Academic journal article The American Midland Naturalist

Reproduction in Etheostoma Zonale across Three Breeding Seasons in Ohio

Academic journal article The American Midland Naturalist

Reproduction in Etheostoma Zonale across Three Breeding Seasons in Ohio

Article excerpt

ABSTRACT.-Etheostoma zonale was collected from the Hocking River in south-central Ohio from April 1999 through August 2001. Ovaries of adult females were classified by developmental stage and appropriate-stage ovaries were used to analyze clutch size, egg size and gonadosomatic index (GSI). Although body condition was significantly low in 1999, we saw no direct evidence for a correlation with any reproductive trait in that year. Clutch size varied among years, though not in parallel with condition. Etheostoma zonale produced larger clutches and had larger GSI toward the middle of the breeding season in each year. Egg size declined over the season in each year. The amount of intraseasonal variation in reproductive traits here was similar to that previously reported for interannual and geographic variation in E. zonale and should caution investigators from generalizing from limited collections during the breeding season.

INTRODUCTION

The reproductive ecology of darters in the genus Etheostoma has been studied fairly extensively for some time (see references in Paine, 1990; Bart and Page, 1992). However, Etheostoma encompasses a large number of species, some of which inhabit large geographic ranges, and our understanding of their ecology often requires generalizing from a very limited number of studies on populations that may represent points on an unknown continuum of geographic variation. For example, of the 51 species of Etheostoma included in a broad study of life history traits (Bart and Page, 1992), only three had published data from more than one geographic location. Moreover, significant geographic variation in both clutch and ovum size was found among populations of E. zonale in Arkansas (Guill and Heins, 1996) and E. whipplei in Mississippi (Heins and Machado, 1993). Further, ovum size varied among populations of E. spectabile in Texas (Marsh, 1984), whereas clutch size varied among populations of E. simoterumin Tennessee (Heins, 2001). These studies, thus, suggest that substantial variation can exist even over limited geographic ranges.

Along with local adaptation to unique selection pressures in individual drainages, environmental effects (phenotypic plasticity) may also be responsible for some of the observed geographic variation and serve to further complicate generalizations of reproductive ecology. These environmental effects may also result in seasonal (within a single season) or annual (among years) variation and can potentially be identified with studies that assess reproductive traits periodically across the entire breeding season and that include several years in the analysis. In various species of Etheostoma, seasonal variation has been found in clutch size (Gale and Deutsch, 1985; Weddle and Burr, 1991), ovum size (Marsh, 1984; but see Fuller, 1998) or both (Hubbs et al., 1968; Heins and Machado, 1993). General trends are for clutch size to peak in the early or mid-season and for egg size to decline with increasing water temperatures. The extent to which these seasonal variations are due to environmental effects or adaptive (genetic) strategies is unknown. In the only study that specifically addressed annual variation (most likely due to proximate environmental influence) in clutch and ovum size in darters of this genus, significant variation was found among 3 y in E. zonale (Guill and Heins, 2000). The objectives of the present study were to investigate annual and seasonal variation in reproductive traits in the banded darter E. zonale across three reproductive seasons from a single stream in south-central Ohio.

MATERIALS AND METHODS

From early April 1999 through late August 2001, Etheostoma zonale was collected from the Hocking River south of Lancaster, Ohio. Collections were made every 2 wk from 2 April through 19 August 1999, then once each month from October 1999 through February 2000 and then every 2 wk again during the breeding seasons of 2000 and 2001 (from late February through mid-August each year). …

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