Predation by northern pike is believed to have initiated a divergence in whitefish into several different morphs, differing in size, habitat use and growth rate.  The development of a small pelagic zooplankton feeding morph is expected to have large impacts on the zooplankton community. In this study the effect of a changing predation regime on Bosmina, before and after introduction of pike in Valsjön, was investigated.  By looking at the change in carapace length (and indication of the level of predation pressure from fish) and mucro index (an indication of the level of invertebrate predation) of Bosmina remains in lake sediment the changing predation pressure from invertebrates and fish could be investigated. These features proved to be good proxys for the level of defense against fish and invertebrate predation.  However, other species than whitefish, and unknown interactions seems to have affected the zooplankton community. This makes it hard to tell which effect is due to diversification in whitefish and which is not. Also it is not clear that it is pike that has induced the divergence in the whitefish population. Other species like brown trout might also have been involved.

En dépit de la ré-oligotrophisation de nombreux lacs d'Europe du nord au cours des deux dernières décennies, les développements massifs de cyanobactéries toxiques, telle que Planktothrix rubescens, adaptée aux écosystèmes mésotrophes, sont encore largement observés. Parmi les cyanotoxines produites par cette espèce, les microcystines (MCs) sont les toxines les plus fréquemment rencontrées et sont reconnues comme des molécules perturbatrices de tous les compartiments trophiques des écosystèmes lacustres. Ces blooms toxiques affectent notamment les lacs péri-alpins pour lesquels des risques de contaminations des populations piscicoles exploitées ont été démontrés. Cependant, il existe encore un manque de connaissances important tant concernant les voies de transfert de ces toxines au sein des réseaux trophiques limniques, que leurs effets physiologiques sur les populations de poisson. Dans le cadre de ce travail de thèse, deux modèles de poissons, dont les répartitions spatiales verticales diffèrent (juvéniles de perche et corégones), ont été considérés. Les objectifs principaux ont été traités d'une part au travers d'une approche expérimentale (par gavage) visant à analyser les processus d'accumulation et de détoxification, ainsi que les effets génotoxiques des MCs sur ces deux espèces modèles. Les réponses physiologiques ainsi étudiées ont permis de mettre en évidence que les juvéniles de perche et les corégones sont capables de détoxifier une partie des MCs ingérées, mais cependant des effets génotoxiques sont observés suite à l'exposition des poissons aux MCs. D'autre part, des approches écosystémiques ont permis (1) d'explorer les effets potentiels de la présence du bloom sur la répartition spatiale des poissons (2) d'évaluer les niveaux de contaminations par les MCs pour les deux espèces de poisson en tenant compte de la variabilité saisonnière (3) d'identifier les principaux vecteurs zooplanctoniques de MCs jusqu'aux poissons. Les résultats acquis montrent que les filaments de P. rubescens constituent une ressource alimentaire en période de bloom pour les organismes zooplanctoniques brouteurs et qu'un transfert de MCs est possible jusqu'aux espèces zooplanctoniques prédatrices et in fine jusqu'aux poissons. Nos résultats mettent également en avant que les voies de contaminations ainsi que les intensités de contamination des poissons peuvent varier aussi bien à l'échelle saisonnière que journalière. Ces variations sont expliquées à la fois par les changements de régime alimentaire des poissons, les variations journalières de la production de MCs par P. rubescens, et les abondances et distributions verticales des différentes proies zooplanctoniques. A l'issue de ce travail, la part importante du transfert trophique des MCs jusqu'aux poissons a été vérifiée dans les cas des contaminations chroniques qui caractérisent les conditions de blooms des lacs péri-alpins (concentrations en cyanobactéries et en toxines modérées à fortes au cours de plusieurs mois). / Many deep peri-alpine lakes which are currently under re-oligotrophication are impacted by Planktothrix rubescens blooms. Among cyanotoxins produced by P. rubescens, microcystins (MCs) are the most commonly studied and are involved in many ecological disturbances. In peri-alpine lakes, these blooms might affect exploited fish species due to toxin contaminations. However, there is still a lack of knowledge regarding both transfer pathways of the toxin and their physiological effects on fish populations. In this work, two models of fish populations were considered (Young-Of-Year (YOY) perch and whitefish which exhibit distinct vertical distributions). The main objectives were on the one hand investigated through an experimental approach to analyze on the two model species, accumulation and detoxification processes as well as genotoxic effects of MCs. From these experiments, we showed that YOY perch and whitefish were able to detoxify part of the MCs but that genotoxic effects were still observed. On the other hand, ecosystemic approaches allowed (1) to explore the potential effects of the presence of bloom on the spatial distribution of fish, (2) to assess the levels of contamination by MCs for both fish species taking into account the seasonal variability, (3) to identify the main zooplanktonic vectors of MCs to fish. Our results revealed that the filaments of P. rubescens are a food resource for zooplankton grazers, and that a trophic transfer of MCs exists from herbivorous to their zooplanktonic predators and in fine to fish. Our results also highlight that the contamination pathways and their intensities could vary both at seasonal and daily scales. These variations are explained by both changes in fish diet, daily variations in the production of MCs by P. rubescens, and abundances and vertical distributions of zooplanktonic preys. Overall, we highlighted the importance of MCs trophic transfer in fish intoxication in the case of chronic contaminations observed in peri-alpine lakes (moderate to severe cyanobacteria/toxins concentrations over several months).

A critical step in ecological speciation is the development of reproductive isolation. The processes leading up to reproductive isolation are difficult to study since they often occur over very long time periods. Populations of European whitefish (Coregonus lavaretus) has gone through reticulate divergent evolution in many Scandinavian lakes during the last 10 000 years. Some populations even exhibit morphological and genetic divergence that involves adaptations to different niches during the first 100-200 years after introduction. This observed rapid diversification into different ecological niches makes whitefish a useful model species for studying ecological speciation and early population divergence. By assessing divergence for three traits in recently introduced whitefish populations, this study aims to elucidate the processes that lead to adaptive phenotypic divergence and reproductive isolation. Whitefish populations of known age (71-170 years) were sampled on their spawning grounds and characterized with respect to, 1) length of spawning season, 2) temporal segregation based on body size, and 3) temporal segregation based on the number of gill rakers. I found that the length of the spawning season and body size differences between early and late spawners increased with population age. No such trend was observed for differences in gill rakers between early and late spawners, but significant divergence within some of the older populations was detected. I conclude that these young whitefish populations have taken the first steps toward reproductive isolation between ecotypes that differs in body size (a highly plastic trait) and gill raker numbers (a trait under strong genetic control).

Broad whitefish, Coregonus nasus, is an important subsistence fish species in Arctic North America, yet virtually nothing is known regarding the genetic population structure of Nearctic populations of this species. In this thesis, microsatellite DNA variation was assayed among 1213 broad whitefish from 47 localities throughout North America, with emphasis on the Mackenzie River system, Northwest Territories. Specifically, I examined geographic variation in allele frequencies to assess how historical factors (Pleistocene glaciations) have shaped the current structuring of genetic variability and population differentiation. Microsatellite data was also used to resolve the relative contributions of broad whitefish populations to subsistence fisheries in the Mackenzie River system. Overall, broad whitefish exhibit relatively high intrapopulation microsatellite variation (average 12.29 alleles/locus, average HE = 0.58) and there were declines in these measures of genetic diversity with distance from putative refugia suggesting historical factors, namely post-glacial dispersal, have influenced current microsatellite variation. Interpopulation divergence was low (overall FST = 0.07), but the main regions assayed in this study (Russia, Alaska, Mackenzie River and Travaillant Lake systems) are genetically differentiated. Strong isolation-by-distance among samples was resolved when including only those populations occupying former Beringia, but not when assaying those at the periphery of the range in the Mackenzie River system, suggesting that broad whitefish in the Mackenzie system have not occupied the region long enough since their invasion post-glacially to have approached equilibrium between gene flow and drift. Mixture analysis indicated that most fish from the lower Mackenzie River subsistence fishery originated from the Peel River, highlighting the importance of this tributary. Additionally the mixture analysis provides evidence for a putative riverine life history form in the Mackenzie River. My results indicate that glaciation and post-glacial colonization have been important in shaping the current genetic population structure of North American broad whitefish. They also illustrate the utility of microsatellite DNA to delineate population structure and patterns of genetic diversity in recently founded populations in addition to resolving contributions to fisheries. My data also support the hypothesis that there are several designatable units of conservation among broad whitefish populations and that management strategies should be implemented accordingly. / Science, Faculty of / Zoology, Department of / Graduate

<p>Natural and constructed rocky reef habitats constitute important areas for lithophilic spawning fishes and their embryonic and larval offspring. Interstitial spaces created by the structure of rocky reefs create micro-environments where incubating embryos and juvenile fishes are potentially protected from predators. However, if interstitial spaces are filled or blocked by sediment deposition or biofouling, the reef structure may lose the protective benefits for embryonic and larval fish survival. Lake whitefish (<i>Coregonus clupeaformis</i>) and walleye (<i>Sander vitreus</i>) are native Great Lake lithophilic broadcast spawning fish that use rocky spawning habitats that are vulnerable to degradation caused by deposition of suspended sediments. To restore degraded rocky reef habitat, common practices include addition of material to existing reef structures or construction of new reefs, but both of these practices can be costly and time intensive. In this study, we measured the effect of different types and amounts of sediment cover on hatching success of walleye eggs and assessed if differences in female walleye (female length and egg size) account for tolerance to sediment cover. Additionally, we explored an alternative approach for reef restoration, custodial maintenance, in which we created two novel devices to potentially clean rocky reef habitat. We carried out two laboratory experiments in 2018 and 2019 to test the effect of sediment cover on hatching success of walleye eggs (2018) and to test how female identity and female length or egg size may interact with sediment cover to influence hatching success (2019). We exposed walleye eggs to instantaneous sediment cover (0 mm – 7mm) of either sand (course) or silt (fine) sediments from fertilization until day 15 of incubation. Our results indicated that walleye eggs were sensitive to silt cover (71% mortality- 2 mm cover silt) but not sand (47% mortality- 7mm cover sand). While there was an indication that hatching success was marginally related to female length and egg size, we concluded that sediment cover seemed to have similar effects on eggs, regardless of female length or egg size. The susceptibility of walleye eggs to mortality caused by sediment cover underscores the need for non-degraded spawning habitat. Our two cleaning devices used either propulsion or pressurized water jets to clean sediments from the rocky structure as they were towed behind a small vessel (i.e., did not require the use of SCUBA divers). We used devices to clean two natural rocky reefs in Saginaw Bay, Lake Huron in 2018 and 2019. We measured relative hardness before and after use of devices on cleaned and uncleaned study plots to determine effectiveness of devices. In addition, we measured egg deposition by fall (lake whitefish) and spring (walleye) lithophilic spawners on study plots to determine potential differences in fish usage of cleaned and uncleaned areas. We found that cleaning devices contributed to changes in relative hardness among study plots. Egg deposition was also variable on study plots but in general, egg deposition was consistently highest on treatment plots cleaned by our device that used propulsion. The practicality of cleaning devices was seemingly related to the magnitude of degradation of rocky reefs, nevertheless, our results show that the use of these or similar devices may potentially increase egg deposition by creating areas of higher-quality habitat. While more testing is necessary to fully understand the potential of our reef cleaning devices, this two-year study suggests that these devices may be capable of restoring degraded rocky spawning habitat which could potentially minimize the negative effects associated with sediment degradation on lithophilic spawning fish.</p>

Growth and food habits of 399 Age 0 mountain whitefish from the Logan River, Utah, were studied between March, 1970, and April, 1971. At the end of their first six months of life, whitefish were 86-96 mm total length and weighed 6-8 grams (wet). Total temperature experience was 2,950-3,430 degree- days above 32° F. The length-weight relationship for Age 0 mountain whitefish was best described by three stanzas with slopes of 4.3333 for fish 12.5-17.0 mm total length, 3.4437 for fish 17.0-55.0 mm total length, and 2.8043 for fish 50.0-112.0 mm total length. Scalation commenced at 30-35 mm total length and was complete at 40-50 mm total length. Feeding began before yolk-sac absorption was complete and 85 percent of the total diet in numbers was chironomid larvae. Age 0 mountain whitefish in the Logan River fed during daylight and evening hours, and selected chironomid larvae and other food organisms 2-4 mm long.

Temperatures selected seasonally by adult mountain whitefish were measured in the laboratory in a horizontal gradient. Final preferendum estimates, based on acute (3-hour) preference tests conducted with fish acclimated to 5, 10, and 15 C each season, were 17.7 C (pre-spawning), 11.9 C (post-spawning), 9.9 C (winter), and 16.3 C (spring). Seasonal influence on temperature selection was evident on the basis of differences in final preferenda, covariance analysis of responses of laboratory-acclimated fish, and temperature selection by fish held at ambient river temperatures. Post-spawning and winter groups selected lower temperatures than did pre-spawning and spring groups. Pre-spawnine fish selected temperatures unsuitable for embryo survival. Reproductive status as reflected by gonad size was evidently not a factor that influenced seasonal temperature selection of adult whitefish.

No description available.

L'exposition à des niveaux faibles de radiation ionisante est connue pour déclencher une réponse adaptative qui inclut la stimulation immunitaire et l'augmentation des effets protecteurs à long terme incluant l’amélioration de la détection et la réparation de dégâts causés à l’ADN, la croissance renforcée et la longévité. Tandis que les aspects hormetique de la réponse adaptative augmentent clairement la santé physique en présence de stress environnementaux, ils doivent la diminuer dans des conditions environnementales normales parce que les mécanismes biologiques responsables ne sont pas maintenus dans un état amélioré, mais exigent plutôt une certaine forme d'exposition sensibilisante. Il a été suggéré que la stimulation de la réponse adaptative pourrait être métaboliquement coûteuse cependant aucune mesure directe du coût métabolique de la croissance stimulée de radiation a été précédemment essayée. Cette thèse a évalué si la croissance stimulée de radiation du grand corégone (Coregonus clupeaformis) est accompagnée par un compromis dans l'efficacité métabolique ou par une augmentation durable de demandes énergiques. L'exposition à un régime fractionné de radiation ionisante d'une source de 137Cs s’est avéré stimuler considérablement la croissance dans des embryons du grand corégone comparés aux contrôles avec une augmentation correspondante de la consommation de jaune. Cependant, les mesures d'efficacité métabolique utilisant une série de temps de poids secs non préservés ont montré que la croissance stimulée était non-accompagnée par une réduction de l'efficacité métabolique. Une température moyenne exponentiellement transformée a été utilisée comme un point de référence quantitative pour évaluer la vulnérabilité du développement des embryons du grand corégone à la disparité phénologique. Le temps d’éclosion différait des prédictions de références sous des régimes thermiques asymétriquement variables. Les écarts ont été attribués aux embryons grandissant à dans un stade plus avancée de développement sous des températures basses. Le terme heterograde est proposé pour décrire la dépendance thermique dans l'étape d’éclosion qui peut avoir évolué comme un mécanisme pour synchroniser l’éclosion de larves viables pour l'augmentation de la densité de zooplancton qui accompagne le débâcle printanière Un modèle de prédiction incorporant l’éclosion heterograde a permis une amélioration significative dans l’exactitude des prédictions comparé aux modèles précédents. L'efficacité énergique a une importance particulière pour le grand corégone comme il a une des périodes d'incubation naturelles les plus longues pour un poisson d'eau douce, avec des températures d'incubation les plus basses et avec des œufs seulement 10 % de la taille de la plupart des salmonidés non-coregonine. L'évolution de mécanismes pour synchroniser l’éclosion au démantèlement de couverture de glace hivernale met en évidence la vulnérabilité du grand corégone à la disparité phénologique et ce par le développement accéléré qui cause l’éclosion asynchrone des embryons avec le démantèlement de la couverture de glace d'hiver ou par une augmentation durable de demandes énergiques qui augmentent leur vulnérabilité à la famine. L'absence de compromis mesurable dans l'efficacité métabolique indique ce dernier comme un coût général plausible de hormesis. / Exposure to low levels of ionizing radiation is known to trigger an adaptive response that includes immune stimulation and the up-regulation of long-lasting protective effects including improved detection and repair of DNA damage, enhanced growth, and longevity. While the hormetic aspects of the adaptive response clearly increase fitness in the presence of environmental stresses, they must decrease fitness under normal environmental conditions because the responsible biological mechanisms are not maintained in an upregulated state but rather require some form of sensitizing exposure. It has been suggested that stimulation of the adaptive response could be metabolically costly however no direct measurement of the metabolic cost of radiation stimulated growth has been previously attempted. This thesis assessed whether radiation-stimulated growth in the lake whitefish (Coregonus clupeaformis) is accompanied by a trade-off in metabolic efficiency, or by a sustained increase in energetic demands. Exposure to a fractionated regime of ionizing radiation from a 137Cs source was found to significantly stimulate growth in lake whitefish embryos compared to controls with a corresponding increase in yolk consumption. However, measurements of metabolic efficiency using a time series of unpreserved dry weights showed that the stimulated growth was unaccompanied by a reduction in metabolic efficiency. An exponentially transformed mean temperature was used as a quantitative baseline to assess the vulnerability of developing whitefish embryos to phenological mismatch. Hatch timing was found to deviate from baseline predictions under asymmetrically variable thermal regimes. The deviations were attributed to the embryos growing to a more advanced stage of development at low temperatures. The term heterograde is proposed to describe the thermal dependency of hatching stage which may have evolved as a mechanism to synchronize the hatching of viable larvae to the increase of zooplankton density that accompanies spring break-up. A predictive model incorporating heterograde hatching yielded a significant improvement in predictive accuracy over previous models. Energetic efficiency is of particular importance to the lake whitefish as it has one of the longest natural incubation periods of any freshwater fish, at some of the lowest incubation temperatures, and with eggs only 10% the size of most non-coregonine salmonids. The evolution of mechanisms to synchronize hatching to the break-up of winter ice cover highlights the vulnerability of the lake whitefish to phenological mismatch whether through accelerated development that causes embryos to hatch asynchronously with the break-up of winter ice cover, or through a sustained increase in energetic demands that increases their vulnerability to starvation. The absence of any measurable trade-off in metabolic efficiency points to the latter as a plausible general cost of hormesis. / Dissertation / Doctor of Philosophy (PhD)

Lake whitefish (Coregonus clupeaformis; LWF) are a cold-adapted freshwater species that are of both economic and cultural value. These fish spawn in lake areas where their embryos are exposed to thermal power plant effluents that may contain low levels of thermal, radiological and chemical stressors. Many studies on LWF embryonic development have looked at the individual effects of these stressors, but few have looked at the potential for combined effects. The combined effects of thermal and radiological stress were of interest due to growing evidence that mild thermal stress can produce an adaptive response, through the induction of the heat shock response (HSR), when followed with subsequent ionizing radiation stress. This thesis examined the combined impacts of thermal and radiological stress during LWF embryogenesis. LWF embryos were exposed to mild heat shocks (HS; Δ3 or 9°C) prior to a high dose of acute 137Cs gamma rays at 2, 6 and 24 hours post heat shock during the gastrulation or eyed stage. Heat shocked embryos were collected at each developmental stage and assessed for induction of heat shock protein (Hsp) genes. Following exposure, embryos were raised until hatch where mortality, morphometry, and embryo weight were measured. Mild HS induced Hsp70 mRNA expression at gastrulation, but not at the eyed stage. Embryos at hatch were not impacted by thermal or radiological exposure at the gastrulation stage. During the eyed stage, acute radiation treatment increased mortality and decreased body size at hatch. Mild HS prior to radiation did not provide protective effects and no adaptive response was observed. This thesis better defines the combined effects of thermal and radiological stress on the embryonic development of LWF. It also suggests that the ontogeny aspects of heat shock responses and radiosensitivity are important to consider for future adaptive response studies. / Thesis / Master of Science (MSc)