Complex sentence: Since altruism takes away resources from the altruist it can be a "honest signal" of resource availability and the abilities needed to gather resources which may signal to others that the altruist is a valuable potential partner.
Split into simpler sentences: Since altruism takes away resources from the altruist it can be a "honest signal" of resource availability and the abilities needed to gather resources. This may signal to others that the altruist is a valuable potential partner.