Jichao Wang

Bigger Is Not Always Better: Females Prefer Males of Mean Body Size in Philautus odontotarsus

Most species are believed to evolve larger body sizes over evolutionary time. Previous studies have suggested that sexual selection, through male-male competition and female choice, favors larger males. However, there is little evidence of selection against large size. The female serrate-legged small treefrogs (Philautus odontotarsus) must carry passive males from leks to breeding grounds over relatively long distances after amplexus to find a suitable place to lay eggs. The costs of large male size may therefore decrease mating success due to reduced agility and/or higher energy requirements. Thus, we hypothesized that selection would not favor larger males in P. odontotarsus. Females can assess male body size on the basis of the dominant frequency of male calls in frogs. To assess female P. odontotarsus preferences for a potential mate’s body size, male calls of high, average and low dominant frequency were played back to the females in phonotaxis experiments. Results showed that most females prefer the advertisement call with average dominant frequency. In addition, we compared the body mass distribution of amplectant males with that of single males in nature. The body masses of amplectant males are more narrowly distributed in the intermediate range than that of single males. The phonotaxis results and the data of actual female preferences in the field show that females strongly prefer potential mates of mean body sizes, consistent with the view that, in this species at least, larger males are not always perceived as better by females. In the present study, P. odontotarsus provides an example of an amphibian species in which large size does not have an advantage in mating success for males. Instead, our results provide evidences that stabilizing selection favors the optimal intermediate size of males.

Effects of Body Size and Environmental Factors on the Acoustic Structure and Temporal Rhythm of Calls in Rhacophorus dennysi

In anurans, the outcomes of male-male contests and female choice are often associated with body size. In some species, males evaluate an opponents fighting ability and females evaluate male quality on the basis of male communication signals, which are thought to reflect information concerning male body size. Nevertheless, previous studies reveal that male call structure is not always correlated with body size. In the present study we investigated the relationships between body size and call structure in the large treefrog, Rhacophorus dennysi, as well as the relationship of its calling behavior with air temperature and humidity. The results show that both the dominant and fundamental frequencies are negatively correlated with body size, while inter-note intervals are positively correlated with body size, indicating that call characters could reflect body size in this species. Additionally, calling in this tropical species exhibits a circadian rhythm insofar as relatively high temperature and low humidity during the day is associated with less vocal behavior. Thus, individual variations in call structure are mainly dependent on body size while the temporal rhythm of calling activity is affected by environmental conditions in large treefrogs.

The spectral structure of vocalizations match hearing sensitivity but imprecisely in Philautus odontotarsus

Abstract It is generally thought that for species using vocal communication the spectral properties of the sender’s calls should match the frequency sensitivity of the receiver’s auditory system. Nevertheless, few studies have investigated both sender and receiver characteristics in anuran species. In the present study, auditory brainstem responses (ABRs) were recorded in the serrate legged treefrog, Philautus odontotarsus, in order to determine if male call spectral structure and hearing sensitivity in males and females have co-evolved in this species. The results showed that the spectral structures of male vocalization match both male and female hearing sensitivity, even though the dominant frequencies of male calls (2.5 kHz) are mismatched with the regions of best frequency sensitivity (1.4 and 2.8 kHz). In addition, the results show that, in contrast with most previous ABR studies in non-human animals, but consistent with human studies, there are noticeable sex differences in peripheral auditory sensitivity in Philautus insofar as females exhibit lower auditory thresholds than males across the entire 1.8–18 kHz frequency range. The results also show that the dominant frequency of male calls is negatively correlated with body size, indicating that call characteristics reflect body size in this species which may be used by females during mate choice.

Background matching and camouflage efficiency predict population density in four-eyed turtle (Sacalia quadriocellata).

Background matching is an important way to camouflage and is widespread among animals. In the field, however, few studies have addressed background matching, and there has been no reported camouflage efficiency in freshwater turtles. Background matching and camouflage efficiency of the four-eyed turtle, Sacalia quadriocellata, among three microhabitat sections of Hezonggou stream were investigated by measuring carapace components of CIE L*a*b* (International Commission on Illumination; lightness, red/green and yellow/blue) color space, and scoring camouflage efficiency through the use of humans as predators. The results showed that the color difference (ΔE), lightness difference (ΔL(*)), and chroma difference (Δa(*)b(*)) between carapace and the substrate background in midstream were significantly lower than that upstream and downstream, indicating that the four-eyed turtle carapace color most closely matched the substrate of midstream. In line with these findings, the camouflage efficiency was the best for the turtles that inhabit midstream. These results suggest that the four-eyed turtles may enhance camouflage efficiency by selecting microhabitat that best match their carapace color. This finding may explain the high population density of the four-eyed turtle in the midstream section of Hezonggou stream. To the best of our knowledge, this study is among the first to quantify camouflage of freshwater turtles in the wild, laying the groundwork to further study the function and mechanisms of turtle camouflage.

An Exception to the Matched Filter Hypothesis: A Mismatch of Male Call Frequency and Female Best Hearing Frequency in a Torrent Frog

Abstract The matched filter hypothesis proposes that the tuning of auditory sensitivity and the spectral character of calls will match in order to maximize auditory processing efficiency during courtship. In this study, we analyzed the acoustic structure of male calls and both male and female hearing sensitivities in the little torrent frog (Amolops torrentis), an anuran species who transmits acoustic signals across streams. The results were in striking contradiction to the matched filter hypothesis. Auditory brainstem response results showed that the best hearing range was 1.6–2 kHz consistent with the best sensitive frequency of most terrestrial lentic taxa, yet completely mismatched with the dominant frequency of conspecific calls (4.3 kHz). Moreover, phonotaxis tests show that females strongly prefer high‐frequency (4.3 kHz) over low‐frequency calls (1.6 kHz) regardless of ambient noise levels, although peripheral auditory sensitivity is highest in the 1.6–2 kHz range. These results are consistent with the idea that A. torrentis evolved from nonstreamside species and that high‐frequency calls evolved under the pressure of stream noise. Our results also suggest that female preferences based on central auditory system characteristics may evolve independently of peripheral auditory system sensitivity in order to maximize communication effectiveness in noisy environments.

Male-male competition and female choice are differentially affected by male call acoustics in the serrate-legged small treefrog, Kurixalus odontotarsus

Background The evolution of exaggerated vocal signals in anuran species is an important topic. Males and females have both evolved the ability to discriminate communication sounds. However, the nature of sexual dimorphism in cognition and sensory discrimination and in the evolution and limitation of sexual signal exaggeration remain relatively unexplored. Methods In the present study, we used male calls of varied complexity in the serrate-legged small treefrog, Kurixalus odontotarsus, as probes to investigate how both sexes respond to variations in call complexity and how sex differences in signal discrimination play a role in the evolution of sexual signal exaggeration. The compound calls of male K. odontotarsus consist of a series of one or more harmonic notes (A notes) which may be followed by one or more short broadband notes (B notes). Results Male playback experiments and female phonotaxis tests showed that increasing the number of A notes in stimulus calls elicits increased numbers of response calls by males and increases the attractiveness of the stimulus calls to females. The addition of B notes, however, reduces male calling responses. Moreover, call stimuli which contain only B notes suppress spontaneous male calling responses. Phonotaxis experiments show that females prefer calls with greater numbers of A notes and calls containing both A notes and B notes, but do not prefer calls with only B notes. Discussion Male-male competition and female choice appear to have played different roles in the evolution and limitation of signal complexity in K. odontotarsus. These results provide new insights into how exaggerated compound signals evolve and how signal complexity may be limited in anurans.

Auditory brainstem responses in the Chinese tiger frog Hoplobatrachus chinensis (Osbeck, 1765) (Anura: Dicroglossidae) reveal sexually dimorphic hearing sensitivity

Abstract Hearing sensitivity affects survival and reproduction in animals that communicate vocally. The Chinese tiger frog exhibits sexual dimorphism in body size, reflecting the evolution of mating behaviour and life-history strategies. In this study, we recorded auditory brainstem responses (ABRs) to determine hearing sensitivity in both female and male frogs. We also compared male and female hearing characteristics with the shape of the tympanic membrane in light of previous studies showing that smaller middle ear cavities improve hearing sensitivity. We found that ABR thresholds differ significantly between males and females, with the greatest sensitivities in both sexes at frequencies close to the dominant frequency of male calls. ABR thresholds were significantly lower in females compared to males for frequencies in the 0.9–1.3 kHz range and at 1.6 kHz. The tympanic membrane diameter was significantly smaller in females (5.94 ± 0.87 mm) than in males (6.71 ± 0.49 mm). Our results indicate that sexual selection has in all likelihood differentially affected male and female hearing sensitivity as well as the shape of the tympanic membrane in frogs.

A test of the matched filter hypothesis in two sympatric frogs, Chiromantis doriae and Feihyla vittata

ABSTRACT The matched filter hypothesis proposes that the auditory sensitivity of receivers should match the spectral energy distribution of the senders’ signals. If so, receivers should be able to distinguish between species-specific and hetero-specific signals. We tested the matched filter hypothesis in two sympatric species, Chiromantis doriae and Feihyla vittata, whose calls exhibit similar frequency characters and that overlap in the breeding season and microenvironment. For both species, we recorded male calls and measured the auditory sensitivity of both sexes using the auditory brainstem response (ABR). We compared the auditory sensitivity with the spectral energy distribution of the calls of each species and found that (1) auditory sensitivity matched the signal spectrogram in C. doriae and F. vittata; (2) the concordance conformed better to the conspecific signal versus the hetero-specific signal. In addition, our results show that species differences are larger than sex differences for ABR audiograms.

Atypical assortative mating based on body size in an explosive-breeding toad from a tropical island of southern China

Mating patterns exhibit considerable intra- and interspecific variation. Sexual selection can lead to the occurrence of random and assortative mating in different populations of the same species. Thus, understanding variation in mating decisions is crucial to understanding variation in the direction of sexual selection. We investigated natural mating patterns in Black-spectacled toads (Duttaphrynus melanostictus), an explosive-breeding species that breeds throughout the year. We captured amplectant pairs (137) and non-amplectant males (212) during breeding seasons from November 2016 to April 2017 in tropical-island population of southern China. Our study found no significant difference in snout-vent length (SVL) between amplectant and non-amplectant males. Female and male SVL were positively correlated with each other. Small females were paired more frequently with small males, less frequently with large males, but had no preference for or against medium males. Medium females exhibited no preference. Large females showed no preference for large males, but were paired less frequently with small males. These data suggested that successful amplectant males had body sizes representative of the entire population. Both random and size-assortative mating were present simultaneously in the same population and within the same breeding season. Female choice was important in shaping the mating behavior of Black-spectacled toads, promoting genotype-frequency stabilization and body-size diversity in the population.

Correction to: Sometimes noise is beneficial: stream noise informs vocal communication in the little torrent frog Amolops torrentis

The article, “Sometimes noise is beneficial.