PDF(Pubmed)
Abstract：
Neoteny is a developmental strategy wherein an organism reaches sexual maturity without associated adult characteristics. In salamanders, neoteny takes the form of individuals retaining aquatic larval characteristics such as external gills upon maturation. Mole salamanders (Ambystoma) occupy a wide range of habitats and areas across the North American continent, and display examples of non-neotenic, facultatively neotenic and obligate neotenic species, providing high variation for investigating the factors influencing the evolution of neoteny. Here, we use phylogenetic comparative methods to test existing hypotheses that neoteny is associated with elevational and latitudinal distribution, cave-associated isolation, and hybridisation-related polyploidy. We also test if neoteny influences the diversity of habitats a species can occupy, since the restriction to an aquatic life should constrain the availability of different niches. We find that neoteny tends to occur in a narrow latitudinal band between 20-30° North, with particularly narrow latitudinal ranges for obligate compared to facultative neotenic species (16-52° North). We also find that facultatively neotenic species occur at elevations more than twice as high as other species on average, and that species with a higher frequency of neoteny typically have lower habitat diversity. Our results suggest that evolutionary transitions between non-neotenic and facultative neoteny states occur at relatively high and approximately equal rates. Moreover, we estimate that obligate neoteny cannot evolve directly from non-neotenic species (and vice versa), such that facultative neoteny acts as an evolutionary \'stepping stone\' to and from obligate neoteny. However, our transition rate estimates suggest that obligate neoteny is lost >4-times faster than it evolves, partly explaining the rarity of obligate species. These results support the hypothesis that low latitudes favour the evolution of neoteny, presumably linked to more stable (aquatic) environments due to reduced seasonality, but once evolved it may constrain the diversity of habitats.
摘要：
新生是一种发育策略，其中生物体达到性成熟而没有相关的成人特征。在sal中，新生的形式是个体在成熟时保留水生幼虫的特征，例如外部g。Molesal（Ambystoma）占据了整个北美大陆的广泛栖息地和地区，并显示非新生的例子，兼有新性和专性新性物种，为研究影响新生进化的因素提供了很高的变异。这里,我们使用系统发育比较方法来检验现有的假设，即新生与海拔和纬度分布有关，与洞穴相关的隔离，和杂交相关的多倍体。我们还测试新生是否会影响一个物种可以占据的栖息地的多样性，因为对水生生物的限制应该限制不同生态位的可用性。我们发现新生倾向于发生在北纬20-30°之间的狭窄纬度带，与兼性新物种（北16-52°）相比，专性的纬度范围特别窄。我们还发现，新兴物种的平均海拔是其他物种的两倍多，新生频率较高的物种通常具有较低的栖息地多样性。我们的结果表明，非新状态和兼性新状态之间的进化转变以相对较高和近似相等的速率发生。此外，我们估计专性新生不能直接从非新生物种进化(反之亦然)，这样，兼性新生就像进化中的“垫脚石”，进出专性新生。然而,我们的过渡率估计表明，专属性新生的丢失速度比进化快4倍，部分解释了专性物种的稀有性。这些结果支持低纬度有利于新生态进化的假设，由于季节性减少，推测与更稳定的(水生)环境有关，但是一旦进化，它可能会限制栖息地的多样性。
