OPUS: MCS: Mechanisms and evolution of premating reproductive isolation along a speciation continuum

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A central question in evolutionary biology is how and why a trillion forms of life, both living and extinct, have emerged. Speciation—the formation of new species— can proceed when two groups of organisms no longer recognize each other as mates due to differences in relevant traits such as behavior (e.g., songs) or appearance (e.g., coloration). This research quantifies the behavioral and neural mechanisms that mediate female mate recognition and preference to understand how speciation proceeds. Researchers will measure female response to males from differentiated populations of the same species (pre-speciation stage) and to males of two closely related species (post-speciation stage), thus spanning a continuum of species-level differentiation. Researchers will first conduct behavioral studies to identify the strength and role of relevant traits in courtship and mating success at each stage. Next, female response will be linked to activation patterns in the regions of the brain associated with visual, acoustic and courtship processing. Examination of neural de-activation patterns in the courtship region of the brain along the speciation continuum addresses a gap in knowledge of whether speciation proceeds gradually or abruptly. This research builds upon 17 years of genetic and behavioral studies of the Neotropical red-eyed treefrog, Agalychnis callidryas, to understand the mechanisms and processes of early-stage speciation. It supports diverse students to experience science in the field and in the lab, and creates active-learning content for ~120 students in an enrichment program at the K5 grade level (82% underserved minority, 60% Free/Reduced Lunch). Finally, this research fosters international collaboration between U.S. and Costa Rican research biologists.This collaborative research provides new and exciting insights into the evolution of signal divergence, female recognition and neural activity patterns, and the consequences of these factors for premating reproductive isolation and speciation. This research has two specific aims. Aim 1 examines female response to divergent cues through both female preference assays and neural activation patterns to test whether incremental increases in trait divergence result in a continuous or all-or-none neural response. Aim 2 tests how mismatched cues alter neural activity response patterns, addressing whether mismatched cues weaken/break courtship response. Neural response will be measured using immunohistochemistry and microscopy. Combined, these two aims identify how the trait(s) that are important for stimulating courtship behavior modulate neural activity function, and thus provide mechanistic insight into how premating reproductive isolation evolves. Computational modeling will explore the dynamic relationship among signal differentiation and female response (behavior and neural activity) using simulated data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.