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Vocal competition in male Xenopus laevis frogs - PubMed

  • ️Fri Jan 01 2010

Vocal competition in male Xenopus laevis frogs

Martha L Tobias et al. Behav Ecol Sociobiol. 2010.

Abstract

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.

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Figures

Fig. 1
Fig. 1

The amount and timing of advertisement calling and clasps made by each male while paired. Top vocally dominant male P (solid bars) calls throughout the experiment while the vocally subordinate male M (open bars) calls only once. The number of clasps (indicated above bars) made by each male is similar for the two males. Bottom two vocally similar males, R (solid bars) and Q (open bars) call during most of the recording session and rarely clasp

Fig. 2
Fig. 2

Establishing a linear vocal hierarchy. The duration over which pairs of frogs within a group were tested (bar length), the number of times each pair met (“X”), the number of individuals in the group (“N”) are shown to the left of each bar; the probability of rejecting the null-hypothesis (that frogs do not form a linear hierarchy) is shown above each bar. (A, B) Groups tested over a brief (<2 weeks) period, (B) examines hierarchy stability. The same group is tested initially and at a later date. Lines represent the time during which animals are individually housed between the first and second test periods. (C) Groups tested over a longer (>3 weeks) period. (B, C) Examines effect of the number of competitions

Fig. 3
Fig. 3

Vocal status in groups that do not form linear hierarchies. Each graph represents one experiment shown in Fig. 2 in which a linear hierarchy was not established. Each graph shows the total amount of time spent calling (left y-axis) for each male (x-axis) and the number of times he called more than any other male with which he was paired (“wins”; right y-axis). Individuals are identified by letters; however, since each graph represents one group, the same letter in different graphs represents different animals. a Group shown in Fig. 2 (B2), right. b group shown in Fig. 2 (C1), c group shown in Fig. 2 (C2). For c, the amount of time spent calling is summed over the three trials

Fig. 4
Fig. 4

Auditory cues alone are sufficient for male vocal suppression. a The amount of advertisement calling produced by males before and during playbacks of advertisement calls from a single male is shown. b The normalized amount of calling in response to advertisement calls from three highest-ranking (filled symbols) and three lowest-ranking (open symbols) males before, during, and after playbacks is shown

Fig. 5
Fig. 5

Advertisement calling in response to all fast, all slow, and control trills. a Sample oscillo-graphs (amplitude vs time) of the control (biphasic; top), all slow trill (middle), and all fast trill (bottom). b The normalized amount of calling in response to the three stimuli is shown. Lines connect data from the same animal. Data from males that discriminate (left) and do not discriminate (right) between all fast and all slow trills are shown separately

Fig. 6
Fig. 6

The effect of sound intensity on advertisement calling. a The normalized amount of advertising in response to each intensity playback is shown (mean ± SD). Significance levels are indicated between bars. b The amount of time spent calling produced by each male (indicated by a symbol) before, during each of the three stimuli, and after playback. Note that only one male, indicated by a filled diamond, calls more to high, than to intermediate or low-intensity stimuli

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