Altruism and Maternal Adaptations in the Female Lion
Altruism can be defined as a behavior in animals that benefits other organisms at its own expense and is measured through the reproductive fitness of each organism. Altruism, in biological terms, is unique in that the acts of the altruist are seen as providing fitness advantages to them, which is very different from the ideas of altruism in social and/or philosophical terms.
Altruistic behaviors are found throughout animal species worldwide but are especially common in species with complex social structures. In exploring these dynamic social structures, lions, Panthera leo, are a prime example. Lions are known for living in social groups called prides, and these prides are created to form cooperative groups amongst all lions in the pride. Lion prides are primarily made up of one to seven males, offspring, and two to 18 females, which defend the territory, cooperatively hunt, and care for offspring. There are many advantages to pride living. A 2015 study highlighted the importance of cooperative cub rearing for female lions to protect them from outside males and increase survival rates. Females who have cubs close in age may pool their offspring together to form a crèche, essentially a lion “nursery,” and associate themselves as a caregiving group in raising all cubs, not just their own. These cooperative, altruistic behaviors are a great defense against an enormous pressure to the pride, infanticide.
Sexual conflict comes in many forms; however, infanticide is one of the earliest recognized forms in which the male lion imposes extreme costs to females and their reproductive success. Infanticide in lions occurs most frequently when new male coalitions take over an existing pride of female lions. These male takeovers lead to considerably high cub mortality rates. The coalition of males will challenge each other to have pride residency; new males will kill offspring from the previous coalition in order to shorten the time between the female’s sexually receptive cycles.
1) Benefits for males.
There are numerous advantages for male coalition takeovers in infanticide. When males kill the offspring from previous coalitions, they enable the female to enter estrus and accelerate her sexual receptiveness by stopping the investment in cubs that aren’t biologically their own. The larger the male coalition, the less competition from other males they will have. This increases likelihood of infanticide and the reproductive success for the males, and the females are forced into fertilizable conditions due to male infanticide. When the males remove the female’s maternal investment, they allow them to exhibit estrus about eight months sooner than those with surviving cubs.
2) Negative implications for females.
Female lionesses suffer great fitness costs associated with infanticide, indicating, “reduced per capita female reproductive successes, lower per capita surviving cubs, higher mortality rates, and more frequent wounding” according to a 2009 study. When infanticide occurs, the female lions suffer immediate fitness losses. Infanticide has the ability to change the entire dynamic of the pride when males take over. While the cooperative aspects of the female lions remain essential in decreasing cub mortality, some losses are inevitable.
There is interesting evolutionary news that goes along with this. Female lions have evolved to increase the survival rate of their offspring in unique, compelling ways. There has been a growing interest in the adaptations females have gained to reduce their losses to infanticide.
Defense: Female lions will go to extreme lengths to protect their offspring and the offspring of females in the pride. When facing threats, females will roar in an attempt to recruit all pride mates to keep the intruders or threats as far away as possible from the cubs. Females will risk injuring themselves and even death to defend the cubs; they will even attack outside males before those males make their attack. Research has shown female lions to be successful at times in taking defensive action against males despite risks and that cooperative defense is extremely important to the communal raising of offspring.
Abandonment: When cubs grow older than one year, males may make them leave the pride. Females, at times, will abandon the pride to accompany their offspring to safety, becoming nomadic at the risk of their own lives. Females that are part of a pride gain higher reproduction and fitness than single females, therefore, lone females decrease their fitness all at the cost of offspring survival.
Pseudoestrus: Although rare, female lions can exhibit pseudoestrus, which is imitating estrus. The female lion will mate with the new male, while pregnant, and confuse the male into thinking the offspring are his. While it takes much time to observe this adaptation, if the female was previously pregnant when the new males takeover and her cubs are not killed when born, this physiological adaptation may have taken place.
Altruism, in all forms, has its tradeoffs. Maternal care is one form where the individual conveys benefits to its offspring at a cost to its own life. In the case of the female lion, all females put their own lives at risk for the sake of the prides offspring. Female lions will exhibit a wide variety of responses to new males, however cub mortality rates are still high as pride takeovers happen. The females have evolved to increase their reproductive fitness and combat infanticide.
Future work on this topic could focus on more in depth behavioral observations of pride takeovers and the effects infanticide may have on the overall population of lions. Current research is lacking on this topic. Lions have had a drastic decline in population numbers over the past decades, disappearing from normal habitat ranges. Information on lion population and behavioral trends is crucial for effective conservation planning.
References
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