Lake Stickleback Research Articles

Differential gene expression and developmental pathologies associated with persistent organic pollutants in sentinel fish in Troutman Lake, Sivuqaq, Alaska

Persistent organic pollutants (POPs) are lipophilic compounds that bioaccumulate in animals and biomagnify within food webs. Many POPs are endocrine disrupting compounds that impact vertebrate development. POPs accumulate in the Arctic via global distillation and thereby impact high trophic level vertebrates as well as people who live a subsistence lifestyle. The Arctic also contains thousands of point sources of pollution, such as formerly used defense (FUD) sites. Sivuqaq (St. Lawrence Island), Alaska was used by the U.S. military during the Cold War and FUD sites on the island remain point sources of POP contamination. We examined the effects of POP exposure on ninespine stickleback (Pungitius pungitius) collected from Troutman Lake in the village of Gambell as a model for human exposure and disease. During the Cold War, Troutman Lake was used as a dump site by the U.S. military. We found that PCB concentrations in stickleback exceeded the U.S. Environmental Protection Agency's guideline for unlimited consumption despite these fish being low trophic level organisms. We examined effects at three levels of biological organization: gene expression, endocrinology, and histomorphology. We found that ninespine stickleback from Troutman Lake exhibited suppressed gonadal development compared to threespine stickleback (Gasterosteus aculeatus) studied elsewhere. Troutman Lake stickleback also displayed two distinct hepatic phenotypes, one with lipid accumulation and one with glycogen-type vacuolation. We compared the transcriptomic profiles of these liver phenotypes using RNA sequencing and found significant upregulation of genes involved in ribosomal and metabolic pathways in the lipid accumulation group. Additionally, stickleback displaying liver lipid accumulation had significantly fewer thyroid follicles than the vacuolated phenotype. Our study and previous work highlight health concerns for people and wildlife due to pollution hotspots in the Arctic, and the need for health-protective remediation.

Fitness maps to a large-effect locus in introduced stickleback populations

Mutations of small effect underlie most adaptation to new environments, but beneficial variants with large fitness effects are expected to contribute under certain conditions. Genes and genomic regions having large effects on phenotypic differences between populations are known from numerous taxa, but fitness effect sizes have rarely been estimated. We mapped fitness over a generation in an F2 intercross between a marine and a lake stickleback population introduced to a freshwater pond. A quantitative trait locus map of the number of surviving offspring per F2 female detected a single, large-effect locus near Ectodysplasin (Eda), a gene having an ancient freshwater allele causing reduced bony armor and other changes. F2 females homozygous for the freshwater allele had twice the number of surviving offspring as homozygotes for the marine allele, producing a large selection coefficient, s = 0.50 ± 0.09 SE. Correspondingly, the frequency of the freshwater allele increased from 0.50 in F2 mothers to 0.58 in surviving offspring. We compare these results to allele frequency changes at the Eda gene in an Alaskan lake population colonized by marine stickleback in the 1980s. The frequency of the freshwater Eda allele rose steadily over multiple generations and reached 95% within 20 y, yielding a similar estimate of selection, s = 0.49 ± 0.05, but a different degree of dominance. These findings are consistent with other studies suggesting strong selection on this gene (and/or linked genes) in fresh water. Selection on ancient genetic variants carried by colonizing ancestors is likely to increase the prevalence of large-effect fitness variants in adaptive evolution.

Metabolic depression and the evolution of hypoxia tolerance in threespine stickleback, Gasterosteus aculeatus.

Anthropogenic increases in global temperature and agricultural runoff are increasing the prevalence of aquatic hypoxia throughout the world. We investigated the potential for a relatively rapid evolution of hypoxia tolerance using two isolated (for less than 11 000 years) populations of threespine stickleback: one from a lake that experiences long-term hypoxia (Alta Lake, British Columbia) and one from a lake that does not (Trout Lake, British Columbia). Loss-of-equilibrium (LOE) experiments revealed that the Alta Lake stickleback were significantly more tolerant of hypoxia than the Trout Lake stickleback, and calorimetry experiments revealed that the enhanced tolerance of Alta Lake stickleback may be associated with their ability to depress metabolic rate (as indicated by metabolic heat production) by 33% in hypoxia. The two populations showed little variation in their capacities for O2 extraction and anaerobic metabolism. These results reveal that intraspecific variation in hypoxia tolerance can develop over relatively short geological timescales, as can metabolic rate depression, a complex biochemical response that may be favoured in long-term hypoxic environments.

Going, going, gone: evidence for loss of an endemic species pair of threespine sticklebacks (Gasterosteus aculeatus) with implications for protection under species-at-risk legislation

Genomic extinction occurs when the unique combination of genetic traits that characterize distinct phenotypes are eliminated by introgressive hybridization even if population size is greater than zero. Benthic and limnetic threespine sticklebacks (Gasterosteus aculeatus) constitute reproductively isolated undescribed biological species that have evolved independently in several lakes in southwestern British Columbia, Canada (known as “species pairs” in each lake). Here we investigated whether the two species that comprise the pair from Enos Lake, southeastern Vancouver Island, remain as two distinct gene pools. Multi-season samples (>1200 fish) obtained over two years from throughout the lake and assayed for variation in morphological traits characteristic of the two species (i.e., body depth, dorsal spine count, gill raker counts) and at 12 microsatellite DNA loci consistently indicated the existence of only a single group of sticklebacks. There was no consistent evidence of two groups in any morphological trait, and mean gill raker counts were consistently intermediate (20–21) to those of known benthics (~18) and limnetics (~24) which together comprised strikingly bimodal distributions in historical samples. Genetic analyses employing model-based clustering also consistently indicated the presence of only a single genetic group of sticklebacks. Compared to historical samples and to benthics and limnetics from other lakes, no Enos Lake fish could be identified confidently as a pure benthic or limnetic. Our results provide the strongest evidence yet that the Enos Lake sticklebacks now consist of a single morphological and genetic population of sticklebacks, that the unique combination of genetic and morphological traits that characterized benthic and limnetic sticklebacks no longer exist, and that their current status under Canada’s Species-at Risk Act as Endangered should be re-evaluated.

Experimental evidence that parasites drive eco-evolutionary feedbacks

Host resistance to parasites is a rapidly evolving trait that can influence how hosts modify ecosystems. Eco-evolutionary feedbacks may develop if the ecosystem effects of host resistance influence selection on subsequent host generations. In a mesocosm experiment, using a recently diverged (<100 generations) pair of lake and stream three-spined sticklebacks, we tested how experimental exposure to a common fish parasite (Gyrodactylus spp.) affects interactions between hosts and their ecosystems in two environmental conditions (low and high nutrients). In both environments, we found that stream sticklebacks were more resistant to Gyrodactylus and had different gene expression profiles than lake sticklebacks. This differential infection led to contrasting effects of sticklebacks on a broad range of ecosystem properties, including zooplankton community structure and nutrient cycling. These ecosystem modifications affected the survival, body condition, and gene expression profiles of a subsequent fish generation. In particular, lake juvenile fish suffered increased mortality in ecosystems previously modified by lake adults, whereas stream fish showed decreased body condition in stream fish-modified ecosystems. Parasites reinforced selection against lake juveniles in lake fish-modified ecosystems, but only under oligotrophic conditions. Overall, our results highlight the overlapping timescales and the interplay of host-parasite and host-ecosystem interactions. We provide experimental evidence that parasites influence host-mediated effects on ecosystems and, thereby, change the likelihood and strength of eco-evolutionary feedbacks.

Meristic variation of the three-spined stickleback from a Small Like (Karelian Coast, White Sea)

Data on the variability of meristic characters in three-spined stickleback from Starushechije Lake (Karelian coast, the White Sea) were obtained. The lateral plate number in fishes from this freshwater population varied from 4 to 16 with mean value (±SE) 8.7±0.37. Caudal set of plates forming a keel was detected in 96% of analyzed specimens. This phenotype of stickleback (low plated with a keel) was observed in the northeastern part of the European range for the first time. The three-spined stickleback from Starushechije Lake differed significantly by the fin rays numbers from the low plated sticklebacks inhabiting Lobanezhskoe and Svyatoe lakes (Velikiy Island, Kandalaksha Bay, White Sea) and by vertebrae number from Svyatoe Lake stickleback.

Differences in susceptibility and immune responses of three-spined sticklebacks (Gasterosteus aculeatus) from lake and river ecotypes to sequential infections with the eye fluke Diplostomum pseudospathaceum.

BackgroundThe eye fluke Diplostomum pseudospathaceum is a frequent parasite of many fresh-water fish species, among those three-spined sticklebacks, particularly in lakes with lymnaeid snails, its first intermediate hosts. Cercariae released from host-snails, penetrate the skin of their fish hosts and within 24 h migrate to the immunologically inert eye lenses. Thus, individual D. pseudospathaceum are exposed to the fish immune system only for a short time, suggesting that only innate immunity can be active against the parasite. However, in nature sticklebacks are exposed to D. pseudospathaceum repeatedly since snails are shedding cercariae from late spring to autumn. Therefore, acquired immunity after initial infection would be advantageous against subsequent parasite encounters.MethodsWe investigated if sticklebacks originating from a lake with high and from a river with low prevalence of D. pseudospathaceum differ in susceptibility to repeated exposure to the parasite. We compared infection success and immune functions in laboratory-bred sticklebacks from both habitats in naïve fish with fish that had been pre-exposed to eye flukes. Head kidney leukocytes (HKL) from experimental sticklebacks were investigated for respiratory burst activity and the proliferation of lymphocytes and monocytes 1.5, 5 and 15 days after infection.ResultsLake sticklebacks were less susceptible than river sticklebacks, however, in both populations pre-exposure led to a similar relative reduction in infection success. The respiratory burst activity was higher with HKL from lake sticklebacks and was up-regulated in pre-exposed fish but dropped 1.5d after an additional exposure, suggesting that activation of phagocytic cells is crucial for the defense against D. pseudospathaceum. Changes in lymphocyte proliferation were only detectable 1.5d after the last exposure in lake sticklebacks, but not 5 and 15d post exposure, indicating that a lymphocyte mediated acquired immune response was not induced. Proliferation of monocytes was significantly increased 1.5d after the last exposure with HKL from both stickleback populations.ConclusionsIncreased resistance to D. pseudospathaceum in sticklebacks from both populations upon pre-exposure cannot be explained by a prominent adaptive immune response. Monocytic leukocytes were more responsive, suggesting that rather cells of the innate than the adaptive immune system are active in the defense of D. pseudospathaceum.

Shifts in morphology and diet of non‐native sticklebacks introduced into Japanese crater lakes

An increasing number of exotic animals are causing ecological problems. Therefore, for better ecosystem management, it is important to understand how exotic species colonize and adapt to novel environments. The threespine sticklebacks (Gasterosteus aculeatus) can be a good vertebrate model system to explore the ecological and genetic mechanisms of adaptation not only in natural populations, but also in non-native populations. Although morphological changes have been documented in several introduced populations of stickleback, little is known about the dietary changes during colonization into novel environments. Here, we investigated the morphological and dietary changes of exotic threespine stickleback populations introduced into three Japanese crater lakes (Lake Towada, Lake Kussharo, and Lake Shikotsu). Sticklebacks were introduced into the crater lakes likely along with salmonids transplanted for aquaculture. The stickleback population in Lake Kussharo had multiple mitochondrial haplotypes and had larger phenotypic variances than other crater lake stickleback populations that had only one mitochondrial haplotype. Compilation of historical data on the morphology and stomach contents of the Lake Towada stickleback population showed that substantial shifts in body size and stomach contents occurred after colonization. Some of these changes may be related to an outbreak of the Schistocephalus parasite. These results suggest that sticklebacks can change their morphology and trophic ecology when they colonize novel environments. Therefore, extreme care should be taken when salmonids are transported between watersheds for aquaculture and that long-term monitoring of exotic species is essential for ecosystem management. In addition, further genetic studies on phenotypic changes in crater lake sticklebacks would help elucidate the genetic mechanisms underlying the adaptation of exotic fishes to novel environments.

Divergent Selection and Then What Not: The Conundrum of Missing Reproductive Isolation in Misty Lake and Stream Stickleback

In ecological speciation, reproductive isolation evolves as a consequence of adaptation to different selective environments. A frequent contributor to this process is the evolution of positive assortative mate choice between ecotypes. We tested this expectation for lake and inlet stream threespine stickleback (Gasterosteus aculeatus) from the Misty system (Vancouver Island, Canada), which show strong genetically based adaptive divergence and little genetic exchange in nature. This, and work on other stickleback systems, led us to expect positive assortative mating. Yet, our standard “no-choice” laboratory experiment on common-garden fish revealed no evidence for this—despite divergence in traits typically mediating assortative mating in stickleback. These results remind us that divergent natural selection may not inevitably lead to the evolution of positive assortative mate choice. The apparent lack of strong and symmetric reproductive barriers in this system presents a conundrum: why are such barriers not evident despite strong adaptive divergence and low gene flow in nature?

Reflectance characteristics are correlated with male condition in a population of threespine stickleback (Gasterosteus aculeatus) that has lost the species typical nuptial signal

Several populations of threespine stickleback (Gasterosteus aculeatus) on the Pacific Coast of North America remain drab during courtship and become melanic during parental care rather than adopt the species typical red signal. Male signal redness is an honest signal of male physiological condition. Here, I test the prediction that reflectance characteristics of drab males also honestly indicate male condition. I located, observed and captured nesting stickleback from Brannen Lake, British Columbia, Canada. I measured reflectance characteristics of each male’s signal right after capture and later measured its wet weight and total length to calculate Fulton’s condition index, K. Males in better condition, higher K, had lower total reflectance (i.e. were darker) than males in poorer condition. The principals underlying honest signaling appear to be operating despite the possession of a novel nuptial signal in Brannen Lake stickleback.

Genetic divergence in morphology-performance mapping between Misty Lake and inlet stickleback

Different environments should select for different aspects of organismal performance, which should lead to correlated divergence in morphological traits that influence performance. The result should be genetic divergence in aspects of performance, morphology and associations ('maps') between morphology and performance. Testing this hypothesis requires quantifying performance and morphology in multiple populations after controlling for environmental differences, but this is rarely attempted. We used a common-garden experiment to examine morphology and several aspects of swimming performance within and between the lake and inlet populations of threespine stickleback (Gasterosteus aculeatus) from the Misty system, Vancouver Island, Canada. Controlling for body size, lake stickleback had shallower bodies, larger caudal fins and smaller pelvic girdles. With or without morphological covariates, lake stickleback showed greater performance in both sustained and burst swimming. In contrast, inlet stickleback showed greater manoeuverability than did lake stickleback in some analyses. Morphology-performance relationships were decoupled when considering variation within vs. between populations. Moreover, morphology-performance mapping differed between the two populations. Based on these observations, we advance a hypothesis for why populations adapting to different environments should show adaptive genetic divergence in morphology-performance mapping.

Habitat-specific adaptation of immune responses of stickleback (Gasterosteus aculeatus) lake and river ecotypes

Freshwater populations of three-spined sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of stickleback ecotypes. Here, naive laboratory-bred sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River sticklebacks in the lake had higher parasite loads than lake sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river sticklebacks exposed to lake when compared with river conditions. Although river sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake sticklebacks in their native habitat. River sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.

Comparison of the fast-start performances of closely related, morphologically distinct threespine sticklebacks (Gasterosteus spp.)

Fast-start escape performances for two species of threespine stickleback, Gasterosteus spp., were investigated using high-speed cinematography (400 Hz). The two fishes (not yet formally described, referred to here as benthic and limnetic) inhabit different niches within Paxton Lake, British Columbia, Canada, and are recent, morphologically distinct species. All escape responses observed for both species were double-bend C-type fast-starts. There were no significant differences between the species for any linear or angular parameter (pooled averages, both species: duration 0.048 s, distance 0.033 m, maximum velocity 1.10 m s-1, maximum acceleration 137 m s-2, maximum horizontal angular velocity 473.6 rad s-1 and maximum overall angular velocity 511.1 rad s-1). Benthics and limnetics have the greatest added mass (Ma) at 0.3 and 0.6 body lengths, respectively. The maximum Ma does not include the fins for benthics, but for limnetics the dorsal and anal fins contribute greatly to the maximum Ma. The deep, posteriorly placed fins of limnetics enable them to have a fast-start performance equivalent to that of the deeper-bodied benthics. Both the limnetic and benthic fishes have significantly higher escape fast-start velocities than their ancestral form, the anadromous threespine stickleback Gasterosteus aculeatus, suggesting that the high performance of the Paxton Lake sticklebacks is an evolutionarily derived trait. In this biomechanical study of functional morphology, we demonstrate that similar high fast-start performance can be achieved by different suites of morphological characteristics and suggest that predation might be the selective force for the high escape performance in these two fishes.

Egg cannibalism and the reproductive strategies of threespine sticklebacks (Gasterosteus aculeatus) in a coastal British Columbia lake

Patterns of egg eating and their association with differences in sex, size, abundance, and reproductive status of free-ranging sticklebacks from Kennedy Lake, British Columbia, were examined as a means of identifying the relative importance of filial cannibalism or heterocannibalism as the source of eggs in the diet. Egg cannibalism was a common event: 23.0 and 11.2% of the sticklebacks examined in 1982 and 1985, respectively, had engaged in egg eating. Eggs were a substantial part of the overall diet of the stickleback population during two breeding seasons: 27.4% of the diet of all fish by weight in 1982, 32.8% of the diet by volume in 1985. Our results do not support Rohwer's contention that filial cannibalism is the source of most eggs in stickleback diets. Ten out of 11 predictions based on the filial cannibalism hypothesis were rejected, whereas the 11th was compatible with either the filial cannibalism hypothesis or the alternative heterocannibalism hypothesis. We conclude that heterocannibalism, not filial cannibalism, is the major source of eggs in the diet of Kennedy Lake sticklebacks. We suggest that nest raiding and egg cannibalism may minimize time spent foraging and maximize time spent on activities that increase the probability of initiating and successfully completing one or more reproductive cycles. Although the benefits of nest raiding and cannibalism are most obvious for populations breeding under conditions where food supplies clearly limit their potential reproductive output, the benefits may still apply even under conditions where alternative prey sources appear to be abundant.

Some effects of the cestode (Schistocephalus solidus) on reproduction in the threespine stickleback (Gasterosteus aculeatus): evolutionary aspects of a host–parasite interaction

Monthly samples of threespine stickleback (Gasterosteus aculeatus) were collected from May through September 1975 from Fuller Lake, Vancouver Island. A total of 2175 adult sticklebacks were collected from 10 trap sites located at depths ranging from 0.25 to 5 m. These samples were assayed for length, weight, sex, state of maturity, and egg number (when applicable). In addition, we recorded the number and weight of the plerocercoids of a cestode tapeworm (Schistocephalus solidus) often found in the abdominal cavities of sticklebacks. The purpose of the study was to document the effects of Schistocephalus on reproduction in Gasterosteus. Stickleback spawning reached a peak in June and declined sharply through July and August. Over the entire breeding season, less than 5% of the gravid females were infected with Schistocephalus, whereas over 40% of the sexually mature but nongravid females were infected. There was no difference between breeding and nonbreeding males in the prevalence of Schistocephalus. In both sexes, the prevalence and severity of Schistocephalus infection were low in May, June, and July but increased sharply through August and September. Since the majority of Fuller Lake sticklebacks live for 1 year, the major adverse effects of Schistocephalus were confined to postreproductive adults. We hypothesize that Schistocephalus plerocercoids have been selected to delay adverse effects on their host until after the host has reproduced.