Release vocalizations in neotropical toads (Bufo): ecological constraints and phylogenetic implications

The release vocalizations of four nominal neotropical toad taxa (Bufo achal ensis, Bufo limensis, Bufo spinulosus, Bufo arenarum) which compose three s ympatric species pairs, were quantitatively analysed and homologous call ty pes statistically compared. The first three laxa are closely related member s of the mainly Andean Bufo spinulosus species group in which advertisement calls are absent. The specific vocal repertoire consisted of a uniform, un pulsed release call and one (in B. arenarum, two) pulsed release trill(s) w hich were given either singly or in series of up to three single calls. The uniform call was similar in structure and dominant (= basic) frequency in all taxa and probably represents an unspecific acoustic signal which is use d to avoid heterospecific amplexus between sympatric toads. The release tri lls significantly differed in most call features among the taxa and, using discriminant analyses, even single calls were correctly assigned to sympatr ic pairs of species. In contrast, calls of allopatric pairs of species were confounded at rates of up to 36% indicating that selection towards species -specific signals increases when different species live in sympatry. The re lease trills of two allopatric populations (Peru, Argentina) assigned to B. spinulosus were similar in structure, but nevertheless features of pulse t rain permitted an unequivocal distinction, suggesting a long-lasting indepe ndent evolution. The taxonomic significance of this finding remains to be e valuated in further investigations. The complex vocal repertoire also offer ed the opportunity to assess phylogenetic relationships among the taxa. The extra-Andean B. achalensis seems to be closer related to the Andean B. spi nulosus than this species is to the widely sympatric B, limensis - a specie s with several primitive character states indicating an early separation fr om the ancestral stock.