Trier University, Department of Biogeography, Universitätsring 15, 54296 Trier, Germany.
Naturalis Biodiversity Centre, PO Box 9517, NL-2300 RA Leiden, The Netherlands.
Mol Phylogenet Evol. 2018 Apr;121:98-109. doi: 10.1016/j.ympev.2018.01.006. Epub 2018 Jan 9.
Amphibians have a complex reproductive behaviour, which shows the highest diversity among tetrapodes. The family Salamandridae, distributed across the entire Holarctic, is one of the most diverse groups of extant salamanders comprising 114 species in 21 genera. The family has a remarkable diversity of courtship modes, amplexus and sperm transfer. It is often hypothesised that this diversity has evolved in adaptation to a specific mating and/or breeding habitat. We test this hypothesis based upon a phylogenetic reconstruction using the complete mitochondrial genome sequences of 45 Salamandridae species, representing all existing genera. We used ancestral character state reconstruction methods and geographic range models and applied relaxed Bayesian molecular clock models to discuss the results in a temporal framework of Salamandridae evolution. Our results show that the family Salamandridae started to diversify in the Late Cretaceous (ca. 87 mya) and is of Western Palearctic origin. Ancestral character state reconstruction predicts that its common ancestor was oviparous, mated on land without amplexus and probably showed a pin wheel spermatophore transfer, which is still found in the Italian endemic Salamandrina terdigidata. Our results suggest that several colonization of continents with subsequent radiations took place, once to the Nearctic and twice into Eastern Asian realms. However, these events were only in one case associated with a change in mating behaviour (dorsal amplexus in Nearctic newts). Around the Cretaceous-Paleogene boundary (K-Pg boundary) several Salamandridae lineages further diverged, again with no obvious changes in mating behaviour. Overall, there is no significant signal for mating character evolution being caused by changes in habitat type, with only a slight tendency that changes in mating habitat might have led to changes in the type of sperm transfer which in turn was associated with changes in the presence or absence of amplexus.
两栖动物的繁殖行为复杂多样，在四足动物中表现出最高的多样性。分布在整个全北界的蝾螈科是现存蝾螈中最多样化的群体之一，由 21 个属的 114 个物种组成。该科具有显著多样的求偶方式、交媾和精子传递。人们常常假设这种多样性是为了适应特定的交配和/或繁殖栖息地而进化的。我们使用 45 种蝾螈科物种的完整线粒体基因组序列进行系统发育重建，以此来检验这一假设，这些物种代表了所有现存的属。我们使用祖先特征状态重建方法和地理范围模型，并应用松弛贝叶斯分子钟模型，在蝾螈科进化的时间框架内讨论结果。我们的研究结果表明，蝾螈科家族在白垩纪晚期（约 8700 万年前）开始多样化，起源于西古北区。祖先特征状态重建预测，它的共同祖先为卵生，在陆地上交配，没有交媾，可能表现出轮形精子传递，这种现象仍然存在于意大利特有物种 Salamandrina terdigidata 中。我们的研究结果表明，有几次蝾螈科物种的迁徙和辐射事件发生，一次发生在北美洲，两次发生在东亚地区。然而，这些事件只有一次与交配行为的变化有关（在北美洲蝾螈中出现背部交媾）。在白垩纪-古近纪边界（K-Pg 边界）前后，一些蝾螈科的谱系进一步分化，交配行为也没有明显变化。总的来说，没有明显的信号表明交配特征的进化是由栖息地类型的变化引起的，只有一个微弱的趋势表明，交配栖息地的变化可能导致精子传递方式的变化，而精子传递方式的变化又与交媾的有无有关。
