Macroecology and macroevolution of the latitudinal diversity gradient in ants.

The latitudinal diversity gradient-the tendency for more species to occur toward the equator-is the dominant pattern of life on Earth, yet the mechanisms responsible for it remain largely unexplained. Recently, the analysis of global data has led to advances in understanding, but these advances have been mostly limited to vertebrates and trees and have not provided consensus answers. Here we synthesize large-scale geographic, phylogenetic, and fossil data for an exemplar invertebrate group-ants-and investigate whether the latitudinal diversity gradient arose due to higher rates of net diversification in the tropics, or due to a longer time period to accumulate diversity due to Earth\u27s climatic history. We find that latitudinal affinity is highly conserved, temperate clades are young and clustered within tropical clades, and diversification rate shows no systematic variation with latitude. These results indicate that diversification time-and not rate-is the main driver of the diversity gradient in ants

Evolution of the latitudinal diversity gradient in the hyperdiverse ant genus Pheidole

AimThe latitudinal diversity gradient is the dominant geographic pattern of life on Earth, but a consensus understanding of its origins has remained elusive. The analysis of recently diverged, hyperâ rich invertebrate groups provides an opportunity to investigate latitudinal patterns with the statistical power of large trees while minimizing potentially confounding variation in ecology and history. Here, we synthesize global phylogenetic and macroecological data on a hyperdiverse (> 1,100 species) ant radiation, Pheidole and test predictions of three general explanations for the latitudinal gradient: variation in diversification rates, tropical conservatism and ecological regulation.LocationGlobal.Time periodThe past 35 million years.Major taxa studiedThe hyperdiverse ant genus Pheidole Westwood.MethodsWe assembled geographic data for 1,499 species and morphospecies, and inferred a dated phylogeny for 449 species of Pheidole, including 167 species newly sequenced for this study. We tested for correlations between diversification rate and latitude with Bayesian analysis of macroevolutionary mixtures (BAMM), hidden state speciation and extinction (HiSSE), geographic state speciation and extinction (GeoSSE), and a nonâ parametric method (FiSSE), evaluated evidence for richness steady state, and examined patterns of diversification as Pheidole spread around the globe.ResultsThere was no evidence of systematic variation of net diversification rates with latitude across any of the methods. We found that Pheidole diversification occurred in bursts when new continents were colonized, followed by a slowdown in each region, but there is no evidence richness has saturated at an equilibrium in any region. Additionally, we found latitudinal affinity is moderately conserved with a Neotropical ancestor and simulations show that phylogenetic inertia alone is sufficient to produce the gradient pattern.Main conclusionsOur results provide no evidence that diversification rates vary systematically with latitude. Richness is far from steady state in each region, contrary to the ecological regulation hypothesis, although there is evidence that ecological opportunity promotes diversification after colonization of new areas. The fact that niche conservatism is strong enough to produce the gradient pattern is in accord with the tropical conservatism hypothesis. Overall, these results shed light on the mechanisms underlying the emergence of the diversity gradient within the past 34 million years, complementing recent work on deeper timeâ scales, and more generally contribute toward muchâ needed invertebrate perspective on global biodiversity dynamics.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/1/geb12867-sup-0001-AppendixS1-S2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/2/geb12867-sup-0005-TableS3.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/3/geb12867-sup-0006-Supinfo.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/4/geb12867-sup-0002-FigS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/5/geb12867.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148253/6/geb12867_am.pd

Socially Parasitic Ants Evolve a Mosaic of Host-Matching and Parasitic Morphological Traits

A basic expectation of evolution by natural selection is that species morphologies will adapt to their ecological niche. In social organisms, this may include selective pressure from the social environment. Many nonant parasites of ant colonies are known to mimic the morphology of their host species, often in striking fashion [1, 2], indicating there is selection on parasite morphology to match the host (Batesian and/or Wasmannian mimicry [3]). However, ants that parasitize other ant societies are usually closely related to their hosts (Emery’s rule) [4–8] and expected to be similar due to common ancestry, making any kind of mimicry difficult to detect [9]. Here, we investigate the diversification of the hyperdiverse ant genus Pheidole in Madagascar, including the evolution of 13 putative social parasite species within a broader radiation of over 100 ant species on the island. We find that the parasitic species are monophyletic and that their associated hosts are spread across the Malagasy Pheidole radiation. This provides an opportunity to test for selection on morphological similarity and divergence between parasites and hosts. Using X-ray microtomography and both linear measurements and three-dimensional (3D) geometric morphometrics, we show that ant social parasite worker morphologies feature a mix of ‘‘host-matching’’ and ‘‘parasitic’’ traits, where the former converge on the host phenotype and the latter diverge from typical Pheidole phenotypes to match a common parasitic syndrome. This finding highlights the role of social context in shaping the evolution of phenotypes and raises questions about the role of morphological sensing in nestmate recognition.All fieldwork was funded by National Science Foundation grants DEB0072713, DEB-0344731, and DEB-0842395 (to B.L.F.). Lab work was supported by a National Science Foundation grant (DEB-1145989) (to E.P.E. and L.L.K.) and subsidy funding to OIS

Phylogenetic Signal of Indels and the Neoavian Radiation

The early radiation of Neoaves has been hypothesized to be an intractable “hard polytomy”. We explore the fundamental properties of insertion/deletion alleles (indels), an under-utilized form of genomic data with the potential to help solve this. We scored >5 million indels from >7000 pan-genomic intronic and ultraconserved element (UCE) loci in 48 representatives of all neoavian orders. We found that intronic and UCE indels exhibited less homoplasy than nucleotide (nt) data. Gene trees estimated using indel data were less resolved than those estimated using nt data. Nevertheless, Accurate Species TRee Algorithm (ASTRAL) species trees estimated using indels were generally similar to nt-based ASTRAL trees, albeit with lower support. However, the power of indel gene trees became clear when we combined them with nt gene trees, including a striking result for UCEs. The individual UCE indel and nt ASTRAL trees were incongruent with each other and with the intron ASTRAL trees; however, the combined indel+nt ASTRAL tree was much more congruent with the intronic trees. Finally, combining indel and nt data for both introns and UCEs provided sufficient power to reduce the scope of the polytomy that was previously proposed for several supraordinal lineages of Neoaves

Data from: Macroecology and macroevolution of the latitudinal diversity gradient in ants

The latitudinal diversity gradient—the tendency for more species to occur toward the equator—is the dominant pattern of life on Earth, yet the mechanisms responsible for it remain largely unexplained. Recently, the analysis of global data has led to advances in understanding, but these advances have been mostly limited to vertebrates and trees and have not provided consensus answers. Here, we synthesize large-scale geographic, phylogenetic, and fossil data for an exemplar invertebrate group—ants—and investigate whether the latitudinal diversity gradient arose due to higher rates of net diversification in the tropics, or due to a longer time period to accumulate diversity due to Earth’s climatic history. We find that latitudinal affinity is highly conserved, temperate clades are young and clustered within tropical clades, and diversification rate shows no systematic variation with latitude. These results indicate that diversification time —and not rate— is the main driver of the diversity gradient in ants

Zip archive of data files

Archive of data, analysis, and results files including control/configuration files used for phylogenetic analyses, DNA sequence alignments, phylogenetic tree sets, and geographic data

BEAST mcc tree

The maximum clade credibility tree inferred with the BEAST analysis and used in the analyses