Drivers of diversification in freshwater gastropods vary over deep time

Abstract

Unravelling the drivers of species diversification through geological time is of crucial importance for our understanding of long-term evolutionary processes. Numerous studies have proposed different sets of biotic and abiotic controls of speciation and extinction rates, but typically they were inferred for a single, long geological time frame. However, whether the impact of biotic and abiotic controls on diversification changes over time is poorly understood. Here, we use a large fossil dataset, a multivariate birth–death model and a comprehensive set of biotic and abiotic predictors, including a new index to quantify tectonic complexity, to estimate the drivers of diversification for European freshwater gastropods over the past 100 Myr. The effects of these factors on origination and extinction are estimated across the entire time frame as well as within sequential time windows of 20 Myr each. Our results find support for temporal heterogeneity in the factors associated with changes in diversification rates. While the factors impacting speciation and extinction rates vary considerably over time, diversity-dependence and topography are consistently important. Our study highlights that a high level of heterogeneity in diversification rates is best captured by incorporating time-varying effects of biotic and abiotic factors.

Short-term paleogeographic reorganizations and climate events shaped diversification of North American freshwater gastropods over deep time

“…Numerous studies found support for diversity dependence across different species groups, time intervals, and geographic regions 2 , 4 , 15 – 17 , 65 . Among European fossil freshwater gastropods, diversity dependence was recently reported as the most important control on diversification over short geological timescales 18 .…”

“…Our results indicate that diversity dependence is only of limited relevance to freshwater biota on a continental scale over extended geological time spans. In contrast, biotic factors are presumably more important at local and regional scales (e.g., in single drainage basins or biogeographic regions) and over shorter time spans 18 , 23 . The absence of diversity dependence of the extinction rate suggests that North American freshwater gastropod faunas were far from approaching equilibrium diversity.…”

“…We compiled the fossil species occurrences of Late Triassic to Pleistocene North American freshwater gastropods from the literature 18 (Fig. S1 ).…”

“…Several abiotic factors have been hypothesized to impact species diversification including climate, sea-level fluctuations, environmental factors, and continental fragmentation 3 , 9 – 14 . A biotic factor found to be relevant in many studies is diversity dependence, whereby greater species richness slows down diversification, e.g., due to competition 2 , 4 , 5 , 15 – 18 . Several studies show a combined effect of abiotic and biotic factors on species diversification 3 , 12 , 19 , 20 .…”

“…Conversely, biotic factors such as diversity dependence are primarily regional phenomena, since species interactions happen at a local scale, while in larger systems not all members of a species group co-occur 23 . Notably though, several studies have still found support for diversity-dependent diversification on continental 2 , 18 , 24 or even global scales 3 , 11 , 25 . Moreover, the drivers of diversification are expected to vary among marine, terrestrial, and freshwater biota given their different environmental conditions and constraints on dispersal mechanisms 26 .…”