Birth of a Backswimmer (Friday 5)

A few months ago, I posted a series of photos for Friday 5 that depicted the development of aquatic snail eggs.  In addition to the two species of snails I had in my tank at the time were a bunch of backswimmers in the genus Notonecta.  The morning after I put them in the tank, I came across a bunch of what could only be backswimmer eggs attached to a leaf, so I started photographing them.  I thought their development was fascinating and spent a little over two weeks watching the snail and the backswimmer eggs to see what happened.  Today I give you the Notonecta part of the story!

The eggs started out looking like what I would consider pretty standard true bug eggs:

Notonecta eggs, 1 day old

Notonecta eggs, 1 day old

They were simple to start off, just translucent white cylindrical eggs with rounded ends.  Many eggs were attached to this leaf in a sort of neat little line along the edges, but there were others attached to rocks and even a few stuck to the large rams horn snail that was oozing its way around the tank, so I suspect this was simply a convenient place to deposit them rather than a preferred method of placement.  In just under a week, some changes were evident:

Notonecta eggs, 6 days old

Notonecta eggs, 6 days old

This photo isn’t as well focused as I’d like, but it illustrates two things.   First, the structure of insect egg shells is absolutely stunning!  All of that patterning mirrors the cells that laid down the chorion (= the insect eggshell), so you’re effectively looking at structure of the mother’s internal organs when you look at an insect chorion.  In both eggs you can also see some faint red markings, more distinctly in the egg on the right.  Those red patches are the developing eyes of the backswimmers, so you can see which end is the head and which is the tail.  What was previously a little cylinder of bug goo had turned into the start of a baby insect with clear evidence of the changes visible without dissecting the egg in just a few days.

Things started to change more rapidly after the first eye spots were visible.  By day 10, the eggs looked like this:

Notonecta eggs, 10 days old

Notonecta eggs, 10 days old

The red eye patches had taken on the shape of backswimmer eyes by this point.  You could also see some black markings within the egg.  The bugs inside were clearly further along than they had been.  You could also easily spot the eggs that were not developing and were never going to hatch at this point.  The egg on the left side of the image was having problems and wasn’t developing properly – it has no eyes or any black patterning visible.  It never hatched.

Shortly before they hatched, you could see all sorts of structures inside the eggs:

Notonecta eggs, 18 days old

Notonecta eggs, 18 days old

You can’t see it very well without enlarging the photo (click to enlarge!), but you can see the outline of the plates on the upper surface of the thorax, the legs, and that the black markings are part of the legs.  By this point, the eggs were two and half weeks old and a few had hatched.  The empty chorions in the lower right corner highlight the cap of the egg the nymph inside popped open to emerge from the egg and a membrane that lined the chorion.  The eggs in this image hatched over three days (if they hatched at all), so they seemed to have some variability in their developmental times.

This is what came out of the egg:

Notonecta first instar

Notonecta first instar

The first instar nymphs were tiny, just a few millimeters long.  You can clearly see the bright red eyes and the black claws, both of which were visible through the egg chorion as they developed.  And, as a bonus this week, this is what these tiny nymphs eventually turn into:

Notonecta mature adult

Notonecta mature adult

The coloration becomes a lot more complex, they gain wings, and their bodies elongate relative to their width as they age.  Check out those gorgeous eyes on the adult!  And, these insects are fairly large, about 1 cm, which means that they have to grow a lot to become adults, and they do it very quickly.  That tiny nymph emerges from the egg and molts just 5 times before it becomes an adult, which means massive growth spurts each time they molt.

I know it probably makes me weird, but I love watching insect eggs develop!  They undergo some pretty amazing changes in a very short amount of time, plus they’re beautiful to look at and you can often see through the chorion and peek at what’s happening inside.  Eggs might not move, but they’re still fascinating and I am thrilled I got an opportunity to document how these eggs developed!  I hope at least some of you find it as interesting as I did.  :)

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth
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Birth of a Snail (Friday 5)

On March 4th, I was in the midst of an all out race to prep curriculum for an insect-themed afterschool citizen science program I’m developing.  One of the things we wanted to provide to the state park rangers who will be implementing the bulk of the program was a couple of vials containing examples of hand sanitizer preserved dragonfly and damselfly nymphs.  That meant getting into the pond to look for nymphs.  I had spent four straight weeks in front of my computer working non-stop on the afterschool program and was thrilled to get outside, even though it was cold in the water and we found only a single dragonfly and a couple of snails.  One of my coworkers needed photos of the snails for our pond field guide, so I promised to take them home and photograph them.  I set up my tank and put the snails in and left them overnight so the bubbles would dissipate.  The next day, I realized that one of the snails had laid eggs.  A LOT of eggs.  There were only two snails in the tank, so it had to be this one:

Physid snail

Pouch snail (family Physidae)

… or this one:

Planorbid snail

Ram’s horn snail (family Planorbidae)

 

And I have to say: those snails and their eggs enthralled me!  I was exhausted and overworked, so nothing gave me more satisfaction than watching my two snails, one of which was going to be a mother of several hundred baby snails, gliding around the tank every evening after work.  I took the photos we needed for the pond guide the day after I set everything up, but I kept watching and kept photographing over a few weeks.  Today I am going to show you what happened.  Let’s start at the beginning…

March 6, 2015

Snail eggs, Day 1

Snail eggs, Day 1

I added the snails to the tank on March 5 and left them overnight, so these eggs were less than 24 hours old when I first saw them.  I love that you can see a little dot in the center of the mostly clear eggs!  Nutritious yolk perhaps?  A little cluster of cells that would become the snails?  I really have no idea as I know little about snails, but I thought they were rather beautiful.  There were lots of clusters like this in the tank.

March 11, 2015

Snail eggs, Day 7

Snail eggs, Day 6

After 6 days, the shape of the little embryos inside the eggs were becoming much more snail-like.  You could see some little curved snail bodies and the very beginnings of their shells.  The color comes from the light hitting a piece of wood in the tank under the leaf these were laid on – they were largely transparent.

March 16, 2015

Snail eggs, Day 12

Snail eggs, Day 11

The snails were now 11 days old and you could definitely tell they were snails!  Most of the developing snails inside the egg cluster had mostly to fully developed shells, though still tiny, and had taken on a distinctively spiraled shape.  A few had already broken free of their eggs and left the cluster, including the one in the lower right of the egg cluster who is making a break for it in this photo.

March 18, 2015

Snail eggs, Day 14

Snail eggs, Day 13

By this point, most of the snails had escaped the egg cluster, though a few late bloomers were left.  You can still see the leftover egg compartments and the jelly that held the cluster together if you look hard.  Looks like there may have been a couple of dud eggs in the lot too that probably won’t ever hatch.

March 19, 2015

Baby snails

Baby snails

Baby snails!  There are now about 50 of these on the loose in the tank, each about 2-3 mm long.  They’re absolutely tiny – small enough you’d mistake them for shmutz on the glass if you didn’t know what you were looking for – but they move pretty darned fast for such tiny little animals!  They’ve spread out across the entire tank in just a couple of days.  For some reason, I feel like this is an impressive feat for a 2mm long snail.

And, now that the baby snails have hatched, I can look at their shells and tell that they are pouch snails and not the ram’s horn snails.  That meant that possible baby mama number one above was the parent of dozens and dozens of eggs that are still developing and many more than have already hatched.  She was rather prolific in her laying and I just found another clutch today.  I’m going to have SO many snails in a couple more weeks!  In the meantime, I’m going to enjoy watching these grow.

While all of this epic snail drama was going on, I had a similar situation happening with a bunch of backswimmers.  I’ll share my baby photos of those guys soon.  In the meantime, have a GREAT weekend everyone!

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth

Well-Nigh Wordless Wednesday: Eggs

It’s blackberry time in North Carolina!  Blackberries all over the Triangle Area are currently laden with ripe fruit, so I went out picking at work before we opened last weekend.  We’d been finding little groups of metallic gold insect eggs all over the grounds for a few weeks, and I found another little group of them while I was blackberry hunting:

Golden insect eggs

Golden insect eggs

The picture doesn’t do the coloration justice at all as these are bright, shiny gold in real life, but I’m sharing them anyway.  After searching around a bit, I believe these are eggs of a leaf-footed bug, an insect in the family Coreidae.  I love it when I randomly come across beautiful bugs when I’m out looking for something else!

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth

Well-Nigh Wordless Wednesday: Eggs in Strange Places

I find insects in strange places sometimes. For example, I was out of town for one of several family emergencies this summer and left my bike chained to the tree in my front yard while I was gone. I was about to lock my bike to a bike rack on campus after I got back when I saw these attached to my front wheel:

lacewing eggs on bike

Lacewing eggs on bike spoke

Lacewing eggs! Apparently a female lacewing had decided the spoke of the front wheel of my abandoned bike was a great place for her children to be born.  Good thing they all hatched before I started riding my bike again!

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Unless otherwise stated, all text, images, and video are copyright ©TheDragonflyWoman.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.

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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.