Can you pick up a drop of water with tweezers?

Some birds can! A group of shorebirds called phalaropes have a curious way of feeding. They feed on the surface of lakes, tidal wetlands and other bodies of water by swimming around in a tight circle on the surface furiously kicking their legs. This creates a vortex in which tiny aquatic invertebrates like shrimp, aquatic insects and copepods are pulled to the surface. Once food items are trapped in the swirling water phalaropes gobble them up with their long thin bills. But, while the phalarope's curious means of concentrating aquatic invertebrates is well known less well understood is how they use their bills to consume their tiny water suspended prey. A team at the Massachusetts Institute of Technology lead by Manu Prakash has uncovered just how suspension feeding birds like phalaropes use their bills to draw up droplets of water packed with their invertebrate prey.

Unlike a straw a bird's bill is open on both sides and opens in an up-and-down motion much like a pair of tweezers so they can't suck up shrimp filled pond water like you would a slushie. In phalaropes their bills are long and very thin (see photo to the right of a Red-necked Phalarope (Phalaropus lobatus) from the Cincinnati Museum Center's Zoology collection). Just how phalaropes can use a tweezer-like bill in a straw-like fashion is a puzzle. Prakash and colleagues found that a drop of water in a very thin bill can be drawn up the bill by what they call a "capillary ratchet". They looked at data in the literature derived from real bills (much of which was originally from museum specimens) and built a mechanical bill with similar properties. When the bill is closed the drop of water is compressed and when opened again it moves a bit further up the bill towards the mouth. Close the bill again the water is compressed. Open again and it moves a bit further up the bill. Click HERE for a Quicktime movie of the Prakash et al. mechanical bill in action. The ability of an artificial bill to serve as a capillary ratchet is highly dependent on both it's shape and it's wetting properties.

This study has several important implications. First, it describes a novel evolutionary adaptation in birds and helps us better understand the myriad of solutions that evolutionary processes can generate to basic challenges in life. Second, an understanding of biomechanics for natural structures like the bill of the phalarope can help human engineers design devices for moving very small amounts of liquid (i.e. microfluidic transport systems). Such devices, inspired by nature, can have important implications in nanotechnology and molecular biology and could potentially advance human health. Finally, because Prakash et al. found that the wetting properties of the bill were critical in its ability to act as a capillary ratchet device environmental managers should look for effects of pollutants on the feeding efficiency of phalaropes and other shorebird species. Petroleum products and detergents could have significant effects on the wetting properties of a phalarope bill and in turn lead to less food for affected birds.

Of course museums, like Cincinnati Museum Center, often play a significant role in these biomechanical studies by serving as storehouses of all the clever tricks invented by evolutionary processes. Taping into nature's diversity is not only good simply for the sake of a greater knowledge of our living world but it also can provide us with designs for our own technology, designs that have been tested over eons of evolutionary tinkering.

Prakash, M., Quere, D., Bush, J.W. (2008). Surface Tension Transport of Prey by Feeding Shorebirds: The Capillary Ratchet. Science, 320(5878), 931-934. DOI: 10.1126/science.1156023

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The weird and wonderful platypus genome

Modern comparative biology has truly entered a new age. The list of species for which researchers have completely sequenced their genomes continues to rapidly grow. Fruit flies (Drosophila melanogaster), chickens (Gallus gallus), sea urchin (Strongylocentrotus purpuratus), pufferfish (Fugu rubripes), Short-tailed Opossum (Monodelphis domestica), mosquitos (Anopheles gambiae), Rhesus Macaque (Macaca mulatta), several plants such as rice (Oryza sativa) and cottonwood (Populus trichocarpa), numerous microbes, and even Humans (Homo sapiens) all have complete genome sequences completed.

Add to that list the Duck-billed Platypus (Ornithorhynchus anatinus). A research team has just completed the first sequencing of the platypus genome. The platypus is truly among the strangest of mammals. Found exclusively in Australia and Tasmania, they have hair and produce milk as do the rest of their mammalian kin but they also lay eggs and have a brain much like a reptile. Male platypus also sport a spur on their hind feet that can deliver a venomous sting. Because of this odd mix of reptilian and mammalian characters the first platypus specimens brought back by the early explorers of the Australian continent were thought to be a hoax, patched together from bits and pieces of other animals. Cincinnati Museum Center's Zoology Collection has an old platypus specimen in it's holdings (see photo left).

Like it's reproductive behavior, physiology and morphology the genome of the platypus reveals it's key evolutionary position at the base of the mammal family tree. For example, mammalian ova have an outer membrane called the zona pellucida which aids in fertilization. Of the proteins make up the zona pellucida in mammals four found in the platypus match those found in the human genome, however, the platypus genome has two additional ova membrane proteins previously found only in birds. Additionally, the platypus genome contains genes for the yolk protein vitellogenin, a protein found in the eggs of birds but neither marsupials or placental mammals.

The genes underlying the venom found in the spurs of male platypus also tell an interesting evolutionary story. Platypus venom, like many venoms found in reptiles, is a complex mix of different proteins. Platypus venom contains 19 different compounds. The venom proteins in platypus venoms appear to have arisen through duplications of genes. Gene duplication is a common evolutionary process that can give rise to new characteristics. When a gene is duplicated the new duplicate is free to accumulate new mutations and take on new functions while the original gene retains it's original function. Not only has gene duplication played a role in the evolution of platypus venom but the same process likely led to the evolution of venoms in reptiles. Also, the venom proteins in the platypus arose from the same gene families as in venomous reptiles providing an interesting case of convergent evolution (evolution of similar traits arising independently in different lineages).

The complete sequence of the platypus genome follows previous work on the sex-determination chromosomes in the platypus (Grutzner et al. 2004. Nature 432: 913-917). For mammals, sex is determined by two sex chromosomes, X and Y. Females have two X chromosomes and males have one X chromosome and one Y. But, platypus have ten sex chromosomes! These ten chromosomes are arranged in a chain such that females are have five pairs of X chromosomes and males have five XY pairs. In birds the sex determination system is different. The sex chromosomes in birds are called W and Z and rather than males being the sex with two different sex chromosomes (called the heterogametic sex) the females are the ones with different sex chromosomes (female birds are WZ and male birds are ZZ). Interestingly, like much of the rest of the platypus genome the sex chromosomes belie their position in the mammalian tree. At one end of the chain of X-chromosomes in the platypus genome is an X chromosome with sequence similarity to the avian Z chromosome. This suggests evolutionary links between the sex chromosomes of birds and mammals and thus a common evolutionary history for these two different groups of animals.

Surely further investigation of the platypus genome will reveal more insights not only into platypus evolution but the evolution of the whole mammalian family tree, including us. As more and more organisms are sequenced we will gain more insight into evolutionary history and processes.

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For bats the nose knows...

Delimiting one species from another can be a difficult thing for biologists to do. This is especially true when the criteria researchers use to define one species from another may not be among the same criteria used by the organisms in question to distinguish themselves from other species. This can result in hidden or cryptic species being subsumed by biologists into a common grouping. Cryptic species lumped together as a single species by morphological data can be discovered through studies of DNA.

Recently Sarah Weyandt of the University of Chicago and the Field Museum visited the Cincinnati Museum Center’s Zoology Collection to look at cryptic species in horseshoe bats from the Philippines. Horseshoe bats (family: Rhinolophidae) are insect eating bats characterized by large ears and elaborate folds of skin forming other structures around their noses called noseleaves. Biologists use these structures, along with other traits, to distinguish between one species and another. However, sometimes two different species can have very similar noseleaf patterns and be difficult to distinguish. There are two varieties of noseleaves in the Philippine bat Rhinolophus arcuatus that differ in very subtle ways (see photos of two Cincinnati Museum Center specimens illustrating these two varieties of noseleaf structure to the left). However, despite very little difference in their morphology these two varieties of bat differ considerably in their genetics, as much as either Rhinolophus arcuatus variety differs from members of another Rhinolophus species.

Sarah is delving deeper into the genetics and morphological variation of this group of bats. To those ends the Cincinnati Museum Center’s Zoology Collection provides valuable specimens for morphological studies and frozen tissue for genetic studies.

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