An official website of the United States government
Abstract AimThe latitudinal diversity gradient of increasing species richness from poles to equator is one of the most striking and pervasive spatial patterns of biodiversity. Climate appears to have been key to the formation of the latitudinal diversity gradient, but the processes through which climate shaped species richness remain unclear. We tested predictions of the time for speciation, carrying capacity and diversification rate latitudinal diversity gradient hypotheses in a trans‐marine/freshwater clade of fishes. LocationGlobal in marine and freshwater environments. TaxonClupeiformes (anchovies, herrings, sardines and relatives). MethodsWe tested predictions of latitudinal diversity gradient hypotheses using a molecular phylogeny, species distribution data and phylogenetic comparative approaches. To test the time for speciation hypothesis, we conducted ancestral state reconstructions to infer the ages of temperate, subtropical and tropical lineages and frequency of evolutionary transitions between climates. We tested the carry capacity hypothesis by characterizing changes in net diversification rates through time. To test the diversification rate hypothesis, we qualitatively compared the diversification rates of temperate, subtropical and tropical lineages and conducted statistical tests for associations between latitude and diversification rates. ResultsWe identified four transitions to temperate climates and two transitions out of temperate climates. We found no differences in diversification rates among temperate and tropical clupeiforms. Net diversification rates remained positive in crown Clupeiformes since their origin ~150 Ma in both tropical and temperate lineages. Climate niche characters exhibited strong phylogenetic signal. All temperate clupeiform lineages arose <50 Ma, after the Early Eocene Climatic Optimum. Main conclusionsOur results support the time for speciation hypothesis, which proposes that climate niche conservatism and fluctuations in the extent of temperate climates limited the time for species to accumulate in temperate climates, resulting in the latitudinal diversity gradient. We found no support for the carrying capacity or diversification rate hypotheses.
more »
« less
This content will become publicly available on February 18, 2027
Phylogenetic estimation of diversity-dependent biogeographic rates using deep learning
Abstract Ecological theory predicts that local species richness can influence biogeographic rates of speciation, extinction, and dispersal. For instance, increasing the number of competing species within a region may cause local speciation and dispersal rates to decrease but local extinction rates to increase, inducing a carrying capacity for local species richness. In this article, we introduce a fully generative, event-based phylogenetic diversification model, called DDGeoSSE, that allows diversity-dependent effects of local species richness to modulate biogeographic rates of diversification and range evolution. DDGeoSSE can accommodate and test a variety of alternative diversification scenarios that involve positive, negative, and neutral interactions among sympatric species for speciation, extinction, and dispersal. We derive mathematical and statistical properties of biogeographic outcomes generated by this model, such as the carrying capacity for a clade at equilibrium, which we validate through simulation. Because diversity-dependent phylogenetic models typically do not have tractable likelihood functions, we use deep learning withphyddleto perform parameter inference and model selection. Separately applying DDGeoSSE to CaribbeanAnolislizards and cloud forest-dwellingViburnumplants, we find evidence that local species richness plays a significant role in shaping diversification dynamics for both clades.
more »
« less
- Award ID(s):
- 2040347
- PAR ID:
- 10679313
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The extraordinary number of species in the tropics when compared to the extra-tropics is probably the most prominent and consistent pattern in biogeography, suggesting that overarching processes regulate this diversity gradient. A major challenge to characterizing which processes are at play relies on quantifying how the frequency and determinants of tropical and extra-tropical speciation, extinction, and dispersal events shaped evolutionary radiations. We address this question by developing and applying spatiotemporal phylogenetic and paleontological models of diversification for tetrapod species incorporating paleoenvironmental variation. Our phylogenetic model results show that area, energy, or species richness did not uniformly affect speciation rates across tetrapods and dispute expectations of a latitudinal gradient in speciation rates. Instead, both neontological and fossil evidence coincide in underscoring the role of extra-tropical extinctions and the outflow of tropical species in shaping biodiversity. These diversification dynamics accurately predict present-day levels of species richness across latitudes and uncover temporal idiosyncrasies but spatial generality across the major tetrapod radiations.more » « less
-
The regions of the Andes and Caribbean-Mesoamerica are both hypothesized to be the cradle for many Neotropical lineages, but few studies have fully investigated the dynamics and interactions between Neotropical bioregions. The New World hawkmoth genus Xylophanes is the most taxonomically diverse genus in the Sphingidae, with the highest endemism and richness in the Andes and Caribbean-Mesoamerica. We integrated phylogenomic and DNA barcode data and generated the first time-calibrated tree for this genus, covering 93.8% of the species diversity. We used event-based likelihood ancestral area estimation and biogeographic stochastic mapping to examine the speciation and dispersal dynamics of Xylophanes across bioregions. We also used trait-dependent diversification models to compare speciation and extinction rates of lineages associated with different bioregions. Our results indicate that Xylophanes originated in Caribbean-Mesoamerica in the Late Miocene, and immediately diverged into five major clades. The current species diversity and distribution of Xylophanes can be explained by two consecutive phases. In the first phase, the highest Xylophanes speciation and emigration rates occurred in the Caribbean-Mesoamerica, and the highest immigration rates occurred in the Andes, whereas in the second phase the highest immigration rates were found in Amazonia, and the Andes had the highest speciation and emigration rates.more » « less
-
Abstract Islands are ideal mesocosms for studying dispersal, speciation, and extinction, but our understanding of insular radiations has long been limited by the difficulty of estimating the timing and tempo of island evolution in the absence of fossils and methods that explicitly account for the role of paleogeography in diversification. We introduce a new generalizable model, TimeFIG, which jointly infers paleogeographically-informed biogeographic rates, ancestral species ranges, and divergence times without using fossils. Using TimeFIG, we reconstruct the phylogeny of Hawaiian Kadua, an ecomorphologically diverse but understudied plant lineage in the coffee family (Rubiaceae), and estimate dispersal, speciation, and extinction rates simultaneously with divergence times and ancestral ranges. Our results support a range of colonization times, either corresponding with the rise of the oldest modern island, Kaua’i, or with older now-eroded, northwestern islands. We detect strong effects of island isolation on dispersal rates, and find highest diversification rates when islands are “middle-aged” (i.e., Goldilocks effect). Our unified spatiotemporal framework unlocks new possibilities for historical biogeography, enabling rigorous tests of foundational hypotheses in island biology and evolutionary theory.more » « less
-
The uneven global distribution of plant diversity remains a fundamental question in biogeography. Using dated phylogenies of >300,000 plant species and ancestral biogeographical stochastic mapping, we show that in situ speciation is the predominant process underlying extant plant diversity and accounts for 78% of biogeographic events across realms. The Neotropic contributed 37% of in situ speciation, likely owing to its role as a center of species diversification. Dispersal between realms was less frequent (16% of events) but facilitated floristic exchanges, especially in the Eastern Hemisphere. Extinction was least frequent but more pronounced in East Asia. These findings support the tropical conservatism hypothesis in which many clades originated in the tropics and only recently expanded into temperate zones, where limited time and biome conservatism have restricted speciation and diversity.more » « less
