Extinction of a weakly armoured threespine stickleback (Gasterosteus aculeatus) population in Prator Lake, Alaska

Abstract –  Threespine stickleback ( Gasterosteus aculeatus ) samples from Prator Lake in southcentral Alaska consist of the relatively rare form of weakly armoured individuals with few lateral plates and no pelvic spines. Prator Lake has been sampled for threespine stickleback since 1983. Exotic northern pike ( Esox lucius ) were first observed in this lake in 1996. The appearance of pike corresponds with a dramatic decrease in stickleback numbers and apparent local extinction. The stickleback population may have been vulnerable to an exotic predator because Prator Lake lacks native piscivorous fishes, and this population had extreme armour reduction.     

Feeding ecology and habitat of the threespine stickleback, Gasterosteus aculeatus microcephalus, in a remnant population of northwestern Baja California, México

Abstract – The feeding ecology and habitat of the threespine stickleback ( Gasterosteus aculeatus microcephalus Girard, 1854) was studied from November 1996 to May 1997 in a remnant population of northwestern Baja California, México. The analysis of the stomach content of 179 individuals (25 to 56 mm standard length [SL]) showed a diet dominated by cyclopoid copepods (43.8%) and chironomid larvae (39.1%). Diet in relation to size and sex of the fish was dominated by copepods in autumn and winter and by chironomid larvae during spring. Diet overlap (Schoener's index) was significant (≥60%) between fish size-classes in January, March and April and between sexes for most sampling months. The average size of prey consumed was independent of fish mouth size. The feeding strategy of the threespine stickleback shifted from opportunist in winter to specialist in spring.     

Over-wintering growth and losses in a small population of the threespine stickleback, Gasterosteus aculeatus (L.), in mid-Wales

Abstract –  Mark-recapture was used to estimate the population abundance of threespine stickleback, Gasterosteus aculeatus , in a backwater of Afon Rheidol in mid-Wales in autumn and early spring, from 1984 to 1998. For the 0+ cohort, there was no evidence of density-dependent losses (mortality and emigration) or growth in the over-wintering period. No systematic size-dependent loss was detected. There was an inverse relationship between autumn abundance and the annual rate of change in abundance of the 0+ cohort.     

The interaction among age,thermal acclimation and growth rate in determining muscle metabolic capacities and tissue masses in the threespine stickleback,Gasterosteus aculeatus

Thermal acclimation may directly modify muscle metabolic capacities, or may modify them indirectly via effects upon physiological processes such as growth, reproduction or senescence. To evaluate these interacting effects, we examined the influence of thermal acclimation and acclimatization upon muscle metabolic capacities and tissue masses in 1 + stickleback, Gasterosteus aculeatus, in which confounding interactions between temperature and senescense should be absent. Furthermore, we examined the influence of thermal acclimation upon individual growth rate, muscle enzyme levels and tissue masses in 2 + stickleback sampled at the beginning of their final reproductive season. For 1 + stickleback, cold acclimation more than doubles mitochondrial enzyme levels in the axial muscle. Thermal acclimation did not change the condition of 1 + stickleback at feeding levels which could not maintain the condition of 2+ stickleback. Compensatory metabolic responses to temperature were not apparent in field acclimatized 1 + stickleback. The growth rate of 2 + stickleback was markedly affected by temperature: warm-acclimated fish generally lost mass even at very high levels of feeding (up to 78 enchytraid worms per day) while cold-acclimated fish gained mass. This suggests that warm temperatures accelerate the senescence of 2 + stickleback. Generally, muscle enzyme activities increased with growth rate. In axial muscle, the relationships between CS activity and growth rate differed with acclimation temperature. Independent of the influence of growth rate, CS activities were consistently higher in cold- than warm-acclimated 2 + stickleback, suggesting compensatory increases of CS activity with cold acclimation. Corresponding author; This paper is dedicated to the memory of Gerry J. FitzGerald who passed away on March 14, 1994.     

Dynamics of extinction of a small population of the three‐spined stickleback (Gasterosteus aculeatus L) caused by habitat modification

• 1. Abundance of a population of three‐spined stickleback, Gasterosteus aculeatus L., in a small backwater of Afon Rheidol in mid‐Wales (UK) was estimated annually each October from 1972 to 1999 by mark–recapture.
• 2. The population became extinct in 2000, because of land‐use changes in 1995, which modified the drainage pattern through the backwater, causing the backwater to eventually dry up.
• 3. The final decline to extinction started from an estimated abundance of 1550 in 1998 and the abundance in 1999, the year before extinction, was 85. The smallest abundance from which the population showed an increase was 670.
• 4. Two years before extinction (1998), the population was characterized by an anomalously high proportion of small fish.
• 5. There was a significant power relationship between the years to extinction and population size, but if the data were analysed in two periods, 1972–1989 and 1990–1999, the relationship was only significant for the second period.
• 6. There was no relationship between time to extinction and per capita annual rate of increase (k), although values of k were unusually low in the last two years before extinction.
• 7. Time to extinction was not related to mean length, mean mass or the condition of the fish.
• 8. The results suggest that the indicators of impending extinction may vary with the causes of extinction and may be ambiguous, even when a long time‐series of demographic data is available. Copyright © 2010 John Wiley & Sons, Ltd.

     

Variation in rates of food consumption and evidence for compensatory responses in the three-spined stickleback, Gasterosteus aculeatus L. in relation to growth and reproduction

Abstract – Evidence that rates of food consumption differ between individuals in a population is noted. Preliminary estimates of individual variation in a population of three-spined sticklebacks ( Gasterosteus aculeatus L.) are provided and compared with similar estimates for a population of Phoxinus . Experimental studies are reviewed to demonstrate the capacity of sticklebacks to compensate for variations in food availability by compensatory changes in food consumption. These changes allowed sticklebacks on fluctuating rations to maintain growth and reproductive performances comparable to sticklebacks receiving constant, daily rations. Such studies start to define the scope for compensation that buffers the effect of environmental variability in food supply. ^NOTE     

Food resource partitioning of Arctic charr, Salvelinus alpinus (L.) and three-spined stickleback, Gasterosteus aculeatus L., in the littoral zone of lake Takvatn in northern Norway

The food resource partitioning of Arctic charr (Salvelinus alpinus L.) and three-spined stickleback (Gasterosteus aculeatus L.) were investigated in the littoral zone of lake Takvatn in northern Norway in the ice-free period June–November. Charr and sticklebacks had different feeding habits. Sticklebacks ate several small benthic prey items that were never eaten by charr, and the sticklebacks' diet were dominated by the benthic microcrustaceans Chydoridae and Ostracoda, chironomid larvae and stickleback eggs. Small charr (<17 cm) consumed a wide spectrum of chironomid pupae, terrestrial insects and zooplankton. Intermediate (17–20 cm) and small charr had quite similar feeding habits, while large charr (>20 cm) frequently ate both benthos, pelagic and terrestrial food. The diet overlap between small charr and sticklebacks was never larger than 0.6 (Schoener's index). The segregation in feeding habits indicates that small charr and sticklebacks are segregated in microhabitat when they are both in the littoral zone.     

Reproductive costs, condition and carotenoid-based colour in natural populations of threespine stickleback (Gasterosteus aculeatus)

Abstract –  Male threespine stickleback, Gasterosteus aculeatus , display an orange/red throat during the breeding season, which is carotenoid-based colour. We examined the relationship between energy-based costs of reproduction and colour in three lacustrine populations of threespine stickleback: two benthic (Willow and Big Beaver) and one limnetic (Lynne) ecotypes. In two lakes (Willow and Big Beaver) where benthic males defend nests against cannibalistic groups, males paid higher energy costs than in the third lake (Lynne) where cannibalistic groups are absent. We then examined colour variation within each population. Males from Lynne Lake did not change colour during the parental stage, whereas males from Willow and Big Beaver lakes became more intensely coloured. In addition, colour was typically independent of condition within stages. We propose that energy-based reproductive costs could explain some of the observed variation in colour by altering the payoffs associated with signalling effort during current versus future reproduction.     

Specific binding of 11-ketotestosterone in an androgen target organ,the kidney of the male three-spined stickleback,Gasterosteus aculeatus

The kidney of male three-spined stickleback,Gasterosteus aculeatus, hypertrophies during the breeding season and produces a glue which is used in the building of the nest. This hypertrophy is androgen dependent, with 11-ketotestosterone (11KT) being more effective than other tested steroids in stimulating this secondary sexual character. In the present study kidneys were excised from stickleback males that had been castrated two days earlier. The purpose of this gonadectomy was to reduce the endogenous levels of androgens without allowing time for the kidney to regress. Tissue fragments were incubated with tritiated 11KT with and without unlabelled steroids at increasing concentrations. Displaceable specific 11KT binding was found in kidney tissue fragments whereas only non-specific binding was observed when liver and muscle were investigated in a similar way. Unlabelled 11KT displaced specifically bound, tritiated 11KT with an ED50-value (50% of displaceable binding) of 28 nM. Similar ED50 values were found for 17\-hydroxy-5-androstane-3,11-dione (29 nM) and 5-dihydrotestosterone (20 nM), whereas higher ED50 concentrations were estimated for testosterone (T; 203 nM) and progesterone (69 nM). No displacement of tritiated 11KT was found for the other investigated substances tested; estradiol, 17,20-dihydroxy-4-pregnen-3-one, flutamide or cyproterone acetate. No specific binding to kidney tissue fragments could be detected when labelled T was used instead of labelled 11KT. Specific binding of 11KT or T was not found either in the kidney cytosol or nuclear extracts. However, using the kidney membrane fraction a displacement of tritiated 11KT with unlabelled 11KT (10^–6M) was observed. In conclusion there is a specific binding of 11KT in the stickleback kidney. The absence of binding in liver and muscle, the ED50 value observed and the displacement with some, but not all steroids are consistent with a receptor function. The presence of binding in membrane fractions, but not in cytosol or nuclear extracts suggests that the binding is not related to classic steroid receptors.     

Intra‐population variability of life‐history traits and growth during range expansion of the invasive round goby,Neogobius melanostomus

Abstract Fish can undergo changes in their life‐history traits that correspond with local demographic conditions. Under range expansion, a population of non‐native fish might then be expected to exhibit a suite of life‐history traits that differ between the edge and the centre of the population’s geographic range. To test this hypothesis, life‐history traits of an expanding population of round goby, Neogobius melanostomus (Pallas), in early and newly established sites in the Trent River (Ontario, Canada) were compared in 2007 and 2008. Round goby in the area of first introduction exhibited a significant decrease in age at maturity, increased length at age 1 and they increased in GSI from 2007 to 2008. While individuals at the edges of the range exhibited traits that promote population growth under low intraspecific density, yearly variability in life‐history traits suggests that additional processes such as declining density and fluctuating food availability are influencing the reproductive strategy and growth of round goby during an invasion.     

Tissue reaction of the three-spined stickleback Gasterosteus aculeatus L. to infection with Glugea anomala (Moniez, 1887)

Abstract. Studies on an experimental infection of the stickleback (Gasterosteus aculeatus L.) with the microsporidian Glugea anomala conducted until day 126 post infection confirmed that xenoparasitic formations typical of the intracellular development of this microsporidian were responsible for a marked tissue reaction in the host. After a single oral infection, xenoparasitic formations developed in the subepithelial connective tissue of the glandular part of the stomach. The course of xenoma development was asynchronous. Up to the 'cyst' stage (xenomas filled with mature spores), their growth and development caused a pressure atrophy in the surrounding tissue. Later, the response to the presence of the xenoparasitic formation was the development of a granulomatous inflammatory reaction. Locally, the host responded to the infection by phagocytosis of mature spores by locally derived macrophages. In massive infections, changes occurred in the subepithelial connective tissue of the glandular part of the stomach (often the complete disappearance of tubular glands), which may result in a permanent influence on the function of this organ.     

Diet-induced phenotypic plasticity of feeding morphology in the orangespotted sunfish, Lepomis humilis

Abstract – Generalist fish species often exhibit two or more recognizable morphotypes specialized to exploit a particular habitat and niche. Divergent benthic and pelagic morphs of sunfish of the North American sunfish genus Lepomis have been found in some populations. The proximate cause of this phenomenon is not known. It could be differential survival and habitat segregation among different morphs produced by different genotypes within a species or it could be a phenotypically plastic response to environmental influences such as diet. I tested the hypothesis that variation in feeding morphology (body shape, gill raker and pharyngeal jaw morphology) in the orangespotted sunfish, Lepomis humilis occurs in response to diet. Fish were collected as young-of-the-year and were reared in individual aquaria and fed three differing arthropod diets. According to a multivariate analysis of covariance on principal components derived from body truss, gill raker and pharyngeal jaw measurements, diet significantly affected morphology. Fish that fed on a diet of mealworms developed a significantly more blunt snout based on a least squares means estimation of component values.     

Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

Abstract – Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life‐history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life‐history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3–5 sea‐winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life‐history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life‐history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world‐wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near‐shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near‐shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour.     

Migration and life history alternatives in a high latitude species, the broad whitefish, Coregonus nasus Pallas

Abstract – We examined the expected changes in the life history trajectory of an Arctic species, broad whitefish, in the lower Mackenzie River between an anadromous population with spawning migrations of 350–450 km and a potamodromous population with spawning migrations of 5–12 km. Based on life history theory we predicted that the anadromous population would have faster growth, later age-at-maturity, and greater reproductive investment than the potamodromous population. Early in its life the anadromous population had faster growth than the potamodromous but later growth was slower. Age-at-maturity was greater in the anadromous population than the potamodromous. Reproductive investment was higher in the anadromous population. We conclude that the broad whitefish did not conclusively follow the pattern of variation observed between migratory and relatively sedentary populations in temperate zones. Fecundity was greater in the migratory population but not conclusively linked to age-at-maturity or growth-rate differences.     

Population size in stream-living juveniles of lake-migratory brown trout Salmo trutta L.: the importance of stream discharge and temperature

Abstract –  Based on the analysis of 17 successive year-classes, this investigation attempted to identify the factors determining year-to-year variation in population size of the stream-living juveniles of Lake Hald-dwelling brown trout Salmo trutta L. Population size appeared to be influenced chiefly by annual recruitment that in turn, was determined by stream discharge and temperature. These patterns matched those previously highlighted for a resident population located >2500 km apart and emphasised the importance of environmental (climatic) variability as a major regulating agent of population size in stream brown trout. However, distinctly shaped recruitment–discharge relationships between the two populations suggested different mechanisms in response to environmental variability and thus to persist in time.     

Searching for sensitivity in the life history of Atlantic menhaden: inferences from a matrix model

We used modified Leslie matrix models to explore the life history of Atlantic menhaden ( Brevoortia tyrannus ). By examining the sensitivity of long-term population growth rates to changes in vital rates, we identified those life history components which can cause large population level responses. Our models subdivide the first year of life into five stages (eggs, early larvae, late larvae, juveniles, and 'peanuts' or subadults), and population growth rate responds most strongly to changes in juvenile and late larval stages. The relative ranking between these stages is dependent on the magnitude of mortality during the prejuvenile stages relative to juvenile mortality. An examination of low-level model parameters indicates that the population growth rate is influenced by the growth and mortality rates during the time when young-of-the-year menhaden are gaining access to and residing in the estuaries. Sensitivity to changes in many adult metrics, such as fishing mortality, were relatively low. We conclude that a better understanding of biotic and abiotic factors that influence the late larval and juvenile stages will further our understanding of population dynamics in this species.     

Effects of hemi-castration on plasma steroid levels in two teleost fishes; the three-spined stickleback, Gasterosteus aculeatus, and the Atlantic salmon, Salmo salar

In order to study the possible homeostatic regulation of gonadal steroids in fishes, plasma steroid levels were measured in hemi-castrated and sham-operated nesting male three-spined sticklebacks, Gasterosteus aculeatus, and in mature 2-year old male Atlantic salmon, Salmo salar. Hemi-castration significantly suppressed androgen levels in both species. In sticklebacks, plasma levels of 11-ketotestosterone (11KT) were 56% and levels of testosterone (T) 55% of those found in sham-operated males. In hemi-castrated salmon the levels of 11KT were 63%, and the levels of T were 75% of the levels in sham-operated males. In contrast, levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P) in salmon (not measured in sticklebacks) were not different between hemi-castrated and sham-operated males. The results suggest that, although levels of the steroid 17,20-P were compensated in hemi-castrated salmon, the androgen levels in fish males in full spawning condition are not closely regulated by negative feedbacks. This revised version was published online in July 2006 with corrections to the Cover Date.     

Life‐history differences of juvenile Chinook salmon Oncorhynchus tshawytscha across rearing locations in the Shasta River,California

Salmon from different locations in a watershed can have different life histories. It is often unclear to what extent this variation is a response to the current environmental conditions an individual experiences as opposed to local‐scale genetic adaptation or the environment experienced early in development. We used a mark–recapture transplant experiment in the Shasta River, CA, to test whether life‐history traits of juvenile Chinook salmon Oncorhynchus tshawytscha varied among locations, and whether individuals could adopt a new life history upon encountering new habitat type. The Shasta River, a Klamath River tributary, has two Chinook salmon spawning and juvenile rearing areas, a lower basin canyon (river km 0–12) and upper basin spring complex (river km 40–56), characterised by dramatically different in‐stream habitats. In 2012 and 2013, we created three experimental groups: (i) fish caught, tagged and released in the upper basin; (ii) fish caught at the river mouth (confluence with the Klamath River, river km 0), tagged and released in the upper basin; and (iii) fish caught at the river mouth, tagged and released in the lower basin. Fish released in the upper basin outmigrated later and at a larger size than those released in the lower basin. The traits of fish transplanted to the upper basin were similar to fish originating in the upper basin. Chinook salmon juvenile life‐history traits reflected habitat conditions fish experienced rather than those where they originated, indicating that habitat modification or transportation to new habitats can rapidly alter the life‐history composition of populations.     

The Three‐spined Stickleback,Gasterosteus aculeatus Linnaeus 1758, plays a minor role as a host of Lepeophtheirus salmonis (Krøyer 1837) in the Gulf of Maine

The sea louse, Lepeophtheirus salmonis (Krøyer 1837), is a significant parasite of farmed salmon throughout the Northern Hemisphere. Management of on‐farm louse populations can be improved by understanding the role that wild fish play in sustaining and providing refuge for the local population of sea lice. In this study, 1,064 sticklebacks were captured. Of these animals, 176 individuals were carrying a total of 238 sea lice, yielding a prevalence and intensity of 16.5% and 1.4 lice per fish, respectively. Detailed examination of the sea lice on the three‐spined sticklebacks captured in Cobscook Bay found two L. salmonis individuals using three‐spined sticklebacks as hosts. A 2012 survey of wild fish in Cobscook Bay, Maine, found multiple wild hosts for Caligus elongatus (von Nordmann 1832), including three‐spined sticklebacks (Gasterosteus aculeatus L.), but no L. salmonis were found in this earlier study.