Ontogeny

The Development of Tool Use

Ontogeny is the development of an organism’s behavior throughout its lifetime. Ontogenetic questions explore the interaction of genes and environment and their effect on the development of an individual. Because tool use in dolphins does not seem connected to any specific genes, this section will focus on the environmental factors associated with this behavior.

Image from http://biology.georgetown.edu/faculty/Mann/

Cultural Transmission

Cultural Transmission is the process by which animals alter their behavior based on learning from other members of their species [8-10]. Tool use in bottlenose dolphins is an example of vertical cultural transmission, where the behavior is learned from parents, as opposed to peers or other adults [5]. Sponge use in Shark Bay is observed almost exclusively in females, and is passed from mother to daughter. Bottlenose dolphins have a prolonged nursing period of 3 to 8 years, allowing calves an extended period of time in which to learn from their mothers. Due to the complexity of sponging behavior and the fact that it involves dives in deep water, this long nursing period is essential for calves to develop this behavior. In an examination of multiple foraging strategies, it had been shown that sponging takes over 20 months for a calf to begin imitating its mother’s sponging, whereas other foraging behaviors were demonstrated within the first 3 to 6 months after birth [4]. This shows that sponging is much more difficult to learn for calves than other foraging strategies. This extended learning period also explains why this behavior is only transmitted vertically (from parents to offspring), as opposed to horizontally (between peers). Peer groups in Shark Bay are relatively fluid, and two individuals would never have the constant, long term contact necessary to learn sponging [3].

Environmental Influences on Behavior

Sponging is predominately observed in deep water channels where marine sponges are most abundant[3]. Dolphin prey in this environment live in the muddy sea floor and are easily disturbed by the sponging behavior[2]. In shallow sea grass this behavior would not be as beneficial to foraging. It has also been suggested that sponging helps shorten foraging time, which is crucial in these regions where deeper dives are required to obtain food[1]. Dolphins have developed other foraging methods to cope with this deep water channel environment, of which sponging is one example. This is evident from the fact that while spongers only make up 11% of the total female population, they make up 30% of the deep water foragers[3]. Despite these apparent benefits, there is no evidence that sponging confers a fitness advantage to the dolphin (see adaptive value).