Daniel J. Durston and Rana W. El-Sabaawi
In today’s rapidly changing world, an important question is how are ecosystems likely to change as a consequence of evolution? The answer here starts with an understanding of why species have the current effects that they do.
We know all species affect their ecosystems through the consumption and release of resources, but these effects often differ from species to species. Previous work has discovered that differences in what resources a species needs to build its body can explain some of the differences in how species collect and release resources. Species that require more of a certain resource tend to consume more or release less of that resource. Thus, if the resource needs of a species were to evolve, it is possible that the ecological effects of this species would also change.
In this paper we investigate whether there is the potential for a species’s resource needs to evolve. We use elements as a currency for resource needs, and investigate this question using a small fish – Threespine Stickleback (Gasterosteus aculeatus). Since phosphorus is a very important element in many ecosystems, we ask if the phosphorus requirements of sticklebacks vary and why. We expected that there would be a lot of variation in phosphorus content, because sticklebacks show a lot of variation in bony traits which are likely phosphorus rich.
We found that the phosphorus content of stickleback does vary widely, with %P ranging from 2.2 – 6.5% and the nitrogen:phosphorus ratio of sticklebacks spanning a range of 3.0:1 – 9.4:1. Most of this variation was related to differences in two bony armour traits (lateral plating, pelvis size), the body size of the fish, and how well mineralized the bones were. We also found that genetic differences which change the amount of lateral plating also affect the phosphorus content of sticklebacks.
Since there is variation in the phosphorus requirements of sticklebacks, and since some of this variation has a genetic basis, we conclude that there is potential for the phosphorus requirements of sticklebacks to evolve through natural selection on this variation. We note that such evolution is likely widespread, since many stickleback populations show evolutionary change in these phosphorus rich traits.
Image Caption: Gasterosteus aculeatus with bony traits stained in red. Individuals are from heavily armoured (Oyster Lagoon) and low armoured (Cranby Lake) populations.
Photo Credit: Dan Durston