Some tiny parasitic nematodes have evolved a remarkable skill: they farm bacteria for food, using the body (larva) of their parasitized insect host as the “soil” in which to cultivate the bacteria. The bacteria feed on the larva, killing it, and the nematodes feed on the bacteria. The bacteria are both symbionts and food and have never been found apart from their nematode hosts.
The larval body is preserved from invasion by other bacteria by antibacterial compounds produced by the nematodes, to which its own symbiotic bacteria are resistant.
When the nematodes reproduce, thousands of juveniles leave to locate new larval hosts, carrying some of the bacteria in their own gut.
The ability of these nematodes to kill insect larvae has not been overlooked by the global agricultural community (12, 13). Species from 2 genera of insect-parasitic nematodes, Steinernema and Heterorhabditis, are sprayed on crops around the world to control the larvae of plant-eating insects and are valued as natural biological pesticides.
Proc (Bayl Univ Med Cent). 2000 July; 13(3): 217–226. MPMID: MPMID: PMC1317043
2000, Baylor University Medical Center
Evolving together: the biology of symbiosis, part 1 Gregory G. Dimijian, MD1
1From the Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas.
Corresponding author: Gregory G. Dimijian, MD, 3277 Brincrest Drive, Dallas, Texas 75234 (Email: firstname.lastname@example.org ).
Symbioses, prolonged associations between organisms often widely separated phylogenetically, are more common in biology than we once thought and have been neglected as a phenomenon worthy of study on its own merits. Extending along a dynamic continuum from antagonistic to cooperative and often involving elements of both antagonism and mutualism, symbioses involve pathogens, commensals, and mutualists interacting in myriad ways over the evolutionary history of the involved “partners.” In this first of 2 parts, some remarkable examples of symbiosis will be explored, from the coral-algal symbiosis and nitrogen fixation to the great diversity of dietary specializations enabled by the gastrointestinal microbiota of animals.
Derived from the Greek word for living together, symbiosis refers to a close and prolonged association between 2 or more organisms of different species that may last for the lifetime of 1 or all “partners.” The definition of symbiosis is not universally agreed upon; in this review, it will be considered in its broadest sense, encompassing associations varying widely in intimacy and types of interaction. Symbioses can be mutualistic (all partners benefiting), commensalistic (one benefiting and the others unharmed), or parasitic, although many symbiotic associations are complex or poorly understood and do not fit neatly into 1 category (1). A continuum can be envisioned that spans a dynamic bridge from antagonism to cooperation. Relationships may shift gradually or abruptly along the continuum (Figure (Figure11).