Tracy Stevens
BIO 353
Making of the Fittest
Stickleback can be marine, freshwater, or anadromous. Stickleback that are marine or
sea-run possess complete pelvises with spines that protect them from large prey. The stickleback
population in Frog Lake are similar to marine and sea-run stickleback as most of them have the
complete pelvises and spines. The stickleback in Bear Lake have mostly reduced or absent
pelvises and spines.
Different things can affect the evolution of the stickleback. There could be environmental
factors playing a role in the differences of stickleback fish in Frog and Bear Lakes. Bear Lake
could have a soft bottom in which the leg-like spines would not be needed to help them move
along the floor of the lake, whereas the ocean has different environments on the floor. Frog Lake
might also have a rocky bottom as opposed to soft. The spines on the Frog Lake stickleback
might use these spines to move along different surfaces of the ocean floor. To test this, divers
could take footage from both the lake bottoms and ocean bottom where the stickleback are found
and compare the results. Another possibility could be the varying amounts of calcium and
minerals needed to form the spines on the stickleback fish. This could be tested by taking water
samples from each lake and the ocean and measuring the amounts of calcium and minerals in
each.
The stickleback fish in Bear Paw lake mostly have a reduced or absent pelvis. This shows
that the phenotype of complete pelvises has been reduced over time. This is what the fossil
evidence points to in the Nevada lake also. The change can be seen in the fossils over time.
Stickleback fish have been compared with mice who had a Pitx1 gene that was either
mutated or did not work. This research showed the mice did not completely develop back legs
and pelvises. They only had partial back legs/pelvises. The parts of the pelvis and back legs that
were remaining were found to be larger on the left side of the body. The stickleback fish in Bear
Paw and Coyote Lakes were found to have pelvic reduction which was also larger on the left
side. This leads us to believe these two lake populations are likely this way due to the mutation
on the Pitx1 gene.