After writing this post back in April, I had the idea to send one of my video cameras to Jan and Ulrika in Finland so that they could get me some footage of this work. Now that I’m working on creating a ‘BIOMUSINGS‘ episode around it, I thought I’d remind you of this fantastic research and why I chose to highlight it!
I hope you enjoy!
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Biological fitness includes a measure of both survival and reproductive ability – one is not nearly as important without the other. So what happens if the ‘unfit’ members of a population are suddenly the ones with all of the reproductive power?
This kind of absurdity can only happen when nature gets a little ‘help’ from humankind.
Eutrophication of waterways is a major environmental disaster in several areas of the world. The virtual ‘choking’ out of native animal and plant species by a fast growth of nutrient-starved algae and phytoplankton has effects that reverberate right through many freshwater ecosystems. The research presented in this paper shows that the indirect effects of eutrophication can have long term effects on evolutionary processes in populations of threespine sticklebacks (Gasterosteus aculeatus) in the Baltic Sea. The shallows of the Baltic in Southern Finland are highly eutropied with filamentous algae, and this alteration of the near-shore benthic environment is drastically shifting the selective pressures on males that nest there…
Through a series of algal density manipulations, researchers were able to determine that more males nest in dense vegetation when it is available (i.e. in eutrophied habitats). However, the males in these areas are subject to high-levels of parasitim (a common problem for high-density populations). Indeed, samples of males from highly vegetated areas showed that these poor fellas carry a much higher level of internal parasites than those living in sparsely vegetated sites. Here’s the kicker: these highly parasitized (aka UNFIT) males are still able to fertilize a large number of eggs. Why? A few reasons: first, a decrease in female choosiness occurs in these habitats. If males are hard to find, a female is more likely with whomever she can see. Second, the heterogeneous environment in the eutrophied areas supports a greater number of male territories because males cannot see each other. This results in an overall relaxation of male:male competition (i.e. males that would have otherwise had to compete with each other for access to a suitable territory no longer need to do so). In areas where vision is NOT blocked by filamentous algae, females are able to discern between high and low-quality mates (i.e. parasitized vs not parasitized) and healthy males compete with each other for territories and access to the females’ eggs.
So, what for the future of the three spined stickleback in the Baltic Sea? The process of eutrophication has resulted in a major alteration in the part of the population that can successfully reproduce. The long-term evolutionary consequences of such a shift could be bad news for the entire stickleback population in this area.
Sorry Chuck, your own species has wreaked havoc on the natural world such that your beautiful theory may no longer be applicable as it was intended.
Heuschele, J., & Candolin, U. (2010). Reversed parasite-mediated selection in sticklebacks from eutrophied habitats Behavioral Ecology and Sociobiology DOI: 10.1007/s00265-010-0937-9