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Life-history Plasticity Among Stream Sites in the Chattahoochee River Drainage, Alabama
Lemuel R. Casten and Carol E. Johnston

Southeastern Naturalist, Volume 7, Number 4 (2008): 679–690

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2008 SOUTHEASTERN NATURALIST 7(4):679–690 Life-history Plasticity Among Stream Sites in the Chattahoochee River Drainage, Alabama Lemuel R. Casten1 and Carol E. Johnston1,* Abstract - Cyprinella venusta (Blacktail Shiner) were studied at four sites to investigate life-history parameter variation in Alabama streams. Consistent with life-history theory, fish from a perceived degraded site were significantly smaller than fish from sites that had less apparent environmental disturbance. Fish from the degraded site had the smallest size at maturity and the smallest propagule size. Egg diameters were not related to standard length of fish among sites. There was no significant difference in mature egg diameters; however, ripening egg diameters differed among sites. Clutch sizes adjusted for standard length varied among sites. There was no difference in gonad mass in females for all spawning months; however, there were differences in gonad mass in males in July. The gonadosomatic index peaked in July for both males and females. Reproductive males were still present in September for three sites, but all females from all sites had become latent by September, indicating that the spawning season had ended. The results of this study suggest that Cyprinella venusta has the ability to alter life-history parameters and this may be a factor contributing to its persistence in habitats where other species are declining. Introduction Phenotypic plasticity, or the ability of an organism to change its phenotype in response to environmental changes, is usually thought of as an adaptive strategy for dealing with differing environments (Miner et al. 2005, Sultan 2000). These phenotypic changes may have effects beyond the individual organism, and may alter ecological processes in the environment by changing many direct and indirect ecological interactions (Miner et al. 2005). Morphological plasticity has been well documented in fishes, and is common in many species of animals with broad geographic ranges (Robinson and Parsons 2002, Stearns 1992). Local adaptation is a process that also may produce differences in morphology, but involves genotypic changes. With some exceptions (e.g., Gasterosteus aculeatus L. [Stickleback]; Kristjánsson et al. 2002), genetic changes involve relatively long time periods and some degree of isolation. Life-history parameters, and reproductive traits in particular, are known to vary across environmental gradients in some fishes (Heins 1991, Mazzoni and Iglesias-Rios 2002). The documentation of such phenotypic plasticity is the first step towards understanding the persistence or extirpation of fishes exposed to various environmental changes. In the Chattahoochee River drainage, Cyprinella venusta (Girard) (Blacktail Shiner) persists and is even increasing its distribution (Johnston and Farmer 2004), whereas a sympatric species, Cyprinella callitaenia 1Fish Biodiversity Lab, Department of Fisheries, Auburn University, Auburn, AL 36849. *Corresponding author - cjohnsto@acesag.auburn.edu. 680 Southeastern Naturalist Vol. 7, No. 4 (Bailey and Gibbs) (Bluestripe Shiner), has been extirpated from much of its native range (Johnston and Farmer 2004, Shepard et al. 1995). Other species sympatric with Blacktail Shiner, such as Notropis amplamala (Pera and Armbruster) (Longnose Shiner), Lythrurus atrapiculus (Snelson) (Blacktip Shiner), Notropis cummingsae (Myers) (Dusky Shiner), and Notropis hypsilepis (Suttkus and Raney) (Highscale Shiner), are also decreasing in abundance and distribution. The proposed reasons for these findings include changes in stream hydrology, sediment input, and temperature (Johnston and Farmer 2004), although less obvious biotic factors are almost certainly important. The objective of this study is to investigate life-history variation in Blacktail Shiner in tributaries to the Chattahoochee River, AL. The persistence of Blacktail Shiner at our study sites could be due to the ability to alter life-history parameters in response to disturbance. Field-site Description Four sites from Chattahoochee River drainage were chosen for this study (Fig. 1). Sites chosen in Uchee Creek are by County Road 39 (Russell County, AL, 32°20'42"N, 85°3'16"W), and Highway 169 (Russell County, AL, 32°22'42"N, 85°10'53"W), (referred to as Uchee Creek 39 and Uchee Creek 169 hereafter) and Moffits Mill (Lee County, AL, 32°30'24"N, 85°10'48"W). An additional site was located in an adjacent stream, Wacoochee Creek (Lee County, AL, 32°37'21"N, 85°8'0"W). The sites were perceived as ranging Figure 1. Sampling localities of Cyprinella venusta (Blacktail Shiner) within the Chattahoochee River drainage in Alabama. 2008 L.R. Casten and C.E. Johnston 681 from relatively pristine with moderate to high species richness (Wacoochee Creek and Uchee 169), to intermediate disturbance and species richness (Moffits Mill), to highly degraded with low species richness (Uchee Creek 39) (Tables 1 and 2). The Uchee 39 site would be predicted to have a much higher species richness based on stream size and historical collections. Potential predators include bass and pickerel species, which were present in collections from Moffits Mill and Uchee 169, but absent from Uchee 39 and Wacoochee. The fish assemblages at all sites included native species, with no exotics present. All of these sites are thought to be within the dispersal distance of individual fish, or in close enough proximity for genetic mixing to occur (Fig. 1; Johnston 2000), and were chosen so as to reduce the possibility of local adaptation. Table 1. Characteristics of study sites. Habitat heterogeneity is based on categorical estimate and coefficient of variation of transect measurements of physical habitat parameters (water depth, fl ow, stream width, substrate). Species Habitat Site richness Riparian zone Substrate heterogeneity Wacoochee 11 Forested Gravel, sand Moderate Uchee 169 20 Forested Gravel, sand High Moffits Mill 10 Partly forested Bedrock, gravel Moderate Uchee 39 7 None Clay, sand, bedrock Low Table 2. Descriptive statistics for habitat measurements (July 2005) and ANOVA results. Means with an * differed from others (Duncan post-hoc test). Variable Site n Mean SD CV Depth, m Wacoochee 21 0.31 0.15 0.48 Moffits Mill 15 0.34 0.27 0.79 Uchee 169 12 0.67* 0.42 0.62 Uchee 39 14 0.57* 0.33 0.57 F = 5.4, P = 0.002 Flow, m/sec Wacoochee 21 0.25* 0.16 0.64 Moffits Mill 15 0.35 0.31 0.88 Uchee 169 12 0.53** 0.32 0.60 Uchee 39 14 0.40 0.21 0.52 F = 3.4, P = 0.022 Width, m Wacoochee 6 11.0* 1.8 0.16 Moffits Mill 4 23.9** 4.5 0.18 Uchee 169 4 16.0 1.2 0.07 Uchee 39 4 24.0** 0.37 0.01 F = 33.2, P = 0.000 Temperature, °C Wacoochee 6 25.4 0.66 0.03 Moffits Mill 4 25.6 0.22 0.008 Uchee 169 4 25.4 1.0 0.04 Uchee 39 4 27.5* 1.7 0.06 F = 4.1, P = 0.028 Turbidity, NTU Wacoochee 6 10.1 2.3 0.22 Moffits Mill 4 8.4 1.1 0.13 Uchee 169 4 14.1 3.9 0.27 Uchee 39 4 11.8 5.1 0.43 F = 2.1, P = 0.143 682 Southeastern Naturalist Vol. 7, No. 4 Uchee Creek has shown a decline in fish species distribution and abundance (Johnston and Farmer 2004, Walser and Bart 1999). Reasons for the decline in species populations may be changes in land use resulting in siltation, deterioration of water quality, and recent water draw down for mining and irrigation (Johnston and Farmer 2004, Howard 1997, Walser and Bart 1999). Fish diversity is especially low in mainstem sites, where species richness may be as low as 2 species (Johnston and Farmer 2004). Uchee Creek 39 was perceived to be the most degraded of the four sites, having eroded banks, no riparian zone, clay-sand substrates, and sluggishto- fast fl ows. There was obvious clear-cutting in the area. Uchee Creek 169 is a typical Coastal Plain stream with sandy gravel and mud substrates and sluggish-to-fast fl ows. The riparian area is rich in vegetation, and snags are present in the stream. Though Uchee Creek is heavily infl uenced by agricultural activity, this site remains relatively undisturbed. Moffits Mill on Little Uchee Creek lies directly on the Fall Line and is characterized by a large shoal with bedrock substrate and fast fl ows. The riparian zone is partially intact at this site. Because of the presence of both disturbed and relatively unchanged sites within the watershed, the sites in Uchee Creek provide a framework for comparison of potential life-history changes among sites. We included a site from an adjacent stream, Wacoochee Creek, for comparison to these Uchee Creek sites. The site on Wacoochee Creek is completely forested and has relatively high species richness, and we considered it relatively pristine. Materials and Methods Blacktail Shiner were collected monthly from May to November 2005 using a backpack shocker and seine in four streams along the Chattahoochee River drainage. From May to July, sampling frequency was twice a month because this is the time when Blacktail Shiner actively spawn. Sampling was conducted once a month from August to November. Samples from May to September were used to quantify life-history parameters. May to November samples were used to determine sex ratios for each site. Physical habitat measurements were taken for each collection at each site, and include: water depth (m) and velocity (fl ow, m/sec), substrate type (bedrock, cobble, gravel, sand, or clay; following a modified Wentworth scale; Ross et al. 1990), turbidity (NTU), temperature (°C), and stream width (m). Measurements were taken at approximately equal intervals along 1–3 transects perpendicular to water fl ow. Water velocity was measured using a Marsh-McBirney fl ow meter, and turbidity was measured using a LaMotte model 2020 turbidimeter (average of 3 measurements per site). All habitat types were sampled to allow for the collection of a representative number of Blacktail Shiners inhabiting various habitats. Fish collected were anesthetized using tricaine methanesulfonate (MS 222), and fixed in neutral 10% buffered formalin before processing. Fish were sexed and measured to the nearest 0.01 mm standard length (SL) with dial calipers. Ovaries were removed from each specimen to assess gonad stage. Ovarian condition of females was categorized using the classification of Heins and 2008 L.R. Casten and C.E. Johnston 683 Baker (1993): (1) latent (LA), (2) early maturing (EM), (3) late maturing (LM), (4) mature (MA), (5) ripening (MR), and (6) ripe (RE). Ovarian stages that were MA, MR, and RE were considered reproductive and LA, EM, and LM females were considered non-reproductive (Heins and Baker 1993). Reproductive condition of males was determined by visual examinations of testes. Mature males have large and opaque testes. Males that have small and transparent testes were considered latent. Seasonal change in gonad mass for both sexes was determined using the gonadosomatic index (GSI). Gonads and eviscerated specimens were air dried for 2 hours (Johnston and Knight 1999) and weighed to the nearest 0.0001 grams. GSI was calculated as dry gonad mass/dry somatic mass (mass of eviscerated specimen) X 100 (Johnston and Knight 1999). Clutch size and egg size (diameter) for each clutch was determined following Heins and Baker (1993). Clutch size was quantified by counting the number of all mature eggs in mature (MA) and ripening (MR) females. Ripe (RE) females were not used because they may have already spawned before sampling collection and will not represent complete clutches. Females showed distinct groups of early maturing (EM), late maturing (LM), mature (MA), mature ripening (MR), and ripe (RE) eggs. Only MA and MR egg classes were measured and analyzed in this study. Due to a limited number of females with clutches having RE eggs, RE egg measurements were not included in statistical analysis. Obtaining ripe eggs from field-caught samples is rare, especially in minnows (Heins and Baker 1993, Machado et al. 2002), and this generality holds true for this study. Size estimates of eggs in each clutch were obtained by measuring the diameter of 10 randomly chosen eggs from the clutch. Because eggs were not spherical in preserved specimens, egg diameters were estimated by averaging measurements to the nearest 0.05 mm of the maximum and minimum dimensions. Size at maturity was determined for each sex by assessing samples collected during the reproductive season. Sexually mature females were those classified as EM, LM, MA, MR, and RE. Latent (LA) individuals were considered sexually immature. Mature males were determined by visual inspection of testes as noted earlier. Following Heins and Baker (1993), the smallest individual that was EM was considered the size of maturity. Mean size at maturity was calculated as the average standard length of specimens in each gonad stage. Sex ratio was determined for fish at each site by using pooled fish from monthly collections. Deviations from the expected 1:1 sex ratio were determined using a chi-square test. Analysis of variance (ANOVA) and analysis of covariance (ANCOVA) were used to test for life-history parameter differences among sites followed by Tukey post hoc tests for pair-wise comparison between site means. Differences in SL of fish among sites were tested for significance using ANOVA. Differences in clutch size, gonad mass, egg size, egg mass, and GSI among sites were tested using ANCOVA with mean SL as a covariate. Linear regression was conducted to determine the relationship of life-history parameters to SL, and correlations in life-history parameters of females were determined using Pearson’s correlation analysis. 684 Southeastern Naturalist Vol. 7, No. 4 All values were log10 transformed prior to analysis and tested for normality and homogeneity of variances to satisfy the assumptions of statistical analysis. All analyses were conducted using SAS (SAS Institute, Inc. 2003) and SPSS 11.0 (SPSS, Inc. 2005) and considered significant at P ≤ 0.05. Results All physical habitat parameters differed significantly among some sites except turbidity (Table 2). Uchee 169 had the greatest water depth and the most heterogeneity (highest CV) of depths (Table 2). This pattern was also true for water velocity (fl ow). Uchee 39 had the highest water temperature for the July samples compared in Table 2, and for the rest of the year as well. This site also had a considerable amount of clay substrate, which was absent at other sites. In addition, turbidity and water temperature showed the greatest variability at Uchee 39. The sex ratio (male:female) for fish from Uchee Creek 39 did not depart from a 1:1 ratio (χ2 = 0.098, df = 1, P = 0.325), while deviations from a 1:1 ratio were found in the other three sites, with skewness towards females. There was a significant difference in sex ratio of Blacktail Shiners at Uchee Creek 169 (0.8:1) (χ2 = 6.556, df = 1, P = 0.010) and a highly significant departure from the expected 1:1 sex ratio in fish from Moffits Mill (0.7:1) (χ2 = 19.702, df = 1, P = 0.0001), and Wacoochee Creek (0.6:1) (χ2 = 17.376, df = 1, P = 0.0001). Female sizes differed significantly among sites (ANOVA: F = 22.88, df = 3, P = 0.0001; Table 3). Wacoochee Creek females were significantly larger than females from the other three sites and were almost 10 mm larger than the smallest mean female size from Uchee Creek 39. Male sizes also differed among sites (ANOVA: F = 5.03, df = 3, P = 0.003). Males from Uchee Creek 169 were largest, while Uchee Creek 39 had the smallest males. There was also a significant size difference of fish among sites when both males and females were combined (ANOVA: F = 7.97, df = 3, P < 0.0001); fish from Wacoochee Creek were largest, and Uchee Creek 39 fish were smallest. Moffits Mill fish had the largest size at maturity for females, and males from Wacoochee Creek had the largest size at maturity (Table 4). Females from Uchee 39 reached maturity at the smallest size relative to fish from other sites, and males from Moffits Mill were the smallest at maturity. Table 3. Mean standard length (SL, in mm) of Cyprinella venusta (Blacktail Shiner) during the spawning season from four sites in the Chattahoochee River Drainage. Numbers in parentheses are standard deviations. Means with same superscripted letters are not significantly different. Mean (SD) Site Female Male Female/male combined Uchee 39 61.7 (8.3)A, n = 119 80.1 (8.0)A, n = 38 65.7 (11.4)A, n = 157 Uchee 169 62.2 (7.6)AB, n = 93 88.0 (8.6)B, n = 31 67.9 (13.4)A, n = 124 Moffits Mill 64.6 (7.0)B, n = 114 82.5 (7.9)A, n = 45 69.2 (10.9)A, n = 159 Wacoochee 71.0 (11.5)C, n = 82 85.1 (11.4)7, n = 14 72.9 (12.4), n = 96 F value 22.8 5.03 7.97 P value 0.0001 0.003 <0.0001 2008 L.R. Casten and C.E. Johnston 685 Clutch size peaked in May and June and started to decrease as the spawning season progressed and as eggs were being spawned. Clutch size increased with female length when fish from all sites were considered together (F = 435.64, P < 0.0001; Table 5). Fish within sites had a significant correlation between clutch size and SL for all sites (Pearson’s: P < 0.0001). Since female SL was not uniform in all sites, we adjusted clutch size for SL in the analysis of data (standard covariate analysis using average SL as the covariate). Among sites, there were significant differences in SL-adjusted mean clutch size for May (ANCOVA: F = 3.21, df = 3, P = 0.0266), June (ANCOVA: F = 4.30, df = 3, P = 0.0069), and July (ANCOVA: F = 4.79, df = 3, P = 0.0035) (Table 6). When all females were pooled for all months, there was a significant clutchsize difference among sites (ANCOVA: F = 4.31, n = 408, P = 0.0053). Mature-egg diameter of fish did not differ among sites (F = 0.71, df = 3, P = 0.5467). For fish from Moffits Mill the range for mature-egg diameter was 0.78–1.23 mm (mean = 0.94), 0.80–1.17 mm (mean = 0.96) for fish from Uchee Creek 169, 0.79–1.24 mm (mean = 0.94) for fish from Uchee Creek 39, and 0.78–1.21 mm (mean = 0.94) for Wacoochee Creek fish. There was no significant relationship between regressions of mature-egg diameter with SL for all sites (P > 0.05); however, when all females were pooled, there was a positive relationship between mature-egg size and SL (F = 123.00, P < 0.0001). Mature-egg diameters were not significantly correlated with SL for all sites and were smaller than ripening eggs. Ripening-egg diameter was not correlated with SL or clutch size among females within sites. There was no significant relationship between regressions of ripening-egg diameter with SL for sites considered separately (P > 0.05), but when all females were pooled, there was a positive relationship between ripening-egg diameter and SL (F = 387.60, P < 0.0001). During June and July, ova from the four sites differed in size (June ANCOVA: Table 4. Sizes at maturity (SL in mm) for Cyprinella venusta (Blacktail Shiner) and mean temperature for each site during spawning months. Means with the same superscripted letters are not significantly different (P > 0.05). Size at maturity (SL,mm) Sites Female Male Temperature (°C) n 2311 128 Uchee 39 38.2A 66.1A 26.2 Uchee 169 44.4BC 65.1A 24.1 Moffits Mill 46.4C 60.1B 23.3 Wacoochee 41.1AB 72.8C 24.0 Table 5. Statistics for clutch size-standardized length relationships of Cyprinella venusta (Blacktail Shiner) for four sites. All values were log10 transformed prior to analysis. Site n Intercept Slope R2 P value Uchee 39 119 -2.881 2.947 0.522 <0.0001 Uchee 169 93 -3.330 3.171 0.506 <0.0001 Moffits Mill 114 -2.097 2.530 0.337 <0.0001 Wacoochee 82 -2.406 2.704 0.478 <0.0001 686 Southeastern Naturalist Vol. 7, No. 4 F = 3.87, n = 95, P = 0.0155; July ANCOVA: F = 5.91, n = 125, P = 0.0014; Table 7). Pair-wise comparison between sites showed that Wacoochee Creek fish had egg diameters that were significantly larger than for fish from Uchee Creek 39 in June. Blacktail Shiner from Uchee Creek 169 had egg diameters that were significantly larger than ripening-egg diameters from the other three sites in July. There was a significant difference in ripening-egg diameters when all females were pooled (ANCOVA: F = 3.07, n = 195, P = 0.0290). Uchee Creek 39 females had the smallest eggs, and Uchee Creek 169 females had the largest ripening eggs among sites. GSI peaked in July for all sites (Fig. 2) and did not differ among sites. Females from all sites became latent by September, indicating that spawning had ended. Fish from Moffits Mill (mean = 5.8, range = 4.1–7.0) showed the highest GSI, and Uchee Creek 169 females showed the lowest GSI (mean = 4.9, range = 3.4–6.6). Fish from Uchee Creek 39 and Wacoochee Creek had mean GSI values of 5.3 (range = 4.1–6.5) and 5.2 (range = 2.5–6.5), respectively. For males, GSI peaked in July, and the values dropped after the peak month, showing a pattern similar to female GSI (Fig. 3). Pair-wise comparison for July showed that the GSI (0.8) for fish from Uchee Creek 169 Table 6. Monthly SL-adjusted mean clutch sizes for Cyprinella venusta (Blacktail Shiner) at each site. Numbers in parentheses are standard deviations. Means with the same superscripted letters are not significantly different. All months Site May June July August combined Uchee 39 366 (117)BC 388 (149)A 286 (101)AB 170 (64)A 281 (145)AB n 25 24 32 38 119 Uchee 169 327 (107)B 318 (125)B 254 (110)A 136 (83)A 252 (124)A n 22 28 24 19 93 Moffits Mill 412 (143)C 396 (133)A 316 (100)B 155 (70)A 300 (140)B n 25 26 38 25 114 Wacoochee 345 (117)BC 390 (124)AB 324 (80)B 137 (87)A 302 (129)B n 25 17 31 9 82 F value 3.21 4.30 4.79 1.54 4.31 P value 0.0266 0.0069 0.0035 0.2104 0.0053 Table 7. Mean ripening ova diameter (mm) of Cyprinella venusta (Blacktail Shiner) from four sites in the Chattahoochee River drainage. Numbers in parentheses are standard deviations. Means with the same superscripted letters are not significantly different. Site May June July August Combined Range Uchee 39 1.08 (0.08) 1.03 (0.06)A 1.02 (0.05)A 1.05 (0.08) 1.04 (0.06)A 0.94 – 1.18 n 9 14 16 18 57 Uchee 169 1.08 (0.06) 1.07 (0.04)AB 1.10 (0.09)B 1.06 (0.06) 1.08 (0.06)B 0.93 – 1.31 n 9 14 11 10 44 Moffits Mill 1.06 (0.06) 1.08 (0.06)AB 1.02 (0.05)A 1.08 (0.05) 1.06 (0.06)B 0.93 – 1.19 n 13 12 18 11 54 Wacoochee 1.09 (0.07) 1.11 (0.05)B 1.04 (0.04)A 1.02 (0.04) 1.06 (0.07)B 0.96 – 1.19 n 13 9 15 3 40 F value 0.52 3.87 5.91 0.84 3.07 P value 0.6732 0.0155 0.0014 0.4812 0.0290 2008 L.R. Casten and C.E. Johnston 687 was significantly higher than the GSI (0.5, 0.4) for fish from Wacoochee and Uchee Creeks 39 (F = 3.24, df = 3, P = 0.0330). For August, fish from Moffits Mill had GSI values that were significantly higher compared to the other three sites (F = 3.20, df = 3, P = 0.0455). Males did not differ in GSI over Figure 2. Monthly variation in gonadosomatic index (GSI) of female Cyprinella venusta (Blacktail Shiner) from four sites in the Chattahoochee River drainage. There were no significant differences in monthly GSI for all sites in all spawning months (F = 1.87, n = 408, P = 0.1339). Figure 3. Monthly variation in gonadosomatic index (GSI) of male Cyprinella venusta (Blacktail Shiner) from four sites in the Chattahoochee River drainage. Uchee Creek 169 GSI was significantly higher than Wacoochee Creek and Uchee Creek 39 in July. GSI for Moffits Mill was significantly higher than the other three sites in August. All other months showed no significant differences in GSI for all sites. Wacoochee Creek males were latent by September. n = 128. 688 Southeastern Naturalist Vol. 7, No. 4 the four sites. The mean GSI for fish was 0.3 from Uchee Creek 39 (range = 0.1–0.4), and 0.3 (range = 0.1–0.8) for fish from Uchee Creek 169, 0.4 (range = 0.1–0.6) for fish from Moffits Mill, and 0.4 (range = 0–0.5) for fish from Wacoochee Creek. Reproductive males were still present during September for three sites (Uchee Creek 39, Uchee Creek 169, Moffits Mill); however, male fish from Wacoochee Creek had become latent a month earlier. Discussion Blacktail Shiner showed significant differences in life-history parameters among sites with varying physical properties. These differences included body size (SL), size at maturity, sex ratio, clutch size, and egg size. The smaller body size, small sizes at maturity, and smaller ova found at Uchee 39 follow a trajectory predicted by life-history theory as a response to harsh environmental conditions (Roff 1992, Stearns 1992) or a decrease in adult survivorship (Reznick et al. 1990). These variations in life history parameters may be phenotypic responses to biotic or abiotic factors, as the sites differed in both species richness (one of many biotic factors that potentially differed among sites) and physical habitat (a measure of abiotic factors). Alternatively, these differences could be due to genetic differentiation, but the close proximity of the sites (<20 km within Uchee Creek) and mobility of Cyprinella (Johnston 2000) makes this explanation less likely. Females from Uchee Creek 39 had smaller sizes at maturity as well as smaller body sizes than fish from the other three sites. This pattern is typical of the trade off in somatic size at onset of reproduction seen in many organisms, and may be a response to stress (Stearns 1992). For example, fish mature earlier in response to predation pressure as a bet-hedging strategy against early mortality (Reznick et al. 1990). There were few predators at Uchee 39, as species richness was diminished (Johnston and Farmer 2004), but it is possible that the relative habitat degradation has stimulated these life-history shifts. Females from Uchee 39 also had the smallest ripening ova, although this was not correlated with standard length or clutch size, which is also in agreement with predictions from life-history theory as a response to environmental stress (Roff 1992). Previous studies of reproductive life-history parameters of Blacktail Shiner found no difference in ova size and female size within sites, but ova size was correlated with female standard length among sites, similar to our findings for all sites pooled (Heins and Baker 1987, Machado et al. 2002). Although earlier studies did not find a significant relationship between female size and clutch size, our results indicated strong relationships between these two variables at all sites. Earlier studies also found correlations between ova size and mean annual runoff of streams, and proposed that larger progeny may be less susceptible to mortality from high-fl ow events. Data for size at maturity and body size were not presented in these previous studies (Heins and Baker 1987, Machado et al. 2002). Blacktail Shiner at our study sites differed in life-history traits associated with reproductive effort, including ova size. At the site we perceive as 2008 L.R. Casten and C.E. Johnston 689 most degraded (no riparian zone, low species richness, highest variation in temperature and turbidity), fish had the smallest body size, and females matured earlier and had the smallest ripening ova as compared to other sites. It is possible that Uchee 39 is a harsher environment for Blacktail Shiner than sites of previous studies, producing stronger life-history shifts. Other studies have found interpopulation differences in life histories of fishes, and such differences may be ubiquitous, at least in fishes with inherent plasticity (Baker 1994; Guill and Heins 1996; Heins 1991, 2000; Heins and Baker 1987; Machado et al. 2002; Reznick and Miles 1989). Many studies also correlate such differences with environmental factors. The effects of these changes in life-history parameters on the ecology of the stream ecosystem have yet to be addressed, but may have substantial consequences (Miner et al. 2005). In particular, changes in reproductive timing may allow the offspring of one species to out compete another for food or shelter, or to escape predation and reach a larger size faster. These differences may help explain why some species, such as Blacktail Shiner, persist while others are extirpated as environmental conditions change. Blacktail Shiner is considered a generalist species and has proliferated in the Uchee Creek system while other species, such as Bluestripe Shiner, are extirpated in this system (Johnston and Farmer 2004). Our findings suggest that life-history plasticity may contribute to the success of Blacktail Shiner. Documentation of life-history plasticity is the first step towards understanding the complex relationships between environmental change and species persistence. These relationships should be taken into account as conservation biologists strive to understand faunal change and habitat protection. Acknowledgments Thanks to A.R. Henderson, R.A. Kennon, N.R. Ozburn, P. Cleveland, and D. Holt for assistance with fish collection. This project was funded by a State of Alabama Wildlife Grant. Fish were collected under State of Alabama scientific collecting permit number 4491 issued to C.E. Johnston. Literature Cited Baker, J.A. 1994. Life-history variation in female Threespine Stickleback. 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