Ovarian fluid in the three-spined stickleback Gasterosteus aculeatus: effects of egg overripening and sex steroid treatment

The ovarian fluid properties of the three-spined stickleback Gasterosteus aculeatus were studied in overripe and non-overripe ovulated female sticklebacks and in females that were implanted with Silastic capsules containing testosterone (T), oestradiol (E2), 17,20β-dihydroxypregn-4-en-3-one (17,20β-P) or progesterone (P4) into the abdominal cavity. Overripe females had less ovarian fluid than non-overripe females, but with higher dry mass, higher protein concentration and lower viscosity. T and 17,20β-P increased the amount of ovarian fluid and the fluid protein concentration was increased by 17,20β-P. 1-D sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) showed that ovarian fluid contains several proteins, with high individual variability but with no consistent differences between groups. Some of the ovarian fluid proteins appeared to correspond to proteins from the eggs. The results suggest that secretion of ovarian fluid may be influenced by steroid hormones and that changes in its properties are related to the overripening of ovulated eggs. In at least some respects it appears that the changes in the ovarian fluid is a result, rather than the cause of overripening.     

Parental energy expenditure of the male three-spined stickleback

The energy expenditure of male three-spined sticklebacks performing parental care was 12·3 and 9·9 J g⁻¹ h⁻¹ estimated by respirometry and ration manipulation, respectively. The energy expenditure of caring male sticklebacks was significantly higher than for non-caring males.     

Sensory drive and nuptial colour loss in the three-spined stickleback

Three-spined sticklebacks Gasterosteus aculeatus , from the Chehalis River drainage. Washington, U.S.A., that have lost the mosaic nuptial signal were more likely to be found in tannin stained sub-drainages whereas those expressing the mosaic nuptial signal were more likely to be found in sub-drainages that were not tannin stained. This result is consistent with the sensory drive model.     

Sperm allocation in the three-spined stickleback

Male three-spined stickleback Gasterosteus aculeatus have a fixed amount of sperm during the breeding season because spermatogenesis is inhibited at this time. A method was developed to estimate ejaculate size in situ by removing the sperm from the male's nest. The reliability of the method was tested using known numbers of sperm. In their first mating, males ejaculated 11·64 × 10⁶ sperm (median), representing c. 5% of the male's sperm store (median 27·88 × 10⁷ sperm). The amount of sperm in the testes was significantly reduced in males that had mated several times (median 8·09 × 10⁷). Additionally, ejaculate size was smaller in these experienced males (median 8·79 × 10⁵). Heavier and larger fish invested absolutely and relatively more sperm in a mating than did lighter and smaller fish. Ejaculate size did not correlate with the mass of the egg clutch.     

Evaluation of ovum fixation and storage in three-spined stickleback

Ripe eggs removed from three-spined sticklebacks stored in 50% isopropyl alcohol showed significantly Sower mean masses than those stored in 10% formalin. These results are considered in relationship to preservation techniques for stickleback.     

Schooling affects growth in the three-spined stickleback, Gasterosteus aculeatus

Three-spined stickleback fry (mean length 20 mm, mean weight 14 mg) were reared for 14 days alone and in groups of six in a constant per capita water volume. The fish originated from two habitats (rock-pools, sea) of different predation pressure. The fry were fed nauplii of Artemia and commercial aquarium fish food ad libitum. Specific growth rates of solitary and schooling fry differed and were also affected by their origin. The specific growth rates of solitary fry from the sea averaged 1.0% day⁻¹ (length) and 6.0% day⁻¹ (weight) and those of solitary rock-pool fry 1.1 and 6.7%, respectively. For group-reared fish the corresponding values were 1.2% (length) and 6.6% (weight), and 1.3% (length) and 7.6% (weight). The finding that schooling sticklebacks grow faster than solitary ones implies that grouping enhances fitness in stickleback fry under the conditions of our experiments.     

Life-history variation within a three-spined stickleback population in the Camargue

Among individuals of female three-spined sticklebacks Gasterosteus aculeatus from a population in the Camargue, southern France, studied in 12 successive years, adult L _T ranged from 31–64 mm, clutch size ranged from 33–660 eggs, and mean egg diameter per clutch ranged from 1.15–1.67 mm. Because the population was strictly annual, inter-annual variation corresponded to variation among generations having experienced different environmental conditions. Body mass varied significantly among years, suggesting an effect of varying environmental conditions. Gonad mass and clutch size increased with body mass, but mean egg diameter was not correlated to body mass. Body mass-adjusted gonad mass, interpreted as reproductive effort per clutch, did not vary significantly among years, suggesting that this trait was not influenced by environmental conditions. Body mass-adjusted clutch size and egg size varied significantly among years. Inter-annual variation in body length at breeding, clutch size and egg size was of the same order of magnitude as inter-population variation reported by other authors for this species. During the breeding season, reproductive effort and clutch size tended to increase. Egg size tended to decrease during the breeding season but this seasonal pattern varied among years. Observed life-history variation is discussed both in terms of its evolutionary significance and methodological implications in the study of life-history variation among populations.     

Migrations of three-spined stickleback, nine-spined stickleback, and pond smelt in the Chignik catchment, Alaska

Upstream spawning migrations of age-2 three-spined stickleback, nine-spined stickleback, and pond smelt, and subsequent downstream migrations of young-of-the-year and age-1 individuals are documented in Black River of the Chignik catchment, Alaska.     

Polymorphism and signature of selection in the MHC class I genes of the three-spined stickleback Gasterosteus aculeatus

The role and intensity of positive selection maintaining the polymorphism of major histocompatibility complex (MHC) class I genes in the three-spined stickleback Gasterosteus aculeatus was investigated. The highly polymorphic set of MHC class I genes found was organized in a single linkage group. Between 5 and 14 sequence variants per individual were identified by single-stranded conformation polymorphism (SSCP) analysis. Segregation analysis studied in 10 three-spined stickleback families followed the expected pattern of Mendelian inheritance. The gamete fusion in three-spined stickleback thus seems to be random with respect to the MHC class I genes. The DNA sequence analyses showed that the expressed MHC class I loci are under strong selection pressure, possibly mediated by parasites. Codons that were revealed to be under positive selection are potentially important in antigen binding. MHC class I sequences did not form significant supported clusters within a phylogenetic tree. Analogous to MHC class II genes, it was not possible to assign the class I sequences to a specific locus, suggesting that the class I genes may have been generated by recent gene duplication.     

Broods of attractive three-spined stickleback males require greater paternal care

The relationship between egg number and survival in nests of three-spined sticklebacks Gasterosteus aculeatus was tested in the field. Nests were deprived of paternal care during a variable period by removal of the father while preventing egg predation by protection of the nest by a net. Upon male removal, a number of male traits were quantified. Nest-content variables and embryo survival were assessed at the end of the deprivation period. Proportional egg mortality was significantly positively correlated with the length of the deprivation period, the number of eggs present in the nest and egg size, thus suggesting that nests with more and larger eggs need more paternal care. Males with the most symmetrical ventral spines achieved the highest reproductive success as measured by the number of eggs in the nest. In addition, their nests contained relatively larger eggs. Spine length symmetry correlated with the blue intensity of the eye thus giving females several cues to assess male quality.     

Reproductive and histopathological effects of long-term experimental exposure to bis(tributyltin)oxide (TBTO) on the three-spined stickleback, Gasterosteus aculeatus Linnaeus

Three-spined sticklebacks, Gasterosteus aculeatus Linnaeus, were exposed to 0, 0.1, 1.0, 2.5 and 10 μg bis(tributyltin)oxide (TBTO) 1⁻¹ for up to 7.5 months in a flow-through system of sea water. As early as 4 weeks after the start of the experiment, fish from the 10 μg TBTO 1⁻¹ group showed diminishing appetite, increasing lethargy and opaque eyes. The mortality in this group after 2 months of exposure was 80%. No significant differences between the control and the exposed groups were noted concerning fecundity, hatched fry and frequencies of malformed fry. The gonad somatic index (GSI) was determined before and during the spawning period. GSI in control fish increased significantly, while that in the exposed groups remained unchanged between the two sampling occasions. Structural examination of the gills from fish exposed for 2 months to 10 μg TBTO I⁻¹ revealed fusion between secondary lamellae and gradual cell degeneration. The chloride cells were characterized by degenerating mitochondria. Hepatocytes in fish exposed to 2.5 and 10 μg TBTO I⁻¹ contained an increased number of lipid-containing vacuoles and the nucleoli were disorganized and fragmented.     

The three-spined stickleback as an environmental sentinel: effects of stressors on whole-body physiological indices

Indicators of a generalized stress response (changes in cortisol, glucose, RNA: DNA ratio and total protein) when measured in whole-body preparations of individual three-spined sticklebacks Gasterosteus aculeatus displayed significant alterations in response to acute (hours) and chronic (days) disturbances and food withdrawal. In addition, changes in alkali-labile phosphorous, a specific biomarker of exposure to oestrogenic contaminants, could be detected in whole-body preparations of oestrogen-exposed three-spined sticklebacks confirming that the measurement of biomarkers normally assessed in a specific tissue can be equally possible in whole fish.     

Phenotypic integration of life history and morphology: an example from three-spined stickleback, Gasterosteus aculeatus L.

Although typically life history and morphology are studied separately, they may evolve most often in concert. Therefore, a full understanding of the evolution of fish life-history patterns may require exploration of the evolutionary interplay between components of life history and other aspects of phenotype. One of the most promising approaches to understanding phenotypic integration is population comparison. This approach is particularly effective when ancestralderived relationships are understood and when multiple populations can be inferred to have evolved derived character states independently. Here we provide an example of this approach using five allopatric populations of freshwater three-spined stickleback ( Gasterosteus aculcatus L.) that have diverged in response to differences in selection regimes among the lakes they inhabit. We demonstrate a relationship between one aspect of reproductive life history, clutch volume and relative body shape. The differences are consistent with those predicted on the basis of differences in trophic habit and overall body form. Finally, we discuss the value of particular groups of fish for use in comparative studies and explore the kinds of evolutionary issues that can be addressed through population comparison.     

Lateral plate morph differentiation of freshwater and marine populations of the three-spined stickleback, Gasterosteus aculeatus, in Poland

The distribution of three main lateral plate morphs of the three–spined stickleback, Gasterosteus aculeatus , in the Polish zone of the Baltic Sea and inland waters is surveyed. Most sites are characterized by predominance of the completely plated morph, although it is only in the Vistula River drainage basin where monomorphic complete populations prevail. Polymorphic populations with a high proportion of the non–complete morphs are found in Puck Bay (the Baltic) and in south–west Poland, Possible causes of this pattern are discussed.     

Juvenile bimodal length distribution and sea-run migration of the lower modal group in the Pacific Ocean form of three-spined stickleback

Juvenile three-spined stickleback Gasterosteus aculeatus in their nursery pond had a bimodal length distribution after October in their first year of life. A sea-run migration of all individuals belonging to the lower modal group was observed, with a peak in early November. These data suggest that partial migration based on the early status of individual juveniles occurs in the Pacific Ocean form of three-spined stickleback.     

Genetic relationships among marine and freshwater populations of the European three-spined stickleback (Gasterosteus aculeatus) revealed by microsatellites

To assess the population genetic structure of the three-spined stickleback, Gasterosteus aculeatus, variability at 18 microsatellite loci was examined in 1724 individuals from 74 locations covering most of the species distribution range in Europe. The results revealed high overall degree of differentiation (F(ST) = 0.21) but contrasting level of divergence and genetic variability between habitat types. Marine populations were genetically relatively uniform even across great geographical distances as compared to substantial differentiation among freshwater populations. Analysis of molecular variance indicated low but significant (2.7%) variation in allele frequencies between geographical regions, but a negligible effect of habitat type (0.2%). The phylogenetic pattern was not explained by habitat type, but a weak signal of populations clustering according to geographical or water system origin was found. The results support the view that three-spined stickleback marine ancestors colonized northern European fresh waters during the postglacial marine submergence c. 10,000 years ago, whereas in the Mediterranean region colonization probably dates back to the Pleistocene. The independent origins of river and lake populations indicate that they originate from multiple colonizations rather than sharing common ancestry. In the continuous marine environment, the low degree of differentiation among populations can be explained by gene flow among subpopulations and large effective population size buffering divergence in neutral markers. In contrast, among postglacially established freshwater populations differentiation appears to be driven by genetic drift and isolation. The stepwise mutations appear to have contributed to the population differentiation in the southern part of the three-spined stickleback distribution range.     

Intraspecific differences in patterns of courtship behaviours between the Pacific Ocean and Japan Sea forms of the three-spined stickleback Gasterosteus aculeatus

The courtship behaviour of the Pacific Ocean and Japan Sea forms of the three-spined stickleback Gasterosteus aculeatus were studied in seven populations. The intraspecific difference in behavioural patterns, zigzag dance and weak dorsal pricking in the Pacific Ocean form and lateral display and vigorous dorsal pricking in the Japan Sea form, was clearly distinguishable regardless of the type of habitat the males lived in.     

Constraints on prey size selection by the three-spined stickleback: energy requirements and the capacity and fullness of the gut

An experiment was designed to study how gut fullness and encounter with 5-mm Asellus aquaticus influenced acceptance or rejection of less profitable 8-mm Asellus . 45-mm sticklebacks were found to always accept 5-mm prey whereas 8-mm prey were accepted with an initial probability of about 0.9. This probability decreased as the gut filled. Fish of differing sizes and sex had similar daily energy intakes per unit body size, however the acceptance of 8-mm prey was related to fish size. Whenever a fish orientated to a prey it was followed by pursuit and manipulation independently of prey size. The decision to accept or reject prey occurred after one manipulation, a criterion that was more variable for the larger prey. For one feeding session per day the total energy intake was almost constant despite the changing combination of prey sizes eaten. The fish ate prey with long handling times if the energetic contents of the stomach had not reached 450 J. Calculations were made of how many of each millimetre prey size group would satisfy the 450 J demand and how long the estimated number would take to handle. This showed that the best option is to consume 5-mm prey if given the choice.     

Sex differences in pectoral muscles but not in pectoral fins in the three‐spined stickleback Gasterosteus aculeatus

The pectoral muscle index ( I _PM)( I _PM = 100 M _PM M⁻¹, where M _PM and M are the pectoral muscle and body masses, respectively) fin‐area and fin ray length were studied over a year in male and female three‐spined stickleback Gasterosteus aculeatus from a marine population (Öresund, Sweden) kept under simulated natural light and temperature conditions. A castration‐replacement experiment was used to test androgen effects on the I _PM, fin‐area and fin ray length. Non‐breeding males were castrated or sham‐operated in winter ( i.e . the fish had low levels of androgens). Castrated control and sham‐operated fish were implanted with empty Silastic capsules and castrated groups with capsules containing the androgens testosterone or 11‐ketoandrostenedione into the abdominal cavity. The experiment was terminated after 41 days, when the controls had matured. No morphological differences were found in pectoral fins between sexes during the year, except during the peak breeding season (May), where females showed larger fin‐area and longer fin ray in length compared to males. No effects of androgens treatment or of castration on pectoral fin‐area or fin ray length was observed. Breeding and non‐breeding males showed higher I _PM compared to females. The lower I _PM in females than in males could not be explained by the larger gonads in the former alone, as a sex difference in I _PM was still present after deduction of the ovaries from the female body mass. The I _PM was higher in sham‐operated compared to castrated fish. No effects of androgens treatment on I _PM was observed.