Thesis Title

Life History of the Spectaclecase, Cumberlandia Monodonta Say, 1829 (Bivalvia, Unionoidea, Margaritiferidae)

Date of Graduation

Spring 2000

Degree

Master of Science in Biology

Department

Biology

Committee Chair

M. Chris Barnhart

Subject Categories

Biology

Abstract

Cumberlandia monodonta is a distinctive species of freshwater mussel that was formerly widespread in the Mississippi River Basin, but has suffered drastic decline. Reproductive biology and demography of Cumberlandia were investigated in the Gasconade and Meramec Rivers, Missouri, which appear to be the present stronghold of the species. During 1999, females were gravid with mature glochidia from early April to late May. No evidence of biannual reproduction was observed. Fecundity was 5.0x10⁶ ± 2.38x10⁶ (1.9x10⁶ - 9.6x10⁶) glochidia [mean ± st. dev. (range), n = 8]. Males as young as 5 years produced gametes, and females as young as 6. However, inferences from growth rate suggest that major investment in reproduction may not occur until after about 10 years of age. The sex ratio did not differ significantly from 50:50, and no hermaphroditic individuals were observed. Thirty species of fishes were tested as potential hosts by artificial infestation with glochidia, but no transformation was observed. Gills from 690 fish of 40 species were examed for natural infestation. One individual each of bigeye chub (Notropis amblpos) and shorthead redhorse (Moxostoma macrolepidotum) carried Cumberlandia glochidia. However, it is not yet known whether these species are suitable hosts. Population density and age structure were investigated at 8 sites. Sites were delimited by the presence of Cumberlandia and ranged from 480-1800 m². Quadrats were placed using an adaptive design, excavated, and searched visually. Approximately 5% of total site area was searched. Over 6,000 live specimens were discovered and 2,880 were measured. The ages of 287 individuals were estimated by counting growth lines in the hinge ligament. Inferred growth rates based on these counts agreed with field measurements of growth, validating the assumption of annual growth lines. Ages estimated from growth lines ranged up to 56 years and were correlated with shell length (mm) as follows: age = (length * 15.4431) / (201.4524-length) (n = 278, R² = 0.83). This equation was used to infer age from shell length in the demographic samples. Inferred age distributions were similar in both rivers. The most abundant age classes were approximately 20-35 years. Among sites, population densities ranged from 1.2 to 12.8 (mean = 6.7) individuals per m², while local (i.e., single quadrat) densities ranged up to 120 individuals per m². Although a few young individuals were found at all sites, individuals less than 10 years old comprised only 13.2% of the sample. Therefore, it appears that these populations might be in decline, despite high population densities of adults.

Copyright

© Michael S Baird

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