Complex sentence: Compared to monogamous house mice, polygamous house mice are shown to mate for longer periods of time, allowing for an increase in both the transfer of sperm and paternity success, which in turn increases male fitness.
Split into simpler sentences: Compared to monogamous house mice, polygamous house mice are shown to mate for longer periods of time. This behaviour allows for an increase in both the transfer of sperm and paternity success, which in turn increases male fitness.