Pitcher perfect- a strange mutualism

Carnivorous plants like the Venus flytrap capture insects and digest them to obtain protein (which is made up of Nitrogen). What could a bat and a carnivorous plant have in common? Recently, a group of German researchers demonstrated that these two organisms can develop a mutualistic association. (Mutualisms develop when both partners of a relationship gain something through their association with the other individual, many examples of which occur nature).

This fascinating study conducted in Brunei demonstrated that bats use pitcher plants as roosting sites and in turn the nitrogen rich feces (guano) from the bats fall into the pitcher of the plant where it like the insects the plant usually digests is incorporated into the plant's tissue.

The bat (woolly bats (Kerivoula hardwickii)) is provided with a place to live while the plant (areal pitcher plant (Nepenthes rafflesiana) gets its highly sought after nitrogen!

The precarious roosting location for the bats aside this fascinating study that uses both radio telemetry and stable isotope ecological methods reveals an unlikely relationship between carnivorous plants and bats.

The article:
Grafe, T. U., C.R. Schoener, G. Kerth, A. Junaidi, and M.G. Schoener. (2011). A novel resource-service mutalism between bats and pitcher plants. Biology Letters

Updated bat activies for May 2011 (year of the bat!)

An updated list of bat related activities around the world in May to celebrate the 'Year of the Bat'!



Unfortunately activities seem restricted to Europe for the time being...



EUROPE

Germany (Frankfurt)



11 May Nachtscwaermer-guided tour (Frakfurt Zoo)



18 May- Nachtscwaermer- guided tour (Frankfurt Zoo)



21 & 22 May- Experiencing bats (Frankfurt Zoo)



25 May- Lecture "night Flight- Fascinating bats" (Frankfurt Zoo)



UK

17 May Bat walk, Bryngarw County Park, Bridgend, South Wales



20May- 16 September Cambridge, 'Bat Safari' river tours

Back to field planing! (and milking bats)

Ah it is 'that time' again the birds are singing, the bees are buzzing and the bats are lactating! Yes, considering that the Artibeus were all pregnant (late-stage) during my mid-march visit if I plan on collecting milk it is time once again to schedule a trip to the field for the 'last' milk collection of my dissertation (assuming all going according to plan). This next trip my lab mate will accompany me which will be an added bonus. Now all that said I imagine one question came to mind rather quickly 'wait... milk bats?' Yes... this is actually not as difficult as it sounds. Basically the mother and pup are captured, kept away from each other for a short while (~1 hour) so she accumulates milk which is natural if the mother is away from her baby. (Also the mother and pup are accustomed to being separated from each other for longer periods of time because the baby that cannot fly must stay behind while its mother is out for several hours every night searching for food.) After about an hour, I inject the mother with a small amount of a hormone called oxytocin. Oxytocin increases milk let down (i.e. lactation) so this combined with what is essentially a miniature version of milking a cow allows me to collect milk from the female before letting her and her baby return to their roost. I then upon returning analyze many nutritional components in the milk (dry mass, protein, fat, and carbohydrate (sugar) content).

Flight (Part 2)

Continuing on the topic of flight... The physics of flight include 4 forces. 2 of these (in bold) are generated by the flying animal (in this case a bat) and 2 of them (drag and gravity) are natural properties that the animal must negotiate (fight) in order to fly. 1. Lift (i.e. upward force) 2. Thrust (i.e. forward force) 3. Drag (backward force (resistance)) 4. Gravity (i.e. downward force)

LIFT

The shape of wings causes air to move over the wing-surface in a unique way. Specifically, air flows faster over the upper curved surface of the wing and slower over the cupped (concave) surface. This causes negative pressure on the upper side of the wing and thus the wing begins to rise. In principle this is what happens when as a child you cupped your hand and played with the wind outside the open car window. Remember how the air would suddenly PUSH your hand upward? That is 'lift'! Additionally that is about the time you were reminded to not put your arms out the window.

Take home: the shape of wings (think of a bird or bat wing) is what causes air to move in a way that LIFTS the wing upward. The opposing force is gravity... without lift (like you or I flapping our arms, sorry to say but we are not going to generate sufficient lift) gravity 'wins' and we stay stuck to the ground. Gravity is complex for despite the fact that physicists can tell us its value (9.81 m/s2) how it 'works' and why it exerts force on objects was perplexing even to Einstein who wrote extensively on the topic. Incidentally, Einstein apparently also noted "Gravity cannot be held responsible for people falling in love." ______________ (I will insert an awkward pause here as you ponder that and why he might have felt it necessary to declare such a fact, if he made this statement in English or German and if it would have been funny regardless). Back to flight: The wings of bats are more flexible than birds because the wing itself is formed by a thin layer of skin rather than stiff feathers. However, birds are able to more easily change their wing area by moving their wings closer to their bodies because bats require the full extension of their 'fingers' i.e. the wing to have it function because of its thin nature. In searching for an analogy the best I have for you follows. This is similar in a way to how airplanes have rigid wings (like bird wings) while a para glider that uses a flexible surface (like a bats wings) is less able to change the shape of the 'wings' or they will loose lift.

THRUST

Basically thrust is the power from a wing-stroke that pushes back against air and results in a force propelling the animal FORWARD. Indeed to understand this idea you must remember that air is made up of molecules and is in actuality a fluid (like water). Thus there is indeed something to 'push upon'.

I will conclude for now and leave you with another Einstein quote as a 'token' physicist

"Science i nothing more than a refinement of everyday thinking".

I refer you to this much more comprehensive explanation of flight (here) and hope you find this topic interesting.

The evolution of flight (Part 1)

Many animals are able to fly and most of these are insects. However, when one stops to consider which vertebrates fly (vertebrates are animals with an internal skeleton including a spine and something resembling a spinal chord) only 3 main groups are able to fly.

These are: birds, Pterosaurs and bats.

The wing surface formed in 3 different ways one for each of these groups (see above).

Both bats and Pterosaurs used a wing-surface created by finger elongation (the 'pinkie' in Pterosaurs and all fingers elongated except the 'thumb' in bats).

Meanwhile, birds fly using a surface created by modified scales (feathers) and a strong series of arm and finger bones that are the result numerous bones fusing. Additional details are left out for brevity but are extremely interesting such as skeletal lightening in birds.

Pterosaurs are extinct and so only two extant flying vertebrate groups (extant = animals that are still alive today) are bats and birds. (What is a Pterosaur? Click here!)

Why did flight evolve?

There are two main thoughts about this. Basically either animals were able to flap and lift UP to escape predators etc. OR they were living in trees and started to glide from tree to tree (like 'flying' squirrels) also to catch food (insects) or avoid predators.

Regardless, the sky is (and was) full of potential food and once they were able to fly bats quickly filled a new niche (a niche is the ecological role of an animal generally relating to the food it eats). Both bats and birds were able to eat flying insects but bats as nocturnal animals compete with a fewer set of birds. Indeed this successful niche 'nocturnal insectivore' has since been radically expanded to include other more unusual food-types such as frogs or fish!

You can read more about the evolution of flight here.

Click here for cool videos of bats flying in slow motion.

For my next I will try to summarize the physics required for flight.

Can pregnant bats fly?

I happened upon the above question incidentally and thought perhaps it is a good one to address since I study reproductive bats and many people who do not study bats might have the same question!

(to the right is a photo of a Jamaican fruit-bat late in her pregnancy)

The simple answer is yes, bats fly while pregnant. That said it is very energetically costly for them and they become increasingly awkward as the pregnancy progresses. Indeed they may be more likely to be eaten by predators as they become slower and less-maneuverable.

Not only do they fly while pregnant, but bats give birth to pups that are much larger relative to the mom's size than human mothers give birth to! So, they are still flying when the developing baby is larger relative to the mother than a human would be walking around with.

After bats give birth (upside-down which is yet another difficulty) the mother will occasionally fly with her ever-growing baby (most bats only have one pup per pregnancy although some have twins and more rarely- triplets). The fortunate bats like Mexican free-tailed bats (Tadarida brasiliensis) or other cave dwelling bats usually leave their young in the roost while they forage but some less-fortunate bats may have to move their young nightly or semi-regularly if they inhabit less-permanent roosts.

So next time you hear a pregnant friend or family member saying how their back hurts or it is hard to get around you can tell them to cheer up and remind them they are lucky that they are not a pregnant bat!

Toothsome (more facts about biologists)

I have come to the conclusion and with increasing confidence that many biologists love to cook. Perhaps you are picturing them throwing some burgers on the grill or making killer chili.... no I mean that numerous biologists I know make on a semi-regular basis and with avid enthusiasm, fancy 4 course gourmet meals and exotic fare.

For example, BOTH of my collaborators in Mexico are involved in a 'gourmet club' that includes a group of several additional Mexican bat biologists who all alternate making and hosting gourmet fancy dinners. My adviser makes pies for fun and attempts to emulate her favorite dishes (generally carne asada comes into play). She may have learned this from an old committee member and bat-biologist of legend 'Mike' who attempts to dis-entangle the exact recipes from his favorite restaurants through rigours and I assume enjoyable experiments. My lab mate is addicted to the food network and is a good cook. Down the hall an undergraduate researcher brings in homemade meringue pies to lab meetings and makes special cheesecakes for birthdays. The field biologist Mike O'Farrell has published a cookbook on how to cook in the field. A favorite evolutionary biologist of mine- Hanna Kokko has a link on her lab page to her 'good food society' which seem very fun. (by the way...I remained strong and did not have a David Letterman trying to get Oprah on his show moment... but really Hanna if I am ever in town....). Even my friend Natalie, the coolest PhD holding biologist I know-who rock climbs and does field work in Alaska after being dropped off by a helicopter field-gear and all by a helicopter. But even cooler: she can fit her material world (mostly books, clothes and ski-gear) into the back of her truck (shes kind of like if Joni Mitchell and McGyver (to return to a recent post) had a daughter). Even she with her bohemian ways stunned me after years of freindship by making me dinner one night and wiping up an amazing and exotic salad (shes vegetarian but I love her anyway...) and admitted she loves to cook. (Mind you as the 'McGyver-esque soul' who's mother may have been a hippie, I imagine she only has one pot and uses it to make tofu stroganoff).

In sum is perhaps no surprise that biology departmental functions are a culinary joy as well as interestingly competitive when it comes to the 'best' stuffing or mashed potatoes.

Why do many biologists love to cook?

I have come up with several possible reasons but I think it has to do with two main things.

1. Cooking is a scientific process: meat turns brown etc. when you cook it in part because proteins are being denatured, bread rises because yeast produce gases, jelly 'sets' i.e. solidifies because a new chemical structure is forming a'la pectin. So there is the main and most obvious 'its because biologists are scientists and cooking is (if you want it to be) scientific.

2. However, I think there is another reason (this is at least how I explain to myself at my sudden affection for cooking). Much of biology is comprised of incomplete days and tasks. Many days you go to the office and read articles to gain knowledge or attend meetings to question it. Some days you write proposals. After several days of proposal tweaks you send it off and wait to see if you get funding. Meanwhile, on another day, you work on getting permits for your research. Days pass and you wait for the permits and if you are lucky you've heard back from granting agency. If you are even more lucky you were funded. More days and you wait on your permits and meanwhile you order your lab supplies and continue to wait. You secure your permits and supplies and start your work. Probably something about your research does not work the first time... you wait. Days and days you may work to perfect an assay to make sure it works before you use your valuable samples that took days and days to collect. Then for days and days you run samples. Days and days you run your statistics (only after days of entering data). You start to make some conclusions and spend a few days talking to others about your results. You spend days or months writing up your results. You send them to co-authors and wait to hear back. You make changes and send the written results to a journal and wait for their decision. So on and so on. This is obviously the less-glamorous version of biology and truly I am happy to be in academia however... with time answering the 'what did you get done today' question wears on a person.

So indeed, most days you do not come home and think 'gee I am so glad I cured cancer and saved the polar bears today.' In fact more likely you don't even think 'Gee I am so glad I finished that side project on why pika prefer grasses over shrubs today'. Nope. So what do you do?

While members of M*A*S*H told jokes and made bootlegged gin in their tents and Zorba the Greek would say 'now... we dance' -my advice?

Now you cook.

Why? When you start you have nothing but....

But then you finish and when you finish you have (hopefully) something delicious to share with your loved ones or at least to eat while you read or watch TV. Suddenly when someone asks "what did you get done today?" you can reply- "I checked e-mail, made a graph, ordered some pipette tips and made stuffed mushrooms and cheese souffle with rhubarb cobbler for desert."

And who can argue with that?