Fine-scale temporal variation of the Miocene stickleback Gasterosteus doryssus

The fossil stickleback, Gasterosteus doryssus, is highly variable for pelvic girdle structure and the number of dorsal spines. Six “sampling pits” were dug at known stratigraphic positions within a continuous section which contains abundant G. doryssus, and the stratigraphic position of each specime...

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Bibliographic Details
Published in:Paleobiology 1982-01, Vol.8 (3), p.282-292
Main Authors: Bell, Michael A., Haglund, Thomas R.
Format: Article
Language:English
Subjects:
Evolution
Fossils
Freshwater
Genetic heterogeneity
Genetic variation
Paleobiology
Phenotypes
Sample size
Specimens
Temporal distributions
Varves
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Summary:The fossil stickleback, Gasterosteus doryssus, is highly variable for pelvic girdle structure and the number of dorsal spines. Six “sampling pits” were dug at known stratigraphic positions within a continuous section which contains abundant G. doryssus, and the stratigraphic position of each specimen within each pit was determined. The deposit apparently is composed of annual layers (varves), allowing relatively precise conversion of stratigraphic distance to years. The temporal distribution of phenotypes is heterogeneous but can be grouped into two temporally contiguous, nonheterogeneous sets. However, absence of heterogeneity for pelvic phenotypes within the two groups of pits could be an artifact of small sample size. The number of sample pits was insufficient to determine whether the observed phenotypic heterogeneity among pits represents temporal trends. Differences also occurred between mean temporal distributions of stickleback phenotypes within one of the pits located within a nonheterogeneous set of pits. Thus, there is within-pit temporal heterogeneity that is unresolved by between-pit comparisons, although the sampling pits are separated by an average of only about thirty thousand years. Larger time intervals usually used in paleontology may seriously underestimate evolutionary rates because fine scale reversals of evolutionary trajectory are undetected. Temporal variation in G. doryssus provides a system in which most limitations of other fossil systems for measuring the rate of evolution can be circumvented. As in virtually all paleontological studies, spatial variation cannot be entirely eliminated as a potential cause of stratigraphic variation.
ISSN:0094-8373
1938-5331
DOI:10.1017/S0094837300006990