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Male courtship acoustic signals from five Lake Malawi cichlid fish species of the Pseudotropheus zebra complex were recorded and compared. Sounds made by males of P. zebra, Pseudotropheus callainos and the undescribed species known as Pseudotropheus ‘zebra gold’ from Nkhata Bay, and Pseudotropheus emmiltos and Pseudotropheus faizilberi from Mphanga Rocks, differed significantly in the number of pulses and in pulse period. The largest differences in acoustic variables were found among the sympatric Mphanga Rocks species that, in contrast to the other three species, show relatively minor differences in male colour and pattern. These findings suggest that interspecific mate recognition is mediated by multimodal signals and that the mass of different sensory channels varies among sympatric species groups. This study also showed that sound peak frequency was significantly negatively correlated with male size and that sound production rate increased significantly with courtship rate.
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Species differences in courtship acoustic signals among
five Lake Malawi cichlid species (Pseudotropheus spp.)
*Unidade de Investigacx˜
ao em Eco-Etologia, ISPA, Rua Jardim do Tabaco 34, 1149-041
Lisboa, Portugal, Departamento de Biologia Animal e Centro de Biologia Ambiental,
Faculdade de Ci^
encias da Universidade de Lisboa. Bloco C2 Campo Grande,
1749-016 Lisboa, Portugal and §Department of Biological Sciences,
University of Hull, HU6 7RX, U.K.
(Received 16 April 2007, Accepted 13 December 2007)
Male courtship acoustic signals from five Lake Malawi cichlid fish species of the Pseudotropheus
zebra complex were recorded and compared. Sounds made by males of P. zebra,Pseudotropheus
callainos and the undescribed species known as Pseudotropheus ‘zebra gold’ from Nkhata Bay,
and Pseudotropheus emmiltos and Pseudotropheus faizilberi from Mphanga Rocks, differed
significantly in the number of pulses and in pulse period. The largest differences in acoustic
variables were found among the sympatric Mphanga Rocks species that, in contrast to the other
three species, show relatively minor differences in male colour and pattern. These findings
suggest that interspecific mate recognition is mediated by multimodal signals and that the mass
of different sensory channels varies among sympatric species groups. This study also showed
that sound peak frequency was significantly negatively correlated with male size and that sound
production rate increased significantly with courtship rate. #2008 The Authors
Journal compilation #2008 The Fisheries Society of the British Isles
Key words: acoustic communication; courtship; mate choice; P. zebra complex; reproductive
isolation; sound production.
Cichlids from the African Great Lakes have undergone some of the fastest and
most extensive adaptive radiations among vertebrates (Turner, 1999; Albertson
et al., 2003). From Lake Malawi alone, at least 450–600 endemic species have
been recorded (Genner et al., 2004). Most of these species are believed to have
arisen within the lake catchment within a relatively short period of time, esti-
mated at between 700 000 and 4 million years (Turner, 1999; Genner et al.,
2007). Many authors have proposed that sexual selection driven by female
choice acting on male courtship colours may be a significant influence on the
†Author to whom correspondence should be addressed. Tel.: þ351 218811700; fax: þ351 218860954;
Journal of Fish Biology (2008) 72, 1355–1368
doi:10.1111/j.1095-8649.2008.01802.x, available online at
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rapid speciation of these fishes (Dominey, 1984; McKaye, 1991; Genner &
Turner, 2005). Visual cues were found to be relevant for interspecific mate rec-
ognition (Knight & Turner, 1999; Jordan et al., 2003), but recent studies have
pointed out that chemical (Plenderleith et al., 2005) and acoustic (Amorim
et al., 2004) signals may also be important.
The recognition of species-specific acoustic signals can promote reproductive
isolation and influence speciation processes in sympatric species (Ryan &
Rand, 1993; Wells & Henry, 1998). Species recognition based on mating acous-
tic signals has been suggested for several teleosts (Crawford et al., 1997;
Amorim et al., 2004) and was verified in damselfishes (Pomacentridae) (Myrberg
et al., 1978; Spanier, 1979). Males of several African cichlids are known to pro-
duce sounds during courtship (Lobel, 1998; Amorim et al., 2004; Amorim, 2006).
A preliminary study by Amorim et al. (2004) found statistically significant differ-
ences between some variables of the sounds produced in the early stage of court-
ship by males of three closely related species from Lake Malawi, Pseudotropheus
zebra (Boulenger, 1899), Pseudotropheus ‘zebra gold’ (Ribbink et al., 1983) and
Pseudotropheus callainos Stauffer & Hert, 1992. If these differences are detected
by females and influence mating decisions, acoustic communication may have an
important role in the evolution of reproductive isolation and consequently on
the impressive rate of speciation of these fishes.
In the present study, male courtship sounds of five Pseudotropheus species
from Lake Malawi are compared: three sympatric species (P. zebra,P. ‘zebra
gold’ and P. callainos) exhibit distinct colours and patterns, while the other
two species [Pseudotropheus emmiltos (Stauffer, Bowers, Kellogg & McKaye,
1997) and Pseudotropheus fainzilberi Staeck, 1976] inhabiting another region
in the lake are less divergent in their appearance. It is predicted that if species
differences in courtship sounds are important in assortative mating, then acous-
tic signals will be more divergent among sympatric species that differ less in
visual cues, such as in P. emmiltos and P. fainzilberi.
The study species belong to the P. zebra complex, one of the most-species rich mbuna
cichlid groups endemic to Lake Malawi. These are also classed as members of the sub-
genus Maylandia, also known by the junior synonym Metriaclima (Stauffer et al., 1997).
Males of this species complex are similar in morphological traits but differ in their
breeding colours (Fig. 1). Pseudotropheus zebra,P. callainos and the undescribed species
P. ‘zebra gold’ co-occur in Nkhata Bay (Fig. 1), on the western shore of Lake Malawi
(11°369N; 34°179E) in reproductive isolation (van Oppen et al., 1998). Pseudotropheus
zebra males are blue with black vertical bars, P. callainos males are blue without bars
and P. ‘zebra gold’ males are yellow with brown vertical bars. At Mphanga Rocks
(10°459S; 34°679E) off the north-western shore of the lake (Fig. 1), P. emmiltos and
P. fainzilberi co-occur sympatrically. Males of both species are blue with dark vertical
bars, but differ in smaller details of their breeding colours: P. emmiltos males have
bright orange-red dorsal fins, while P. fainzilberi have blue dorsal fins with prominent
black horizontal bands.
Populations of the two sympatric groups do not differ in the degree of sympatry or
relatedness. All three populations at Nkhata Bay are fully sympatric, as are both at
1356 M. C. P. AMORIM ET AL.
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Mphanga Rocks. Although the study species at Nkhata Bay show microhabitat prefer-
ences, including some depth preference, substantial overlap in breeding ranges of all
three species have been demonstrated (van Oppen et al., 1998). Similarly, at Mphanga
Rocks, the depth range of P. fainzilberi was fully contained within that of P. emmiltos,
although individuals of the latter species were found at greater depths than those of the
former (pers. obs.). Phylogenetic relationships of the study taxa have not been fully
resolved. Mitochondrial DNA studies of mbuna populations have typically shown poor
phylogenetic resolution, with extensive sharing of polymorphisms even between mem-
bers of different genera. Genome-wide surveys of DNA polymorphisms (AFLPs) have
shown that all of the Pseudotropheus (Maylandia) complex populations from the north-
ern half of the lake (like the five taxa used in the present study) are very closely related
(Allender et al., 2003).
Males defend territories to which they try to attract females to spawn with by means
of a series of stereotyped visual displays (Baerends & Baerends van Roon, 1950), acous-
tic signals (Amorim et al., 2004) and chemical cues (Plenderleith et al., 2005). During
spawning, females take both eggs and sperm into their mouth, where the eggs are fer-
tilized, and leave the male territory to mouthbrood in quiet shelters for up to 3 weeks.
Each group of the studied sympatric species mate assortatively in the laboratory
(Knight et al., 1998; Plenderleith et al., 2005), indicating that reproductive isolation
can be maintained by direct mate choice alone.
All fishes used were first generation laboratory stock (c. 200 adults per species), bred
from parents collected at Nkhata Bay and Mphanga Rocks. Fishes were kept in 220 l
tanks in a 5500 l re-circulation system, with a density of c. 40 fishes per tank, under
a 12L:12D regime and fed on a mixture of commercial fish flakes and pellets. Water
temperature was kept at 25–27°C.
Pseudotropheus spp. males were recorded in experimental tanks (Nkhata Bay species:
two tanks 1200 600 450 mm high; Mphanga Rocks: four tanks (1000 500 400 mm
FIG. 1. Comparison of interspecific differences of male courtship acoustic signals was carried out using
five species from the northern-west part of Lake Malawi. Pseudotropheus fainzilberi and Pseudo-
tropheus emmiltos are native to Mphanga Rocks and males are blue with black vertical bars and
differ mainly in the colour of the dorsal fin. Pseudotropheus ‘zebra gold’, Pseudotropheus zebra and
Pseudotropheus callainos are found at Nkhata Bay. Males from the last three species differ more
extensively in their courtship colour, with P. ‘zebra gold’ exhibiting brown vertical bars on a yellow
background, P. zebra black vertical bars on a blue background, while P. callainos are plain blue.
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high) divided into three compartments by two opaque removable partitions. Lateral com-
partments (300 mm wide) held a single male, with a terracotta pot that served as refuge
and as a prospective spawning site, and the central compartment (c. 400 mm wide)
housed five to seven females throughout the experiment. Each tank housed a single spe-
cies. Recording tanks were placed on top of thick layers of rock–wool that insulated
tanks from external noise transmitted through floor vibrations. Males were left to accli-
matize for a minimum of 12 h before the start of recording trials.
Approximately 5–10 min prior to the start of a recording session all electric applian-
ces (aeration, filters and lights) were switched off. Each recording session started when
one of the opaque partitions was removed, allowing the focal male free access to fe-
males for 20 min, after which males were placed back in their lateral compartment.
Each male was recorded in a maximum of three sessions. Once recordings were com-
plete, the tested subject was weighed (mass, M), measured (standard length, L
), re-
turned to a stock tank and replaced with another male of the same species. Males
were identified by electronic tags that were previously inserted in their abdominal cavity
or by natural marks such as number of egg spots in the anal fin.
Sounds were recorded using two High Tech 94 SSQ hydrophones (High Tech Inc.,
Gulfport, MI, U.S.A.) (sensitivity of 165 dB re 1VmPa
) to improve the probability of
recording sounds close to the sound emitter, and a Pioneer DVD Recorder DVR-3100
(Tokyo, Japan) (sampling frequency 48 kHz, 24 bit resolution). This audio chain had a flat
frequency response up to 6 kHz 15 dB. Sounds were analysed with Adobe Audition
2.0 (Adobe Systems, Inc.) and Raven 1.2.1 for Windows (Cornell Lab of Ornithology).
Acoustic analysis only considered sounds associated with the behaviour quiver that is
characteristic of the early stages of courtship (Baerends & Baerends van Roon, 1950).
Moreover, only sounds that showed a clear structure, typically registered at a distance
of 1–2 total lengths of the focal fish, were analysed. Recorded sounds could be attributed
to the subject males because their intensity varied with distance from the hydrophone and
were consistently associated with particular courtship displays, such as quiver and circle
(Amorim et al., 2004).
The following acoustic variables were analysed (Fig. 2; Amorim et al., 2004): sound
duration (ms); number of pulses in a sound; mean pulse period (average peak-to-peak
interval between consecutive pulses, ms). In addition, two frequency peaks at c. 150 Hz
(PF1) and at 450 Hz region (PF2) were measured (Fig. 2). Temporal features were mea-
sured from oscillograms and peak frequencies from power spectra based on 2048 point
FFT with a Hamming window applied.
A total of 12 P. ‘zebra gold’, 12 P. zebra,13P. callainos,13P. fainzilberi and 14
P. emmiltos adult males were recorded and analysed (Table I provides details on male
size and number of sounds recorded per male).
During sound recording sessions male courtship behaviour was also tallied. Male
courtship behaviour includes the behavioural patterns quiver, dart, lead-swim and circle
(Baerends & Baerends van Roon, 1950; Amorim et al., 2004). Quiver rate (number
), courtship rate (total number of courtship activities min
) and sound produc-
tion rate (number min
) were considered for each recording session.
One-way ANOVA was used to compare differences among species in the duration,
number of pulses and pulse period of ‘quiver’ sounds. The square root transformation
was applied to the number of pulses to meet the ANOVA assumptions of normality
and homoscedasticity. Comparison among species for variables other than sound fre-
quency were not controlled for the effect of L
because the variables were not signifi-
cantly correlated with L
(Spearman rank correlation, r
,P>005; Amorim et al.,
1358 M. C. P. AMORIM ET AL.
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2004). Because the dominant sound frequency is dependent on male size (Amorim et al.,
2004), however, an ANCOVA was conducted to test differences among species for the
frequency variables PF1 and PF2, using L
as a covariate. The assumption of slope par-
allelism was tested before carrying out the above ANCOVA models (PF1 and PF2, both
d.f. ¼4, 54, P>005).
Spearman rank correlation, r
, was used to test whether quiver rate and courtship rate
were related to sound production rate in each species. In addition, sound production
rate was compared among species with ANOVA. Sound production rate was log
(xþ1) transformed to meet the ANOVA assumptions. An average of two recording
sessions were considered per male. All statistical analyses were conducted using Statis-
tica 7.1 for Windows (StatSoft, Inc.).
FIG. 2. (a) Oscillogram, (b) sonogram and (c) power spectrum of a typical courtship sound emitted by
males of Pseudotropheus spp. (P. fainzilberi in the example) during ‘quivering’. Some of the acoustic
variables measured are depicted in the figure: number of pulses (P is an example of a pulse), sound
duration (SDur), pulse period (PP), and peak frequency 1 (PF1) and 2 (PF2). Relative amplitude is
shown in the y-axis of the oscillogram and the power spectrum.
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TABLE I. Male Pseudotropheus spp. standard length (L
), mass (M) and number of analysed sounds. Values are mean (range)
P. ‘zebra gold’
P. zebra
P. callainos
P. fainzilberi
P. emmiltos
(mm) 1073 (890–1230) 1077 (880–1220) 977 (868–1150) 1187 (1090–1280) 1263 (1160–1390)
M(g) 388 (235–561) 405 (220–577) 287 (207–463) 539 (415–773) 653 (549–779)
Number of sounds 167 (4–33) 165 (4–40) 184 (14–27) 110 (4–23) 97 (4–17)
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Sound production by females was never observed during courtship interac-
tions in any species. Males courted females mostly by repeated sequences of
darting and quivering. During quivering, males from the five studied species
commonly produced low-frequency pulsed sounds (Table II and Fig. 3). Quiv-
ering behaviour could last longer than sound production especially after the
male emitted a few sounds.
When comparing all five Pseudotropheus species, no significant differences in
sound duration were found (ANOVA, d.f. ¼4, 59, P>005; Fig. 4). Sounds
lasted c. 700 ms in all species. The number of pulses differed significantly
among species (ANOVA, d.f. ¼4, 59, P<0001), with P. emmiltos producing
the greatest number of pulses per sound (mean ¼163 pulses), followed by P.
‘zebra gold’ (mean ¼127) and by the three other species (means ¼86–95;
Fig. 4). Pulse period also showed significant interspecific differences (ANOVA,
d.f. ¼4, 59, P<0001) with P. emmiltos producing pulses with significantly
shorter periods, i.e. at a faster rate than the remaining species, followed by
P. ‘zebra gold’ and P. callainos, and then by P. zebra and P. fainzilberi (Fig. 4).
Pseudotropheus ‘zebra gold’ and P. callainos did not differ significantly in pulse
period, nor did P. z e b r a and P. fainzilberi (Fig. 4). Mean pulse period was c. 50 ms
for P. emmiltos,70msforP. ‘zebra gold’ and P. callainos, and near 90 ms for the
remaining species. Neither PF1 (ANCOVA, d.f. ¼4, 58, P>005) nor PF2
(ANCOVA, d.f. ¼4, 58, P>005) differed among species after controlling for
the effect of male size (Fig. 4). Male L
decreased significantly PF1 (ANCOVA,
covariate L
,d.f.¼4, 58, P<005) and especially PF2 (ANCOVA: covariate
,d.f.¼4, 58, P<0001).
When comparing the two groups of sympatric species, the largest differences
in acoustic variables were found among the Mphanga Rocks species both for
number of pulses and pulse period. The largest mean pair-wise differences in
the acoustic variables of the Nkhata bay group were found between P. ‘zebra
gold’ and P. zebra that typically differed by 4 pulses and 21 ms in pulse period.
In contrast, mean differences between Mphanga Rocks species were almost
double than the previous and amounted to 7 pulses and 38 ms in pulse period.
Sound production rate was positively correlated with both quiver rate (n¼
12–29, P<0001) and total courtship rate (n¼12–29, P<0001) in all five
studied species. Sound production rate was significantly higher in P. emmiltos
than in the other four species (ANOVA, d.f. ¼4, 45, P<0001), with P.
emmiltos producing on average 14 sounds min
and the remaining species
07–08 sounds min
The present study demonstrated the existence of interspecific differences in
the courtship sounds of members of the P. zebra complex that may allow spe-
cies recognition. Males from the five species studied, including P. fainzilberi and
P. emmiltos which were studied for the first time, produced low frequency
pulsed sounds that differed in the number and rate of pulse production. These
sounds were produced mostly when males were quivering to females.
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TABLE II. Description of quiver-sound acoustic variables as overall mean (range), produced by males of Pseudotropheus spp. Overall means
and ranges are based on individual fish means
P. ‘zebra gold’
P. zebra
P. callainos
P. fainzilberi
P. emmiltos
Duration (ms) 7741 (5584–10224) 6717 (4214–8568) 6177 (3494–10327) 7226 (3978–11176) 7595 (3018–9874)
Number of pulses 127(7
9–199) 86(6
6–124) 95(6
4–147) 90(6
7–114) 163(9
Mean pulse
period (ms)
659 (527–782) 868 (675–1133) 725 (606–834) 867 (635–1080) 484 (314–616)
PF1 (Hz) 1518 (1348–2019) 1556 (1294–2207) 1497 (1324–1823) 1380 (1243–1514) 1337 (1120–1454)
PF2 (Hz) 4769 (4321–5449) 4888 (4239–5578) 5195 (4744–5668) 4732 (4378–5486) 4484 (4177–4851)
PF1, peak frequency 1; PF2, peak frequency 2.
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The Nkhata Bay species differed in number of pulses and pulse period, with
P. ‘zebra gold’ emitting longer sounds and with a higher number of pulses than
P. zebra and P. callainos, and P. zebra exhibiting lower pulse rates (i.e. longer
pulse periods). The present findings are consistent with the earlier study by
Amorim et al. (2004) who found that P. ‘zebra gold’ males produced sounds
with more pulses than P. callainos did.
According to the a priori hypothesis, P. fainzilberi and P. emmiltos from
Mphanga Rocks presented larger differences in pulse number and period
than the Nkhata Bay species, which showed greater differences in male colour.
FIG. 3. Oscillograms of typical courtship sounds emitted by males of (a) Pseudotropheus ‘zebra gold’, (b)
Pseudotropheus zebra,(c)Pseudotropheus callainos,(d)Pseudotropheus fainzilberi and (e) Pseudotropheus
emmiltos. Differences among species and especially in P. fainzilberi and P. e m m i l t o s can be observed in
number of pulses and in the pulse period. Sound amplitude (relative amplitude) in oscillograms is not
absolute and comparisons of this variable can only be made among pulses of the same sound.
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Similarly, Nelissen (1978) has found that the number of colour patterns and
sound types was inversely proportional in six Tanganyikan cichlid fishes.
In Pseudotropheus spp., as well as in other fishes, mate recognition and eval-
uation may involve the integration of different sensory components (Candolin,
2003). Acoustic signals of teleosts are thought to be part of a multimodal signal
system as they are usually produced in tight association with particular visual
displays (Amorim et al., 2004) and because playback of sound alone often fails
to elicit a response unless the sounds are accompanied by visual stimuli (Ladich,
2004). This study suggests that the acoustic sensory channel may have more
FIG. 4. Comparison of courtship mean S.E. sound variables: (a) duration, (b) number of pulses, (c) pulse
period (PP), (d) peak frequency 1 (PF1) and (e) peak frequency 2 (PF2) among the five species:
Pseudotropheus ‘zebra gold’ (PZG), Pseudotropheus zebra (PZ), Pseudotropheus callainos (PC),
Pseudotropheus fainzilberi (PF) and Pseudotropheus emmiltos (PE) ( , Nkhata Bay species; ,
Mphanga Rock species). Sample sizes were n(PZG) ¼n(PZ) ¼12; n(PC) ¼n(PF) ¼13; n(PE) ¼
14. Significant differences for pair-wise comparisons (Tukey test, P<005) are indicated by different
lower case letters. Notice that the largest differences in acoustic variables within bays were found
among the Mphanga Rocks species.
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weight in the multimodal courtship displays of the Mphanga Rocks species
than in the Nkhata Bay ones. Consistent with this suggestion, P. fainzilberi
and P. emmiltos failed to mate assortatively in laboratory mating trials when
females had access only to visual signals from males (Plenderleith et al., 2005).
Reports of sound production in other cichlid species indicate that they pro-
duce only one type of sound during courtship (Amorim, 2006), typically asso-
ciated with the quivering behaviour, an early courtship behaviour when mate
recognition is likely to occur (Amorim et al., 2004; Ripley & Lobel, 2005).
Other African cichlid species that are often closely related and sympatric also
differ in the pulse number, pulse rate and in sound duration (Lobel, 2001; Rice
& Lobel, 2004). These consistent differences in temporal patterning in cichlid
courtship sounds suggest that these signal variables may play a role in interspe-
cific recognition in sympatric species of cichlids, including members of the P.
zebra complex. In fishes as in other taxa, temporal information is important
for interspecific and intraspecific communication, such as species recognition
(Winn, 1964; Honda-Sumi, 2005). In other fishes, e.g. Pomacentridae, several
species of the genus Stegastes are sympatric and male courtship chirps show
species-specific duration, number of pulses and pulse repetition rate (Myrberg
et al., 1978; Lobel & Mann, 1995). Playback experiments have confirmed that
the number of pulses and pulse rate can promote species-specific recognition
(Myrberg et al., 1978; Spanier, 1979), demonstrating that species recognition
based on acoustic cues occurs in fishes. These experiments, however, did not
demonstrate that male chirps were effective in species isolation, as only the
male response to playbacks was measured.
Premating mechanisms among sympatric species are essential for the mainte-
nance of reproductive isolation in recently evolved species where hybridization
is still possible. Divergent mating signals can be effective mechanisms in pre-
venting hybridization (Qvarnstro
¨met al., 2006) and closely related species
may use different sensory channels to recognize conspecific mates (Rafferty
& Boughman, 2006). Recent studies involving members of the P. zebra complex
have emphasized the possible use of different sensory channels in the mainte-
nance of reproductive isolation among sympatric species and allopatric forms.
Choice experiments where olfactory and possibly also acoustic communication
were prevented suggested that male colour, shape and pattern are the most
important cues for mate recognition in some species (Jordan et al., 2003; Kidd
et al., 2006). In other P. zebra complex species, however, olfactory cues must be
present for preference for conspecific males to occur (Plenderleith et al., 2005).
Up to present there is no study that investigated the contribution of the acous-
tic channel for mate recognition by species of this rich group of Lake Malawi
cichlids. Nevertheless, in view of the diversity of acoustic signals it is possible
that different species may use this sensory channel balanced with the visual and
olfactory ones in interspecific and intraspecific recognition and mate choice.
Notably, other sound features did not differ among the Pseudotropheus spe-
cies but presented intraspecific variation associated with male traits, suggesting
that some sound variables of signalling males might contain information about
species identity while others could be used in the evaluation of conspecific
males and hence in intraspecific mate choice. Sound peak frequency, in partic-
ular PF2, was negatively correlated with fish size in all studied species with PF2
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decreasing on average by c. 22 Hz per mm increase in male L
. This inverse
relation between dominant frequency and fish size is common in cichlids
(Rowland, 1978; Amorim et al., 2003) and in other fishes (Myrberg et al., 1993),
and may be used by females as a cue in mate choice. For example, female dam-
selfishes (Pomacentridae) prefer sounds of lower frequency that, as in Pseudotro-
pheus spp. males, indicate a larger male body size (Myrberg et al., 1986). The
rate of sound production, that was positively correlated with quiver frequency
and total courtship frequency in all five Pseudotropheus species, could also be
used by females for assessing the condition and motivation of a conspecific male.
Females of several taxa commonly have a preference for males that show
a higher courtship display activity, as it may be related to higher genetic quality
or other preferred male traits (Svensson et al., 2004).
The present results suggest that different features of the courtship calls may
contain information about species identity and intraspecific differences in traits,
such as size, relevant to mate choice. In particular, the number of pulses and
pulse period of courtship sounds are species-specific and these acoustic cues,
in conjunction with visual and chemical information, may promote reproduc-
tive isolation. Finally, the present findings suggest that the weight of different
sensory channels used in interspecific mate recognition may vary among sym-
patric species assemblages.
This study was supported by a grant POSI SFRH/BPD/14570/2003 of FCT and the
pluriannual programmes (UI&D 331/94)/FCT (M.C.P.A.) and POCTI-ISFL-4-329/
FCT (P.J.F.). The Treaty of Windsor funded mutual visits between the Portuguese
and English teams. We are grateful to I. Duarte for assistance during some recordings,
and to N. Wreathall, A. Smith, K. Woodhouse and P. Nichols for help with logistics
and fish maintenance.
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Allender, C. J., Seehausen, O., Knight, M. E., Turner, G. F. & Maclean, N. (2003).
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... It has been well known for a long time that cichlids display complex behaviors during the behavior of mate selection (Baerends and Baerends-van Roon 1950;Keenleyside 1991;Barlow 2000). Cichlids are clearly multi-modal in their communication (Rosenthal and Lobel 2006;Amorim et al. 2008;Verzijden et al. 2010). Vision and coloration are key in the mate selection process for the Pseudotropheus zebra species complex of Lake Malawi (Couldridge and Alexander 2002). ...
... Species divergence in closely related sympatric cichlids, especially in the Great Lakes of Africa has been hypothesized to have occurred, in part, due to assortative mating. Cichlid mate choice studies confirm that assortative mating does occur in several species in the field and in captivity (Blais et al. 2009;Egger et al. 2008;Knight and Turner 2004; (1) Myrberg et al. (1965) Amorim et al. (2004Amorim et al. ( , 2008, Simoes et al. (2006); Simoes et al. (2008a, b), Bertucci et al. (2010), Van Staaden and Smith (2011), Danley et al. (2012), Bertucci et al. (2012a, b), Bertucci et al. (2013) Copadichromis conophorus Mchenga conophoros (Stauffer, LoVullo and McKaye, 1993) (2) Lobel (1998Lobel ( , 2001 Melanochromis auratus (Boulenger, 1897) (3) Smith (2007), Smith and Van Staaden (2009), Van Staaden and Smith (2011) Neochromis omnicaeruleus (Seehausen and Bouton, 1998) (1) Verzijden et al. (2010) Neolamprologus pulcher (Trewavas and Poll, 1952) (2) Spinks et al. (2017); Pisanski et al. (2015) Tilapia mossambicus Oreochromis mossambicus (Peters, 1852) (9) Rodman (1966), Konstantinova et al. (1979), Amorim et al. (2003), Amorim and Almada (2005), McPherson (2012), Pujiyati et al. (2016), Lanzing (1974), Marshall (1971Marshall ( , 1972 ...
... (3) Amorim et al. (2004Amorim et al. ( , 2008, Simoes et al. (2006) Pseudotropheus "zebra gold" x Maylandia zebra ...
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Bioacoustics has become a key feature of cichlid behavioral studies over the last 20 years, due in large part to new technologies and software. The hypothesis that some cichlid species produce species-specific sounds is gaining support with data from several studies. Sounds are specific to behavioral context for many species. Cichlids are advanced teleost fishes possessing a complex pharyngeal jaw. This morphological feature has been proposed as the key functional innovation responsible for the evolutionary success and explosive adaptive radiation of the group. This evolutionary success has been mostly attributed to their expanded adaptability to process a wide variety of food types due to the capability of thoroughly grinding food in the pharyngeal apparatus, an ability that most other fishes lack. The evidence regarding the role of the pharyngeal jaw complex in sound production is evaluated, and suggests that this same morphology enables cichlids to produce a complex and varied acoustic repertoire. Although, the sonic mechanism may be more complex morphologically than just the pharyngeals clacking. More studies are needed to carefully document the sounds correlated to specific behaviors of cichlids and to statistically examine the species specificity of sympatric species sounds. Future research is needed that experimentally tests the response of female fish to acoustic playback combined with visual and chemical cues in order to determine how critical sound communication is to the sympatric evolution of cichlid species.
... Cichlids are capable of producing a variety of different sounds involving the pharyngeal jaw, stridulation or body movements (Lobel 2001, Amorim 2006, Danley et al. 2012. Variation in acoustic parameters is observed across species, among different populations within species and sometimes even high levels of inter-and intraindividual variation are reported (Amorim et al. 2004, Amorim et al. 2008, Van Staaden and Smith 2011, Danley et al. 2012. Several studies show that cichlids are sensitive to the range of frequencies of the sounds they produce, but compared to goldfish (Carassius auratus), they appear to have poor sensitivity (Kenyon et al. 1998, Ladich and Wysocki 2003, Smith et al. 2004. ...
... Thus, predictions about the relative importance of acoustic cues, compared to visual and auditory ones, in mating are difficult to make and might differ between species. As with chemical signals, sounds alone appear not to be sufficient for mate attraction and only constitute effective signals in combination with visual/olfactory cues (Amorim et al. 2008, Estramil et al. 2014. Further evaluation of the contribution of acoustic cues to premating isolation will depend on future research investigating sound discrimination capability of cichlids. ...
... Cichlids also communicate through acoustic signals and produce a variety of sounds that are associated with agonistic interactions [141,142], courtship behavior, mate preference [143], and maintenance of species barriers [144,145]. Variation in sound detection can result from morphological differences in their inner ear (direct stimulation) or in their swim bladder (indirect stimulation). The swim bladder contains gas that is less dense than that in the fish body. ...
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Cichlid fishes are a very diverse and species-rich family of teleost fishes that inhabit lakes and rivers of India, Africa, and South and Central America. Research has largely focused on East African cichlids of the Rift Lakes Tanganyika, Malawi, and Victoria that constitute the biodiversity hotspots of cichlid fishes. Here, we give an overview of the study system, research questions, and methodologies. Research on cichlid fishes spans many disciplines including ecology, evolution, physiology, genetics, development, and behavioral biology. In this review, we focus on a range of organismal traits, including coloration phenotypes, trophic adaptations, appendages like fins and scales, sensory systems, sex, brains, and behaviors. Moreover, we discuss studies on cichlid phylogenies, plasticity, and general evolutionary patterns, ranging from convergence to speciation rates and the proximate and ultimate mechanisms underlying these processes. From a methodological viewpoint, the last decade has brought great advances in cichlid fish research, particularly through the advent of affordable deep sequencing and advances in genetic manipulations. The ability to integrate across traits and research disciplines, ranging from developmental biology to ecology and evolution, makes cichlid fishes a fascinating research system.
... Sound production plays an important role in species identification (Tavolga, 1964;Winn, 1964;Fine et al., 1977;Ladich et al., 2006;Amorim, 2008;Parmentier et al., 2009;Phillips and Johnston, 2009;Bass et al., 2019). Fish produce sounds to communicate with one another during feeding, mating, and aggression (Amorim, 2006). ...
The male and female southern black drum possess highly specialized, bilateral, striated sonic muscles used in sound production during courtship by males and in the production of disturbance calls by both males and females. Androgen-driven hypertrophy of the sonic muscles in males during the late spring spawning period results in increased growth of sonic muscle mass followed by post-spawning atrophy of sonic muscles. We examined changes in sonic muscle morphology and in the sound characteristics of males and females underlying seasonal changes in sonic muscle mass and muscle contraction as measured by sound production. In males, the sound pressure level increased while sound pulse duration decreased with increasing sonic muscle mass, indicating that sonic muscle fibers contract with greater force and shorter duration during the spawning season. Interpulse interval and the total number of pulses varied seasonally with muscle mass, which suggests that the effects of steroids on male southern black drum sound characteristics are more pronounced peripherally than in the central nervous system. In females, no increase in sonic muscle mass was found, and therefore, a change was not observed in the acoustic variables analyzed. Seasonal sonic muscle hypertrophy in males likely functions as a secondary sexual characteristic that maximizes vocalization amplitude or loudness during the spawning period.
... In different cichlid species, the display of agonistic and/or courtship behaviors can be accompanied by species-specific sounds (Lobel, 1998;Amorim et al., 2004;Amorim et al., 2008;Bertucci et al., 2012b). In Nile tilapia, both males and females can emit sounds during aggressive and non-aggressive (including courtship) behaviors, presumably to reinforce visual behaviors (Longrie et al., 2013;Akian et al., 2020). ...
In some fish species, sex is determined by the combination of genetic and environmental factors. In most species concerned, extreme temperatures during the sensitive period of sex differentiation drives masculinization, independently of the female sex chromosomes. In Nile tilapia (XY male heterogamety), XX juveniles exposed to high temperatures (>32 °C) can masculinize and become phenotypical males (neomales). Whether these neomales exhibit a different behavior than XY males remains however unclear. Sex reversal being naturally relevant, we investigated the agonistic behavior of neomales during dyadic fights and the preference of gravid females for one of the two male types. We quantified the behavior, size of the nest, hormone circulating levels (testosterone, 11-ketotestosterone and cortisol) and sound production of the two male types in both contexts. Independently of the individual they face, neomales seem to display more aggressive behaviors than XY males but often fail to become dominant. Agonistic interactions were mainly silent, suggesting that sounds are unnecessary for the establishment of social hierarchy. Although males and neomales produce different kinds of sounds when facing a gravid female, the female does not exhibit a preference. Overall, no differences were observed for hormone circulating concentrations between the two male types. We suggest that the sex chromosomes and/or the sex reversal procedure may have differently shaped the brain of neomales, resulting in differences in the expression of behavior.
... Despite the time spent under the same rearing conditions, no spawning was observed in interspecific batches. Acoustic features are different between the two species; this supports that acoustic signals may be potentially involved in the mechanisms of reproductive isolation (Amorim et al., 2008;Lobel, 1998;Ptacek, 2000). Because hybridizations between O. niloticus and S. melanotheron were obtained in previous studies (Amon et al., 2013a(Amon et al., , 2013b and not in this study, the authors assume the lack of hybridization during the present experiments is attributed to environmental factors (e.g., salinity, turbidity in lagoon) that changed the perception of the vocal signature of the two species or reduced their capacity of acoustic and visual communication. ...
Reproduction involves multiple complex behaviours and the effects of familiarity on such social interactions are seldom described in fish. This is particularly true for sound production and communication within aggressive or non-aggressive context. Here we explore the effects of a common garden rearing without parental care of two closely related cichlid species (Nile tilapia Oreochromis niloticus and black-chinned tilapia Sarotherodon melanotheron) on their sound production features and social interactions. After 9 months in common garden rearing, from embryonic stage to first maturity, sound production and associated behaviours were recorded on specimens of the two species in intraspecific and interspecific pairings. We found that fish were able to produce the same kind of sounds as those recorded in similar context for their parents. Drums sounds were associated to chasing, lateral attack and courtship in O. niloticus and only in fleeing or avoidance in S. melanotheron. Specific grunts were produced in chasing, after biting and in nest building by O. niloticus and specific rolling sounds were associated to courtship in S. melanotheron. Sounds production and behaviours were not correlated to sex steroid levels but the number of sounds recorded in aggressive context was correlated to dominance in O. niloticus. We conclude that one generation of common garden rearing does not modify sound features which remain specific and innate in the two cichlids. Despite the familiarity, O. niloticus remained dominant on S. melanotheron but the aggressiveness between the two species decreased. This article is protected by copyright. All rights reserved.
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The best practices for conducting bioacoustical research are described in this chapter. Ethical considerations, including the need for research integrity, animal ethics (e.g., in the USA, the Institutional Animal Care and Use Committee, IACUC) approvals, and data management and archiving are discussed. Suggestions for conducting a bioacoustical study in the laboratory, field, and captivity are described, including designing a data sheet. Recommendations for carrying out playback studies, a special type of bioacoustical study, are also provided. Finally, the importance of historical data, properly logging the details of a recording, documenting equipment specifications, and correctly storing analog and digital acoustic data are summarized.
Animals evolve mechanisms to send and receive communication signals through multiple sensory channels during crucial behavioral contexts like aggression and reproduction. This assures the transmission of important context-dependent signals that supply either the same (redundant) or different (nonredundant) information to the receiver. Despite the importance of multimodal communication, there are relatively few species in which information on sender signals and receiver responses are known. Further, little is known about where context-dependent unimodal and multimodal information is processed in the brain to produce adaptive behaviors. We used the African cichlid, Astatotilapia burtoni, to investigate how unimodal and multimodal signals are processed within the female brain in a reproductive context. During courtship, dominant males produce low frequency sounds in conjunction with visual displays (quivers) directed towards receptive gravid females. We compared affiliation behaviors and neural activation patterns in gravid females exposed to visual, acoustic, and visual-acoustic signals from courting dominant males. Females displayed reduced affiliation in auditory only conditions, but similar affiliation during visual and visual-acoustic conditions, demonstrating that visual-acoustic signaling from males is nonredundant but vision dominates. Using the neural activation marker cfos, we identified differential activation in specific socially-relevant brain nuclei between unimodal and multimodal conditions and distinct neural co-activation networks associated with each sensory context. Combined with our previous work on chemosensory signaling, we propose that A. burtoni represents a valuable vertebrate model for studying context-dependent behavioral and neural decision making associated with nonredundant multimodal communication.
The complex social behaviour of cichlids has fascinated scientists and hobbyists alike for almost 100 years. In this chapter, we review the breadth and complexity of cichlid behaviour, particularly with respect to social interactions. We present the case that cichlids are one of the best model systems for understanding both the mechanisms and evolution of behaviour. This is due to the fact that cichlids can be observed without being greatly disturbed, both in the aquarium and field and because of the unique opportunity to experimentally manipulate their environment and behaviour. We first give a brief account of the diversity of social systems in the cichlids and the diverse research in this area, from the very early work of authors like Curtis, Noble, and Baerends, to modern studies into the dynamics and structure of social behaviour in these fish. In Sect. 2, we explore the causal factors leading to the evolution of social complexity, discussing the occurrence and evolution of different social systems across ecological and life-history contexts. We investigate the behavioural complexity displayed by cichlids in Sect. 3, including a brief treatment of the different modalities of behavioural interactions. In Sect. 4, we discuss the immense potential for using cichlids as model species in studying social and behavioural evolution, before ending in Sect. 5 with exciting future directions for research employing the latest technical advances in both the laboratory and field.
The visual ecology of cichlids has contributed greatly to our understanding of mechanisms driving spectacular, colorful cichlid radiations. Interactions between the underwater light environment, the transmission of visual signals, and the visual sensitivity of the signal receiver are integral to the processes driving this diversity. Researchers recognized the importance of vision early in the study of African cichlids, citing the diversity of habitats in which cichlids are found and brilliant male nuptial coloration as potential forces shaping visual differentiation. Later work focused more on visual systems, adapted to the local light environment, as drivers of color pattern diversification. Most recently, researchers have focused on the evolution of visual systems under both ecological and sexual selection and the mechanisms of spectral tuning by investigating opsin gene expression and co-expression across the cichlid phylogeny. In this chapter, I describe the historical context of cichlid vision research, the diversity in cichlid visual ecology, and the current state of our understanding of cichlid visual ecology. Additionally, I discuss the possible consequences of human-induced changes to the underwater visual environment for cichlid diversity and suggest avenues for future research.
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A new genus, Metriaclima, is described for members of the Pseudotropheus zebra complex from Lake Malaŵi. The presence of bicuspid teeth in the anterior portion of the outer row of both the upper and lower jaws distinguishes Metriaclima from many of the previously described genera of rock-dwelling cichlids that inhabit Lake Malaŵi, including Cyathochromis, Cynotilapia, Gephyrochromis, Labidochromis, and Petrotilapia. The absence of two horizontal stripes along its flanks, distinguishes it from Melanochromis. The isognathous jaws of Metriaclima delimits it from Genyochromis, which is characterized by having the lower jaw extend in front of the upper jaw. The mouth of Metriaclima is terminal, while that of Labeotropheus is inferior. Within the genus Pseudotropheus as it is now recognized, species of Metriaclima are unique because they have a moderately sloped ethmo-vomerine block and a swollen rostral tip. Ten previously undescribed species that have a slight variation from the characteristic blue/black barring are described. The new species are recognized primarily by their distinctive adult coloring in conjunction with the discontinuity of morphological differences throughout their range.
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Fish sound characteristics are associated with different sound-generating mechanisms. Sounds produced by swimbladder-related mechanisms usually comprise low-frequency pulses produced at different rates. Fishes emit one to five sound types that do not show such outstanding variability as found in other taxa. However, closely related species show consistent differences in their sounds and in some species even individuality is found. Of particular interest are differences in courtship sounds made by closely related sympatric species that may promote reproductive isolation. Differences between individuals of the same species may in turn play a role in sexual selection through male-male competition and female mate choice. Other known sources of variability are related to context, including motivation and recent social status, season, time of day, ontogenetic changes and sexual dimorphism. Fish sound variability is mainly based on temporal patterning of sounds or pulses within a sound and on frequency variation (sometimes modulation). Such variability has been found to play a role in the social life of fishes.
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Courtship sounds made by three sympatric cichlid species, Pseudotropheus zebra, P. callainos and an undescribed species known as P. ‘zebra gold’ were recorded and compared to investigate the potential role of acoustic signals in mate choice. Sounds were emitted during ‘quiver’ and ‘circle’ components of the male courtship display and consisted of rapidly repeated pulse units. Some sound variables differed significantly among species with P. callainos generally being separated from the other two species. This species produced sounds with higher peak frequency (for a given length) and lower number of pulses than P. ‘zebra gold’ and higher pulse durations than P. zebra. In addition, standard length was inversely related to peak frequency in both P. ‘zebra gold’ and P. callainos(this relation was not tested in P. zebra due to the small sample size). These differences might indicate different regimes of intraspecific sexual selection among the three species.
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The mechanisms that underlie the diversity of cichlids in the East African Great Lakes are poorly understood. Sexual selection through female choice based on male body coloration has often been suggested as a driving force behind the speciation of these fishes. The objectives of this study were to investigate, through mate choice trials, the cues that guide species-isolating female choice. In a group of sympatric Lake Malawi mbuna (rock-dwelling fish), we investigated both visual and chemical cues that might guide female choice by giving gravid females a choice between a heterospecific and a conspecific male. Visual cues, in contrast to olfactory cues, were sufficient to stimulate courtship and thus guide female choice of males. Furthermore, in contrast to other studies on related species, we found that females courted only with conspecifics even if color was not a cue. Species-isolating female choice is likely based primarily on visual information.
Intensely displaying sand goby Pomatoschistus minutus males had lower lipid content, indicating that signalling increased energy expenditure, or that low condition males increased their signalling effort. Display intensity correlated positively with nest-defence and tended to correlate positively with filial cannibalism. (C) 2004 The Fisheries society of the British Isles.