When a novel female was presented, initially, there was a small increase in the levels of dopamine, however, after continued copulation with the novel female, a significant increase in dopamine levels was observed. From these results, they concluded that an increase in mesolimbic dopamine efflux is associated with the appetitive and consummatory stages of sexual behaviour in male rats. Their data also suggest that stimuli associated with a novel female may increase dopamine transmission in a rat that is sexually satiated, and hence have a role in the reinitiation of sexual behaviour. Additional studies have also provided further evidence for the role of the nucleus accumbens on sexual behaviour in rats. In a study conducted by Wood et al., male rats were divided into three conditions, and were presented with a cotton ball laden in either saline (control group), estrous vaginal smear of a familiar female (experimental group), and estrous vaginal smear of a novel female (experimental group). In this experiment, the role of the nucleus accumbens was characterized through recording neuronal activity of single cells in this area of the brain. Results from this study showed a greater proportion of neuronal activation when initially presented with a novel estrus stimulus in comparison to familiar estrus stimulus. Subsequent presentations of the novel estrus stimulus did not show an increase neuronal activity. It has been observed that in certain species, males allocate sperm differently due to the Coolidge effect. The allocation is usually according to level of sperm competition, female novelty, and female reproductive quality. An experiment performed on an external fertilizing fish called "Rhodeus amarus", also known as the European bitterling, was used to show that sperm can be allocated differently if a novel partner is around, but that it also happens if there is male-male competition. It is important to know that the European bitterling mating system works by females depositing their eggs into the gill filaments of freshwater mussels by her long ovipositor and then males proceed by ejecting their sperm into the gills of the mussel hosting the eggs. This means fertilization and development of the offspring relies on the quality and survival of the mussel. When the Coolidge effect was applied to this system, the experiment showed that it is the mussels, or the site of fertilization, that the males prefer to be novel. However, the takeaway from the experiment performed was that in male-male competition of the "Rhodeus amarus," the dominant male will allocate more sperm when a novel mussel is present, while the subordinate male conserved its sperm until a proper opportunity came where it had a better chance of fertilization.