Fine-scale temporal variation of the Miocene sticklebackGasterosteus doryssus

Abstract

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.

Evolutionary Novelty and Atavism in the Semionotus Complex: Relaxed Selection During Colonization of an Expanding Lake

“…Obviously this requires either an exceptionally long-term study or an exceptional fossil record. While there may be more gap than record through the total history oflife, certain fossiliferous sequences are superb and can be used to supply detailed historical sequences ofcharacter change (e.g., Bell, 1982).…”

Implications of a fossil stickleback assemblage for Darwinian gradualism

“…Gasterosteus doryssus provides a case with sufficient temporal resolution and background information on natural selection and genetic architecture to document and interpret the transition from an ancestral species to a descendant in the fossil record. At a coarse time scale, this transition was nearly undetectable (Bell & Haglund, 1982). By increasing temporal resolution to 5000 years, which is the lower limit of temporal resolution for most fossil deposits (Schindel, 1980), the crude outlines of evolutionary change in G. doryssus became apparent.…”

“…The main study section, where research on G. doryssus has focused, consists mostly of annual couplets of white diatom‐rich sediment alternating with darker terrageneous sediment that usually range in thickness between 0·3 and 0·5 mm year −1 (Bell & Haglund, 1982; Bell, 1994; Houseman, 2004; Bell et al , 2006). A section comprising laminated diatomite also occurs in the exposure that produced the inshore sample.…”

Intraspecific variation in fossil vertebrate populations: Fossil killifishes (Actinopterygii: Cyprinodontiformes) from the Oligocene of Central Europe

“…Among fossil tetrapods, studies on intraspecific variation have been conducted for example for dinosaurs (Raath, 1990;Bever et al, 2011;Foth and Rauhut, 2013), ichthyosaurs (Maxwell, 2012), rodents (Renaud et al, 2006;Lazzari et al, 2010) and horses (MacFadden, 1997). Several studies on variation in extinct populations of fishes have been carried out during the last three decades, mostly concerning microstratigraphic changes in variation of meristic and morphometric characters of different body parts, or phenotypic variation as it relates to taxonomically informative characters (Bell and Haglund, 1982;Bell et al, 1985;Bell and Legendre, 1987;Cloutier, 1997;Smith, 1987;McCune, 1990McCune, , 1996Barton and Wilson, 1999;Micklich and Klappert, 2004;Grande, 2010; Table 1). …”