module # 10 – component # 2 wildlife toxins and toxic plants · 2018-06-09 · – wildlifecampus...

– WildlifeCampus Wildlife Management Course

This course material is the copyrighted intellectual property of WildlifeCampus. It may not be copied, distributed or reproduced in any format whatsoever without the express written permission of WildlifeCampus

1

Wildlife Toxins and Toxic Plants © Copyright

Module # 10 – Component # 2

Wildlife Toxins and Toxic Plants

Objective Investigate plant poisonings and their subsequent effect on wildlife and their ultimate implications for management

Expected Outcome

Account for the methods used by wildlife in dealing with plant toxins Recognise the common symptoms of a suspected poisoning Able to advise on the treatment of a poisoned animal Allow for the presence of toxic plants into wildlife management activities, and

what to do about them

Blue Wildebeest: Connochaetes taurinus



2


Perspective This is the second time that this wide topic has been included in this Wildlife Management Programme. However, even though similar issues have been brought up before in Module # 6, this component focuses on the expansion of these concepts with new ideas, insights, examples and conclusions.

For the Student who is doing the courses in the order that they have been presented, the intervening topics of nutrition, disease, parasites and toxic plants will have given you a greater perspective of the ecology of wildlife and therefore an enhanced understanding of this topic in context.



3


Detoxifying Mechanisms & Innate Resistance of Wildlife Animals cope with plant toxins / poisons and secondary plant compounds by either anatomic and/or physiologic adaptations or one or more of the following strategies:

Avoidance Dilution Degradation Detoxification

Sable Antelope: Hippotragus niger



4


Animal anatomic and physiologic adaptations

Modifications of the gastrointestinal tract are the most common anatomical adaptations to mitigate the effects of toxins. Digestive physiological adaptations are also very important.

Herbivores require the assistance of micro-organisms and protozoa to utilise nutrients encased in lignin and cellulose. There are two basic types of gastrointestinal configurations:

Hindgut fermenters Stomach fermenters

Even though ruminants are considered to have the most complex stomach arrangement of all mammals, they are not unique in the development of complex stomachs and other gastrointestinal fermentation organs. Certain marsupials, rodents, lagomorphs, edentates (the Order of mammals including sloths, armadillos, and anteaters), Perissodactyla, sirenians, and primates have evolved complex stomachs in parallel with ruminants.

The Great Basin kangaroo rat (Dipodomys microps) has highly adapted incisors for removing the hypersaline (very salty) outer layers of the stems of salt bush (Atriplex confertifolia), allowing the rat to feed on the nutritious inner layers rich in starches and

low in electrolytes.

Chacma baboon: Papio ursinus



5


Avoidance The skill to avoid potential harmful plants is a crucial one that must be learned early in life. Behavioural adaptation is a significant factor in the ability of a wild animal to avoid toxic plants.

The behavioural adaptation of the wild Norway rat (Rattus norvegicus) is attributed to a learning process. Wild rats are suspicious of strange foods and will either avoid it or will sample it lightly until proven to be safe. They become more suspicious with repeated attempts to poison them and will refuse poisonous bait up to the point of starvation.

According to scientists there is a genetic basis for forage selection since artificially reared animals showed similar forage preferences to their free-ranging counterparts when first introduced to native forages in a feeding experiment.

It is important to note that some factors can override basic avoidance patterns. Animals will, for instance, be more likely to consume poisonous plants when they are driven by extreme hunger. This is of importance when translocating game. Due to variation in elevation, soil types, and moisture plant communities may vary markedly even though short distances apart. A translocated animal might not be adapted to the different flora and grow hungry or the animal might even lack the avoidance behaviour to distinguish between safe and poisonous unfamiliar plants.

Giraffe: Giraffa camelopardalis



6


Dilution A wild herbivore’s diet usually includes a large variety of plants. A toxic agent from any plant will thus be diluted in such a diet. Researchers estimate that at least 40% of the plants in the environment of herbivores contain secondary plant compounds. If this is true, then it would be impossible for a large mammal to obtain sufficient food by simply eating small amounts of all the plants and thus diluting the toxin.

Dilution therefore does not satisfactorily explain the ability of wildlife to deal with secondary plant compounds. Animals must have intrinsic mechanisms for dealing with secondary plant compounds.

Sable antelope: Hippotragus niger



7


Degradation and Detoxification

A toxin can be destroyed either in the gastrointestinal tract through a process of degradation or following absorption from the gut through both general and specific detoxification mechanisms.

After a toxic substance is absorbed from the gastrointestinal tract an animal’s body can react in a few ways.

The toxin can either be:

Excreted unchanged by the body Sequestered into a non-active storage site Detoxified through molecular rearrangement Or, the toxin can cause the poisoning of the animal

All vertebrates have general detoxification pathways that can deal with toxins such as alkaloids, glycosides, saponins and tannins through oxidation, reduction, hydrolysis, esterification, N-dealkylation and conjugation. Besides these general detoxifying mechanisms certain species may develop specific pathways to deal with unique toxins.

One of the colobus monkey’s (Colobus guereza caudatus) favourite food items is a Rauwolfia sp. This is a known poisonous plant that contains alkaloidal tranquilizing compounds. It is not precisely known how this monkey can cope with these compounds, but the unusual, complex, fermenting-type stomach definitely plays a part.

A great deal of detoxification occurs in the liver through microsomal enzyme activity. The age, size, sex and reproductive status of the animal influence the efficiency of the enzyme activity. The enzyme systems of young animals are less developed than that of older animals which also have more reserves of material for conjugation than younger animals. Cortisol increases microsomal enzymes’ capacity to detoxify toxins, while sex hormones can either enhance or diminish the effect of various toxins. Well-nourished animals are also more likely than poorly nourished animals to support a gastrointestinal microflora that is capable of detoxifying toxins.

Some detoxifying mechanisms are inherent, but factors other than genetics also operate in these mechanisms. One such factor is prior stimulation of the mechanisms involved. Only minimal quantities of a particular enzyme will be present unless the enzyme system has been stimulated by prior exposure to the toxin involved. Microsomal stimulation can be induced by the consumption of non-lethal amounts of poisonous plants. Such an animal will be able to survive an otherwise lethal dose of the toxin. Prior ingestion of some toxins is not always beneficial, since some toxins are cumulative. This has been demonstrated frequently in humans as we learn the cumulative effects of being exposed to lead, mercury, asbestos and a host of other toxins.



8


General Symptoms of Poisoning Since there is such a variety of secondary plant compounds it is understandable that these compounds cause a variety of clinical signs, and it is not within the scope of this course to dwell on these. There is no one set of symptoms indicative of plant poisoning in wildlife.

However, when animals:

Suddenly become sick Suddenly showing signs of an acute dysfunction of the gastrointestinal tract Sudden dysfunction of the central nervous system Sudden weight-loss and without a fever

Then poisoning should be considered.

Further signs of poisoning include:

Irritation of the gut Increase and variation in heartbeat Lethargy Vomiting

These signs are often followed by:

Weakness Respiratory distress Loss of consciousness And finally, death.

Most toxins damage a specific organ/system more severely than the rest of the body. A blood-, muscle-, nerve-, or intestinal tract poisoning will thus cause specific signs of poisoning of that system.

Common signs to take note of are:

Muscle spasms Excitement Paralysis and paresis Constipation Diarrhoea Blindness Skin lesions



9


Treatment of Poisoned Animals Since our knowledge on plant poisonings of wildlife are insufficient there is not much information on the use of antidotes in the treatment of specific poisonings. Treatment is therefore aimed at general supportive therapy and might include the following:

Prevent any further intake of hazardous material Keep all animals, both healthy and poisoned, away from water for a day or two if

possible Remove toxic material not yet absorbed from gastrointestinal tract General supportive therapy (warm and dry area)

Note that it is of great importance that the animals are not stressed during treatment as this may cause convulsions and the subsequent death of the animals.

Giraffe: Giraffa camelopardalis



10


Conclusion The co-evolution of wildlife with all their natural enemies, including poisonous plants, usually leads to the improvement of their defence mechanisms to such an extent that wildlife co-exists with their enemies. Individuals that are most susceptible to the effects of the enemy are usually removed by predators before they can reproduce. This long term natural selection process leads to a stable ecosystem.

Usually an ecological balance must be disrupted for wild animals to die from the effects of poisonous plants. A lack of suitable forage such as during a drought can be a cause of the disruption. Frequently the first green plants to appear after winter are poisonous plants and animals may ingest these to such an extent that they can be poisoned. Overstocking and deterioration of ranges causes a decrease in forage and

can thus enhance the risk of poisoning of animals.

Unusual poisonings may occur when game is kept under unnatural circumstances. When a feed company accidentally included the ionophore ‘narasin’ in game cubes 11 white rhino (Ceratotherium simum), eight eland, nine zebra (Equus burchelli) and four nyala (Tragelaphus angasi) died on two farms in the Orange Free State.

When poisonous plants are introduced to new locations, the resident native wildlife are exposed to secondary plant compounds to which they have neither resistance nor experience to avoid these plants.

Thus, when animals are confined to smaller areas than they are used to and in unfamiliar surroundings they may ingest strange toxins and die because of lack of proper defence mechanisms. There is inadequate stimulation of the systems and processes involved in detoxification and this could cause poisonings when the animals are subsequently exposed to more poisonous plants.

Nyala: Tragelaphus angasii

module # 10 – component # 2 wildlife toxins and toxic plants · 2018-06-09 · – wildlifecampus...

Documents