In anurans, male clasps can elicit release calls from either sex. Male release calls have been observed in many anuran genera and this vocal response is thus highly conserved. Female release calls, however, are not as prevalent, suggesting that evolutionary trajectories for anuran release calls differ by sex. We analyzed male and female release calls in all available species of Xenopus, a fully aquatic African genus. Phylogenetic relationships in this genus include three species groups, two of which are clades and one of which is characterized by a reticulated phylogeny due in part to hybridizations between species with different ploidy levels (Evans et al., 2004; Evans, 2008). In all species, males produce release calls when clasped by another male. Females in the reticulated group do not produce release calls, but females in the rest of the genus do. Release calls consist of click trains of variable durations and inter-call intervals. In both sexes, inter-click interval divides the genus into groups with different click rates and these groups are phylogenetically related. In general, inter-click interval is shorter in male than in female release calls. Across species and sexes, release calls are characterized by a single, low (∼1000 Hz) dominant frequency. In X. laevis Congo and X. borealis, clasp duration is longer for male–female than for male–male pairs and clasp duration is correlated with the number, but not the duration, of release calls in male–male pairs. We discuss evolutionary scenarios for release call traits as well as the sex difference in occurrence.

Male Xenopus laevis frogs produce underwater advertisement calls that attract gravid females and suppress calling by male competitors. Here we explore whether groups of males establish vocal ranks and whether auditory cues alone suffice for vocal suppression. Tests of male–male pairs within assigned groups reveal linear vocal dominance relations, in which each male has a defined rank. Both the duration over which males interact, as well as the number of competitive opportunities, affect linearity. Linear dominance across the group is stable for about 2 weeks; rank is dynamic. Males engage in physical interactions (clasping) while paired but clasping and vocal rank are not correlated. Playbacks of advertisement calls suppress calling and calls from high- and low-ranking males are equally effective. Thus, auditory cues alone suffice to suppress vocal behavior. Playback intensities equivalent to a nearby male advertising effectively suppress calling while low-intensity playbacks are either ineffective or stimulate vocal behavior. X. laevis advertisement calls are biphasic, composed of alternating fast and slow click trills. Approximately half the males tested are more vocally suppressed by all slow than by all fast trills; thus, these males can distinguish between the two phases. The fully aquatic family Pipidae diverged from terrestrial ancestors approximately 170 mya. Vocal suppression in the X. laevis mating system may represent the translation of an ancient anuran social strategy to underwater life.

Salter-Harris type I (SH-I) fractures of the distal fibula are commonly encountered in pediatric orthopedics. We describe 2 unique cases of adolescents with completely displaced SH-I distal fibula fractures that were treated operatively. In the first case, a closed reduction attempt failed and the patient required open reduction and internal fixation of the distal fibula and syndesmosis. The syndesmotic ligaments were avulsed from the distal fibular metaphysis. In the second case, closed reduction of the distal fibula fracture was partially successful, but anatomic reduction could not be achieved without open reduction. The distal fibula fracture was fixed with an intramedullary screw. We believe this pattern of injury represents a variant of the adolescent transitional ankle fracture. Because the distal tibial physes were nearing complete closure in these patients, the energy propagated through the distal fibular physis. To the best of our knowledge, this combination of injuries has not been previously reported. This type of physeal fracture raises concern for premature physeal closure, fibular growth disturbance, syndesmotic instability, and medial (deltoid ligament) injury. Both patients had excellent outcomes after anatomic reduction and fixation of the displaced SH-I distal fibula fractures at 1 and 6 years of follow up, respectively.