Data from: The origins and diversification of the exceptionally rich gemsnakes (Colubroidea: Lamprophiidae: Pseudoxyrhophiinae) in Madagascar

Processes leading to spectacular diversity of both form and species on
islands have been well documented under island biogeography theory, where
distance from source and island size are key factors determining
immigration and extinction resistance. Less understood are the processes
governing in-situ diversification on the world’s mega islands, where large
and isolated land masses produced morphologically distinct radiations from
related taxa on continental regions. Madagascar has long been recognized
as a natural laboratory due to its isolation, lack of influence from
adjacent continents, and diversification of spectacular vertebrate
radiations. However, only a handful of studies have examined rate shifts
of in-situ diversification for this island. Here we examine rates of
diversification in the Malagasy snakes of the family Pseudoxyrhophiinae
(gemsnakes) to understand if rates of speciation were initially high,
enhanced by diversification into distinct biomes, and associated with key
dentition traits. Using a genomic sequence-capture dataset for 366
samples, we determine that all previously described and newly discovered
species are delimitable and therefore useful candidates for understanding
diversification trajectories through time. Our analysis detected no shifts
in diversification rate between clades or changes in biome or dentition
type. However, we did detect a significant slowdown in diversification
during the Pleistocene. We comment on the apparent paradox where most
living species originated in the Pleistocene, yet diversification rates
were highest during the previous 15 million years.

岛屿上物种与形态多样性爆发式形成的过程，已在岛屿生物地理学理论（island biogeography theory）的框架下得到充分阐释。该理论指出，与物种源种群的距离及岛屿面积，是决定物种迁入率与灭绝抗性的核心因子。
而针对全球巨型岛屿上的原位分化（in-situ diversification）过程，学界目前的认知仍较为有限：这类大型且孤立的陆块，孕育出了与大陆近缘类群形态迥异的辐射演化（radiation）类群。
马达加斯加因其长期隔离、不受邻近大陆的生态影响，以及孕育了众多极具特色的脊椎动物辐射演化类群，长期以来被视作天然研究实验室。然而，针对该岛屿的原位分化速率变化，目前仅有少量研究开展。
本研究以马达加斯加钝头蛇亚科（Pseudoxyrhophiinae，宝石蛇gemsnakes）的蛇类类群为研究对象，对其分化速率展开分析，旨在明确三个科学问题：物种形成速率是否初始即处于较高水平、是否因向不同生物群区（biome）的分化而得到提升，以及是否与关键的齿型特征相关联。
我们利用针对366个样本的基因组序列捕获（genomic sequence-capture）数据集，证实所有此前已描述及新发现的物种均可被有效界定，因此可作为探究随时间推移的分化轨迹的可靠候选类群。
分析结果显示，各演化分支（clade）间的分化速率未出现显著偏移，生物群区或齿型类型也未发生显著改变。但我们确实检测到，在更新世（Pleistocene）时期，类群的分化速率出现了显著放缓。
我们还就这一表观悖论展开讨论：绝大多数现生物种均起源于更新世，但分化速率的峰值却出现在此前的1500万年期间。