Which came first?
The Chicken or the Egg?
The proverbial question asks the circular question of the order of event between a chicken and an egg. The question, when viewed from the evolutionary perspective, is trivial. Animals of all shapes and sizes have been reproducing using eggs long before the modern domestic chicken came around just a couple thousand years ago. Dinosaurs, primitive birds, reptiles, amphibians, and fish all come from eggs that develop outside their mother’s body (there are are exceptions to this rule in the ovoviviparous species develop inside their mother). Some mammals still reproduce using this most primitive means of sexual reproduction. Placental mammals, including humans, reproduce using a modified egg in the form of the womb. The anatomy is all there it is just a different form.
A Brief History of EggsAmong the most ancient of egg layers on land are the insects. Insects were the first animals able to break the aquatic shackles of early life. They were welcomed into a terrestrial world full of plants, a food source, ready for the taking. Once the herbivorous insects established themselves on land the predatory insects were right behind. For a few million years insects were the dominate form of animal life on land. Our tetrapod ancestors were still at the water’s edge only able to watch as insects of different shapes and sizes flitted by on wings and exploited nearly every available niche on land.
Some of these insects have changed very little in the 200 million years since they first claimed the land for all of animal-kind. There are fossils of dragonflies that look identical to its modern ancestors only with a three-foot wing-span. (the rationale for this size is another interesting topic!!) Another common insect that has changed very little is the common lacewings (order Neuroptera, family Chrysopidae).
Despite the delicate sounding name, Lacewings are a beneficial predator of many insects we have deemed as “pests”. Their larvae feed on aphids and other pest insects and that preference follows them into adulthood. Even with this voracious personality as larvae and adults there is still a time in life that they are defenseless, as an egg. Natural selection states that most of the organisms that are produced do not survive to reproduce. This is true for nearly every species (except the modern human). To improve these odd lacewings have come up with a unique way to ensure their eggs are out of sight and out of mind from any potential predators.
The female lays each egg at the end of a thread of silk that dangles from the underside of a leaf. When the silken web dries it becomes a sturdy pillar that keeps the egg and developing larvae just out of reach from predators like ants, spiders or others. The picture above is upside down. This egg is sticking straight up supported by the dried silk along.
Natural selection also states that the more eggs that are produced the more will survive to reproduce. The lacewing follows this idea. The underside of this lily leaf was lined with eggs, each on their own silken strand. This process has been like this for millions of years and has been shaped by competition and predatory pressures between and within species.
Not all eggs or larvae are so safe. For every protection or deterrent from predation, there will be another adaptation to exploit it. The best example of this in the insect world is the parasitic wasps. For nearly every insect there is a parasite that exploits and takes advantage of it. The parasitic wasps have a rather devious and disturbing way of peddling their trade. Female Ichneumonoid wasps are identified by their large ovipositors. The ovipositor is the long tube like structure protruding from abdomen that serves as an “egg injector” or sorts. Ichneumon wasps come in all shapes and sizes depending on the species and location of their host.
Ichneumons are the among the most diverse of the wasps. There are at least 33,000 different species in North America alone. Many species are indistinguishable by sight alone. Recently a population of identical looking ichneumons in the Central American tropics was revealed to be at least 15 genetically distinct species!
(Please forgive my leg hair! This little wasp would not stop moving until it landed on my knee!!)
Better Than a Hollywood Horror Movie!
The small ichneumon was pictured above has a relatively large ovipositor compared to her body length. The ovipositor cannot sting and functions only for the delivery of the egg to the host. The host, in this case, is likely a boring beetle. The larvae of many beetles live just beneath the surface of plants, shrubs or trees. They feed on the sugars and tissue of the plant. The ichneumon wasp locates the larvae beneath the surface using a still known mechanism. It then bends its ovipositor perpendicular with the surface. The ovipositor is sheathed on each side with a protective layer. These sheaths split and the ovipositor begins to “drill” into the surface. The wasp will drill down until it reaches the unsuspecting larvae below. An egg is laid on, or in, the larvae. The egg will eventually hatch into a wasp larva. The wasp larvae will then feed on the host slowly killing it as the wasp larva grows bigger. The important part here is that the host larvae is still alive as the wasp is feeding on it. This is natural selection in action.
Go Big or Go Home!
Not all Ichneumons are small. Genus Megarhyssa has the behemoths of the ichneumon world. Theses giants function in the same way described above but their host is a bit more difficult to reach. Wasps of this genus parasitize Horntail Wasps (large insects in their own respect). Horntails also have large ovipositors that they use to drill into dead or decaying wood. Their larvae feed on the wood several inches below the surface. The Ichneumon wasp is able to “divine” where the horntail larvae is beneath several inches of wood, and with surgical precision, it delivers its egg into the larvae.
Push and Shove
This wasp was about 8 inches long from head to the tip of the ovipositor. This disproportional size is a direct result of the millions of years of natural selection that have pressured host and parasite to adapt. As the pressure from parasitic wasps increases there is an advantage to those horntail wasps that can lay their eggs deeper. This selective pressure also gives an advantage to those ichneumons that can “dig deeper” to reach their host. This process is natural selection in the most primal form. The clownish appearance of the ichneumon wasp is the result of hundreds of millions of years of evolution and natural selection with its host. If the host evolves a resistance the parasite counters with another way to exploit. This is the same process we are starting to see with antibiotic resistance bacteria and viruses.
How does this affect you?
Humans are subject to the same pressures as every other organism on this planet. We are products of evolution and not a divine creation placed here to exploit the land and reproduce freely. Our modern population has grown independent of the natural checks and balances. We think we have broken free from the selective pressures of the environment. We are the horntail wasps in this story we have to keep digging deeper to avoid the building masses of ichneumons waiting to exploit our population and resources. We see this in herbicide resistant weeds and insects. We have bacteria that are immune to nearly every available antibiotic and viruses that evolve quicker than we can produce a vaccine.
This perspective makes it sounds like a pretty gloomy outlook. It’s really not if we stop pretending we are better than all those other living things. If we can start to appreciate every living thing we will find that there is much to learn. We must recognize and understand the importance of evolution and how it has shaped our world and our own bodies. The world is a beautiful place and an even more amazing place when viewed as an interconnected system of organisms continually fighting for survival.
Go outside and give thanks!