FIGURE 3. Partner preference test.
From the following article:
Enhanced partner preference in a promiscuous species by manipulating the expression of a single gene
Miranda M. Lim, Zuoxin Wang, Daniel E. Olazábal, Xianghui Ren, Ernest F. Terwilliger and Larry J. Young
Nature 429, 754-757(17 June 2004)
doi:10.1038/nature02539
a, V1aR-vp meadow voles spent significantly more time huddling with the partner (filled column) than the stranger (open column), whereas control animals (Ctrl-vp) and stereotactic misses (Ctrl-other) did not (P < 0.01, Student's t-test). Error bars, standard error. b, A plot of the percentage of time spent with the partner for each subject indicates a shift from randomly distributed preferences in the control groups to 100% of animals preferring the partner in the V1aR-vp group (P < 0.001, 
2 analysis). The y axis was calculated as the time spent huddling with the partner divided by the total time spent huddling with the partner and stranger, multiplied by 100.