Abstract
BackgroundChemical communication plays a critical role in sexual selection and speciation in fishes; however, it is generally assumed that most fish pheromones are passively released since most fishes lack specialized scent glands or scent-marking behavior. Swordtails (genus Xiphophorus) are widely used in studies of female mate choice, and female response to male chemical cues is important to sexual selection, reproductive isolation, and hybridization. However, it is unclear whether females are attending to passively produced cues, or to pheromones produced in the context of communication.Methodology/Principal FindingsWe used fluorescein dye injections to visualize pulsed urine release in male sheepshead swordtails, Xiphophorus birchmanni. Simultaneous-choice assays of mating preference showed that females attend to species- and sex-specific chemical cues emitted in male urine. Males urinated more frequently in the presence and proximity of an audience (conspecific females). In the wild, males preferentially courted upstream of females, facilitating transmission of pheromone cues.Conclusions/SignificanceMales in a teleost fish have evolved sophisticated temporal and spatial control of pheromone release, comparable to that found in terrestrial animals. Pheromones are released specifically in a communicative context, and the timing and positioning of release favors efficient signal transmission.
Highlights
A fundamental concern of animal communication is when and where to emit signals
Males showed a substantial increase in urination rate when in the presence of females as opposed to when females were absent (WSR test: z = 2.073, n = 9, p = 0.038; Figure 3)
Males spent much more time in quadrant 1, the area closest to females, when females were present in the adjacent stimulus tank (72% versus 39% when females were absent; Wilcoxon signed-rank (WSR) test: z = 2.666, n = 9, p = 0.008)
Summary
A fundamental concern of animal communication is when and where to emit signals. While some signals, like many morphological ornaments, are always ‘‘on,’’ most signals like song, advertisement calls, and motor displays are emitted in a way that optimizes transmission to intended receivers [1]. E. the ‘audience effect,’ [3] and in such a way as to optimize transmission in the physical environment [4] Such tactical signaling has contributed to the effectiveness of chemical communication across taxa. Swordtails (genus Xiphophorus) are widely used in studies of female mate choice, and female response to male chemical cues is important to sexual selection, reproductive isolation, and hybridization. It is unclear whether females are attending to passively produced cues, or to pheromones produced in the context of communication
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