Why The Hawaiian Jackson's Chameleons Have Often Deformed Horns?

Some chameleons of the genus Trioceros have developed impressive anatomical features, which has led to the naming of their genus as the "three-horned" (Trioceros). Within this genus, having horns is primarily a characteristic of the males, which can have between one and six horns depending on species or subspecies. Among these, the so-called "true horned chameleons" possess spiky bony protrusions on their heads that are covered by a thick layer of keratin, a protein that forms the outer layer of the skin in reptiles and other animals.

The most well-known member of this genus is Jackson's three-horned chameleon, native to Tanzania and Kenya, and popular in the pet trade. This popularity has led to many of these chameleons being transported thousands of miles to the Hawaiian Islands, where they have become feral and are now considered an invasive species. Studies have shown that the Hawaiian population of Jackson's chameleons originated from a small number of individuals that were imported, specifically relating to the subspecies T. j. xantholophus, which were wild-caught from the eastern slopes of Mount Kenya.

While genetic studies indicate that the Hawaiian Jackson's chameleons are identical to the natural populations in Kenya, they exhibit some differences that may result from their new environment. The founders of the Hawaiian population numbered around only 30 individuals, which limits genetic diversity and may contribute to observable variations.

Interestingly, research has suggested that Hawaiian Jackson's chameleons are more brightly colored than their Kenyan counterparts. However, it's crucial to note that the Kenyan specimens studied may not represent the full range of color variation within the subspecies, as they were collected from a transitional zone near Nairobi, which typically hosts significantly less vibrant individuals than the population around Meru. Therefore, the conclusion that the Hawaiian chameleons are brighter should be approached with caution.

Additionally, many of the Jacksons Chameleons available in the U.S. pet trade are sourced from Hawaii, despite regulations against such practices. One notable difference observed by many keepers and noted by herpetologists is that Hawaiian Jackson's chameleons frequently exhibit crooked, uneven, and non-straight horns. These horns may be shorter or point in various directions, such as upwards, which is a stark contrast to their Kenyan counterparts, where such deformities are extremely rare. While some specimens in Kenya have been reported to show minor developmental abnormalities, the prevalence of deformed horns in Hawaiian chameleons raises intriguing questions about the underlying causes. Especially when we take into consideration, that in parallel, horn developmental abnormities are very frequent in captivity.

To explore this phenomenon, we can frame our investigation around three essential questions:

1. What purpose do the chameleons' horns serve?

Primarily, horns in chameleons, particularly in males, are believed to play significant roles in sexual selection and species recognition. They may serve as visual signals to attract mates or as a display of strength and fitness during territorial disputes. 

Secondarily, the horns of male chameleons are utilized in combat between territorial males. These horns play a significant role in physical confrontations as they help assert dominance and push opponents from branches, forcing them to fall and retreat. This behaviour is a crucial aspect of territorial disputes, where males compete for access to resources and mates.

Thirdly, the horns of chameleons may also play a role in anti-predatory mechanisms. In this context, the horns can serve as a defensive weapon when threatened by predators, allowing the chameleon to point or display their horns in a way that could deter an attacker. Additionally, the presence of these prominent features can make the chameleons appear larger, more formidable, or less palatable to potential predators, such as snakes that swallow their prey whole. This adaptation could enhance their survival by making it more challenging for predators to consume them. By leveraging their physical traits, chameleons can not only defend themselves but also potentially influence a predator's decision to engage. 

2. What factors contribute to the proper symmetrical and straight growth of horns

The growth of horns is influenced by several factors, including genetic predisposition, environmental conditions, and nutritional availability during development. In a stable, natural habitat, chameleons may develop more evenly shaped horns due to optimal conditions. 

The growth of horns in Jackson's chameleons is influenced by three key factors:

• Availability of Calcium: The original habitats of Jackson's chameleons in Kenya and Tanzania are often located in volcanic regions surrounded by vast areas rich in calcium carbonate (CaCO₃), commonly found in limestone sediments. Over time, harsh climatic conditions cause the limestone to degrade into dust, which is then carried by cyclones and winds. This dust, enriched with calcium, is deposited in mountainous areas with higher humidity and more frequent rainfall, making calcium readily available in the environment.

• Role of Vitamin D3: Vitamin D3, also known as cholecalciferol, is a fat-soluble vitamin composed of carbon, hydrogen, and oxygen. It plays a crucial role in calcium metabolism by facilitating the absorption of calcium in the gut. It helps regulate calcium levels in the blood and promotes bone health, which is essential for the proper development of horns in chameleons.

• Importance of UV Rays: Ultra-violet (UV) rays from sunlight are essential for synthesizing vitamin D3 in reptiles. Exposure to UV radiation enables chameleons to produce vitamin D3 in their skin, which subsequently enhances calcium absorption. 

The interplay between calcium availability, vitamin D3 metabolism, and UV radiation is vital for the healthy growth of horns in Jackson's chameleons.

3. What causes developmental abnormalities in horn formation?

Developmental abnormalities in chameleon horns can arise from various factors, including genetic issues, environmental stressors, injuries and health problems. Captive conditions can introduce numerous challenges, such as inadequate lighting, improper diet, or limited space, which can contribute to abnormal horn growth. Additionally, inbreeding among a limited gene pool, as observed in the Hawaiian population, can lead to increased occurrence of genetic issues, resulting in deformities.

However, the most probable reasons for abnormal horn development in Jackson's chameleons are as follows:

• Lack or Shortage of Calcium: The wild environments where Jackson's chameleons reside may have specific conditions that limit the availability of calcium necessary for proper bone growth. In captivity, this issue can be exacerbated if calcium supplementation is insufficient, leading to deficiencies.

• Insufficient Vitamin D3: A lack of adequate vitamin D3 is another significant factor, particularly in captive settings. 

• Improper lighting that does not provide enough UV exposure is the reason, the synthesis of vitamin D3 from provitamins is not triggered effectively.

In summary, insufficient UV exposure and limited availability of calcium can hinder chameleons' ability to synthesize vitamin D3, resulting in impaired calcium metabolism and, consequently, abnormal horn development. These deficiencies highlight the importance of providing appropriate environmental conditions for chameleons, both in the wild and in captivity.

Calcium in Sedimentary vs. Volcanic Environments

The content of calcium (Ca) in the environment and in biomass can differ significantly between sedimentary rock areas and volcanic regions.

Calcium in Sedimentary vs. Volcanic Environments

1. Sedimentary Rock Areas:

• Source: Sedimentary rocks often contain calcium carbonate (CaCO₃) and other calcium-rich minerals, particularly in depositional environments like marine or freshwater settings.

• Calcium Availability: The weathering of these rocks can release calcium into the soil and water, leading to higher concentrations of bioavailable calcium in the ecosystem.

• Biomass: Plants and animals in these areas often show higher calcium concentrations, as they derive their nutrients from the soil rich in calcium.

2. Volcanic Areas:

• Source: Volcanic soils, particularly those from basaltic lava, tend to be rich in minerals like magnesium and iron but have lower calcium content compared to sedimentary soils.

• Calcium Availability: Over time, weathering processes can release some calcium, but it may not be as abundant as in sedimentary environments. The initial volcanic ash can be nutrient-rich but may lack certain minerals until fully weathered.

• Biomass: Vegetation in volcanic areas may show different mineral compositions, often adapted to the unique nutrient profile and pH of the soil.

Situation in Hawaii

Hawaii Islands present a unique case due to its volcanic origin:

Volcanic Soil Composition:

• Hawaii Island is primarily composed of volcanic rock, particularly basalt, resulting from the activity of the Hawaiian hotspot.

• The volcanic soils (Andosols) are typically rich in nutrients initially but have lower calcium levels than more mature soils found in sedimentary regions.

Calcium Dynamics:

• Over time, weathering processes and the addition of organic matter can increase the availability of calcium in the soil, but it may still not reach the concentrations found in sedimentary environments.

• The leaching of soils due to rainfall and runoff can also affect calcium levels in the ecosystem.

Biomass and Plant Adaptation:

• The native flora of Hawaii has adapted to the volcanic soil conditions, showing tolerance to varying nutrient availability, including calcium.

• Different plant species have developed mechanisms to acquire nutrients effectively in such environments, but overall, the calcium content in biomass may be lower compared to plants from calcium-rich sedimentary environments.

In summary, while sedimentary areas tend to have higher and more bioavailable calcium levels, volcanic areas like those on Hawaii Island have different dynamics that can affect calcium availability and biomass composition. The unique geological and ecological context of Hawaii necessitates careful study to understand the nuances of nutrient cycling in its volcanic soils.

Conclusion: 

The Jackson's chameleons in Hawaii have crooked horns so often due to limited availability of calcium in their environment of volcanic origin.

The curse of snail diet

One very interesting phenomenon surrounding Jackson's chameleons, particularly in Hawaii, is their interaction with snails. In their native volcanic habitats, these chameleons have developed specific behaviors that enhance their calcium intake compared to chameleons from other regions. Notably, they have a well-documented preference for feeding on snails, a behavior that became widely recognized through the efforts of German herpetologist Günther Masurat and his wife, Irene, who conducted extensive research in captivity.

Fecal analysis often yields limited evidence of mollusks in their diet because snail shells and bodies are easily digested, leaving no undigested matter. Rarely, a radula—the specialized feeding structure of snails—can be detected in fecal samples. I have confirmed this through hundreds of fecal samples collected from both wild and freshly imported chameleons from Kenya, indicating that snails are indeed part of their diet.

This evolutionary adaptation has persisted for millions of years, and as Jackson's chameleons migrated to the Hawaiian Islands, they continued to incorporate snails into their diets. The Hawaiian snail species they feed on, including certain native species (Achatinella mustelina) that are small and fragile, reflecting the limited availability of calcium in Hawaii environments.

Unfortunately, evidence has emerged that Jackson's chameleons in Hawaii also feed on these endangered native mollusks. This has fueled concerns about their status as an invasive species, as studies suggest they negatively impact local snail populations. However, it is important to note that the decline of some snail species is primarily attributed to habitat loss due to extensive human activities such as deforestation and intensive agriculture. This critical context is often overlooked, as chameleons are wrongly blamed for being predators responsible for the decline of these vulnerable snail populations.

In summary, while Jackson's chameleons' feeding behavior on snails is a fascinating example of adaptation, it also highlights the complexities of their ecological interactions in a new environment and the need for a nuanced understanding of their impact on native species. Their adaptation that supports survival in one location can paradoxically become a liability in a new territory.

A particularly bizarre aspect of this situation is that these chameleons are blamed for the consequences of habitat disruption and species decline caused evidently and predominanrly by human activities. Ironically, it is humans (Homo sapiens) who introduced them to Hawaii, yet the chameleons bear the brunt of the criticism for ecological imbalances stemming from the very actions of the "hairless apes" that brought them there. This underscores the importance of addressing the root causes of ecological issues and recognizing the roles that invasive species and humans play in shaping ecosystems.

ADDITIONAL READING

Proper calcium metabolism in reptiles is crucial for their overall health, growth, and development, particularly for bone health and physiological functions. Here are the essential factors that contribute to proper calcium metabolism in reptiles:

1. Dietary Calcium:

• Calcium Intake: Reptiles require a diet rich in calcium. This can come from whole prey items (like rodents for carnivores) or specifically formulated diets for herbivores that are calcium-enriched.

• Supplementation: In captivity, calcium supplements (often in the form of calcium carbonate or calcium citrate) may be necessary, especially for species that do not obtain sufficient calcium from their diet.

2. Vitamin D3:

• Cholecalciferol (Vitamin D3): This vitamin is essential for calcium absorption in the intestines. Reptiles can synthesize vitamin D3 through exposure to ultraviolet B (UVB) radiation from sunlight.

• UVB Exposure: Providing appropriate UVB lighting in captivity is critical for preventing metabolic bone disease (MBD) and ensuring adequate calcium absorption.

3. Phosphorus Balance:

• Phosphorus Ratio: The balance of calcium to phosphorus in the diet is important. An appropriate ratio is typically around 2:1 (calcium to phosphorus) for most reptiles. Excess phosphorus can inhibit calcium absorption.

• Dietary Sources: Care should be taken with the provision of certain foods that are high in phosphorus (e.g., certain legumes and seeds) relative to their calcium content.

4. Environmental Temperature:

• Thermoregulation: Reptiles are ectothermic (cold-blooded) animals, meaning they rely on ambient temperature to regulate their body functions. Optimal temperatures are necessary for proper digestion and metabolic processes, including calcium absorption.

• Basking: Providing basking areas with appropriate temperatures allows reptiles to thermoregulate effectively, aiding in digestion and nutrient absorption.

5. Hydration:

• Water Intake: Adequate hydration is necessary for the proper metabolic processing of calcium and other nutrients. Dehydration can impair metabolic functions and lead to health issues.

• Calcium Regulation: Water helps in the proper excretion of excess calcium and maintains overall physiological homeostasis.

6. Health and Stress Management:

• Stress Factors: Chronic stress can negatively impact calcium metabolism by disrupting hormonal balance, including hormones like parathyroid hormone (PTH) and calcitonin, which regulate calcium levels in the body.

• Health Monitoring: Regular health checks and minimizing stressors (such as improper housing or handling) can help ensure optimal calcium metabolism.

7. Bone Health:

• Bone Turnover: Calcium is vital for bone health. Adequate intake ensures that bones remain strong and are less susceptible to fractures and deformities.

• Prevention of Metabolic Bone Disease (MBD): Insufficient calcium, vitamin D3 deficiency, or poor dietary balance can lead to MBD, causing weakness and deformities in bones.

Conclusion

To facilitate proper calcium metabolism in reptiles, it is essential to provide a balanced diet, ensure adequate UVB exposure for vitamin D3 synthesis, maintain proper environmental temperatures, and manage hydration and stress levels. Proper understanding and management of these factors will lead to better health outcomes and reduced risk of related disorders in reptiles.

courtesy Carson Fillin: development of correctlky developed horns in captivity due to perfect captive care