AI-generated avatars in science communication offer potential for conveying complex information. However, highly realistic avatars may evoke discomfort and diminish trust, a key factor in science communication. Drawing on existing research, we conducted an experiment (n = 491) examining how avatar realism and gender impact trustworthiness (expertise, integrity, and benevolence). Our findings show that higher realism enhances trustworthiness, contradicting the Uncanny Valley effect. Gender effects were dimension-specific, with male avatars rated higher in expertise. Familiarity with AI and institutional trust also shaped trust perceptions. These insights inform the design of AI avatars for effective science communication while maintaining public trust.