If you know about the relationship between flowers and bees, you know the basics of symbiosis—two dissimilar species living together interdependently. To account for the occurrence of symbiosis, some biologists have developed a theory of “coevolution” wherein increasingly cooperative interaction between two species supports their mutual competition for survival.
In other words, cooperation must be as important as competition in driving evolutionary advance. This view takes the complexity of adaptation and natural selection to a whole new level. One might say it introduces a paradox, if not an out-and-out contradiction. I believe this paradox is best understood as the intricate, creative work of a Designer rather than as a multitude of lucky coincidences amid the undirected chaos of nature.
Figure 1: Bee-Flower Symbiosis
The bee pollinates the flower. the flower provides nectar for the bee. Neither species can survive without the other. (Credit: Charles Lam)
During recent months, a number of published papers have shown that symbiosis is much more prevalent and complex than anyone had previously recognized. And researchers express the likelihood that many more examples of it will come to light as research continues.
A pair of entomologists from the University of Arizona just published a paper entitled, “Extraordinarily Widespread and Fantastically Complex.”1 The study begins by reviewing recent research into the symbiotic relationship between certain insects and bacteria, studies that reveal how the insects feed the bacteria while the bacteria assist their insect hosts in processing nutrients, facilitating digestion, regulating reproduction, and defending against pathogenic microorganisms. But then it goes on to note that fungi also are frequently associated with insects and that researchers have tended to ignore the additional symbiotic roles these fungi may play. According to their thinking, the data “suggest that insect-fungal endosymbionts are hyperdiverse.”2 (Endosymbionts live inside their partners; ectosymbionts live outside.)
Insect-fungal symbiosis is not a new concept. It was first discovered in 1991 by Patrick Dowd, an agricultural scientist. Dowd found that certain fungal species help their insect hosts by neutralizing defensive toxins in plants.3 Because of the fungi, insects are able to feed on plants that would otherwise be poisonous. The insects, in turn, provide food for the fungi. (Dowd suggested that industrial biotechnologists exploit these fungi to detoxify a wide range of enzymes, an idea that seems well worth pursuing.)
In the past decade, ecologists discovered that fungal symbionts assist many insects, both terrestrial and aquatic.4 Similar to what Dowd observed, gut fungi help both kinds of insects digest food they otherwise would not be able to metabolize.
A few months ago I reported (in TNRTB, 11/23/09) on the most prevalent known plant-fungal symbiosis—the relationship between vascular plants and arbuscular mycorrhizal fungi (AMF).5 At sites all along the root systems of vascular or flowering plants, colonies of AMF assemble and feed on the nutrients there while the AMF supply phosphorus, nitrogen, and carbon in molecular forms that the plant can readily assimilate.
Further research on AMF has now revealed a more complex three-partner symbiosis.6 It appears that the fungus can provide the plant host with nutrients only if it (AMF) has physical contact with certain species of bacteria. Specifically, microbiologists have observed that only a few bacterial species will attach to AMF hyphae (long, branching filamentous fungi cells) and those that do, including oxalobacteraceae, attach in such high abundances as to indicate the likelihood of specific symbiotic interactions with the fungi.
More remarkable still is the four-part symbiotic relationship discovered involving an ant, a plant, a macro-fungus, and a micro-fungus (see Figure 2).7 Here’s how the four species interact:
(1) the ants cut waxy leaves from the plant, chew them into a pulp, and lay down the pulp on a substrate for the mushrooms;
(2) the mushrooms that grow from the pulp-lined substrate produce structures called gongylidia, which the ants then harvest for food;
(3) a micro-fungus in the ants’ gut enables the ants to digest the gongylidia.
Neither the ants nor the mushrooms can feed on the leaves directly. The leaves contain biochemical toxins (insecticide) dangerous to the ants and are covered with a waxy coating the mushrooms cannot penetrate. The ants remove the waxy coating for the benefit of the mushrooms. The mushrooms “process” the chemical toxins so that the ants, with crucial assistance from gut micro-fungi, can then digest their food.
Figure 2: Leaf-Cutting, Fungus-Farming Ants
Ants process leaves, from which mushrooms grow to feed the ants, which then digest the mushrooms with the aid of gut fungus.
Naturalistic evolutionary models must explain how both or all the symbiotic partners emerged and developed simultaneously—and in proximity—with the specific morphological and biochemical features in place to permit the transfer of mutually beneficial—or absolutely essential—goods and services to the other(s). An even greater challenge may be to explain how symbiotic relationships became so ubiquitous in the biological realm.
As the University of Arizona entomologists commented, symbiotic relationships in nature are indeed “extraordinarily widespread and fantastically complex.” And, the more we study them the more reasonable it seems to view such findings as evidence for purposeful, intricate design.
- Cara M. Gibson and Martha S. Hunter, “Extraordinarily Widespread and Fantastically Complex: Comparative Biology of Endosymbiotic Bacterial and Fungal Mutualists of Insects,” Ecology Letters 13 (February 2010): 223–34, https://www3.interscience.wiley.com/journal/123210330/abstract?CRETRY=1&SRETRY=0.
- Gibson and Hunter, 223.
- Patrick F. Dowd, “Insect-Fungal Symbionts: A Promising Source of Detoxifying Enzymes,” Journal of Industrial Microbiology and Biotechnology 9 (May 1992): 149–61.
- Merlin M. White and Robert W. Lichtwardt, “Fungal Symbionts (Harpellales) in Norwegian Aquatic Insect Larvae,” Mycologia 96 (April 2004): 891–910, https://www.mycologia.org/cgi/reprint/96/4/891.pdf?ck=nck.
- Hugh Ross, “Arbuscular Mycorrhizal Fungi Design,” Today’s New Reason to Believe (November 23, 2009), https://www.reasons.org/ArbuscularMycorrhizalFungiDesign2.
- Paola Bonfante and Iulia-Andra Anca, “Plants, Mycorrhizal Fungi, and Bacteria: A Network of Interactions,” Annual Review of Microbiology 63 (October 2009): 363–83; Tanja R. Scheublin et al., “Characterisation of Microbial Communities Colonising the Hyphal Surfaces of Arbuscular Mycorrhizal Fungi,” The International Society for Microbial Ecology, advance online publication 11 February 2010, doi: 10.1038/ismej.2010.5, https://www.nature.com/ismej/journal/vaop/ncurrent/abs/ismej20105a.html.
- Eric J. Caldera et al., “Insect Symbioses: A Case Study of Past, Present, and Future Fungus-Growing Ant Research,” Environmental Entomology 38 (January 2009): 78–92, https://currielab.wisc.edu/pubs/Caldera2009.pdf.