Final answer:
Female vampire bats that engage in altruism by sharing food have been observed to live longer, a behavior that promotes survival and benefits the group. Hence the correct answer is option A- Vampire bats who share food tend to live longer than other bats.
Step-by-step explanation:
The observed effect of altruistic tendencies among female vampire bats is that vampire bats who share food tend to live longer than other bats. This phenomenon can be seen as a form of reciprocal altruism, where bats benefit by having the favor of sharing food returned when they are in need. This mutual cooperation among bats aids in their survival and can contribute to the longevity of individuals within the group. This behavior aligns with the broader understanding of how social behaviors can have evolutionary advantages by supporting survival and reproductive success, as seen in other species as well.