Presentation October 31 at Biosphere II

If anyone in the Tucson area happens to be available tomorrow, Saturday, October 31 (Halloween!), I am giving my first presentation at the Biosphere II at 2PM.  The title of my talk is Monsters of the Deep: The Lives of Giant Water Bugs.  I’ll have live bugs, representative specimens, and a biologically appropriate costume.  The talk is free with admission to the Biosphere.  Feel free to stop by and learn more about giant water bugs and their amazing behaviors!

_______________

Text and images copyright © 2009 DragonflyWoman.wordpress.com

Biological Trade-offs, or Why Brooding is Bad For Dad!

In biology, we talk a lot about trade-offs.  This usually means that when something gets better in one aspect of an organism’s biology, something else suffers.  Consider a tree species in a forest and its ability to survive a forest fire.  Now imagine that this species almost always experiences one type of forest fire.  If it almost always encounters the same type of fire, it probably doesn’t need to hold onto any of the traits that allow it to survive other types of fires.  Those traits require resources that could go toward other things – getting taller, growing faster, making more seeds or leaves, things that will help it survive the fire it always encounters.  Over time, the tree adapts to this fire and loses its resistance to other types of fires.  But what happens when a new kind of fire comes along, one the tree hasn’t ever experienced?  How well will it be able to resist that?  Because the tree has adapted so that it survives the fire it has always experienced, it has lost part or all of  its ability to resist new or very rare fires.  In this scenario, there is a trade-off between wasting resources to survive an event that almost never happens and using those resources to better survive the one that happens all the time.

Almost every biological organism exhibits trade-offs at some level, from viruses and bacteria to humans and other mammals.  Giant water bugs are no exception.  There are at least two major trade-offs related to giant water bug brooding: egg size and brooding costs (check out my post on giant water bug parents for more information about brooding behaviors!).  Let’s talk about egg size first.

Lethocerus indicus eating a small fish

Lethocerus indicus eating a small fish

Giant water bug eggs are, well, giant!  For aquatic insects, they have particularly enormous eggs.  In fact, one researcher, Dr. Bob Smith of the University of Arizona, has suggested that the size of the eggs was what led to the origin of brooding behaviors in the first place (Smith 1997 – full citation available at the end of this post).  Smith suggests that the giant water bugs started off a lot smaller than they are now and probably laid their eggs in water like most of their close insect relatives.  Giant water bugs are predators, and to become more efficient predators, they needed to get bigger.  In order to produce a bigger adult bug, Smith suggests they either needed to add an additional instar or they needed to start from bigger eggs.  True bugs, including the giant water bugs, almost all have 5 instars, so it seems that it is hard to for them to add one.  So, that left making the eggs bigger.  The eggs increased in size, allowing the bugs to become bigger as adults.  Eventually, the eggs got so big that they were no longer able to survive underwater, probably because they couldn’t get enough oxygen.  So, brooding evolved because the eggs got too big to survive without help.

In this scenario, there is a trade-off between making bigger eggs that require care, but result in bigger adults, and making smaller eggs that result in smaller adults, but do not require care.  You know which side of this trade-off eventually won: brooding evolved to allow the eggs to get bigger, and the giant water bugs became the huge, fierce predators that they are today!

Another trade-off relates specifically to the brooding behaviors of giant water bugs .  Brooding is likely bad for the father water bug, but the eggs do not survive if they are not cared for.  A water bug father thus faces this trade-off: he can care for his eggs, but at a cost to himself, or he can abandon his eggs to protect himself, but at the cost of his offspring.  Either the eggs are going suffer or the father is going to suffer.  Usually, the father makes a sacrifice himself in favor of the survival of his offspring, though the occasional aborted egg clutch has been observed.

So just why IS brooding bad for dad?  This is a question that several giant water bug researchers have addressed and there have been many suggestions.  Three broad categories of brooding costs have been identified (spelled out in an excellent paper by Kraus et al 1989):

Abedus herberti

Brooding Abedus herberti male

1. Brooding decreases a male’s mating opportunities. A male who is brooding cares for only one clutch of eggs at a time.  This means that while he is caring for eggs, he does not mate with other females.  If he did not have to care for his eggs, he could mate with many more females.  Thus, brooding decreases a male’s opportunities to mate.

2.  Brooding interferes with a male’s ability to move around. A brooding male experiences decreased mobility compared to non-brooding males.  At the very least, he is stuck in one place while he broods.  A back brooder has eggs glued to his wings, so he is unable to fly.  An emergent brooder has eggs stuck to a immobile object, so he can’t take his eggs with him if he needs to move to another location.  Back brooders might also suffers further costs including increased buoyancy (though Kraus et al provide evidence to the contrary), slower swimming speeds, reduced ability to find and capture food, and reduced ability to escape predation.

Lethocerus medius

Lethocerus medius brooding eggs

3.  Brooding increases a bug’s exposure to predators. Giant water bugs are big and full of high quality protein.  Brooding males are likely at a higher risk of predation than non-brooding males.  Back brooders may spend more time at the surface and have an increased surface area while they are brooding.  Emergent brooders spend more time out of the water while brooding.  In fact, a brooding emergent brooder is right out in the open, visible to everything!  Most emergent brooders will also try to defend their clutch from anything that might try to take it away, including predators and the occasional graduate students who need their eggs for their research.

So, brooding males sacrifice mating opportunities, mobility, and safety from predators to brood.  One might then ask, why do they do it?  One simple reason: giant water bug eggs do not survive if are not cared for!  Biologists generally believe that the ultimate goal of all biological organisms is to pass their genes on to the next generation.  If so, a male water bug will do whatever it takes to ensure that his offspring survive, that his genes are passed on.  This tips the trade-off in favor of the eggs, to the detriment of the father.

Next time, I’ll share another field story, one about an amazing water bug father who fought to protect his eggs as I tried to collect them.  It would make a good premise for a B-grade horror movie, and just in time for Halloween, so tune in!

Literature Cited:

Kraus, W.F., Gonzales, M.J., and Vehrencamp, S.L., 1989.  Egg development and an evaluation of some of the costs and benefits for paternal care in the belostomatid, Abedus indentatus (Heteroptera: Belostomatidae).  Journal of the Kansas Entomological Society 62, 548-562.

Smith, R.L., 1997.  Evolution of paternal care in the giant water bugs (Heteroptera: Belostomatidae).  In: Choe, J.C. and Crespi, B.J. (eds), The Evolution of Social Behavior in Insects and Arachnids, Cambridge Univ. Press, Cambridge, pp 116-149.

_______________

Text and images copyright © 2009 DragonflyWoman.wordpress.com

Kraus, W.F., Gonzales, M.J., and Vehrencamp, S.L., 1989.  Egg development and an evaluation of some of the costs and benefits for paternal care in the belostomatid, Abedus indentatus (Heteroptera: Belostomatidae).  Journal of the Kansas Entomological Society 62, 548-562.

Field Stories: Collecting Giant Water Bug Eggs for Study

I’ve found that there are two types of field biologists.  There are those that have cushy, fabulous research positions that everyone is jealous of.  The husband of one of my good friends works with squirrels in Arizona.  He spends a good part of the summer on top of a gorgeous mountain hiking through the forest studying adorable little frolicking squirrels.  If you’re an outdoorsy person, this job is one little slice of heaven.  His wife, on the other hand, is my coworker for one of my jobs.  We are on the other end of the spectrum – field biologists who tell people what we do and watch them cringe in horror or utter disgust.  We’re the ones that get questions like, “Ugh!  Why would anyone want to do that?”

In order to stay sane, I find that biologists like us revel in the intensity or relative digustingness of our work.  We share stories and try to one-up each other so that we can convince people that we have the worst field assignments ever.  We are martyrs to science, gosh darn it!  Many of our conversations involve the words, “You think that’s bad?  Let me tell you about MY field site!”  So before I get to my post on why brooding is bad for male water bugs, allow me to tell you about my lovely field site and my experiences there.

This is the pond at my field site:

My field site!

My field site!

Isn’t it lovely?  Let me tell you about this pond.  This is what’s considered a “cattle tank” in Arizona.  If you’re not from AZ, you probably think a cattle tank is a round metal container that is filled with water from which cattle can drink.  I certainly did before I moved here.  No, in Arizona, cattle tanks are little man-made ponds.  Farmers basically pile up dirt at the low point of a natural depression to create a pond that fills with water during rains.  My particular pond collects an amazing amount of overland flow.  It can go from almost empty to completely overflowing in a single rain event, so it’s a great example of a cattle tank.

All that green stuff on top is algae.  Because it is fed by overland flow, the water brings a lot of organic materials, soil, and nutrients with it as it flows into the pond.  When the pond first fills up, the water is opaque brown from all the dirt.  But when you have a body of water with a whole lot of nutrients in it, you get algae.  LOTS of algae.  If you get into my pond, you come out green!

And then there’s the livestock.  This pond is used by cows and horses.  They don’t seem to have any problems with using the pond as both their drinking water and their toilet.  If you get into the water, you have to watch for floating road apples and cow patties and you smell like urine for the rest of the day, sometimes even after you shower.  It’s lovely.  And all that stuff the livestock dump in the pond contributes to the algae growth, making it even more green!

Finally, there is the mud.  Between the cow and horse “contributions,” the dirt flowing into the pond with the rainwater, the algae that dies and falls to the bottom, and the decaying plants and wood that fall in, the mud in the bottom of the pond is sticky, stinky, and deep.  Every time you take a step, you sink into the mud, almost up to your knees.  It’s hard work moving through this sort of mud.

Did I mention the tempature of this pond?  The water is really warm, a lot warmer than you would expect it to be from the air temperature.  All the cows and horses and other lovely things that are in the water promote the growth of bacteria.  The water is so hot in part due to the fermentation and other bacterial processes that are occurring in the water.  All those chemical reactions produce heat, so the water becomes warmer than it would be if it were clean.

There’s nothing  quite like getting into hot, stinky, opaque green-brown water and sinking into putrid mud, let me tell you.  I dread getting into my pond.  If I have to meet with people after I go to my field site, I have to warn them that I’m going to my field site in case I show up covered in mud and scented with urine.  I complain about it to my collagues and definitely drag out the list of offenses my field site provides in those one-upping conversations – and often win!  So, why do I do it?  This is why:

Lethocerus medius

Lethocerus medius brooding eggs

My pond is a fantastic place to collect Lethocerus medius eggs!  If you recall from my post on giant water bug parents, Lethocerus are emergent brooders and lay their eggs on emergent vegetation.  This means the bugs require emergent vegetation if they want to reproduce, and Lethocerus medius is no exception.  It is worth putting up with the nasty conditions of my pond for this reason: there are tons of Lethocerus medius, but almost no emergent vegetation!  This means there are lots and lots of bugs looking for places to lay eggs, but almost nowhere to lay them. This creates great conditions if you need to collect eggs from a Lethocerus species, which are notoriously hard to breed in the lab.  All you need to do to get eggs is provide artificial emergent vegetation.

We use sticks clipped from desert broom bushes, strip the leaves off, and then I wade into the pond and stick them into the mud:

Artificial emergent vegetation

Artificial emergent vegetation

Once you’ve put the sticks in, the bugs are more than happy to use them for mating.  During the right time of the year (monsoon season for this species and location), if you come back the next day you are likely to find clutches of eggs attached to the sticks.  I pull the sticks out and bring them back to the lab with me so I can do experiments with the eggs.  Then we go back the next day to get some more.

In spite of the general ick factor of my field site, it is completely worth it to use this pond.  There are very few ponds that have this little emergent vegetation and collecting eggs anywhere else would be a whole lot harder to do.  It is also definitely easier than setting up a brooding operation in the lab.  It might not be glamorous and I’m waiting for the day I fall in head first, but the results of my experiments are exciting enough to keep me going back.  Hooray for the thrill of scientific discovery!

_______________

Text and images copyright © 2009 DragonflyWoman.wordpress.com

Lethocerus medius hatching!

I entered a video into a contest being held by the Entomological Society of America.  My movie is a short educational film about the giant water bug Lethocerus medius hatching from its eggs.  Seeing as this blog is intended to be an educational blog, I thought I’d post the link here.  But first, let me define a few words that you might not already know so the video will make sense.

Chorion: the eggshell of an insect.  Why we can’t just say eggshell, I’m not sure.  We entomologists like our big words!

Operculum: a lid-like structure in a biolgical organisms.  Many insect eggs have operculums surrounded by weakened fault lines that allow the insect to push the top of the egg off easily when it is ready to hatch.  You can see the operculums in the giant water bug eggs in the video.  Look for the little egg caps that are pressed up against the faces of the bugs when they first start to squeeze out of the eggs!

If you have been following my blog, you probably already know what these terms mean: paternal care, back brooding, emergent brooding, sclerotize.  If not, click on the links to find the definitions in my glossary.

Without further ado, I present my video: Giant Water Bugs Hatching (Lethocerus medius)!

_______________

Text and images copyright © 2009 DragonflyWoman.wordpress.com

Giant Water Bug Parents

Now that I’ve made a quick detour to talk about ants and other stinging insects and the dragonflies at a local wetland for a few posts, it’s back to the giant water bugs!  Today I want to go over parental care in giant water bugs.  If you remember from my post on insect child care, giant water bugs use a special type of parental care: paternal parental care.  This means that only the father participates in the care of offspring, and it is a very unusual behavior among insects.  So let’s go over how the water bugs care for their eggs!  First, though, I need to provide a little background information about giant water bug taxonomy (the organization of biological organisms) so everyone can make sense of it all.

I’ve already gone over the order, family, and American genera of the giant water bugs in previous posts, so I’m not going to go over them again here.  (Please see my taxonomy page for more information if you get confused along the way.)  However, there is another taxonomic group that falls between the family and the genera that I haven’t discussed yet, one that is important when considering paternal care behaviors in the giant water bugs.  This group is the subfamily.  You can easily tell when you are looking at a subfamily, at least when dealing with animals, by the suffix -nae at the end of the name.  Most giant water bugs belong to two big subfamilies, Lethocerinae (which includes only the genus Lethocerus, the truly giant water bugs) and Belostomatinae (which includes everything except Lethocerus, usually the smaller, rounder, and/or less robust water bugs).  There is one genus, however, that is very rare and only found in a very small part of South America, HorvathiniaHorvathinia is so rare, in fact, that researchers don’t even know where to look for it in the wild or whether it does any sort of paternal care like its close water bug relatives.  Horvathinia is generally placed within its own subfamily, Horvathininae, but some researchers think it might belong to either Lethocerinae or Belostomatinae instead.  Time and more DNA analyses will answer this question, but for now we’re going to ignore it.  After all, we don’t know what sort of parental care it uses, so we don’t need to talk about Horvathinia more here.

So, why do we need to know the subfamilies?  There are two basic known types of paternal care in giant water bugs.  These behaviors are known collectively as brooding behaviors – the word brood refers to a group of offspring all cared for at one time – and they are divided along the subfamilial lines.  This means that Lethocerus, a lethocerine, uses a different brooding behavior than the belostomatines, such as Abedus and Belostoma.  Let’s go over belostomatine brooding first as it is generally more familiar outside of the entomological community.  This is Abedus herberti:

Abedus herberti

Abedus herberti

Isn’t he a handsome father-to-be?  This is one of my favorite aquatic insects – I think they are gorgeous, amazing insects!  Take a look at those brown, round things on this bug’s back.  Those are the eggs that this bug fathered!  The belostomatines are back brooders, which means that the males care for the eggs attached to their backs.  How to the eggs get there?  In the belostomatines, the male and female mate, and then the female lays a few eggs on the back of the male.  The male then insists that they mate again (more about this in the next post), and then the female lays a few more eggs.  Several hours later, the female finishes laying whatever eggs she has available (up to about 150 in A. herberti) and leaves the area.

The male cares for the clutch of eggs on his back in several different ways.  All of the belostomatines carry their clutches to the surface periodically.  This allows the embryos developing inside eggs to breathe more efficiently – it is a lot easier to get oxygen from the air than from the water.  (In fact, providing oxygen in this way may be the primary function of back brooding behaviors.)  In the the bug you see here, Abedus herberti, the father further cares for his clutch by doing push ups underwater.  The eggs are able to absorb some oxygen directly from the water, so the push ups are probably a way to stir the water around the eggs and help the developing embryos breathe more efficiently when they are submerged.  Other species of belostomatines will do other underwater behaviors.  Eggs that are abandoned (male belostomatines can abort their eggs if they aren’t developing properly) or deposited anywhere other than on the backs of the male never hatch.  In contrast, almost 100% of brooded eggs hatch.  Brooding is thus an obligate behavior, one that is necessary for the continued survival of these species.

Now let’s take a look at how a lethocerine broods and compare their behaviors to those of the belostomatines.  This is Lethocerus medius:

Lethocerus medius

Lethocerus medius

As you can clearly see, the eggs are not on the back of the male in this species.  Instead, the eggs are laid on a stick above the water line.  Can you see them?  If not, take a look at the stick below the bug – those light colored, rounded blobs are the eggs.  (You can see a previously hatched clutch under the back end of the bug as well.)  This bug obviously cares for his eggs very differently than the belostomatine we looked at above.  If he’s not carrying his eggs around on his back, how does he care for them?

Lethocerus medius is an emergent brooder.  This means that the eggs are laid on vegetation above the water line instead of on the backs of the males.  However, like in the belostomatines, the eggs still need care and will die without it.  Giant water bug eggs have likely been brooded for millions of years.  During that time, it seems they have lost most of their ability to retain water.  Lethocerine eggs that are left out of water without parental care dry out so badly that the embryo inside dies.  So, lethocerines, like the one you see here, care for their eggs by bringing them water.  The male will typically remain attached to the stick that holds his brood, but is usually found at the base of the stick underwater, using his respiratory siphon to breathe.  Every now and again, the male will climb up the stick to his clutch and let all the water on his body drip down onto the eggs.  There is evidence that suggests that the males of some species might also swallow water that they then regurgitate onto the eggs.  Once the eggs are nice and wet, the male then climbs back down his stick and waits underwater until he has to water his eggs again.

So there you have it.  One group of giant water bugs cares for their underwater eggs by bringing them to the surface to get air and the other cares for their eggs, which get plenty of air, by bringing them water.  Pretty cool, eh?  Next time, I’ll discuss some of the costs and trade offs associated with parental care in giant water bugs.  In other words, I’ll be talking about why brooding is bad for dad.  Stay tuned!

_______________

Text and images copyright © 2009 DragonflyWoman.wordpress.com