Females Preferred Calls Research Articles

Conspecific disturbance odors act as alarm cues to affect female mate choice in a treefrog

Mate choice in frogs depends heavily on acoustic communication, and females in many species possess an inherent preference for longer and/or more complex calls. Recently, it has become clear that conspecific chemical cues can also be useful in attracting potential mates in anuran species. However, how conspecific chemical cues influence mate choice decisions when paired with acoustic signals remains less clear. In the present study, we conducted three experiments to investigate whether and how male odor cues affect female choice decisions in the absence or presence of acoustic signals in serrate-legged small treefrogs (Kurixalus odontotarsus). We found that disturbance odors alone can trigger avoidance behavior of females, suggesting that the odors of disturbed K. odontotarsus can act as an alarm cue for conspecifics. Females also avoided disturbance odors in the presence of advertisement calls, except for calls with five notes. In addition, females preferred calls with two notes to calls with four notes when the latter was paired with disturbance odors. In contrast, female choice decisions were not affected by the odors of undisturbed males, either in the absence or the presence of advertisement calls. Our results indicate that disturbance odors can influence, or even reverse, mate choice by females for acoustic signals. In addition to acoustic signals, chemical cues can also be used in close-range communication in some anuran species. In the present study, we investigated how female Kurixalus odontotarsus use male chemical cues and/or acoustic signals during the mate choice process. We demonstrate that male disturbance odors can act as an alarm cue to trigger the avoidance behavior of females. Furthermore, this alarm cue can even reverse mate choice by females for acoustic signals. Our study highlights the importance of integrating multisensory signals and cues in mate choice decisions and has important implications for understanding chemical communication in anurans.

Call recognition and female choice in a treefrog with a multicomponent call

AbstractAcoustic mating signals are typically species‐specific, and often additionally are subject to directional female preferences. Male executioner treefrogs, Dendropsophus carnifex, produce a multicomponent advertisement call composed of an introductory screech note followed by two or more click notes. Here, we tested (i) call recognition by comparing female directed phonotaxis towards individual and combined call components: screech vs. clicks vs. screech + clicks, (ii) female preferences for greater numbers of click notes and (iii) female preferences for faster call rates. The results demonstrated that screeches and clicks, presented either separately or together as a complete call, evoke similar female responses, suggesting that either note was sufficient to elicit a mate‐recognition response. Additionally, females preferred calls with greater numbers of click notes and with faster call rates. We interpret these results within the context of female mate selection in natural choruses.

Multitasking males and multiplicative females: dynamic signalling and receiver preferences in Cope's grey treefrog

The ‘multitasking hypothesis’ for complex signal function predicts performance trade-offs between signal components that negatively covary (e.g. due to energetic or mechanical constraints) and receiver preferences for more extreme values of the negatively covarying components that are difficult to produce simultaneously. We tested these two predictions in Cope's grey treefrogs, Hyla chrysoscelis. In a field study, we recorded and analysed 1000 advertisement calls from males calling in breeding choruses to test the prediction that two signal components important in female mating decisions (call rate and call duration) negatively covary under natural conditions. In a laboratory study, we conducted phonotaxis tests with female subjects to test the prediction that females prefer calls with higher overall ‘call efforts’ (the product of call rate × call duration). Consistent with predictions of the multitasking hypothesis, call rate and call duration were significantly negatively related and females preferred calls produced with higher call efforts, manifested through preferences for greater values of both call rate and call duration. We conducted an additional playback experiment to test the hypothesis that males increase their call effort in competitive situations to maximize their attractiveness to females. Compared to quiet conditions, male subjects increased their call duration and decreased their call rate, but did not alter call effort, in response to a simulated calling neighbour or broadcasts of chorus noise. Together our data have implications for understanding the function of multicomponent signals when signallers must balance performance trade-offs in mate attraction with dynamic signal modifications in other social contexts.

Female preferences for spectral call properties in the western genetic lineage of Cope's gray treefrog (Hyla chrysoscelis)

Female frogs discriminate among potential mates based on individual variation in male advertisement calls. While considerable data have accumulated allowing comparisons of female preference functions among species, we still lack fundamental knowledge about how and why the shapes of preference functions for particular call properties vary among populations within all but a few species. Here, we report results from a study aimed at describing female preference functions for spectral call properties in Cope's gray treefrog (Hyla chrysoscelis). Widespread throughout the eastern half of North America, Cope's gray treefrog is the diploid member of the cryptic diploid-tetraploid Hyla versicolor species complex, and its populations are divided into two distinct genetic lineages (eastern and western). In this study of a western lineage population, we recorded and analyzed the spectral properties of 1000 advertisement calls from 50 males and conducted two-choice phonotaxis experiments to estimate a population-level preference function. Females preferred calls with average frequencies over calls with frequencies that were 2 or 3 semitones (1.4 or 2.1 standard deviations, respectively) lower than the population mean. We observed no behavioral discrimination between calls with average and higher-than-average frequencies. Preferences discriminating against low-frequency calls were weak and were abolished by attenuating the preferred average call by 3 dB. We discuss these results in light of previous studies of eastern lineage populations, geographic variation in female preference functions, and the potential adaptive value of discriminating against calls with low frequencies.

Male and female crickets use different decision rules in response to mating signals

Males that produce conspicuous mating signals may attract competitors in addition to sexually receptive females. In manyspecies, for example, females use male calls to locate and choose mates and males respond to competitors’ signals by modulatingsignal production or changing location, thereby escalating or decreasing competition. Do these different receivers make deci-sions using male signals in the same way? We compared how male and female field crickets (Gryllus integer) made decisions toapproach male calls differing in calling bout length, a heritable trait known to play an important role in female mate choice.When offered a simultaneous choice between playbacks, both males and females preferred calls with long bouts to those withshort bouts. When presented with calls in isolation, however, only females preferred long-bout calls. Females thus appear to usean internal standard to evaluate calls, whereas males apparently compare the relative attractiveness of alternatives. We also foundthat males assess calls in relation to their own competitive potential by testing 2 hypotheses that make different predictionsregarding variation in male responses to competitor signals. We found no support for the satellite male hypothesis, as unattractivemales did not preferentially approach female-preferred calls; in support of the aggressive displacement hypothesis, males likely towin contests preferentially approached the female-preferred call. Our work demonstrates that even though the sexes process thesame information, different mechanisms of reproductive success (mate location vs. mate attraction) can result in sex differencesin the perception and use of conspecifics’ signals. Key words: contests, decision rules, Gryllus integer, male phonotaxis, matechoice, satellite males, sexual dimorphism, thresholds. [Behav Ecol]

Female Mate Choice and No Detected Predation Risk in Relation to the Calling Song of <I>Oecanthus niveus</I> (Gryllidae: Oecanthinae)

Oecanthus niveus (Gryllidae: Oecanthinae), a tree cricket species, inhabits the Tehuacan Valley, Mexico, year-round. Solitary males radiate calling songs that attract receptive females. The calling song is composed of discrete trains of five pulses with regular intertrain intervals. The courtship and mating behaviors are similar to other tree cricket species. In this study, we evaluated 1) the relationship between male body size and train duration, and the train period of its calling song; 2) female choice by exposing females to contrasting trains and train periods of the calling songs; and 3) the predation risk associated with the song patterns preferred by females. We hypothesized that 1) there is a significant relationship between male body size with train duration and the train period of calling songs, 2) females prefer song patterns associated with larger males, and 3) that a high predation risk is associated with these patterns. In line with our hypotheses, we found a significant relationship between male body size and song patterns. Females preferred calls with a train duration corresponding to a male 11% larger than an average male of the population. Nevertheless, no increase in invertebrate predation was detected in a field experiment for this song pattern. The train duration of the song is a reliable indicator of male size that does not have associated predation costs. Females may obtain direct or indirect benefits, or both, as a result of their mate choice preferences.

GEOGRAPHIC VARIATION OF GENETIC AND BEHAVIORAL TRAITS IN NORTHERN AND SOUTHERN TÚNGARA FROGS

We use a combination of microsatellite marker analysis and mate-choice behavior experiments to assess patterns of reproductive isolation of the túngara frog Physalaemus pustulosus along a 550-km transect of 25 populations in Costa Rica and Panama. Earlier studies using allozymes and mitochondrial DNA defined two genetic groups of túngara frogs, one ranging from Mexico to northern Costa Rica (northern group), the second ranging from Panama to northern South America (southern group). Our more fine-scale survey also shows that the northern and southern túngara frogs are genetically different and geographically separated by a gap in the distribution in central Pacific Costa Rica. Genetic differences among populations are highly correlated with geographic distances. Temporal call parameters differed among populations as well as between genetic groups. Differences in calls were explained better by geographic distance than by genetic distance. Phonotaxis experiments showed that females preferred calls of males from their own populations over calls of males from other populations in about two-thirds to three-fourths of the contrasts tested. In mating experiments, females and males from the same group and females from the north with males from the south produced nests and tadpoles. In contrast, females from the south did not produce nests or tadpoles with males from the north. Thus, northern and southern túngara frogs have diverged both genetically and bioacoustically. There is evidence for some prezygotic isolation due to differences in mate recognition and fertilization success, but such isolation is hardly complete. Our results support the general observation that significant differences in sexual signals are often not correlated with strong genetic differentiation.

Female preference for symmetric calls in a grasshopper

Grasshoppers produce calls by alternating use of a row of pegs on the two hind legs. The number of pegs per row in the grasshopper Myrmeleotettix maculatus demonstrated fluctuating asymmetry as shown by signed right-minus-left number of pegs having a frequency distribution not differing from a normal distribution with a mean value of zero. Peg asymmetry was significantly negatively related to mean number of pegs per leg. Peg asymmetry was relatively larger than asymmetry in femur length. A larger degree of peg asymmetry resulted in a larger degree of asymmetry in maximum frequency of chirps and asymmetry in the duration of chirps produced by the two legs. Calls produced by males with experimentally manipulated numbers and asymmetries of pegs were used in a female phonotaxis experiment. Females preferred calls of males with a larger and more symmetrical number of pegs. Peg asymmetry differed in a field sample of mated and unmated males with mated males having a smaller degree of peg asymmetry. These results demonstrate that females can discriminate male asymmetry directly on the basis of calls.

The neuroethology of frequency preferences in the spring peeper

We studied the relationship between auditory activity in the midbrain and selective phonotaxis in females of the treefrog,Pseudacris crucifer. Gravid females were tested in two-stimulus playback tests using synthetic advertisement calls of different frequencies (2600 versus 2875Hz; 2800 versus 3500Hz; 2600 versus 3500Hz). Tests were conducted with and without a background of synthesized noise, which was filtered to resemble the spectrum of a chorus of spring peepers. There were no significant preferences for calls of any frequency in the absence of background noise. With background noise, females preferred calls of 3500Hz to those of 2600Hz. Multi-unit recordings of neural responses to synthetic sounds were made from the torus semicircularis of the same females following the tests of phonotaxis. We measured auditory threshold at 25 frequencies (1800–4200Hz) as well as the magnitude of the neural response when stimulus amplitude was held constant and frequency was varied. This procedure yielded isointensity response contours, which we obtained at six amplitudes in the absence of noise and at the stimulus amplitude used during the phonotaxis tests with background noise. Individual differences in audiograms and isointensity responses were poorly correlated with behavioural data except for the test of 2600Hz versus 3500Hz calls in noise. The shape of the neural response contours changed with stimulus amplitude and in the presence of the simulated frog chorus. At 85dB sound pressure level (SPL), the level at which females were tested, the contours of females were quite flat. The contours were more peaked at lower SPLs as well as during the broadcast of chorus noise and white noise at an equivalent spectrum level (45–46dB/Hz). Peaks in the isointensity response plots of most females occurred at stimulus frequencies ranging from 3200 to 3400Hz, frequencies close to the median best excitatory frequency (BEF) of 3357Hz but higher than the mean of the mid-frequency of the male advertisement call (3011Hz). Addition of background noise may cause a shift in the neural response-intensity level functions. Our results highlight the well-known nonlinearity of the auditory system and the danger inherent in focusing solely on threshold measures of auditory sensitivity when studying the proximate basis of female choice. The results also show an unexpected effect of the natural and noisy acoustic environment on behaviour and responses of the auditory system.

Female mate selection in the natterjack toad: active choice or passive atraction?

Variation in seasonal mating success among male natterjack toads (Bufo calamita) was influenced by the number of nights that males spent at the pond and by male body size. Large males produced louder and lower frequency calls than small males, and maintained larger acoustic territories. After arriving at the pond, one half of all observed females mated with the first male they encountered. The remainder visited several males before initiating amplexus, but no criteria could be identified that females might have used when deciding whether to accept or reject a male. Movements between several males seem to be best explained by low female responsiveness to male advertisement calls on cold nights which were nonoptimal for oviposition. Females attempted to reject non-calling males both before and after amplexus, but this may be a mechanism to avoid mismating with males of the common toad (Bufo bufo), an explosive breeder that utilised the same pond. In two-choice playback experiments using synthetic advertisement calls, females showed no preference for calls based on their frequency. Females preferred calls of intermediate pulse repetition rate equivalent to those produced by a male at the same body temperature. Pulse rate is thus potentially subject to stabilishing selection and may be an important character for species-recognition. Females preferred fast rather than slow call rates, but only when the alternative rates were extreme. They also preferred calls which they perceived at the highest sound pressure level, but did not discriminate between absolute sound pressure levels of alternative stimuli at different distances. Since females that delay mating and oviposition may suffer predation, it is suggested that female preference for loud, rapidly repeated calls may be adaptive in the sense of minimizing the costs of locating conspecific males, rather than maximizing the probability of obtaining a high quality mate. Competition between males to maintain large acoustic territories and produce calls that can be easily detected by females would seem to be a sufficient mechanism to explain the evolution of the striking calls produced by male natterjacks.