Basic Mechanisms and Evolution of Acoustic Communication

声学通信的基本机制和进化HOWARD CARL GERHARDT， JR.，首席研究员（姓名：H. CARL GERHARDT）：通信影响信号发送者和接收者的繁殖成功率。因此，交流在进化和物种形成中起着至关重要的作用，信号的差异往往是种群状态的可靠指标，这些种群在外表上几乎没有差异，如果有的话。发送者和接收者施加的相互选择压力可能会在信号特性和感觉系统的选择性之间产生精确的匹配。原因是发出不同信号的人不太可能吸引异性，而接收信号的人有非常独特的偏好，可能不会被自己物种的任何男性所接受。然而，已经发现了一些例外的例子，在这些例子中，接受者更有效地受到不是由自己物种成员（=同种雄性）而是由密切相关物种成员（=异种雄性）产生的信号的刺激。这些新的偏好被称为“隐藏偏好”，系统发育分析有时表明，这种偏好在进化时间的信号出现之前就存在，因此这种偏好可以被认为是“预先存在的偏见”。本项目是对九种密切相关的北美树蛙的信号特性和接收器偏好匹配的比较研究。雄性树蛙会发出简单、刻板的声音，雌性树蛙会对这些声音或计算机合成的声音做出反应，它们会靠近发出这些声音的扬声器。使用合成叫声的回放实验将确定雌性在选择信号时使用的关键物理特性（=偏好标准）。这些实验将确定每个物种的雌性是否对具有同种雄性典型特征的信号做出最好的反应，或者其他物种的叫声或叫声元素是否更有吸引力或可能增强同种叫声的吸引力。可能会发现，在所有9个物种中，同种鸣叫属性的匹配都很好，不匹配在所有物种中都很普遍，或者在某些物种中存在匹配，而在其他物种中不存在匹配。不管这些实验的结果如何，系统发育分析——它将依赖于所有9个物种的形态和分子特征——将被用来提出偏好和信号的进化顺序。这组特殊的树蛙还有两个特征，可以帮助解释一种模式，即在某些物种中出现匹配，而在其他物种中出现不匹配。首先，群体中的一些物种经常与近亲发出类似的叫声，形成混合物种的合唱。在这里，为了防止物种之间的交配，可能会期望发送者和接收者的匹配会很强。该组中的其他物种已经与其他具有类似叫声的物种隔离了很长一段时间，而其他物种。这些是寻找不匹配（“隐藏偏好”和“预先存在的偏见”）的最佳候选者，因为这些偏见可能是祖先的特征，可以在没有与其他物种交配风险的情况下表达出来。其次，研究发现，该种群中某些物种的染色体数量是其他物种的两倍，染色体数量的变化会影响叫声特性。这种染色体数目的变化也可能以某种方式影响雌性的偏好，这种方式要么可以跟踪呼叫的变化，要么导致发送者和接受者的不匹配。这一假设将通过研究实验诱导的额外染色体组青蛙的偏好来验证。

BASIC MECHANISMS AND EVOLUTION OF ACOUSTIC COMMUNICATION HOWARD CARL GERHARDT, JR., PRINCIPAL INVESTIGATOR(Name used as an author: H. Carl Gerhardt)Communication affects the reproductive success of signalers and receivers. Thus, communication plays a critical role in evolution and speciation, and differences in signals are often reliable indicators of the status of populations that have diverged little, if at all, in their physical appearance. Mutual selective pressures exerted by senders and receivers might be expected to generate precise matching between signal properties and the selectivity of the sensory system. The reason is that senders that produce very different signals are unlikely to attract mates, and receivers that have very unique preferences may not find any male of their own species acceptable. However, some exceptional examples have been found in which receivers are more effectively stimulated by signals that are not produced by members of their own species (=conspecific males), but by those of closely related species (=heterospecific males). These novel preferences have been called "hidden preferences," and a phylogenetic analysis sometimes shows that the preference predates signals in evolutionary time and can hence such preferences can be considered "pre-existing biases." This project is a comparative study of the matching of signal properties and receiver preferences in a complex of nine closely related North American treefrogs. Male treefrogs produce simple, stereotyped sounds, and females respond to these sounds or to synthetic, computer-generated sounds by approaching a speaker that emits them. Playback experiments using synthetic calls will identify the key physical properties (=preference criteria) used by females to select among signals. These experiments will determine for each species whether females respond best to signals with properties typical of conspecific males or whether calls or call-elements of other species might be more attractive or might enhance the attractiveness of conspecific calls. It might be found that matching to conspecific call properties is good in all nine species, that mismatches are prevalent in all species, or that matching occurs in some species but not in others. Regardless of the results of these experiments, a phylogenetic analysis - which will rely on morphological and molecular characters of all nine species - will be used to suggest the order of evolution of preferences and signals. This particular group of treefrogs also has two features that could help to explain a pattern in which matches occur in some species and mismatches in others. First, some species in the group routinely form mixed-species choruses with close relatives having similar calls. Here it might be expected that matching of senders and receivers will be strong in order to prevent mating between species. Other species in the group have been isolated from any other species with similar calls for long periods of time whereas others. These are the best candidates for finding mismatches ("hidden preferences" and "pre-existing biases") because these biases might be ancestral traits that can be expressed without the risk of mating with another species. Second, it has been found that some species in the group have twice the number of chromosomes of the other species and that changes in chromosome number affect call properties. Such a change in chromosome number might also affect female preferences in ways that could either track the changes in the calls or result in mismatches of senders and receivers. This hypothesis will be tested by studying the preferences of frogs with experimentally induced extra sets of chromosomes.