Behavior-altering parasites and parasitoids

Behavior-altering Parasites and Parasitoids

Behavior-altering parasites and parasitoids are fascinating organisms that can manipulate the behavior of their hosts to increase their own chances of survival and reproduction. These organisms have evolved complex mechanisms to influence host behavior, often in ways that benefit the parasite or parasitoid at the expense of the host.

Introduction

Parasites and parasitoids are organisms that live on or in a host organism and derive nutrients at the host's expense. While parasites typically do not kill their hosts, parasitoids often do. Some of these organisms have developed the ability to alter the behavior of their hosts in ways that enhance the parasite's or parasitoid's life cycle.

Mechanisms of Behavior Manipulation

Behavior-altering parasites and parasitoids employ a variety of mechanisms to manipulate their hosts. These mechanisms can be broadly categorized into:

Neurochemical Manipulation

Some parasites produce chemicals that affect the host's nervous system, altering neurotransmitter levels and influencing behavior. For example, the Toxoplasma gondii parasite can alter the behavior of infected rodents, making them less fearful of predators such as cats, which are the definitive hosts of the parasite.

Physical Manipulation

Certain parasitoids physically manipulate their hosts. For instance, the wasp species Hymenoepimecis argyraphaga lays its eggs on the orb-weaver spider Plesiometa argyra. The wasp larva injects chemicals that cause the spider to spin a special web that is more suitable for the wasp's cocoon.

Behavioral Conditioning

Some parasites condition their hosts to perform specific behaviors. The hairworm Spinochordodes tellinii infects grasshoppers and crickets, causing them to jump into water, where the adult worm can emerge and reproduce.

Examples of Behavior-altering Parasites

Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite that infects warm-blooded animals. It is known for its ability to alter the behavior of rodents, reducing their fear of predators and increasing the likelihood of being eaten by cats, the parasite's definitive host.

Ophiocordyceps unilateralis

The fungus Ophiocordyceps unilateralis infects ants, causing them to climb vegetation and attach themselves to leaves or stems before dying. The fungus then grows out of the ant's body, releasing spores to infect more ants.

Leucochloridium paradoxum

The flatworm Leucochloridium paradoxum infects snails, causing their tentacles to swell and pulsate, mimicking caterpillars. This attracts birds, which eat the tentacles and become the next host in the parasite's life cycle.

Ecological and Evolutionary Implications

The ability of parasites and parasitoids to alter host behavior has significant ecological and evolutionary implications. These interactions can influence predator-prey dynamics, host population control, and the evolution of host defenses.

Also see

• Parasitism
• Parasitoid
• Neuroparasitology
• Host-parasite interaction