Time for speciation and niche conservatism explain the latitudinal diversity gradient in clupeiform fishes

Abstract

Aim The 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. Location Global in marine and freshwater environments. Taxon Clupeiformes (anchovies, herrings, sardines and relatives). Methods We 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. Results We 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 conclusions Our 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.

Same process, different patterns: pervasive effect of evolutionary time on species richness in freshwater fishes

“…Overall, the positive effect of evolutionary time on species richness is constant across freshwater fish orders. This result supports previous findings (but see [72]) for distinct taxonomic levels, as observed for all freshwater fishes [19], orders like Clupeiformes [47], and families such as Poeciliidae [23], as well as for distinct spatial extents from global [19,47] to continental domains [23], and for distinct spatial grains as drainage basins [19], latitudinal bands [47] and grid-cells [23]. Finally, even though the positive effect of the evolutionary time on species richness seems to be generalized, other evolutionary and ecological drivers also influenced species richness variation of all freshwater fishes and/or individual orders.…”

“…Indeed, evolutionary time had a pervasive effect on the species richness gradients of different freshwater fish orders despite their large differences in diversity, geographical distribution, colonization/origination time, ecological and physiological requirements, as well as dispersal abilities [19,67]. Our findings support the time-for-speciation hypothesis, agreeing with previous studies in terrestrial, flying and aquatic vertebrates in which both expected [19,24,47,71] and inverse LDGs have been explained by the longer establishment of these clades in species-rich regions [11,20,23]. Overall, the positive effect of evolutionary time on species richness is constant across freshwater fish orders.…”

“…An expected LDG along with a tropical origin of most rich orders [19,47] support the tropical niche conservatism hypothesis in which most lineages are limited to their ancestral tropical conditions [12]. For example, a recent study including marine and freshwater species found an expected LDG in Clupeiformes, supporting that most species are restricted to the tropics with few transitions from tropical to temperate regions [47]. By contrast, fishes that diversified in temperate regions and showed an anti-tropical distribution and inverse LDG (e.g.…”

“…The time-for-speciation hypothesis has been tested using several metrics as a proxy of evolutionary time, namely the elapsed time that a clade has had to accumulate species since it originated or colonized a region [11,46]. Previous studies have used the stem and crown age of a clade [24,46] as well as distinct phylogenetic metrics such as mean pairwise distance, mean root distance and MBL as a proxy of time [3,45,47,48]. However, some of these phylogenetic metrics could be biased by involving other evolutionary processes, thus not directly describing the time that a clade has had in a region.…”

The Habitat Persistence Hypothesis: a new perspective on the distribution of coral-reef organisms

“…Meseguer and Condamine (2020) found higher rates of extirpation and extinction of reptiles in temperate latitudes, when habitats turned from "hothouse to icehouse". In this regard, HPH may link well with 'time for speciation' hypotheses, which posit that greater diversity in tropical versus temperate climates is because temperate habitat lacks the stability and timeframe necessary for new species to emerge (Stephens and Wiens 2003;Egan et al 2022). In a metaanalysis of ray-finned fishes (Percomorpha), Miller et al (2018) found support for 'time for speciation' in marine faunas.…”