There are several research papers and studies that you can refer to for Paper II of the UPSC Zoology Optional Subject. These papers and studies can provide you with valuable insights, information, and references that can enhance your understanding of the subject. Here are a few examples:

1. "Evolutionary Biology of the Genus Drosophila" by J.B.S. Haldane:
- This seminal paper discusses the evolutionary biology of the fruit fly genus Drosophila, which has been extensively studied in genetics and evolutionary biology.
- It provides insights into various aspects of Drosophila biology, including their mating behavior, reproductive strategies, genetic variation, and adaptation.

2. "The Role of Hormones in Animal Behavior" by Niko Tinbergen:
- This influential study explores the role of hormones in animal behavior and how they mediate various behavioral responses.
- It discusses examples from different animal species, highlighting the importance of hormonal regulation in activities such as aggression, courtship, and parental care.

3. "Ecology and Behavior of the African Elephant" by Cynthia Moss:
- This research paper focuses on the ecology and behavior of African elephants, providing a comprehensive understanding of their social structure, communication, feeding habits, and conservation issues.
- It presents data and observations from long-term field studies conducted in African elephant populations.

4. "The Origin of Species" by Charles Darwin:
- This groundbreaking book by Charles Darwin is a must-read for any student of zoology.
- It outlines the theory of evolution by natural selection and provides a comprehensive understanding of how species originate, adapt, and diversify.

5. "Animal Behavior: An Evolutionary Approach" by John Alcock:
- This textbook is a valuable resource for understanding animal behavior from an evolutionary perspective.
- It covers a wide range of topics, including behavioral ecology, sociobiology, and the evolutionary basis of animal behavior.

By referring to these research papers and studies, you can gain a deeper understanding of various aspects of zoology and develop a strong foundation in the subject. Remember to cite the sources appropriately in your paper and use the information to support your arguments and analysis.