Back in the early 80s, Don McPhail worked on sticklebacks in Vancouver Island, and specifically in some intriguing lakes that had not one but two different species of sticklebacks in them. Ten years later, McPhail and Schluter would build on this research and help to catapult stickleback to the forefront of evolutionary biology.
But for now, let’s go back to the 80s and look at a little paper with big implications.
The Enos Lake stickleback species pair consisted of a benthic species and a limnetic species, though they are sadly no longer with us due to an invasive species introduction. As is generally the case with these species pairs, benthics are larger, with deep bodies and small short gill rakers, whereas limnetics are smaller with slim bodies and lots of long filamentous gill rakers.
However, morphological differences do not necessarily translate into ecological differences, so the authors tested the performance of the different species on its preferred habitat. Three experiments were performed: a prey size trial, a feeding trial on benthic substrate, and a plankton feeding trial.
In the size trial, benthics ate significantly larger prey than either limnetics or hybrids between the two forms. In the feeding trial on the benthic substrate, limnetics and benthics made similar numbers of strikes, but benthics were significantly more successful at capturing prey. In the zooplankton trial, the stomachs of limnetic stickleback contained a much higher number of prey items than than the stomachs of benthic stickleback.
The performance data from these three experiments supports the hypothesis that the Enos Lake stickleback pair does have ecological as well as morphological differentiation, though there are some interesting issues with limnetic stickleback in particular. When the authors allowed female limnetics to feed on the benthic substrate, the sticklebacks did not, though male limnetics fed freely, and made just as many feeding strikes as benthics of both sexes.
A possible reason might be that male limnetic stickleback have to spend time near the benthos to construct their nests, so it would make sense to eat benthic prey items, whereas a female only has to approach the benthos to find a suitable male, and can spend the rest of her time in the water column eating zooplankton.
When Stickleblog returns, we’ll continue our look into the species pairs with a Schluter paper that examines hybrid performance relative to limnetics and benthics.
P. Bentzen, & J. D. McPhail (1984). Ecology and evolution of sympatric sticklebacks (Gasterosteus): specialization for alternative trophic niches in the Enos Lake species pair Can. J. Zool, 62 (11), 2280-2286 DOI: 10.1139/CJZ-62-11-2280