Final answer:
Reeve and Pfennig's theory suggests that sexual selection may favour elaborate male displays in ZW sex-determination system species. The ZW system involves females that can pass on a greater variability in mate preference, potentially driving selection for impressive ornamental traits in males.
Step-by-step explanation:
The question references Reeve and Pfennig's work regarding sexual selection, specifically in relation to the ZW sex-determination system. In species with a ZW sex-determination system, such as birds and some reptiles, females are ZW and males are ZZ. The theory proposed by Reeve and Pfennig suggests that the sexual selection process might indeed favour elaborate or lavish male displays. This is because females, having two different sex chromosomes (ZW), can potentially exhibit more variability in their offspring's traits, which includes their preference for mates. This variability could result in a stronger selection for males that display the most impressive ornamental traits, as these males might be more likely to attract a mate and pass on their genes. Therefore, the elaborate displays seen in males of ZW species, such as peacocks and birds-of-paradise, are believed to be a result of such sexual selection pressures.