In my Did You Know series, learn some fun facts about an animal in 5 minutes. I’ll tell you stuff you didn’t already know (hopefully). Let me know if I surprised you!
Today I’ll tantalise your curiosity taste buds with a master of masquerade: the leafy sea dragon.
Did You Know?
It is a species of fish named after the dragons described in Chinese mythology and folklore (and more recently in George R. R Martin’s Game of Thrones)
It is the only member of the Phycodurus genus in the Syngnathidae family of fishes.
Its resemblance to a piece of drifting seaweed may help to protect it from predators. Its seaweed-like appearance not only allows it to match the background of seaweed and kelp it lives amongst (making it very hard for predators to spot), but it may also serve as a type of camouflage called ‘masquerade’. This is when an animal tricks its predator into thinking it’s an inedible object that isn’t dinner, similarly to that seen in leaf and stick insects. If you’re interested, you can read more about masquerade here and here.
Another aspect of this ‘floating seaweed’ trick seems to be the sea dragon’s sedate movement through the water. It moves at a slow rate of about 150m per hour propelled by fins along the side of its head but often stays in the same place for long periods of time.
Unusually in the animal kingdom, the male is the sole responsible parent. The female deposits 150-250 bright pink eggs onto the male’s tail, and then leaves him to it. He carries them in a honeycomb-like structure called the brood patch for 8 weeks where they are supplied with oxygen until the young emerge (like its relatives: seahorses, pipefish and other sea dragons). Only about 5% of the eggs survive and the young are completely independent at birth.
It feeds exclusively on small crustaceans like mysid shrimp.
Their natural habitat is calm, cold water (10-12 degrees Celsius) in the southern coasts of Australia, where they are known locally as ‘leafies’.
Recent research published in The Condor: Ornithological Applications has shown that greater sage grouse mothers (Centrocercus urophasianus) can choose nesting habitats that better ensure the survival of their chicks after they fledge.
Evolution not only drives animals to act to benefit their own survival (direct fitness) but also that of their own offspring (indirect fitness). Maximising such lifetime reproductive success is probably what drives us to protect our own children.
But can animals actually make active decisions that benefit their reproductive success? This is the question that Dr Daniel Gibson and his colleagues set out to answer in their study of the greater sage grouse.
These birds are the largest grouse in North America, inhabiting open grassland habitats that make them particularly vulnerable to predators. The species is classified as Near Threatened by the IUCN Red List. They have a complex mating system, whereby males gather in groups (leks) to perform lively, colourful mating displays to attract females [see picture]. This means that females get to be extremely picky about who they mate with.
Dr Gibson and his team found that females are not only choosy about their sexual partners but also are picky about where they nest. They tend to choose nesting habitats with characteristics that ensure reproductive success: specifically, greater shrub cover and forb (flowering plant) diversity. By observing over 200 mothers over a period of 8 years, they found that these habitat features predicted the survival of chicks after fledging.
This means that even our feathery friends can make active choices that determine the survival of their offspring, which is pretty impressive. What isn’t so clear is whether the mothers themselves were more likely to survive – were they also acting to protect themselves as they sat helpless on their nests? Or is their behaviour purely selfless?
Whatever the answer, it is likely that many other animals are able to protect their young by making these real-time decisions – what can be termed ‘behavioural plasticity’ – something that evolution is likely to promote in order to maximise indirect fitness and pass on genes to future generations.
Knowing this will also help conservation efforts because land managers now have clues about where these birds are most likely to nest, and hence which habitats they should protect the most.