (Taeniopygia guttata), song and its social context play an important role in female mate selection. The song of the zebra finch is unique in that it can only be produced by males, which makes the species ideal for analyzing the components of male song that influence female song preference and mate selection. There are three consistent features of zebra finch song that affect female mate preference: 1) the amount of time a male sings, 2) the size and complexity of his song repertoire, and 3) the structural conformation to species or population norms (reviewed in Nowicki et al. 2002). During courtship, male zebra finches often express ‘static-visual’ and ‘dynamic-visual’ elements in sync with song (Morris 1954), which would suggest that such behaviors also play a role in influencing female mate preference. However, with courtship comes the competition between males for the attention of potential mates. These agonistic interactions between males act settle disputes over access to mates, and as such, are also likely to influence female mate selection. As follows, we predict that, at the initial onset of courtship, there would be a higher prevalence of male-to-female courting interactions and singing behavior in comparison to male-to-male agonistic tendencies if female mate selection is fundamentally determined by song preference. However if female mate selection is more complicated than simple song preference, we would expect to initially observe a higher number of agonistic interactions between males as they compete for dominance. This hypothesis was tested by recording and analyzing the behavioral interactions between male and female zebra finches in the context of song complexity. We found that different males scored higher for song complexity than those for expression of courtship behaviors, which indicates that different elements of male courtship display likely influence female mate preference. Our data comparing male-to-male interactions and male-to-female interactions within the first 30 minutes after introduction was statistically insignificant, suggesting that female mate selection is more complicated than simple song preference. This preliminary research can be used as a basis for future studies using quantitative movement tracking analysis, which would further strengthen these initial observations. By increasing our understanding of the influence the male song has on female mate selection, we can better expound upon the nature and function of the favored traits that male songbirds possess and the benefits that females and their progeny might gain from choosing a male with these particular attributes.

Il a été récemment démontré que l'activateur de transcription ZEBRA du virus Epstein-Barr contenant un motif "basic-leucine zipper (bZIP)" traverse la membrane externe des cellules vivantes et s'accumule dans le noyau des lymphocytes. Durant mon travail de thèse, j'ai étudié la possibilité d'utiliser ZEBRA comme protéine de transport afin de faciliter la transduction de protéines cargo. L'analyse de différentes formes tronquées de ZEBRA a permis de mettre en évidence que le domaine minimal (MD) nécessaire à l'internalisation inclut les résidus 178-220. Le MD a permis de transporter de manière efficace des protéines rapporteur comme la EGFP et la -galactosidase dans plusieurs lignées cellulaires normales et tumorales. La fonction des protéines cargo internalisées a été confirmée par l'activité -galactosidase dans les cellules transduites, et aucune toxicité cellulaire associée au MD n'a été détectée. La translocation du MD à travers la membrane cellulaire nécessite la liaison aux héparanes sulfates protéoglycans associés à la surface de la cellule comme cela a été démontré par la forte inhibition du transport de protéines en présence d'héparine. En outre, l'internalisation est également bloquée à basse température (4 °C). De plus, une réduction de seulement 25 % du transport de protéines cargo dans des cellules avec des stocks d'ATP épuisés démontre que l'internalisation est un processus indépendant de l'ATP. Les inhibiteurs classiques d'endocytose n'ont aucun effet significatif sur le transport de MD-EGFP. Seul le methyl--cyclodextrin inhibe de 40 % le transport de MD-EGFP, indiquant l'implication d'une voie d'endocytose médiée par les radeaux lipidiques. Ces résultats suggèrent que le transport de la protéine rapporteur ZEBRA-MD se produit principalement par translocation directe à travers la membrane cellulaire et non par endocytose. La distribution tissulaire d'EGFP ou de la β-galactosidase couplés ou non avec ZEBRA-MD a été étudiée après injection dans la souris. Seules les protéines de fusion avec ZEBRA-MD ont pu être révélées dans les cellules de différents tissus. De plus, la séquence de translocation de ZEBRA-MD a été fusionnée avec la protéine anti-tumorale IL-24/MDA-7. La mort cellulaire induite par l'internalisation de ZEBRA-MD-IL-24/MDA-7 a été mise en évidence par le clivage des caspases de la voie d'apoptose aussi dans des cellules normales que dans des cellules tumorales du sein. En conclusion, le mécanisme d'internalisation de ZEBRA-MD est approprié pour un transport efficace de protéines biologiquement actives.

African horse sickness (AHS) was reported in the south-western Khomas Region, central Namibia (22° 24.063´ S, 17° 01.791´ E; 23° 32.617´ S, 15° 53.870´ E), contrary to expectations that the arid conditions in the area would limit its occurrence. This prompted investigation into the occurrence of AHS in horses, a possible reservoir animal, the Hartmann’s mountain zebra (Equus zebra. hartmannae) and the occurrence of the Culicoides midge vector (Diptera: Ceratopogonidae) of the disease in the area. Questionnaires were used to explore the geographic characteristics of the study area, the occurrence of an expected AHS virus reservoir animal, E. z. hartmannae and AHS in horses in the study area. According to the questionnaire, rainfall patterns seem to follow topography of the area, where the north-east formed the higher rainfall (420 mm/a) high-ground and the south-western formed the lower rainfall (120 mm/a) pediment zone in the south-west. Cases of AHS occurred mostly in mid-rainfall zones. E. z. hartmannae were present throughout the area. They migrated from the southwest towards the north-eastern high-grounds during droughts, presumably along ephemeral river beds. E. z. hartmannae were sampled for blood and tissues and analysed for evidence of African Horse Sickness Virus (AHSV) infection by indirect ELISA, RT-PCR and virus isolation techniques. All useable samples tested positive for anti-AHSV antibodies. Viral RNA was demonstrated in 26% of all the zebra sampled. No viable viruses were isolated from these samples, however further research is required, as difficult sampling conditions may have yielded false-negatives. From 6 July to 21 September 2009, Culicoides midges were collected during the dry winter season in suction UV-light traps installed at five selected sites along a rainfall gradient. In 38 collections, a total of 9091 Culicoides individuals, representing 25 species were collected. The dominance of the proven vector of AHSV, Culicoides imicola Kieffer, varied in dominance from 94% near Windhoek with high altitude and relatively higher annual rainfall, to 12% at the site situated farthest southwest, with the lowest altitude and annual rainfall. From what was observed of the occurrence of AHS in horses, E. z. hartmannae and the distribution and abundance of the AHSV vector (Culicoides spp.), it was concluded that AHS can be maintained in the south-western Khomas Region even in the lowest mean annual rainfall zones. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012

African horse sickness (AHS) was reported in the south-western Khomas Region, central Namibia (22° 24.063´ S, 17° 01.791´ E; 23° 32.617´ S, 15° 53.870´ E), contrary to expectations that the arid conditions in the area would limit its occurrence. This prompted investigation into the occurrence of AHS in horses, a possible reservoir animal, the Hartmann’s mountain zebra (Equus zebra. hartmannae) and the occurrence of the Culicoides midge vector (Diptera: Ceratopogonidae) of the disease in the area. Questionnaires were used to explore the geographic characteristics of the study area, the occurrence of an expected AHS virus reservoir animal, E. z. hartmannae and AHS in horses in the study area. According to the questionnaire, rainfall patterns seem to follow topography of the area, where the north-east formed the higher rainfall (420 mm/a) high-ground and the south-western formed the lower rainfall (120 mm/a) pediment zone in the south-west. Cases of AHS occurred mostly in mid-rainfall zones. E. z. hartmannae were present throughout the area. They migrated from the southwest towards the north-eastern high-grounds during droughts, presumably along ephemeral river beds. E. z. hartmannae were sampled for blood and tissues and analysed for evidence of African Horse Sickness Virus (AHSV) infection by indirect ELISA, RT-PCR and virus isolation techniques. All useable samples tested positive for anti-AHSV antibodies. Viral RNA was demonstrated in 26% of all the zebra sampled. No viable viruses were isolated from these samples, however further research is required, as difficult sampling conditions may have yielded false-negatives. From 6 July to 21 September 2009, Culicoides midges were collected during the dry winter season in suction UV-light traps installed at five selected sites along a rainfall gradient. In 38 collections, a total of 9091 Culicoides individuals, representing 25 species were collected. The dominance of the proven vector of AHSV, Culicoides imicola Kieffer, varied in dominance from 94% near Windhoek with high altitude and relatively higher annual rainfall, to 12% at the site situated farthest southwest, with the lowest altitude and annual rainfall. From what was observed of the occurrence of AHS in horses, E. z. hartmannae and the distribution and abundance of the AHSV vector (Culicoides spp.), it was concluded that AHS can be maintained in the south-western Khomas Region even in the lowest mean annual rainfall zones. / Thesis (MSc (Environmental Sciences))--North-West University, Potchefstroom Campus, 2012

Toxic antifouling agents such as tributyltin (TBT) and triphenyltin (TPT) have been released in aquatic ecosystems through the use of antifouling paint applied to ship hulls, pleasure crafts and fish nets. The purpose of this study was to assess the use of zebra mussels (Dreissena polymorpha ) as a biomonitor for investigating the geographical variations of organotin bioavailability along the St. Lawrence River. Organotins TBT and TPT and their degradation products were first measured in the soft tissues of zebra mussels collected from along the River. High concentrations of TBT were found in mussels from Bassin Louise, a marina in Quebec City (1442 ng/g wet weight). TPT concentrations were elevated at 2 sites near Quebec City (252 and 530 ng/g wet weight). A follow-up study assessed the extent of the distribution of organotins from the contaminated marina to the River system by measuring organotin concentrations in zebra mussels and in sediments collected River near Quebec City. The highest concentration of TBT was found in Bassin Louise (1078 ng/g wet weight) and elevated concentrations were found in two other marinas. The concentrations decreased sharply to background levels just outside the marinas. All butyltins were detected in all sediments analysed. There was a significant correlation between TBT in sediments and mussels. These studies suggest that organotin contamination may remain a problem in localized freshwaters in the St. Lawrence River.

Freshwater ecosystems worldwide are being altered by multiple stressors. One of the most important stressors is biological invasion---the introduction of exotic species, which can contribute to the loss of native species. The effects of an introduced species are correlated with its abundance and typically vary across ecosystems, suggesting that its impact on native species is mediated by its environment, i.e. the physical habitat and the recipient community. However, there are few studies that explore the effects of environment on the interactions between exotic and native species. My thesis examines the influence of physical habitat variables and community interactions on the relative abundance of exotic and native freshwater crustaceans in the St. Lawrence River. / The Eurasian amphipod Echinogammarus ischnus invaded the Great Lakes-St. Lawrence River system in the mid-1990s and has replaced the native North American Gammarus fasciatus as the dominant amphipod in littoral areas throughout Lake Erie and Lake Ontario.

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