Male jewel beetles are literally dying to mate with brown beer bottles in Australia. The orange-brown coloration and manner of light reflection from dimples in the bottles resemble female jewel beetle wing covers, or "elytra".
University of Toronto professor Darryl Gwynne and colleague David Rentz observed this behavior while conducting field work alongside a road littered with the bottles. The bottles may act as "supernormal releasers", or exaggerated stimuli that evoke an instinctive behavioral response. In this case, the males may view the bottles as "super females" and will mate with them at all costs. These relentless mating attempts often result in death by overheating in the sun or through predation by ants. This week Gwynne and Rentz were awarded an Ig Nobel prize at Harvard University for their discovery, which was originally documented in 1983.
Besides the mild humor involved, the discovery highlights one of the many ways that littering can adversely affect wild populations, such as the mating system of a beetle species.
Watch out, because what you eat can kill you! At least this is what Gil Wizen and Dr. Avital Gasith (Tel-Aviv University, Israel) discovered when observing interactions between amphibians and ground beetle larvae (Genus Epomis). In an extraordinary case of predator-prey role reversal, some Epomis species have evolved anti-predator behaviors that enable them to deceive and devour their much larger would be predators. These beetle babies subsist solely on amphibians, such as frogs and salamanders, and exploit their predatory instincts by moving their antennae and mandibles, presenting themselves as tasty treats. As the unsuspecting victim is lured in, the larva heightens the excitement by flailing it's appendages more vigorously until the amphibian goes in for the kill.
Epomis larva luring a prey item through movement of antennae and mandibles. Video credit: Gil Wizen.
The tables are soon turned, however, as the larva stealthily avoids the frog's protracting tongue and harpoons the animal with hooked jaws, latching on tightly. The predator will then "suck the life" out of it's prey, ingesting bodily fluids followed by the tissues. In many instances, only bones are left behind. Those able to escape the clutches of the larvae are literally scarred, bearing the marks of being "hooked".
Amphibian metamorph attempting to ingest an Epomis larva. Photo credit: Gil Wizen.
Leftovers. Photo credit: Gil Wizen.
Wizen and Gasith performed 382 trials where Epomis larvae and various amphibians "faced off" in test arenas. In 100% of the interactions, the beetle larvae were successful in subduing their prey, even if they were initially ingested by the amphibian! These findings have been featured in a great article published in PLoS ONE.
Predator-prey role reversal in action. Video credit: Gil Wizen.
Once the beetles have matured, they exhibit a more varied diet, however, amphibians are still not safe. Adult Epomis beetles are known to immobilize their amphibian prey with a paralyzing bite before ingesting them alive.
When I was an undergraduate at UC Santa Barbara I had the fortunate opportunity to take a parasitology course with Dr. Armand Kuris. During this intensive course we learned that parasites face unique challenges in life, and that our typical day is drastically different from that of a parasite. For example, we may wake up everyday and go to work or school, and come home for a nice dinner before going to sleep. For most of us, these activities are not exceptionally hostile experiences.
Consider the life of a parasite. A parasite must first encounter a host, which can be quite challenging if hosts are scarce or patchy, or not around at opportune times. Some infective stages only have a few hours to find a host before they perish in the environment. Next, the parasite must be compatible with it’s new host. Just because a parasite may find a potential home doesn't mean it will be able to live there. For example, have you ever been the unfortunate recipient of "swimmer's itch"? Perhaps you went for a dip in a lake or pond, only to be covered with small, intensely itchy bumps later on? That uncomfortable rash was caused by parasitic worms called trematodes (see below) that burrowed into your skin and tried to take up residence in your body. However, you were not a compatible host (these trematodes often use birds as their final hosts), and your immune system was able to quickly destroy the little invaders.
Another thing to keep in mind is that once a parasite successfully locates and enters an appropriate host, their new residence will soon try to kill them. Imagine living in a house that is alive and constantly assaulting you with the sole intention of ending your life. A parasite's life can be tough, and only a fraction of them may survive to reproduce.
How is one to thrive given so many obstacles? Parasites have evolved a variety of ways to locate hosts and once inside, many can combat or even evade the host immune system. They have conquered the host-time to celebrate! Well, not really. What if the parasite needs to leave it’s cozy home it worked so hard to obtain to complete its life cycle? This is the harsh reality faced by many parasites. Some must travel to mating locales that the host does not frequent, while others require transmission to additional hosts for their survival and reproduction. Still, others must find proper accommodations for their offspring inside an unwilling provider. This is when things get bizarre and where the science fiction writers come for ideas. This is why I am in graduate school.
Parasites that encounter these challenges will often hijack their hosts, manipulating their physiology, appearance, and/or behavior in ways that benefit the parasites. This phenomenon is termed “host manipulation”, and it has been identified in a wide variety of host-parasite relationships. Manipulations may be subtle (such as an increase in host activity levels) or spectacular (such as dramatic changes in host appearance and/or behavior). Although these manifestations are highly variable, the end result is often the same: the parasite prospers at the expense of the host. I have highlighted some cool examples below.
Zombie snails
Snails get infected with the Leucochloridium spp. parasite after inadvertently ingesting their eggs as they graze on contaminated vegetation. Once ingested, the trematode eggs release larvae called miracidia that develop into sporocysts which then form broodsacs that engorge the snail's eyestalks. These broodsacs contain hundreds of infective stages called cercariae that must get to a bird to complete the lifecycle. How will they get from a snail into a bird? The infested eyestalks begin to resemble caterpillars or grubs, and the broodsacs within pulsate when exposed to light! Birds searching for a meal may mistake these bags of worms for yummy insect larvae and go in for the kill.
Mind control by wasps
The Jewel Wasp (Ampulex compressa) mother has her work cut out for her. She must find a suitable host and somehow lure it back to her burrow where it will be held hostage, serving as a safe haven and living meal for her future offspring. What host would agree to this? Remarkably, this is not a problem for Jewel Wasps are they are powerful manipulators of the mind! When a female is ready to lay eggs, she locates an unsuspecting host for her young, usually a cockroach. She ambushes the roach, delivering a venomous sting into a specific region of it's brain. The neurotoxic venom does not paralyze the roach, but rather it makes the host submissive and seemingly undisturbed by the turn of events. The roach does not fight back, nor does it attempt to escape. Instead, it stands still while the wasp clips its antennae, drinking hemolymph ("insect circulatory fluid") from the open ends. Like leading a dog on a leash, the wasp grasps the host's antenna and leads it into her burrow. Once inside she will lay an egg on the zombified roach and the hatched larva will burrow into it's body, feasting on the internal organs. After five days or so, the larva will pupate and later exit the hollowed out carcass as an adult wasp.
Suicidal crickets
It is thought that "horsehair worms" (Phylum Nematomorpha) got their name from an old superstition that supposed the worms arose from horse hairs that fell into watering troughs. We now know that these worms do not arise from horse hairs, but are instead free-living adults that enter pools of water in search of mates for reproduction. As juveniles, the worms are obligate parasites that require an insect or crustacean for food and development (adults do not feed). However, a challenge arises once they mature and are ready to mate because their terrestrial hosts do not frequent aquatic habitats. How does one lead a cricket to water? Research suggests the worms chemically manipulate the central nervous system of their hosts, causing them to actively seek out watery areas. When the host eventually finds water it will jump in, stimulating the worm to exit the body, often killing the host in the process.
Additional reading sources:
1. D.G. Biron, L. Marche, F. Ponton, H.D. Loxdale, N. Galeotti, L. Renault, C.
Joly, and F. Thomas. 2005. Behavioural manipulation of a grasshopper
harboring a hairworm: a proteomics approach. Proc. R. Soc. B. 1577: 2117-2126.
2. C. Combes. 2001. Parasitism: the ecology and evolution of intimate interactions.
University of Chicago Press.
3. R. Gal and F. Libersat. 2010. On predatory wasps and zombie cockroaches:
investigations of "free will" and spontaneous behavior in insects. Commun.
Integ. Biol. 5: 458-461.
4. R. Gal and F. Libersat. 2010. A wasp manipulates neuronal activity in
sub-esophageal ganglion to decrease to decrease the drive for walking in its
cockroach prey. PLoS ONE 5 (4): e10019.
4. K.D. Lafferty and A.K. Morris. 1996. Altered behavior of parasitized killifish
increases susceptibility to predation by bird final hosts. Ecology 77: 1390-1397.
5. J. Moore. 2002. Parasites and the behavior of animals. Oxford University Press.
6. J.C. Shaw, W.J. Korzan, R.E. Carpenter, A.M. Kuris, K.D. Lafferty,
C.H. Summers, and O. Overli. 2009. Parasite manipulation of brain monoamines
in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis. Proc. R. Soc. B. 276: 1137-1146.
This idea has been on my mind for a while, and I am excited to have finally brought it to fruition. My goal with this blog is to write about exciting research and science stories that are in the news. I am writing this blog for a broad audience, so a strong background in the sciences is not required. Please feel free to comment on my posts and let me know which stories you particularly like. Also, if you come across some neat science stuff that you want to share, send it my way and I will post it! Thanks for visiting and I hope you enjoy reading and learning some new things along the way!
