鸟类鸣声结构地理变异及其分类学意义

鸟声作为鸟类重要的生物学特征,是鸟类行为与声学研究相互交叉,相互渗透的新的边缘学科,近年来录音及声谱分析技术的发展使得鸟声研究已渗透到鸟类的各个研究领域。鸟类鸣声结构的地理变异,有时也称“鸟声方言”,不仅具有一定的种群稳定性而且具有个体性。它不仅与种群的遗传有关,而且与环境的异质性以及鸣声学习有关;鸣声方言可部分地阻碍种群的扩散,阻碍种群的基因漂移,从而影响到种群的基因库,长时间的地理隔离和生类学     

武汉地区大山雀（Parus major minor）对major与minor亚种组鸣唱回放的差别反应

分析鸟类鸣声能为研究鸟类系统学和生物地理学提供重要信息。鸟类鸣声的地理变异能影响鸟类的性选择,进而导致不同地理种群间的生殖隔离,从而促进地方种群(或亚种)的分化,乃至新种的形成。在鸟类系统学研究中,鸣声回放实验是研究物种分化并衡量分类地位的一项重要研究手段。本实验以武汉地区大山雀(Parus major minor,隶属于minor亚种组)为实验对象进行鸣唱回放实验,观测其对来自欧亚大陆西部及北部各地的major亚种组和来自我国各地的minor亚种组大山雀鸣唱回放的反应,探讨实验对象能否区分来自上述两个不同亚种组的鸣唱,从而推断两亚种组之间是否存在足以导致识别障碍的鸣声分化,以致产生行为上的生殖隔离。本实验共测试了24只雄性大山雀,每个亚种组的鸣唱各回放给12只个体,通过记录不同行为反应指标来衡量每只受试个体的反应程度。统计分析结果显示,受试大山雀对major和minor亚种组鸣唱的反应有显著差异,对同为minor亚种组的鸣唱反应程度激烈,而对major亚种组鸣唱的反应微弱甚至大多无反应。由此认为,大山雀major和minor亚种组之间存在显著的鸣声分化,已达到能形成配对前生殖隔离的程度,从而一定程度上支持将大山雀拆分成不同种的说法。     

山地隔离和空间距离对高黎贡山灰腹地莺(Tesia cyaniventer)鸣唱特征的影响

鸟类鸣唱存在广泛的地理变异，研究鸟类鸣唱变异的模式及其影响因素可帮助解释自然界中广泛而复杂的鸣声变异现象。灰腹地莺（Tesia cyaniventer）是在高黎贡山海拔2000-2800 m分布的小型地栖性森林鸟类。高黎贡山南北走向的山脊海拔通常在3000m以上，这导致灰腹地莺东、西坡种群被山脊所隔离。该种小鸟鸣声洪亮易于鉴别，其鸣声地理变异可揭示山地对鸟类种群产生的隔离效应。在高黎贡山片马垭口和独龙江垭口的东西坡4个地点录制了灰腹地莺的鸣声（n=58），基于声谱分析比较了种群间鸣唱的质量特征，发现种群间鸣唱型的共享程度极低，而音节型在4个种群间均有共享。进一步测量了11个鸣唱的数量特征参数，有6个参数在不同种群间有显著差异：最低频率、中心频率、频率宽度、起始音节频率、首二音节的时间间隔、句子平均音节数。种群间的两两比较表明，鸣声特征差异呈现"隔离-距离"共同作用的格局，但隔离的影响更大。研究表明山地系统中影响鸟类鸣声地理变异的因素较为复杂，山地隔离和空间距离均对灰腹地莺的鸣唱特征产生了影响。     

鸟类鸣声地理变异的形成机制

鸣声在鸟类的通讯和性选择中具有重要的意义.鸣声地理变异广泛存在于鸟类中,对其研究有助于了解近缘种的分类和演化历史.鸣声地理变异格局的形成是一个复杂的过程,可能是某一因素起主导、多因素协同作用的结果.主要影响因素有奠基者效应、鸣声漂变、遗传差异、性选择、生境等.年际间鸣声的稳定性和种群内鸣声的变异性,是鸣声地理变异研究中应该重视的问题,通过鸣声学习和扩散机制来研究鸣声地理变异,可能是将来本领域的研究热点.     

杭州市区白头鹎鸣声的微地理差异

2002年5—8月,对中国东部浙江省杭州市区的白头鹎鸣声的微地理差异进行研究。在约60 km2的 研究区内,选择8个调查点(4个城区,4个丘陵山地),录制了80个雄性白头鹎的511个鸣声样本,并随机选 取每一调查点的20个鸣声样本进行分析。其结果显示,白头鹎在杭州市区至少有8种微地理鸣声方言,每个微 地理鸣声方言都有一典型鸣句;它们在听觉上、波形结构、音节组成、音节频谱特征等方面均不相同。有的一 路之隔的相邻微地理鸣声方言之间存在明显差异;部分区域出现鸣声混合现象;有的个体还具有“多语”功 能。白头鹎鸣声产生微地理差异的原因可能与鸟类个体的扩散和城市中鸟类栖息地的人为改变有关。     

斑胸草雀的鸣声学习

鸣声是鸟类重要的生物学特征和分类特征。由于生理结构和神经控制方面的差异，不同种群和同一种群的不同个体都有自己特有的鸣声特征，正是利用这些特征，鸟类才能在集群、取食、迁徙、喂雏、御敌和求偶等行为中进行通讯。作为一种能够利用语音信息进行交流的高等脊椎动物，斑胸草雀的鸣声特别是鸣啭能力获得，需要有一个适宜的学习对象，并在一段特定的时间内，经历复杂的学习过程才能实现。     

体征对灰眉岩鹀鸣唱特征的影响

声信号是鸟类交流的重要方式。鸟类的鸣声特征受到生境的塑造和性选择,也受到发声器官的影响,如种间的比较研究发现,体重大的鸟类鸣声频率低,喙短的鸟类鸣声频宽大。在种内是否也存在类似的规律,目前的结论还不一致。2012年6月,在北京小龙门地区(40°00'N,115°26'E)测量了17只灰眉岩鹀(Emberiza godlewskii)的形态参数以及鸣声的频率特征,未发现体重或喙长与鸣声的最高频率、最低频率、峰频或频宽存在显著的相关性。本研究的结果支持在小型雀形目鸟类中,体型对繁殖期鸣唱频率特征的影响不显著。     

背条螳臂树蛙鸣声的繁殖性状替代

繁殖性状替代(RCD)是指为减弱种间的繁殖干扰而产生的性状进化现象。重叠分布的物种通过繁殖性状的分化降低繁殖干扰,维持种间界线,是物种应对种间繁殖干扰的重要策略之一。无尾两栖类的求偶/择偶过程主要依赖声音通讯,本研究以声音通讯为手段研究背条螳臂树蛙Chiromantis doriae鸣声的RCD过程和机制。背条螳臂树蛙和侧条费树蛙Feihyla vittata分别属于树蛙科Rhacophoridae螳臂树蛙属Chiromantis和费树蛙属Feihyla,但二者形态特征相似、繁殖期重叠、鸣声频率接近、求偶信号彼此遮蔽,因此二者间存在一定程度的繁殖干扰。同域/异域背条螳臂树蛙的鸣声特征比较分析结果表明,背条螳臂树蛙的求偶鸣声包含4～8音节,对鸣声提取8项声音特征参数进行主成分分析,得到3个主成分。混合线性模型分析结果表明,反映时域特征及调频特征的主成分PC3在同域/异域分布的种群间的差异有统计学意义,而另2个主成分在同域/异域分布的种群间的差异无统计学意义。为比较同域/异域种群间的音节特征,对音节主频、音节时长和音节间隔3个参数进行混合线性模型分析,结果表明,音节主频和音节时长在同域/异域种群间的差异有统计学意义,音节间隔在同域/异域种群间的差异无统计学意义。总体而言,同域分布的背条螳臂树蛙鸣声频率更低、时长更长、调频更明显,有助于拉大与侧条费树蛙主频高、时长短的单音节鸣声间的差异。背条螳臂树蛙在鸣声特征上存在RCD现象,证明非近缘物种也可产生RCD,拓展了RCD的范围。     

白头鹎方言的初步研究

对浙江省乘泗岛，普陀岛，温岭，长兴，杭州和龙游等６个地区白头鹎的鸣声进行了研究，发现它们鸣声主句的语调，音节数，持续时间，频谱特征和频率范围等均有差异，说明白头鹎鸣声中普遍存在“方言”，但它们作为同一个种在鸣声主句上有其共同特征：主要是鸣声多在１．５－３ｋＨｚ的低中频段内变化，单音节的鸣叫声等都极为相似。     

鹤科鸟类鸣声特征的演化

本文在分析鹤科(Gruidae)鸟类鸣声特征的基础上,结合其分子系统树,重建了鸣声特征的演化,并检验了体重与鸣声特征及鸣声特征之间在演化上的相关性。同时比较了体重与鸣声特征在物种间的关系。演化支上各物种体重的变化与鸣声时长特征的变化存在显著的关联(对数线性模型,似然比=9.69,P=0.002;Cohen′s d=1.48):体重的增加伴随着鸣声时长的增加。鸣声特征之间在演化上没有显著的关联(对数线性模型,似然比≤0.15,P≥0.701;Cohen′s d≤0.17)。在物种间鸣声时长与体重存在显著的正相关(Pearson相关分析,r=0.54,P=0.048;Cohen′s d=1.27);鸣声的主频特征与体重存在显著的负相关(Pearson相关分析,r=﹣0.56,P=0.036;Cohen′s d=1.37)。本文以鹤科鸟类鸣声为例,分析了非鸣禽鸟类鸣声特征的演化,及影响鸣声特征的因素。     

Female, but not male, tropical sparrows respond more strongly to the local song dialect: implications for population divergence

In addition to the observed high diversity of species in the tropics, divergence among populations of the same species exists over short geographic distances in both phenotypic traits and neutral genetic markers. Divergence among populations suggests great potential for the evolution of reproductive isolation and eventual speciation. In birds, song can evolve quickly through cultural transmission and result in regional dialects, which can be a critical component of reproductive isolation through variation in female preference. We examined female and male behavioral responses to local and nonlocal dialects in two allopatric populations of rufous-collared sparrows (Zonotrichia capensis) in the Andes Mountains of Ecuador. Here we show that female sparrows prefer their natal song dialect to the dialect of an allopatric population that is just 25 km away and separated by an unsuitable higher-elevation habitat (pass of 4,200 m), thus providing evidence of prezygotic reproductive isolation among populations. Males showed similar territorial responses to all conspecific dialects with no consistent difference with respect to distance, making male territoriality uninformative for estimating reproductive isolation. This study provides novel evidence for culturally based prezygotic isolation over very short distances in a tropical bird.     

Evolutionary Dead End in the Galápagos: Divergence of Sexual Signals in the Rarest of Darwin's Finches

Understanding the mechanisms underlying speciation remains a challenge in evolutionary biology. The adaptive radiation of Darwin''s finches is a prime example of species formation, and their study has revealed many important insights into evolutionary processes. Here, we report striking differences in mating signals (songs), morphology and genetics between the two remnant populations of Darwin''s mangrove finch Camarhynchus heliobates, one of the rarest species in the world. We also show that territorial males exhibited strong discrimination of sexual signals by locality: in response to foreign songs, males responded weaker than to songs from their own population. Female responses were infrequent and weak but gave approximately similar results. Our findings not only suggest speciation in the mangrove finch, thereby providing strong support for the central role of sexual signals during speciation, but they have also implications for the conservation of this iconic bird. If speciation is complete, the eastern species will face imminent extinction, because it has a population size of only 5–10 individuals.     

Vocal communications and the maintenance of population specific songs in a contact zone

Bird song has been hypothesized to play a role in several important aspects of the biology of songbirds, including the generation of taxonomic diversity by speciation; however, the role that song plays in speciation within this group may be dependent upon the ability of populations to maintain population specific songs or calls in the face of gene flow and external cultural influences. Here, in an exploratory study, we construct a spatially explicit model of population movement to examine the consequences of secondary contact of populations singing distinct songs. We concentrate on two broad questions: 1) will population specific songs be maintained in a contact zone or will they be replaced by shared song, and 2) what spatial patterns in the distribution of songs may result from contact? We examine the effects of multiple factors including song-based mating preferences and movement probabilities, oblique versus paternal learning of song, and both cultural and genetic mutations. We find a variety of conditions under which population specific songs can be maintained, particularly when females have preferences for their population specific songs, and we document many distinct patterns of song distribution within the contact zone, including clines, banding, and mosaics.     

Nested biological variation and speciation

The modes of speciation that are thought to have contributed most to the generation of biodiversity require population differentiation as the initial stage in the speciation process. Consequently, a complete understanding of the mechanisms of speciation requires that the process be examined not just after speciation is complete, or nearly so, but also much earlier. Because reproductive isolation defines biological species, and it evolves slowly, study of the process may require a prohibitive span of time. Even if speciation could be observed directly, selection of populations in the process of speciation is typically difficult or impossible, because those that will ultimately undergo speciation cannot be distinguished from those that will differentiate but never assume the status of new biological species. One means of circumventing this problem is to study speciation in taxa comprising several sibling species, at least one of which exhibits extensive population differentiation. We illustrate this approach by exploring patterns of population variation in the post-glacial radiation of the threespine stickleback, Gasterosteus aculeatus. We focus on lacustrine populations and species within this complex, demonstrating parallel axes of divergence within populations, among populations and among species. The pattern that emerges is one of parallel relationships between phenotype and fitness at all three hierarchical levels, a pattern that facilitates exploration of the causes and consequences of speciation and secondary contact. A second outcome of this exploration is the observation that speciation can be the consequence of a cascade of effects, beginning with selection on trophic or other characteristics that in turn force the evolution of other population characteristics that precipitate speciation. Neither of these conclusions could have been reached without comparative studies of wild populations at several hierarchical levels, a conclusion reinforced by a brief survey of similar efforts to elucidate the process of speciation. We address the issues most likely to be resolved using this approach, and suggest that comparisons of natural variation within taxa at several hierarchical levels may substantially increase our understanding of the speciation process.     

Reproductive isolation via divergent genital morphology due to cascade reinforcement in Ohomopterus ground beetles

Secondary contact between incipient species and selection against maladaptive hybridization can drive reinforcement between populations in contact and result in reproductive character displacement (RCD). Resultant divergence in mating traits within a species may generate downstream reproductive isolation between populations with displaced and non-displaced traits, referred to as the cascade reinforcement hypothesis. We examined this hypothesis using three allopatric populations of the ground beetle Carabus maiyasanus with a genital lock-and-key system. This species shows RCD in male and female genital morphologies in populations in contact with the sister species C. iwawakianus. In a reciprocal mating experiment using three allopatric populations with differences in male and female genital sizes, insemination failure increased as the difference in genital size increased. Based on the reproductive isolation index, insemination failure was the major postmating-prezygotic isolation barrier, at least in one population pair with comparable total isolation to those of other species pairs. By contrast, there was only incomplete premating isolation among populations. These results suggest that RCD in genital morphologies drives incipient allopatric speciation, supporting the cascade reinforcement hypothesis. These findings provide insight into the roles of interspecific interactions and subsequent trait diversification in speciation processes.     

Differentiation of Mating Vocalizations in Birds: Acoustic Features in Mainland and Island Populations and Evidence of Habitat-Dependent Selection on Songs

Local environments can act as selective agents on some characteristics of birds’ songs, whereas other song traits may not reflect local genetic adaptation. Geographic variation in songs of two Australian bird species (red‐capped robins Petroica goodenovii, western gerygones Gerygone fusca) was studied to examine one component of the ‘habitat‐dependent selection’ hypothesis. This hypothesis suggests that: (1) the detailed spectral characteristics of male songs are an evolved response to local habitat conditions affecting signal propagation and detection and (2) parallel evolution of other fitness traits sets up the potential for assortative mating by female choice. To examine the first part of the hypothesis, I made comparisons among widespread mainland populations and an island population using two levels of analysis: a typological analysis of song morphology (phonology: notes, syllables, syntax, temporal pattern, repertoires) and a spectral analysis of acoustic characteristics of songs (mean frequency, Wiener entropy, frequency modulation) using an automated procedure of feature extraction (Sound Analysis Pro). Spectral analysis was also used to extract values of the same acoustic features from the background sound environment of each recorded population. The typological analysis revealed no differences among mainland populations of either species, but large differences between mainland songs and those on the island. In contrast, the spectral analysis revealed acoustic divergence among populations, both mainland and island. For both species, Wiener entropy of songs correlated negatively with that of the ambient sound environment, consistent with predictions of the habitat‐dependent selection hypothesis of environmental selection on signal design.     

Geographical differentiation, acoustic adaptation and species boundaries in mainland citril finches and insular Corsican finches, superspecies Carduelis [citrinella]

Aim In birds, differentiation of acoustic characters is an important mechanism of reproductive isolation that may lead to an ethological–acoustic barrier, resulting in the formation of new species. We examined acoustic variation in mainland citril and insular Corsican finch populations, with the aim of assessing the degree of acoustic differentiation between both members of the superspecies Carduelis [citrinella] and documenting possible variation between local subpopulations that are geographically isolated. Location We chose study sites throughout the geographical ranges of citril and Corsican finches. For the citril finch, we obtained samples from the Black Forest (Germany), the Cevennes (France) and the Pyrenees (Spain); for the Corsican finch, we obtained samples from the islands Capraia and Sardinia (Italy) and Corsica (France). Methods We analysed frequent contact calls and elements of the perch song. Vocalization patterns of the study populations were compared by means of discriminant and hierarchical cluster analyses. Results There were significant differences in vocalization characteristics of perch songs and contact calls, which permitted unambiguous discrimination of citril and Corsican finch populations. However, we also detected significant differences in contact calls between mainland citril finch subpopulations. There was a pattern of clinal variation in vocalization: short, steeply modulated signals in the northern part of the geographical range (Black Forest) and long, shallowly modulated signals in the southern part (Pyrenees). Main conclusions Acoustically, mainland citril and insular Corsican finches separate well in their contact calls and perch songs. However, variation in the two vocalization patterns between subpopulations of mainland citril finches indicates that acoustic characteristics can evolve very quickly, not only on islands but also on the mainland. Local habitat differences may play a crucial role in the rapid evolution of these signals under full or partial isolation of small subpopulations. To judge the importance of signal variation as a pre‐mating isolating barrier, future studies will have to determine whether members of the distinct subpopulations are able to match their signals to each other if they re‐meet, and whether intraspecific species recognition is still possible.     

Lack of evidence for reproductive isolation among ecologically specialised lycaenid butterflies

Abstract 1. The evolution of reproductive isolation between recently diverged or incipient species is a critical component of speciation and a major focus of speciation models. In phytophagous insects, host plant fidelity (the habit of mating and ovipositing on a single host species) can contribute to assortative mating and reproductive isolation between populations adapting to alternative hosts. The potential role of host plant fidelity in the evolution of reproductive isolation was examined in a pair of North American blue butterfly species, Lycaeides idas and L. melissa .
2. These species are morphologically distinct and populations of each species utilise different host plants; however they share 410 bp haplotypes of the mitochondrial cytochrome oxidase subunit I (COI) gene, indicating recent divergence.
3. Some populations using native hosts exhibited strong fidelity for their natal host plant over the hosts used by nearby populations. Because these butterflies mate on or near the host plant, the development of strong host fidelity may create reproductive isolation among populations on different hosts and restrict gene flow.
4. Tests of population differentiation using allozyme allele frequency data did not provide convincing evidence of restricted gene flow among populations. Based on morphological differences, observed ecological specialisation, and the sharing of genetic markers, these butterflies appear to be undergoing adaptive radiation driven at least partially by host shifts. Neutral genetic markers may fail to detect the effects of very recent host shifts in these populations due to gene flow and/or the recency of divergence and shared ancestral polymorphism.     

The role of mating preferences in shaping interspecific divergence in mating signals in vertebrates

Vertebrates represent one of the best-studied groups in terms of the role that mating preferences have played in the evolution of exaggerated secondary sexual characters and mating behaviours within species. Vertebrate species however, also exhibit enormous interspecific diversity in features of mating signals that has potentially led to reproductive isolation and speciation in many groups. The role that sexual selection has played in interspecific divergence in mating signals has been less fully explored. This review summarizes our current knowledge of how mating preferences within species have shaped interspecific divergence in mate recognition signals among the major vertebrate groups. Certain signal modalities appear to characterize mating signal diversification among different vertebrate taxa. Acoustic signals play an important role in mating decisions in anuran amphibians and birds. Here, different properties of the signal may convey information regarding individual, neighbor and species recognition. Mating preferences for particular features of the acoustic signal have led to interspecific divergence in calls and songs. Divergence in morphological traits such as colouration or ornamentation appears to be important in interspecific diversity in certain groups of fishes and birds. Pheromonal signals serve as the primary basis for species-specific mating cues in many salamander species, most mammals and even some fishes. The evolution of interspecific divergence in elaborate courtship displays may have played an important role in speciation of lizards, and particular groups of fishes, salamanders, birds and mammals. While much research has focused on the importance of mating preferences in shaping the evolution of these types of mating signals within species, the link between intraspecific preferences and interspecific divergence and speciation remains to be more fully tested. Future studies should focus on identifying how variation in mating preferences within a species shapes interspecific diversity in features of mating signals in order to better understand how sexual selection may have led to speciation in vertebrates.     

Assortative mating by white-crowned sparrows at song dialect boundaries

We tested the hypothesis that female Nuttall's white-crowned sparrows (Zonotrichia leucophrys nuttalli) mate assortatively with males from the same dialect population. Young birds of both sexes learn their natal dialect during an early sensitive period, and for females, this early experience may be the basis of future mate choice. A total of 32 female sparrows were mist-netted for three experiments at or near dialect boundaries just inside the Limantour, Drake and Clear dialect populations in Marin Co., California. The mates of all captured females sang the home dialect. All females were implanted with testosterone and maintained in captivity. Of the females which began to sing, 25 sang recognizable white-crowned sparrow songs. Of those 25 females, 24 had mated assortatively, thus supporting the assortative mating hypothesis.