The three general body armour forms of Gasterosteus aculeatus (Linnaeus), high, intermediate and low plate count forms, are found in nonbreeding marine populations. In breeding season initially the population in the nontidal portion of Bonsall Creek consisted of the low and intermediate plate count forms. Later when the tidal zone was occupied by breeding sticklebacks all three body armour forms were present and from the limit of the tidal influence the low and intermediate forms became less frequent seaward. In Chase Creek there exists an anadromous breeding population but there was no adjoining freshwater population. In Chase Creek however there did exist a zone where all three body armour form were present. Therefore, the development of the pattern of plate variation in the creek's tidal zone does not appear to be dependent upon the presence of both freshwater and marine population tyrjes.
In Bonsall Creek where both a freshwater and a marine population bred, low plate count individuals from the freshwater zone and high plate count individuals from the adjoining tidal zone were reciprocally transferred in wire baskets. Mortalities of transferred fish were shown to be significantly higher than those of the controls indicating a possible barrier to gene exchange between the two populations. However, the presence of the intermediate plate count form in
the freshwater zone of Bonsall creek strongly implicates gene flow between these two groups of fishes.
all three forms collected from the tidal zone of Chase Creek. Showed the same mortality rate when placed in freshwater. This suggests that the low and intermediate plate count fish breeding in the tidal portion of Chase Creek were of marine origin.
Ten morphological characters were combined in a discriminant function and used to classify breeding individuals from Bonsall Creek. The discriminant function showed a gradual change in morphology of the fish distributed from marine to freshwater.
It is concluded that while there was considerable differentiation between adjoining freshwater and anadromous breeding populations of Gasterosteus aculeatus, no evidence of a morphological discontinuity as would be expected of separate species. However, the presences of the hybrid form in the freshwater zone of Bonsall Creek strongly implicates gene flow between those freshwater and marine groups of fish.
Eleven populations ranging geographically from the Alaska Peninsula to Chehalis Biver in Washington State were similarly subject to discriminant function analysis. These samples did not show clinal variation in their scores, though the scores of the populations were significantly different suggesting local adaptation and possible restriction of gene flow within the marine environment. / Science, Faculty of / Zoology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/20749 |
| Date | January 1977 |
| Creators | Black, E. A. (Edward Adam) |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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