Genetic and developmental basis of evolutionary pelvic reduction in threespine sticklebacks

Michael D. Shapiro, Melissa E. Marks, Catherine L. Peichel, Benjamin K. Blackman, Kirsten S. Nereng, Bjarni Jonsson, Dolph Schluter &

David M. Kingsley

Kelsey ByersMonica Chu

http://www.colby.edu/chemistry/CH217/Fish%20Page/Pictures/Species/three%20spine%20stickleback.JPG

Vertebrate Limb Structures

• Highly varied

• In phylogenetically diverse sets of vertebrates, hindlimb structures are reduced or completely absent

• Little is known about the mechanisms underlying the genetic changes that lead to hindlimb reduction in vertebrate evolution

• Marine threespine sticklebacks

- prominent pelvic skeleton

- protection against predators

• Freshwater threespine sticklebacks- reduced or complete loss of pelvic structures

F1

Marine stickleback Benthic Paxton Lake Stickleback

F2 375 F2 progeny

(289 unaffected : 86 affected)

mednews.stanford.edu/story_images/stickleback.jpg

• One major QTL on linkage group 7• Four minor QTL on linkage groups 1, 2, 4, and 10 • Region near linkage group 7 accounts for a large amount of variance in pelvic structure• Presence of freshwater alleles decreased the average size of pelvic structures

Table 1

Figure 1

Increasing the total number of benthic alleles at the minor QTL of linkage groups 1, 2 and 4 resulted in greater reduction of pelvic structures than the effects of a minor QTL alone

Figure 1

• Tbx4 gene mapped to linkage group 1

• Pitx2 gene mapped to linkage group 4

• Pitx1 gene mapped to the area that seems to be the major controlling region for pelvic reduction

Left-right assymetry in stickleback pelvic reduction

• Pitx1 gene in the mouse is responsible for hindlimb development

• Pitx1 knockout mice exhibit strong directional assymetry

• Directional assymetry observed in F2 progeny

-stronger development on the left side in 78% of fish with pelvic assymetry