Department of Ecology, Evolution, and Behavior, University of Minnesota - Twin Cities, St Paul, MN 55126, USA.
School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA.
J Exp Biol. 2021 Dec 1;224(23). doi: 10.1242/jeb.243405. Epub 2021 Dec 9.
Sexual traits that promote species recognition are important drivers of reproductive isolation, especially among closely related species. Identifying neural processes that shape species differences in recognition is crucial for understanding the causal mechanisms of reproductive isolation. Temporal patterns are salient features of sexual signals that are widely used in species recognition by several taxa, including anurans. Recent advances in our understanding of temporal processing by the anuran auditory system provide an opportunity to investigate the neural basis of species-specific recognition. The anuran inferior colliculus consists of neurons that are selective for temporal features of calls. Of potential relevance are auditory neurons known as interval-counting neurons (ICNs) that are often selective for the pulse rate of conspecific advertisement calls. Here, we tested the hypothesis that ICNs mediate acoustic species recognition by exploiting the known differences in temporal selectivity in two cryptic species of gray treefrog (Hyla chrysoscelis and Hyla versicolor). We examined the extent to which the threshold number of pulses required to elicit behavioral responses from females and neural responses from ICNs was similar within each species but potentially different between the two species. In support of our hypothesis, we found that a species difference in behavioral pulse number thresholds closely matched the species difference in neural pulse number thresholds. However, this relationship held only for ICNs that exhibited band-pass tuning for conspecific pulse rates. Together, these findings suggest that differences in temporal processing of a subset of ICNs provide a mechanistic explanation for reproductive isolation between two cryptic treefrog species.
促进物种识别的性特征是生殖隔离的重要驱动因素，尤其是在亲缘关系密切的物种之间。确定塑造识别物种差异的神经过程对于理解生殖隔离的因果机制至关重要。时间模式是性信号的显著特征，被包括蛙类在内的多个类群广泛用于物种识别。我们对蛙类听觉系统时间处理的理解的最新进展为研究特定物种识别的神经基础提供了机会。蛙类的下丘包含对叫声时间特征具有选择性的神经元。具有潜在相关性的是听觉神经元，称为间隔计数神经元 (ICN)，它们通常对同种广告叫声的脉冲率具有选择性。在这里，我们通过利用两种隐秘的灰色树蛙（Hyla chrysoscelis 和 Hyla versicolor）在时间选择性方面的已知差异，测试了 ICN 介导声学物种识别的假设。我们检查了在每个物种内，引发雌性产生行为反应和 ICN 产生神经反应所需的脉冲数阈值在多大程度上是相似的，但在两个物种之间可能不同。支持我们的假设，我们发现行为脉冲数阈值的物种差异与神经脉冲数阈值的物种差异非常匹配。然而，这种关系仅适用于对同种脉冲率表现出带通调谐的 ICN。总之，这些发现表明，一组 ICN 的时间处理差异为两种隐秘树蛙之间的生殖隔离提供了一种机制解释。
