Final answer:
The main disadvantage of asexual reproduction for whiptail lizards that reproduce via parthenogenesis is a lack of genetic diversity, leading to potential problems with adaptability and increased susceptibility to diseases.
Step-by-step explanation:
One disadvantage of asexual reproduction for species like whiptail lizards that reproduce through parthenogenesis is the lack of genetic diversity. Since the offspring are genetically identical to the mother, they all share the same vulnerabilities to diseases and environmental changes. In contrast, sexually reproducing organisms benefit from a mix of genetic traits from both parents, which can provide a better chance of survival in changing environments and against various diseases. Thus, a major downside of asexual reproduction is the potential for decreased adaptability and increased risk of extinction if the environment shifts or if a disease to which the species is susceptible becomes widespread.