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Species differences in courtship acoustic signals among
five Lake Malawi cichlid species (Pseudotropheus spp.)
M. C. P. AMORIM*†,J.M.SIMO
˜ES‡, P. J. FONSECA‡
AND G. F. TURNER§
*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.
INTRODUCTION
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;
email: amorim@ispa.pt
Journal of Fish Biology (2008) 72, 1355–1368
doi:10.1111/j.1095-8649.2008.01802.x, available online at http://www.blackwell-synergy.com
1355
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Journal compilation #2008 The Fisheries Society of the British Isles
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.
MATERIALS AND METHODS
EXPERIMENTAL ANIMALS
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
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
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.
SOUND RECORDING AND ANALYSIS
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.
SPECIES-SPECIFIC LAKE MALAWI CICHLID SOUNDS 1357
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
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
S
), 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
1
) 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).
BEHAVIOUR RECORDING AND ANALYSIS
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
min
1
), courtship rate (total number of courtship activities min
1
) and sound produc-
tion rate (number min
1
) were considered for each recording session.
DATA ANALYSIS
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
S
because the variables were not signifi-
cantly correlated with L
S
(Spearman rank correlation, r
s
,P>005; Amorim et al.,
1358 M. C. P. AMORIM ET AL.
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
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
S
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
s
, 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
10
(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.
SPECIES-SPECIFIC LAKE MALAWI CICHLID SOUNDS 1359
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
TABLE I. Male Pseudotropheus spp. standard length (L
S
), mass (M) and number of analysed sounds. Values are mean (range)
P. ‘zebra gold’
(n¼12)
P. zebra
(n¼12)
P. callainos
(n¼13)
P. fainzilberi
(n¼13)
P. emmiltos
(n¼14)
L
S
(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)
1360 M. C. P. AMORIM ET AL.
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
RESULTS
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
S
decreased significantly PF1 (ANCOVA,
covariate L
S
,d.f.¼4, 58, P<005) and especially PF2 (ANCOVA: covariate
L
S
,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
1
and the remaining species
07–08 sounds min
1
.
DISCUSSION
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.
SPECIES-SPECIFIC LAKE MALAWI CICHLID SOUNDS 1361
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Journal compilation #2008 The Fisheries Society of the British Isles, Journal of Fish Biology 2008, 72, 1355–1368
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
Variables
P. ‘zebra gold’
(n¼12)
P. zebra
(n¼12)
P. callainos
(n¼13)
P. fainzilberi
(n¼13)
P. emmiltos
(n¼14)
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
8–224)
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.
1362 M. C. P. AMORIM ET AL.
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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.
SPECIES-SPECIFIC LAKE MALAWI CICHLID SOUNDS 1363
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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.
1364 M. C. P. AMORIM ET AL.
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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
S
. 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.
References
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