Thesis (M.S.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 63-68). Also available via Humboldt Digital Scholar.

Endocrine disrupting compounds (EDC) are environmental contaminants that disrupt reproduction, development and behaviour in aquatic organisms. A thorough evaluation of the impacts of EDCs on aquatic organisms is currently limited by a lack of robust biomarkers in small model fish, particularly for assessing EDCs with (anti-)androgenic activity. Male sticklebacks build nests using spiggin, an androgen-responsive glycoprotein, which can be used to assess (anti-)androgenic exposure. EDC assessment in the field using threespine stickleback and the spiggin biomarker is limited to coastal and estuarine environments. However, their freshwater relative, brook stickleback (Culaea inconstans), also possess spiggin and their widespread distribution suggests that they may have applications as a bioindicator of EDCs in freshwater systems. Therefore, the overall objective of this thesis was to determine if brook stickleback are a suitable bioindicator species for EDCs by evaluating their response and sensitivity to estrogenic and (anti-)androgenic chemicals. Basal transcript levels of spiggin in kidney and vitellogenin in liver were first measured in wild-caught brook stickleback using qPCR and found to be differentially expressed in males and females. Brook stickleback were then exposed to two model compounds, 17α-ethinylestradiol (EE2) and 17α-methyltestosterone (MT), at 1, 10 and 100 ng/L for 21 days (sampled at 7 and 21 days) via static-renewal to determine the responsiveness of these transcripts to exogenous hormones. The effect of hormone exposure on condition factor, organosomatic indices and histopathology of kidneys was also measured. Exposure to MT and EE2 significantly induced spiggin and vitellogenin transcripts in female kidneys and male livers, respectively. Exposure to EE2 also significantly increased the hepatosomatic index in females after 7 days and in both sexes after 21 days whereas the gonadosomatic index was reduced in females after 21 days. An increase in kidney epithelium cell height was also observed in MT-exposed females and males after 7 days. These results mirror those of threespine stickleback and suggest that brook stickleback are responsive to androgenic and estrogenic chemical exposure and more specifically, possess quantifiable and sensitive biomarkers for exposure to compounds with androgenic activity. In a third experiment, female fish were co-exposed to MT at 500 ng/L and an anti-androgen (flutamide; FL) at 25, 150 and 250 µg/L for 14 days (sampled at 4 and 14 days) to validate this bioassay for the evaluation of anti-androgens using the same endpoints as in the previous two experiments. In females, exposure to MT increased spiggin transcript levels and nephrosomatic index (NSI) but co-exposure to FL did not result in a significant suppression of these endpoints because of high inter-individual variability. In males, exposure to MT increased NSI and co-exposure to FL resulted in a reduction in this endpoint, illustrating anti-androgenic effects. Although the response of brook stickleback to hormone exposure was endpoint-specific and was at times lower than other small model fish species, the ability to simultaneously assess estrogenic and (anti-)androgenic chemical exposure in a single fish using quantitative endpoints is an advantage exclusively held by members of the stickleback family. The results of this thesis suggest that brook stickleback hold promise as an additional small fish model for the evaluation of EDCs, with potential application in EDC biomonitoring in the freshwaters of North America.

Morphological, biochemical, and trophic evidence from other studies indicate that two populations of stickleback (Gasterosteus) co-exist in Enos Lake, Vancouver Island. One population is limnetic and the other is benthic (the names allude to their foraging behaviour and use of space). In this study, field observations, mate selection experiments, and courtship behaviour experiments were conducted to determine if the two stickleback populations are reproductively isolated. When breeding, limnetic males develop red throats whereas benthic males become uniformly black. In the field limnetic and benthic males nest in different habitats. Despite this difference, reproductive males and females of each population encountered each other, but in the few cases where courtship occurred, it never went beyond the initial stages of the lead-follow sequence. Apparently behavioural differences in courtship contributed to the break off of these natural courtships. In mate selection experiments, males and females of each population preferred mates from their own population. In the courtship experiments, behavioural differences between limnetics and benthics were found to be greatest in the early stages of courtship. With females from their own population, benthic males were more aggressive in their approach and leading sequences than limnetic males. In the beginning of the lead-follow phase, benthic females tend to position themselves above benthic males whereas limnetic females tend to position themselves alongside limnetic males. Male courtship behaviour was sometimes dependent on the phenotype of the female courted; benthic males bit and chased limnetic females whereas, limnetic males bit and led benthic females in a meandering path to the nest. Since the mate choice experiments indicated total positive assortative mating between limnetics and benthics, it is likely that the behavioural differences found in courtship behaviour contribute to reproductive isolation between the limnetic and benthic sticklebacks in Enos Lake. / Science, Faculty of / Zoology, Department of / Graduate

Behavioural asymmetry (laterality) is widespread among conspicuously bilaterally symmetrical organisms, playing a part in many aspects of life history from reproduction to feeding. Laterality is typically thought to occur due to morphological asymmetry within the brain, in which one hemisphere becomes specialized for a given task. However, the influence of sensory receptor asymmetry on the development of lateralized behaviour has undergone little investigation. The role of inconspicuous receptor asymmetry in behavioural laterality is particularly important, given the ubiquity of small deviations from symmetry. Here I have investigated morphological asymmetry in the lateral line, a series of mechanoreceptors called neuromasts that comprise one of the major sensory modalities of fishes. I examined a subset of the lateral line of 3,987 threespine stickleback from 64 populations from coastal British Columbia, characterizing neuromast count and asymmetry among habitats. Furthermore, I scored 657 stickleback from four experimental transplant populations relocated from stained lakes to unstained ponds, to determine whether or not neuromast count or asymmetry changes in a novel habitat. Neuromast count did not differ between oceanic and freshwater stickleback, or between sympatric lake-stream pairs but did differ among clarity regimes, ranging from a complete lack of neuromasts to a doubling of neuromasts compared to oceanic stickleback. Loss of neuromasts was associated with reduced light transmission, lower pH and a lack of piscivorous fishes. Stickleback with more lateral plates developed more neuromasts and males bore more neuromasts than females. One transplant pond underwent a 70% increase in neuromast count within just a couple of generations, whereas the other three transplant populations underwent more gradual change, suggesting both phenotypically plastic and genetic mechanisms underlying difference in neuromast counts among populations. Asymmetry was widespread among individuals, differing by up to seven neuromasts between the two sides on a single bony plate. However, no populations exhibited a strong directional bias. The degree of absolute asymmetry differed among clarity regimes, with stickleback in stained habitats having less asymmetry in their neuromasts counts. Asymmetry did not differ between oceanic and freshwater populations or sympatric lake-stream pairs. Males exhibited greater asymmetry than females, particularly in large-bodied populations. As with neuromast count, neuromast asymmetry quickly changed in some transplant populations and more gradually in others, increasing by up to 14% in just a couple of generations. To assess the functional consequences of my geographic survey, I experimentally tested 40 stickleback for their response to a simulated predator, localization of vibrations in the dark and rheotaxis. I compared behaviour and laterality to neuromast count and asymmetry measured by fluorescent microscopy. Stickleback with fewer neuromasts were more likely to respond to simulated predator strikes, but other non-lateralized behaviours were independent of neuromast count. The strongest laterality I observed was the ‘hugging’ of the arena wall with the right side 57% of the time, with laterality being present in other behaviours, albeit weakly. While some behaviours correlated with lateral line asymmetry, there was no consistent association between lateralized behaviour and asymmetry in the lateral line. I found that ecological factors such as predation landscape and photo-regime shape both mechanoreceptor count and asymmetry in the lateral line, with potential phenotypic plasticity in both traits. The lateral line’s role in response to a model predator and lateralized behaviour supports the influence of mechanosensory asymmetry in eco-evolutionary dynamics. / Graduate / 2022-05-05

Climate change is causing water temperature to rise, and many lakes in the boreal zone will experience browning of waters (brownification) due to increased input of dissolved organic carbon (DOC). In fish, warming may cause resource limitation and decrease both fish size and population abundance. Many fish species display ontogenetic niche shifts during their lifetime, shifting to larger prey as they grow. Brownification may change the timing for, the benefits from or prevent individuals from displaying ontogenetic niche shifts by decreasing large prey abundance in the benthic zone or making fast-moving prey harder to see. This can cause resource limitations, suppressing growth and population growth. This study investigated the effects of increasing DOC and water temperature on ontogenetic diet shifts, size structure, and population abundance in nine-spine stickleback (Pungitius pungitius) in an experimental pond system with a warming treatment and a gradient of DOC concentration. Warming had a negative effect on population number, biomass, maximum fish size, stomach fullness, and consumption of large prey. Contrary to expected outcomes, increasing DOC input resulted in higher population, biomass, and larger maximum sized fish as DOC increased. DOC did not negatively affect ontogenetic diet shifts. In the relatively shallow enclosures, the highest DOC concentration may not have reached the threshold where the shading effect of DOC overturns the benefits of extra nutrients associated with DOC. Hence, in shallow lake ecosystems, climate change induced DOC increase may support fish production, while warming may have strong negative effects on fish population abundance and size.

No description available.

I here explore the dual roles of gene flow in determining evolutionary and demographic processes in the Misty Lake threespine stickleback (Gasterosteus aculeatus L.). In the Misty watershed, the lake fish have streamlined bodies and numerous gill rakers whereas the inlet stream fish have deeper bodies and reduced number of gill rakers, differences that are adaptive for lake and stream environments respectively. The outlet stream population, however, is morphologically intermediate between the lake and inlet populations as a result of high gene flow from the lake preventing adaptation to the stream environment. First, I quantify the constraining effect of gene flow on adaptive divergence in the Misty outlet using two complementary approaches. By comparing phenotypic values and environmental differences between the three habitats (i.e. lake, inlet and outlet), I estimate that the constraint imposed by gene flow on phenotypic divergence is in the order of 80%, i.e. the outlet population only achieves 20% of the phenotypic divergence expected in the absence of gene flow. Parameterization of a quantitative genetic model confirms this value is possible given a biologically realistic range of parameter values. Second, I demonstrate that this constraint imposed by gene flow on adaptation likely contributes to an observed reduction in abundances along the outlet stream. I do so using a transplant experiment and a three-year selection experiment. Quantification of the amount of dispersal suggests that the negative influence of gene flow offsets the positive demographic influence of the immigration of individuals. In summary, gene flow has profound consequences for both evolutionary and demographic processes taking place in the Misty system.

The costal populations of perch (Perca fluviatilis) in some parts of the Baltic Sea have been in decline for about two decades. Recruitment failure in the early larval stages has been put forward as a possible cause and the decline has also been suggested to coincide with increases in three-pined stickleback (Gasterosteus aculeatus) densities. The aim of this study was to study the effects of growth and survival of newly hatched perch larvae in the presence of the three-pined stickleback, and if possible determine the main mechanism behind any negative effects the perch may suffer under such conditions. Using large scale experimental ponds as a controlled habitat, an experiment was conducted where perch larvae were being exposed to sticklebacks under four different stages of their development. Results showed that the three- spine stickleback can have a strong negative effect on the survival of young perch. This effect was strongest in the earliest stage of perch development and decreased as they grew bigger. The zooplankton densities didn't differ between the controls and stickleback treatments, suggesting that the young perch didn't suffer from food limitation. Instead predation was identified as the main mechanism behind the high mortality. The results of this study highlight the potential danger of the observed patterns of decreasing predator populations in conjunction with increasing populations of smaller prey species in the Baltic Sea.

acase@tulane.edu

In this thesis I have investigated the effects of invading top and intermediate consumers in a size-structured fish community, using a combination of field studies, a lake invasion experiment and smaller scale pond and aquaria experiments. The lake invasion experiment was based on introductions of an intermediate consumer, ninespine stickleback (Pungitius pungitius L.), in to allopatric populations of an omnivorous top predator, Arctic char (Salvelinus alpinus L.). The invasion experiment was performed in two tundra lakes and in two birch forest lakes to investigate the effect of climate on the invasion success. I found that the effect of sticklebacks on char was size dependent. Small char suffered reduced growth from resource competition with sticklebacks whereas the maximum size of adult char increased from the addition of a larger prey resource, stickleback. The negative effect of sticklebacks on the growth of small char suggests that sticklebacks may be a better resource competitor than char, which was also supported by the pond and aquaria experiments. The pond experiments also suggested that char were more efficient cannibals than interspecific predators on sticklebacks. Cannibalism in char may limit the recruitment of char and decrease both their predatory and competitive effect on coexisting species and thereby also promote the coexistence of char and sticklebacks. The successful invasion by sticklebacks and their subsequent increases in density suggest that the absence of sticklebacks in char lakes in this region is not caused by biotic interactions with char. Instead, it may be suggested that co-occurrence of sticklebacks and char in the region is limited by dispersal. The char – stickleback system resembles an intraguild predation system with char as the top consumer and stickleback as the intermediate consumer. The effects of the stickleback invasion is also contrasted with a field study of a northern pike (Esox lucius L.) invasion into a system with coexisting char and stickleback, where pike can be viewed as the top consumer and char as the intermediate consumer both feeding on sticklebacks. In this case pike excluded char. The identity of the invading species and the relative strength of the predatory and competitive interactions in the two contrasting systems are discussed in relation to coexistence in intraguild predation systems. I found that the identity of the invading species is of crucial importance for the response at the ecosystem level, and that the inherent size dependency of competitive and predatory interactions in fish communities is important for attaining a mechanistical understanding of the effects of invasive species in lake ecosystems.