There used to be two species of stickleback thriving in Enos Lake near Nanoose Bay on Vancouver Island, but University of British Columbia researchers say the two species are becoming one.

Seth Rudman, a zoology PhD candidate, says pressure from an invasive species of crayfish in the lake is causing "reverse speciation."

He says other research shows that process is playing out more frequently and in more places around the globe.

"Twenty years ago, people would have said reverse speciation is not a thing. It wasn't on the radar of evolutionary biologists yet," Rudman told All Points West host Robyn Burns.

At an increasing rate these days, there are cases popping up suggesting reverse speciation could be a widespread phenomenon and a big problem for biodiversity."

Enos Lake has been a renowned spot for evolutionary biologists, because it had two distinct species of threespine stickleback that are believed to have split from one another since the last ice age.

One species fed on juvenile insects in the near-shore environment, while the other fed on plankton in more open water.

Rudman says his study suggests the crayfish started competing with the near-shore stickleback for food, pushing them out into the open water, which caused them to start breeding with the open-water fish.

"This is a highly studied population of stickleback. There's a time sample from the late 80s into the 90s and early 2000s," he said.

"The researchers were able to show the differences between them both in their shape, their morphology and their genetics decreased over time. So they've sort of become blended together."

Rudman says in Enos Lake, reverse speciation led to the stickleback becoming "intermediate" between their two former specialist selves, and now populations of their former prey are increasing dramatically in the lake.

"We saw the effects on the ecosystem actually extended out into the terrestrial ecosystem," he said. "The hybrid stickleback fed quite a bit on large insects, and that led to an increase in the emergence of small insects out of the aquatic environment and into the terrestrial environment."

Rudman says that while reverse speciation cases are always different, a common factor is emerging.

"Almost all of the cases have something to do with human alteration of habitat," Rudman said. "It seems likely that the crayfish was an invasive that was potentially brought to Vancouver Island by humans."


To hear the full story, click the audio labelled: 'Reverse speciation' causing two fish to become one in Vancouver Island's Enos Lake

With files from All Points West