Tawny dragon, Tawny crevice-dragon
Ctenophorus decresii, also known commonly as the tawny dragon or the tawny crevice-dragon, is a species of lizard in the family Agamidae. The species is endemic to Australia. The average snout-to-vent length (SVL) of the species is 80.76 mm (3.180 in) with larger individuals being around 89 mm (3.5 in) and smaller individuals around 72 mm (2.8 in). The optimal time for mating in this species is two to three weeks after the females emerge from hibernation. Eggs are typically laid from September to October with most of them being laid earlier in the period. C. decresii is known for its variations in throat colors which change based on environmental conditions. Its primary food sources consist of both vegetation and invertebrates, and it prefers to live in rocky habitats.
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TerrestrialTerrestrial animals are animals that live predominantly or entirely on land (e.g., cats, ants, snails), as compared with aquatic animals, which liv...
Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
Precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. Precocial species are normall...
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starts withC. decresii are often characterized by the color of their throats. Variations of color in these lizards were previously attributed to different levels in sexual maturity. However, these variations are most likely due to environmental conditions such as “maternal effects, incubation conditions or post-hatching conditions”. There is also a possibility that genetics are primarily responsible for the variations. The colors of male lizards can vary, but they are usually orange only, yellow only, orange surrounded by yellow, or grey only throats. The colors can also vary in degree of intensity and are due to different lineages, northern and southern. Males with orange throats tend to be more aggressive when it comes to defending their territory. It is still unclear how the lineages of females impact the expression of their colors especially since females from wither lineage tend to have the same coloration. From this, it can be concluded that throat color in these lizards is polymorphic, specifically in determining whether the phenotype is yellow or orange. Although both colors are polymorphic, the yellow color is also greatly influenced by environment and levels of testosterone present. Polymorphism and environmental factors play major roles in color expression, but it is impossible to say which one is more significant without genomic analysis and linkage mapping.
Magnetic resonance imaging (MRI) has been used on the tawny dragon lizards to examine their brains. A study found that the brain had 224 structures that could be seen. The left hemisphere in the brain is associated with the optic system. This research was fundamental in the study of evolutionary neuroscience in lizards. By having the neuroanatomy of lizards, scientists are able to see how behavior and cognitive function are related to structures of the brain.
The intensity of colors in these lizards indicates the amount predation they are susceptible to. As expected, individuals with more brightly colored bodies are at a higher risk of predation, because they are more easily spotted. In these habitats, the rocks in which the lizards bask are darker, so the bright oranges and yellows contrast greatly Individuals that are not as bright, or duller, are attacked significantly less than their brightly colored counterparts. The main predator of the tawny dragon lizard is birds. C. decresii are a species that use crypsis as a defense mechanism, however females use this mechanism more than males. Although more prevalent in females, both sexes use the coloration to blend it with their surroundings. The exact colors depend on the environment, but the colorations are usually localized to the exposed body regions, so individuals can avoid predation.
Depending on the environmental conditions, C. decresii can be more or less conspicuous. Typically, the most abundant rock colors are grey or orange. The colors differ in the region where the lizards reside. Dorsal and lateral coloration are vital in ensuring individuals in either region are not as susceptible to predators. The lizards are least conspicuous when their color matches the abundant rock color of their region. When individuals are placed in the opposite region, they are at a much more conspicuous/noticeable. However, individuals can still use behavioral tactics to protect themselves from predators even though they stand out more.
C. decresii consume a wide variety of foods and are omnivores. Their main diet consists of invertebrates and vegetation. Invertebrates include crickets, moths, fly maggots, and locusts.
C. decresii are characterized by their ability to produce multiple clutches in a year but a short lifespan. Incubation temperature affects the hatchling tail length and sex. At intermediate incubation temperatures, the proportion of males to females was much higher compared to extreme incubation temperatures (very high or very low) where females were the only sex seen. This shows that the season in which the females lay the eggs is good indicator of which sex will be seen in the hatchlings and body size, also known as temperature-dependent sex determination. Very low incubation temperatures are often associated with slower, less developed hatchlings. If incubated at a suitable temperature, hatchlings will have a higher body mass. These individuals will also have a higher probability of reproductive success especially in terms of clutch size and offspring body mass. Studies suggest that body mass is also influenced by the length of incubation. Eggs laid closer to the beginning of the season have more time to develop thus giving them more of an opportunity to gain more body mass. On the other hand, those laid later in the season do not have the same opportunity. Larger body sizes provide an advantage to males and females. Males are better able to defend their territories, and females have higher fecundity. Males with more territory also had larger body masses.
As mentioned in the description section, the coloration of the male tawny dragon lizards can vary, especially by region (northern and southern). For mating, southern females are more likely to mate with southern males however, they are much less selective in their mate preferences than northern females. Both southern and northern males are more likely to be rejected by northern females. Southern males also prefer to mate with southern females because they share the same lineage. This suggests that preferences by either sex are driven by behavioral differences regionally. These lizards primarily prefer to mate with partners that are in the same region geographically. Overall, it appears that speciation is primarily driven by sexual selection with neither sex being more selective than the other.
