Alternative models of vertebrate speciation in Amazonia: an overview

The main hypotheses proposed to explain barrier formation separating populations and causing the differentiation of vertebrate species in Amazonia are based on different (mostly historical) factors, as follows. (1) Changes in the distribution of land and sea or in the landscape due to tectonic movements or sea-level fluctuations (Paleogeography hypothesis). (2) The barrier effect of Amazonian rivers (River hypothesis). (3) A combination of the barrier effect of broad rivers and vegetational changes in Northern and Southern Amazonia (River-refuge hypothesis). (4) The isolation of forest blocks near areas of surface relief in the periphery of Amazonia during dry climatic periods of the Tertiary and Quaternary (Refuge theory). (5) Competitive species interactions and local species isolations in peripheral regions of Amazonia due to invasion and counterinvasion during cold/warm periods of the Pleistocene (Disturbance-vicariance hypothesis). (6) Parapatric speciation across steep environmental gradients without separation of the representative populations (Gradient hypothesis). Several of these hypotheses are probably relevant to a different degree for the speciation processes in different faunal groups or during different geological periods. The paleogeography hypothesis refers mainly to faunal differentiation during the Tertiary and in combination with the Refuge hypothesis; Milankovitch cycles leading to global climatic-vegetational changes affected the biomes of the world not only during the Pleistocene but also during the Tertiary and earlier geological periods. New geoscientific evidence for the effect of dry climatic periods in Amazonia supports the predictions of the Refuge theory.     

Research Trails Affect the Abundance of an Epiphytic Tropical Bromeliad

Concerns have been expressed that research methods and research infrastructure may affect the systems under study, which could lead to biased results. Effects of research activities on seedlings, saplings, and understory plants that are subjected to trampling and injury have been demonstrated. However, as of yet, no effects on epiphytic plants have been reported. In this paper, we demonstrate the impact of research trails on the abundance of an epiphytic tropical bromeliad, Guzmania vittata, at a research site in Peruvian Amazonia. Compared to the interior of the forest, the abundance of this bromeliad is significantly higher along the research trails. While we do not know the exact cause for the increased bromeliad abundance along the trails, we discuss enhanced dispersal of anemochorous seeds as a potential mechanism that generates this impact.     

Remains of palms (Palmae) at archaeological sites in the New World: A review

A review of palm remains recorded at archaeological sites throughout the New World is presented. Remains have been found at 130 sites from the southern United States to southern Uruguay. They are of four kinds: carbonized or dry endocarps or seeds, phytoliths, pollen, and implements. Twenty-nine genera and at least 50 species of palms (i.e., about 9% of all American species) have been recorded. The oldest record dates back to 14,700b.p. for carbonized endocarp fragments of an unidentified palm in Rondônia, Brazil. The use of palms, as recorded from remains, was particularly widespread after 9000b.p. The predominant remains are endocarps ofAcrocomia, Attalea s.l.,Astrocaryum, Bactris, Syagrus, Elaeis, andOenocarpus, all of which are important sources of edible oils or edible fruits and are still widely used by aboriginal peoples. The review supports the hypothesis that human groups have played an important role in the dispersal of some palm species in the neotropics. Humanaided dispersal ofAcrocomia aculeata from South America into Central America, and ofOenocarpus bataua from northwestern Amazonia to other areas, is postulated. Archaeological remains support the hypothesis that pejibaye (Bactris gasipaes) was domesticated in the inter-Andean valleys or on the adjacent Pacific lowlands of Colombia and later introduced into the Amazon Basin.     

Ecological Aspects of Equestrian Adaptations in Aboriginal North America

Considerable attention has been given by anthropologists, including ethnohistorians, to the impact of domesticated horse use on aboriginal societies in western North America. The spatial and temporal distribution of horses, as well as variation in herd size, has traditionally been explained within a cultural diffusionist or historical particularist paradigm. It is argued here that not only has such an approach failed to account for the distribution and abundance of horses, but it also has proven to be an unproductive research strategy. An ecologically based explanatory model is presented that accounts for 65% of the observed variability in aboriginal horse herd size(s). An explanation of variability in horse numbers and horse-to-person ratios is essential if anthropologists seek to better understand equestrian adaptations. [equestrian adaptations, horse ecology, Plains-Basin-Plateau ethnology]     

Crop Diversity on Anthropogenic Dark Earths in Central Amazonia

A recent archaeological survey demonstrates that one of the most durable of all forms of pre-Columbian landscape transformation, Amazonian Dark Earths (ADE; soils formed by pre-Columbian settlement), are widespread along the course of the Madeira River, Central Amazonia, Brazil. We hypothesize that processes of crop cultivation and management by human populations today in landscapes that were intensively transformed during the pre-Columbian period will diverge from those in environments where human agency has not left such a heavy footprint. In order to test this hypothesis, we compare bitter manioc fields, homegardens and secondary forests on ADE with those on non-anthropogenic soils along the lower and middle Madeira River. We demonstrate that crop species and landrace populations diverge on anthropogenic and non-anthropogenic soils as a result of the interaction between human selection and management, soil physical and chemical properties, and plant responses over time. Hence, crop species selection and abundance and therefore agrobiodiversity is contingent on anthropogenic soils in Central Amazonia.     

Effects of age, ethnicity and health behaviours on the prevalence of adverse birth outcomes in Taiwan

This study sampled 8432 singleton first live births from Taiwan's 2005 Birth Registration Database to determine if there were more pre-term or low birth weight deliveries among aboriginal women than there were among Han Chinese women, and if the 'weathering' hypothesis applied to aboriginal women in Taiwan. Although the aboriginal women were socially disadvantaged and engaged in more unhealthy behaviours, including smoking, drinking, chewing betel quid and exposure to second-hand smoke, the evidence did not support the hypothesis that these teenaged minority women would have better birth outcomes, as has been demonstrated among teenage African-American women in the United States. Behaviours and not ethnicity were risk factors for teenage aboriginal mothers, who started deleterious health behaviours earlier than did their older counterparts. Teenage mothers had more adverse outcomes regardless of ethnicity and aboriginal mothers had more risky behaviours in all age groups. The prevalence of detrimental health behaviour among teenage mothers in Taiwan is of concern, particularly for aboriginal teenage mothers.     

Historical diversification of a terra-firme forest bird superspecies: a phylogeographic perspective on the role of different hypotheses of Amazonian diversification

Among those few hypotheses of Amazonian diversification amenable to falsification by phylogenetic and population genetics methods, three can be singled out because of their general application to vertebrates: the riverine barrier, the refuge, and the Miocene marine incursion hypotheses. I used phylogenetic and population genetics methods to reconstruct the diversification history of the upland (terra-firme) forest superspecies Xiphorhynchus spixii/elegans (Aves: Dendrocolaptidae) in Amazonia, and to evaluate predictions of the riverine barrier, refuge, and Miocene marine incursion hypotheses. Phylogeographic and population genetics analyses of the X. spixiilelegans superspecies indicated that the main prediction of the riverine barrier hypothesis (that sister lineages occur across major rivers) hold only for populations separated by "clear-water" rivers located on the Brazilian shield, in central and eastern Amazonia; in contrast, "white-water" rivers located in western Amazonia did not represent areas of primary divergence for populations of this superspecies. The main prediction derived from the refuge hypothesis (that populations of the X. spixii/elegans superspecies would show signs of past population bottlenecks and recent demographic expansions) was supported only for populations found in western Amazonia, where paleoecological data have failed to support past rainforest fragmentation and expansion of open vegetation types; conversely, populations from the eastern and central parts of Amazonia, where paleoecological data are consistent with an historical interplay between rainforest and open vegetation types, did not show population genetics attributes expected under the refuge hypothesis. Phylogeographic and population genetics data were consistent with the prediction made by the Miocene marine incursion hypothesis that populations of the X. spixii/elegans superspecies found on the Brazilian shield were older than populations from other parts of Amazonia. In contrast, the phylogeny obtained for lineages of this superspecies falsified the predicted monophyly of Brazilian shield populations, as postulated by the Miocene marine incursion hypothesis. In general, important predictions of both riverine barrier and Miocene marine incursion hypotheses were supported, indicating that they are not mutually exclusive; in fact, the data presented herein suggest that an interaction among geology, sea level changes, and hydrography created opportunities for cladogenesis in the X. spixii/elegans superspecies at different temporal and geographical scales.     

Riqueza y Distribución Ecológica de Especies de Pteridofitas en la Zona del Río Yavarí-Mirín, Amazonía Peruana

We studied the ecological distribution of pteridophytes (ferns and fern allies) along eight 8-km transects covering 12.7 ha in Peruvian Amazonia. Subunits of 200 m² of the transects have previously been classified into four different forest types, and here we document and quantify the floristic differences among these forest types. Pteridophytes have been suggested as an indicator group to classify rain forest habitats, but this requires that the ecological preferences of the species are well documented and consistent across geographic regions. Here we analyzed in detail the distribution and diversity patterns of 130 species across the four rain forest types. Relative species abundance and species diversity were similar among some of the forest types and differed among others, but the species composition differed markedly. Our results largely confirmed the earlier interpretation of the edaphic preferences of the pteridophyte species in western Amazonia. This supports the proposition that deterministic processes have an important role in influencing the floristic composition of Amazonian forests.     

An alternative hypothesis for the origin of Amazonian bird diversity

Aim To determine the origin of the high diversity of birds and other animals and plants in Amazonia. Previous hypotheses are: palaeogeography hypothesis, river hypothesis, river-refuge hypothesis, refuge hypothesis, disturbance-vicariance hypothesis, gradient hypothesis, pest-pressure hypothesis, intermediate disturbance hypothesis, riverine disturbance hypothesis, models of fine-scale habitat heterogeneity, lake hypothesis, and museum hypothesis. Methods At present there is agreement between areas of high species diversity and sites located over 100 m. As these sites would have been islands during a sea-level rise of this value, it was important to determine the probable distribution of these islands in Amazonia during a marine transgression. For that purpose, I traced the 100 m contour line from topographic maps. Results Two broad marine transgressions would have been produced from the Atlantic Ocean via the Amazon and Orinoco rivers. Two very large islands would have been formed to the north of the Amazon River, and other islands and archipelagos would have been formed along the coastal lowlands of Guiana, and at the periphery of the Amazon basin. The area located between the Solimoýes and Negro rivers and in the lower Branco would have been completely covered by the sea. Main conclusions A substantial part of the high diversity of forest and nonforest birds in lowland Amazonia can be hypothetysed to have originated during sea-level rises of about 100 m in the Quaternary and late Tertiary. These transgressions would have fragmented the Amazonian lowland into a large number of true islands and archipelagos, thus favouring active allopatric speciation. Values appreciably higher than 100 m above the present sea-level during previous periods of the Tertiary would have produced segregation of the biota earlier than the Tertiary–Quaternary boundary. Sea-level rises and vegetational changes (by aridity or cooling) would thus have driven the speciation pump, and local disturbances and other processes, would maintain the diversity.     

A comparison of the efficiencies of the shotgun and the bow in neotropical forest hunting

Whenever introduced into Amazonia and its neighboring regions, the shotgun has quickly replaced the bow and arrow and other aboriginal weapons of the hunt. The quick and widespread adoption of the shotgun is plainly a matter of its superiority over most aboriginal weapons. This paper compares the hunting efficiencies of the shotgun and the bow by means of a controlled field experiment among the Ye'kwana and Yanomamö Indians of the Upper Orinoco River of southern Venezuela. It also examines the impact of the shotgun on local animal populations and the economic changes brought about by the need to cash-crop in order to purchase Western hunting technology.Funds for the research and writing of this paper were made possible by an NIMH predoctoral fellowship to Napoleon A. Chagnon, Grant No. NIMH 5 R01 MH 26008-SSR.     

Variation in wood density determines spatial patterns inAmazonian forest biomass

Uncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field‐based estimates of the aboveground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site‐specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand‐level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB. Mean stand‐level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand‐level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional‐scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia.     

Variation in tropical bird survival across longitude and guilds: a case study from the Amazon

Survival estimates of tropical birds have been used to examine life‐history variation across latitudes and dietary guilds. Here, we provide apparent survival estimates of 31 rainforest species from central Amazonian Brazil and compare our results with estimates from Ecuador, Peru (western Amazonia) and French Guiana (eastern Amazonia) to examine geographic variation in demography. Our averaged annual survival estimate for central Amazonian species (?= 0.59, SE = 0.10) was concordant with previously published estimates from the western Amazon (?= 0.58, SE = 0.02), and eastern Amazon (?= 0.63, SE = 0.06). Two predominate demographic patterns were detected across the study areas: within species, survival was highest or lowest in eastern or western Amazonia, but rarely in central Amazonia. The most striking demographic variation was exhibited by Pithys albifrons, for which apparent survival estimates were nearly twice as high in eastern Amazonia (?= 0.80, SE = 0.06) than in western Amazonia (?= 0.42, SE = 0.06) but intermediate in central Amazonia (?= 0.54, SE = 0.04). Although variation in survival may be associated with differences in life history characteristics, our analysis of flocking guild, body size, and nest architecture revealed only moderate differences in survival associated with nest architecture. These results suggest that geographic variation in population processes may be significant for widespread Amazonian species.     

Vertebrate responses to fruit production in Amazonian flooded and unflooded forests

We document patterns of fruit and vertebrate abundance within an extensive, virtually undisturbed mosaic of seasonally flooded (várzea and igapó) and unflooded (terra firme) forests of central Amazonia. Using phenological surveys and a standardised series of line-transect censuses we investigate the spatial and temporal patterns of immature and mature fruit availability and how this may affect patterns of habitat use by vertebrates in the landscape. All habitats showed marked peaks in fruiting activity, and vertebrate detection rates varied over time for most species both within and between forest types. Many arboreal and terrestrial vertebrates used both types of flooded forest on a seasonal basis, and fluctuations in the abundance of terrestrial species in várzea forest were correlated with fruit availability. Similarly, the abundance of arboreal seed predators such as buffy saki monkeys (Pithecia albicans) and macaws (Ara spp.) were closely linked with immature fruit availability in terra firme forest. We conclude that highly heterogeneous landscapes consisting of terra firme, várzea and igapó forest appear to play an important role in the dynamics of many vertebrate species in lowland Amazonia, but the extent to which different forest types are used is highly variable in both space and time.     

Beta diversity of frogs in the forests of New Guinea, Amazonia and Europe: contrasting tropical and temperate communities

Aim To test the hypothesis that animal communities within environmentally relatively uniform lowland forests are characterized by low beta diversity, both in tropical and in temperate areas. Location Lowland forests in the basins of the Sepik and Ramu rivers in New Guinea, the Amazon river in Bolivia, and the Elbe and Dyje rivers in the Czech Republic. Methods A network of 5–6 study sites spanning distances from 20–80 to 300–500 km in each study area was systematically surveyed for all frogs, using visual detection and call tracking. The community data were analysed for alpha and beta diversity. Results Local (alpha) diversity of frog communities was similar in the two tropical areas, New Guinea (mean ± SE of 22 ± 1.4 species per site) and Amazonia (24 ± 1.7 species), but was significantly lower in Europe (8 ± 0.8 species). In Amazonia, 36 of the total of 70 species were recorded from single sites. In contrast, widespread species dominated in Europe, whereas New Guinea exhibited an intermediate pattern with both local and widespread species well represented. The rate of species accumulation across different sites was lowest in Europe, intermediate in New Guinea and highest in Amazonia. The regional species diversity, expressed as the combined number of species from five study sites, was 1.5 times higher than the local species diversity at a single site in Europe, 2.0 times higher in New Guinea and 2.7 times higher in Amazonia. The proportion of species shared between communities decreased with geographic distance in New Guinea and Europe, but not in Amazonia. Main conclusions Frog communities in the lowland tropical rain forests of New Guinea and Amazonia had similar numbers of species, but differed in their beta diversity. More species in Amazonia had restricted distributions than in New Guinea. Both tropical areas had markedly higher alpha and beta diversity than the temperate area in Europe.     

Seasonal differences in rainfall,food availability,and the foraging behavior of Tropical Kingbirds in the southern Amazon Basin

ABSTRACT Little is known about the relationship between seasonal food availability and the foraging strategies of insectivorous Neotropical birds. We studied a population of Tropical Kingbirds (Tyrannus melancholicus), a primarily insectivorous species, in eastern Bolivia to examine relationships between rainfall, food availability, and foraging strategies throughout the year. Our study site in the southern Amazon Basin was characterized by strong seasonal variation in the abundance of the kingbird's main insect prey (coleopterans and hymenopterans), with reduced abundance during the nonbreeding season which largely overlaps the dry season. Overall, mean search times for insect prey by Tropical Kingbirds during the breeding (96.9 ± 85.6 [SD] sec) and nonbreeding (83.7 ± 91.2 sec) seasons did not differ (P= 0.23). However, during the nonbreeding season, kingbird search times were negatively, but nonsignificantly, correlated with coleopteran abundance (r²= 0.43, P= 0.16) and significantly and negatively correlated with hymenopteran abundance (r²= 0.72, P= 0.03). Although insect abundance differed seasonally, kingbird search times did not, perhaps because kingbirds forage on a greater variety of insects during the nonbreeding season or, during the breeding season, kingbird search times may be influenced by the need to monitor and defend nests as well as constraints on the types of prey that can be fed to nestlings. However, the reduced abundance of their primary insect prey and negative relationships between the abundance of those prey and search times during the dry, nonbreeding season suggest that Tropical Kingbirds in southern Amazonia may be food limited, potentially explaining why some migrate and spend that season elsewhere.     

Carbon stock loss from deforestation through 2013 in Brazilian Amazonia

The largest carbon stock in tropical vegetation is in Brazilian Amazonia. In this ~5 million km² area, over 750 000 km² of forest and ~240 000 km² of nonforest vegetation types had been cleared through 2013. We estimate current carbon stocks and cumulative gross carbon loss from clearing of premodern vegetation in Brazil's ‘Legal Amazonia’ and ‘Amazonia biome’ regions. Biomass of ‘premodern’ vegetation (prior to major increases in disturbance beginning in the 1970s) was estimated by matching vegetation classes mapped at a scale of 1 : 250 000 and 29 biomass means from 41 published studies for vegetation types classified as forest (2317 1‐ha plots) and as either nonforest or contact zones (1830 plots and subplots of varied size). Total biomass (above and below‐ground, dry weight) underwent a gross reduction of 18.3% in Legal Amazonia (13.1 Pg C) and 16.7% in the Amazonia biome (11.2 Pg C) through 2013, excluding carbon loss from the effects of fragmentation, selective logging, fires, mortality induced by recent droughts and clearing of forest regrowth. In spite of the loss of carbon from clearing, large amounts of carbon were stored in stands of remaining vegetation in 2013, equivalent to 149 Mg C ha^?1 when weighted by the total area covered by each vegetation type in Legal Amazonia. Native vegetation in Legal Amazonia in 2013 originally contained 58.6 Pg C, while that in the Amazonia biome contained 56 Pg C. Emissions per unit area from clearing could potentially be larger in the future because previously cleared areas were mainly covered by vegetation with lower mean biomass than the remaining vegetation. Estimates of original biomass are essential for estimating losses to forest degradation. This study offers estimates of cumulative biomass loss, as well as estimates of premodern carbon stocks that have not been represented in recent estimates of deforestation impacts.     

Precipitation gradients,plant biogeography,and the incidence of drip-tips in Cerrado plant species

Examining how both climate and species distribution patterns correlate with leaf morphology can give insights into the ecological and evolutionary patterns that drive adaptive selection of leaf form and function. Drip-tips are a common feature of leaves in rain forest tree species; they are thought to be an adaptation that aids leaf drying and maximizes photosynthesis in areas with high-rainfall climates. We tested whether this macroecological pattern holds true across the precipitation gradients in a non-rain forest region—the woodland savannas of Brazil known as the Cerrado—and compared our results with previous studies from Amazonia. Drip-tips were, as expected, less common overall in the drier Cerrado than in Amazonia. In addition, within the Cerrado, drip-tips were more prevalent in areas with higher rainfall as well as in Cerrado sites that were closer to Amazonia. Moreover, species that occurred across both the Cerrado and Amazonia had drip-tips more often than species that were found only in the Cerrado. These findings support the hypothesis that drip-tips are adaptive and that either the cost of retaining drip-tips is low or that in drier regions they have other benefits.     

From Amazonia to the Atlantic forest: Molecular phylogeny of Phyzelaphryninae frogs reveals unexpected diversity and a striking biogeographic pattern emphasizing conservation challenges

Documenting the Neotropical amphibian diversity has become a major challenge facing the threat of global climate change and the pace of environmental alteration. Recent molecular phylogenetic studies have revealed that the actual number of species in South American tropical forests is largely underestimated, but also that many lineages are millions of years old. The genera Phyzelaphryne (1 sp.) and Adelophryne (6 spp.), which compose the subfamily Phyzelaphryninae, include poorly documented, secretive, and minute frogs with an unusual distribution pattern that encompasses the biotic disjunction between Amazonia and the Atlantic forest. We generated >5.8kb sequence data from six markers for all seven nominal species of the subfamily as well as for newly discovered populations in order to (1) test the monophyly of Phyzelaphryninae, Adelophryne and Phyzelaphryne, (2) estimate species diversity within the subfamily, and (3) investigate their historical biogeography and diversification. Phylogenetic reconstruction confirmed the monophyly of each group and revealed deep subdivisions within Adelophryne and Phyzelaphryne, with three major clades in Adelophryne located in northern Amazonia, northern Atlantic forest and southern Atlantic forest. Our results suggest that the actual number of species in Phyzelaphryninae is, at least, twice the currently recognized species diversity, with almost every geographically isolated population representing an anciently divergent candidate species. Such results highlight the challenges for conservation, especially in the northern Atlantic forest where it is still degraded at a fast pace. Molecular dating revealed that Phyzelaphryninae originated in Amazonia and dispersed during early Miocene to the Atlantic forest. The two Atlantic forest clades of Adelophryne started to diversify some 7Ma minimum, while the northern Amazonian Adelophryne diversified much earlier, some 13Ma minimum. This striking biogeographic pattern coincides with major events that have shaped the face of the South American continent, as we know it today.     

Effects of Geomorphology and Primary Productivity on Amazonian Leaf Litter Herpetofauna

The Amazon Basin, representing the largest expanse of intact tropical rain forest on the planet, harbors the largest diversity of amphibians and reptiles in the world. Limited elevation and climate differences across the Basin belie one major division of upland forests – geomorphological soil age and induced nutrient levels. We hypothesized that secondary consumers in the leaf litter herpetofauna community on ancient soils of Central Amazonia would exhibit reduced biomass compared with those found on younger soils of Western Amazonia, and that population densities on ancient soils could be driven below viable thresholds, reducing species richness. We found overall herpetofauna abundance, biomass and richness on young soils in Ecuador were significantly greater than those on ancient soils in the Brazilian Amazon. Separately, amphibians were only slightly more abundant, but their biomass on younger soils was twice that on ancient soils. Even more impressive was the variation exhibited by lizards: abundance was not significantly different, but biomass was five times greater on younger soils. Diversity of both taxa was greater on young soils. The most important driver of differences in herpetofauna biomass, abundance and possibly diversity across Amazonia may be the underlying geomorphologic differences. Reduced primary productivity on ancient soils appears to reverberate up the food chain, leaving fewer resources for higher trophic levels. We suggest that conservation initiatives must compensate for reduced biomass on ancient soils through increased reserve size, especially as forest fragmentation escalates. This study highlights the importance of including biomass as a standard measure in herpetofauna sampling.     

Colour forms of Amazonian cichlid fish represent reproductively isolated species

Laboratory mate choice experiments have confirmed species status for cichlid fish in the African Great Lakes that differ in colour and little else. Colour differences between allopatric populations of the South American cichlid genus Apistogramma are known for many species, yet the status of such populations has not been previously tested. Analysis of the genetic relationships and mate choice characteristics of populations previously described as Apistogramma caetei from eastern Amazonia indicates genetic differentiation into at least three allopatric lineages, which also show strong prezygotic isolation through female mate choice, confirming them as Biological species. If future studies confirm that this result is indicative of a general trend, the species richness of the South American cichlid fishes may presently be seriously underestimated.