School size affects individual feeding success in three-spined sticklebacks (Gastevosteus aculeatus L.)

The effect of school size on the feeding success of individual three-spined sticklebacks was studied. We found that the proportion of fish feeding on benthic prey increased with school size and that fish in large schools tended to start feeding sooner than fish in small schools. The total number of strikes also increased in larger schools. Despite this evidence for a foraging benefit associated with school membership we propose that improved feeding returns do not alone explain stickleback schooling.     

Inbreeding and developmental stability in three-spined sticklebacks (Gasterosteus aculeatus L.)

Fluctuating asymmetry, small non-directional departures from perfect symmetry in bilateral traits, results from the inability of individuals to buffer development against genetic and environmental perturbations. Fluctuating asymmetry is a widely used measure of developmental stability, and developmental stability has been hypothesised to be inversely related to heterozygosity. We compared male three-spined sticklebacks (Gasterosteus aculeatus L.) that had been inbred for one generation to outbred control males with respect to the asymmetry of a set of bilateral morphometric traits. Inbred fish developed significantly more asymmetric pectoral fins than their outbred counterparts, whereas neither the magnitude of asymmetry for pelvic spines nor for gill covers significantly responded to the treatment. Our results conform to a pattern of heterogeneity amongst traits in their tendency to develop asymmetrically in response to stress.     

Female mate choice and male red coloration in a natural three-spined stickleback (Gasterosteus aculeatus) population

Under laboratory conditions, female three-spined sticklebacks(Gasterosteus aculeatus L.) show a mating preference for intenselyred-colored males. We verified this female choice in the fieldby observing a freshwater stickleback population in its naturalhabitat. During the egg collection phase, individual courtingmales were localized with the aid of a dummy of a ripe female,caught and photographed under standardized conditions, and released.After males had stopped collecting eggs, we counted the numberof eggs in the nests. The more intense a male's red breedingcoloration, the more eggs he received. Simultaneous female choiceexperiments in the laboratory suggested that ripe females ofthis population preferred redder males. Breeding activitiesof the males in the field were clustered and seem to be synchronizedwithin clusters. At one of the breeding sites, more intensered males were in better physical condition, but this was notthe case at another site. Although several synchronized breedingcycles were observed, the majority of males seem to completeonly one breeding cycle.     

Fecundity of the three-spined stickleback, Gasterosteus aculeatus (L.)

The number of eggs spawned by female three-spined sticklebacks Gasterosteus aculeatus (L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.     

Attractive males have faster sperm in three-spined sticklebacks Gasterosteus aculeatus

Recent studies have revealed that sexually selected traits may signal sperm quality and hence male fertilisation ability. There is also evidence that the expression of male sexual ornamentation and associated sperm characteristics depend on an indi- vidual＇s ability to cope with oxidative stress. Carotenoids are known for their antioxidant properties and carotenoid-based orna- ments might represent honest signals as these pigments can be traded offbetween the investment in sexual ornamentation, sperm function as well as immune response. In this study, we examined the relationship between sexual ornamentation （breeding colo- ration） and sperm characteristics （e.g., velocity and morphology） in the three-spined stickleback Gasterosteus aeuleatus, an ex- ternally fertilising fish species, in which sperm competition commonly occurs. During the breeding season males are sperm limi- ted and develop a conspicuous carotenoid-based coloration, which is under strong pre-copulatory sexual selection due to female mate choice and male-male competition. The results of the present study show that the expression of stickleback male breeding coloration is significantly positively associated with the linearity of sperm movement, whereas sperm morphology （head length to tail length ratio） is significantly negatively related to the trajectory of sperm movement. Moreover, there is some support for the phenotype-linked fertility hypothesis as the intensity of male red breeding coloration is significantly positively correlated with sperm velocity, which is supposed to be an important determinant of fertilisation success in external fertilisers, indicating the honesty of the sexually selected nuptial red coloration.     

Oxygen consumption by sticklebacks (Gasterosteus aculeatus L.) exposed to zinc

The rate of oxygen consumption by sticklebacks has been studied by long-term continuous-flow respirometry. Exposure to 1 p.p.m. zinc in calcium-free water causes wide variations in individual responses, but oxygen uptake tends to rise and then become extremely erratic, before declining as death approaches. Behavioural abnormalities such as increased ventilation rate, loss of balance, and long periods of inactivity alternating with spasmodic swimming also occur. Exposure to 6.5 p.p.m. zinc in high-calcium water generally causes a rise in oxygen consumption, followed by fluctuations in the rate of uptake, but no behavioural abnormalities occur and deaths are rare even after exposure for 400 h. If restored to zinc-free water after 40 h exposure to zinc, recovery is generally complete, although fluctuating rates of oxygen uptake persist. These results are discussed in relation to previous work on the effects of heavy metals on fish respiration.     

Cost of egg production in the three-spined stickleback (Gasterosteus aculeatus L.)

In the interval between successive spawnings, female sticklebacks consumed approximately their own wet weight of Tubifex. On average, for 100 cal of food consumed, 26 cal of eggs, 3 cal of somatic growth and 11 cal of faeces were produced. In the absence of somatic growth, the efficiency of egg production was estimated as nearly 30%, and it was predicted that in the absence of egg production, the efficiency of somatic growth would range from 20% for a fish of 0.8 g wet weight to 3% for 2 g fish.
The weight of eggs produced at a spawning was a function of the weight of the female but not of the amount of food consumed. If food consumption was not sufficient to cover the cost of egg production, the fish lost weight. Total production (the summation of egg production and somatic growth) was a function of the amount of food consumed.     

Population biology of three-spined sticklebacks, Gasterosteus aculeatus, in Scotland

The age of maturation, longevity and aspects of anti-predator morphology were studied for seven Gasterosteus aculeatus L. populations in Scotland during 1978 and 1979. All seven populations are annual with less than 1% of adults surviving a second year. At the four mainland study sites, breeding adult sticklebacks were larger than at any of the three Hebridean sites. Adult females were larger than adult males at all sites, except Lennox Castle where parasitism may account for the lack of sexual dimorphism. Two of the Hebridean sites, Loch Fada and Loch a Bharpa have spine-deficient G. aculeatus populations which are morphologically unprotected from predation. In the five normally spined populations, some aspects of defensive morphology (index of increase in critical dimension, ventral spine size) are associated with predation risk, while others (lateral plate number) are not. These data are discussed in relation to the current stickleback literature.     

Population genetic dynamics of three-spined sticklebacks (Gasterosteus aculeatus) in anthropogenic altered habitats

In industrialized and/or agriculturally used landscapes, inhabiting species are exposed to a variety of anthropogenic changes in their environments. Genetic diversity may be reduced if populations encounter founder events, bottlenecks, or isolation. Conversely, genetic diversity may increase if populations adapt to changes in selective regimes in newly created habitats. With the present study, genetic variability of 918 sticklebacks from 43 samplings (21.3 ± 3.8 per sample) at 36 locations from cultivated landscapes in Northwest Germany was analyzed at nine neutral microsatellite loci. To test if differentiation is influenced by habitat alterations, sticklebacks were collected from ancient running waters and adjacent artificial stagnant waters, from brooks with salt water inflow of anthropogenic and natural origin and adjacent freshwater sites. Overall population structure was dominated by isolation by distance (IBD), which was significant across all populations, and analysis of molecular variance (AMOVA) revealed that 10.6% of the variation was explained by river catchment area. Populations in anthropogenic modified habitats deviated from the general IBD structure and in the AMOVA, grouping by habitat type running/stagnant water explained 4.9% of variation and 1.4% of the variation was explained by salt-/freshwater habitat. Sticklebacks in salt-polluted water systems seem to exhibit elevated migratory activity between fresh- and saltwater habitats, reducing IBD. In other situations, populations showed distinct signs of genetic isolation, which in some locations was attributed to mechanical migration barriers, but in others to potential anthropogenic induced bottleneck or founder effects. The present study shows that anthropogenic habitat alterations may have diverse effects on the population genetic structure of inhabiting species. Depending on the type of habitat change, increased genetic differentiation, diversification, or isolation are possible consequences.     

Laboratory and field studies on diet choice in three-spined sticklebacks, Gasterosteus aculeatus L., in relation to profitability and visual features of prey

Diet choice by three-spined sticklebacks was investigated under both laboratory and field conditions. In the laboratory, sticklebacks did not always choose the more profitable of two prey items; instead, they apparently selected prey according to a set of proximate decision rules based on visual cues provided by the prey. Studies of the diet of sticklebacks in the field suggest that they may use the same set of proximate decision rules to select their food and that in these more complex conditions this may lead them to feed preferentially on the more profitable types of prey. In general, sticklebacks selected zooplanktonic rather than benthic prey (which is less profitable), but the importance of benthos in the diet increased as the density of zooplankton decreased.     

Acoustic noise induces attention shifts and reduces foraging performance in three-spined sticklebacks (Gasterosteus aculeatus)

Acoustic noise is known to have a variety of detrimental effects on many animals, including humans, but surprisingly little is known about its impacts on foraging behaviour, despite the obvious potential consequences for survival and reproductive success. We therefore exposed captive three-spined sticklebacks (Gasterosteus aculeatus) to brief and prolonged noise to investigate how foraging performance is affected by the addition of acoustic noise to an otherwise quiet environment. The addition of noise induced only mild fear-related behaviours--there was an increase in startle responses, but no change in the time spent freezing or hiding compared to a silent control--and thus had no significant impact on the total amount of food eaten. However, there was strong evidence that the addition of noise increased food-handling errors and reduced discrimination between food and non-food items, results that are consistent with a shift in attention. Consequently, noise resulted in decreased foraging efficiency, with more attacks needed to consume the same number of prey items. Our results suggest that acoustic noise has the potential to influence a whole host of everyday activities through effects on attention, and that even very brief noise exposure can cause functionally significant impacts, emphasising the threat posed by ever-increasing levels of anthropogenic noise in the environment.     

Ultrastructural modifications of renal cells in the three-spined stickleback (Gasterosteus aculeatus L.) after castration

Summary The mechanisms of cellular autophagy have been studied in the renal epithelium of male sticklebacks (Gasterosteus aculeatus L.) following castration. Two main types of alteration are described at the level of the proximal tubule cells. At first, the formation of endoplasmic reticulum whorls is observed, followed immediately by the secretion of lacunar progranules and by nucleolar modifications. These alterations lead to a progressive decrease of the glandular activity of the cells. The other main effect of castration is a general involution of the secretory granules still present in the cells. The involutive processes which lead to the complete destruction of the secretory material and, sometimes, of entire proximal cells, are described.In the collecting tubules, a marked and rapid decrease in glandular activity occurs, followed by disappearance of the mucous secretions. Small dense granules, supposedly lysosomes, are present.The processes described also appear to be characteristic of the normal involution of the renal cells occurring at the end of the breeding period. The findings strongly suggest that the male sex hormone may exert a double control on the renal cells in the stickleback, at both the cytoplasmic and nucleolar levels.I am greatly indebted to Prof. E. Follénius, who contributed to this work with innumerable suggestions and valuable advice. I also wish to thank Mr. C. Chevalier and Miss A. Meunier for their technical collaboration     

The influence of hunger on shoal size choice by three-spined sticklebacks, Gasterosteus aculeatus

Single sticklebacks ( Gasterosteus aculeatus ) were presented with a choice between (a) a shoal and an empty compartment, and (b) two different sized shoals of conspecifics. The choice of hungry test fish (food-deprived for 24 h and 72 h, respectively) was compared to that of fish which were fed to satiation once a day. It was hypothesized that due to the increased level of competition for food in large shoals, hungry fish would spend less time with the larger of two shoals than their well-fed conspecifics. The results showed that there was indeed a significant trend for test fish to spend a decreasing amount of time near the compartment with the larger number of fish with increasing duration of food deprivation.