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The anuran vocal sac: a tool for multimodal signalling.

Starnberger I, Preininger D, Hödl W - Anim Behav (2014)

Bottom Line: The diversity in vocal sac coloration and shape found in different species is striking and recently its visual properties have been given a more important role in signalling.Chemosignals seem to be the dominant communication mode in newts, salamanders and caecilians and certainly play a role in the aquatic life phase of anurans, but airborne chemical signalling has received less attention.Thus, the anuran vocal sac might be of great interest not only to herpetologists, but also to behavioural biologists studying communication systems.

View Article: PubMed Central - PubMed

Affiliation: University of Vienna, Department of Integrative Zoology, Wien, Austria.

ABSTRACT
Although in anurans the predominant mode of intra- and intersexual communication is vocalization, modalities used in addition to or instead of acoustic signals range from seismic and visual to chemical. In some cases, signals of more than one modality are produced through or by the anuran vocal sac. However, its role beyond acoustics has been neglected for some time and nonacoustic cues such as vocal sac movement have traditionally been seen as an epiphenomenon of sound production. The diversity in vocal sac coloration and shape found in different species is striking and recently its visual properties have been given a more important role in signalling. Chemosignals seem to be the dominant communication mode in newts, salamanders and caecilians and certainly play a role in the aquatic life phase of anurans, but airborne chemical signalling has received less attention. There is, however, increasing evidence that at least some terrestrial anuran species integrate acoustic, visual and chemical cues in species recognition and mate choice and a few secondarily mute anuran species seem to fully rely on volatile chemical cues produced in glands on the vocal sac. Within vertebrates, frogs in particular are suitable organisms for investigating multimodal communication by means of experiments, since they are tolerant of disturbance by observers and can be easily manipulated under natural conditions. Thus, the anuran vocal sac might be of great interest not only to herpetologists, but also to behavioural biologists studying communication systems.

No MeSH data available.


Related in: MedlinePlus

Male cinnamon-bellied reed frog, Hyperolius cinnamomeoventris, with inflated vocal sac. The gular gland and prominent blood vessels are clearly visible in the centre of the vocal sac.
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fig2: Male cinnamon-bellied reed frog, Hyperolius cinnamomeoventris, with inflated vocal sac. The gular gland and prominent blood vessels are clearly visible in the centre of the vocal sac.

Mentions: Furthermore, there is increasing evidence that the vocal sac might also play a role in chemical signalling. In the family of African reed frogs (Hyperoliidae) there is substantial variation in body coloration, morphology and reproductive modes, but males of all reed frog species share a common feature: a prominent gular patch on the vocal sac, which is particularly conspicuous once the vocal sac is inflated (Fig. 2). Although the presence, shape and form of the gular patch are well-known diagnostic characters for these frogs, its function remained unknown until recently. Starnberger et al. (2013) demonstrated that the gular patch is a gland (Fig. 3) and produces species-specific volatile compound mixtures, which might be emitted while the male is calling. In the most species-rich hyperoliid genera (Afrixalus, Heterixalus, Hyperolius and Phlyctimantis) the proposed signal cocktails consist of 65 different compounds, whereas specific combinations of sesquiterpenes, alcohols and macrolides are correlated with species identity (Starnberger et al., 2013). Additionally, a surprisingly high contrast between the gular patch and the surrounding vocal sac skin makes the gland stand out from its background and might serve as a visual cue facilitating the localization of a male calling in dense vegetation (I. Starnberger, own observations). Thus, reed frogs might use a complex combination of acoustic, visual and chemical signals in species recognition and mate choice, so far not described in any other terrestrial anuran. Hyperoliids often call in mixed choruses with closely related species without an apparent spatial segregation (Lötters et al., 2004; Schiøtz, 1999), and multimodal signals might have evolved to avoid mismating and to facilitate navigation towards a conspecific mate in dense vegetation. In one genus of the family Hyperoliidae, Rödel, Kosuch, Veith, and Ernst (2003) described two mute species which may rely solely on chemical communication via their gular glands. Several further behavioural observations suggest chemical communication in a different social context. For example, in Fausto's button frog, Cycloramphus faustoi, males were observed to rest their vocal sac on egg clutches, possibly to transmit pheromones that influence larval development (L.F. Toledo, personal communication). In Canebrake frogs, Aplastodiscus perviridis, males rest their vocal sac on females suggesting pheromone transmission during courtship (Haddad, Faivovich, & Garcia, 2005).


The anuran vocal sac: a tool for multimodal signalling.

Starnberger I, Preininger D, Hödl W - Anim Behav (2014)

Male cinnamon-bellied reed frog, Hyperolius cinnamomeoventris, with inflated vocal sac. The gular gland and prominent blood vessels are clearly visible in the centre of the vocal sac.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4222773&req=5

fig2: Male cinnamon-bellied reed frog, Hyperolius cinnamomeoventris, with inflated vocal sac. The gular gland and prominent blood vessels are clearly visible in the centre of the vocal sac.
Mentions: Furthermore, there is increasing evidence that the vocal sac might also play a role in chemical signalling. In the family of African reed frogs (Hyperoliidae) there is substantial variation in body coloration, morphology and reproductive modes, but males of all reed frog species share a common feature: a prominent gular patch on the vocal sac, which is particularly conspicuous once the vocal sac is inflated (Fig. 2). Although the presence, shape and form of the gular patch are well-known diagnostic characters for these frogs, its function remained unknown until recently. Starnberger et al. (2013) demonstrated that the gular patch is a gland (Fig. 3) and produces species-specific volatile compound mixtures, which might be emitted while the male is calling. In the most species-rich hyperoliid genera (Afrixalus, Heterixalus, Hyperolius and Phlyctimantis) the proposed signal cocktails consist of 65 different compounds, whereas specific combinations of sesquiterpenes, alcohols and macrolides are correlated with species identity (Starnberger et al., 2013). Additionally, a surprisingly high contrast between the gular patch and the surrounding vocal sac skin makes the gland stand out from its background and might serve as a visual cue facilitating the localization of a male calling in dense vegetation (I. Starnberger, own observations). Thus, reed frogs might use a complex combination of acoustic, visual and chemical signals in species recognition and mate choice, so far not described in any other terrestrial anuran. Hyperoliids often call in mixed choruses with closely related species without an apparent spatial segregation (Lötters et al., 2004; Schiøtz, 1999), and multimodal signals might have evolved to avoid mismating and to facilitate navigation towards a conspecific mate in dense vegetation. In one genus of the family Hyperoliidae, Rödel, Kosuch, Veith, and Ernst (2003) described two mute species which may rely solely on chemical communication via their gular glands. Several further behavioural observations suggest chemical communication in a different social context. For example, in Fausto's button frog, Cycloramphus faustoi, males were observed to rest their vocal sac on egg clutches, possibly to transmit pheromones that influence larval development (L.F. Toledo, personal communication). In Canebrake frogs, Aplastodiscus perviridis, males rest their vocal sac on females suggesting pheromone transmission during courtship (Haddad, Faivovich, & Garcia, 2005).

Bottom Line: The diversity in vocal sac coloration and shape found in different species is striking and recently its visual properties have been given a more important role in signalling.Chemosignals seem to be the dominant communication mode in newts, salamanders and caecilians and certainly play a role in the aquatic life phase of anurans, but airborne chemical signalling has received less attention.Thus, the anuran vocal sac might be of great interest not only to herpetologists, but also to behavioural biologists studying communication systems.

View Article: PubMed Central - PubMed

Affiliation: University of Vienna, Department of Integrative Zoology, Wien, Austria.

ABSTRACT
Although in anurans the predominant mode of intra- and intersexual communication is vocalization, modalities used in addition to or instead of acoustic signals range from seismic and visual to chemical. In some cases, signals of more than one modality are produced through or by the anuran vocal sac. However, its role beyond acoustics has been neglected for some time and nonacoustic cues such as vocal sac movement have traditionally been seen as an epiphenomenon of sound production. The diversity in vocal sac coloration and shape found in different species is striking and recently its visual properties have been given a more important role in signalling. Chemosignals seem to be the dominant communication mode in newts, salamanders and caecilians and certainly play a role in the aquatic life phase of anurans, but airborne chemical signalling has received less attention. There is, however, increasing evidence that at least some terrestrial anuran species integrate acoustic, visual and chemical cues in species recognition and mate choice and a few secondarily mute anuran species seem to fully rely on volatile chemical cues produced in glands on the vocal sac. Within vertebrates, frogs in particular are suitable organisms for investigating multimodal communication by means of experiments, since they are tolerant of disturbance by observers and can be easily manipulated under natural conditions. Thus, the anuran vocal sac might be of great interest not only to herpetologists, but also to behavioural biologists studying communication systems.

No MeSH data available.


Related in: MedlinePlus