CALL VARIATION IN THE BUFO-MICROSCAPHUS COMPLEX - IMPLICATIONS FOR SPECIES BOUNDARIES AND THE EVOLUTION OF MATE RECOGNITION

Since the Modern Synthesis, many species concepts have considered char acters mediating mate recognition essential to both the identification and definition of species. To explore divergence in mate recognition systems, calls were recorded and toads measured from all three species of the monophyletic Bufo microscaphus species complex including five populations of Bufo californicus, three populations of B. microscaphus , and one population of B. mexicanus. Call duration, dominant frequenc y, and pulse rate were significantly related to temperature, but not s nout-vent length. When adjusted for temperature, calls of B. californi cus,:had a significantly longer call duration, higher dominant frequen cy, and slower pulse rate than B. mexicanus and B. microscaphus, which did nor differ from one another. However, the magnitude of variation among Populations of B. californicus was similar to that between speci es. Discriminant analysis using call variables provided some separatio n of B. californicus and B. mexicanus From B. microscaphus, and cross- validation analysis correctly classified approximately 75% of B. calif ornicus and B. mexicanus. Given only slight divergence in mate recogni tion systems between B. californicus and the other two taxa, the biolo gical significance of this difference remains ambiguous. Comparisons a mong B. americanus group members indicate that hybridizing taxa may or may nor exhibit divergence in advertisement calls. Maintenance of ind ependently evolving lineages may be driven by other evolutionary mecha nisms: These results support the notion that species recognition is be st viewed as an effect of mate recognition.