Intraspecific Variation Among Emerald Shiners (Notropis atherinoides) of the Missouri River

Fishes of the Missouri River are separated by six dams and impoundments and inhabit a variety of natural and engineered habitat types. Concern over the effects of river alteration led to an investigation of whether the Missouri River fish have been segregated into differentiated sub-populations. Emerald shiners (Notropis atherinoides) were chosen as a representative species because of their wide distribution, record of morphologic and meristic plasticity, and life history characteristics. These conditions led to the hypothesis that the differing and disjunct habitats of the Missouri River may be acting as selective pressures to produce distinct sub-populations within the Missouri River. To test this hypothesis I designed a set of four analyses to determine if l) there were any intraspecific differences among sites, 2) the differences were related to a genetic population structure, 3) the differences were correlated with habitat types, and 4) if the differences provided a measurable performance advantage. Emerald shiners were collected from both reservoir and river habitats. Differences in body form were measured using a box-truss protocol. This created a 2- dimensional projection of the fish using fixed body landmarks to define body shape. A principal components analysis of these data indicated that posterior body length, eye position, and head length account for the variation seen among sites. Other morphological characters such as jaw width (P<0.001), head depth (P<0.001), and eye diameter (P<0.001), provided more discrimination between sites. Larger eye diameters were associated with lentic and low turbidity sites. Shape was highly variable among mainstem Missouri River sites, but less variable among lentic and tributary sites. Local adaptation may occur on a small scale, but large scale morphometry appears to be highly variable thus precluding the need for specialized forms. Meristic values (counts of vertebrae, fin rays, scales, teeth, taste buds, etc.) are governed by genotype, but can vary during embryonic development in response to temperature, sunlight, and stress. Naturally, a predictable longitudinal gradient or random insignificant variation should be seen. When conditions change abruptly or are altered, marked interruptions in the gradient and significant variation in meristic counts may arise. I measured dorsal, anal, pectoral, and pelvic fin rays and vertebrae on emerald shiners from all portions of the Missouri River. Only the pectoral fin ray numbers (9-14) and vertebrae counts (35-43) significantly differed among sites (P<0.001). Pectoral ray numbers seemed to be disrupted by the presence of reservoirs, but vertebrae number followed a gradual increase with increasing latitude. These results suggest that local conditions can have site-specific effects on some characteristics during development, but may leave others unaffected. To measure genetic variation I collected 30 individuals from four mainstem Missouri River sites, a site in the Yellowstone River, and an outgroup from Lake Erie. Using 28 surveyed loci, I found 14 of them to be polymorphic. The Yellowstone River was 2-4 magnitudes different from its Missouri River neighbors, identifying the Yellowstone River as genetically isolated to a degree from the rest of the Missouri River mainstem sites. The Montana site was more genetically similar to the Missouri site than to its neighboring Yellowstone River site. This relationship suggests a degree of reproductive isolation between the Y cllowstone River and the entire mainstem Missouri River. The mainstem Missouri River was genetically panmictic (genetically mixed through immigration and emigration) from headwaters to mouth and has not been measurably affected or segregated genetically by impoundments at this point in time. These genetic data do not support the pattern of differing characteristics associated with specific habitats seen in either the morphometric or meristic analyses. The logical conclusion then is that the physical variation in emerald shiners was a result of intraspecific plasticity unrelated to genetic isolation or drift. I next used a laminar flow tunnel to detern1ine the functional significance of physical and behavioral changes among emerald shiners from different habitats. Fish were swum for five minutes at increasing velocity intervals until they were fatigued. Fish of the same size class were used from each site. Performance varied erratically among individuals from each site (45<Ucri1<93 cm/sec), but did not differ significantly between sites, indicating that neither the habitat in which they were reared nor their differences in physical characteristics provided any measurable difference in swimming performance. Intraspecific plasticity may be a response to differences in habitat, but the differences do not seem to substantially affect the functionality or performance potential of fish from either site. The alterations to the Missouri River appear to have affected certain physical aspects of emerald shiners, however the inherent plasticity of the species seems to allow it to adapt or react locally without the loss of genetic integrity. These integrated analyses then support the conclusion that selective pressures in different habitats may cause change in morphometric and meristic characters, but are likely attributable to local adaptive plasticity rather than genetic drift resulting from subpopulation formation.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation - University Access Only

Discipline thesis:degree_discipline

Wildlife and Fisheries Science

Year

2001

Author dc:creator

• Young, Bradley A.

Contributors dc:contributor

• Charles R. Berry

• Natural Resources and Conservation

Statement dc:rights

• Copyright © 2001 Bradley A. Young. All rights reserved.

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/609

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-1609