Southern blue-ringed octopus (Hapalochlaena maculosa). Image by Alex Barley.
Southern blue-ringed octopus (Hapalochlaena maculosa) These octopuses are found all along the southeast coast of Australia in shallow, rocky waters. Though normally inconspicuous, blue-ringed octopuses flash bright blue when threatened, and have a venomous bite loaded with neurotoxins that can cause fatal paralysis if untreated.
The blue color of the rings is not caused by a pigment, but by tiny iridophores – cells with special mirror-like structures that reflect light in the blue-green wavelength. The bunching of dark melanin pigments below these iridophores serves to increase contrast, making the rings even more eye-catching.
Sunbittern (Eurypyga helias). Image by Alex Barley.
Sunbittern (Eurypyga helias) Found in the tropical areas of the Americas, this drab-looking bird is the only member of its family, Eurypygidae, and originated from the Gondwana supercontinent. Normally plain and inoffensive, these birds react to threats by spreading their wings, revealing huge eyespots, accompanied by hissing, in an attempt to startle predators.
Hatchling bitterns have been seen attempting this display before they have even fully developed the feathers required, though by 12 days their feathers are considered to be fully functional. These birds also use these fancy feathers to attract mates, combining outstretched, downward-angled wings with duets of bill-clattering and trilling.
Mountain katydid (Acripeza reticulata). Image by Alex Barley.
Mountain katydid (Acripeza reticulata) These little-known katydids are found all along the Eastern coast of Australia, from the Snowy Mountains, all the way north to Brisbane. They are rather clumsy when moving, but have a dramatic display when disturbed, lifting their wings to reveal a colorful abdomen coated with noxious chemical secretions.
A 2015 study by Dr Kate Umbers determined that the katydids only display after being touched. Displaying only after being physically attacked seems counter-intuitive, but it has been suggested that they are tough enough to survive this initial attack, and predators may also better learn to avoid them once tasting the noxious chemicals they produce.
Despite how eye-catching these species are, the evolution and exact mechanisms of startle displays remain poorly understood in even the more well-studied species, like the blue-ringed octopus. Visual displays are reliant on the fact that a predator primarily uses sight to detect and identify its prey. These displays are, in essence, a message to the would-be predator: Stop! These messages between predator and prey have a complex, poorly understood evolutionary history.
Scientists study these animals to better understand what part of the display is the most meaningful and how much information each component of a display conveys, from the pattern to the colors used. Some colors seem to be selected over and over, across many different species, to send a specific message. A good example is the combination of black and yellow, which is used by many species to signal toxicity, a phenomenon observed in Mullerian mimicry.
For all the mysteries surrounding the evolution and persistence of deimatic displays, these species can be important for conservation. Eye-catching animals make excellent ambassadors, especially for insects that are so often overlooked in favor of familiar mammal species. There is a lot of conservation potential for charismatic critters like the few featured here.
References
Kate Umbers and Johanna Mappes, “Towards a Tractable Working Hypothesis for Deimatic Displays,” Animal Behaviour 113 (February 1, 2016), doi:10.1016/j.anbehav.2016.01.002; John Skelhorn, Grace G. Holmes, and Candy Rowe, “Deimatic or Aposematic?,” Animal Behaviour 113, no. Supplement C (March 1, 2016): e1–3, doi:10.1016/j.anbehav.2015.07.021.
Lydia M. Mäthger et al., “How Does the Blue-Ringed Octopus (Hapalochlaena Lunulata) Flash Its Blue Rings?,” Journal of Experimental Biology 215, no. 21 (November 1, 2012): 3752–57, doi:10.1242/jeb.076869.
Betsy Trent Thomas and Stuart D. Strahl, “Nesting Behavior of Sunbitterns (Eurypyga Helias) in Venezuela,” The Condor 92, no. 3 (1990): 576–81, doi:10.2307/1368675.
Kate D. L. Umbers and Johanna Mappes, “Postattack Deimatic Display in the Mountain Katydid, Acripeza Reticulata,” Animal Behaviour 100 (February 2015): 68–73, doi:10.1016/j.anbehav.2014.11.009.
Rowe, Candy, and Christina Halpin. "Why are warning displays multimodal?." Behavioral ecology and sociobiology 67, no. 9 (2013): 1425-1439.
Rowe, Candy. "Receiver psychology and the evolution of multicomponent signals." Animal behaviour 58, no. 5 (1999): 921-931.
Guiney, Margaret S., and Karen S. Oberhauser. "Insects as flagship conservation species." Terrestrial Arthropod Reviews 1, no. 2 (2009): 111-123.
Image Credit:
Alex Barley
Alex
Barley
Guest Writer
