Life History Patterns and Reproduction in the Threespine Stickleback (Gasterosteus aculeatus L.)

Ukegbu, Angela Adanze (1986) Life History Patterns and Reproduction in the Threespine Stickleback (Gasterosteus aculeatus L.). PhD thesis, University of Glasgow.

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This thesis describes research on life history patterns and reproduction in the three spined stickleback (Gasterosteus aculeatus L.) from three Scottish populations. The populations are from Rivers Kelvin and Luggie and the Aurs Burn which are broadly similar habitats located in and around Glasgow. Age structure of the populations was studied using length frequency distribution and otolith analysis and both methods showed the life span of the fish to be just over a year, with a few females of the River Kelvin and Aurs Burn surviving to two years. Although the patterns of length frequency distribution of the three populations were generally the same, Kelvin fish were longer and heavier compared to fish from the other two populations. Most sticklebacks from these populations reproduce in the breeding season of the year following hatching when they are about a year old. However in all three populations, some fail to reproduce at this age. There is a protracted breeding season from April to August and there is evidence to suggest that those fish that do not breed at one year are offspring bred at the end of the previous season. They only reach maturity when the breeding season is almost over and therefore are not able to reproduce. The chances of this group of fish surviving to breed in the subsequent year at age two plus are very slim. Thus in these populations, there is a category of fish hatched late in the season which is extremely unlikely to breed at any stage of life. Monitoring the food intake of the sticklebacks showed that stomach fullness levels were low in winter and high just prior to the breeding season. No differences in food intake were found between the sexes or between age classes. Kelvin and Luggie fish of both sexes were however found to be consuming more food than the Aurs Bum fish. Quantitative histological examination of the gonads showed that the more mature stages of the ova were predominant in the females of all 3 populations during the breeding season, as would be expected. In the males, high levels of spermatozoa appeared at different times in the 3 populations. High levels could be seen in the Aurs Bum males as early as December but not until much later in males of the other two populations. Older and larger females had relatively heavier gonads and higher maturation scores and in Kelvin and Aurs Bum fish this was positively related to body condition. No relationship was found between age and relative gonadal weight in males, although older fish had more mature gonads. In one year old males from the Kelvin and Aurs Bum, a negative relationship was found between gonadal development and body condition. In fish from the Rivers Kelvin and Luggie, there was no relationship between percentage stomach fullness and body condition, suggesting that food is not limiting for these fish. However, Aurs Burn fish had a positive relationship between percentage stomach fullness and body condition. They also had the lowest food intake suggesting that food is in short supply. These fish appeared to be investing in growth and gonadal development at the expense of body condition. Since late hatched broods have little chance of breeding and so are less valuable, experiments were carried out at different stages of the breeding season to investigate allocation of time between nesting, territorial behaviour and self defense of parental males when at a risk of predation. These showed that male sticklebacks take risks to defend their young and that the intensity of this defense is greater in the presence of a brood. The presence of a predator affects this response; while males with eggs were attacking the conspecific intruder (placed near the nest) and visiting their nests more, males with empty nest tended to hide in the weed or investigate the predator. Males breeding early in the season showed a higher degree of parental investment compared to those breeding late in the season. This last result was attributed to the higher value of broods at the beginning of the breeding season. However, it remains enigmatic, since in these populations at least, the males have an almost non-existent chance of surviving to breed again in the next year.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Zoology
Date of Award: 1986
Depositing User: Enlighten Team
Unique ID: glathesis:1986-77386
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53

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