The presence or absence of pelvic spines or eyes are two traits studied in the fish below
(a) Thre
e-
spined stickleback (
Gasterosteus aculeatus
). (b) Blind cave fish (
Astyanax mexicanus
) (
top
) and its sighted, surface relative (
bottom
).
[
(b) Masato Yoshizawa and William Jeffery, University of Maryland
.]
