Academic journal article The American Midland Naturalist

Unusually Long Spines in Brook Stickleback (Culaea Inconstans) from the Mad River Drainage, Ohio

Academic journal article The American Midland Naturalist

Unusually Long Spines in Brook Stickleback (Culaea Inconstans) from the Mad River Drainage, Ohio

Article excerpt

.-Spine length, pelvic girdle morphology and body form vary markedly among populations of the brook stickleback (Culaea inconstans). Predation may drive the evolution of well developed defensive structures because these traits increase handling times and allow captured prey to escape from small predators. Previous studies indicate that C. inconstans from Macochee Creek (Champaign Co., Ohio), a tributary of the Mad River, appear to have spine lengths that approach the extremes for the species. However, it is unclear whether long spines are common throughout the Mad River drainage or are limited to this single tributary. Morphometric analysis revealed that C. inconstans from the Mad River drainage have longer spines than other populations in its southeastern range and that long spines are consistently found throughout the Mad River drainage. The selection pressures responsible for long spines in C. inconstans from the Mad River drainage are presently not clear.

INTRODUCTION

Studies of life history, ecology, behavior and morphology suggest that variation among populations of sticklebacks (Gasterosteidae) evolved in response to local selection pressures (Hagen and McPhail, 1970; Bell, 1976; Bell and Foster, 1994 and references therein). The selective forces leading to local adaptation of stickleback populations have been debated, but it is generally accepted that predation is important (Bell, 1976, 1988). It appears that sticklebacks under intense predation pressure from gape-limited predators have long spines and robust pelvic girdles because these structures may improve chances of escape if captured (Hoogland et al., 1957; Hagen and Gilbertson, 1972; Moodie, 1972; Gross, 1978; Reimchen, 1991).

Spines of sticklebacks are thought to be effective defensive structures against gape-limited predators because sticklebacks can erect their dorsal and pelvic spines and lock them into place (Hoogland et aL, 1957; Hagen and Gilbertson, 1972; Moodie, 1972; Gross, 1978; Reist, 1983; Reimchen, 1991). Reimchen (1991) measured effective diameter (defined by a circle circumscribing the erect dorsal and pelvic spines) in Gasterosteus aculeatus and found that as effective diameter of stickleback approached the gape of the predator (Oncorhynchus clarki), escape efficiency increased to nearly 100%.

Most work on morphological variation within Gasterosteidae has focused on Gasterosteus aculeatus. However, large-scale clinal variation has also been reported for Culaea inconstans (Kirtland), the brook stickleback (Nelson, 1969; Nelson and Atton, 1971; Reist, 1981). In the southeastern portion of their range, C. inconstans generally have long dorsal and pelvic spines, robust pelvic girdles and deep bodies, whereas C. inconstans from the northwestern portion of the range have short spines, poorly developed pelvic girdles and shallow bodies (Nelson, 1969). Of the 62 localities Nelson (1969) reported, C. inconstans from Macochee Creek (Champaign Co., Ohio), a tributary of the Mad River, are particularly interesting to us because they appear to have spines lengths that approach the extremes for the species (Nelson, 1969). Because Nelson (1969) only sampled fish from Macochee Creek, it is unclear whether long spines are common throughout the Mad River drainage or are limited to this single tributary. The objectives of our study were to further quantify spine length of C. inconstans in the Mad River drainage and to compare populations in the Mad River drainage to other populations across the southeastern range of this species.

METHODS

We measured 285 preserved specimens from 18 populations in the southeastern range of Culaea inconstans for which at least five specimens were available (Table 1). Most specimens examined were from the Ohio State University's (OSU) Museum of Biological Diversity (Columbus, Ohio). These represented 14 populations from Ohio, Illinois and Michigan. We also measured specimens that we collected from four additional populations in Ohio, Pennsylvania and Wisconsin. …

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