Bone-Eater of the Dark Depths

osedax_colorWeb_JMLandin

When a whale dies, its body often sinks to the bottom of the sea. From death comes life – an entire ecosystem blooms from the resource-rich remains.

Scavenger fish (sharks and hagfish), as well as crabs, shrimp, and octopuses, consume the flesh, leaving only a massive skeleton behind. Even the bones are devoured in this cold, dark place. Osedax worms, a.k.a. bone-eating or zombie worms, slowly dissolve and ingest the protein- and fat-rich bone. Very slowly… for up to a century. The worms grow root-like structures into the bone’s marrow. These “roots” contain symbiotic bacteria that help digest the nutrients.

Descriptions of bone-eating worms were first published just 15 years ago. Since then, more than a dozen species of bone-eating worms have been identified from every ocean. Originally, researchers thought that the worms evolved with whales but more fossil evidence indicates that Osedax were likely present on the bones of marine reptiles at least 50 million years earlier. (1)

The whale-fall ecosystem was recently captured on video (the fuzzy reddish-brown coating on the bones are large numbers of the worms).

  1. Danise, S. and N.D. Higgs. 2015. Bone-eating Osedax worms lived on Mesozoic marine reptile deadfalls. Royal Society Biology Letters. 11(4)

Misfit? Or totally Fit?

sloth

The term “fitness” congers images of six-pack abs, yoga poses, and 90’s spandex leotards (for me, anyway).  But those images can be misleading when it comes to understanding evolutionary fitness.

Good “fitness” in evolution means “a good fit.” Organisms that fit well in their environmental niche spend less energy just trying to survive; they have more energy left over for reproduction. So fitness is often measured by the number of offspring produced.

A sloth is well camouflaged with its slo-mo movement. Many predators detect prey by movement (if we stick with the 90’s imagery, remember the T.rex in Jurassic Park “can’t see us if we don’t move”). Low metabolism in sloths means very low food requirements. One study measured sloth metabolic rate at 174 kJ (kilajoules) per day. (1) Just for comparison, an average human requires 6000-7000 kJ per day.

  1. Nagy, KA and GG Montgomery. 1980. Field metabolic rate, water flux, and food consumption in three-toed sloths (Bradypus variegatus). Journal of Mammalogy 61(3)465-472

There Be Dragons!

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Australian Water Dragons (Intellagama lasueurii) lounge and bask around pond edges at the University of Queensland, where I saw this handsome fellow. The colorful markings under his chin advertise his masculinity to the local lizard ladies… and to rival males too.

Researchers painted a model Water Dragon (actually a plastic iguana with a few glued-on additions) with either brown markings or red markings. (1) The toy was then introduced among resident Water Dragons to record their response to the intruder. When the toy had brown markings, the real Dragons attacked faster and more often.

Those fancy red and yellow stripes attract mates, but also deter rivals.

  1. Baird, TA, TD Baird, and R Shine. 2013. Showing Red: Male Coloration Signals Sam-Sex Rivals in an Australian Water Dragon. Herpetologica 69(4) 436-444

Disruptive Patterns & the Artist-Scientist

MabeeSalamander_JMLandin

Many animals display disruptive coloration, a pattern that visually breaks up the edge of their shape. For example, Mabee’s Salamander (Ambystoma mabeei) wears speckles like frost along its side. And it was an artist who first described this biological phenomenon – Abbott Thayer. (1) His studies of these patterns influenced the use of camouflage in the military.

In a recent fun study, researchers placed graphic squiggle-snakes on a mock-leaf background or plain background. They manipulated the coloration – solid, patterned, or patterned with bold and bright edges to the shapes. The edge-enhancement made the squiggle-snakes more difficult to spot on a leafy background. It also confused the observer about the shape of the snake when it was on a plain background.

  1. Behrens RR. 2008. Revisiting Abbott Thayer: non-scientific reflections about camouflage in art, war and zoology. Philosophical Transactions of The Royal Society 364(1516) 497-501
  2. Sharman RJ and PG Lovell. 2019. Edge-enhanced disruptive camouflage impairs shape discrimination. i-Perception 10(5) 1-9

Fattest Animal

JMLandin_cutworm

This cutworm moth (Family Noctuidae) is the fattest animal in the world. In just two summer months of feasting on flower nectar, the migratory moths balloon from 20% to 80% body fat (1). Storing this much energy has a price though – no romance. Migratory moths put reproduction on hold to save up energy for their journey.

Thanks to all that fat, cutworm moths are a major food item for grizzly bears in the summer (2).

It got me wondering: These moths delay reproduction so they can migrate, but putting on fat makes them more delicious. Why not just stay put and make some babies instead? Since their migration is basically east-west, major temperature/seasonal shifts don’t require the move*. Local plants (food) don’t require the move either **. Parasites might. Army cutworm moths are highly parasitized. Moths with parasites stay in the Rocky Mountains longer, growing larger and fatter. So the bears may do the whole population of moths a favor by culling those with parasites.

* Altitude is a factor in temperature and season. But if moths stayed near the mountains, they could stay put moving up and down in altitude without flying a few hundred miles to and from the plains.

** Larvae eat a wide range of leaves and stems. Adults suck up flower nectar. So a large number of larvae may reduce some food for the adults.

  1. Kevan, PG and DM Kendall. 1997. Liquid Assets for Fat Bankers: Summer Nectarivory by Migratory Moth in the Rocky Mountains, Colorado, U.S.A. Arctic and Alpine Research 29(4):478-482
  2. French, SP, MG French and RR Knight. 1992. Bears: Their Biology and Management. p 389.

Fight, Flight, or FREEZE

tadpole_web

When a predator approaches, options are limited – especially if you’re a tadpole. The woodfrog tadpole (Rana sylvatica) is known to stop swimming and sink to the pond bottom, an action called “freezing behavior.”

In one study, researchers exposed woodfrog embryos to some water from a predator’s tank with or without an injured tadpole (1). When the embryos hatched, the ones that had smelled both the predator and injured relative showed very reduced activity (freezing behavior) if re-exposed to just predator-water.

In mice, freezing behavior is affected by the size and speed of an object. Video showing lab mice exposed to various dots indicates that small, slow objects trigger mice to freeze. When exposed to terrifying large dots, mice take off.

  1. Mathis, A., M.C.O. Ferrari, N. Windel, F. Messier, and D.P. Chivers. 2008. Learning by embryos and the ghost of predation future. Proc Biol Sci. 275(1651): 2603-2607.