Final answer:
In the context of evolutionary biology, extra-pair copulation does not confer increased fitness to monogamous males via reduced energy investment in reproduction; rather, it can undermine the energetic contributions that these males contribute to parental care as understood through several behavioral biology hypotheses.
Step-by-step explanation:
The question raises the point that extra-pair copulation does not lead to increased fitness of monogamous males due to less energy expended on reproduction. This concept is a part of behavioral biology, particularly concerning mating systems and reproductive strategies.
Extra-pair copulation is an event often observed in monogamous species where an individual mates outside the primary pairing. This contrasts with the situation in monogamous systems described by the mate-guarding hypothesis, the male-assistance hypothesis, and the female-enforcement hypothesis.
These hypotheses support the idea that monogamous males contribute significantly to offspring care, which can be energetically costly. By engaging in extra-pair copulation, a male potentially risks losing paternity in the pair's offspring to other males and thus reduces the aforementioned benefits of monogamous relationships. Consequently, one of the benefits of monogamy for males is precisely the energetic investment in their offspring, which is undermined by extra-pair copulation.
Moreover, when organisms like fruit flies are sperm-depleted, they exhibit altered mating behaviors to maximize the efficiency of their limited reproductive resources. This indicates that energy budget and investment in reproduction and offspring care are critical considerations in evolutionary biology.