Adaptive Value of Tool Usesbb

Questions concerning adaptive value look at why a behavior evolved and how it is beneficial for an animal. Adaptive value can be measured by looking at Lifetime Reproductive Fitness (LTR) for an individual or group of individuals that display a particular phenotype. LTR is often measured in terms of the number of viable offspring an individual produces in its lifetime.
At this point, no study has shown any data demonstrating that tool use in Shark Bay bottlenose dolphins has any adaptive value. Females who forage using sponges do not produce any more young than average, and neither they nor their young live longer. Although spongers are more solitary with fewer social interactions, and spent more time foraging in deep water, there were also no apparent fitness costs to their behavior [3]. Two hypothesis address possible adaptive costs and values of this behavior, although there is no evidence to support them.


Niche Exploitation

While spongers constitute only 11% of the adult female population, they make up 50% of the females in deep-water channels [3]. It is possible that sponge use allows females to more efficiently find prey in this area, thus exploiting an underutilized foraging niche. So while there is no apparent adaptive advantage to tool use, perhaps these females would show decreased fitness if they were forced to compete with the rest of the population for food.


Why Females?

Sponge use is an almost exclusively female behavior. Because both male and female calves nurse from their mother for the same amount of time, why is it that only the female calves develop their mother’s feeding strategy? It is possible that sponging behavior would be disadvantageous for males because of the high degree of solidarity and specialization involved in the behavior. After a male calf leaves his mother, he makes alliances with other males and spends his time in a social group, while female calves spend time with their mother’s circle of female associates. The male alliances are essential due to breeding cooperation between allied males. Because sponging requires so much specialization and solidarity, this behavior would hinder a male’s ability to form the necessary social bonds with other males. For this reason it is unsurprising that males do not develop sponging.

A satellite photo of an algal bloom at Shark's bay.

Image from http://en.wikipedia.org/wiki/File:Shark_Bay_Phytoplankton_in_Bloom.jpg