The 2019/2020 Australian Bushfires caused 10 million hectares to burn, which affected 1,25 billion wildlife. Koalas in Australia and around the world are at risk of extinction. The Koala has seen a decline in population since European settlement began in Australia. The decline of the Koala population is partly due to the introduction of new threats that the population was not anatomically equipped to handle.
Koalas rely on climbing to move from one branch to another. Comparing Koalas to their closest terrestrial relatives, the Wombats, will help describe the Koalas’ functional anatomy in relation to climbing. Koalas share many characteristics with Wombats. These include a similar dentition pattern, a posteriorly oriented marsupium, and a vestige tail. Koalas use their sedentary climbing and feeding position to develop palms with medial facings to allow them grip trees. Wombats on the other hand have palms with plantigrades to provide stability and even pressure distribution. Koalas are able to supinate their forelimbs more easily thanks to the bowed radius. Wombats, on the other hand, have a radius that is compact and restricts them from doing so (Fig.2) This skeletal configuration is good for climbing. However, it can make it difficult for Koalas to move from one habitat to another in search of food or mates. Koalas share the same elongated forelimbs as Wombats. Arboreal species are known to have increased stride-lengths, which may reduce peak forces during the traverse of narrow branches. The slenderness of the humerus prevents an excessive amount of terrestrial locomotion. A lack of a significant olecranon is also responsible for reducing stability at the elbow when it comes to weight bearing. Koalas have opposable halluxes on both feet and hands to provide them with extra grip strength. All of their digits feature large, curled claws, which allow them to grip on bark and hold onto a branch (Young 1882) or secure their position. But they also make it difficult to move on land, because the claws force the limbs to be stretched out, and the hands and foot to be splayed. This leads to a significant amount of lateral movement when the limbs swung. This claw reduces the speed of locomotion on land as it increases the stance phase because the digits are more dependent on the precise placement for the application of pressure (Gaschk Frere Clemente, 2019,). In the same way as the forelimbs, the hindlimb’s musculature has been adapted to invert it. In addition, there is no soleus or iliac attachment in the gluteus extensus. There is also only a single origin to the biceps and gracilis. This muscular arrangement also results in reduced hip mobility, which is a major factor in the biomechanical inefficiency in terrestrial movement. (Grand & Barboza 2001). Koalas have a low speed on the land, and they do not travel in packs. They are therefore more susceptible to road fatalities and predator attacks. Recent climate change and human settlement have led to an increase in fragmentation of the Eucalyptus forest (Narayan & Williams, 2016). Koalas spend a long time traveling over land in search of food, water or mates. Koalas don’t have many predators so they aren’t able to protect themselves. Koalas can’t thrive in the peri-urban area because of the intense human activity. The Koala’s diet has also influenced their adaptations, which are a major factor in their disadvantage. Koalas are one of few species capable of digesting and absorbing the energy and nutrients from the Eucalyptus tree leaf. Koalas have a caecum that is enormous in comparison to their body size. Koalas have been referred to as some of the most specialized folivores in mammals (Shipley Forbey Moore, 2009). The Eucalyptus is the main part of their diet, accounting for over 93% (Grand, Barboza and Moore, 2001). Koalas might have adapted by eating Eucalyptus as the leaves are toxic to most other animals (Moore and Foley 2000). Koalas’ Eucalyptus leaf diet is notoriously low-energy and hard to digest. Koalas are known to require 19-22 hrs/day for eating and sleeping in order to satisfy their basal energy needs. As they are unable spare energy to socialise or move around excessively, the Koala leads a sedentary existence. Koalas are unable to spare the energy for excessive movement or socialising, so their basal metabolic rate is lower than average (Grand & Barboza, 2001). In order to conserve energy, they have adopted a number of metabolic conservationist strategies. Koalas use a thick, insulating pelt to keep warm, despite the high winds in the treetops. Koalas try to stay cool by pressing their thin skin against the cool ground and bark. These methods may reduce the energy required to maintain a body temperature, but their insulating fur led to the species’ exploitation by the pelt-trade in the nineteenth and twentieth centuries. This resulted millions of deaths. As climate change intensifies, leading to more extreme weather, and as their habitat fragments, it’s unlikely that these species can maintain a healthy temperature with just these methods. Koalas may die from overheating or dehydration due to a lack of water and the increasingly rare shade. Koalas get 91% of energy from Eucalyptus from digesting its contents and not the cell wall. Koalas grind their jaws to reduce cell walls. This increases the surface of the mouth, which will promote fermentation. The dentition has been adapted by the species to maximize the amount of cell content exposed (Lanyon & Sanson, 1986). Koalas grind leaves with their mandibulars in a lateral motion before swallowing. Their large mouths allow them to chew more food. A decreasing brain size is evident in fossils as mastication was given more importance, resulting in larger masticatory musculature and their attachment site (Grands and Barbozas, 2001; Louyset al. (2009)). Grand and Barboza described a Koala’s skull in 2001 as “a chewing-machine housing a small mind”. Smith (1979), who hypothesized koalas may lack social skills and adaptability because of their smaller brains compared to their body sizes, suggested that this could be the case. Smith argued that as they were not opportunistic creatures, such as primates and carnivores like humans, they could simply evaluate whether what was in front them was palatable by looking at it, its smell or moisture content without needing to assess their surroundings. Moore and Foley, (2000) as well as Ellis et.al. (2010) confirm these findings. (2010). Koalas can be limited by their inability to process different environments due to the small size of their heads. They may also reject good food because they are not able to differentiate between species. It is partly due to plant secondary metabolites that the Eucalyptus tree is toxic. Koalas have a higher detoxification ability, so they can digest the plant. But this doesn’t mean the PSMs don’t have any impact on Koalas. Their uncontested food access comes with a price. PSMs still reach high levels in the bloodstream and have been proven to be immunomodulatory in many animals, including Koalas. PSMs are known to reduce expression of important signaling glycoproteins used by immune cells. This results in a decrease or complete negation of the effectiveness for certain immune responses pathways. Suppression of immune pathways, however, may have made it easier to adapt to low-energy foods by reducing some energy-demanding immune reactions. This may have worked in the past relative to the benefits that came with an uncontested source of food, but it’s possible this trade-off no longer works in their favor. Habitat degradation reduces dietary diversity, which is crucial in regulating PSM concentrations. New diseases that are associated with new species or habitats also pose a massive threat to the population. Chlamydia infection is one of the biggest threats to Koalas. It was introduced by sheep, cattle and early humans. Of the two chlamydial strains seen in Koalas, Chlamydia pecorum (C.pecorum) is the most prevalent and pathogenic, and infection can result in severe symptoms such as blindness (caused by keratoconjunctivitis), urinary incontinence, cystitis, infertility, reproductive tract lesions, bursitis, pneumonia and, in severe cases, death (Gonzalez-Astudillo et al., 2019). As many as 88% Koalas infected are either infected or infected both with these chlamydials. The infertility that C.pecorum can cause is well documented (Robbins, et.al.,2018). It is difficult to manage infection in populations when 66% of male carriers are asymptomatic (Hulse, 2020). Due to their increased detoxification capabilities, Koalas need a longer treatment cycle of 35-40 days to treat diseases like chlamydials. Kollipara et al. (2012). It is stated that the only solution to eradicate or control the disease among the Koalas population would be to create a vaccination with the fewest booster immunisations possible. But the cost and trauma of capturing, restraining and treating these animals means that this solution will be a while off. Narayan, Williams and Hulse (2016) suggested that Koalas suffer from immunosuppression due to the stress they experience when humans invade their area. (2020) found that the areas with the highest C.pecorum prevalence were peri-urban, an area known to be stressful for wildlife. Stress can cause a decrease in reproduction, development and feeding. This in turn leads to increased mortality. Inbreeding rates are also higher among Koalas, especially in South Australia, where islands have been formed from just two or three individuals. Low genetic variations can lead to morphological disorders, decreased reproduction success, and even inbreeding. As a result, populations with high levels of inbreeding will be less able to survive harsh environmental conditions. Koalas have been adapted well in one environment. But, because of human interference, their adaptations to this particular environment are changing. They now face significant disadvantages. Koalas are facing unprecedented threats. Their deaths could be caused by disease, bushfires and introduced predators. It may also result from an inability of the Koala to survive in harsh climates. Koalas are not able to adapt as quickly to changes in their environment because they lack phenotypic flexibility.
