Synaptic

Stephanie and Jessica wrote this for Evolution, an upper level biology class. Students have to develop a proposal of research they would like to conduct that answers an evolutionary question. I chose their paper because they did a beautiful job of explaining what is known about vocalizations in killer whales. They were able to identify a gap in the knowledge of the evolution of vocalizations for hunting and developed a hypothesis and a way to test that hypothesis.

-Paulina Mena

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Background Information

It was when baby killer whale, Kasaka, was born into SeaWorld and then transported to another park location when mother Takara was observed producing an extreme long-range vocal pattern never heard before by humans. Frequently studied today, killer whales have evolved the ability to produce a variety of vocalizations with a wide range of frequencies. These vocalizations seem to serve several functions, some known, but as witnessed with Takara in the film Blackfish (Cowperthwaite, 2013), some unknown. Because of these whales’ geographical range, they are difficult research subjects but nevertheless deserve to be studied due to their complex cognitive and communication capabilities. From this research review, we would like to know: what is the evolutionary function of different vocalization forms in killer whale communication and how does this affect observed behavior? Our hypothesis is that if changes in auditory communication, in response to adapted vocalizations in prey, leads to increased fitness in killer whales, then the individuals who are able to perceive and respond to the new vocalizations will be successful predators and a change in auditory perception will be observed.

Communication among species in the Animal Kingdom is regularly observed, however, some organisms have evolved in both auditory function as well as vocalized communication. Many different forms of communication through vocalization have been observed such as songs, clicks, whistles, squawks, barks, and quacks in many different frequencies. The ability of vocal learning—vocalizations produced by choice in order to achieve a certain goal—has been studied among few groups of organisms such as birds, bats, elephants, Cetaceans (whales, dolphins, and porpoises), and some primates, but is considered rare (Sewall, 2012, p 1). This type of call, often referred to as a matched call, provides benefits to those that produce the vocalization as well as to those who listen and respond to the call. These calls serve many purposes including finding a mate, parental care of young, group membership, teamwork, and hunting.

Bottlenose dolphins and killer whales are well studied for their match calls. Male dolphins often form alliances and change their calls to match each other. This is an example of group membership in organisms (p 10). Likewise, killer whales form social groups referred to as pods, and are extremely successful hunters in these groups working together in order to find food. Their strategy heavily relies on the communication between individuals in the pod (p 9).

Despite the disadvantage to studying Cetaceans in their aquatic habitat, this group of organisms is studied often due to the abundance of vocalization abilities including chirps, cries, moans, clicks, and whistles. Also, because of human advances in technology and mobility, these animals have been caught and heavily studied in captivity. Dolphins in particular are favored because of their size and adaptability to controlled environments. Captivity for Cetaceans, however, has disadvantages because of certain species’ large body sizes, food preferences, and highly mobile behavior. Though they can be studied at sea, it is difficult for humans to observe Cetaceans without disturbing their natural behavior and because of the complications associated with working at sea (Sebeok, 1977, p 794).

With the data that has been observed in Cetaceans, it is evident that their complex communication style is highly advanced, probably meaning their physical features involved with auditory vocalizations and sound perception is the result of the evolutionary development within their order. The ability to learn vocalizations is part of this complexity. Beluga whales and killer whales have been known to imitate signals from other individuals and species. This was witnessed by scientists in a study devoted to beluga whales, particularly a calf imitating its father’s call but only after he was introduced to the group—a clear indication of vocal learning (Janik, 2014, p 60). The first discovered evidence of vocal learning was recorded in baleen whale males; all males within a Hawaiian breeding ground were found to all sing the same song to attract a mate but with elements in each theme that changed over time. Interestingly, the males synchronized this change, which also suggests vocal learning was involved (p 61). Cetaceans’ large range of vocalizations have developed due to cognitive capabilities—a result of complex social behaviors and dependence on social relationships in large societies.

How Cetaceans use their abilities varies depending on behavior and function. Calls in killer whales and whistles in dolphins seem to serve a shared purpose of spatial awareness and social relationships (p 61). Filatova (2013) found that different call types were used for different situations. For example, low frequency vocalizations in killer whales were used while in close proximity to each other—probably just to maintain spatial cohesion—whereas higher frequencies were used for long distance travel as well as in the presence of mixed pods—perhaps to ensure that sound is received by intended individuals.

Whistles in dolphins not only indicate spatial awareness but also serve as a mechanism for individual recognition in pods, contact calls between mother and calf, distress calls, and aggression. Signature whistles exchanged between the mother and calf is an essential form of communication in the first few months of calf development. These vocal communicative interactions are important for bonding and recognition (Janik, p 62). Distress whistles are different in acoustic structure from contact/signature whistles in that they are emitted in stressful situations, and a whistle rising and falling in frequency twice can be a form of intimidation signaling (Stebbins, 1983, p 115).

As important as vocal signals are, the presence of silence is also an informative communication style. For example, because dolphins are commonly vocal within pods, the sudden absence of vocals can act as an alarm call, perhaps to warn other individuals of predators. Silence is also typical in killer whale pods while resting in close proximity to pod members (p 115). It is also used in attempt for killer whales to ambush prey (dos Santos & Almada VC, 2004, p 402). The absence of acoustic signaling in Cetaceans represents the strong bond that individuals share within pods as well as the vast intelligence they have evolved.

Being the ocean’s top predator, Orcinus orca, more commonly known as the killer whale, this organism has evolved to obtain this status. Their high level of intelligence displayed through predation is evidence of the overall species’ fitness, which was acted on by the forces of natural selection. These evolutionary changes as well as those pertaining to their auditory development have been studied widely. Originally, researchers thought that vertical transmission—from mother to calf—and changes that occurred in pod dialect was due to mimicking error. Filatova (2010) however argues that horizontal transmission exists within pods between adults. If the original evolutionary theory holds true, the similarity in calls between observed pods should change at an identical rate, however, they were found to change at different rates suggesting that cognitive development directly relates to the species’ auditory signaling (p 965-968). The signaling was carried from the calf stage to the adult stage in an individual’s lifetime, thus leading to the development of horizontal transmission.

Vocalizations are found in various animals; however, the ability for vocal learning is limited to only a few groups of organisms including Cetaceans. This order has developed many unique auditory communication styles over time that has increased their fitness. Killer whales have surpassed other Cetaceans due to their highly evolved intelligence and vocalization capabilities. Their dependence on community for successful hunting strategies demonstrates their evolutionary need for developed auditory communication. Finally, their status as a top predator of the ocean is an indicator of the species’ overall successful fitness.

Statement of the Problem

Our research proposal is based off the work of Morisaka and Connor (2007) and their findings. Their focus was on the coevolution of killer whales and their prey. In terms of evolutionary studies, the concept of coevolution is key in understanding relationships between two different species. The idea is that the relationship is always changing; one species determines the response of another. In this situation, the ability to adapt quickly will generate the best-fit individuals; therefore, sexual reproduction is highly favored for its beneficial gene selection. This relationship is observed in killer whales and their prey that have adapted over time in response to one another’s vocal communication styles. Various species of sperm whales, porpoises, and dolphins (known as odontocetes), which are preyed upon by killer whales, have experienced loss in vocal whistles. This suggests these vocalizations are costly to produce either because of energy consumption or predation risk (May-Collado et al., 2007, p 9). Morisaka and Connor found that some of these odontocetes have adapted to using narrow-band click communication and high frequency sound (p 1439). In return, it would be assumed that killer whales, being the top predator, would respond through adaptation specialized in hearing narrow-band clicks and high frequency sound over time. Significance Our study is important for further comprehension of this predator-prey relationship that demonstrates mechanisms observed in coevolution. By researching the evolution of killer whales, we can better understand their level of intelligence and how this directly correlates to their fitness. The complexity of their communicative evolution may also aid in further research and knowledge focusing on how the human language came to be (Janik, 2014, p 1).

Methods

As stated previously, our hypothesis is that if changes in auditory communication, in response to adapted vocalizations in prey, leads to increased fitness in killer whales, then the individuals who are able to perceive and respond to the new vocalizations will be successful predators and a change in auditory perception will be observed. If we were to conduct this research, the focus would be on multiple killer whale individuals in captivity. Since this type of interaction between prey and predator would be difficult to observe in the wild by researchers, captive killer whales are a viable alternative for research purposes.

Since Morisaka and Connor (2007) have shown that odontocetes often preyed on by killer whales are capable of producing narrow-band clicks and high frequency sounds, playing recordings of these vocalizations to the killer whales in captivity allow to observe which individuals, if any, can perceive them. To obtain these recordings, we would use sperm whales, porpoises and dolphins as subjects for vocalization. All recordings would be taken from wild populations in order to simulate more naturalistic responses in the killer whales. A variety of recordings including narrow-band clicks, high frequency sound, as well as other natural communication styles used in socializing, hunting, and traveling will be played for killer whales in captivity to trigger a response or change in behavior. Playing sounds meant to go as “undetected” or “detected” will help distinguish the fitness of individuals in captivity. If an individual responds to a narrow-band click or high frequency sound, then this individual would be considered more fit than the others.

Recordings would be referred to as “undetected”— narrow-band clicks and high frequency—or “detected”—all other vocalizations. Both undetected and detected sounds would be played for whales in captivity. Once a week, for four months, each sound—undetected and detected—would be played on different days randomly selected each week. Each sound would be played before being fed to test if individuals would respond more strongly. Playing each vocalization before meal times would be done to mimic Pavlov’s classical conditioning experiment in psychology with dogs and bells, hopefully to receive similar responses. Over time, various vocalizations would be played for the captive killer whales, and after the vocalizations were played, the whales would be fed. Eventually, we would get to a point where the undetected vocalizations would be played, and the whales that can perceive these sounds would respond as if they are receiving food. This would tell us which individuals are the most fit and evolved specialized hearings. The purpose of not performing the experiment at a set time each day would prevent the whales from becoming accustomed to schedule and therefore exhibit natural behaviors. Our target subject group would include individual whales of all ages to best simulate a wild pod. A microphone playing the recording would be placed on the side of the tanks.

Individuals who respond to the undetected vocalizations at the end of the experiment will be considered to have the beneficial hearing adaptation. Individual recognition of captive whales would be needed in order to document which individuals are responding and perceiving the sound emitted. If individuals were in fact interpreting the undetected vocalizations, then we would expect to see the same individuals responding each time the experiment is conducted.

Expected Results, Analysis, and Interpretation

Since killer whales are considered to be top predators, we would expect that they would eventually evolve in response to the behavior of their prey. In our study specifically, we would expect roughly one-third to one-half of the individuals to perceive and respond to the undetected recordings. All individuals would most likely respond to the detected recordings, because these would definitely be perceived unless the individual suffers from a hearing handicap. It is possible that none of the individuals perceive or respond to the undetected recordings; this could be simply because all individuals are not adapted to this frequency of sound emitted by their prey. Also, if individuals can perceive the undetected vocalizations, then we would expect the more fit whales to respond as if they are going to be fed when the vocalization recording is played. These assumptions are based on the results of Pavlov’s dog and bell experiment in psychological classical conditioning.

Responses from the target subject grouping would be important when interpreting results, because responses in juvenile individuals would tell us that this adaptation is beneficial and is being passed down in generations. Responses in any individual might give us more information on the pods of their ancestors and the pod’s overall fitness. If individuals can perceive the undetected frequencies, this would suggest that they come from a more successful pod.

In our results section, to help analyze data, we would include all observations in a table. Separating individuals who perceive undetected sounds versus those who only perceive detected sounds would be beneficial, because we could use this information to locate pod fitness on a geographical scale. This may include a map of pods around the world related to the individuals capable of perceiving undetected sound. We could then compare the location of pods to the distribution of recorded toothed whale species. If pods capable of hearing undetected sound are found in areas with less prey species in number, it may be that other factors are causing this evolutionary change in killer whale auditory perception.

Since age is another factor, showing results in the form of graphing may be beneficial to identify if this adapted hearing is due to genetics in juveniles. If the trait were passed on, we would expect to see responses to the undetected vocalizations. Graphs would allow us to visualize the results and show the differences between perception in adults and juveniles.

The problem with studying marine organisms is the vast size and depth of the ocean that limit our human technological capabilities. This prevents us from being able to study Cetaceans at full potential. However, much research has been conducted with organisms in captivity, but these results differ from what would be expected in the wild likely because these individuals live in controlled environments. In captivity, individuals are not exposed to predation, interactions with various Cetacean species, or interactions with other Cetaceans of the same species. Also, the fact that Cetaceans are so mobile in the ocean and humans are so limited affects the research that can be done. Finally, human presence and disturbance could cause unnatural behavioral and vocal responses that will skew the data. Because of these limitations, not much research has been published on certain aspects of Cetacean behavior and communication in the wild, which is why our study could be used to advance our knowledge on this subject.

Conclusion

Our data could provide more evolutionary knowledge on the coevolution between killer whales and their prey. This would be an enormous step to understanding killer whale auditory communication adaptation and their intelligence. We may also be able to identify where these changes are geographically occurring, which pods are more successful in hunting, and how these changes correlate with prey distribution. Age may be an important indication of the rate of change in the species. Overall, our study is important, because this area of gained undetected calls in prey has little research. Knowing which individuals perceive undetected sound will help us identify the most fit individuals in captivity, which may indicate killer whale pod success rates worldwide.

Works Cited

Cowperthwaite G. 2013. Blackfish. Netflix. Directed by Gabriela Cowperthwaite. Dallas, Magnolia Pictures.

Dos Santos M, Almada V. 2004. A Case for Passive Sonar: Analysis of Click Train Production Patterns by Bottlenose Dolphins in a Turbid Estuary. In: Thomas JA, Moss CF, Vater M, editors. Echolocation in Bats and Dolphins in Illinois. Chicago: The University of Chicago Press. p 401-403.

Filatova OA, Burdin AM, Hoyt, E. 2010. Horizontal Transmission of Vocal Tradiitons in Killer Whale (Orcinus orca) Dialects. Biology Bulletin. 37: 965-971.

Filatova O, Guzeev M, Fedutin I. 2013. Dependence of Killer Whale (Orcinus orca) Acoustic Signalson the Type of Activity and Social Context. Biology Bulletin [Internet]. [2013, cited 2015 Feb 10] Vol. 40, No. 9 pp.790-796.

Janik VM. 2014. Cetacean vocal learning and communication. Current Opinion in Neurobiology. 28: 60-65.

Morisaka T, Connor R.C. 2007. Predation by killer whales (Orcinus orca) and the evolution of whistle loss and narrow-band high frequency clicks in odontocetes. Journal of Evolutionary Biology. 20: 1439-1458.

May-Collado L, Agnarsson I, and Wartzok D. 2007. Phylogenetic review of tonal sound production in whales in relation to sociality. BMCEvolutionary Biology. 7:136.

Sebeok TA. 1977. How Animal Communicate. Bloomington, (IN): Indiana University Press. p 794-806.

Sewall K. 2012. Vocal Matching in Animals. American Scientist. 100(4): 306-315.

Stebbins, WC. 1983. The Acoustic Sense of Animals. Cambridge, (MA): Harvard University Press. p 110-118.