Thursday, March 29, 2018

[Herpetology / Behaviour • 2018] Limb-use by Foraging Marine Turtles, An Evolutionary Perspective


A green turtle (Chelonia mydas) holding a mosaic jellyfish (Thysanostoma thysanura) in the water column near the ocean surface in the Similan Islands, Thailand, taken June 2017 

in Fujii​, McLeish, Brooks, et al. 2018. DOI: 10.7717/peerj.4565
photo: Rich Carey 

Abstract

The use of limbs for foraging is documented in both marine and terrestrial tetrapods. These behaviors were once believed to be less likely in marine tetrapods due to the physical constraints of body plans adapted to locomotion in a fluid environment. Despite these obstacles, ten distinct types of limb-use while foraging have been previously reported in nine marine tetrapod families. Here, we expand the types of limb-use documented in marine turtles and put it in context with the diversity of marine tetrapods currently known to use limbs for foraging. Additionally, we suggest that such behaviors could have occurred in ancestral turtles, and thus, possibly extend the evolutionary timeline of limb-use behavior in marine tetrapods back approximately 70 million years. Through direct observation in situ and crowd-sourcing, we document the range of behaviors across habitats and prey types, suggesting its widespread occurrence. We argue the presence of these behaviors among marine tetrapods may be limited by limb mobility and evolutionary history, rather than foraging ecology or social learning. These behaviors may also be remnant of ancestral forelimb-use that have been maintained due to a semi-aquatic life history.


Figure 2: Evolutionary links between marine tetrapods known to use limbs while feeding and the diversity of body plans and types of limb use. Silhouettes show a representative body plan for each family. Specific feeding behaviors are listed for each family. 

A green turtle (Chelonia mydas) holding a mosaic jellyfish (Thysanostoma thysanura) in the water column near the ocean surface in the Similan Islands, Thailand, taken June 2017 (photo: Rich Carey/Shutterstock.com)

Figure 1: Limb use in marine turtle foraging.
(A) A hawksbill sea turtle (Eretmochelys imbricata) holding a lobe coral (Porites lobata) to eat the black-brown protein sponge (Chondrosia chucalla) clinging to its surface in Kahekili, Maui USA, taken March 2010. (B) A green turtle (Chelonia mydas) holding a mosaic jellyfish (Thysanostoma thysanura) in the water column near the ocean surface in the Similan Islands, Thailand, taken June 2017 (© Rich Carey/Shutterstock.com).
(C) A hawksbill sea turtle leveraging against the reef substrate to pry away a magnificent sea anemone (Heteractis magnifica). This was a frame grab from a video in Cook’s Bay, Moorea, French Polynesia from June 2013. (D) A green turtle leveraging against the reef substrate to pry away bites of red macroalgae (Amansia glomerata) in Kahekili, Maui, taken October 2016.
(E) A loggerhead sea turtle (Caretta caretta) swiping the shell of an Atlantic deep-sea scallop (Placopecten magellanicus) while it consumes the edible tissue. This is a frame grab from a video in the mid-Atlantic Bight USA taken on July 2009 and available courtesy of the Coonamessett Farm Foundation (Patel et al., 2016). (F) A green turtle swiping the stinging jellyfish (Cyanea barkeri) in the water column at Hook Island, Queensland, Australia, taken June 2017. Image credits by the authors, save (B) © Rich Carey/Shutterstock.com and (E) Coonamessett Farm Foundation.

A green turtle swiping the stinging jellyfish (Cyanea barkeri) in the water column at Hook Island, Queensland, Australia, taken June 2017.


Conclusions: 
The use of limbs to directly aid in foraging, while still relatively rare, is a strategy used by a variety of marine tetrapods. Despite being the oldest extant line of marine tetrapods, this is the first time such a wide range of limb-use has been described in marine turtles. We argue that these limb-use behaviors across marine tetrapods are limited by limb mobility and that the frequent use of forelimbs for other behaviors may promote the development of these feeding strategies. These observations provide additional insight into the diversity and possible evolution of limb-use behaviors.


Jessica A. Fujii​, Don McLeish, Andrew J. Brooks, John Gaskell and Kyle S. Van Houtan. 2018. Limb-use by Foraging Marine Turtles, An Evolutionary Perspective. PeerJ. 6:e4565. DOI: 10.7717/peerj.4565

Monterey Bay Aquarium study finds sea turtles use flippers to manipulate...  eurekalert.org/e/8c8n via @ThePeerJ @EurekAlert

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