Monday, June 29, 2015

Loony Locomotion (A Guest Post)

By Emma Doden

For those of us who have worn fins while snorkeling or swimming before, we know how much faster you are able to cut through the water with them on your feet. But as soon as you try to walk on land with those big flippers on, that grace and speed turns into awkward and ungainly steps. You have to concentrate very hard on not falling flat on your face and find yourself thinking that your own two small feet are much more convenient for walking on land than the flippers.

The common loon in flight. Notice how far back on the body its feet are placed!
Photo by Ano Lobb from Wikimedia Commons.
The common loon is a familiar flipper-footed bird for those of us residing in the Northern Midwest. Found on many lakes in the North Woods from late March to September, their black and white plumage, ruby red eyes, and haunting calls make them unforgettable. However, just like any other waterbird, as soon as they come onto land, all of their beauty and poise vanish. Loons do not have the luxury of removing their flippers when they come onto land. Instead they flip and flop clumsily on their bellies, probably feeling just as frustrated as any person frog-stepping with flippers on.

So why do loons have so much trouble walking on land?

Because most of their lives are spent in water, the common loon’s legs and feet are located extremely far back on their bodies, allowing them to swim and dive more efficiently. Loons don’t use their wings to aid in propulsion while underwater, so they need all the power they can get from their legs and feet to catch tasty fish.

The placement of their legs means that they must slide on their belly while on land. Their legs can’t support the weight of their body and so they instead use them to push off of the ground and slide forward. The only time you will find a loon on land is for mating or nesting. Common loons will build their nests on the shore, usually no more than 5 meters from the water, because it takes a lot of effort to belly flop even that short distance!

Watch the video below to see how comical a loon looks when stranded on land:

Though loons are strong fliers as well as divers, coming in for a landing can also be challenging. Their legs are too far back to thrust forward and use as landing gear, so they stick them straight back and make a splash-landing on their bellies, penguin style!

But what makes their legs and flippers so good for swimming and diving?

Common loons propel themselves through the water with sideways strokes of their legs and feet, similar to oars on a boat. Diving birds have leg bones with a long spike-like extension at the knee where very strong muscles connect. This part of their leg acts like a lever when a loon paddles, allowing the leg and foot to be powerfully propelled through the water. Each foot is fairly large with webbing between each toe. When a loon paddles through the water, the webbing fans out and the foot rotates slightly in relation to the body on the downstroke, allowing the maximum surface area to push off of the water. On the upstroke the toes will compress together and the webbing will bunch up so that there is minimal resistance cutting through the water. The motion of the foot splaying out and compressing in with each stroke creates an efficient mode of transportation for the water-loving loon. With legs and feet like these, they are able zoom through the water as fast as fish and dive up to 200 feet!

Loons rarely come onto land, and so it is not often that you will find one of these majestic creatures floundering through the mud of a lakeshore. You are much more likely to see them gliding effortlessly across a lake, until they disappear below the surface. Then you can imagine them easily hunting fish using their powerful legs and feet to propel them while diving. Even more so than wearing flippers to help you swim, just think how much faster you could be in the water with the streamlined body and strong legs and feet of a common loon!

To learn more about common loons and their flipper-foot conundrums visit these websites:

Piper, Walter. The Loon Project.

The Cornell Lab of Ornithology. 2011. Common Loon, Life History. All About Birds.

Evers, David C., James D. Paruk, Judith W. Mcintyre and Jack F. Barr. 2010. Common Loon (Gavia immer), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; The Birds of North America Online.

Michigan Department of Natural Resources. 2014. Common loon (Gavia immer).

Shearwater Seabird Osteology. 2013. Divers/loons: Osteology.

Monday, June 22, 2015

Suicidal Sex

A brown antechinus. Males of this species mate like crazy
for two weeks, then die. Photo by Alan at Wikimedia.
Although most species breed repeatedly over their lifetimes, a select few invest everything they’ve got in a single reproductive bout, after which they keel over and die. This strategy, called semelparity, can be beneficial in species that can have many offspring at once and that are not likely to survive long enough for a second breeding attempt anyway. It is most commonly seen in plants, invertebrates and some fish. It is a rare strategy in mammals, in part because mammalian females do not have many offspring at once and they need to live long enough to care for their young after they are born, which dying early would obviously prevent. Despite this, there are over a dozen species of mammals of which all the males die after their one and only breeding season. How could this possibly be adaptive?

Today at Accumulating Glitches, I talk about how patterns of insect abundance and competitive sperm have pushed some mammals to mate themselves to death! Check out the article here.

Monday, June 15, 2015

Loving to Death

The brown antechinus may look like a
mouse - but that is where the similarities
end. Photo by Glen Fergus at Wikimedia.
Although most animal species breed multiple times throughout their lives, a few oddballs put everything they've got into a single reproductive season, after which they promptly die. This is a rare strategy (for obvious reasons), especially in mammals. One Australian mammal, the brown antechinus, is just odd enough to pull it off.

The brown antechinus is a small insectivorous mouse-sized critter from Australia that in fact is not a mouse at all. It is a marsupial; but unlike kangaroos and koalas, females do not carry their young in a pouch, but rather let them hang off their eight teats for four months. All males die when they are 11 months old (if not sooner) after a single 2-3 week long mating season during which they do little else than mate as often as possible. The mating season leaves all the males (whether mated or not) sterile, coursing with stress hormones, immunosuppressed, and riddled with microorganisms and parasites. Shortly thereafter all the males die, balding and bleeding messes.

The reproductive strategy of putting everything you've got into a single mating season and then dying is only an advantage if you can have many offspring in that single reproductive event. Male brown antechinuses can only succeed in this suicidal mating strategy if they father many of the young of many of the females. As a result, both male and female brown antechinuses are promiscuous (mate with many individuals).

Male brown antechinuses are generally bigger than females, and DNA testing has shown us that in the wild, larger males and males with bigger testes impregnate the most females. Diana Fisher and Andrew Cockburn from Australian National University tested whether larger male brown antechinuses were more likely to get the girls because females were more likely to choose them or because they were outcompeting other males.

Diana and Andrew trapped brown antechinuses and brought them into the lab. In one test, they placed three males in separate nest boxes next to one another in an arena and allowed females to choose among them and mate with whichever one she chose. Surprisingly, when presented with this choice, females did not consistently choose the largest males. They didn't even check them all out - The females mated with whatever male happened to be in the first nest box she entered.

When the researchers put three males into a single nest box and allowed the females to mate, she almost always immediately mated with one of the three males. The next day, the researchers put the female in a nest box with either the two losers from the day before or with two randomly chosen males she did not know. On this second day, females presented with two strangers immediately mated with one male, whereas females presented with the two losers from the day before were more likely to spend more time evading both males, but often eventually mated with one of them. On the third day, the researchers put the female in a nest box with either the loser from the previous two days or with another randomly chosen stranger. Nine out of ten females paired with a stranger mated with him on this third day, whereas only one female paired with a double-loser was willing to mate with him at all. Males that successfully mated on the first day were generally the largest of the three. Loser males that mated on the second day were generally the second-largest and unsuccessful males were generally the smallest.

Interestingly, when given a choice of males one at a time, female brown antechinuses do not seem to care at all about male size. But when males are directly competing with one another, the largest male seems to get the girl. It appears that body size plays a role in the dominance interactions among the males, and that females are paying attention to how the males relate to one another. Additionally, larger males that were more successful in mating also lived longer and had fewer parasites. This could be because it is more stressful to be a loser than to be a winner. Stress increases the production of stress hormones, which in turn reduces immune function. In all of these ways, bigger males are more likely to father more young, who in turn will be more likely to grow up to be big males too... but not for long...

Want to know more? Check these out:

Fisher, D., & Cockburn, A. (2005). The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death Behavioral Ecology, 17 (2), 164-171 DOI: 10.1093/beheco/arj012

Doing it to death: suicidal sex in "marsupial mice" at The Conversation