Wednesday, March 28, 2012

Sex, Lies and Spider Silk

Are you trying to get the girl, but you’re too cheap to get her a nice gift? You could take a page out of the nursery web spider’s Guide to Love and Sex.

WARNING: Do not date this nursery web spider. He's a jerk.
Photo from Wikimedia Commons by Mathias Krumbholz.

When a male of this species has his eye on a female, he will usually offer her a nuptial gift, which is typically a tasty prey insect nicely giftwrapped in spider silk. While the female is unwrapping her meal, the male has an opportunity to mate with her; That is, unless she discovers the meal is good enough to take the gift and run away. If this happens, the male will try to hold on to the gift and will often play dead, stretching out his legs and getting dragged by the female until she stops. At this point he will “revive” and resume mating with her. Surprise!

If that deceptive behavior weren’t obnoxious enough, researchers have discovered that males can also achieve mating success by giving crappy gifts, as long as they are well-wrapped (and concealed) in silk. In the wild, nearly 4 out of 10 wrapped gifts were found to contain nothing more than empty insect carcasses, which likely resulted from the male sucking out the nutritive-value of the prey item himself, and then giftwrapping the remaining trash for his gift. Brilliant, right guys? What a jerk, right girls?

But do the females fall for it?

Maria Albo, Gudrun Winther, Cristina Tuni, Søren Toft and Trine Bilde at Aarhus University in Denmark set out to see if the quality of the gift would affect whether or not a female mates, and if she does mate, how long she mates for. The research team went outside and collected a bunch of juvenile nursery web spiders, and then raised them up on a housefly diet until adulthood (This way the researchers knew that all the spiders were virgins, which is important). Then they offered males items to wrap: a normal housefly, a protein-enriched housefly, a worthless gift (a cotton ball, dry flower head or leftovers of a previously eaten fly), or nothing at all. They allowed each male to interact with a female for up to 30 minutes, and observed the female responses.

It turned out, females were equally likely to mate with males providing a normal gift, protein-enhanced gift, or worthless gift. But females were much less likely to mate with males that didn’t have any gift. So, to get sex, it was important to have a gift – any gift. The scientists also noted that males with worthless gifts did not play dead as often as males with quality gifts. That is probably because playing dead is a strategy males use when the female is trying to run away with the gift, and females didn’t try to run away with worthless gifts. Why bother?

Seems like a good strategy, doesn’t it? But be warned, fellas, a male may be able to get sex with a worthless gift, but that doesn’t mean good sex. Males that gave a worthless gift or no gift could not keep their pedipalps (their sperm-transferring bits) inserted as long as males that gave a normal or protein-enhanced gift.

What’s the moral to this spider-story? If you want to get the girl, it’s important to give her a gift. And if you want to hang on to her, you’re better off giving her a good gift. But unless your girl-of-interest is a spider or an entomologist, I don’t suggest giving her bugs.

Want to know more? Check this out:

Albo, M., Winther, G., Tuni, C., Toft, S., & Bilde, T. (2011). Worthless donations: male deception and female counter play in a nuptial gift-giving spider BMC Evolutionary Biology, 11 (1) DOI: 10.1186/1471-2148-11-329

Wednesday, March 21, 2012

Reduce Stress with this Animal Behavior Meditation

In a search for the promised inner peace and tranquility of meditation, I attended a meditation class at a local yoga studio. In a room with dim fluorescent lights and an artificial wood floor I laid on my back on my yoga mat, sandwiched between a fidgety woman who kept her smartphone on the edge of her mat and a man whose stress had apparently resulted in a flatulence problem. I was told to close my eyes, breathe deeply, and think about nothing. I closed my eyes, took a deep breath, and thought: “How do I think about nothing?” I thought about black. “Does black count as nothing? Wondering if I’m thinking about nothing is definitely not nothing. Am I doing this wrong? Is this going to work? If this isn’t going to work, I’m just wasting my time. I could be working through my to-do list right now. Oh! I forgot to put laundry on my to-do list. Oh, right… think about nothing. Black?

This ring-tailed lemur has found her inner peace - Can you find yours?
Photo by Margaret at Wikimedia Commons

It was years later that I realized that meditation doesn’t have to be so painfully contrived. I do it all the time naturally. Maybe you do too. We just have to nurture those moments. Here’s one way to do it:

1) Go to a place where you have seen at least one animal in the recent past. Maybe you saw a squirrel or a songbird in that tree in your yard. Maybe you saw fish in the creek you pass over on your way to school. Maybe there’s an occupied spider web in the corner. Maybe you have a favorite spot at the local zoo or aquarium. Go there. Don’t worry if there is an animal there now or not.

2) Sit down in a comfortable position and take a deep breath. Look around and take in your surroundings. Feel the environmental conditions. Listen to the sounds around you. Wait and observe. If you’re quiet, they will come.

3) When an animal shows up, focus on it. If multiple animals show up, pick one to be your focal animal. Observe every possible detail of your focal animal: What does it look like? Does it have any markings? What is it doing? How does it position itself with respect to its surroundings? What is its posture? How does it respond to changes in its surroundings?

4) Allow your mind to wander into your focal animal’s world (or umwelt). How do you think your focal animal perceives its surroundings?

5) Allow your mind to ponder explanations and consequences of your focal animal’s behavior.

6) Continue for as long as you can keep your mind focused on your animal, or until you have somewhere else you are supposed to be.

Try this out for yourself, and then let us know what you experienced!

Wednesday, March 14, 2012

Social butterflies or wallflowers? Two brain regions and a peptide

Zebra finches are really social little birds. When conditions are not right for breeding (usually when there’s not enough rain), they hang out in flocks of hundreds. And in the intimate mood the rain brings, groups break up into more manageable sizes of 10-20 birds, which still seems like a lot to me. Although, if you’re the type to have a “quiet night in” with just a dozen or so of your closest friends, you may be able to relate to the gregarious zebra finch. 

This is a zebra finch pair.
Photo by Keith Gerstung, Wikimedia commons.
This is not a flock of zebra finches, but it kinda looks like one. This is a flock
of chestnut-breasted munias, which is another Australian species of the
same family (Estrildidae). Photo by Duncan McCaskill, Wikimedia commons.

What makes some individuals more social than others? And what makes one individual change from being more social to less social (and vice versa)? One of the secrets to sociality in birds may lie in a neuropeptide called vasotocin. 

Vasotocin is a chemical messenger in the brains of birds, reptiles, amphibians and fishes (very similar to vasopressin in mammals) and it is known to be involved in several social behaviors. Researchers from Indiana University (including Aubrey Kelly, Marcy Kingsbury, Sara Schrock, David Kabelik and Jim Goodson) and Bowdoin College (Kristin Hoffbuhr, Brandon Waxman and Rick Thompson) got together to explore if and how vasotocin may be involved in how social zebra finches are. 

The top picture is a cartoon of a slice of
zebra finch brain, showing where BSTm
and LS are. The bottom image is a photo
of a brain section under the microscope.
Vasotocin is labeled in green. Figure from
Kelly, et al. (2011) Hormones and Behavior.
Chemical messengers, like vasotocin, generally don’t act equally on all parts of the brain, but rather have particular effects on specific brain regions. This is in part because certain chemicals are only produced by neurons (a type of brain cell) in some brain regions. Perhaps more importantly, the action of a chemical messenger is almost completely dependent on its receptors, and the receptors are also typically only located in specific brain regions. When you consider that neurons all project and talk to different areas of the brain, you can see that this system can get very complicated very quickly. Despite these complexities, this research team has narrowed in on two regions of the zebra finch brain that seem to be using vasotocin to regulate how social they are. 

The medial bed nucleus of the stria terminalis is a ridiculously long name for a brain region that is part of the extended amygdala (We’ll call it BSTm). Many neurons in the BSTm produce vasotocin (and are therefore called vasotocinergic neurons) and release the peptide in another brain area called the lateral septum (We’ll call it LS). The LS does not contain neurons that produce vasotocin (like the BSTm does), but instead contains neurons with vasotocin receptors, which vasotocin can bind to and take effect. 

Jim Goodson and another colleague, Yiwei Wang, had previously found that when zebra finches are allowed to socialize with other zebra finches, more of their vasotocinergic neurons in the BSTm become active. Could vasotocin produced in the BSTm and released in the LS underlie how social an animal is? 

If you were the zebra finch in the middle cage, which perch would you prefer to be on?
Figure from Kelly, et al. (2011) Hormones and Behavior paper.

One way to ask a zebra finch how social he’s feeling is to use a choice paradigm: that is, to put him in a cage with ten birds on one side, two birds on the other side, then see what side he hangs out on. The middle section (containing our bird of interest) contains a bunch of perches at different distances from the “flocks”. In this scenario, a zebra finch will sit on the perch next to the big flock on average 82% of the time, ‘cuz he’s social like that. But if the researcher injects a drug that blocks vasotocin receptors in the LS, he will sit on the perch next to the big flock on average 0% of the time. What do you think he does with all this free time? Typically, he sits on the perch next to the flock of two birds. So blocking vasotocin receptors in the LS seems to make zebra finches less social (but not asocial – If that were the case they would probably avoid both groups of birds). This suggests that more vasotocin binding to vasotocin receptors in the LS makes birds want to hang out with a large group. But, is the vasotocin that’s being released in this region and causing this behavior coming from the BSTm or another brain region? To figure this out, the researchers needed to look at (and experimentally alter) the vasotocin neurons in the BSTm.

Vasotocin is a peptide, and peptides are produced by a process in which the instructions for producing the peptide on the DNA is transcribed onto a molecule of messenger RNA. The instructions on the messenger RNA are then used to build the peptide. A drug called an antisense oligonucleotide can bind to that messenger RNA and confuse the instructions so the peptide doesn’t get made as much. This kind of drug was used to reduce the amount of vasotocin produced by BSTm neurons. 

Birds that had less vasotocin produced in the BSTm spent less time on the perch next to the large group, and spent more time on the perch next to the small group, compared to birds with natural vasotocin levels. They also explored less and took longer to feed if a strange object was in the cage, indicating that they were anxious. Together, it looks like vasotocin produced by neurons in the BSTm and acting on receptors in the LS may increase sociality and reduce anxiety (maybe social anxiety?) in gregarious birds like zebra finches. 

When you’re at a party, do you find yourself the life of the party or are you more comfortable hanging out in the corner with a few friends? Maybe you’re feeling more social at one party and less social at another? Could we have a system in our brain similar to the zebra finches? We have BST and LS brain regions and we have vasopressin, which is a lot like vasotocin. Hmmm… I guess this could be something to break the ice with at your next social mixer. 

Check out this zebra finch rockin’ out on electric guitar at a zebra finch party: 

Want to know more? Check these out:

1. Kelly, A., Kingsbury, M., Hoffbuhr, K., Schrock, S., Waxman, B., Kabelik, D., Thompson, R., & Goodson, J. (2011). Vasotocin neurons and septal V1a-like receptors potently modulate songbird flocking and responses to novelty Hormones and Behavior, 60 (1), 12-21 DOI: 10.1016/j.yhbeh.2011.01.012

2. Scientific American blogger Scicurious talks more about zebra finch brains here

Wednesday, March 7, 2012

Interrupting Insects

What do you think of when I say “communicate”? Most likely, you are imagining people communicating by an auditory mode (talking and listening, making expressive sounds) or by a visual mode (observing body language, reading and writing). As a species, humans inherently rely heavily on our hearing and vision to perceive the world around us and so it makes sense that we communicate with one another using these modalities. But animal species are incredibly diverse in their means of perceiving their worlds and their modes of communication. Because we have been so focused on studying animal signals that we can perceive, we have only recently begun to more actively explore animal communication in these other modes. One of these modes is soundless surface vibrations.
The photo is of an adult Tylopelta gibbera on a host plant stem
(photo (c) Rex Cocroft).
Despite the fact that we do not perceive most animal surface vibration signals around us, vibrational communication is very common, especially among insects and spiders. Rex Cocroft at the University of Missouri at Columbia and Rafa Rodríguez at the University of Wisconsin at Milwaukee point out in a review of vibrational communication that over 195,000 species of insects communicate using soundless surface vibrations. We can experience many of these substrate vibration signals by broadcasting them through a speaker as an airborne vibration (which we perceive as sound).

Vibrational signals serve a number of functions in the insect worlds. Social insects, like ants, termites, and bees, often use vibrational signals to coordinate foraging. Groups of juvenile thornbug treehoppers vibrate when a predator approaches, calling in the mother to defend them. Males of many species have been found to use vibrational signals to attract females and the females often use these signals to choose a mate.

Vibrational signals are carried through a solid substrate, so they can only travel as far as the substrate is continuous and they are affected by attributes of the substrate (like changes in density). Because of these constraints, most vibrational signals can only travel about the length of a human arm. Many insects that use vibrational communication live on host plants, and it is these host plants that transmit the vibration signals. These animals face many challenges in transmitting their signals to the intended recipient. For example, wind, rain, and environmental sounds can create competing vibrations (background noise). In addition to environmental background noise, the vibrational soundscape of a given plant stem will likely include many signaling individuals, often of many species. Not only are there difficulties in getting your signal to your intended audience, but there are also risks of eavesdropping predators and competitors.

Frédéric Legendre, Peter Marting and Rex Cocroft at the University of Missouri at Columbia, demonstrate the social complexities of vibrational communication in a new study of competitive signaling in a treehopper species, Tylopelta gibbera. Tylopelta gibbera is a small treehopper in the southern United States, Mexico and Guatemala, that only lives on plants from the Desmodium genus. Males will attract and court females with vibrational signals and interested females will respond to the male with vibrational signals of their own. However, many individuals can often be found on a single plant and if two signaling males are present, the receptive female will typically respond to both of them and only mate with one (generally the first one she encounters). What is a competing male to do?

Listen to a male Tylopelta gibbera advertisement signal here.

The researchers performed a series of experiments, in which they observed treehoppers on potted host plants in the lab. With this set-up, they could control the environmental conditions, decide the number of males and females on the plant, record vibrational signals and play them back. They found that once a male signals and detects a female response, he will actively search for her along the plant, alternating signals and steps in a “Marco Polo” mating game until he finds her. Males found the females almost twice as fast if they were the only male on the plant, indicating that the presence of a second male on the plant somehow interferes with their ability to locate the female. Also, when two males were on the plant, they produced a new signal type that was never produced by a lone male on a plant. Males that had no male competition only produced signals that had a whine sound, followed by a series of pulses (and the female would then immediately respond with a harmonic sound of her own). This male signal is called the advertisement signal. Males that had a competing male on the plant would produce an additional signal that was a short tonal note. Interestingly, these males often produced this second signal at the same time that their competitor was advertising himself. Hmmm… could this be a masking signal used to interrupt the competitor? How could you figure that out?

This figure from Legendre, Marting and Cocroft's 2012 Animal Behaviour paper shows
the whine and pulses of a male advertisement signal (top) and a histogram of when the
masking signal occurs in relation to the timing of the advertisement signal (bottom).
First, the researchers asked, “When do males produce this second signal?” The researchers put two males on a plant with one female and recorded their vibrations. They found that in this situation, males typically produced this second signal while his competitor was just beginning the pulse section of his advertisement signal. Next, the researchers played back recordings of male advertisement signals followed by female responses to a lone male on a plant. All of the males tested produced the masking signal during the pulse section of the male advertisement signal on the recording.

Don't you hate it when someone does this?

Next, the researchers asked, “How do females respond to this second signal?” On plants with one female and two males, females didn’t respond as much to advertisement signals overlapped by a second signal as they did to advertisement signals alone. The researchers then played recordings of male advertisement signals to lone females on the plants. Females responded significantly more often if the advertisement signal was not overlapped by a masking signal.

So, male treehoppers get an edge up on getting the girl by interrupting the other competing males. Sneaky buggers!

Want to know more? Check these out:

1. COCROFT, R., & RODRÍGUEZ, R. (2005). The Behavioral Ecology of Insect Vibrational Communication BioScience, 55 (4) DOI: 10.1641/0006-3568(2005)055[0323:TBEOIV]2.0.CO;2

2. Legendre, F., Marting, P., & Cocroft, R. (2012). Competitive masking of vibrational signals during mate searching in a treehopper Animal Behaviour, 83 (2), 361-368 DOI: 10.1016/j.anbehav.2011.11.003

3. A Japanese research team has harnessed this phenomenon to create a remote-control that makes annoying people stop talking. Find out more at the blog Gaines on Brains!