Thesis (Ph. D.)--University of Wisconsin--Madison, 1985. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

Recently, the growth and condition of Lake Whitefish (Coregonus clupeaformis), an important commercial fishery commodity, has declined in some areas of the Great Lakes. As Lake Whitefish are benthic feeders, historically the bulk of their diet was made up of the energy rich Diporeia hoyi, an amphipod whose abundances declined concurrently with reductions in Lake Whitefish growth and condition. Lake Whitefish populations from lakes Michigan, Erie and Superior have been used to determine whether there is a plausible link between the declines in Lake Whitefish condition and Diporeia abundance as indicated by stable isotope analysis, dietary and condition indices for Lake Whitefish. The first study was Lake Michigan specific and tested the hypothesis that condition, in terms of relative weight, percent lipid and docosahexaenoic acid (DHA), improved as the proportion of high quality prey (e.g., Diporeia) in the diet increased. Samples of spawning whitefish from four regions (northwest, Naubinway, Elk Rapids and southeast) around Lake Michigan had distinct mean carbon and nitrogen isotope signatures. The signatures indicated Lake Whitefish may be using a variety of prey items, especially the Naubinway population where fish occupy the largest isotopic niche space. Relative weight was significantly higher in the southeast and lower for all northern regions. The mean measured lipid from Lake Whitefish dorsal skinless muscle biopsies was highest for northwest region fish. DHA was significantly different among studied regions, with higher mean values in Elk Rapids and the northwest. No linear relationships between stable isotope measures and condition metrics were found. These results suggest that Lake Whitefish are coping with declining Diporeia abundances by feeding on alternate prey. Results do not substantiate the hypothesis of a relationship between condition and prey use, although Lake Whitefish from Elk Rapids and the northwest had high quality prey and good condition. The second study incorporated eight spawning populations around lakes Michigan, Erie and Superior to determine if there were differences in energy available to female Lake Whitefish. The hypotheses tested were three fold: (1) observed differences in growth and reproduction among populations were driven by energy availability, (2) populations with low energy reserves exhibit reproductive trade-offs and (3) high energy reserves are related to Diporeia consumption. Lake Whitefish from lakes Erie and Superior both displayed high growth and no trade-offs between egg size and number. Populations from Lake Michigan all had low investment in growth, significantly lower gonadosomatic index (GSI) and four of these populations displayed significant trade-offs between egg size and number. Growth and GSI tended to increase with mean total lipid stored in muscle and populations displaying reproductive trade-offs had significantly lower muscle lipid, however, these trends were not evident when using DHA as a measure of good nutrition. No relationship was evident between Diporeia consumption and populations with high muscle lipid stores. Overall, my results suggest that while changes in the availability of prey resources has had an effect on Lake Whitefish populations, the impact of declining abundances of Diporeia alone cannot explain the systemic changes in Lake Whitefish condition across the Great Lakes basin.

The ecological communities we observe today are a product of the bidirectional interactions between ecological and evolutionary processes. Although the effects of ecological processes on population divergence and speciation have been studied extensively, far less is known about the effects of divergence and speciation on ecological dynamics. This is especially true for effects of ecological speciation processes on higher trophic levels. In this thesis I focus on how divergence in the European whitefish (Coregonus lavaretus) affects a guild of six piscivorous bird species. Previous studies have indicated that population densities of these species are higher on lakes with polymorphic whitefish than on lakes with monomorphic whitefish. Here I test the hypothesis that the high densities of piscivores is a response to the rich food resource provided by dwarf whitefish ecotypes, which are of suitable size and occur in very high abundance.To test this hypothesis I analyzed fecal samples from piscivorous birds in lakes with polymorphic whitefish, using samples from lakes with monomorphic whitefish as controls. With the method of ddPCR (digital droplet Polymerase Chain Reaction) the amount of DNA from different prey fish species in the droppings of six fish-eating birds was quantified and converted to proportional abundances. The results shows that the proportion of whitefish in the diet of the entire fish-eating guild was significantly higher in lakes with polymorphic whitefish (44%) than in lakes with monomorphic whitefish (18%). Species-level analyses showed that this result also holds for both black-throated loon (Gavia artica) and red-throated loon (Gavia stellata). Common merganser (Mergus merganser), red-throated merganser (Mergus serrator) and terns (Sterna paradisaea and Sterna hirundo) did not show any difference between the two lake categories. Thus, my study supports the idea that the evolution of small-sized whitefish ecotypes provides a profitable food source for piscivorous birds. However, the finding that only some species of piscivorous bird populations seem to rely heavily on dwarfed whitefish as food suggests that also some other aspect of the speciation process may favor these species. Thus, more studies are needed to further assess what effects polymorphic whitefish have on piscivorous bird populations.

Top predators in aquatic ecosystems often have strong top-down effects on the ecosystem. Northern pike (Esox lucius) has been documented to cause whitefish (Coregonus lavaretus) populations to diverge into different ecomorphs. This can facilitate piscivory in other predators as a novel resource becomes available to them in the form of dwarf whitefish. The aim of this study is to examine whether the presence of pike causes Eurasian perch (Perca fluviatilis) to shift their diet from insectivory to piscivory, and whether this is directly driven by whitefish polymorphism. Stomach contents of 147 perch from lakes with and without pikes were analyzed. The results show that the presence of pike has a clear influence on the diet of the perch. In lakes without pike, perch are mostly insectivorous, and in lakes with pike, they are mostly piscivorous. This diet shift appears to be driven by whitefish availability, as a majority of the diet of perch in pike lakes consisted of whitefish, while none of the fish eaten by perch in non-pike lakes was whitefish. In addition, the results showed that perch undergo the diet shift from insectivory to piscivory at a smaller size when coexisting with pike. This study can be added to the growing body of evidence for the ecological significance of pike.

Conserving biodiversity is suggested to be one of the most important challenges being faced by the global community. The field of conservation biology has been developed to examine the threats that drive species to low abundance, the dynamics of species in low abundance and the methods to rebuild abundance. Typically, assessing these issues requires substantial data inputs; however we are often faced with situations where little information exists. In this thesis, I addressed several key conservation priorities in the endangered Atlantic Whitefish (Coregonus huntsmani), a data poor species, which has been restricted to one watershed for most of the past century. Using molecular genetic markers Atlantic Whitefish were determined to be a distinct and basal species within the genus. Population size was suggested to be low and the incidence of inbreeding high as genetic effective population size was among the lowest of any fish species examined and genetic diversity was 2-6 times lower than regional congeners. Through laboratory experiments environmental threats to the persistence of Atlantic Whitefish were examined. Overall, Atlantic Whitefish were tolerant to a broad range of environmental conditions and were capable of surviving in harsher environments than many other regional species. Furthermore, their persistence in current habitats will likely not be influenced by the assessed environmental conditions. As part of this work, a suite of methods and metrics to compare thermal sensitivity across a range of finfish species were assessed. In order to inform recovery efforts, I developed simulation models to evaluate habitat suitability for translocation of Atlantic Whitefish. As part of this work, I examined the role of incorporating variability in species response, environment and / or life history into simulations. The results showed that the inclusion of multiple sources of variability altered the perception of optimal habitats; however, several watersheds offered suitable translocation habitats. Throughout this thesis I explored novel tools to address some of the key issues facing conservation programs of data poor species. This work is not only applicable to the conservation of Atlantic Whitefish, but also outlines some of the potential tools useful in addressing conservation priorities in other species.

Bythotrephes longimanus is an invasive, macroinvertebrate from Eurasia that was introduced into the Great Lakes region in the mid 1980s. Bythotrephes introductions into lake ecosystems have resulted in substantial changes in zooplankton communities, including declines in species richness, abundance, biomass and production. Changes in zooplankton communities may alter the quantity and quality of prey to other predators such as cisco (Coregonus artedii), a pelagic forage fish. Here, I conduct a current day comparison of cisco populations to determine if prey consumption by cisco differs in the presence of Bythotrephes, and whether changes in diet result in energetic consequences (changes in growth and condition) for cisco. Effects of Bythotrephes on native zooplankton communities have resulted in substantial changes in the variety and proportion biomass of zooplankton and macroinvertebrate prey types in cisco stomachs, which have in turn modified growth of cisco. Cisco taken from invaded lakes achieve greater total lengths but changes in condition were not detected. This effect may be driven by improved growth in the second and subsequent growing seasons, suggesting that growth consequences for young fish (that do not feed on Bythotrephes) are different than for older individuals. Length-at-structure age data indicate that by the end of the first growing season (age 1) cisco achieve comparable total body lengths in invaded and reference lakes, suggesting that food consumption by young cisco remains unchanged by Bythotrephes. Alternatively, young cisco forage may be reduced in the presence of Bythotrephes, resulting in decreased survival and similar growth among individuals that survive to age 1. In contrast, despite changes in the zooplankton community; growth of older fish (≥ age 2) was enhanced in lakes that have Bythotrephes. Improved growth among older cisco (≥ age 2) in invaded lakes may be related to the presence of a newly attainable, high energy prey source (Bythotrephes). Alternatively, enhanced growth may be explained by lower competition due to reduced recruitment of young cisco (≤ age 1) in invaded lakes. Increased knowledge regarding the effects of Bythotrephes on growth of cisco is important in furthering our understanding of its impact on lake ecosystems. / Thesis (Master, Biology) -- Queen's University, 2010-04-28 22:46:07.756

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).

The origin and maintenance of much of natural biodiversity can likely be explained by theecological speciation theory. Ecological speciation is defined as the process whenreproductive isolation arises through divergent selection caused by ecological factors, such asbiotic interactions and abiotic conditions. Many populations of European whitefish(Coregonus lavaretus) are currently going through sympatric speciation from a single littoralecotype to two or more ecologically separate ecotypes. It has been hypothesized that northernpike (Esox lucius) is promoting speciation in whitefish by exposing it to a trade-off betweenpredation risk and resource availability causing an initial divergence in size eventuallyleading to two or more ecologically and genetically distinct ecotypes. After initial divergencesmall whitefish ecotypes often abandon ancestral spawning sites to spawn in streams or deepwater suggesting that the ecotypes are at least partially reproductively isolated. The driver ofthis reproductive isolation could be predation risk as pike mainly forage in the littoral. If thisis true, we would expect to find significantly higher predation risk for small whitefish at thelittoral spawning sites than on alternative spawning sites. To test this idea, hooks baited withsmall whitefish was placed at different spawning sites during the fall spawning season andchecked every 12 hour for 36 hours. Relative predation risk for small whitefish wassignificantly higher at the ancestral littoral spawning sites than at stream spawning sites. Inaddition, there was a significant decrease in predation risk later in the spawning season. Thisindicates that predation is promoting reproductive isolation in European whitefish byselecting against small individuals spawning at littoral spawning sites, but potentially also byselecting for delaying spawning in small individuals in the littoral. To fully understand thespeciation process in this system more studies must be done considering the complexity ofthe speciation process. Because of the lack of studies investigating predation as a cause ofbehavioral changes, that in turn promotes reproductive isolation, future studies should putmore emphasis on predation as a possible driver of reproductive isolation.

The spawning time differs between sympatric ecotypes of lake-dwelling whitefish (Coregonus lavaretus) and this temporal divergence can be linked to the type of spawning habitat used (i.e., streams, littoral or profundal). It has been hypothesized that the divergence in spawning time between spawning habitats is due to differences in incubation temperature regimes, and a need to synchronize hatching with the spring zooplankton bloom. An alternative hypothesis is that the hatching time of eggs is controlled by cues such as rising temperatures or increasing day length, and the divergence in spawning time occurs due to later maturation in colder habitats. To test these hypotheses, whitefish eggs were sampled on different spawning grounds and the median hatching time was estimated using logistic regression. Temperature logger data and information based on interviews and earlier studies were used to study accumulation of thermal energy during incubation in the form of degree-days. According to this thesis, the hypothesis that hatching time is dependent on rising temperatures and day length is supported, due to high variation in the amount of accumulated thermal energy, and little variation in hatching time. The egg sampling was not successful on profundal spawning grounds, nor on littoral spawning grounds of old populations, which made the results of this study weaker. Further studies are needed to fully confirm either of these hypotheses regarding spawning time of mature whitefish and hatching time of eggs. Sampling methods need to be advanced in order to enable egg sampling on all types of spawning grounds.

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)