ERRATUM: Freshwater input, upwelling, and the evolution of Caribbean coastal ecosystems during formation of the Isthmus of Panama

Note that Ethan L. Grossman and Aaron O’Dea contributed equally to this work.

Microbiome divergence of marine gastropod species separated by the Isthmus of Panama

The rise of the Isthmus of Panama ~3.5 mya separated populations of many marine organisms, which then diverged into new geminate sister species currently living in the Eastern Pacific Ocean and Caribbean Sea. However, we know very little about how such evolutionary divergences of host species have shaped their microbiomes. Here, we compared the microbiomes of whole-body and shell-surface samples of geminate species of marine gastropods in the genera Cerithium and Cerithideopsis to those of congeneric outgroups. Our results show that the effects of the Isthmus on microbiome composition varied among host genera and between sample types within the same hosts. In the whole-body samples, microbiome compositions of geminate species pairs in the focal genera tended to be similar, likely due to host filtering, although the strength of this relationship varied among the two groups and across similarity metrics. Shell-surface communities show contrasting patterns, with co-divergence between the host taxa and a small number of microbial clades evident in Cerithideopsis, but not Cerithium. These results suggest that (i) the rise of the Isthmus of Panama affected microbiomes of geminate hosts in a complex and clade-specific manner and (ii) host-associated microbial taxa respond differently to vicariance events than the hosts themselves.

Evidence for a Recent Formation of the Isthmus of Panama 0.6 Mya

The exact age of the final formation of the Isthmus of Panama is a critical reference point for oceanographic, climatic, biogeographic, and evolutionary hypotheses. Geotectonic evidence suggests that the isthmus was completed between 12 Mya and 3 Mya, and an age of 3–4 Mya has been used as a benchmark in hundreds of studies over the past 30 years. Phylogeographic data indicate the existence of marine connections across the isthmus much more recently, however. I reconsider the available geotectonic, biostratigraphic, oceanographic, and paleoclimatic data and show that multiple lines of indirect evidence suggest that four transisthmian seaways may have persisted until as recently as the onset of the Middle Pleistocene (~ 0.6 Mya). Subduction of the Cocos Plate beneath one transisthmian seaway (the only seaway featuring a deep sill) caused rapid tectonic shoaling and reorganisation of oceanic currents, which coincided with a major glacioeustatic sea level fall ~ 950–917 Mya that led to a temporary closing of the Bering Strait. This resulted in unusual and contrasting climate phenomena, including the “900-Kyr (cold) event” and the “greening” of South Greenland during the MIS 22 glacial maximum. The concurrence of the final formation of the Isthmus of Panama with the mid-Pleistocene Transition of glacial/interglacial periodicity suggests a tight relationship between these events.

Amazonia as the Origin and Diversification Area of Didelphidae (Mammalia: Metatheria), and a Review of the Fossil Record of the Clade

Didelphidae is the largest New World radiation of marsupials, and is mostly represented by arboreal, small- to medium-sized taxa that inhabit tropical and/or subtropical forests. The group originated and remained isolated in South America for millions of years, until the formation of the Isthmus of Panama. In this study, we present the first reconstruction of the biogeographic history of Didelphidae including all major clades, based on parametric models and stratified analyses over time. We also compiled all the pre-Quaternary fossil records of the group, and contrasted these data to our biogeographic inferences, as well as to major environmental events that occurred in the South American Cenozoic. Our results indicate the relevance of Amazonia in the early diversification of Didelphidae, including the divergence of the major clades traditionally ranked as subfamilies and tribes. Cladogeneses in other areas started in the late Miocene, an interval of intense shifts, especially in the northern portion of Andes and Amazon Basin. Occupation of other areas continued through the Pliocene, but few were only colonized in Quaternary times. The comparison between the biogeographic inference and the fossil records highlights some further steps towards better understanding the spatiotemporal evolution of the clade. Finally, our results stress that the early history of didelphids is obscured by the lack of Paleogene fossils, which are still to be unearthed from low-latitude deposits of South America.

Base-substitution mutation rate across the nuclear genome of Alpheus snapping shrimp and the timing of isolation by the Isthmus of Panama

Background The formation of the Isthmus of Panama and final closure of the Central American Seaway (CAS) provides an independent calibration point for examining the rate of DNA substitutions. This vicariant event has been widely used to estimate the substitution rate across mitochondrial genomes and to date evolutionary events in other taxonomic groups. Nuclear sequence data is increasingly being used to complement mitochondrial datasets for phylogenetic and evolutionary investigations; these studies would benefit from information regarding the rate and pattern of DNA substitutions derived from the nuclear genome. Results To estimate the genome-wide neutral mutation rate (µ), genotype-by-sequencing (GBS) datasets were generated for three transisthmian species pairs in Alpheus snapping shrimp. A range of bioinformatic filtering parameters were evaluated in order to minimize potential bias in mutation rate estimates that may result from SNP filtering. Using a Bayesian coalescent approach (G-PhoCS) applied to 44,960 GBS loci, we estimated µ to be 2.64E−9 substitutions/site/year, when calibrated with the closure of the CAS at 3 Ma. Post-divergence gene flow was detected in one species pair. Failure to account for this post-split migration inflates our substitution rate estimates, emphasizing the importance of demographic methods that can accommodate gene flow. Conclusions Results from our study, both parameter estimates and bioinformatic explorations, have broad-ranging implications for phylogeographic studies in other non-model taxa using reduced representation datasets. Our best estimate of µ that accounts for coalescent and demographic processes is remarkably similar to experimentally derived mutation rates in model arthropod systems. These results contradicted recent suggestions that the closure of the Isthmus was completed much earlier (around 10 Ma), as mutation rates based on an early calibration resulted in uncharacteristically low genomic mutation rates. Also, stricter filtering parameters resulted in biased datasets that generated lower mutation rate estimates and influenced demographic parameters, serving as a cautionary tale for the adherence to conservative bioinformatic strategies when generating reduced-representation datasets at the species level. To our knowledge this is the first use of transisthmian species pairs to calibrate the rate of molecular evolution from GBS data.

First record of Caecilia guntheri Dunn, 1942 (Gymnophiona, Caeciliidae) in Central America

I report the first encounter in Central America of an individual of Caecilia guntheri Dunn, 1942 (Gymnophiona, Caeciliidae). The individual was observed and collected in a primary evergreen submontane forest in Cerro Pirre, Darien Province, Republic of Panama. It was identified mainly by the low counts of secondary and primary folds. The encounter of this individual of C. guntheri highlights the disjunct populations and apparently the results of dispersion of this species from South to Central America by biotic exchange as result of the closure of the Isthmus of Panama.

Picturing the River’s Racial Ecologies in Colonial Panamá

This article explores the local histories and ecological knowledge embedded within a Spanish print of enslaved, Afro-descendant boatmen charting a wooden vessel up the Chagres River across the Isthmus of Panamá. Produced for a 1748 travelogue by the Spanish scientists Antonio de Ulloa and Jorge Juan, the image reflects a preoccupation with tropical ecologies, where enslaved persons are incidental. Drawing from recent scholarship by Marixa Lasso, Tiffany Lethabo King, Katherine McKittrick, and Kevin Dawson, I argue that the image makes visible how enslaved and free Afro-descendants developed a distinct cosmopolitan culture connected to intimate ecological knowledge of the river. By focusing critical attention away from the print’s Spanish manufacture to the racial ecologies of the Chagres, I aim to restore art historical visibility to eighteenth-century Panamá and Central America, a region routinely excised from studies of colonial Latin American art.

<i>Selenogonus narinoensis</i> Stirton, 1947 (Tayassuidae, Cetartiodactyla, Mammalia): taxonomic status and paleobiogeographic implications

The species Selenogonus narinoensis was described by Stirton (1947) based on a single specimen which comes from sediments cropping out in the Cocha Verde locality, Nariño Department (Colombia), tentatively referred to the late Pliocene–Pleistocene (MGN 931; IGM p002118, Museo Geológico Nacional, Servicio Geológico Colombiano, Bogotá). However, morphological studies and comparative morphometric observations of the specimen suggest that (1) no diagnostic character supports the validity of the species Selenogonus narinoensis (here considered species inquirenda); (2) a combination of features (e.g., the mandibular condyle located behind the posterior edge of the vertical mandibular ramus, the angular process which projects laterally outwards, a bunolophodont crown morphology, a mesodont crown height, and a simple crown morphology of the third lobe of m3) indicates it belongs to the genus Platygonus; (3) this specimen corresponds to one of the largest South American peccaries; (4) taking into account certain anatomical characters as well as its morphometric range, this specimen is assigned to Platygonus cf. marplatensis. Even though the stratigraphic provenance of the specimen is still doubtful, it can be proposed that (1) it could be one of the most ancient records of tayassuids in South America, as would be expected given its geographical position, and (2) considering the new taxonomic proposal, this specimen represents the first record of Platygonus cf. marplatensis in Colombia and represents one of the northernmost South American records of the genus. This new interpretation would be of great relevance in the Great American Biotic Interchange due to its strategic geographical proximity to the Isthmus of Panama.

Darien, the Golden Dream

This chapter focuses on literary and cultural works dealing with Scotland's attempt to colonize Darien, at the Isthmus of Panama, in the 1690s. It establishes Darien as a central trope in Scottish literature by analyzing works from the seventeenth to the twenty-first century, including novels, poetry, drama, songs, and political treatises by William Paterson, William Burnaby, Eliot Warburton, Douglas Galbraith, David Nicol, Alistair Beaton, and anonymous female authors. It illustrates how these depictions interact with other political and ideological trajectories in Scotland and the UK, including Jacobitism, Anglo-Scottish relations, and revisionist historical writing. The chapter establishes images of Darien gold and material possession as central structuring devices of Scottish colonial literature, which stand in conflict with depictions of Scotland's alleged kindness towards the indigenous populations of Panama. The chapter argues that narratives of benevolence together with narratives of gold and material possessions turn the colonial utopian tradition into a full-fledged myth of the Scottish Atlantic by the end of the seventeenth century. The mythologization of the colonial sphere together with the mythologization of the Scottish settlers functions as an aesthetic instrument to enter the competition over power in the late-seventeenth-century Atlantic.