Comparing the Evolution of Echolocation in Dolphins and Bats
Jaylene Garcia
Panther ID: 5694709
Section U14
TA: Wendy Villavicencio
I. Introduction
• This topic will focus on comparing the evolution of echolocation from two organisms, common bottlenose dolphins (Tursiops truncatus) and big brown bats (Eptesicus fuscus). These organisms diverge in order and family, have different diets, lifestyles, habitats, and method of transportation. Despite all their differences they both evolved the natural sonar called echolocation.
II. Background Information on the Dolphin
• Dolphins develop their echolocation within a few months of life and after the maturation of structural features such as animal length and the amount of isovaleric acid in the melon. (harder, Jennifer)
• Dolphins are extremely diverse in the environments they occupy, ranging from open sea, to rivers, and to coastline habitats. (Herzing & Santos)
• Through the analysis of the stomach contents it was indicated that dolphins primary source of food are fishes. (Herzing & Santos)
• Dolphins echolocation signals can be divided into two groups: broadband-short, and narrow-long. Broadband-short emit frequencies below 100 microseconds and energy peaks under 70 kilohertz. Narrowband-long emit frequencies above 125 microseconds with energy peaks at approximately 110 kilohertz. (Herzing & Santos)
• Dolphins use their sonar to catch preys, once they come in contact with a target they increase their clicks to hone in on the location. (A.Kaveh & N.Farhoudi, 2013)
III. Background Information on the Bat
• The earliest evidence of the existence of bats, and winged bats at that, begins with fossils dating back 49-53 million years ago, which were recovered in Europe, North America, Africa, and Australia that showed enlarged scapula and detailed articulation of the shoulder joint, which were perfect for the attachment of the flight muscles. (Speakman, 2001)
• Bats primary thrive on a diet of insects, fish, fruit, pollen, nectar, mammals, birds, and blood and within this diet they play a major role in the act of pollination of flowers. (S. Blair Hedges, 2009)
• Bats are classified into two subgroups, based on their capacity to utilize laryngeal echolocation; Megachiroptera bats are large in size do not utilize echolocation but rather large eyes to see, while Microchiroptera on the other hand are capable of producing echolocation emissions and use it to see. (Teeling, 2009)
• Although initially it was believed that Microchiroptera bats developed echolocation and differentiated themselves from their species mates, the Megachiroptera, it is now understood that the laryngeal echolocation originated in the ancestor of both subgroups and eventually the ability was lost in lineage for Megachiroptera bats. (S. Blair Hedges, 2009)
• The Eptesicus fuscus species of the subgroup microchitoptera practices their ability of echolocation in order to maintain large maternal social colonies and for means of foraging for food using species-specific high stereotyped sounds. (Monroy, Carter, Miller, & Covey, 2011)
IV. Echolocation Emission in Dolphins
• Bottlenose dolphins are one of a few species of dolphins that appear to use echolocation for other than a communicative aspect, relying on the sensory input from the sonar output in order to navigate their environment for daily tasks such as hunting. (Harder, 2016)
• Sonar signals are modified based on the environment and the distance of the expected object subject to echolocation, with lower intensity clicks being a displayed behavior of dolphins in captivity tanks where objects remain close and somewhat permanent in location. (Harder, 2016)
• Dolphins produce clicking, which are at higher frequencies than those utilized for communication purposes. The clicking sound produced will travel through water and hit an object, the sound is then reflected and bounces back to the dolphin. This causes a back and forth, known as a click train, which allows the dolphin to measure the dimension, direction, and distance of the sounds in relation to the entity. (A.Kaveh & N.Farhoudi, 2013)
• Dolphins use echolocation as a means of learning its preys patterns of escape and using this to increase their effectiveness as predator. (Herzing & Santos)
• The air gaps and the spatial arrangement have been shown to aid in the protection of the ears and enhance the dolphins hearing abilities. (Houser, et al., 2004)
V. Echolocation Emission in Bats
• Bats are one of the only mammals with the ability to produce sounds generated from the larynx at possible durations of 0.3 to 300 microseconds, and varying in frequencies between 8 to 210 kilohertz. (Teeling, 2009)
• The environment that the bat habituates affects the frequency bandwidth that they emit; a bat in an open habitat typically produces a low-frequency, long-duration with a narrow-frequency bandwidth whereas a bat in a densely forested habitat will produce short broadband sounds. (Teeling, 2009)
• The emission of echolocation sounds begins its production in the larynx, via the tension placed on the vocal cords from the cricothyroid muscles. (Carter & Adams, 2016)
• Bats have adapted the ability to maintain hypertrophied cricothyroid muscles as well as calcified laryngeal cartilages which aid in their production of a large range of sound frequencies. (Carter & Adams, 2016)
• Testing of the effectiveness of the echolocation abilities in obstacle avoidance in the big brown bat species showed that the performance of the bat was determinant on the size of the spacing of wires, as the spacing between the wires decreased, the precision of the echolocation ability was also decreased. (Sändig*, Schnitzler, & Denzinger, 2014)
VI. Evolution Process of Echolocation in Bats and Dolphins
• A few hypotheses exist for when the development of echolocation in bats occurred, some believe echolocation developed first, others oppose this idea and believe flight was developed first, and there are others that believe they both developed simultaneously. (Speakman, 2001)
• Echolocation is a complex trait that relies on many pathways and physiological aspects of an organism’s systems, thus making isolation of a specific gene that allows for the capability extremely difficult, but scientists have determined the FOXP2 gene is responsible for the vocalization, and the PRESTIN gene is responsible for the hearing of the echolocation sounds. (Teeling, 2009)
• Both bats and dolphins demonstrate various parallels, such as their status as both prey and predator in their environment; leading to the combining of passive and active echolocation. (Herzing & Santos)
• It is a possibility that echolocation is a result of the coevolution that occurs between prey and predators, some coevolving tactics are passive tracking of prey and an increase in frequencies outside of the predator’s auditory scope. (Herzing & Santos)
• Bats spend a high amount of energy emitting and adjusting sonars, while the metabolic price dolphins pay is negligible. (Norena, M.Holt, C.Dunkin, & M.Williams, 2017)
VII. Conclusion
Bibliography
A.Kaveh, & N.Farhoudi. (2013). A new optimization method: Dolphin echolocation Author links open overlay panel. Advances in Engineering Software, 53-70.
Carter, R. T., & Adams, R. A. (2016). Integrating Ontogeny of Echolocation and Locomotion Gives Unique Insights into the Origin of Bats. Springer Science+Business Media, 413-421.
Harder, J. H. (2016). The Development of Echolocation in Bottlenose Dolphins. International Journal of Comparative Psychology, 1-19.
Herzing, D. L., & Santos, M. E. (n.d.). Functional Aspects of Echolocation in Dolphins. N/A: N/A.
Houser, D. S., Finneran, J., Carder, D., Bonn, W. V., Smith, C., Hoh3, C., . . . Ridgway, S. (2004). Structural and functional imaging of bottlenose dolphin (Tursiops truncatus) cranial anatomy. BIOMIMETICA, 3657-3665.
Monroy, J. A., Carter, M. E., Miller, K. E., & Covey, E. (2011). Development of echolocation and communication vocalizations in the big brown bat, Eptesicus fuscus. J Comp Physiol A, 459-467.
Norena, D. P., M.Holt, M., C.Dunkin, R., & M.Williams, T. (2017). Echolocation is cheap for some mammals: Dolphins conserve oxygen while producing high-intensity clicks. 103-109.
S. Blair Hedges, S. K. (2009). The Timetree of Life. In S. K. S. Blair Hedges, The Timetree of Life (pp. 499-503). New York: OUP Oxford.
Sändig*, S., Schnitzler, H.-U., & Denzinger, A. (2014). Echolocation behaviour of the big brown bat (Eptesicus fuscus) in an obstacle avoidance task of increasing difficulty. The Journal of Experimental Biology, 2876-2884.
Speakman, J. R. (2001). The evolution of flight and echolocation in bats: another leap in the dark. Mammal Rev., 111-130.
Teeling, E. C. (2009). Hear, hear: the convergent evolution of echolocation in bats? Trends In Ecology and Evolution, 351-354.