Koala: Plant - Animal Interactions - Herbivory Practical

Part A – Adaptations of herbivores to plant diets

Invertebrates

Species/group: Morpho Menelaus

Diet: these butterflies have a different diet for each stage of their lifecycle from a range of plants including several species of legume. Caterpillars feed on a variety of leaves but prefer pea plant leaves and new leaves. While butterflies drink their food from plants (Godawa, 2019).

Challenges involved in finding, processing and gaining nutrients or energy from diet: Morpho Menelaus are neotropical butterflies. There is a lack of food during the dry season during which adults don’t generally emerge. However, caterpillar peak is during this season (Freire et al., 2014).

Adaptations to that diet: depending on food availability, these butterflies collectively emerge at the end of the wet season to avoid wing damage during the wet season. Caterpillars enter diapause during the dry season to cope with a lack of food and water (Freire et al., 2014). Leaves are difficult to eat so caterpillars chew new leaves and pea plants as they are softer and more nutritious (Godawa, 2019; Freire et al., 2014). Butterflies drink their food as they are unable to chew. The varied diet of Morpho Menelaus ensures that if one plant is scarce, they will be able to feed on another suitable plant.

Species/group: chiton (genus) (Kangas et al., 1984).

Diet: chitons are generally herbivorous grazers. They can be specialist herbivores or generalist herbivores. Their diet consists of seagrass, algae, diatoms and small invertebrates

Challenges involved in finding, processing and gaining nutrients or energy from diet: most chiton species eat drift seagrass and algae. However, these are abundant only at a depth of 4 to 5 meters.

Adaptations to that diet: there is an abundance of chiton at the same depth of drift seagrass and algae to maximize feeding. Chitons are generally cryptic invertebrates by day as they hide in narrow rock crevices during the day. At night, they emerge to graze. Chiton can pull themselves along rounds with their feet. Their feet scrape the algae and the plant nutrition off the rocks. Their tongue like structures (radula) have rows of teeth with are also used to scrape algae and plants off surfaces.

Species/group: Rhino Beetle (National Wildlife Federation, 2019)

Diet: all rhinoceros beetles are herbivores. Their diet differs throughout their life cycle. Larvae feed on decaying plant matter and rotting wood during their two-year life stage while adults eat fresh and rotting fruit on moist forest ground and, nectar and sap.

Challenges involved in finding, processing and gaining nutrients or energy from diet: the amount of nutrition that the beetle larva consumes is proportional to the size of the male’s horns. Deforestation could affect the availability of food for the beetle as the branches will be removed before they are able to decay.

Adaptations to that diet: rhino beetles live in rain forests in Central and South America. The male rhino beetles have large thoracic and cephalic horns which can be used to dip and burrow through rotting plant material. Rhino beetles also have spines on their legs to help dig (pers. obs).

Vertebrates

Species/group: Koala (Phascolarctos cinereus)

Diet: koalas are specialist herbivores that feed almost exclusively on Eucalyptus foliage (Moore et al.,2000; Moor et al., 2005).

Challenges involved in finding, processing and gaining nutrients or energy from diet: eucalypt foliage distribution has spatial and temporal variation in quality and quantity which makes it difficult for koalas (Moore et al.,2000). Eucalypt foliage have complex chemical defenses which differ within and between species. Eucalypt globulus contain phenolics including tannins and formylated phloroglucinol compounds (FPC). FPC concentrations and nutrition differ between different eucalypt species. E. viminalis plants provide more nutrition and FPC concentrations are less deterrent than E. globulus (Moor et al., 2005). Eucalypts also have morphological defenses which makes feeding on them more difficult as the plants are small, hard, thick and leathery (Moore et al.,2000).

Koala teeth are especially adapted for their gumleaf diet. Their sharp front teeth nip the leaves from the tree and their back teeth are shaped for cutting and grinding the leaves to extract the most nourishment.

Adaptations to that diet: koalas have sharp claws which allows them to climb up Eucalyptus trees to reach their foliage (pers. obs). The chemicals in eucalypt are poisonous to most animals but, koalas have adapted their intestine and teeth to suit this diet. They have a caecum in their intestine which is long, broad and contains millions of micro-organisms that break down the leaves so that they are easier to absorb. Koala’s front teeth are sharp so that they can nip leaves and grind them with their back teeth (Savethekoala.com, 2019). Koalas also use the leaves as a source of water, so they rarely need to drink.

Koala’s preferences for eucalypt species changes with the seasons this is likely due to the increased concentration of toxic compounds and seasonal changes in the koala’s physiology and nutritional demands linked to changes in thermoregulation (Moore et al.,2000).

Species/group: grey rhebok (Pelea capreolus)

Diet: grey rheboks are herbivores that predominately feed on forbs and shrubs. They have selective diets with 90% consisting of broadleaf forbs and dwarf shrubs which are lower than 30 cm (Furstenburg, 2011). They also consume grasses, flowers, seeds, and roots and get most of their water from food (Taylor et al., 2017).

Challenges involved in finding, processing and gaining nutrients or energy from diet: grey rheboks mainly browse on nutritious plants which are rich in protein. However, during droughts, these may not be as widely available so the need to adapt their specialist diets (Furstenburg, 2011).

Adaptations to that diet: grey rheboks are not migratory animals so during droughts they have adapted to graze on the more resilient grasses which have lower nutritional value than their normal diet and have a high crude-fibre content.

Species/group: hoatzin (Opisthocomus hoazin)

Diet: hoatzins are obligate herbivores. They predominately feed on the young leaves (82%), shoots and buds of a wide variety of tree species. 10% of their diet is flowers and 8% is fruit. Hoatzins are generalists and can feed on up to 50 species of plants, but their diets mainly consist of 12 species (Thomas, 1996).

Challenges involved in finding, processing and gaining nutrients or energy from diet: hoatzin’s diet of vegetable material have aromatic compounds which are difficult to digest (Wright et al., 2009).

Adaptations to that diet: Hoatzins can fly to reach plants and their claws help them to cling to branches and remove foliage (pers. obs). Hoatzins are the only birds which have an active foregut fermentation. They use bacterial fermentation in their foregut to break down plant material. They have an expanded esophagus for digestion and can retain digestive material for as long as sheep. Their unusually large crop helps them to balance on branches and displaces the flight muscles and keel of the sternum (Wright et al., 2009).

Part B – Adaptations of plants to herbivory

Species: Cascabela thevetia

Main herbivores in native range of this species Cascabela thevetia is a poisonous plant which is native in Mexico and Central America. Sunbirds, Asian koel, red-whiskered bulbul, white-browed bulbul, red-vented bulbul, brahminy myna, common myna and common grey hornbill are all bird species which can feed on the plant without being poisoned (Krishnan, 1954).

Adaptations present which reduce herbivory, and/or help the plant to benefit from animal-interactions: the plant uses chemical defense to deter herbivory. All parts are toxic as they contain cardiac glycosides and toxins including cardenolides and peruvoside (Krishnan, 1954). These compounds affect herbivores cardiovascular systems by increasing the output force of the heart and its rate of contractions (Bose, 1999).

Species: Vachellia (Acacia) karroo

Main herbivores in native range of this species: Vachellia karroo is native in parts of South Africa. In its native range, it is eaten by domestic and wild species including goats and giraffes. Its foliage, seeds ad dehiscent pods are all eaten as they are protein rich (Dingaan et al., 2019).

Adaptations present which reduce herbivory, and/or help the plant to benefit from animal-interactions: Vachellia karroo uses chemical, physical and communication defence against herbivores. The plant’s chemical defences include tannins which are secondary metabolites. These tannins are also used in communication defence. The scent of the tannin is picked up by nearby acacia trees which respond by producing their own tannins (Dingaan et al., 2019). Long, paired, straight thorns act as a physical defence of the plant against herbivores. Thorns are larger and more abundant on lower branches which animals can more easily reach (pers.obs).

Species: Nicotiana Sylvestris

Main herbivores in native range of this species: Nicotiana Sylvestris is native in South America, in the Andes region in Argentina and Bolivia. Caterpillars are the plants main herbivores (Sierro et al., 2013).

Adaptations present which reduce herbivory, and/or help the plant to benefit from animal-interactions: Nicotiana Sylvestris produce a range of alkaloids which are toxic to insects. These chemicals defend against damage to leaves and flowers by herbivores. Nicotine is the most dominant of alkaloid produced by the plant. It is produced in response to leaf damage to further deter pests, but it is difficult to prevent it from mixing with the plant’s nectar and thus it can also deter pollinators (Sierro et al., 2013).

References

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3. Dingaan, M. and J. du Preez, P. (2019) Vachellia (Acacia) karroo Communities in South Africa: An Overview. In book: Pure and Applied Biogeography
4. Freire, G., Nascimento, A., Malinov, I., Diniz, I. (2014). Temporal Occurrence of Two Morpho Butterflies (Lepidoptera: Nymphalidae): Influence of Weather and Food Resources. Environmental Entomology, 43(2), pp.274-282.
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10. Moore, B., Foley, W., Wallis, I., Cowling, A., Handasyde, K. (2005). Eucalyptus foliar chemistry explains selective feeding by koalas. Biology Letters, 1(1), pp.64-67.
11. National Wildlife Federation. (2019). Rhinoceros Beetles | National Wildlife Federation. [online] Available at: https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Rhinoceros-Beetles [Accessed 30 Oct. 2019].
12. Savethekoala.com. (2019). Diet & Habitat | Australian Koala Foundation. [online] Available at: https://www.savethekoala.com/about-koalas/diet-habitat [Accessed 30 Oct. 2019].
13. Sierro, N., Battey, J. N., Ouadi, S., Bovet, L., Goepfert, S., Bakaher, N., … Ivanov, N. V. (2013). Reference genomes and transcriptomes of Nicotiana sylvestris and Nicotiana tomentosiformis. Genome biology, 14(6)
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15. Thomas BT (1996) Family Opisthocomidae (Hoatzin). In: del Hoyo J, Elliott A, Sargatal J (eds) Handbook of the birds of the world, vol 3. Hoatzin to Auks. Lynx Edicions, Barcelona, pp 24–32
16. Wright, A.-D. G.; Northwood, K. S.; Obispo, N. E. (2009). ‘Rumen-like methanogens identified from the crop of the folivorous South American bird, the hoatzin (Opisthocomus hoazin)’. The ISME Journal. 3 (10): 1120–1126