雄性西藏蟾蜍的鸣声特征及听觉敏感性

西藏蟾蜍(Bufo tibetanus)主要生活在海拔2 400～4 300 m的高海拔地区,本研究分析了这一高原两栖物种雄性个体的鸣声特征和听觉敏感性。采用录音机和指向性话筒,在野外记录西藏蟾蜍的广告鸣声,使用听觉脑干反应(ABR)检测听觉敏感性。采用Praat声音分析软件绘制广告鸣声的波形图和频谱图,鸣声特征参数通过Adobe Audition软件获取。广告鸣声由多个单音节鸣叫组成,鸣声主频为(1150±99)Hz。ABR对于刺激的响应以谷峰波形展示,听力图结果显示,听觉敏感区域在1.4～2.0 kHz,但在0.6～6.0 kHz范围的听觉阈值均高于70 dB,表明雄性西藏蟾蜍相较于其他物种听觉敏感性较差。尽管雄性西藏蟾蜍的最佳听觉敏感频率(1.6kHz)稍高于鸣声主频,但其鸣声能谱结构与听觉敏感性曲线在1.0～1.4 kHz存在一定程度重叠,符合"匹配过滤假说"。     

An exception to the matched filter hypothesis: A mismatch of male call frequency and female best hearing frequency in a torrent frog

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.     

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

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.     

A comparative study of hearing ability in fishes: the auditory brainstem response approach

Auditory brainstem response (ABR) techniques, an electrophysiological far-field recording method widely used in clinical evaluation of human hearing, were adapted for fishes to overcome the major limitations of traditional behavioral and electrophysiological methods (e.g., invasive surgery, lengthy training of fishes, etc.) used for fish hearing research. Responses to clicks and tone bursts of different frequencies and amplitudes were recorded with cutaneous electrodes. To evaluate the effectiveness of this method, the auditory sensitivity of a hearing specialist (goldfish, Carassius auratus) and a hearing generalist (oscar, Astronotus ocellatus) was investigated and compared to audiograms obtained through psychophysical methods. The ABRs could be obtained between 100 Hz and 2000 Hz (oscar), and up to 5000 Hz (goldfish). The ABR audiograms are similar to those obtained by behavioral methods in both species. The ABR audiogram of curarized (i.e., Flaxedil-treated) goldfish did not differ significantly from two previously published behavioral curves but was lower than that obtained from uncurarized fish. In the oscar, ABR audiometry resulted in lower thresholds and a larger bandwidth than observed in behavioral tests. Comparison between methods revealed the advantages of this technique: rapid evaluation of hearing in untrained fishes, and no limitations on repeated testing of animals. Accepted: 8 August 1997     

The Evolution of Reversed Sexual Size Dimorphism in Hawks,Falcons and Owls: A Comparative Study

Many hypotheses have been proposed to account for the origin and maintenance of reversed size dimorphism (RSD, females being larger than males) in hawks, falcons and owls, but no consensus has been reached. I performed comparative analyses, using both cross-taxa data and phylogenetically independent contrasts, to investigate potential correlates of reversed size dimorphism. Using a similar set of explanatory variables, covering morphology, life history and ecology, I tested whether any trait coevolved with size dimorphism in all three groups and hence provided a general explanation for the evolution of RSD. For hawks, strong correlates were found in the foraging-variable complex, so RSD might have evolved in species hunting large and agile prey. This is consistent with the intersexual-competition hypothesis (sexes have evolved different sizes to lessen intersexual competition for food), but especially the small-male hypothesis (males have evolved to be smaller to be more efficient foragers). Evolutionary pathway analyses suggest that RSD evolved most likely as a precursor of changes in hunting strategy but as a consequence of high reproduction. The falcons showed a similar pattern: species with strong RSD hunted larger and more agile prey. The evolutionary pathway analysis supported the idea that RSD evolved before the specialisation on more agile and/or larger prey. Finally for owls, the results showed clear parallels. RSD increased with prey size, consistent with the small-male hypothesis. Evolutionary pathway analysis suggests that RSD in owls has most likely evolved before specialisation on large prey, so a small and more agile male might be advantageous even when hunting small prey. These results suggest that RSD in hawks, falcons and owls evolved due to natural-selection pressures rather than sexual-selection pressures. Co-ordinating editor: J. Tuomi     

The acoustic ecology of an Amazonian bird assemblage: the role of allometry,competition and environmental filtering in the acoustic structure

Communication among birds constitutes the foundation of social interactions, and acoustic signals should evolve based on their efficiency to convey information. We examined the acoustic signals of an Amazonian bird assemblage by testing whether vocal allometry was the main driver in song evolution. We expected the acoustic parameters of the songs to follow general allometric rules, as the size of the vocal apparatus limits the vibration capacity of the syrinx. We tested whether smaller species use lower than expected frequencies due to environmental filtering by examining deviations from allometric relationships. Alternatively, small species could use higher than expected frequencies as a consequence of competitive processes that promote the use of vacant portions of the acoustic spectrum. We recorded birdsongs between 2013 and 2018 and measured three spectral parameters: the dominant frequency (FDOM), the minimum fundamental frequency (FFMIN) and the maximum fundamental frequency (FFMAX). We created an allometric model based on the acoustic pattern of the larger species and used it to predict the frequencies of the smaller species. We compared the frequency values expected by allometry with the observed parameters of the avian assemblage. We found that FDOM and FFMIN were higher than expected by allometry alone, supporting competition structuring in the acoustic ecology of the assemblage. The successful insertion of many species into the acoustic space is the result of long processes of natural selection, with our data highlighting the importance of competition in the vocal structuring of the community.     

The sexual arms race and phenotypic correlates of mating success in the waterstrider,Aquarius remigis (Hemiptera: Gerridae)

Intersexual conflicts over mating decisions may have an important impact on the evolution of mating behaviours and strategies and may develop into an arms race between the sexes. In waterstrider species, where intersexual conflict is known to occur, the evolution of male traits that allow them to overcome female reluctance to mate is expected. Reproductively active waterstriders,Aquarius remigis, were videotaped in the laboratory to examine the influence of total body length and front femoral width of males, male: female body size ratio, and female reproductive condition (number of mature eggs) on three variables associated with mating success: duration of the premating struggle, duration of mating, and number of successful matings. None of these behaviors was significantly correlated with the size ratio of the mating pair. However, total body length was negatively correlated with premating struggle duration, male front femoral width was positively correlated with number of successful matings, and number of mature eggs in females was positively correlated with duration of both the premating struggle and the mating itself. The relative influence of male sexual armaments and female choice on the outcome of mating interactions is discussed.     

The sensitivity of breeding songbirds to changes in seasonal timing is linked to population change but cannot be directly attributed to the effects of trophic asynchrony on productivity

A consequence of climate change has been an advance in the timing of seasonal events. Differences in the rate of advance between trophic levels may result in predators becoming mismatched with prey availability, reducing fitness and potentially driving population declines. Such “trophic asynchrony” is hypothesized to have contributed to recent population declines of long‐distance migratory birds in particular. Using spatially extensive survey data from 1983 to 2010 to estimate variation in spring phenology from 280 plant and insect species and the egg‐laying phenology of 21 British songbird species, we explored the effects of trophic asynchrony on avian population trends and potential underlying demographic mechanisms. Species which advanced their laying dates least over the last three decades, and were therefore at greatest risk of asynchrony, exhibited the most negative population trends. We expressed asynchrony as the annual variation in bird phenology relative to spring phenology, and related asynchrony to annual avian productivity. In warmer springs, birds were more asynchronous, but productivity was only marginally reduced; long‐distance migrants, short‐distance migrants and resident bird species all exhibited effects of similar magnitude. Long‐term population, but not productivity, declines were greatest among those species whose annual productivity was most greatly reduced by asynchrony. This suggests that population change is not mechanistically driven by the negative effects of asynchrony on productivity. The apparent effects of asynchrony on population trends are therefore either more likely to be strongly expressed via other demographic pathways, or alternatively, are a surrogate for species' sensitivity to other environmental pressures which are the ultimate cause of decline.     

The evolution of sexual size dimorphism in cottontail rabbits (Sylvilagus,Leporidae)

In mammals, ‘female‐biased’ sexual size dimorphism (SSD), in which females are larger than males, is uncommon. In the present study, we examined Sylvilagus, a purported case of female‐biased SSD, for evolutionary correlations among species between SSD, body‐size, and life‐history variables. We find that: (1) although most species are female‐biased, the degree and direction of SSD vary more than was previously recognized and (2) the degree of SSD decreases with increasing body size. Hence, Sylvilagus provides a new example, unusual for a female‐biased taxon, in which allometry for SSD is consistent with ‘Rensch's Rule’. As a corollary to Rensch's Rule, we observe that changes in SSD in Sylvilagus are typically associated with larger, more significant changes in males than females. Female‐biased SSD could be produced by selection for larger females, smaller males, or both. Although larger female size may be related to high fecundity and the extremely rapid fetal and neonatal growth in Sylvilagus, we find little evidence for a correlation between SSD and various fecundity‐related traits in among‐species comparisons. Smaller male size may confer greater reproductive success through greater mobility and reduced energetic requirements. We propose that a suite of traits (female dispersion, large male home ranges, reduced aggression, and a promiscuous mating system) has favoured smaller males and thus influenced the evolution of SSD in cottontails. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 141–156.     

A mutation in the heparin-binding site of noggin as a novel mechanism of proximal symphalangism and conductive hearing loss

The access of bone morphogenetic protein (BMP) to the BMP receptors on the cell surface is regulated by its antagonist noggin, which binds to heparan-sulfate proteoglycans on the cell surface. Noggin is encoded by NOG and mutations in the gene are associated with aberrant skeletal formation, such as in the autosomal dominant disorders proximal symphalangism (SYM1), multiple synostoses syndrome, Teunissen–Cremers syndrome, and tarsal–carpal coalition syndrome. NOG mutations affecting a specific function may produce a distinct phenotype. In this study, we investigated a Japanese pedigree with SYM1 and conductive hearing loss and found that it carried a novel heterozygous missense mutation of NOG (c.406C > T; p.R136C) affecting the heparin-binding site of noggin. As no mutations of the heparin-binding site of noggin have previously been reported, we investigated the crystal structure of wild-type noggin to investigate molecular mechanism of the p.R136C mutation. We found that the positively charged arginine at position 136 was predicted to be important for binding to the negatively charged heparan-sulfate proteoglycan (HSPG). An in silico docking analysis showed that one of the salt bridges between noggin and heparin disappeared following the replacement of the arginine with a non-charged cysteine. We propose that the decreased binding affinity of NOG with the p.R136C mutation to HSPG leads to an excess of BMP signaling and underlies the SYM1 and conductive hearing loss phenotype of carriers.