Effect of river size on Amazonian primate community structure: A biogeographic analysis using updated taxonomic assessments

Whole genomes of Amazonian uakari monkeys reveal complex connectivity and fast differentiation driven by high environmental dynamism

Despite showing the greatest primate diversity on the planet, genomic studies on Amazonian primates show very little representation in the literature. With 48 geolocalized high coverage whole genomes from wild uakari monkeys, we present the first population-level study on platyrrhines using whole genome data. In a very restricted range of the Amazon rainforest, eight uakari species (Cacajao genus) have been described and categorized into the bald and black uakari groups, based on phenotypic and ecological differences. Despite a slight habitat overlap, we show that posterior to their split 0.92 Mya, bald and black uakaris have remained independent, without gene flow. Nowadays, these two groups present distinct genetic diversity and group-specific variation linked to pathogens. We propose differing hydrology patterns and effectiveness of geographic barriers have modulated the intra-group connectivity and structure of bald and black uakari populations. With this work we have explored the effects of the Amazon rainforest's dynamism on wild primates' genetics and increased the representation of platyrrhine genomes, thus opening the door to future research on the complexity and diversity of primate genomics.

Ongoing introgression of a secondary sexual plumage trait in a stable avian hybrid zone

Hybrid zones are dynamic systems where natural selection, sexual selection, and other evolutionary forces can act on reshuffled combinations of distinct genomes. The movement of hybrid zones, individual traits, or both are of particular interest for understanding the interplay between selective processes. In a hybrid zone involving two lek-breeding birds, secondary sexual plumage traits of Manacus vitellinus, including bright yellow collar and olive belly color, have introgressed ~50 km asymmetrically across the genomic center of the zone into populations more genetically similar to Manacus candei. Males with yellow collars are preferred by females and are more aggressive than parental M. candei, suggesting that sexual selection was responsible for the introgression of male traits. We assessed the spatial and temporal dynamics of this hybrid zone using historical (1989-1994) and contemporary (2017-2020) transect samples to survey both morphological and genetic variation. Genome-wide single nucleotide polymorphism data and several male phenotypic traits show that the genomic center of the zone has remained spatially stable, whereas the olive belly color of male M. vitellinus has continued to introgress over this time period. Our data suggest that sexual selection can continue to shape phenotypes dynamically, independent of a stable genomic transition between species.

Update of the geographic range of Humboldt's squirrel monkeys (Saimiri cassiquiarensis cassiquiarensis Lesson, 1840) using a model-based approach

Saimiri cassiquiarensis cassiquiarensis (Cebidae) is a primate subspecies with a wide distribution in the Amazonian region of Brazil, Colombia, and Venezuela. However, the boundaries of its geographic range remain poorly defined. This study presents new occurrence localities for this subspecies and updates its distribution using a compiled data set of 140 occurrence records based on literature, specimens vouchered in scientific collections, and new field data to produce model-based range maps. After cleaning our data set, we updated the subspecies' extent of occurrence, which was used in model calibration. We then modeled the subspecies' range using a maximum entropy algorithm (MaxEnt). The final model was adjusted using a fixed threshold, and we revised this polygon based on known geographic barriers and parapatric congeneric ranges. Our findings indicate that this subspecies is strongly associated with lowland areas, with consistently high daily temperatures. We propose modifications to all range boundaries and estimate that 3% of the area of occupancy (AOO, as defined by IUCN) has already been lost due to deforestation, resulting in a current range of 224,469 km2. We also found that 54% of their AOO is currently covered by protected areas (PAs). Based on these results, we consider that this subspecies is currently properly classified as Least Concern, because it occupies an extensive range, which is relatively well covered by PAs, and is currently experiencing low rates of deforestation.

Two hundred and five newly assembled mitogenomes provide mixed evidence for rivers as drivers of speciation for Amazonian primates

Mitochondrial DNA remains a cornerstone for molecular ecology, especially for study species from which high-quality tissue samples cannot be easily obtained. Methods using mitochondrial markers are usually reliant on reference databases, but these are often incomplete. Furthermore, available mitochondrial genomes often lack crucial metadata, such as sampling location, limiting their utility for many analyses. Here, we assembled 205 new mitochondrial genomes for platyrrhine primates, most from the Amazon and with known sampling locations. We present a dated mitogenomic phylogeny based on these samples along with additional published platyrrhine mitogenomes, and use this to assess support for the long-standing riverine barrier hypothesis (RBH), which proposes that river formation was a major driver of speciation in Amazonian primates. Along the Amazon, Negro, and Madeira rivers, we found mixed support for the RBH. While we identified divergences that coincide with a river barrier, only some occur synchronously and also overlap with the proposed dates of river formation. The most compelling evidence is for the Amazon river potentially driving speciation within bearded saki monkeys (Chiropotes spp.) and within the smallest extant platyrrhines, the marmosets and tamarins. However, we also found that even large rivers do not appear to be barriers for some primates, including howler monkeys (Alouatta spp.), uakaris (Cacajao spp.), sakis (Pithecia spp.), and robust capuchins (Sapajus spp.). Our results support a more nuanced, clade-specific effect of riverine barriers and suggest that other evolutionary mechanisms, besides the RBH and allopatric speciation, may have played an important role in the diversification of platyrrhines.

Filtering Effect of Large Rivers on Primate Distribution in the Brazilian Amazonia

Over a century after Wallace’s proposition of the riverine barrier hypothesis, the role of rivers in the diversification of species remains a matter of interest in Amazon biogeography. Amazonian rivers, in particular those large and fast flowing rivers, are widely recognized to act as barriers to the dispersal of some organisms. However, the extent to which primate species changes across interfluves (β-diversity) in response to river features remains to be explicitly tested. In this study, we examine how river characteristics affect the variation in taxonomic and phylogenetic β-diversity to elucidate the ecological processes behind the differences in primate assemblages between neighboring interfluves in the Brazilian Amazonia. We compiled International Union for Conservation of Nature (IUCN) distribution maps of 80 river-bounded primate species in 10 interfluves separated by major rivers throughout the Brazilian Amazonia. We assessed both the taxonomic (disregarding phylogenetic relationships between species) and phylogenetic β-diversities. We applied multiple linear models to evaluate whether annual discharge, sinuosity, and reflectance (as a proxy for amount of sediments) in each river or river section that separates neighboring interfluves make rivers effective barriers to primates. We found that mean discharge has a positive effect, while both sinuosity and amount of sediments have negative effects on primate β-diversity. These variables have significant effects on total taxonomic and phylogenetic β-diversity between neighboring interfluves, and their species turnover components. River features, however, have no effect on species richness differences. Genera are capable of traversing almost all interfluves, but species are replaced by others in opposite interfluves. Discharge affected both small- and large-sized primate total β-diversity, but sinuosity only affected large-sized primate assemblages in neighboring interfluves. Our results indicate that although Amazonian rivers act as barriers for many primate species, this barrier effect seems limited to the short/medium time scales, as primate lineages are able to cross them over long-time scales.

Phylogenetic relationships, population demography, and species delimitation of the Alouatta belzebul species complex (Atelidae: Alouattinae)

Howler monkeys (genus Alouatta) exhibit the most extensive distribution among platyrrhines, comprising Mesoamerican and South American species groups, with the South American group including the Brazilian endemic A. belzebul species complex encompassing A. belzebul, A. discolor, and A. ululata. We herein analyzed their phylogenetic relationship, nucleotide and haplotype diversity, and population demography based on the mitochondrial gene cytochrome b. The phylogenetic and median-joining network analyses distinguished A. discolor, distributed in the west bank of the Xingu River, from A. belzebul on the east bank. This river is a zoogeographic barrier for these species. We did not find evidence of phylogenetic structure between the A. belzebul populations of opposite banks of the Tocantins River, likely related to the changes in the position of this river to the northeast in the late Pleistocene. The A. belzebul along this river showed great morphologic and haplotype diversity, and A. belzebul from the Amazon have kept a larger population size than A. discolor. We herein describe the karyotype of A. discolor, which was similar to those described for A. ululata and A. belzebul. Our results showed two well-defined and supported clades for A. discolor and A. belzebul. However, a new assessment of A. ululata across a large distribution of sampling is required due to the lack of a clear phylogenetic structure.

Geological and Pleistocene glaciations explain the demography and disjunct distribution of red panda (A. fulgens) in eastern Himalayas

Pleistocene glaciations facilitated climatic oscillations that caused for enormous heterogeneity in landscapes, and consequently affected demography and distribution patterns of the mountain endemic species. In this context, we investigated demographic history and population genetic structure of red panda, distributed along the geographical proximity in the southern edge of the Qinghai-Tibetan Plateau. Bayesian based phylogeny demonstrated that red panda diverged about 0.30 million years ago (CI 0.23-0.39) into two phylogenetic (sub) species, that correspond to the middle-late Pleistocene transition. The observed intraspecific clades with respect to Himalayan and Chinese red panda indicated restricted gene flow resulting from the Pleistocene glaciations in the eastern and southern Tibetan Plateau. We found Himalayan red panda population at least in KL-India declined abruptly in last 5-10 thousand years after being under demographic equilibrium. We suggest revisiting the ongoing conservation activities through cross border collaboration by developing multi-nationals, and multi-lateral species-oriented conservation action plans to support the red panda populations in transboundary landscapes.