Phaseolin-protein Variability in Wild Forms and Landraces of the Common Bean(Phaseolus vulgaris): Evidence for Multiple Centers of Domestication

A sample of 106 wild forms and 99 landraces of common bean (Thaseolus vulgaris) from Middle America and the Andean region of South America were screened for variability in phaseolin seed protein using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) and two-dimensional isoelectric focusing SDS/PAGE. The Middle American wild forms exhibited phaseolin patterns similar to the ‘S’ pattern described previously in cultivated forms, as well as a wide variety of additional banding patterns—‘M’ (Middle America) types—not encountered among common bean cultivars. The Andean wild forms showed only the ‘T’ phaseolin pattern, also described previously among cultivated forms. Landraces from Middle America showed ‘S’ or ‘S’-like patterns with the exception of 2 lines with ‘T’ phaseolin. In Andean South America, a majority of landraces had the ‘T’ phaseolin. Additional types represented in that region were (in decreasing order of frequency) the ‘S’ and ‘C’ types (already described among cultivated forms) as well as the ‘H’ (Huevo de huanchaco) and ‘A’ (Ayacucho), (new patterns previously undescribed among wild and cultivated beans). In each region—Middle America and Andean South America—the seeds of landraces with ‘T’ phaseolin were significantly larger than those of landraces with ‘S’ phaseolin. No significant differences in seed size were observed among landraces with ‘T,’ ‘C,’ ‘H,’ and ‘A’ phaseolin types of the Andean region. Our data favor 2 primary areas of domestication, one in Middle America leading to small-seeded cultivars with ‘S’ phaseolin patterns and the other in the Andes giving rise to large-seeded cultivars with ‘T’ (and possibly ‘C,’ ‘H,’ and ‘A’) phaseolin patterns.     

Dissemination pathways of common bean (Phaseolus vulgaris,Fabaceae) deduced from phaseolin electrophoretic variability. II. Europe and Africa

Phaseolin type, determined by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis, was used to suggest dissemination routes of common bean (Thaseolus vulgaris) cultivars from their areas of domestication to Europe and Africa. In the Iberian Peninsula, ‘C’ was the most frequent phaseolin type. Only in Chile has a comparably high ‘C’ frequency been observed previously, indicating that many Iberian cultivars may have been introduced from Chile, or that many Chilean cultivars may have come from the Iberian Peninsula. In Europe (outside the Iberian Peninsula), most cultivars exhibited a ‘T’ type. The high frequency of this type may be related to the high frequency of green pod cultivars among European cultivars. Most African cultivars exhibited a ‘T’ or a ‘C’ type and may have been introduced from Brazil, the Iberian Peninsula, or western Europe. ‘T’ or ‘C’ cultivars had larger seeds than ‘S’ cultivars. The phaseolin patterns of cultivars with different seed types and of early French cultivars are discussed.     

Novel Phaseolin types in wild and cultivated common bean (Phaseolus vulgaris,Fabaceae)

Forty-one wild types and 41 cultivars of common bean (Phaseolus vulgaris) from Meso-and South America were screened for variability of phaseolin seed protein using one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) and two-dimensional isoelectric focusing SDS/PAGE. Wild accessions from the Andean region showed phaseolin types which had not been previously identified in wild material from that region. Other wild accessions from Argentina exhibited novel phaseolin patterns collectively designated as ‘J’ (‘Jujuy’) phaseolin types, and one accession from northern Peru exhibited a novel phaseolin type, the ‘I’ (‘Inca’) type. The ‘H’ and ‘C’ phaseolins, previously identified only in cultivars, were observed in several wild accessions from Argentina. Among cultivars, two minor variants of the ‘S’ phaseolin type were identified. The ‘Sb’ (‘S Brazil’) was characteristic of a limited number of cultivars from Brazil whereas the ‘Sd’ (‘S Durango 222’) predominated in cultivars of the Mexican central highlands. The distribution of the previously described ‘B’ phaseolin appeared to be larger than formerly known as it extended not only in Colombia but also in Central America. It is possible to correlate the ‘Sb’, ‘Sd’, and ‘B’ phaseolin types with certain agronomic traits.     

Phaseolin variability among wild and cultivated common beans (Phaseolus vulgaris) from Colombia

Phaseolin seed protein variability in a group of 8 wild and 77 cultivated common bean (Phaseolus vulgaris) accessions was determined using 1-dimensional SDS/ PAGE and 2-dimensional IEF-SDS/PAGE. Wild common bean accessions exhibited the 'CH' and 'B' patterns, previously undescribed among either wild or cultivated common beans. The cultivated genotypes showed (in decreasing frequency) the previously described 'S,' T,' and 'C phaseolin patterns as well as the new 'B' pattern similar to the pattern identified in a Colombian wild common bean accession. In the northeastern part of the Colombian bean-growing region, the cultivars exhibited almost exclusively an 'S' phaseolin type, while in the south-western part, the 'T' and 'C phaseolin cultivars were more frequent. Seed size analysis indicated that 'T' and 'C' phaseolin cultivars had larger seeds than 'S' and 'B' phaseolin cultivars. Our results suggest that Colombia is a meeting place for Andean and Middle American common bean germplasms, as well as a domestication center for the common bean.     

DNA from herbarium specimens settles a controversy about origins of the European potato

Landrace potato cultivars are native to two areas in South America: the high Andes from eastern Venezuela to northern Argentina and the lowlands of south-central Chile. Potato first appeared outside of South America in Europe in 1567 and rapidly diffused worldwide. Two competing hypotheses suggested the origin of the "European" potato from the Andes or from lowland Chile, but the Andean origin has been widely accepted over the last 60 years. All modern potato cultivars predominantly have Chilean germplasm, explained as originating from breeding with Chilean landraces subsequent to the late blight epidemics beginning in 1845 in the UK. The Andean origin has been questioned recently through examination of landraces in India and the Canary Islands, but this evidence is inferential. Through a plastid DNA deletion marker from historical herbarium specimens, we report that the Andean potato predominated in the 1700s, but the Chilean potato was introduced into Europe as early as 1811 and became predominant long before the late blight epidemics in the UK. Our results provide the first direct evidence of these events and change the history of introduction of the European potato. They shed new light on the value of past breeding efforts to recreate the European potato from Andean forms and highlight the value of herbarium specimens in investigating origins of crop plants.     

Evidence for phosphorylation of the major seed storage protein of the common bean and its phosphorylation-dependent degradation during germination

Phaseolin is the major seed storage protein of common bean, Phaseolus vulgaris L., accounting for up to 50 % of the total seed proteome. The regulatory mechanisms responsible for the synthesis, accumulation and degradation of phaseolin in the common bean seed are not yet sufficiently known. Here, we report on a systematic study in dormant and 4-day germinating bean seeds from cultivars Sanilac (S) and Tendergreen (T) to explore the presence and dynamics of phosphorylated phaseolin isoforms. High-resolution two-dimensional electrophoresis in combination with the phosphoprotein-specific Pro-Q Diamond phosphoprotein fluorescent stain and chemical dephosphorylation by hydrogen fluoride–pyridine enabled us to identify differentially phosphorylated phaseolin polypeptides in dormant and germinating seeds from cultivars S and T. Phosphorylated forms of the two subunits of type α and β that compose the phaseolin were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) and MALDI-TOF/TOF tandem MS. In addition, we found that the levels of phosphorylation of the phaseolin changed remarkably in the seed transition from dormancy to early germination stage. Temporal changes in the extent of phosphorylation in response to physiological and metabolic variations suggest that phosphorylated phaseolin isoforms have functional significance. In particular, this prospective study supports the hypothesis that mobilization of the phaseolin in germinating seeds occurs through the degradation of highly phosphorylated isoforms. Taken together, our results indicate that post-translational phaseolin modifications through phosphorylations need to be taken into consideration for a better understanding of the molecular mechanisms underlying its regulation.     

中国普通菜豆种质资源朊蛋白变异及多样性分析

朊蛋白是研究普通菜豆遗传多样性的一种重要且有效的生化标记。本试验通过SDS-PAEG凝胶电泳检测中国普通菜豆种质资源的朊蛋白变异类型,分析中国普通菜豆种质资源的遗传多样性及组成特点。来自中国13个省(自治区)的445份供试材料共检测到S、Sb、Sd、B、C、CA、T、PA、To、H、H1、CH 12种朊蛋白类型,表明中国普通菜豆种质朊蛋白变异类型丰富,遗传多样性水平较高。其中,Sb型朊蛋白种质最多,占比29.0%;T型其次,占比28.1%。依据朊蛋白类型在不同基因库的特异性,将研究材料明显地区分为中美基因库和安第斯基因库两大类。研究还发现中国普通菜豆种质资源中地方种质朊蛋白类型变异丰富,多样性明显高于现代育成品种或品系。最后,对种质朊蛋白类型与百粒重、子粒颜色、粒型进行相关性分析,结果表明朊蛋白类型与百粒重呈极显著正相关,而朊蛋白类型与子粒颜色、粒型2个性状之间无明显相关性。本研究结果将为普通菜豆种质资源的保护及有效地挖掘优质种质资源提供理论依据。     

Bean lectins

Summary Seeds of forty bean cultivars having different lectin types based on two-dimensional isoelectric focusing-sodium dodecyl sulfate polyacrylamide gel electrophoresis (IEF-SDS/PAGE) were analyzed for quantities of lectin, phaseolin and total protein. Significant differences were found among groups of cultivars with different lectin types for the quantity of lectin and phaseolin. Cultivars with more complex lectin types based on IEF-SDS/PAGE tended to have higher quantities of lectin and lower quantities of phaseolin than cultivars with simple lectin types. An association between lectin type and the quantity of lectin and phaseolin was found also in the seeds of F₂ plants that segregated in a Mendelian fashion for two lectin types. Seeds from plants with the complex lectin type had more lectin and less phaseolin than seeds from plants with the simple lectin type. Therefore, the genes controlling qualitative lectin variation also may influence the quantitative variation of lectin and phaseolin. The results of this study are related to other studies on the quantitative variation for seed proteins and to the possible molecular basis for variation in the quantity of lectins in beans.     

Patterns of variation in cultivated common bean (Phaseolus vulgaris,Fabaceae)

More than 18,000 accessions of common bean (Thaseolus vulgaris, Fabaceae) from the Centro Internacional de Agricultura Tropical (CIAT) germplasm bank were examined at two locations in Colombia. A large variation in cultivated dry bean was found among accessions from primary centers of domestication in Middle and South America. For some bean types, such as medium- and large-seeded white, variation was greater among germplasm from western Asia (Turkey) and Europe (Portugal, Spain, Greece, France, Italy, and Bulgaria). Based on growth habit, on seed, pod, and leaf characteristics, and on ecological regions of adaptation, dry-bean germplasm was divided into a total of six gene pools from Middle American and four gene pools from South American centers of domestication. Most of the variation in the snap or stringless bean appears to be of relatively recent origin; it was greatest among cultivars from China, Europe, and the United States. These could be grouped into two additional gene pools. A strategy for breeding and transfer of genes across gene pools is also discussed.     

Bruchid resistance of common bean lines having an altered seed protein composition

 Arcelin seed proteins of common bean (Phaseolus vulgaris L.) are toxic to one of the most damaging pests of bean seeds, Zabrotes subfasciatus (Boheman), but they appear to have little effect on another important bean pest, Acanthoscelides obtectus (Say), when introduced into standard cultivars by backcrossing. With the goal of increasing arcelin concentration to improve resistance, we modified seed-protein composition by introducing a null allele for the major seed protein, phaseolin, into lines (SMARC1, 2 and 4) or three phytohemagglutinin types (SMPHA lines). These lines were tested for resistance to both insects by measuring percentage insect emergence (%E) and days-to-adult emergence (DAE). For SMARC lines, arcelin type was the most important factor in resistance levels, with SMARC1 lines being most resistant, SMARC2 lines intermediate, and SMARC4 lines the least resistant to both bruchids. Additionally, the absence of phaseolin was a significant factor in the resistance of SMARC lines to A. obtectus. SMARC1 lines without phaseolin had half the percentage insect emergence of lines with phaseolin. SMARC1 lines with an altered seed composition had the highest levels of resistance to both bruchids of any large-seeded line reported to-date. Received: 2 April 1997 / Accepted: 20 May 1997     

Evolution of genetic diversity during the domestication of common-bean (Phaseolus vulgaris L.)

M13 DNA fingerprinting was used to determine evolutionary changes that occurred in Latin American germ plasm and USA cultivars of commonbean (Phaseolus vulgaris L.) during domestication. Linkage mapping experiments showed that M13-related sequences in the common-bean genome were either located at the distal ends of linkage groups or that they were unlinked to each other or to any previously mapped markers. Levels of polymorphism observed by hybridization with M13 (1 probe-enzyme combination) were comparable to those observed by hybridization with single-copy random PstI genomic probes (36 enzyme-probe combinations) but were higher than those observed for isozymes (10 loci). Results indicated that the wild ancestor had diverged into two taxa, one distributed in Middle America (Mexico, Central America, and Colombia) and the other in the Andes (Peru and Argentina); they also suggested separate domestications in the two areas leading to two cultivated gene pools. Domestication in both areas led to pronounced reductions in diversity in cultivated descendants in Middle America and the Andes. The marked lack of polymorphism within commercial classes of USA cultivars suggests that the dispersal of cultivars from the centers of origin and subsequent breeding of improved cultivars led to high levels of genetic uniformity. To our knowledge, this is the first crop for which this reduction in diversity has been documented with a single type of marker in lineages that span the evolution between wild ancestor and advanced cultivars.     

Evolution into and out of the Andes: a Bayesian analysis of historical diversification in Thamnophilus antshrikes

The Andean uplift played important roles in the historical diversification of Neotropical organisms, both by producing new high-elevation habitats that could be colonized and by isolating organisms on either side of the mountains. Here, we present a molecular phylogeny of Thamnophlius antshrikes, a clade of 30 species whose collective distribution spans nearly the entirety of lowland habitats in tropical South America, the eastern slope foothills of the Andes, and the tepuis of northern South America. Our goal was to examine the role of the Andes in the diversification of lowland and foothill species. Using parsimony and Bayesian ancestral state reconstructions of a three-state distribution character (lowland-restricted, lowland-to-highland, highland-restricted), we found that the Andes were colonized twice independently and the tepuis once from lowland-restricted ancestors. Over the entire evolutionary history of Thamnophilus, the highest transition rates were between highland-restricted and lowland-to-highland distributions, with extremely low rates into and out of lowland-restricted distributions. This pattern suggests lowland-restricted distributions are limited not by physiological constraints, but by other forces, such as competition. These results highlight the need for additional comparative studies in elucidating processes associated with the colonization of high-elevation habitats and the differentiation of populations within them.     

Trachemys medemi n. sp. from northwestern Colombia turns the biogeography of South American slider turtles upside down

South America was invaded by slider turtles (Trachemys spp.) twice, with one immigration wave estimated to have reached South America 8.6–7.1 million years ago (mya) and a second wave, 2.5–2.2 mya. The two widely disjunct South American subspecies of Trachemys dorbigni (northeastern and southern Brazil, Río de la Plata region of Argentina and Uruguay) are derived from the first dispersal pulse, while the two South American subspecies of Trachemys venusta (Colombia, Venezuela) originated from the second immigration event. We describe a new species of slider turtle from the lower Atrato river basin of Antioquia and Chocó departments, northwestern Colombia. This new species, the Atrato slider (Trachemys medemi n. sp.), is the first representative of the older immigration wave inhabiting northern South America. Using phylogenetic analyses of 3,242 bp of mitochondrial and 3,396 bp of nuclear DNA, we show that T. medemi is more closely related to T. dorbigni than to the geographically neighboring subspecies of Trachemys grayi and T. venusta from Central America and northern South America. The two subspecies of T. dorbigni are separated from the Atrato slider by the Andes and the Amazon Basin, and occur approximately 4,600 km and 3,700 km distant from T. medemi. According to molecular clock calculations, T. medemi diverged from the last common ancestor of the two subspecies of T. dorbigni during the Pliocene (4.1–2.8 mya), with T. dorbigni diversifying later (2.3–1.9 mya) in eastern South America beyond the Amazon basin. The divergence of the T. dorbigni subspecies overlaps with the estimated arrival of T. venusta in South America (2.5–2.2 mya). This time is characterized by massive climatic and environmental fluctuations with intermittent dispersal corridors in South America. According to their distribution, it seems likely that the ancestors of the extant subspecies of T. dorbigni dispersed along the eastern corridor, leaving a relict population northwest of the Andes with T. medemi. The distribution range of T. medemi is surrounded by taxa derived from the second southern range expansion of slider turtles, so that it can be concluded that T. venusta circumvented the habitats occupied by the ancestors of the Atrato slider when entering South America.     

Status and challenges for conservation of small mammal assemblages in South America

South America spans about 44° latitude, covers almost 18 million km², and is second only to Africa in continental mammal species richness. In spite of this richness, research on the status of this fauna and on the nature and magnitude of contemporary threats remains limited. Distilling threats to this diverse fauna at a continental scale is challenging, in part because of the limited availability of rigorous studies. Recognizing this constraint, we summarize key threats to small mammals in South America, emphasizing the roles of habitat loss and degradation, direct persecution, and the increasing threat of climate change. We focus on three regional ‘case studies’: the tropical Andes, Amazonia and adjacent lowland regions, and the southern temperate region. We close with a brief summary of recent findings at our long‐term research site in north‐central Chile as they pertain to projected threats to this fauna. Habitat alteration is a pervasive threat that has been magnified by market forces and globalization (e.g. extensive agricultural development in Amazonia), and threatens increasing numbers of populations and species. Climate change poses even greater threats, from changes in rainfall and runoff regimes and resulting changes in vegetative structure and composition to secondary influences on fire dynamics. It is likely that many changes have yet to be recognized, but existing threats suggest that the future may bring dramatic changes in the distribution of many mammal taxa, although it is not clear if key habitat elements (vegetation) will respond as rapidly as climatic factors, leading to substantial uncertainty. Climate change is likely to result in ‘winners’ and ‘losers’ but available information precludes detailed assessment of which species are likely to fall into which category. In the absence of long‐term monitoring and applied research to characterize these threats more accurately, and to develop strategies to reduce their impacts, managers already are being faced with daunting challenges. As the line between ‘pure’ and ‘applied’ research blurs in the face of converging interests of scientists and society we hope that solutions to these critical issues will be incorporated in addressing anticipated conservation crises.     

Population structure and genetic diversity of New World maize races assessed by DNA microsatellites

Because of the economic importance of maize and its scientific importance as a model system for studies of domestication, its evolutionary history is of general interest. We analyzed the population genetic structure of maize races by genotyping 964 individual plants, representing almost the entire set of ～350 races native to the Americas, with 96 microsatellites. Using Bayesian clustering, we detected four main clusters consisting of highland Mexican, northern United States (US), tropical lowland, and Andean races. Phylogenetic analysis indicated that the southwestern US was an intermediary stepping stone between Mexico and the northern US. Furthermore, southeastern US races appear to be of mixed northern flint and tropical lowland ancestry, while lowland middle South American races are of mixed Andean and tropical lowland ancestry. Several cases of post-Columbian movement of races were detected, most notably from the US to South America. Of the four main clusters, the highest genetic diversity occurs in highland Mexican races, while diversity is lowest in the Andes and northern US. Isolation by distance appears to be the main factor underlying the historical diversification of maize. We identify highland Mexico and the Andes as potential sources of genetic diversity underrepresented among elite lines used in maize breeding programs.     

Characterization and density of trichomes on three common bean cultivars

Trichomes have been implicated as a mechanism which can confer resistance to both plant pests and drought. A study was conducted to provide information regarding genetic variability for trichome distribution and density among three diverse dry bean (Phaseolus vulgaris L.) cultivars, and to characterize the types of trichomes present among the cultivars. Trichomes on the leaf surfaces were micrographed with a scanning electron microscope (SEM) and counted using a stereomicroscope on both the abaxial and adaxial leaf surfaces of the cultivars ‘Bill Z’, ‘Pompadour Checa’ and ‘Diacol Calima’. Straight, hooked, and glandular trichomes were observed on the leaf surfaces of each cultivar. SEM micrographs are presented for the leaf surfaces of each cultivar and trichome type. The abaxial leaf surface had more straight trichomes than the adaxial leaf surface for ‘Pompadour Checa’ and ‘Diacol Calima’, however ‘Bill Z’ had more on the adaxial surface. The opposite relationship existed among the cultivars and leaf surfaces for the hooked trichomes.     

No population genetic structure in a widespread aquatic songbird from the Neotropics

Neotropical lowland organisms often show marked population genetic structure, suggesting restricted migration among populations. However, most phylogeographic studies have focused on species inhabiting humid forest interior. Little attention has been devoted to the study of species with ecologies conducive to dispersal, such as those of more open and variable environments associated with watercourses. Using mtDNA sequences, we examined patterns of genetic variation in a widely distributed Neotropical songbird of aquatic environments, the Yellow-hooded Blackbird (Icteridae, Chrysomus icterocephalus). In contrast to many forest species, Yellow-hooded Blackbirds showed no detectable genetic structure across their range, which includes lowland populations on both sides of the Andes, much of northeastern South America, Amazonia, as well as a phenotypically distinct highland population in Colombia. A coalescent-based analysis of the species indicated that its effective population size has increased considerably, suggesting a range expansion. Our results support the hypothesis that species occurring in open habitats and tracking temporally dynamic environments should show increased dispersal propensities (hence gene flow) relative to species from closed and more stable environments. The phenotypic and behavioral variation among populations of our study species appears to have arisen recently and perhaps in the face of gene flow.     

Life in proto‐Amazonia: Middle Miocene mammals from the Fitzcarrald Arch (Peruvian Amazonia)

The Middle Miocene has been identified as a time of great diversification in modern lineages now distributed in tropical South America, and when basic archetypal traits defining Amazonia appear, including climatic humid conditions, basic floral physiognomy and phylogenetic composition of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one species‐rich locality, La Venta in Colombia, has been extensively studied. The present contribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the ‘Miocochilius assemblage zone’ in La Venta. The mammalian fauna of Fitzcarrald comprises 24 taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible marsupial. At this time, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its disappearance in the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic similarity between Fitzcarrald and other Miocene faunas throughout South America support these scenarios. The Fitzcarrald mammal fauna exhibits first appearance datums and last appearance datums of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record from the southern cone of the continent.     

Between Andes and Amazon: The genetic profile of the Arawak‐speaking Yanesha

The Yanesha are a Peruvian population who inhabit an environment transitional between the Andes and Amazonia. They present cultural traits characteristic of both regions, including in the language they speak: Yanesha belongs to the Arawak language family (which very likely originated in the Amazon/Orinoco lowlands), but has been strongly influenced by Quechua, the most widespread language family of the Andes. Given their location and cultural make‐up, the Yanesha make for an ideal case study for investigating language and population dynamics across the Andes‐Amazonia divide. In this study, we analyze data from high and mid‐altitude Yanesha villages, both Y chromosome (17 STRs and 16 SNPs diagnostic for assigning haplogroups) and mtDNA data (control region sequences and 3 SNPs and one INDEL diagnostic for assigning haplogroups). We uncover sex‐biased genetic trends that probably arose in different stages: first, a male‐biased gene flow from Andean regions, genetically consistent with highland Quechua‐speakers and probably dating back to Inca expansion; and second, traces of European contact consistent with Y chromosome lineages from Italy and Tyrol, in line with historically documented migrations. Most research in the history, archaeology and linguistics of South America has long been characterized by perceptions of a sharp divide between the Andes and Amazonia; our results serve as a clear case‐study confirming demographic flows across that ‘divide’. Am J Phys Anthropol 155:600–609, 2014. © 2014 The Authors. American journal of physical Anthropology published by Wiley Periodocals, Inc.     

Trypanosoma cruzi: a considerable phylogenetic divergence indicates that the agent of Chagas disease is indigenous to the native fauna of the United States.

Thirty U.S. Trypanosoma cruzi stocks isolated mainly from wild mammals were characterized by multilocus enzyme electrophoresis at 22 genetic loci and random amplification of polymorphic DNA for 10 primers. Two main phylogenetic clusters, separated by large genetic distances, were discriminated by both methods, corresponding, respectively, to the formerly described zymodemes I and III. Two stocks isolated from indigenous human cases were identified as zymodeme I. Genetic diversity of the U.S. T. cruzi isolates was considerable, comparable to that scored in similarly sized samples from South America. These results favor the hypothesis that T. cruzi U.S. stocks were not imported at a historical time and are indigenous to the native fauna of the United States. The population structure of these stocks appeared to be basically clonal, as previously reported in South America, and no evidence of hybrid genotypes was found in the United States.