Signal Synchrony and Alternation Among Neighbor Males in a Japanese Stream Breeding Treefrog, Buergeria japonica

Abstract

Animals that aggregate in leks to attract mates often time the production of their mating signals against the signals of neighboring conspecifics. Such signal timing usually falls into general patterns within these aggregations, which can be categorized based on the amount of overlap between the signals. In many species, individuals produce signals in an alternating pattern, avoiding signal overlap to reduce interference and increase mate attraction. In contrast, individuals in some species produce signals in synchrony, maximizing overlap and interference. The prevalence and function of signal synchronization is still unknown in many species. Here we examine the call timing strategies of the Ryukyu Kajika frog (Buergeria japonica). Using acoustic playback experiments we characterize a divergence in timing patterns between the two call types in this species, one produced in alternation and one in synchrony. Specifically, male B. japonica responded to playbacks of the first call type (Type I calls) with delayed Type I calls, avoiding overlap with the playbacks. In contrast, males responded to playbacks of the second call type (Type II calls) with synchronized Type II calls, overlapping their calls with the playbacks. Such variation in temporal signaling strategies within a species provides insights into how social and environmental pressures shape signal timings.

The dual benefits of synchronized mating signals in a Japanese treefrog: attracting mates and manipulating predators

“…The signalling behaviour of B. japonica , for example, has been the focus of previous studies [38,40], including the population on Iriomote Island [39] where this study was performed. Yet, synchronization in B. japonica has only recently been described and discussed [37]. Even in long-studied and common anuran species, signal synchronization has received limited consideration.…”

“…During their breeding season, March to October, males of this species form choruses along the banks of streams and roadside ditches [36]. Chorus attendance is correlated with rainfall, and large choruses of over 300 males have been observed on nights following periods of heavy rains [37]. Although specific calling behaviour is variable between populations, calls are generally divided into two types, one of which is produced in synchrony [37].…”

“…Chorus attendance is correlated with rainfall, and large choruses of over 300 males have been observed on nights following periods of heavy rains [37]. Although specific calling behaviour is variable between populations, calls are generally divided into two types, one of which is produced in synchrony [37]. This synchronized call is a trill of variable duration (ranging from less than 0.5 s to more than 3.0 s [38]) with a dominant frequency around 3 kHz and likely plays a role in attracting mates [39,40].…”

“…This synchronized call is a trill of variable duration (ranging from less than 0.5 s to more than 3.0 s [38]) with a dominant frequency around 3 kHz and likely plays a role in attracting mates [39,40]. Male B. japonica respond to the calls of neighbouring males at an average latency of 0.35 ± 0.05 s, resulting in around 70% overlap in call duration between leading and following calls [37]. In addition, B. japonica calls attract multiple species of eavesdropping insects (figure 1 a ), frog-biting midges ( Corethrella spp.)…”

“…In other systems, such as frogs in the Neotropics, the same eavesdropper collection methods result in capturing hundreds of frog-biting insects in the same 45 min period [34,70]. In addition, B. japonica produce two calls types, a synchronized call type (the focus of our study) and a call type that is produced in alternation between neighbouring males [37]. When both call types are broadcast without overlap, both eavesdropping midges and mosquitoes prefer the alternating call type [71].…”