The inter-spawning interval of the female Three-spined stickleback, Gasterosteus aculeatus

Female Three-spined sticklebacks spawn several times in a breeding season, at intervals of a few days. The changes that take place in females during the interval between successive spawnings were analysed. The average time between spawnings was 87.5 hours. Between spawnings females increased in weight by between 15 and 30%. The bulk of this weight increase was lost when the eggs were spawned. The increase in weight was because of an increase in weight of the ovaries, which showed an increase in both dry matter and water content. After spawning the ovaries formed 8 to 9% of the total body weight, and this increased to up to 24% just prior to the next spawning. The ovaries were maximally hydrated immediately after spawning. There were no significant changes in the calorific value of the ovaries, but the calorific value of the rest of the body was a minimum just after spawning. It was estimated that between spawnings females were making a net gain of energy at an average rate of 2 cal/hour. After spawning, courtship behaviour by the females waned, but recovered over the last half of the interval between spawnings. The inter-spawning interval of the Three-spined stickleback provides a useful situation in which physiological and nutritional aspects of reproduction in a teleost fish can be studied.     

The ACTH-interrenal axis in the freshwater stickleback,Gasterosteus aculeatus form leiurus

Summary The ACTH-interrenal axis of the freshwater stickleback has been examined with the fish in a variety of physiological conditions. A morphometric analysis of ACTH cell ultrastructure in spring animals revealed that the only change from the winter condition was a significant decrease in the amount of perinuclear RER. The interrenal gland responded to metopirone treatment by an increase in both nuclear and cell size, although only a high dose of metopirone could degranulate the ACTH cells. Morphometry of the ACTH cells from metopirone-treated animals showed a significant increase in the amount of RER and a significant decrease in the number of free ribosomes and secretory granules, compared with control animals maintained in freshwater. Such ultrastructural changes may be expected of a cell that is stimulated to increase its secretion of polypeptide hormone. The ACTH-interrenal axis also responded to 70% seawater, as this treatment increased the interrenal cell and nuclear sizes.     

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.     

Migratory history of the threespine stickleback Gasterosteus aculeatus

 The migratory history of two highly divergent forms (the Japan Sea and Pacific Ocean forms) of the threespine stickleback Gasterosteus aculeatus collected from Japanese brackish water (seawater) and freshwater was studied by examining strontium (Sr) and calcium (Ca) concentrations in their otoliths using wavelength dispersive X-ray spectrometry on an electron microprobe. The Sr : Ca ratios in the otoliths changed with salinity of the habitat. The otolith Sr : Ca ratios of the freshwater resident-type samples of the Pacific Ocean form showed consistently low Sr : Ca ratios, averaging 0.85–0.96 × 10⁻³ from the core to the edge. In contrast, the otolith Sr : Ca ratios of the anadromous type of both the Japan Sea and Pacific Ocean forms fluctuated strongly along the life history transects in accordance with their migration patterns from seawater to freshwater. The higher ratios in the anadromous type, averaging 5.4 × 10⁻³, in the otolith region from the core to 200 μm, corresponded to the seagoing period, suggesting that otolith Sr : Ca ratios are affected by ambient water salinity. These findings clearly indicate that otolith Sr : Ca ratios reflect individual life histories, and that these two highly divergent forms of stickleback have a flexible migration strategy. Received: May 23, 2002 / Revised: July 29, 2002 / Accepted: August 19, 2002 Acknowledgments We are grateful to Dr. S. Mori of Gifu Keizai University, and Miss M. Yamada and Messrs. M. Kume and T. Kitamura of Hokkaido University, for their assistance in sampling. This work was supported in part by Grant-in-Aid No. 13760138 from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Correspondence to:Takaomi Arai     

Divergence in reproductive ecology of the three-spined stickleback,Gasterosteus aculeatus

An anadromous population (trachurus form) and three freshwater populations (leiurus form) of the three-spined stickleback,Gasterosteus aculeatus, in central Japan were compared with one another in the reproductive traits: body length at maturity, egg size, clutch size, the swell of abdomen and the number of eggs per nest. The anadromous fish which become larger in body size at maturity spawn eggs smaller in size and greater in number than the freshwater fish. The abdomen swell of gravid females expressed by the proportion of abdomen width to body length was greater in the freshwater fish. The anadromous male fish collected a mean of 2,638 eggs with a range of 1,119 to 4,052 eggs from about 6–7 females. In the three freshwater (the Yamayoke, the Tsuya and the Jizo) populations, males must have mated with about 9–22, 7–18 and 4–7 females respectively. It seems that theleiurus form increases its reproductive success by its much more mating opportunities and the parental efforts of nesting males as well as by spawning large eggs. Furthermore, among the freshwater populations, the Jizo one inhabiting the upper stream was clearly larger in body size, in egg size and in clutch size than the Yamayoke and the Tsuya ones which inhabit stable waterbodies with springs. It is possible that the Jizo population adopted the strategy of spawning a few large eggs as an adaptation to its habitat. The causal and functional explanations in reproductive characteristics among the four populations are discussed in regard to differences in the environmental conditions.     

The pineal complex of the three-spined stickleback,Gasterosteus aculeatus L.

Summary The pineal complex of the three-spined stickleback (Gasterosteus aculeatus L.) was investigated by light and electron microscopy, as well as fluorescence histochemistry for demonstration of catecholamines and indolamines. The pineal complex of the stickleback consists of a pineal organ and a small parapineal organ situated on the left side of the pineal stalk. The pineal organ, including the entire stalk, is comprised mainly of ependymal-type interstitial cells and photoreceptor cells with well-developed outer segments. Both unmyelinated and myelinated nerve fibres are present in the pineal organ. Nerve tracts from the stalk enter the habenular and posterior commissures. A small bundle of nerve fibres connects the parapineal organ and the left habenular body. The presence of indolamines (5-HTP, 5-HT) was demonstrated in cell bodies of both the pineal body and the pineal stalk, and catecholaminergic nerve fibres surround the pineal complex.     

Ultraviolet light and visual behaviour in the three-spined stickleback, Gasterosteus aculeatus

The ability of various vertebrates to perceive visual information in the ultraviolet region of the electromagnetic spectrum (300-400 nm) is receiving increasing interest. To date, many of these studies have concentrated on the role of ultraviolet perception in mate choice, yet there are several ways in which the ability to perceive ultraviolet information may affect other behaviours. Until now, it has been widely assumed that colour in the three-spined stickleback can be quantified by methods appropriate to the human visual system. However, evidence does exist that suggests that, in some populations, sticklebacks are capable of perceiving ultraviolet wavelengths. Using a behavioural technique, we tested the ability of the stickleback to perceive ultraviolet light under full-spectrum conditions to establish whether such wavelengths are utilised within their normal behavioural repertoire. We tested this ability by assessing whether subjects could locate hidden food in a foraging task where food position was indicated by the position of landmarks. These landmarks differed only in their ultraviolet content, appearing identical when viewed across the human visible region of the spectrum. We found that sticklebacks were able to use ultraviolet perception to locate a foraging patch under full-spectrum conditions.     

Armor morphology and reproductive output in threespine stickleback,Gasterosteus aculeatus

Synopsis The threespine stickleback, Gasterosteus aculeatus, is an extensively armored fish inhabiting both marine and fresh waters across its holarctic distribution. Marine fish nearly always possess a full complement of bony lateral plates running from just behind the head to the tail, and a robust pelvic girdle complex. These armor features appear to constrain lateral and ventral abdominal distention, and therefore clutch volume. Freshwater populations in many areas exhibit variable reduction in lateral plate number, and in some regions the pelvic girdle is also reduced or lost. Freshwater populations also vary in the degree of abdominal distention exhibited by gravid females. We tested whether reduction in armoring might be correlated with increased clutch volume using five populations from the Cook Inlet area of Alaska. The hypothesis that populations having reduced pelvic girdle complexes would have greater size-adjusted clutch volumes was not supported. In fact, our two full-pelvic populations as a group had larger volumes. Similarly, size-adjusted clutch volumes were not related to pelvic phenotype within either of our two pelvic-reduced populations, nor to lateral plate morph within a fifth population. Other factors that may explain the interpopulation differences in clutch volume in threespine stickleback include body shape, food quantity and quality, intensity of predation, and even behavior. Except for a preliminary analysis of body shape, these possibilities remain unexplored. The concept of phenotypic integration suggests that these factors should be analyzed as a suite rather than individually.     

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.     

Dyadic relationships in nesting males of the three-spined stickleback, Gasterosteus aculeatus

Multidimensional scaling analysis of nest site location, nesting interval, and aggressive and mating interactions revealed that male three-spined sticklebacks, Gasterosteus aculeatus, formed nesting clusters comprising five patterns of dyadic relationships. These patterns were defined by intervening variables such as size difference between the two males, nest site locations, synchronization of nesting cycles (egg presence in the nest), distance between two nests, and nest raiding behaviours. Several patterns of dyadic relationships were integrated among nesting males and their constellations indicated an expression of the social structure. Through an understanding the social structure, I described effects of social context or situations on individual reproductive success.     

A three-spined stickleback, Gasterosteus aculeatus L. from the North Atlantic

An unusual occurrence of a three-spined stickleback, Gasterosteus aculeatus , is described from Ocean Weather Station India in the North-east Atlantic. Previous records of G. aculeatus caught well offshore are summarised and reasons for these occurrences are suggested. Mention is made of the possibility of sticklebacks breeding in the open ocean.     

A temperature-dependent growth model for the three-spined stickleback Gasterosteus aculeatus

Specific growth rates of individually reared juvenile three-spined sticklebacks Gasterosteus aculeatus were investigated under laboratory conditions to parameterize a complete temperature-dependent growth model for this species. To test the applicability of experimentally derived optima in growth response rates to natural conditions, the effects of commercial pellets and natural prey on growth rates were investigated. In addition, to test for seasonal effects on growth, laboratory trials were performed in both spring and winter. Growth took place from 5 to 29° C with a temperature for optimum growth reaching a sharp peak at 21° C. Modelled optimal temperature for maximum growth was estimated to be 21.7° C and lower and upper temperatures for growth were estimated to be 3.6 and 30.7° C, respectively. There were no significant differences in growth rates between fish reared on invertebrates or commercial pellets. Seasonal effects on growth were pronounced, with reduced growth rates in the winter despite similar laboratory conditions. On average, 60% higher growth rates were achieved at the optimum temperature in summer compared to the winter. The strong seasonality in the growth patterns of G. aculeatus indicated here reduces the applicability of the model derived in this study to spring and summer conditions.     

Genetic basis of sexual dimorphism in the threespine stickleback Gasterosteus aculeatus

Sexual dimorphism (SD) in morphological, behavioural and physiological features is common, but the genetics of SD in the wild has seldom been studied in detail. We investigated the genetic basis of SD in morphological traits of threespine stickleback (Gasterosteus aculeatus) by conducting a large breeding experiment with fish from an ancestral marine population that acts as a source of morphological variation. We also examined the patterns of SD in a set of 38 wild populations from different habitats to investigate the relationship between the genetic architecture of SD of the marine ancestral population in relation to variation within and among natural populations. The results show that genetic architecture in terms of heritabilities, additive genetic variances and covariances (as well as correlations) is very similar in the two sexes in spite of the fact that many of the traits express significant SD. Furthermore, population differences in threespine stickleback body shape and armour SD appear to have evolved despite constraints imposed by genetic architecture. This implies that constraints for the evolution of SD imposed by strong genetic correlations are not as severe and absolute as commonly thought.     

Inheritance of vertebral number in the three-spined stickleback (Gasterosteus aculeatus)

Intraspecific variation in the number of vertebrae is taxonomically widespread, and both genetic and environmental factors are known to contribute to this variation. However, the relative importance of genetic versus environmental influences on variation in vertebral number has seldom been investigated with study designs that minimize bias due to non-additive genetic and maternal influences. We used a paternal half-sib design and animal model analysis to estimate heritability and causal components of variance in vertebral number in three-spined sticklebacks (Gasterosteus aculeatus). We found that both the number of vertebrae (h² = 0.36) and body size (h² = 0.42) were moderately heritable, whereas the influence of maternal effects was estimated to be negligible. While the number of vertebrae had a positive effect on body size, no evidence for a genetic correlation between body size and vertebral number was detected. However, there was a significant positive environmental correlation between these two traits. Our results support the generalization-in accordance with results from a review of heritability estimates for vertebral number in fish, reptiles and mammals-that the number of vertebrae appears to be moderately to highly heritable in a wide array of species. In the case of the three-spined stickleback, independent evolution of body size and number of vertebrae should be possible given the low genetic correlation between the two traits.     

Heritability of DNA methylation in threespine stickleback (Gasterosteus aculeatus)

Epigenetic mechanisms underlying phenotypic change are hypothesized to contribute to population persistence and adaptation in the face of environmental change. To date, few studies have explored the heritability of intergenerationally stable methylation levels in natural populations, and little is known about the relative contribution of cis- and trans-regulatory changes to methylation variation. Here, we explore the heritability of DNA methylation, and conduct methylation quantitative trait loci (meQTLs) analysis to investigate the genetic architecture underlying methylation variation between marine and freshwater ecotypes of threespine stickleback (Gasterosteus aculeatus). We quantitatively measured genome-wide DNA methylation in fin tissue using reduced representation bisulfite sequencing of F1 and F2 crosses, and their marine and freshwater source populations. We identified cytosines (CpG sites) that exhibited stable methylation levels across generations. We found that additive genetic variance explained an average of 24–35% of the methylation variance, with a number of CpG sites possibly autonomous from genetic control. We also detected both cis- and trans-meQTLs, with only trans-meQTLs overlapping with previously identified genomic regions of high differentiation between marine and freshwater ecotypes. Finally, we identified the genetic architecture underlying two key CpG sites that were differentially methylated between ecotypes. These findings demonstrate a potential role for DNA methylation in facilitating adaptation to divergent environments and improve our understanding of the heritable basis of population epigenomic variation.