Data from: Cryptic species diversity reveals biogeographic support for the ‘mountain passes are higher in the tropics’ hypothesis

The ‘mountain passes are higher in the tropics’ (MPHT) hypothesis posits that reduced climate variability at low latitudes should select for narrower thermal tolerances, lower dispersal and smaller elevational ranges compared with higher latitudes. These latitudinal differences could increase species richness at low latitudes, but that increase may be largely cryptic, because physiological and dispersal traits isolating populations might not correspond to morphological differences. Yet previous tests of the MPHT hypothesis have not addressed cryptic diversity. We use integrative taxonomy, combining morphology (6136 specimens) and DNA barcoding (1832 specimens) to compare the species richness, cryptic diversity and elevational ranges of mayflies (Ephemeroptera) in the Rocky Mountains (Colorado; approx. 40°N) and the Andes (Ecuador; approx. 0°). We find higher species richness and smaller elevational ranges in Ecuador than Colorado, but only after quantifying and accounting for cryptic diversity. The opposite pattern is found when comparing diversity based on morphology alone, underscoring the importance of uncovering cryptic species to understand global biodiversity patterns.

“‘热带山地隘口更高’假说（mountain passes are higher in the tropics，MPHT）提出：与高纬度地区相比，低纬度地区气候变率更低，这会驱动物种演化出更狭窄的热耐受范围、更弱的扩散能力以及更小的海拔分布范围。这类纬度梯度差异本可提升低纬度地区的物种丰富度，但该增益大概率以隐存多样性的形式存在——因为分隔种群的生理与扩散性状，未必与形态学差异相对应。然而，此前针对该MPHT假说的检验均未涉及隐存多样性的相关议题。本研究采用整合分类学（integrative taxonomy）方法，结合形态学数据（6136份标本）与DNA条形码（DNA barcoding），对比了落基山脉（美国科罗拉多州；约北纬40°）与安第斯山脉（厄瓜多尔；约赤道0°）地区蜉蝣（Ephemeroptera，蜉蝣目）的物种丰富度、隐存多样性及海拔分布范围。研究结果显示：厄瓜多尔地区的物种丰富度更高、海拔分布范围更小，且这一格局仅在量化并校正隐存多样性后才成立；若仅基于形态学数据进行多样性比较，则会得到截然相反的格局，这凸显了揭示隐存物种对于理解全球生物多样性格局的关键意义。