Chirpless: Camel Crickets

Camel crickets (Ceuthophilus sp.) enjoy hanging out with humans. Perhaps you provide shelter to some in your garage or basement. These insects lack one major cricket trait though – chirping. Sound production should allow camel crickets to find each other in a dark cave or crawlspace. So, why no chirps?

A Chirp Mystery

One possible reason for the lack of chirps is a high risk of predation. In other species of crickets, those who call more or longer often end up as a snack. ^{1, 2} While I would hope camel crickets are relatively safe from bats and birds in your basement, spiders and mice are the crickets’ major predators. Both possess a solid sense of hearing.

Many crickets have parasites who also seek hosts by sound. Chirps attract female crickets, but they also draw mama parasites searching for a cozy spot to lay eggs. The developing parasitic larvae eat the cricket from the inside, exploding out of its body as they grow. Crickets in areas with these parasites quickly evolve “chirplessness.” Do camel crickets need to worry about these “Alien” chest-bursting scenes? While they do have a doozy of a parasite (an intestinal parasite that weakens the cricket enough to ensure predation), the infections are not related to sound production.

Perhaps camel crickets simply lost their physical ability to chirp. Most crickets produce sound by rubbing their wings together. Camel crickets, though, don’t have wings. In a basement, flying is probably not the most effective means of transportation.

The Scent of a Cricket

So, how do camel crickets find each other without sound? One word: pheromones.

Pheromones are used by many cricket species to indicate dominance, reproductive readiness, and location. Camel crickets release a scent that causes them to congregate. Researchers determined the pheromone is unrelated to reproduction since juveniles move toward the scent too. Nagel and Cade³ think the pheromone prevents camel crickets from drying out. We do know the antennae detect these pheromones. In a rather disturbing experiment, researchers found that camel crickets don’t aggregate when their antennae are lopped off.

 

1. Baily, W.J. & Haythornthwaite, S. (1998). Risks of calling by the field cricket Teleogryllus oceanicus: potential predation by Australian long-eared bats. Journal of Zoology. 244(4) 505-513.
2. Hedrick, A.V. (2000). Crickets with extravagant mating songs compensate for predation risk with extra caution. Proceedings of the Royal Society B 267(1444) 671-675.
3. Nagel, M.G. & Cade, W.H. (1983). On the role of pheromones in aggregation formation in camel crickets, Ceuthophilus secretus (Orthopter: Gryllacrididae). Canadian Journal of Zoology 61(1).

Hole-y Eggs

The hard shell of an egg may seem like a thin yet impenetrable fortress. At the microscopic level, though, it’s more like a colander. Thousands of pores allow oxygen into the egg (and carbon dioxide out) so the developing embryo won’t suffocate.

Those pores could potentially allow bacteria into the egg. In most birds, though, a thin layer of protein called the cuticle (or bloom) is added to the outside of the shell just before it’s laid. That layer blocks bacteria from moving inside the egg. Considering that eggs and waste products all pass through the same opening in birds, that cuticle can be extremely valuable. If you’re looking for the cuticle on eggs you bought at the grocery store, you won’t find it. Eggs here in the U.S. are washed before heading to market. The process is surprisingly complex since washing eggs improperly can cause bacteria to enter through those pores. It’s also the reason you’ll find eggs in the refrigerated section. In Europe, the cuticle stays on and eggs are sold at room temperature.

Our understanding of eggshell microstructure impacts Canada Goose populations. The process of “addling” by wildlife management professionals controls the population size of the birds. A thin layer of oil is rubbed on the outside of the eggshell, cutting off the oxygen supply for developing goose. The parents, who see a whole nest full of eggs, stop laying more. But only the un-oiled offspring will survive to hatch. [FYI: it is illegal to do this without a permit – see the Migratory Bird Treaty Act of 1918.]

Dinosaur eggs had pores too, and the structure and placement of those pores tell paleontologists a thing or two about how dinosaurs lived. For instance, some dinosaurs laid eggs in an exposed nest while some buried their eggs. Exposed eggs generally have fewer pores than the buried ones since gas exchange proves more difficult underground. Fewer pores are also found in eggs laid in dry environments to limit water loss. The Museum of Paleontology at Berkley has an excellent site with more information about dinosaur eggs.

Beech Bodies

Take a walk in a winter forest and you can’t help but notice beech trees. Silky smooth bark and sand-colored dry leaves stick out like Christmas lights against a dull and gloomy background. While every other leaf drifted to the forest floor months ago, beech leaves hold tight like cat hair on a sweater.

It’s called marcescence – these leaves that just won’t drop – and it’s common in oak and beech (the trees are close relatives). But why keep the leaves? Are these trees just photosynthetic versions of hoarders?

One possible reason may be to protect that bud, the thin tapered structure often described as “cigar-shaped.” Inside the scaly covering are the beginnings of the new year’s growth. Hungry deer can ruin a tree’s plans for spring. But with beech trees, deer tend to get a mouthful of dry leaves whenever aiming for a yummy bud. (1)

What about attacks from smaller enemies? Insects seem to prefer infesting trees with leaves hanging on over winter.  R. Karban decided to yank all the leaves off a few dozen small oaks and compare infestation levels of a tree-noshing wasp. (2) His numbers indicate that wasps prefer leaf-hoarding trees three-to-one compared to his denuded ones.

I believe Nature is constantly sending messages of wisdom if we’ll just listen. In this case, perhaps she’s saying “every action has an upside and downside, but with diversity, there’s always hope for a better future.”

1. Svendsen, Claus R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces 37(2): 475-482.
2. Karban, R. 2007. Deciduous leaf drop reduces insect herbivory. Oecologia. 153: 81-88.

The Corpse Flower Opens – and Stinks!

Many flowers use insects to transfer pollen from one plant to another. Some flowers attract bees or butterflies. The corpse flower, though, uses carrion beetles and flesh flies. What attracts these pollinators? The color of decaying flesh, putrid scents, and the warm temperature of a freshly dead body. Lovely.

While we humans tend to focus on color, beetles and flies who pollinate the corpse flower may be more attracted to the scent and temperature. Angioy et al. (2004) showed that certain insects have the abilities to “see” temperatures and are attracted to heat. The heat generated by the spadix of the flower is unusual in the plant kingdom. Not many plants expend tons of energy to warm up to around 100 degrees Fahrenheit. Those few that do are called “thermogenic plants.” It’s generally accepted that the heat increases the range of the odors (Barthlott et al. 2009), which is true of course. But wouldn’t all plants benefit by increasing scent ranges? Yet this mechanism is found in plants that only mimic carcasses to attract pollinators – plants like the skunk cabbage and voodoo lily.

While most flowers give their pollinators a reward of some kind (think nectar), the corpse flower seems to just take, take, take. The plant mimics carrion, where pollinators normally lay their eggs, yet gives the pollinators no food or reward. Or could it?

I personally found it interesting that the spathe of the corpse flower closed back up after it bloomed. It’s probably protecting the developing fruit. Yet the fruit takes 6-9 months to mature. At the Chicago Botanic Garden, the spathe of their corpse flower wilted after about 3 months, exposing yet unripe fruit. Could the flower serve as protection for the developing carrion beetles? Is there any food supply for those youngsters when they hatch? Or is it just a dead end (pun intended)?

FYI: while other arums smell like corpses too (my personal favorite is the “pig-butt arum”), some species of Amorphophallus smell like bananas or carrots.

1. Angioy AM et al. 2004. Function of the heater: the dead horse arum revisited. Proceedings of the Royal Society Biological Sciences. 271(3) S13-15.
2. Barthlott W et al. 2009. A torch in the rain forest: thermogenesis of the Titan arum (Amorphophallus titanium). Plant Biology 11. 499-505.

The Corpse Flower, a Botanical Marvel

It’s rare to see a corpse flower bloom. If you ever have the opportunity, take it… especially if you get to visit Sumatra. Lucky for me, a corpse flower (Amorphophallus titanium) blossomed in the greenhouse next to my office last weekend at NC State University (https://cals.ncsu.edu/corpse-flower-at-nc-state/).

It took the corpse flower, dubbed Lupin, 13 years to save up enough energy to bloom.  It’ll probably be another five years before it does so again. So corpse flowers are rather special. Actually, fewer than 200 cultivars have been recorded since 1889. But now’s your opportunity. For some yet unknown reason, a bunch are flowering at once (1).

Lupin grew six feet tall in under two months! That tall, purple-grey phallic structure is called a spadix. At its base are about 700 vibrant orange and purple female flowers and thousands of male flowers (2). When the one giant petal (actually a bract known as a spathe) opens, the spadix releases a stench to attract carrion beetles and flies who pollinate all those female flowers.

So actually, the corpse flower isn’t a flower at all. It’s over a thousand flowers wrapped into one giant, stinky, gorgeous inflorescence.

1. http://www.sciencealert.com/no-one-really-knows-why-but-america-s-corpse-flowers-are-all-blooming-at-once
2. Gandawijaja, D, S. Idris, R. Nasution. 1983. Amorphophallus titanium Becc.: a Historical Review and Some Recent Observations. Ann. Bot. 51:269-278.

Happy Darwin Day!!!

Barnacles. Not that appealing, right? Charles Darwin probably would have agreed… until he ran into a small problem. He found a new species of barnacle on his trip around the world and couldn’t place it into a taxonomic category. So, Darwin ended up examining, dissecting and analyzing every known species of barnacle, re-ordering the entire crustacean sub-class to figure out where his little guy fit.

It took 8 years… of barnacles… and microscopes. Turns out that Darwin’s newly discovered species (which he politely called “Mr. Arthrobalanus”) was the smallest barnacle in the world. With close and careful observation, Darwin also realized that some species of barnacle, thought to consist only of females, actually housed minuscule males inside small compartments of the feminine form. However, the most influential aspect of such this detailed study was the realization that immense variation occurs within and among species (variation being a key component in natural selection). Those barnacles changed not just biology, but our understanding of the world.

February 12, 2016 is Darwin’s 207th Birthday. Enjoy some cake (and maybe even send some love to Mr. Arthrobalanus)!

 

Interested in learning more about Darwin? I recommend three books: The Autobiography of Charles Darwin,  The Voyage of the Beagle, and Origins: Selected Letters of Charles Darwin (although all of Darwin’s letters can be found online at the Darwin Correspondence Project).