Threespine sticklebacks are genetically polymorphic for the number and arrangement of bony plates on the sides of the body. The adaptive significance and maintenance of plate variation was investigated in Heisholt Lake, a small British Columbia lake with two separate basins. The population contains the low plated, partially plated, and completely plated freshwater morphs of threespine sticklebacks, and plate number varies considerably within morphs. Frequencies of the plate phenotypes changed in space and time. Morph frequencies change spatially both between depths within an area, owing to segregation of breeding females, and between areas at the same depth. Phenotypic frequencies changed temporally both within and between generations. Phenotypes favored within a generation also increased in frequency from that generation to the next. At most stations in basin 1, low and completely plated sticklebacks increased,and partially plated sticklebacks decreased in frequency both within and between generations. In basin 2, partially plated sticklebacks were favored at many stations both within and between generations. Extreme phenotypes within all morphs increased in frequency both within and between generations, and asymmetrical disruptive selection acted during at least one generation within all morphs. Interactions between genetic variation and structure of the stickleback population appear to explain changes in the frequency jf phenotypes in both space and time. Experiments to investigate the movement pattern of sticklebacks in Heisholt Lake show that the population is composed of resident individuals, which remain in a restricted area and maintain either a feeding or "breeding territory, and non-residents, which move from area to area and do not breed. The phenotype of an individual influences its chances to become a resident. Low and completely plated sticklebacks were favored in competition for territories in basin 1, but partially plated sticklebacks were often favored in basin 2.) Females with extreme phenotypes had the greatest chance of breeding, and asymmetrical disruptive selection acted within all morphs. The phenotype of a stickleback also influences its chances of being infected with Schistocephalus solidus, a cestode parasite that reduces the chances of infected sticklebacks to survive and reproduce. Partially plated sticklebacks had the highest rate of infection in basin 1, but had the lowest rate of infection in basin 2. Differential infection of phenotypes was at least part of the explanation for the observed temporal changes in phenotypic frequencies. Spatial changes in phenotypic frequencies are caused by changes in space in the results of competition for territories. Temporal changes in phenotypic frequencies are explained by differential survival and reproduction of phenotypes as a result of differences between phenotypes in chancegto obtain a territory. / Science, Faculty of / Zoology, Department of / Graduate

Male three-spined sticklebacks without territories cannot reproduce; and in order to establish and maintain a territory, a male must behave aggressively toward other fish. Such social organization raises questions about determination of the size of the breeding population and the selective advantage of particular levels of aggressive behaviour. Experiments varying the amount and kind of social contact with other fish showed some of the effects of social organization. Grouped males build nests sooner, and hatch a smaller proportion of clutches of eggs than isolated males. Fry survive less well with grouped males. There are consistent differences between individual males in aggressiveness during the reproductive cycle. Changes in aggressive behaviour and territory size have similar U-shaped temporal patterns which are common to all males. Aggression is lowest and territory size smallest just before the clutch hatches when the male spends most time fanning. Males without clutches sometimes attack the nests of other males. Interference by these males is often responsible for hatching failure. Individuals that hatch clutches seem no more aggressive than those that do not. However, males hatching clutches have larger territories during the first part of the reproductive cycle. They spend more time at the nest, and tend to remain closer to it. / Science, Faculty of / Zoology, Department of / Graduate

Parental investment, defined as any parental activity that1 increases the survival of offspring at a cost to the parent, is a useful concept for examining the selective bases of parental behavior. To maximize its lifetime production of surviving offspring, a parent should adjust its level of risk in a parental investment depending on the value of its future "prospects" in relation to its present young. as present young increase in value, either by number or age, a parent should expend more risk in a parental investment so long as the effectiveness of its behavior does not diminish. This will often be the case for a parent that defends a nest containing eggs. The prediction of an increase in parental risk for more eggs or older eggs has been tested using two natural populations of threespine stickleback, Gasteros teus- acule^tus L. Male sticklebacks that were guarding nests were presented with a dummy predator, the prickly sculpin Cottus asper, and their responses were measured. Those males that remained within their nest area and attacked the dummy sculpin had a larger number of eggs or older eggs than those males that deserted their nests and never attacked the dummy. In the population that is sympatric with sculpins, males that initially attacked the sculpin's head had older eggs than those which avoided the head but attacked the tail area. The level of the male's responsiveness, and associated risk, was recorded in a series of quantitative measures. The time it took a male to return to its nest, as well as the time to attack the sculpin dummy, was shorter for males with a larger number of eggs or older eggs. The number of bites at the dummy in the first minute after the initial attack increased as the egg number and egg age increased. Changes in male risk were in the predicted direction and none of the responses could be associated with any single biological or environmental factor other than the number or age of the eggs. / Science, Faculty of / Zoology, Department of / Graduate

To date, models of sexual size dimorphism do not explain selection for small females, and they are also limited in their ability to explain intraspecific variation in sexual size dimorphism. I propose that small females, in species which produce multiple clutches in a breeding season, could have a selective advantage if the interval between clutches is shorter for small clutches of eggs. When the breeding season is long, small females may produce more eggs in total than large females by producing more clutches, and thus small size could be selected for. Two populations of threespine stickleback (Gasterosteus aculeatus) showing divergence in the sexual bias of size dimorphism were used to determine if large or small females had a seasonal fecundity advantage in these multiple spawning fish, and whether the two populations had diverged in life-history characteristics (age at first reproduction, number of clutches, length of breeding season). In addition, the mechanisms by which the differences in size were achieved was investigated. Size-frequency diagrams obtained from field samples indicated that the Lewis Slough population was an annual one, while fish at the Angus Campbell site apparently survived for more than one breeding season. The larger size of females at the Angus Campbell site resulted primarily from continued growth with age, while males stopped growing in about one years time. In an environment chamber female fish from Lewis Slough grew more slowly, as they approached maturity, than males and were therefore were smaller than males. Data from field collections, fry raised to maturity in an environment chamber, and females individually monitored in captivity over the course of a breeding season indicated that the populations have diverged in life-history characters. Females from the Angus Campbell ditch site produced fewer clutches and eggs over the breeding season (a measure of reproductive effort), delayed maturity and matured at a greater size, and had a longer life-span than Lewis Slough females. These observations are more in accordance with the predictions from bet-hedging theory than r & K selection theory. Data from individually monitored females held in a common environment indicated that clutch size and interclutch interval increased with increasing body size but small females still did not attain the seasonal fecundity advantage predicted by the model. However, these results suggest that small females are capable of achieving a greater seasonal fecundity relative to large females than would be predicted by the difference in average clutch size alone. Actual counts of the total numbers of eggs produced by individuals in a breeding season showed seasonal fecundity to be independent of body size. Female body size and fecundity are more weakly linked than previously realized and this confers an increased flexibilty for responding to diverse selective pressures. / Science, Faculty of / Zoology, Department of / Graduate

The present longitudinal study examines a natural population of threespine sticklebacks, Gasterosteus aculeatus form Little Mud Lake in British Colombia, Canada to determine if individual fish within a given population exhibited a preference for finding prey on the bottom of the lake, prey floating in the water column of the lake, or prey in other microhabitats of the lake. Foraging behaviors were recorded to determine the presence of individual specialization within the focal sympatric population. Comparing the proportion of strikes on various microhabitats for multiple individuals shows that individual specialization is present within the focal population of sticklebacks. Data shows that some fish prefer the feed on benthic prey while others prefer to feed on prey found on the surface of the water. Diet preferences were also compared to morphology to determine if individual fish traits had a relationship to preferred foraging location. Length of the longest gill raker and protrusion length results showed a relationship to limnetic-like and benthic-like feeding behaviors. / text

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Proefschrift (Ph. D.)--Groningen, 1956. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 203-213).

Proefschrift (Ph. D.)--Groningen, 1956. / Includes bibliographical references (p. 203-213). Also issued in print.

Hoogloand, Morris and Tinbergen (1957) demonstrated that the spines of two species of sticklebacks, Gasterosteus aculeatus and Pygosteus pungitius, are an effective defence against the pike (Esox lucius) and perch (Percha fluviatilis) as predators, and the present study was undertaken to compare the fright behaviour (i.e. responses to a predator) of the same two species.