Phylogenomics indicates Amazonia as the major source of Neotropical swarm-founding social wasp diversity

Abstract

The Neotropical realm harbours unparalleled species richness and hence has challenged biologists to explain the cause of its high biotic diversity. Empirical studies to shed light on the processes underlying biological diversification in the Neotropics are focused mainly on vertebrates and plants, with little attention to the hyperdiverse insect fauna. Here, we use phylogenomic data from ultraconserved element (UCE) loci to reconstruct for the first time the evolutionary history of Neotropical swarm-founding social wasps (Hymenoptera, Vespidae, Epiponini). Using maximum likelihood, Bayesian, and species tree approaches we recovered a highly resolved phylogeny for epiponine wasps. Additionally, we estimated divergence dates, diversification rates, and the biogeographic history for these insects in order to test whether the group followed a ‘museum’ (speciation events occurred gradually over many millions of years) or ‘cradle’ (lineages evolved rapidly over a short time period) model of diversification. The origin of many genera and all sampled extant Epiponini species occurred during the Miocene and Plio-Pleistocene. Moreover, we detected no major shifts in the estimated diversification rate during the evolutionary history of Epiponini, suggesting a relatively gradual accumulation of lineages with low extinction rates. Several lines of evidence suggest that the Amazonian region played a major role in the evolution of Epiponini wasps. This spatio-temporal diversification pattern, most likely concurrent with climatic and landscape changes in the Neotropics during the Miocene and Pliocene, establishes the Amazonian region as the major source of Neotropical swarm-founding social wasp diversity.

1. Introduction

Neotropical rainforests are among the most diverse global biomes [1,2], and understanding the origins and drivers behind this exceptional diversity has long been a central challenge for biologists (e.g. [2,3]). Generally, the diversification of Neotropical biota has been explained by past climatic oscillations or intense landscape alterations over time. For instance, the uplift of the Andes mountains and hydrologic changes (e.g. the evolution of the Amazonian drainage system) are historical landscape alterations related to the diversification of Neotropical biota [4,5]. Between 23 and 10 million years ago (Ma), the western Amazonia was covered by a large, long-lived lake named the Pebas system, which grew in size to one million square kilometres in the Middle Miocene (by approx. 16 Ma) [4,6,7]. Notably, the diversification age of several modern Neotropical taxa coincides with these intense landscape changes in the Amazonian region [4]. Moreover, Amazonia is considered as the source of much Neotropical biodiversity [2]. However, empirical studies seeking to understand the processes underlying biological diversification in the Neotropical biota generally are focused on model vertebrates (e.g. birds, frogs, mammals, and squamates) (e.g. [2,3,8,9]) and plants (e.g. [2,10–14]), with limited attention paid to insects and other components of this rich biota.

The integration of niche specialization, rapid diversification, extinction, and constant species accumulation is considered to be crucial in explaining diversity in the Neotropics [15]. Moreover, contrasting hypotheses have been suggested in order to explain the extraordinary diversity of the Neotropical region. The first is called the ‘museum model of diversification’, whereby the constant accumulation of diversity has occurred in Amazonia over the past 30 million years (Myr) due to a stable tropical climate [16]. Under this model of diversification, a steady accumulation of species is expected with low extinction rates, constant diversification rates over time, and larger geographical range sizes that correlate with evolutionary persistence. By contrast, the ‘cradle model of diversification’ suggests that geologically recent events triggered large-scale climatic and geographical changes resulting in rapid accumulation of species via high speciation rates [17]. Therefore, under this model of diversification distinct shifts in rates over time is expected with a recent increase in diversification rates and the geographical region is acting as a centre of origin for species diversity.

Polistine wasps are a highly diverse insect group in the Neotropics and have proven to be an excellent model for the study of social behaviour evolution because they show different degrees of caste differentiation [18]. These organisms also are useful for biogeographic investigations [19,20] because they are sensitive to climate changes [20,21] and geographical barriers [20,22]. Within Polistinae, swarm-founding social wasps (also called paper wasps) (Hymenoptera, Vespidae, Polistinae, Epiponini) are a monophyletic tribe of approximately 246 described species within 19 genera. These insects are endemic to the Neotropical region, except for three species of Agelaia, two species of Brachygastra, two species of Parachartergus, two species of Polybia, and one species of Synoeca that are found in southern regions of the United States and/or Mexican plateau [23,24]. They exhibit remarkable social characteristics, such as cyclic oligogyny (variable number of functional queens), complex nest architecture, swarm reproduction, subtle morphological difference among castes, and alternative modes of caste determination (i.e. during immature development or after adult emergence) [25]. Previous investigations of the phylogenetic relationships of Epiponini wasps have been conducted with sparse taxon sampling and are derived from studies focusing on higher-level relationships within the Polistinae group. These studies have used morphological data (e.g. [26–28]), a combination of morphology and a few molecular markers (e.g. [29,30]), and most recently approximately 380 genomic loci from 19 epiponine taxa within 18 genera [31], but they have revealed conflicting topologies for some clades of Epiponini. Hence, the sparse sampling within Epiponini and resulting phylogenetic incongruences hamper the robust reconstruction of their evolutionary history.

Here, we used massively parallel sequencing of ultraconserved elements (UCEs) to reconstruct a robust phylogenetic tree, infer divergence times, diversification rates, and the biogeographic history of Epiponini wasps. UCEs are a group of abundant nuclear markers distributed throughout the genomes of most organisms [32]; notably, these markers outperform traditional multi-locus approaches [33,34], they can be collected from historical museum specimens for phylogenetics and population genetics [35,36], and they have been successfully employed for phylogenomic studies on a variety of hymenopteran groups [37–41]. Although these genomic elements are highly conserved, hence carrying little phylogenetic information, their flanking regions increase in variable sites as the distance from the core UCE increases, making UCEs excellent markers to study evolutionary relationships across variable timescales [3,42].

Equipped with a phylogenomic approach to investigate the evolutionary history and macroevolutionary dynamics of Epiponini wasps, we tested which diversification model (e.g. ‘cradle’ or ‘museum’) could explain the diversity of the group. We addressed the following questions: (i) was the diversification of Epiponini lineages gradual and ancient (favouring the ‘museum’ model) or more recent and rapid (according to the ‘cradle’ model)? (ii) Is Amazonia the source of Epiponini diversity in the Neotropics with subsequent dispersals across the Neotropics or the group originated outside of Amazonia or even the Neotropics and dispersed to this region before radiating?

2. Material and methods

(a). Taxon sampling and DNA extraction

We sampled 115 Neotropical swarm-founding wasp specimens, representing all 19 genera and 109 of 246 currently described species (see electronic supplementary material, table S1, Appendix S1). We also included 16 other species of Vespidae and one distantly related taxon (Rhopalosomatidae) as outgroups for our phylogenetic analyses. For nine species, we downloaded raw sequencing reads from the Dryad Digital Repository [43]. We extracted DNA from 65 pinned museum specimens ranging in age from 1921 to 2006 and 58 specimens which were field collected and immediately preserved in ethanol (for detailed information see electronic supplementary material, table S1, Appendix S1).

The thorax (for ethanol preserved samples) or two legs (for pinned museum specimens) were removed from each sample and total DNA was extracted using a DNeasy Blood and Tissue Kit (Qiagen, Valencia, CA, USA) following the manufacturer's protocol, except the samples were soaked in Proteinase K overnight and the total DNA was eluted in 130 µl ddH₂O instead of the supplied buffer. Specifically for pinned museum specimens, before DNA extraction we adopted the recommendations suggested by Blaimer et al. [35] as follows: the tissues were washed in 95% ethanol to remove dust accumulated on the wasp legs and, after evaporation of the ethanol (by drying the tissue on a clean Kimwipe™), the samples were placed in a freezer for at least 6 h before the DNA extraction process.

(b). UCE data capture

We employed a targeted sequencing approach to collect phylogenomic data from UCE loci [42,44]. For UCE enrichment, we used an RNA bait library for Hymenoptera targeting 2590 loci [40]. The laboratory protocol is outlined in electronic supplementary material, Appendix S2.

(c). Bioinformatics and phylogenetic analyses

We performed all bioinformatics steps, including read cleaning, assembly, alignments, and descriptive statistics using the Phyluce v.1.5 software package [45] (see electronic supplementary material, table S1 in Appendix S1 for all sequencing and assembly descriptive statistics). We cleaned and trimmed FASTQ files for adapter contamination and low-quality bases using Illumiprocessor [44] based on the package Trimmomatic [46] and assembled contigs using Trinity v.r2013-02-25 [47]. Subsequently, we used several Phyluce scripts to identify and extract assembled contigs representing enriched UCE loci from each specimen. We used MAFFT v.7.221 [48] and Gblocks v.0.91b [49] to align and trim UCE loci, respectively. We filtered the aligned dataset for taxon occupancy (percentage taxa required to be present in a given locus) (electronic supplementary material, table S2, Appendix S1 for all matrix statistics). Additional detail on matrix preparation is outlined in electronic supplementary material, Appendix S2.

We examined the effects of phylogenetic inference methods, minimum number of UCE loci per specimen, and data partitioning in the phylogenetic trees. For phylogenetic inference, we compared maximum likelihood (ML), Bayesian inference (BI), and species tree (ST) approaches (electronic supplementary material, tables S3, Appendix S1). For concatenated ML, we performed analyses with four different partitioning schemes using RAxML v.8.2.11 [50]: unpartitioned, partitioned by locus, partitioned using PartitionFinder v.2.1.1 (PF) [51] with the hcluster algorithm [52], and partitioned using PF with the rcluster algorithm [52]. For each analysis, we executed 100 rapid bootstrap inferences, best tree search (‘-f a’ option), and we used the GTR+Γ model of sequence evolution (for both best tree and bootstrap searches).

For BI using only unpartitioned data matrices, we used ExaBayes v.1.5 [53]. For all BI, we executed two runs in parallel with 500 000 generations, each with four coupled chains (one cold and three heated chains). We assessed burn-in, convergence among runs, and run performance by examining log files with the Tracer v.1.6 [54]. We computed consensus tree using the ‘consense’ utility, which is included in the ExaBayes package. We performed ST using the program ASTRAL-III v.5.5.9 [55,56]. First, we used RAxML to generate unpartitioned gene tree for each UCE locus. We ran the ASTRAL-III analysis with 100 multi-locus bootstrap replicates. Additional details on all phylogenetic analyses are outlined in electronic supplementary material, Appendix S2.

(d). Divergence time, historical biogeography, and diversification rate analyses

We used BEAST v.1.8.4 [57] to generate a time-calibrated phylogenetic tree for Neotropical swarm-founding social wasps. We used ‘clocklikeness’ scores to sample 100 UCE loci and a fixed tree (see electronic supplementary material, Appendix S2 for details). We used four fossil calibrations to constrain the dating analysis (electronic supplementary material, table S4, Appendix S1). We performed four independent BEAST runs, each with 100 million generations, and sampled every 10 000 generations. For the clock model, we selected uncorrelated lognormal, for the substitution model we used GTR+Γ, and for the tree prior we used a birth–death model. We assessed burn-in, convergence among runs, and run performance by examining log files with Tracer v.1.6. After removing burn-in, we combined trees using LogCombiner and generated a maximum clade credibility tree using TreeAnnotator (both programs included in BEAST package). Additional details are outlined in electronic supplementary material, Appendix S2.

We inferred the ancestral range of the Neotropical swarm-founding wasps applying a dispersal extinction cladogenesis (DEC) model [58] implemented in the R package BioGeoBEARS [59] using a variety of constraints. Because both the standard biogeographic model-selection framework and the model describing founder event speciation (the ‘j-model’) may be biased [60], we chose to apply the DEC model alone since it is robust to complex biogeographic scenarios [61]. As a comparison, we also performed a DEC analysis in RASP v.4.2 [62]. For these analyses, we used the BEAST maximum credibility tree pruned to include only Epiponini wasps. For each terminal species, we coded for the presence/absence in the following areas: (A) Nearctic, (B) Andes and Mesoamerica, (C) northern Amazon, (D) south-western Amazon, and (E) eastern South America. Additional details are outlined in electronic supplementary material, Appendix S2.

Additionally, we used the Bayesian program BAMM (Bayesian analysis of macroevolutionary mixtures) v.2.5 [63–66] and the R package BAMMtools [67] to identify diversification rate shifts on the phylogeny. For input into BAMM, we used the BEAST maximum credibility tree with all outgroups pruned. We used BAMMtools to select appropriate priors for the BAMM analysis. We then ran the BAMM analysis with four chains for 100 000 000 generations and sampling event data every 10 000 generations. Finally, we explored the BAMM output using BAMMtools and selected the best rate-shift configuration by assessing posterior probabilities. Additional details are outlined in electronic supplementary material, Appendix S2. Moreover, we investigated the temporal accumulation of Epiponini lineages assessing a lineage-through-time (LTT) plot using the R package phytools 0.6-44 [68] with the maximum credibility tree obtained in the BEAST analysis with all non-Epiponini taxa pruned.

3. Results

(a). UCE capture results

The sequencing of UCE loci resulted in an average of 2.36 million reads per sample (electronic supplementary material, table S1, Appendix S1), and an average of 23 845 contigs with a mean length of 419 base pairs (bp) that were assembled by Trinity after adapter- and quality-trimming, and showing an average coverage of 11X. The average of n50 and n50_size were 7735 and 282, respectively. Considering contigs representing UCE loci, we recovered an average of 782 UCE loci. Notably, we successfully recovered a considerable number of UCE loci from several pinned museum specimens older than 30 years (for details see electronic supplementary material, table S1, Appendix S1), despite the degradation of DNA in historical museum specimens. Across levels of taxon completeness, our concatenated supermatrices exhibited a range of 12–2097 UCE loci, a range of length of 2595–549 840 bp, and a range of 605–79 936 informative sites (see electronic supplementary material, table S2, Appendix S1).

(b). Phylogeny of Polistinae and the Neotropical swarm-founding social wasps

When we compared our different partitioning schemes (unpartitioned, by locus, and both PF hcluster and rcluster algorithms), the phylogenetic results from partitioned by locus ML showed the best log likelihood and clocklikeness scores (see electronic supplementary material, table S3, Appendix S1), an expected result since more parameters are used with partitioning by locus. Our multiple phylogenetic analyses showed that the interspecific relationships for the subfamily Polistinae could be described as follows: (Ropalidiini + (Mischocyttarini + (Polistini + Epiponini))) (figure 1). Thus, our analyses supported with a high bootstrap score (greater than 95%) the cosmopolitan genus Polistes (Polistini) as sister to Epiponini. The only exception was when we performed ST analyses that exhibited Mischocyttarini as the sister of Polistini, but with weak support.

Figure 1.

Time-calibrated phylogeny of Neotropical swarm-founding social wasps and closely related groups. The tree topology was recovered by analysing the Epiponini-102T-200 L-F50 matrix using RAxML (partitioned by locus; 950 UCE loci; 257 561 bp). We estimated divergence dates using BEAST with the 100 best (based on clocklikeness score) UCE loci, fixed topology, and four-node calibrations (see electronic supplementary material, table S4, Appendix S1). Scale bars next to wasp photos correspond to 5 mm. (Online version in colour.)

All phylogenetic analyses (ML, BI, and ST) recovered a highly resolved phylogeny for Epiponini with most nodes showing 100% bootstrap scores (ML and ST) and posterior probabilities (BI) (figure 1, electronic supplementary material, table S6 in Appendix S1, and phylogenetic trees in electronic supplementary material, Appendix S3). There was no topological difference between ML and BI analyses and almost all nodes received maximum support, but ST analyses exhibited a few topological differences when compared to ML and BI. Some relationships (considering all methods) recovered here conflict with previous studies using morphological, behavioural, and molecular (Sanger sequencing) data [27–29], but were very similar to a study using genomic information [31]. As found by Piekarski et al. [31], we inferred Angiopolybia as sister to all remaining swarm-founding social wasps, rather than Apoica as previously suggested [26,28,29]. Agelaia and Apoica are sister genera, and Epipona is the sister of Synoeca, rather than Polybia. All phylogenetic analyses recovered a monophyletic Polybia with a deep split into two major clades, but most of the subgenera are paraphyletic. Relationships among all epiponine genera were recovered with high support.

(c). Divergence times, biogeographic history, and diversification dynamics of Neotropical swarm-founding social wasps

We estimated for the first time the timescale of the evolution of Epiponini. The tribe originated during the Eocene around 44.9 Ma (95% of high posterior density (HPD): 37.6–51.3 Ma) (figure 1 and electronic supplementary material, Appendix S3). The crown-group age estimates for several genera occurred during the Miocene, including: Agelaia (15.8 Ma; 95% of HPD: 13.6–19.4 Ma), Angiopolybia (19.9 Ma; 95% of HPD: 8.5–34.1 Ma), Apoica (11.7 Ma; 95% of HPD: 5.5–20.6 Ma), Brachygastra (13.6 Ma; 95% of HPD: 9.1–19.1 Ma), Charterginus (12.1 Ma; 95% of HPD: 6.8–18.2 Ma), Chartergus (9.7 Ma; 95% of HPD: 3.8–17.2 Ma), Chartergellus (5.4 Ma; 95% of HPD: 2.0–10.3 Ma), Leipomeles (8.7 Ma; 95% of HPD: 3.0–16.1 Ma), Parachartergus (13.7 Ma; 95% of HPD: 8.5–19.9 Ma), Protopolybia (15.5 Ma; 95% of HPD: 9.9–21.3 Ma), Pseudopolybia (15.6 Ma; 95% of HPD: 6.3–25.5 Ma), and Synoeca (5.5 Ma; 95% of HPD: 3.0–9.0 Ma). The crown-group age estimates of Epipona (2.3 Ma; 95% of HPD: 0.6–4.4 Ma) and Metapolybia (3.3 Ma; 95% of HPD: 1.5–5.9 Ma) were more recent, during the Pliocene. The diversification of all sampled extant Epiponini species occurred during the Miocene and Plio-Pleistocene (figures 1 and 2).

Figure 2.

Biogeographic history and diversification dynamic of Neotropical swarm-founding social wasps. (a) Ancestral ranges inferred using the R package BIOGEOBEARS with the DEC model. Coloured squares indicate current or putative ancestral geographical ranges. We used the following ranges: (A) Nearctic, (B) Andes and Central America, (C) northern Amazon, (D) south-western Amazon, and (E) eastern South America. The upper panel is adapted from Hoorn et al. [4]. (b) Net diversification rate through time for Epiponini. Blue shaded areas represent posterior probability distributions of rate estimates. (c) Extinction rate through time for Epiponini. Blue shaded areas represent posterior probability distributions of rate estimates. (d) Phylorate showing diversification rate. Colours of branches indicate the mean evolutionary rate (relative rates from blue (slower) to red (faster)). (e) Lineages-through-time plot for Epiponini. Red dashed line marks a relatively gradual accumulation of lineages in Epiponini. (Online version in colour.)

Our results from DEC biogeographic analyses using BioGeoBEARS and RASP are provided in figure 2a and electronic supplementary material, Appendix S3. Epiponine wasps likely evolved from an Amazonian ancestor, and this area was indicated in our biogeographic reconstructions as having played a major role in the diversification of epiponine wasps, as supported by the fact that all genera have an Amazonian ancestor and its highest taxonomic diversity is also in this geographical region. Additionally, some lineages are inferred to have dispersed from the Amazon to Central America and eastern South America. Moreover, our results show no major shifts in diversification rates for Epiponini over the past 40 Ma, but there was a slight increase in diversification rate over time (figure 2b,c). Extinction rates appear to have remained low over the evolutionary history of Epiponini (figure 2d) and lineage accumulation was gradual (figure 2e).

4. Discussion

Our extensive sampling of taxa and UCE loci not only produced a strongly supported phylogeny for Epiponini but also provides a detailed window into the evolution of this insect group. Epiponini originated in the Eocene and most diversification events probably occurred gradually within the Amazon region, especially during the Neogene (Miocene and Pliocene) when Andean mountain building caused large-scale climatic, geological, and hydrological changes in South America [4,15] (figures 1 and 2). For example, the intensification of the Andean uplift and subsequent changes in the Amazonian landscape generated the formation of the Pebas system—a large wetland of shallow lakes and swamps in western Amazonia between 23 and 10 Ma [4] (figure 2)—which favoured the diversification of several South American lineages [69]. The gradual accumulation of lineages and no major shifts in diversification rates over the past 30 Myr, as indicated for Epiponini, is a pattern also revealed for the Neotropical plant genus Brownea (Fabaceae) [14] but different from that observed for the Neotropical bellflowers (Campanulaceae: Lobelioideae) and Inga plants (Fabaceae: Mimosoideae) that experienced rapid radiation within the last 5 Myr [11,12].

Our biogeographic reconstructions suggest the Amazonian region as the major source of Epiponini diversity, which can be explained by the highest taxonomic diversity of the tribe in this geographical region and recent colonization events to other geographical areas (e.g. eastern South America, and Central and North America). An Amazonian ancestral distribution during much of the evolution of the tribe is also supported by the fact that all Epiponini genera also have an Amazonian ancestor. Additionally, we can infer recent colonization events to other Neotropical regions in some Epiponini lineages. For instance, the Pebas system may have acted as a barrier preventing Epiponini from reaching Central and North America, but during this same period some lineages colonized eastern South America (figure 2a). Only after the end of the Pebas system during the late Miocene did these wasps colonize Central and North America (figure 2a). Thus, we propose the Amazon Forest as the major centre of origin for Epiponini wasps, as previously suggested for some Neotropical Polistinae groups [70,71] and plant taxa (for example, the Brownea clade) [14], with subsequent migration events across the Neotropics.

Phylogenetic hypotheses for the four tribes of Polistinae are historically controversial. Phylogenies based exclusively on morphological and behavioural data suggest that Polistini is the sister taxon to the remaining lineages of Polistinae [26,72]. However, molecular phylogenies [29,31,73] and our phylogenomic analysis using UCE data showed Ropalidiini as the first lineage of Polistinae and recovered with high support Polistini and Epiponini as sister groups. All our analyses recovered a consistent, highly supported phylogeny for Epiponini wasps; the only exception was ST analysis which exhibited slight topological differences (but with low support) when compared to ML and BI. Incongruences between ST and concatenation methods have been explained by the presence of incomplete lineage sorting (ILS) [74] or gene flow in the form of hybridization or introgression [75,76]. Despite demonstrations of hybridization events in other hymenopterans such as bees [77] and ants [78,79], we currently do not possess clear evidence of such events between lineages of Epiponini.

Our study now provides the first comprehensive phylogeny of Neotropical swarm-founding social wasps using both genomic data and complete genus sampling. Our results strongly support the monophyly of Epiponini and all genera within the tribe. Regarding the systematics of the tribe, a striking result in our study, and also found by Piekarski et al. [31], is the strong support for Angiopolybia as sister to the other lineages of Epiponini as well as Agelaia and Apoica as sister taxa. These results conflict with previous studies [27–29], but as suggested by Noll et al. [80] the shape difference of queens may be a synapomorphy for Agelaia and Apoica. A second interesting result is strong support for the monophyly of Polybia, with previously proposed subgenera as paraphyletic, suggesting the need for future work on the systematics of Polybia. Carpenter et al. [81] found Polybia as monophyletic with weak support and Pickett & Carpenter [29] did not recover Polybia as a monophyletic group.

In summary, our results provide a robust phylogeny for Polistinae and detailed information on the diversification, macroevolutionary dynamics, and historical biogeography for Epiponini. We suggest that the group diversified according to the ‘museum’ and the ‘cradle’ models of diversification as also proposed for ants [82] and the cladogenetic events occurred mainly in Amazonia. These conclusions are supported by several results: (i) the diversification of many genera and all sampled extant species occurred during the Miocene and Plio-Pleistocene, (ii) the Amazon region remained the dominant ancestral distribution during much of the tribe's evolution, and (iii) we inferred no major shifts in diversification rates for Epiponini over the past 40 Ma but with a slight increase towards the present, and lineage accumulation was gradual, probably with a low extinction rate. The spatio-temporal pattern recovered herein for Epiponini reflects an evolutionary history most likely concurrent with climatic and landscape changes during the Miocene and Pliocene and establishes the Amazonian region as the major source of Epiponini diversity. Additionally, we suggest that further studies accounting for diversification rates and variables such as paleotemperature or Andean paleoelevation are needed to determine the impact of past geological and temperature changes in the diversification of social wasps of Amazonia.

Data accessibility

Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.59j3k8p [83].

Authors' contributions

R.S.T.M. and S.G.B. conceived and designed the study. R.S.T.M. carried out the molecular laboratory work and performed the analyses. R.S.T.M. drafted the manuscript. M.W.L. helped carry out the molecular laboratory work and revised the manuscript. S.G.B. helped with data analysis and manuscript revision. All authors gave final approval for publication.

Competing interests

The authors have identified no conflict of interest to disclose.

Funding

R.S.T.M. is thankful to the São Paulo Research Foundation (FAPESP) by postdoctoral fellowships and grants nos. 2015/02432-0 and 2016/21098-7 and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) by grant no. 431249/2018-0. S.G.B. received research support from the U.S. National Science Foundation grant no. DEB-1555905.