Selective predation and the intensity of selection acting upon the lateral plates of threespine sticklebacks

Abstract

SUMMARYSticklebacks in Lakes Wapato and Chelan are far inland and highly isolated from other populations. They live about one year. Rainbow trout prey on sticklebacks most heavily during the winter, and this predation is random on males and females and on the three plate morphs. However, trout show strong selective predation on sticklebacks with respect to plate number. The selective advantage of seven plated sticklebacks under predation is highly significant and consistent over three years. The frequency of seven plated adults in Lake Wapato was 56 per cent, in 1968, but increased to 65 per cent, in 1969 and has since remained at about 62 per cent. This large increase coincides with the time interval when predation was heaviest and when selective predation favouring sevens was greatest. The heritabilities for number of plates and gill rakers are high, and so the values obtained for the increase in mean relative fitness show that natural selection is acting strongly on these traits. Predation acting on the variation in plate number and food specialisation acting on gill rakers are two of the major selective agents.

Evolution in parallel: new insights from a classic system

“…Upon invasion of freshwater, the posterior lateral plates are typically lost, leaving a few anterior lateral plates that articulate with the pelvic girdle [12] (Figure 1b,c). Loss of the lateral plates can be rapid [13] (Figure 1d), supporting an earlier inference of strong selection against the full complement of lateral plates in freshwater, probably as a result of reduced ion availability and lower predation intensity [12,14].…”

The adaptive significance of dorsal spine variation in the fourspine stickleback, Apeltes quadracus. III. correlated traits and experimental evidence on predation

“…Variation in the number of anterior plates confers no obvious mechanical advantage against predation, nevertheless the morphs are subject to strong selective predation (Bell and Haglund, 1978;Gilbertson, 1980;Hagen and Gilbertson, 1973;Moodie, 1972b;Moodie et aL, 1973). And, like variation in dorsal spines in Apeltes, lateral plate number in G. aculeatus is correlated with spine length and body length among populations (Hagen and Gilbertson, 1972;Moodie, 1972a, b), but not within populations (Bell and Haglund, 1978;Hagen and Gilbertson, 1972;Kynard and Curry, 1976;Moodie, l972a).…”

SELECTIVE PREDATION FOR VERTEBRAL PHENOTYPE INGASTEROSTEUS ACULEATUS: REVERSAL IN THE DIRECTION OF SELECTION AT DIFFERENT LARVAL SIZES

“…Predation has been implicated as an important agent of selection acting on other morphological characters of sticklebacks (e.g., Moodie, 1972;Hagen and Gilbertson, 1973;Moodie et al, 1973;Bell and Haglund, 1978;Reimchen, 1980Reimchen, , 1983Reist, 1980aReist, , 1980bBlouw andHagen, 1984a, 1984b). Behavioral differences between phenotypes, and the lack of any obvious mechanical advantage to particular phenotypes, have led to suggestions that selective predation for these other morphological characters is indirect, resulting from selection acting more directly on the correlated behavioral traits (e.g., Moodie, 1972;Moodie et al, 1973;Blouw andHagen, 1984a, 1984b).…”

“…The main block used offspring of parents collected from Holden Lake (49°06'N, I 23°50'W), a small eutrophic lake containing the low and partially plated morphs (Hagen and Gilbertson, 1972) of G. aculeatus. The second block used offspring ofparents collected from Kennedy Lake (49°06'N, 125°33'W), a large oligotrophic lake containing all three lateral plate morphs.…”