The Eyespots Have It

Young Ambon Damselfish on the reef, small and extremely vulnerable to predation. Image: Oona Lonnstadt. The old proverb about a leopard not being able to change its spots now has a new biological footnote after researchers in Australian recently found that fish exposed to predatory danger can, indeed, transform their spots to make them less vulnerable to attack. Working with young Ambon Damselfish, Pomacentrus amboinensis, researchers from Australia’s ARC Centre of Excellence for Coral Reef Studies (CoECRS) have made the remarkable discovery that, when constantly threatened with being eaten, the fish not only grow a larger false ‘eyespot’ near their tail–but also reduce the size of their real eyes. Small prey fish with bigger “false eyes” on their rear fins dramatically boosted their chances of survival on the reef, they found. Relationships between eyespot size and eyeball size and body length. The relationship between standard length and eyespot diameter (A) and standard length and eye diameter (B) in presence and absence of predators. All prey fish exposed to predator cues over a 6 week period had significantly larger eyespots (F,H) and smaller eyes (F,G) than fish from the control treatments (C–E). The changes were not evolutionary—over a succession of generations—but rather a relatively rapid response by individual fish tracked over a period of six weeks. The enlargement of the eyespots results in a fish that looks like it is heading in the opposite direction–potentially confusing predatory fish targeting them to be eaten, says Oona Lönnstedt, working toward her Ph.D. at CoECRS and James Cook University. These spots are known as ocelli, and for decades scientists have debated whether false eyespots, or dark circular marks on less vulnerable regions of the bodies of prey animals, played an important role in protecting them from predators–or were simply a fortuitous evolutionary accident. The widely accepted theory is that these spots, found in the juveniles of many species, tend to cause predators to strike at the eyespotted tail or fin rather than the much more vulnerable head region. Researcher and lead author the paper, Oona Lonnstadt. The CoECRS team has found the first clear evidence that fish can change the size of both the misleading spot and their real eye to maximise their chances of survival when under threat. “It’s an amazing feat of cunning for a tiny fish,” Lonnstedt says. “Young damsel fish are pale yellow in colour and have this distinctive black circular ‘eye’ marking towards their tail, which fades as they mature. We figured it must serve an important purpose when they are young.” “We found that when young damsel fish were placed in a specially built tank where they could see and smell predatory fish without being attacked, they automatically began to grow a bigger eye spot, and their real eye became relatively smaller, compared with damsels exposed only to herbivorous fish, or isolated ones. “We believe this is the first study to document predator-induced changes in the size of eyes and eye-spots in prey animals.” When the researchers investigated what happens in nature on a coral reef with lots of predators, they found that juvenile damsel fish with enlarged eye spots had an amazing five-fold increase in survival rate compared to fish with a normal-sized spot. “This was dramatic proof that eyespots work—and give young fish a hugely increased chance of not being eaten,” says Lonnstedt. Comparison of depth to length ratio. The relationship between standard length (SL) and body depth (BD) of P. amboinensis when in the presence and absence of predators (A). Fish had significantly deeper bodies when exposed to predator cues (B) compared to the shallow bodied controls (C). “We think the eyespots not only cause the predator to attack the wrong end of the fish, enabling it to escape by accelerating in the opposite direction, but also reduce the risk of fatal injury to the head,” she explains. The team also noted that when placed in proximity to a predator the young damsel fish also adopted other protective behaviours and features, including reducing activity levels, taking refuge more often and developing a chunkier body shape less easy for a predator to swallow. “It all goes to show that even a very young, tiny fish a few millimetres long have evolved quite a range of clever strategies for survival which they can deploy when a threatening situation demands,” Ms Lonnstedt says. Their paper Predator-induced changes in the growth of eyes and false eyespots by Oona M. Lonnstedt, Mark I. McCormick and Douglas P. Chivers appears in the latest issue of the journal Scientific Reports. ABSTRACT The animal world is full of brilliant colours and striking patterns that serve to hide individuals or attract the attention of others. False eyespots are pervasive across a variety of animal taxa and are among natures most conspicuous markings. Understanding the adaptive significance of eyespots has long fascinated evolutionary ecologists. Here we show for the first time that the size of eyespots is plastic and increases upon exposure to predators. Associated with the growth of eyespots there is a corresponding reduction in growth of eyes in juvenile Ambon damselfish,Pomacentrus amboinensis. These morphological changes likely direct attacks away from the head region. Exposure to predators also induced changes in prey behaviour and morphology. Such changes could prevent or deter attacks and increase burst speed, aiding in escape. Damselfish exposed to predators had drastically higher survival suffering only 10% mortality while controls suffered 60% mortality 72 h after release. Sources From materials released by the ARC Centre of Excellence for Coral Reef Studies (CoECRS). http://www.coralcoe.org.au/ Featured Image credit: http://www.ibrc-bali.org/research/project/pomacentrus-amboinensis/ Indonesian Biodiversity Research Center Images this page: Oona Lonnstadt, top.

New “Walking Shark” Species Discovered

Hemiscyllium halmahera, a new species of small bamboo shark discovered in the Maluku Islands of eastern Indonesia. Image by Mark Erdmann/Conservation International. Jakarta, Indonesia – A highly charismatic species of walking shark has been discovered in the remote eastern Indonesian island of Halmahera. The epaulette (long tailed carpet) shark, Hemiscyllium halmahera, uses its fins to “walk” across the ocean floor in search of small fish and crustaceans. The discovery comes at a time when Indonesia is significantly ramping up its efforts to protect shark and ray species that are now considered vulnerable to extinction, including whale sharks and manta rays. Indonesia is the world’s largest archipelagic nation with a marine area of over 5.8 million km2 (including a 2.55 million km2 EEZ), and harbors a vast wealth of marine resources. Among these is an amazing diversity of marine life; besides hosting well over 75% of the world’s coral species, Indonesia also is home to at least 218 species of sharks and rays. “This is the third walking shark species to be described from eastern Indonesia in the past six years, which highlights our tremendous shark and ray biodiversity,” said Fahmi, a shark expert at the Indonesian Institute of Sciences. “We now know that six of the nine known walking shark species occur in Indonesian waters, and these animals are diver favorites with excellent potential to help grow our marine tourism industry.” The shark was described in a recent paper in the Journal aqua, authored by Dr. Gerald R. Allen of Conservation International and colleagues Mark Erdmann and Christine Dudgeon. They report that the species reaches a maximum length of just 70 cm (28 cm). Bamboo sharks are among the few elasmobranchs suited to keeping in home aquariums because of their relative small size and bottom dwelling behaviors. The new bamboo shark perching on a rock in a remote area of Indonesia in the heart of the Coral Triangle. The bamboo sharks have the curious ability to “walk” along the bottom on their pectoral and pelvic fins. Image: Mark Erdmann/Conservation International Mark Erdmann CI’s senior advisor to the Indonesian Marine Program and regional coordinator for the Bird’s Head Seascape Program said, “After nearly three decades as the world’s largest exporter of dried shark fins and other shark and ray products, Indonesia is now focusing on the tremendous economic potential of its sharks and rays as living assets. In the last six months’ alone, two of the country’s top marine tourism destinations, Raja Ampat and West Manggarai (home of the famed Komodo National Park) have declared their waters as fully protected shark and ray sanctuaries. It is great to see our findings supporting the valuation and conservation of this natural capital for the long-term wellbeing of the nation.” “This tremendous biodiversity of sharks and rays is a natural heritage that must be conserved for future generations,” said Dr. Sudirman Saad, the Director General of Coasts and Small Islands at the Indonesian Ministry of Marine Affairs and Fisheries, who confirmed the government’s commitment to manage these important marine assets in a sustainable manner. He noted that the Ministry is currently developing regulations and management plans to ensure the conservation and viability of key threatened species of sharks and rays in Indonesian waters. “In addition to securing the long-term sustainability of our national fisheries, we have launched this initiative to prove Indonesia’s commitment to protect our marine biodiversity and ensure the long-term sustainable use of sharks and rays well into the future,” said Saad. SOURCES Allen GR et al. 2013. Hemiscyllium halmahera, a new species of Bamboo Shark (Hemiscylliidae) from Indonesia. aqua, International Journal of Ichthyology, 19 (3): 123-136 Excerpt from materials released by Conservation International.  Images: Mark Erdmann/Conservation International.

Preview: CORAL July/August 2013 Issue

k COVER FEATURES: CORAL Volume 10, Number 4 Family Acanthuridae: The Tangs and Surgeonfishes Text and Images by Robert M. Fenner, Scott W. Michael, Daniel Knop, Keoki Stender Tang Captive Culture-A Progress Report: A Special Report by Matthew L. Wittenrich, PhD ALSO Forthcoming: Aquarium Safety, Classroom Marine Aquariums, Breeding Apogon spp. Cardinalfishes, Diving Lembeh Strait, and much more. Publication Date: July 9, 2013 Materials Deadline: June 14, 2013 Cover Image: Naso lituratus (Naso Tang or Orangespine Surgeonfish) by Keoki Stender, Marinelife Photography
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