Electric communication during courtship and spawning in two sibling species of dwarf stonebasherfrom southern Africa, Pollimyrus castelnaui and P. marianne (Mormyridae, Teleostei): evidence for anon species-specific communication code

摘要

The fixed part of the electrocommunication signal,-the electric organ discharge (EOD) waveform, is well differentiated in the two vicariant dwarf stonebasher species, Pollimyrus castelnaui and P. marianne. However, differentiation regarding the variable, situation-dependentpart, i.e., inter-discharge interval (IDI) patterns, has never been studied in a pair of siblingspecies of mormyrid fish. We here compare the electrical signalling that accompanies different motor behaviours (such as resting and swimming, territorial agonistic interactions,courtship and spawning) in the two species. Double pulse patterns of regularly alternatingshort IDIs of 8-11 ms and long ones of 16-100 ms accompanied threat displays in bothspecies. In three pairs of P. marianne and five pairs of P. castelnaui, courtship was characterised by nest building, territory patrolling and acoustic displays (advertisment calls) thatwere accompanied by long discharge breaks in the male and highly regular IDIs around 50ms in the female of both species. Nest-tending males showed IDI sequences consisting ofregularly alternating double pulse patterns, similar to threat displays. During spawning bothsexes generated stereotyped IDI sequences of a low discharge rate. All IDI patterns occurringin one species were also found in the other, and no species-specifity was identified at thatlevel. Playback experiments contrasting conspecific and heterospecific IDI sequences (thathad been recorded from nocturnally swimming fish) revealed preferences in none of the sixexperimental subjects. Double pulse patterns, high discharge rate displays (HD) and regularisations of the IDI sequence accompanying specific'behaviours occurred in similar form inboth dwarf stonebasher species of the present study. Therefore, we conclude that in the speciation of P. castelnaui and P. marianne the fixed part of the EQD, its waveform, was undermore differential selection pressure than its variable part, the patterns of IDI.