Isthmus Of Panama Research Articles

Weaving Mitochondrial DNA and Y-Chromosome Variation in the Panamanian Genetic Canvas.

The Isthmus of Panama was a crossroads between North and South America during the continent’s first peopling (and subsequent movements) also playing a pivotal role during European colonization and the African slave trade. Previous analyses of uniparental systems revealed significant sex biases in the genetic history of Panamanians, as testified by the high proportions of Indigenous and sub-Saharan mitochondrial DNAs (mtDNAs) and by the prevalence of Western European/northern African Y chromosomes. Those studies were conducted on the general population without considering any self-reported ethnic affiliations. Here, we compared the mtDNA and Y-chromosome lineages of a new sample collection from 431 individuals (301 males and 130 females) belonging to either the general population, mixed groups, or one of five Indigenous groups currently living in Panama. We found different proportions of paternal and maternal lineages in the Indigenous groups testifying to pre-contact demographic events and genetic inputs (some dated to Pleistocene times) that created genetic structure. Then, while the local mitochondrial gene pool was marginally involved in post-contact admixtures, the Indigenous Y chromosomes were differentially replaced, mostly by lineages of western Eurasian origin. Finally, our new estimates of the sub-Saharan contribution, on a more accurately defined general population, reduce an apparent divergence between genetic and historical data.

The puzzling history of South American mammals

After millions of years of isolation, the emergence of the Isthmus of Panama connected South America with North America, allowing the interchange of two previously separated faunas. The interchange was not balanced because more mammals from North America are recorded in South America than vice versa. Could this be caused by extinctions that left fewer South American mammals to move northward? - submission by Juan D. Carrillo

The Panama Low Level Jet: extension, annual cycle and modes of variation

The Panama Low Level Jet (PLLJ) is the inter-isthmic jet closest to the equator, whose activation modifies circulation, sea surface temperature and climate in most of the Eastern Tropical Pacific off Colombia. Through the analysis of 26 years (1992-2018) of sea wind data, the extent of the jet and its main frequencies of variability were determined, in addition to its relationship with phenomena of climatic variability. The area of direct influence of the jet was estimated to be 59295.34 km², being located between 4.63° and 9oN. The PLLJ is activated annually during the boreal summer (December-April) with intense intra-seasonal variability (with frequencies between 1 to 5 months) and inter annual perturbations associated with El Nino Southern Oscillation events. During warm ENSO events, the PLLJ activity last ~ 2 months more (from mid-November to the end of May) and its spatial extent increases southerly reaching ~ 2 ° N. Additionally, during warm ENSO years, there is an extemporaneous activation of PLLJ in the boreal summer, possibly linked to the intensification of the North Trade Winds over the Caribbean basin in the middle of the year and the increase in the north-south pressure gradient through the Panama isthmus during intense El Nino events. The entry of Caribbean winds in unusual seasons changes the climatology of the PLLJ and increasing its influence in the Eastern Tropical Pacific during the ENSO warm phases.

The Inachoididae spider crabs (Crustacea, Brachyura) from the Neogene of the tropical Americas

AbstractThe spider crabsWillinachoides santanain. gen. n. sp. from the early-middle Miocene of north Brazil andParadasygyius rodriguezin. sp. from the late Miocene of Venezuela are described and illustrated. Additionally,Eoinachoides senniVan Straelen, 1933, from the late Oligocene–early Miocene of Venezuela, is redescribed based on photographs of the holotype, and the diagnosis ofEoinachoides latispinosusCarriol, Muizon, and Secretan, 1987, from the late Miocene of Peru, is emended also on the basis of photographs of the holotype. The past distribution points to a Tethyan background for the current amphi-American Inachoididae, with the oldest fossil species known from the early Eocene Tethyan regions (Pakistan and Italy), and from the late Eocene–late Pliocene of the Americas. The high number of monotypic genera in Inachoididae could be the result of rapid dispersion followed by diversification during the Neogene of the tropical America, facilitated by global and regional events (e.g., eustatic sea level changes, the Mi-1 Oligocene-Miocene boundary global cooling, the global warming period of the Middle Miocene Climate maximum, closure of the Panama Isthmus, and marine incursions into the Amazon Basin). The shoaling and final closure of the Central American Seaway are thought to have critically affected the evolution of the inachoidids and shaped their current distribution patterns.UUID:http://zoobank.org/6275fdc4-4bfa-4873-9320-3143d4915172.

A morphological, phylogenetic and phylogeographic reappraisal of the land crabs Gecarcinus quadratus De Saussure, 1853, and G. lateralis Fréminville in Guérin, 1832 (Decapoda: Gecarcinidae). Are they different species?

Land crabs of the genus Gecarcinus are distributed along both versants of the American continent. At some point four species were recognized: G. lateralis, G. nobilii, G. quadratus, and G. ruricola. Taxonomically, several authors have tried to differentiate Gecarcinus lateralis from the Atlantic coast and G. quadratus from the Pacific coast. Because morphologic characters used showed high intra-population variability, identification were very difficult. Consequently, these two species have occasionally been considered synonyms. To establish the degree of genetic difference between them a molecular analysis was performed with both species, G. lateralis and G. quadratus, including Mexican Pacific and Atlantic specimens, using the mitochondrial COI and 16S genes. The maximum clade credibility and maximum likelihood trees showed two clades with high support values, one corresponding to the Gulf of Mexico population and the other one to the Pacific coast population, with a genetic distance of 6.1%. The within-clade average distance for the Atlantic populations (G. lateralis) was 1.1% and 0.2% for those of the Pacific coast (G. quadratus). This supports the status of G. quadratus as a valid species, not as a synonym of G. lateralis. The estimated time of divergence between both species ranged between 2.3 to 4.3 million years, coinciding with the proposed closure of the Isthmus of Panama. Morphologically, some populations show high variability in somatic characters, whereas sexual appendices of males of both species showed very little variation. Color in life, shape of sternite 3, and shape and degree of coverage of the abdomen of thoracic sternites, in both sexes, are traits that can be used to differentiate both species.

De Novo Genome Assembly of the Electric Fish Brachyhypopomus occidentalis (Hypopomidae, Gymnotiformes).

The bluntnose knifefish Brachyhypopomus occidentalis is a primary freshwater fish from north-western South America and Lower Central America. Like other Gymnotiformes, it has an electric organ that generates electric discharges used for both communication and electrolocation. We assembled a high-quality reference genome sequence of B. occidentalis by combining Oxford Nanopore and 10X Genomics linked-reads technologies. We also describe its demographic history in the context of the rise of the Isthmus of Panama. The size of the assembled genome is 540.3 Mb with an N50 scaffold length of 5.4 Mb, which includes 93.8% complete, 0.7% fragmented, and 5.5% of missing vertebrate/Actinoterigie Benchmarking Universal Single-Copy Orthologs. Repetitive elements account for 11.04% of the genome, and 34,347 protein-coding genes were predicted, of which 23,935 have been functionally annotated. Demographic analysis suggests a rapid effective population expansion between 3 and 5 Myr, corresponding to the final closure of the Isthmus of Panama (2.8–3.5 Myr). This event was followed by a sudden and constant population decline during the last 1 Myr, likely associated with strong shifts in both precipitation and sea level during the Pleistocene glacial-interglacial cycles. The de novo genome assembly of B. occidentalis will provide novel insights into the molecular basis of both electric signal productions and detection and will be fundamental for understanding the processes that have shaped the diversity of Neotropical freshwater environments.

An annotated and illustrated checklist of the porcelain crabs of Panama (Decapoda: Anomura).

The present study is the first exhaustive checklist of porcelain crabs (Porcellanidae) distributed on the Pacific and Atlantic (Caribbean) coasts of Panama, based on literature records and material collected between 2006 and 2019. The Panamanian porcellanid fauna is currently composed of a total of 76 species, with 26 species reported from the Caribbean coast, 45 species reported from the Pacific coast, and five species reported from both sides of the Central American Isthmus (Isthmus of Panama). In other words, the Caribbean and Pacific coasts of Panama each harbour, respectively, 31 and 50 species of porcellanid crabs. However, this total includes two problematic porcellanid records from Panama, viz. Clastotoechus nodosus (Streets, 1872) and Petrolisthes brachycarpus Sivertsen, 1933, as well as a putatively undecribed taxon reported as Pachycheles sp. The following four species are recorded for the first time from Panama, viz. Euceramus panatelus Glassell, 1938, Pachycheles riisei (Stimpson, 1859) [also being new for Mexico], Petrolisthes dissimulatus Gore, 1983 and P. tonsorius Haig, 1960. In addition, Minyocerus kirki Glassell, 1938 is newly recorded from Colombia, extending its previously known distributional range significantly southwards. Most species are illustrated in colour, several for the first time, based on material from Panama or other localities. At least 20 further species (16 in the Atlantic, 5 in the Pacific, and 1 in both oceans) are suspected to occur in Panamanian waters, based on their records from the neighbouring Costa Rica and/or Colombia, or their wide distribution in the Caribbean Sea or the tropical eastern Pacific. The presence of several cryptic or pseudocryptic species (at least some of them presumably undescribed), especially in the taxonomically challenging Petrolisthes galathinus (Bosc, 1802) species complex, or the eventual species splitting within some taxa currently seen as transisthmian, will likely further increase the total number of species present in Panama. The porcellanid fauna of Panama is also ecologically remarkably diversified. Most Panamanian porcelain crabs are free-living under rocks, in crevices of rocks, dead coral heads, coralline algae, coral rubble etc., or on mud, among mangrove roots. Euceramus panatelus lives in possibly self-dug burrows in soft mud or muddy sand, whereas its congener E. transversilineatus (Lockington, 1878) may occasionally be found in association with holothuroids. At least 15 further porcellanid species occurring in Panama live in permanent or facultative associations with a variety of other marine organisms, including sponges, cnidarians (octocorals), echinoderms (sea urchins, sea stars, sea cucumbers), polychaetes (parchment worms) and other decapod crustaceans (hermit crabs), making them one of the most attractive groups for studies of symbiosis-related behaviour and evolution.

Diversification and distribution of gall crabs (Brachyura: Cryptochiridae: Opecarcinus) associated with Agariciidae corals

Coral reefs are home to the greatest diversity of marine life, and many species on reefs live in symbiotic associations. Studying the historical biogeography of symbiotic species is key to unravelling (potential) coevolutionary processes and explaining species richness patterns. Coral-dwelling gall crabs (Cryptochiridae) live in obligate symbiosis with a scleractinian host, and are ideally suited to study the evolutionary history between heterogeneous taxa involved in a symbiotic relationship. The genus Opecarcinus Kropp and Manning, 1987, like its host coral family Agariciidae, occurs in both Indo-Pacific and Caribbean seas, and is the only cryptochirid genus with a circumtropical distribution. Here, we use mitochondrial and nuclear DNA gene fragments of Opecarcinus specimens sampled from 21 Indo-Pacific localities and one Atlantic (Caribbean) locality. We applied several species delimitation tests to characterise species diversity, inferred a Bayesian molecular-clock time-calibrated phylogeny to estimate divergence times and performed an ancestral area reconstruction. Time to the most recent common ancestor (tMRCA) of Opecarcinus is estimated at 15−6 Mya (middle Miocene—late Miocene). The genus harbours ~ 15 undescribed species as well as several potential species complexes. There are indications of strict host-specificity patterns in certain Opecarcinus species in the Indo-Pacific and Atlantic, however, a robust phylogeny reconstruction of Agariciidae corals—needed to test this further—is currently lacking. The Indo-West Pacific was inferred to be the most probable ancestral area, from where the Opecarcinus lineage colonised the Western Atlantic and subsequently speciated into O. hypostegus. Opecarcinus likely invaded from the Indo-West Pacific across the East Pacific Barrier to the Atlantic, before the full closure of the Isthmus of Panama. The subsequent speciation of O. hypostegus, is possibly associated with newly available niches in the Caribbean, in combination with genetic isolation following the closure of the Panama Isthmus.

Erratum

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

Hypoxia from depth shocks shallow tropical reef animals

Coastal deoxygenation is poorly documented in the tropics. When the Isthmus of Panama separated the Caribbean from the Pacific, sister lineages diverged and adapted to changing oxy-thermal conditions along both coasts. This provides unique insight into the ecological consequences of ocean warming and deoxygenation. We find deoxygenated, or hypoxic, waters shoal to the shallow depths of 10 m on both sides of the Isthmus, with Caribbean waters generally warmer than those in the Pacific. We tested the performance of two Caribbean Echinometra sea urchin species and their Pacific sister species under different warming and oxygen scenarios. Performance, measured as righting ability, was reduced by 50–100% under hypoxia compared to normoxia in one species from each coast. Only one Caribbean species performed well under hypoxia and did so at ambient temperatures (≤ 29 °C) but not under warming. This tolerant species, E. viridis, appears to be specialized for living on protected Caribbean reefs, unlike its two sister species that occur on well-oxygenated reefs. Our results emphasize the danger of shoaling hypoxia compressing well-oxygenated habitat from beneath and the importance of evolved hypoxia tolerance. This highlights the underappreciated risk deoxygenation poses for shallow tropical ecosystems.

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.

Morphological and genetic diversification of Russula floriformis, sp. nov., along the Isthmus of Panama

ABSTRACT Species of Russula are ubiquitous members of ectomycorrhizal fungal communities in tropical ecosystems. However, an important part of the total tropical diversity of this genus and its biogeographic patterns is unknown due to the lack of studies on Russula in tropical ecosystems. We combined molecular, morphological, ecological, and biogeographic data to elaborate concepts for two new subspecies of R. floriformis (subsection Substriatinae). Russula floriformis subsp. floriformis and R. floriformis subsp. symphoniae are described as new from montane forest dominated by Quercus and/or Oreomunnea (Fagales) from Colombia and Panama, respectively. Phylogenies were constructed using nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS), D1–D2 domains of nuc 28S rDNA (28S), and partial regions of the second largest subunit of RNA polymerase II (rpb2) and translation elongation factor 1-alpha (tef1). Similar environmental conditions, similar morphology, and an ITS sequence similarity higher than 99% with only three different positions indicate that these two subspecies are closely related. Detailed observations of microscopic structures and analyses of further DNA loci, however, revealed morphological and molecular characteristics that allow distinguishing the two subspecies of R. floriformis. Spatial distribution and phylogenetic proximity of the two Russula subspecies and their ectomycorrhizal hosts, i.e., species of Quercus, suggest that their diversification is a result of comigration, adaptation, and geographic isolation along the Isthmus of Panama during the Pliocene and Pleistocene.

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

BackgroundThe 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.ResultsTo 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.ConclusionsResults 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.

Around the world in 10 million years: Rapid dispersal of a kleptoparasitoid spider wasp (Pompilidae: Ceropales)

ABSTRACTAimCosmopolitan distributions have classically been explained by Pangaean vicariance. However, evidence of recently diverged cosmopolitan groups has re‐opened consideration on the processes involved. Our aim is to estimate the processes leading to the worldwide distribution of the kleptoparasitoid genus Ceropales.LocationWorldwide.TaxonCeropales spider wasps (Pompilidae).MethodsData from three molecular markers for 52 specimens of Ceropales and two calibration points from previous analyses were used to reconstruct a dated phylogeny under a relaxed molecular clock. We compared the fit of 12 models using BioGeoBEARS: DEC (subset sympatry, narrow vicariance), DIVALIKE (narrow and wide vicariance), BAYAREALIKE (widespread sympatry), and these same models with an added jump dispersal parameter and constraining dispersal rates among areas. Using the AIC best‐fit model (DEC+J), we performed Biogeographic Stochastic Mapping (BSM) to infer biogeographic processes by simulating 200 BSM on the BEAST chronogram.ResultsThe origin of crown‐group Ceropales was ca. 10.6 Ma (15.7–6.5 95% HPD), and 11 jump‐dispersal events explain its distribution. A constrained DEC+J model, allowing adjacent area dispersal was the best‐fit AIC model. Dispersals across the Bering land bridge, Isthmus of Panama, Mediterranean Sea, and Sunda Plains took place from the late Miocene to present times.Main conclusionsCeropales is a recently diverged group that originated in Eurasia in the Miocene and dispersed to occupy the Americas, Africa, and Australia. Colonization was probably favored by the already diversified hosts (Pompilinae and Pepsinae), which reduced limiting factors such as food resource and nest construction. The evolution of a generalist parasitic lifestyle could facilitate long‐distance dispersal. This is the first study addressing the global historical biogeography of a cosmopolitan spider wasp.

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

Abstract. 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.

Lianas have more acquisitive traits than trees in a dry but not in a wet forest

Abstract Lianas are increasing in relative abundance and biomass in many tropical forests. We tested the hypothesis that lianas conform to the fast and acquisitive end of the continuum of plant strategies, allowing lianas to acquire resources faster than trees. We assessed functional traits representative of the leaf (LES) and wood economics spectrum (WES), including plant hydraulics, in 16 liana and 16 tree species in the canopy of two tropical forests at the extremes of the climatic and geological gradient across the Isthmus of Panama. For both forests, we observed a trade‐off between the construction of more productive leaves with rapid turnover and expensive leaves with slower turnover. We also found trait variation associated with wood and hydraulic traits. These two axes were orthogonal, suggesting that trade‐offs at the leaf and stem, including plant hydraulics, operate independently. For the dry forest, lianas had cheaper and more efficient leaves than trees. For the wet forest, lianas and trees overlapped in leaf and stem characteristics. Moreover, the duration of green foliage highly explained the variation between dry forest species, reflecting different adaptations to drought. In the wet forest, fast‐growing species benefited from a higher return on investments of leaf vascular tissues than slow‐growing species and they had a higher capacity to transport water through the leaf. A higher capacity to construct more productive leaves and display leaves with lower costs may favour lianas over trees in light interception, photosynthetic rates, and growth under high light and nutrient availability in dry forests. Synthesis. Lianas in a dry tropical forest had a more acquisitive strategy than trees, characterized by more productive leaves and more efficient display for light interception. In dry environments, lianas appear to benefit from high‐light and nutrient‐rich soils and thus take advantage of higher resource conditions compared to trees. By contrast, in a wet tropical forest, lianas and trees overlapped in leaf and stem characteristics and lianas were not more acquisitive than trees. In wet environments, low light availability and nutrient‐poor soils in a context of low water limitation may constrain variation in resource acquisition strategies between lianas and trees.

On the Supposed Presence of Miocene Tayassuidae and Dromomerycinae (Mammalia, Cetartiodactyla) in South America

The earliest record of North American mammals in South America is significant for constraining the timing of intercontinental faunal interchange. At present, the oldest securely dated remains of a North American terrestrial mammal in South America pertain to a late Miocene procyonid; a few other North American mammal groups are present in late Miocene and early Pliocene outcrops in South America, but most are not recorded until the late Pliocene or Pleistocene, after the complete emergence of the Panamanian Isthmus. This long-established pattern has recently been called into question by reports of a proboscidean, two tayassuids, and a dromomerycine cervoid in supposed late Miocene deposits of Peruvian Amazon. In this contribution, we analyze the taxonomic identities and stratigraphic provenances of the tayassuid and dromomerycine fossils in detail. We conclude that these specimens are not distinguishable from modern tayassuids (Tayassu pecari and Dicotyles tajacu) and cervids, and that previous taxonomic identifications are based on misinterpretation of characters or inadequate specimens. In addition, there is insufficient evidence to support a late Miocene age for these terrestrial cetartiodactyl fossils; the stratigraphic provenance of the specimens is highly dubious, and the fossils are likely Quaternary in age.

The alteration of Miraflores Basalt (Panama): Mineralogical and textural evolution

Samples of The Miraflores Basalt sub-volcanic rocks (Miocene Late Basalt Formation) collected from different quarries on the Isthmus of Panama and several samples collected from the excavation of the third set of locks in the New Panama Channel were characterised in this study. All rocks studied had similar petrological and mineralogical characteristics; however, the samples had substantially different degrees of alteration, which varied in the NW–SE direction. The most altered areas were located at the SE (Sosa Hill Quarry), next to the Pacific Ocean, while the Cerro Escobar rocks, located further inland, showed only slight alteration. The rocks from the excavation and from the Cocolí and Aguadulce Hills area, located in the middle of the study region, exhibit features consistent with intermediate alteration between the two aforementioned extreme cases. Images and data from different alteration stages were obtained using optical microscopy, electron microprobe (EMP), and scanning electron microscopy (SEM). The earliest stage of alteration was characterised by the presence of iddingsite, which was almost the only product of alteration. As the alteration progressed, the generalisation of smectites throughout the rock was characteristic. The glass disappeared and transformed to palagonite, and the plagioclase and pyroxene crystals became altered both at the edges and inside the crystals. The crystals also showed numerous nanofractures, which were mainly perpendicular to the longer faces and that were filled by smectite. In the most advanced alteration state, all crystals and glass were deeply affected. Crystals were deeply transformed into smectite, and the porosity of the rock increased in a process that conserved the volume. Smectite appeared as the end-alteration product both from the major minerals (olivine, plagioclase, pyroxenes), as well as from the glass.

Biogeography of Neotropical mastiff bats: A case of multiple dispersals between the Caribbean and mainland

AbstractAimBats are the only group of mammals with extant native species present throughout the islands of the Antilles, Central America, and South America. Here, we test competing hypotheses of species diversification in mastiff bats and deepen our understanding of the dominant biogeographical processes involved in evolution and distribution in the Neotropics. We estimated the number of dispersals between the major geographic areas and whether vicariant events, such as the Andean uplift in the Miocene/Pliocene and Pleistocene glaciations, disrupted gene flow.LocationSouth America, Central America, and Caribbean.TaxonMolossus, Neotropical mastiff bats.MethodsWe used the phylogeny derived from a Genotype by Sequencing approach to test different biogeographical models in the Neotropics. Bayesian inference with molecular and geological calibration points was also used to estimate the age of major lineage divergences within Molossus and to infer speciation events.ResultsMost diversification within Molossus occurred relatively recently and over a short period of time during the Pleistocene. The best‐fit model, dispersal‐extinction cladogenesis, showed that anagenetic dispersal, sympatric speciation, and vicariance all appear to have been involved in the evolutionary history of the Neotropics. Divergence times suggest that geological and paleo‐climatic events were important factors in Molossus diversification.Main conclusionsPleistocene refugia in South America and the formation of the Panama Isthmus are likely to have played an important role in speciation within Molossus, while the Caribbean species are the result of at least two independent dispersal events to the archipelago from South America and Central America, coinciding with low sea levels during the Pleistocene.