Herbivorous vertebrates

Is there evidence of coevolution between herbivorous vertebrates and their food plants. ... 

For approximately 65 million years, the only true herbivorous vertebrates have been the mammals. The Mesozoic reptiles disappeared following the mesophytic flora. Birds, though a few species feed on seeds and berries, seldom eat leaves (except geese and grouse), and they frequently use insects, in addition to plant parts, as a food source (18). 

While most insects which feed on plants are monophagous or oligopha-gous, i.e., they feed only on one or a few species of plants, the vertebrates are usually polyphagous. There are, of course, some exceptions, such as the Australian koala, but the majority of herbivorous mammals feed on a broad spectrum of plants. For 65 million years, the only truly herbivorous vertebrates have been the mammals. The Mesozoic reptiles disappeared following the mesophytic flora. Birds, while they feed on seeds and berries, seldom do so on leaves, and they frequently use insects, in addition to plant parts, as a food source (Emlen, 1971). While a single plant can be a host for hundreds of insect larvae, hundreds of plants comprise a daily menu for a... 

Many bacteria, fui, and Actinomyces produce cellulolytic enz5mies. Most higher animals cannot metabolize cellulose, but herbivorous vertebrates, whose intestinal flora contain ceUulose-splitting anaerobic bacteria make use of cellulose indirectly in this manner. Actinomyces species are mainly responsible for the aerobic breakdown of cellulose in the soil, while many fungi will attack wood and utilize its cellulose metabolically. 

In contrast to the controlled use of these compounds in the neighborhood of farms and human habitation, they have sometimes been used in a less controlled way against rodents and vertebrate predators, which causes problems in conserved areas. In a number of conserved islands in New Zealand, for example, bait containing brodiphacoum has been used for rodent control, both at bait stations and by aerial distribution (Eason et al. 2002). In the latter case, poisoned bait is freely available, and herbivores and omnivores, as well as predators and scavengers are at high risk. This problem will be discussed further in Section 11.6. 

Previous studies have found that cyanotoxic compounds may accumulate in sym-patric plants as well as in the tissues of herbivorous fish and invertebrates (reviewed in Zurawell et al. 2005). The accumulation of cyanotoxins at these trophic levels provides a direct path to both aquatic and, potentially, terrestrial consumers (Negri and Jones 1995 Kotak et al. 1996 Giovannardi et al. 1999). However, these compounds are rarely encountered in higher trophic levels in freshwater systems (Kotak et al. 1996 Zurawell et al. 2005). Nevertheless, attempts to minimize cyanotoxins in water bodies for recreational use should remain a major focus of environmental and public health managers, especially in light of the evidence that low doses may still have sublethal effects on the larval development of aquatic vertebrates (Oberemm et al. 1999). 

Foley WJ, Moore BD (2005) Plant secondary metabolites and vertebrate herbivores - from physiological regulation to ecosystem function. Curr Opin Plant Biol 8 430 135 Freeland WJ (1991) Plant secondary metabolites biochemical coevolution with herbivores. In Palo RT, Robbins CT (eds) Plant defenses against mammalian herbivory. CRC, Boca Raton, FL, pp 61-81... 

Broadly speaking herbivorous animals (guinea-pig excepted) show cardiac symptoms and carnivores develop central nervous system convulsions or depression with omnivores both heart and central nervous system may be affected. Cold-blooded vertebrates are usually less sensitive to fluoroacetate, but frogs are more sensitive in summer than in winter.2 Fish appear to be insensitive to fluoroacetate dissolved in water.3 Insects are easily killed by fluoroacetate, and the use of sodium fluoroacetate as a systemic insecticide is described on p. 182. 

The interactions of plants and vertebrate herbivores can be broken down into several questions. 

The great diversity of terpenes helps to cormteract tolerance by herbivores. In all, terpenes are not very toxic to vertebrates. Many mammals ingest a significant amount of terpenoids with their diet. Monoterpenes from pine oil added to the diet reduces food intake in red deer, Cervuselaphus, calves (Elliot and Loudon, 1987). The brush-tailed possmn, Trichosurus vulpecula, detoxifies (-l-)-a-pinene to alcohol and carboxylic acid derivatives. 

An example of a hallucinogen affecting mammalian herbivores is the isox-azole muscimol (fig. 11.13), a mushroom toxin. It is a y-aminobutyric acid agonist in the central nervous system of vertebrates. Muscimol s role in nature... 

Table 11.4 Plant parts differ in chemical defense against vertebrate herbivores...

Adams, M. A. and Johnsen, P. B. (1986). Chemical control of feeding in herbivorous and carnivorous fish. In Chemical Signals in Vertebrates, vol. 4, ed. D. Duvall, D. Miiller-Schwarze, and R. M. Silverstein, pp. 45-61. New York Plenum. 

Table I. Studies Dealing with the Consuirption of Tannins by Vertebrate Herbivores...

With the nature of the evidence to hand now established, the effects of tannins on vertebrate herbivores will be described. Thereafter a concluding section will ccarpare these and examine the differing effects dependent on the chemical nature of the tannins involved. 

Recent publications on tannins and their effects on herbivores liave tended to deal specifically with only vertebrate (2,3) or invertebrate (, ) herbivores, and have drawn slightly different conclusions for the two groups. Sirtplistically, these are tliat tannins do not act as effective digestibility - reducers in insects, and that they have sotb, but not completely effective, deterrent action against maitmals. 

Dearing MD, Foley WJ, McLean S. 2005. The influence of plant secondary metabolites on the nutritional ecology of herbivorous terrestrial vertebrates. Annu Rev Ecol Evol Syst 36 169-189. 

Herbivores in the sea are phylogenetically more diverse than on land. Seaweeds are eaten by diverse vertebrate ectotherms and an array of invertebrate consumers that vary both in their selectivity and in their impact on algae. Vertebrate herbivores are comprised of various fish families and species, as well as some turtles.24 111 120 125 Invertebrate herbivores span at least four different phyla and include an array of gastropods (such as snails, limpets, sacoglossans, sea hares, cephalaspideans, and chitons), urchins, crabs, amphipods, isopods, shrimps, polychaete worms, copepods, and a few insect species that feed on algae living in the upper littoral zone.24 110 123 126-135... 

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