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.     

Inference of evolutionary pattern: diversionary displays of three-spined sticklebacks

In three lakes and one marine lagoon in British Columbia, Canada,groups of three-spined sticklebacks (Gasterosteus aculeatus)cannibalize embryos and fry guarded by conspecific parentalmales. At the approach of these groups, males perform displaysthat divert the groups, often causing them to bypass the male'sterritory. Similar large groups failed to elicit such displaysfrom males in three noncannibalistic populations. The diversionarydisplays in two lakes are similar, apparently attracting conspecificsthrough foraging deception, but sticklebacks in a third lakeand in a marine lagoon perform a more complex array of displaytypes, some of which appear to incorporate ritualized elementsof other behavioral repertoires. Because the freshwater populationsare derived from marine populations of Gasterosteus, the complexdisplay repertoire is apparently ancestral relative to thefreshwater radiation. This inference is strengthened by comparisonwith the diversionary display repertoire in an Atlantic marinepopulation (primitive outgroup). Thus, the absence of the displayin some populations and the relatively limited display formsin others appear to represent a loss of all or part of theancestral display. Loss of the display in noncannibalistic populations may be adaptive because it enhances mating success.The significance of partial loss in some cannibalistic populationsis less clear. Interpretations of these patterns demonstratethe value of accounting for past historical relationships amongpopulations when inferring historical patterns of behavior evolution.     

Juvenile three-spined sticklebacks avoid parasitized conspecifics

Synopsis Juvenile three-spined sticklebacks,Gasterosteus aculeatus, were given a series of four choice tests to determine whether they avoided schools of conspecifics in which individuals were parasitized with the ectoparasiteArgulus canadensis. Results from these tests indicate that juvenile sticklebacks can avoid schools of parasitized conspecifics. Furthermore, parasites alone did not elicit an avoidance response, suggesting that it is both the presence of the parasite and its effect on stickleback behavior that causes avoidance of parasitized individuals.     

Daily growth increments in the otoliths of the three-spined stickleback, Gasterosteus aculeatus L.

Daily increment formation was demonstrated in the sagittae of the three-spined stickleback, Gasterosieus aculeatus L., under both laboratory and field conditions. The onset of daily increment formation coincided with the day of hatching. The main sources of inaccuracy in age determination resulted from difficulties in resolving narrow increments in the sagittae of fish held at low temperatures and the increasing incidence of checks with age. The advantage of daily increments for investigating growth in this species was demonstrated from a comparison between increment-derived age-at-length data and length-at-capture data, since the latter significantly under-estimated early growth rate within a population.     

The effects of habitat- and diet-based cues on association preferences in three-spined sticklebacks

A number of recent articles have investigated the potentialof familiarity preferences to influence group membership infree-ranging animals. However, it is not clear to which extentindividual recognition or a more general recognition of a groupodor is responsible for familiarity preferences. First, we testedthe sensory basis of the recognition of familiars in stickleback.When allowed to choose between a familiar and a nonfamiliarstimulus shoal on the basis of both visual and chemical communication,visual communication only, and chemical communication only,the preference of focal fish for familiars was shown to dependon the presence of chemical cues. We subsequently investigatedthe effects of recent habitat and diet on shoaling preferencesin the three-spined stickleback (Gasterosteus aculeatus). Experimentalfish were divided into four treatment groups consisting of twowater treatments (saline and freshwater) and two diet treatments(Daphnia spp. and bloodworm). Focal fish subsequently showedsignificant association preferences for groups of nonfamiliarfish that had undergone the same water or diet treatment asthemselves. These data indicate that individual recognitionis not a prerequisite for the expression of association preferences.     

Genetic variation in MHC class II expression and interactions with MHC sequence polymorphism in three-spined sticklebacks

Genes of the major histocompatibility complex (MHC) have been studied for several decades because of their pronounced allelic polymorphism. Structural allelic polymorphism is, however, not the only source of variability subjected to natural selection. Genetic variation may also exist in gene expression patterns. Here, we show that in a natural population of three-spined sticklebacks (Gasterosteus aculeatus) the expression of MHC class IIB genes was positively correlated with parasite load, which indicates increased immune activation of the MHC when infections are frequent. To experimentally study MHC expression, we used laboratory-bred sticklebacks that were exposed to three naturally occurring species of parasite. We found strong differences in MHC class IIB expression patterns among fish families, which were consistent over two generations, thus demonstrating a genetic component. The average number of MHC class IIB sequence variants within families was negatively correlated to the MHC expression level suggesting compensatory up-regulation in fish with a low (i.e. suboptimal) MHC sequence variability. The observed differences among families and the negative correlation with individual sequence diversity imply that MHC expression is evolutionary relevant for the onset and control of the immune response in natural populations.     

Colour perception in three-spined sticklebacks: sexes are not so different after all

Sexual selection theory implies a tight coupling between the evolution of male sexual display and the sensory capabilities of the female. In sexually dimorphic species it is proposed that this might lead to sex differences in a species’ perceptive abilities. However, supporting evidence for this is rare, and to date there is only one example; three-spined sticklebacks, Gasterosteus aculeatus. Here, the female’s visual system is reported to become more red-sensitive during the summer breeding season; a time when sexually mature males display a red throat and belly to potential mates. In contrast, a shift in sensitivity is not apparent in males. These results, although commonly quoted, are surprising because previous observations suggest that both sexes may benefit from the detection of the male’s red colour patch; in females the intensity of red coloration can influence the choice of mate, and in males the conspicuous red colouration can aid the detection of rival males. To investigate this paradox we repeated the original optomotor experiment using a fully controlled design. In contrast to the earlier result, we found that both males and females exhibit a shift in their sensitivity to red during the reproductive period. These new data therefore do not support the hypothesis that sex differences in perceptual abilities occur in sexually dimorphic species.     

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.     

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.     

Sex-specific survival and parasitism in three-spined sticklebacks: seasonal patterns revealed by molecular analysis

A molecular method of identifying sex in three-spined sticklebacks Gasterosteus aculeatus showed that adult males had a higher prevalence of dermal Glugea anomala cysts than adult females, and young-of-the-year had more than adults. At the end of the breeding season, as predicted, the adult sex ratio became female biased and there was a disproportionate increase in G. anomala parasitism in adult males.