In a short time span in evolutionary terms—about 10, years—the fish population can be seen to dramatically reduce the size of their pelvic spines. This particular fossil record is remarkably complete with nearly year-by-year detail which includes documentation of intermediate forms. Fossil Record of Stickleback Evolution Background By studying the fossils from different layers of the fossilized lakebed, one can follow the evolution of the local stickleback population over tens of thousands of years, since each layer corresponds to a specific year. Sticklebacks from this quarry can be divided into three categories.
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This article has been cited by other articles in PMC. Abstract While the genetic basis to plate morph evolution of the three-spined stickleback Gasterosteus aculeatus is well described, the environmental variables that select for different plate and spine morphs are incompletely understood. Using replicate populations of three-spined sticklebacks on North Uist, Scotland, we previously investigated the role of predation pressure and calcium limitation on the adaptive evolution of stickleback morphology and behavior.
While dissolved calcium proved a significant predictor of plate and spine morph, predator abundance did not. They failed to detect a significant effect of dissolved calcium on morphological evolution, but did establish a significant effect of predation; albeit in the opposite direction to their prediction.
Adaptation, calcium concentration, Gasterosteus aculeatus, natural selection, phenotypic adaptation, selective predation Introduction We are grateful to MacColl and Aucott for prompting discussion of our work and for furthering the debate on three-spined stickleback Gasterosteus aculeatus Stickleback evolution evolution.
Despite several decades of research, it is surprizing that the selective agent for morphological evolution in this species remains a subject of active research.
We also agree that it is instructive, and somewhat sobering, that different research groups working on largely the same populations and using comparable data can draw conflicting conclusions.
However, as we will show, our conclusions are actually not as divergent to those of MacColl and Aucott as might appear. The three-spined stickleback is a valuable model for understanding the mechanism of evolution in nature through the evolution of its bony plates and spines.
The size, number, and arrangement of these bony elements show wide variation, although most populations predominantly express a single morph, that is either the complete morph, with a continuous row of plates from immediately Stickleback evolution the head to the caudal peduncle; the partial morph with an anterior row of plates, then a length of the body that lacks plates, succeeded by a posterior row of plates, and the low morph with only an anterior row of plates and the remainder of the body naked.
There is a striking correlation between the frequency of these morphs and the ionic concentrations of the water in which they live, for at least part of their life Heuts ; Wootton Complete and partial morphs are associated with marine and estuarine conditions, although some populations migrate into freshwater to spawn in spring.
Low morphs usually reside in freshwater throughout their life Wootton In a few locations, including the Hebridean Island of North Uist off northwest Scotland, sticklebacks display morphs with plates and spines more reduced even than in the freshwater low plate morph. In some populations, fish have no dorsal and pelvic spines, or lack a pelvic girdle altogether.
In others, all but a vestige of the lateral plates is present Campbell Consequently, the three-spined stickleback populations of North Uist offer an exceptional opportunity to examine the selective agent for plate and spine reduction.
In a recent study Spence et al. We concluded that dissolved calcium was a significant predictor of plate and spine morph, while we failed to detect an effect of predator abundance.
The chief predator of three-spined sticklebacks on North Uist is believed to be the brown trout Salmo trutta. MacColl and Aucott raise three main issues with our work, and we will address each in turn. Our aim is that these responses will contribute to a broader discussion of the likely role of dissolved calcium and predation rate on understanding morphological evolution in sticklebacks.
Qualitative measure of stickleback plate morph In Spence et al. The minimal morph included discrete, previously described morphs with unusual degrees of plate and spine reduction. We adopted this conservative approach, of grouping highly reduced morphs, to maximize statistical power, but also because it reflected our view that the same agent of selection is likely to select for a reduction in any or all of these skeletal elements, whether selection is generated from a deficiency of dissolved calcium or an absence of predators.
A high correlation of variables contributing to PCA is not desirable, as the variables simply mirror each other and do not independently contribute to the PC.
Consequently, it is difficult to see what added information this approach provides over the more robust low versus minimal classification used in Spence et al. In fact, MacColl and Aucott do acknowledge as much in their discussion, and their analysis using our binomial classification of morphs generates the same result as their PCA analysis.
Measurement of dissolved calcium concentration MacColl and Aucott adopted a more comprehensive procedure for measuring dissolved calcium than the one used in Spence et al.
Overall, our measurements of dissolved calcium were consistently lower than those of MacColl and Aucottalthough not of Giles The distribution of dissolved calcium concentrations among our 36 fieldsites on North Uist was strongly bimodal.
Lochs on North Uist are essentially calcium poor or calcium rich, corresponding with whether they are located on a band of calcium-rich shell-sand grassland, termed the machair, that supports rich vegetation and alkaline lochs, or blanket peat bogs supporting highly acidic lochs Beveridge ; Friend For the subset of our sites that MacColl and Aucott also measured dissolved calcium concentration, our data and theirs agree in assigning lochs to these two distributions.
Thus, while our estimates lack the precision of those of MacColl and Aucottour respective discrimination of calcium poor and calcium rich sites was identical. We also note that our measurements of dissolved calcium correlate significantly both with those of MacColl and Aucott and Gileswho measured the same sites 30 years earlier.
Differences between our data and those of MacColl and Aucott within low calcium sites might be owing to our less precise methodology.The Virtual Stickleback Evolution Lab is appropriate for high school biology as an excellent companion to an evolution unit.
Because the trait under study is fish pelvic morphology, the lab can also be used for lessons on.
A worksheet that guides students through The Stickleback Evolution Virtual Lab. The virtual lab lets students learn firsthand the methods for analyzing body structure in stickleback collected from lakes and fossils recovered from a quarry.
Students measure, record, and graph their results to discover evolutionary patterns. "We've now moved the timescale of the evolution of stickleback fish to decades, and it may even be sooner than that," said Cresko, who also is the UO's associate vice president for research and a.
Stickleback reproductive and parental behavior have been studied for several decades, and extensive knowledge of morphology, behavior, and life history has been .
Incidentally there’s already evidence that the threespine stickleback Von Hippel introduced into Cheney Lake are already undergoing evolution from their anadromous (meaning the fish, like salmon, are born in freshwater, travel to the ocean, and then come back to the freshwater to mate) ancestral form, to freshwater forms.
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