Fig. 7.

Effect of an intruder male on circulating hormone levels of resident dominant males. Circulating levels of 11-ketotestosterone, testosterone, estradiol and cortisol (rows) from a control group and a group exposed to an intruder challenge are shown for stable males (left column) and escalating males (right column). 11-ketotestosterone, testosterone, estradiol and cortisol levels increased significantly in escalating males when faced with an intruder, but no effect was observed in stable males. Data are plotted as concentration (ng/ml). Top and bottom of boxes represent the first and third quartiles, respectively; whiskers extend to the most extreme data points no more than 1.5 times the interquartile range from the box; and horizontal lines within the boxes represent group medians. Asterisks indicate a statistically significant difference (*P<0.05, Mann–Whitney).