In the dark-eyed junco, the offspring of females and their extra-pair mates are more likely to survive to reproduce, and have higher reproductive success, than the offspring of females and their pair-bonded mate. While this could be explained by the good genes hypothesis, it could also be the result of maternal effects (females invest more in eggs sired by extra-pair mates). Describe how you could test if these offspring differences are due to good genes or maternal effects.

(Answers will vary) One option is to eliminate the possibility of genetic benefits by only allowing one male to sire all the offspring of polyandrous females (by sterilizing the other males). If there is no difference in survival and reproductive success of the offspring of monogamous versus "polyandrous" females, then this supports the good gene hypothesis. If there is a difference, then this must be attributed to maternal effects. Another option is to test the hormone levels in eggs, or egg size, laid by monogamous and polyandrous females to determine if females are investing differently in eggs.