Complex sentence: In general, females' sexual swellings are responded to by males in the group as though they provide indications of female fertility and males therefore use these swellings in order to decide their level of investment and effort in courting females.
Split into simpler sentences: In general, females' sexual swellings are responded to by males in the group as though they provide indications of female fertility. Males therefore use these swellings in order to decide their level of investment and effort in courting females.