ACOUSTIC COMMUNICATION IN THE TOADFISH, HALOBATRACHUS DIDACTYLUS: THE ROLE OF ACOUSTIC SIGNALS IN MATE ATTRACTION AND PARENTAL CARE

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How effective are acoustic signals in territorial defence in the Lusitanian toadfish?

Publication . Conti, Carlotta; Fonseca, Paulo Jorge; Picciulin, Marta; Amorim, Maria Clara Pessoa

The function of fish sounds in territorial defence, in particular its influence on the intruder's behaviour during territorial invasions, is poorly known. Breeding Lusitanian toadfish males (Halobatrachus didactylus) use sounds (boatwhistles) to defend nests from intruders. Results from a previous study suggest that boatwhistles function as a 'keep-out signal' during territorial defence. To test this hypothesis we performed territorial intrusion experiments with muted Lusitanian toadfish. Males were muted by making a cut and deflating the swimbladder (the sound-producing apparatus) under anaesthesia. Toadfish nest-holder males reacted to intruders mainly by emitting sounds (sham-operated and control groups) and less frequently with escalated bouts of fighting. When the nest-holder produced a boatwhistle, the intruder fled more frequently than expected by chance alone. Muted males experienced a higher number of intrusions than the other groups, probably because of their inability to vocalise. Together, our results show that fish acoustic signals are effective deterrents in nest/territorial intrusions, similar to bird song.

2015Journal article

Open access

Vocal differentiation parallels development of auditory saccular sensitivity in a highly soniferous fish

Publication . Vasconcelos, Raquel Ornelas; Alderks, Peter W.; Ramos, Andreia; Fonseca, Paulo Jorge; Amorim, Maria Clara Pessoa; Sisneros, Joseph A.

Vocal differentiation is widely documented in birds and mammals but has been poorly investigated in other vertebrates, including fish, which represent the oldest extant vertebrate group. Neural circuitry controlling vocal behaviour is thought to have evolved from conserved brain areas that originated in fish, making this taxon key to understanding the evolution and development of the vertebrate vocal-auditory systems. This study examines ontogenetic changes in the vocal repertoire and whether vocal differentiation parallels auditory development in the Lusitanian toadfish Halobatrachus didactylus (Batrachoididae). This species exhibits a complex acoustic repertoire and is vocally active during early development. Vocalisations were recorded during social interactions for four size groups (fry: <2 cm; small juveniles: 2-4 cm; large juveniles: 5-7 cm; adults >25 cm, standard length). Auditory sensitivity of juveniles and adults was determined based on evoked potentials recorded from the inner ear saccule in response to pure tones of 75-945 Hz. We show an ontogenetic increment in the vocal repertoire from simple broadband-pulsed 'grunts' that later differentiate into four distinct vocalisations, including low-frequency amplitude-modulated 'boatwhistles'. Whereas fry emitted mostly single grunts, large juveniles exhibited vocalisations similar to the adult vocal repertoire. Saccular sensitivity revealed a three-fold enhancement at most frequencies tested from small to large juveniles; however, large juveniles were similar in sensitivity to adults. We provide the first clear evidence of ontogenetic vocal differentiation in fish, as previously described for higher vertebrates. Our results suggest a parallel development between the vocal motor pathway and the peripheral auditory system for acoustic social communication in fish.

2015Journal article

Open access

Agonistic sounds signal male quality in the Lusitanian toadfish

Publication . Amorim, Maria Clara Pessoa; Conti, Carlotta; Modesto, Teresa; Gonçalves, Amparo; Fonseca, Paulo Jorge

Acoustic communication during agonistic behaviour is widespread in fishes. Yet, compared to other taxa, little is known on the information content of fish agonistic calls and their effect on territorial defence. Lusitanian toadfish males (Halobatrachus didactylus) are highly territorial during the breeding season and use sounds (boatwhistles, BW) to defend nests from intruders. BW present most energy in either the fundamental frequency, set by the contraction rate of the sonic muscles attached to the swimbladder, or in the harmonics, which are multiples of the fundamental frequency. Here we investigated if temporal and spectral features of BW produced during territorial defence reflect aspects of male quality that may be important in resolving disputes. We found that higher mean pulse period (i.e. lower fundamental frequency) reflected higher levels of 11-ketotestosterone (11KT), the main teleost androgen which, in turn, was significantly related with male condition (relative body mass and glycogen content). BW dominant harmonic mean and variability decreased with sonic muscle lipid content. We found no association between BW duration and male quality. Taken together, these results suggest that the spectral content of fish agonistic sounds may signal male features that are key in fight outcome.

2015Journal article

Restricted access

Lusitanian toadfish song reflects male quality

Publication . Amorim, M. C. P.; Simoes, J. M.; Mendonca, N.; Bandarra, Narcisa M.; Almada, Vítor Carvalho; Fonseca, P. J.

Lusitanian toadfish males that provide parental care rely on acoustic signals (the boatwhistle) to attract females to their nest. We test the hypothesis that male quality, namely male size and condition that are relevant for parental success, is reflected in vocal activity and boatwhistle characteristics and thus advertised to females. We recorded 22 males over a week during the peak of the breeding season. Calling rate and calling effort (percentage of time spent calling) strongly reflected male condition (lipid content of somatic muscles) and to a smaller extent sonic muscle hypertrophy and larger gonads. Males in better condition (increased body lipid and relative higher liver mass) also contracted the sonic muscles at faster rate as shown by the shorter boatwhistle pulse periods. Amplitude modulation reflected the degree of sonic muscle hypertrophy. None of the measured male quality parameters were good predictors of boatwhistle duration and dominant frequency. Altogether this study strongly suggests that Lusitanian toadfish males advertise their quality to females primarily with boatwhistle calling rate and calling effort, which mainly reflect male condition. Because pulse period had low variability, consistent with the existence of a vocal central pattern generator, we suggest that males that sustain sonic muscles contraction at a very fast rate close to their physiological limit may be honestly advertising their quality (condition). Similarly, males that produce boatwhistles with higher amplitude modulation, a feature that seems dependent on sonic muscle hypertrophy, could be more attractive to females.

2010Journal article

Open access

Chorusing Behaviour in the Lusitanian Toadfish: Should I Match My Neighbours' Calling Rate?

Publication . Jordão, Joana; Fonseca, Paulo; Amorim, Maria Clara P

Choruses have been described mostly in birds, anurans and insects but have been poorly studied in fish. Research in batrachoidid (toadfishes) species suggest vocal facilitation among neighbouring males, but whether chorusing fish present more complex interactions is unknown. In this study, we test the hypothesis that chorusing fish males compete actively to increase attractiveness to females. We first describe vocal interactions in natural choruses of Lusitanian toadfish males. Our analysis found positive correlations between the calling rates of neighbouring males in several occasions. However, we also found that males that showed an overall low vocal activity throughout the observation period exhibited peaks of increased calling activity when neighbours decreased their calling rate, suggesting an opportunistic maximisation of attractiveness. We further test with playback experiments how toadfish males adjust calling activity relative to their neighbours’. We observed that males silent at the time of the playbacks but who had an overall high vocal performance tended to start calling when exposed to playbacks in contrast to low-activity males. Playback experiments further showed that males initially calling at a high rate adjust their calling rate according to the neighbour’s vocal activity level, that is, they increased calling rate when exposed to a high calling rate and decreased it when confronted with a low calling rate. However, males calling at a low rate did not significantly alter their calling rate when presented with a low (similar) or higher calling rate, probably due to temporary physiological and/or ecological constraints. We argue that Lusitanian toadfish males tend to optimise calling effort in relation to their neighbours when they are actively advertising. Further studies are necessary to better understand vocal behaviour with increased chorus size.

2012Journal article

Restricted access