Ecology of the fourspine stickleback, Apeltes quadracus, with respect to a polymorphism for dorsal spine number

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Abstract
The subject of this research is the ecological genetics of a polymorphism for dorsal spine number in A. quadracus. Information is presented on its ecology and on dorsal spine variation. Estimating age from otoliths is subject to several serious errors and spine sections are questionable. Generation time was estimated at .apprx. 1 yr using length frequency distributions. Dorsal spine number varies from 1-7, but the 4- and 5-spined morphs predominate. The polymorphism is ubiquitous; where samples are available for comparisons over time, morph frequencies have remained relatively constant for at least 50 yr. Sex ratio is highly variable among sites and among samples at particular sites. Morph frequencies are independent of sex and age. Morph frequencies are homogeneous among samples taken at differing times day, tide levels, months within a year and among years. They are also homogeneous among the microhabitats sampled in an estuary. The relevance of these results is the following: 1 yr is the generation time, sexes and ages can be pooled to estimate morph frequencies, and since morph frequencies remain relatively constant, at least within the time period of the survey, comparisons frequencies among sites to detect geographical and ecological patterns of variation seems valid.
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