Abstract
The latitudinal diversity gradient (LDG), that is, the increase in species richness from the poles to the equator, is one of the oldest known ecological patterns. Its inverse (iLDG), where species richness increases toward higher latitudes, is less common but has recently attracted growing scientific interest. Here, we investigate the causes for iLDG in a highly diversified group: the slant‐faced grasshoppers (Gomphocerinae). We examine two hypotheses: the temporal hypothesis, which attributes diversity gradients to differences in the time available for diversification, and the evolutionary hypothesis, which suggests gradients arise from differences in diversification rates. We reconstructed a molecular phylogeny using the most comprehensive sampling to date, incorporating six mitochondrial and two nuclear markers. We confirmed the subfamily's paraphyly and identified a Gomphocerinae sensu stricto clade that we used to test iLDG hypotheses. Molecular dating and the reconstruction of historical biogeography refuted the temporal hypothesis, as the time available for the diversification of tropical lineages was greater than for lineages of temperate regions. Conversely, we found evidence for a contribution of diversification rates to the observed iLDG. A diversification rate shift was detected in the Gomphocerinae s.s. clade, with much higher rates in some species‐rich clades distributed in temperate regions compared to tropical clades.