Parasites and size-assortative schooling in three-spined sticklebacks

Recent field studies carried out in lacustrine environments have suggested that fish schools may be assorted with respect to parasite infections, but the generality and strength of parasite-assortative schooling in fish is unclear. In this study, data are presented on the body size and externally visible macroparasite load of 366 individual three-spined sticklebacks Gasterosteus aculeatus L. (Gasterosteidae, Teleostei) from six naturally formed schools captured in the Gullmarsfjord on the west coast of Sweden. Length–frequency analysis suggested that two separate year classes (presumed 0+ and 1+) were represented in the sample. Individual schools were assorted by body size, and contained largely fish of a single year class. The number of fish in the school was negatively related to median body size of members. Probability of infection increased significantly with fish length for two parasites ( Cryptocotyle lingua (Trematoda) and Glugea anomala (Microsporidia)), and marginally for a third (chalimus larvae of Caligus sp. (Copepoda)). After correcting for body-size effects, the proportion of school members infected with C. lingua and G. anomala did not differ significantly from a model of random assortment by infection status. However, two of the six schools were found to have significantly more, or significantly fewer, members infected with Caligus sp. chalimus larvae than predicted by the random model. Significant inter-school differences in the intensity of C. lingua infection were also detected, but these resulted from the combined effects of size-assortment and a strong correlation between body size and infection intensity. The results of this study provide only limited support for the existence of active parasite-assortative schooling in marine sticklebacks, and are discussed in relation to recent studies of parasite assortment amongst host fish in other ecosystems.     

Population differences in spatial learning in three-spined sticklebacks

In a changing environment, learning and memory are essential for an animal''s survival and reproduction. The role played by the environment in shaping learning and memory is now attracting considerable attention. Until now, studies have tended to compare the behaviour of two, or at best a few species but interspecific comparisons can be misleading as many life history variables other than environment may differ between species. Here we report on an experiment designed to determine how learning varies between different populations of the same species, the three-spined stickleback. We found differences between the populations in their ability to solve a spatial task and also in the spatial strategies they used. A second simple learning task showed that these differences were not the result of gross differences in learning ability or adaptation to laboratory conditions. We discuss these results and suggest that the behavioural differences may relate to features of the respective habitats from which the fish were sampled.     

Olfactory mate recognition in a sympatric species pair of three-spined sticklebacks

Mate recognition is critical to the maintenance of reproductiveisolation, and animals use an array of sensory modalities toidentify conspecific mates. In particular, olfactory informationcan be an important component of mate recognition systems. Weinvestigated whether odor is involved in mate recognition ina sympatric benthic and limnetic species pair of three-spinedsticklebacks (Gasterosteus spp.), for which visual cues andsignals are known to play a role in premating isolation. Weallowed gravid females of each species to choose between waterscented by a heterospecific male and water scented by a conspecificmale. Benthic females preferred the conspecific male stimuluswater significantly more often than the heterospecific malestimulus water, whereas limnetic females showed no preference.These species thus differ in their odor and may also differin their use of olfaction to recognize conspecific mates. Thesedifferences are likely a consequence of adaptation to disparateenvironments. Differences in diet, foraging mode, habitat, andparasite exposure may explain our finding that odor might bean asymmetric isolating mechanism in these sympatric sticklebackspecies.     

No sibling odor preference in juvenile three-spined sticklebacks

Laboratory-bred juvenile three-spined sticklebacks from 11 sibshipsdid not prefer to shoal with their siblings when they were offeredthe choice between odor from unfamiliar siblings and non-kinin a fluviarium, although the power for finding a significantpreference was very high (0.99). The test fish preferred theside where odor from the heavier shoal was supplied; this shows thatthey could appreciate odor cues from conspecifics in our apparatusand should have preferred their siblings if such a preferenceexists. Our results are compatible with theoretical predictionsbut are at variance with previous findings by other authors.We used independent replicates in a blind protocol with strictrandomization of fish and procedures.     

Acid stress increases pelvic spine asymmetry in juvenile three-spined sticklebacks

In the evaluation of the effect of acidic water on the symmetrical development of the pelvic spines in juvenile three-spined sticklebacks Gasterosteus aculeatus , directional rather than fluctuating asymmetry was found, with left spines being, on average, longer than the right. Fish that were exposed for a period of c. 2 months to acidic pH levels grew significantly more asymmetrical pelvic spines than their control full-siblings held in unmanipulated water. Average spine size was not affected by the experimental treatment.     

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.     

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.     

The impact of three-spined sticklebacks on the Zooplankton of a previously fish-free pool

SUMMARY.

• 1 In the Camargue (southern France), most invertebrates inhabiting temporary shallow oligohaline marshes and pools are large-bodied, conspicuous and defenceless taxa that are restricted to fish-free environments. Management practices, by creating drainage canals, strongly affect the invertebrate community by allowing colonization by fish.
• 2 Sticklebacks colonizing the study pool were sampled daily and Zooplankton sampling was carried out at weekly intervals. From early October until the pool dried in June, 1365 sticklebacks entered and only 139 stickleback's fry and seven adults left the pool. Zooplankton abundance was high during the whole study period with a mean density of 1360 ind. 100cm^?2. Larger forms (Daphnia magna, Simocephalus vetulus, Arctodiaptomus wierzejskii) quickly disappeared after the first wave of sticklebacks entered the pool in November. Subsequently, smaller species (Diacyclops bicuspidatus odessanus, Chydorus sphaericus and ostracods) replaced the larger ones until the pool dried.
• 3 Food selectivity of sticklebacks and daily Zooplankton consumption were investigated under experimental conditions within the pool in spring. After introduction of sticklebacks, densities of Zooplankton species dropped quickly (D. b. odessanus, C. sphaericus) with the exception of Ostracoda. Estimates of daily Zooplankton consumption by adult sticklebacks varied between 2.8 and 10.7% of fish body weight. Examination of gut contents showed that fry mainly ingested Chydorus sphaericus.
• 4 Given that the stickleback is an annual species in the Camargue, and that few fry are able to leave the pool due to the early drying out, the colonization of such a former fish-free pool is not beneficial for the stickleback population. However, a more serious effect of such colonization is the progressive local extinction of the most typical Zooplankton species inhabiting these formerly fish-free environments.

     

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.     

Pattern of hyperphagia in immature three-spined sticklebacks after short-term food deprivation

Juvenile three-spined sticklebacks Gasterosteus aculeatus were fed live enchytraeid worms, and mean daily ad libitum consumption in the absence of periods of deprivation was 11·7% of initial body weight. Then, six groups of five replicate fish were subjected to 1, 3 and 6 days without food. Each period of deprivation was followed by 1 day of ad libitum feeding. The sequential order of deprivations differed between groups. Over the sequence of deprivations and re-feedings, mean cumulative consumption did not differ between groups. Mean daily consumption was 19·8% of initial body weight after a 1-day deprivation, 22·3% after 3 days and 19·5% after 6 days. However, consumption in the 24 h after a given length of deprivation also depended on the prior history of deprivation. Specific growth rate over the experiment did not differ between groups. The results provide evidence for an effective regulation of appetite in growing sticklebacks.     

Impaired reproduction in three-spined sticklebacks exposed to ethinyl estradiol as juveniles

To investigate the population-level effects of exposure to environmental endocrine disrupters, a mesocosm-scale study was carried out in which the reproductive performance of groups of free-spawning three-spined sticklebacks, Gasterosteus aculeatus, exposed as juveniles to a model estrogen, was assessed. Juvenile sticklebacks were exposed to ethinyl estradiol (EE(2)) at measured concentrations of (mean +/- SEM) 1.75 +/- 0.37 ng L(-1) and 27.7 +/- 1.08 ng L(-1) for 4 wk posthatch and then reared thereafter in pristine lake water until they reached adulthood. Exposure to the higher EE(2) concentration resulted in the occurrence of ovotestis among males, whereas no gonadal abnormalities were evident among males exposed to the lower concentration of EE(2). In addition, when spawning was allowed in the mesocosm environment, fewer nests were built per male, and fewer eggs were deposited per nest, in the group exposed to 27.7 ng L(-1). Males from this group also exhibited a less intense nuptial coloration than control males. In the group exposed to 1.75 ng L(-1) EE(2) posthatch, significantly fewer nests were built than in the control group. These results demonstrate that the timing of exposure to estrogenic contaminants, in developmental terms, is critically important. Short-term exposure to estrogens as juveniles can clearly influence reproductive performance as adults, despite all growth and development subsequent to the exposure period taking place in an estrogen-free environment. In addition, these results suggest that reproductive dysfunction can occur even in fish with no gross abnormalities in gonadal structure. This suggests that the absence of gonadal intersex is not a reliable indicator of the reproductive potential, or estrogen-exposure history, of fish populations or the only important factor involved in compromising the reproduction of estrogen-exposed fish.     

Environmental deterioration compromises socially enforced signals of male quality in three-spined sticklebacks

Social costs are often important in promoting the honesty of sexually selected traits. What happens, then, when social costs are relaxed? In species that breed in shallow coastal waters, increases in the frequency and severity of phytoplankton blooms may undermine the value of visual signals by reducing visibility and, in so doing, lead to dishonest signaling by relaxing the social consequences of high signaling effort for poor-quality individuals. Here, we experimentally test the effects of algally induced water turbidity on the role of male-male competition in facilitating reliable sexual displays in three-spined sticklebacks. We found that males in poor condition reduced their courtship effort in the presence of competition in turbid water. This reduction, however, was to a much lesser extent than that observed in clear water. Thus, courtship under conditions of algal turbidity did not reflect male condition as honestly as courtship in clear water. Algal turbidity also influenced breeding coloration, with males in poor condition reducing their area of red nuptial coloration in turbid conditions. Our findings suggest that anthropogenic disturbance to the signaling environment can potentially reduce the evolutionary potential of sexual selection by diminishing the efficacy of visual displays and weakening socially enforced signals of male quality.     

Dispersion patterns of parasites in 0+ year three-spined sticklebacks: a cross population comparison

Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an 'individual parasitation index' ( I _PI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks.     

Effects of gravidity on habitat use and antipredator behaviour in three-spined sticklebacks

Habitat use was examined in six Alaskan populations of three-spined sticklebacks Gasterosteus aculeatus . In three lakes with predatory fishes, gravid female sticklebacks remained closer to refuge than did non-gravid females, while those in lakes devoid of piscivores did not display this shift in behaviour. Gravid females in a lake with predatory rainbow trout Oncorhynchus mykiss used different evasive manoeuvres than did non-gravid females during in situ encounters with a model rainbow trout. Gravid females were more likely to incorporate a protean element in their flight moffements than were non-gravid females. Offerall, these data suggest that gravid female three-spined sticklebacks modify habitat use and escape behaviour to reduce vulnerability to predators.