While elucidating the evolutionary trajectory of green anacondas, we previously documented the ex... more While elucidating the evolutionary trajectory of green anacondas, we previously documented the existence of two distinct species, Eunectes akayima sp. nov. and Eunectes murinus (Linnaeus, 1758), that separated approximately 10 million years ago. Our research integrates a novel molecular clock approach, focuses on tectonic plate movements with fossil records as minimal chronological markers, and offers a refined understanding of speciation events in relation to major biogeographical occurrences in South America. Mitochondrial DNA analysis demonstrates a significant genetic divergence between the species, which is supported by a notable difference in sexual size dimorphism (SSD) intensity between the two species, along with other morphological differences. This paper also rectifies earlier oversights in the description of the new species and clarifies taxonomic ambiguities in compliance with the International Code of Zoological Nomenclature (henceforth ICZN). In addition, we designate a neotype for E. murinus to stabilize the group. In an effort to honor Indigenous nations, E. akayima sp. nov. derives its name from the Carib language, advocating for the inclusion of traditional names in scientific discourse. Our paper not only contributes to the taxonomic stability of anacondas but also advocates for the usage of Indigenous names in zoological nomenclature by adopting a more inclusive and flexible approach to the ICZN and eliminating unintended exclusionary practices that we have inherited in science as in other disciplines.
Anacondas, genus Eunectes, are a group of aquatic snakes with a wide distribution in South Americ... more Anacondas, genus Eunectes, are a group of aquatic snakes with a wide distribution in South America. The taxonomic status of several species has been uncertain and/or controversial. Using genetic data from four recognized anaconda species across nine countries, this study investigates the phylogenetic relationships within the genus Eunectes. A key finding was the identification of two distinct clades within Eunectes murinus, revealing two species as cryptic yet genetically deeply divergent. This has led to the recognition of the Northern Green Anaconda as a separate species (Eunectes akayima sp. nov), distinct from its southern counterpart (E. murinus), the Southern Green Anaconda. Additionally, our data challenge the current understanding of Yellow Anaconda species by proposing the unification of Eunectes deschauenseei and Eunectes beniensis into a single species with Eunectes notaeus. This reclassification is based on comprehensive genetic and phylogeographic analyses, suggesting closer relationships than previously recognized and the realization that our understanding of their geographic ranges is insufficient to justify its use as a separation criterion. We also present a phylogeographic hypothesis that traces the Miocene diversification of anacondas in western South America. Beyond its academic significance, this study has vital implications for the conservation of these iconic reptile species, highlighting our lack of knowledge about
Introduction: Trophic cascades can produce important effects on a community where some species ma... more Introduction: Trophic cascades can produce important effects on a community where some species may have strong effects on other parts of the community up, down the food chain, or both. Top predators are often controlled from the bottom-up by the abundance of their prey base while prey animals are often controlled from the top-down. Studies of trophic interactions in the tropics suggest that the trophic chains are longer because of the high productivity; and because of the high diversity there is abundant intraguild redundancy which results in weak interactions. Methods: We studied the effect of bottom-up forces affecting the population of green Anaconda (Eunectes murinus) in the Venezuelan llanos; looking at net primary productivity, precipitation, and the abundance of an important prey item, Capybara (Hydrochaeris hydrochaeris). Results: Our data show a strong interaction of these variables on the percentage of Anacondas that reproduce in a given year (here forth breeding ratio). In particular Capybara abundance has a strong effect. Capybara abundance itself is also under strong bottom-up influence determined by precipitation and Net Primary Productivity. Discussion: These strong interactions are not what is expected from a tropical ecosystem. We also found an unexpected strong influence of precipitation and primary productivity on Anaconda breeding ratio not related to the abundance of Capybara, likely affecting abundance of other prey or affecting non-trophic variables. This later evidence supports the notion that there is redundancy in tropical food chains and, strong as the effect of Capybara abundance might be, Anacondas do not entirely rely on them.
Capital breeders are animals that breed with the stored energy they have gathered prior to the re... more Capital breeders are animals that breed with the stored energy they have gathered prior to the reproductive event. The amount of energy stored by a given individual can be quantified using morphological measurements and estimating a condition index that can help study the reproductive biology of wild-caught animals. Several condition indices have been used to study the biology and natural history of snakes, with the residual of the log-transformed data being one of the most popular. Here, I develop a simple condition index that assumes that the animals do not change shape throughout life except for changes in condition. This condition with isometry assumption (CIA) is unbiased for all size classes and simple to calculate. With data of animals whose breeding condition was known, I determine a cutoff of 0.875. Animals with a higher condition had a high chance of breeding, while those with lower condition did not. This method correctly predicts the breeding status of 94% of the observations. Using the same data set, I tested the residuals of the log-transformed regression and found far worse results. The CIA was also able to predict breeding status in other snakes opportunistically found in the study. The fact that it is possible to reliably predict the breeding status of anacondas based on their condition confirms that anacondas are capital breeders.
Article provide evidence that the Pebas system was the result of the damming of the original Pale... more Article provide evidence that the Pebas system was the result of the damming of the original Paleo Amazon/Orinoco River
The maximum size that snakes can reach has been a mater of long held debate until the discovery o... more The maximum size that snakes can reach has been a mater of long held debate until the discovery of Titanoboa cerrejonensis (Boidae). It was an aquatic predator that lived 60–58 million years ago in what is currently eastern Colombia, occupying tropical swamps. It was calculated to measure 12.82 meters and it was speculated that it grew so much due to a warmer planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas Eunectes murinus, this study makes inferences about aspects of the natural history of T. cerrejonensis that perhaps will not be easily available by studying the fossil record. Drawing parallels with anaconda's biology, I estmate that a non-breeding female T. cerrejonensis weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born Titanoboa were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that Titanoboa had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like.
Movement ecology is an important tool for understanding animal behaviour toward basic needs, as w... more Movement ecology is an important tool for understanding animal behaviour toward basic needs, as well as to design conservation and management priorities. Animals usually do not move randomly and may prefer certain types of habitats over others. The yellow anaconda (Eunectes notaeus) is one of the largest snakes in South America. However, little is known about its natural history. Here, we present results from a telemetry study to quantify movement patterns and habitat use of eight yellow anacondas in a protected, seasonally flooded area in Midwestern Brazil. Yellow anacondas were associated to small channels with macrophyte stands and bushy vegetation. They moved relatively little (188 m monthly) and had small home range (mean 6.2 ha); they used native pastures and abandoned farmlands with forest patches more than expected by chance. Our results contribute to the understanding of dispersal patterns, habitat choices, and life history of this large aquatic snake and to the body of knowledge needed for management and conservation of its populations and habitats.
Understanding the origin of South America's diversity is of great importance especially consideri... more Understanding the origin of South America's diversity is of great importance especially considering our current extinction crisis in the face of climate change. While great debate exists about the sources of Amazonian diversity, there is no consensus about an overarching process that explains the Amazon's uniquely high diversity. In this contribution, I present the following model considering the impact of tectonics on the hydrology of the continent. When the Andes rose, it dammed the paleo-Amazon, which ran west at the time. This produced generalized flooding with a mosaic of forest in the more elevated areas surrounded by flooded habitats. Because of the flat relief of the Amazon basin, small changes in water level produced forest expansion and contraction, resulting in speciation pulses. Using data from the literature on species distribution, as well as the age of new lineages from molecular studies, I show that the space and timing of speciation process in the South America was consistent with the predictions of this model. This model also posits that there were no marine incursions on the continent. Rather, marine conditions developed in situ, might be a better explanation for the marine conditions found in paleo-history of the region. This model provides a theoretical framework for evolutionary processes in South America that explains its uniquely high diversity. K E Y W O R D S Amazon, biodiversity, macroevolution, paleo-ecology, speciation.
Opportunitic encounter of P trigonatus nest in the Ecuatorian amazon describes the nest's locatio... more Opportunitic encounter of P trigonatus nest in the Ecuatorian amazon describes the nest's location and success.
osteomyelitis is frequently reported in turtles, lizards and snakes and Salmonellae are increasin... more osteomyelitis is frequently reported in turtles, lizards and snakes and Salmonellae are increasingly reported as the causative organism. however, very little is known of this disease occurring in crocodilians. crocodilians are shy, robust animals and often hide clinical symptoms, especially when submerged in water. Knowledge of disease in crocodilians is important, especially in zoos and farms where they are often kept in high densities. here we report the first known case of trunk vertebrae osteomyelitis in the order Crocodilia. A six year old, captive raised spectacled caiman (Caiman crocodilus) was admitted for veterinary examination after developing a postural abnormality in the vertebral region, including spinal curvature and dorsal indentation. radiographic and computed tomographic studies showed muscle wastage and multifocal vertebral osteolytic changes suggestive of osteomyelitis. the caiman was euthanized and post-mortem examination revealed coelomic serosanguinous effusion and a diffuse severe fibrinous coelomitis with firm visceral adhesions involving the liver and spleen. a 15 cm irregular mass was found within and greatly expanding a major blood vessel ventral to the trunk vertebrae. examination of the mass revealed an organized thrombus and examination of the affected trunk vertebrae revealed severe osteolytic changes with extensive remodeling. Salmonella enterica houtenae was isolated from the vertebral lesions. Salmonellae, a common constituent of the reptilian gut microbiota, are potentially pathogenic and can become clinically important in times of stress. Salmonella enterica houtenae was previously isolated from reptiles and humans with pathological symptoms. However, this appears to be the first documented case in association with osteomyelitis in vertebrates.
Opportunistic encounter of wild nest of reintroduced Orinoco crocodiles allows to determine the a... more Opportunistic encounter of wild nest of reintroduced Orinoco crocodiles allows to determine the age at which the start reproducing in the wild
While elucidating the evolutionary trajectory of green anacondas, we previously documented the ex... more While elucidating the evolutionary trajectory of green anacondas, we previously documented the existence of two distinct species, Eunectes akayima sp. nov. and Eunectes murinus (Linnaeus, 1758), that separated approximately 10 million years ago. Our research integrates a novel molecular clock approach, focuses on tectonic plate movements with fossil records as minimal chronological markers, and offers a refined understanding of speciation events in relation to major biogeographical occurrences in South America. Mitochondrial DNA analysis demonstrates a significant genetic divergence between the species, which is supported by a notable difference in sexual size dimorphism (SSD) intensity between the two species, along with other morphological differences. This paper also rectifies earlier oversights in the description of the new species and clarifies taxonomic ambiguities in compliance with the International Code of Zoological Nomenclature (henceforth ICZN). In addition, we designate a neotype for E. murinus to stabilize the group. In an effort to honor Indigenous nations, E. akayima sp. nov. derives its name from the Carib language, advocating for the inclusion of traditional names in scientific discourse. Our paper not only contributes to the taxonomic stability of anacondas but also advocates for the usage of Indigenous names in zoological nomenclature by adopting a more inclusive and flexible approach to the ICZN and eliminating unintended exclusionary practices that we have inherited in science as in other disciplines.
Anacondas, genus Eunectes, are a group of aquatic snakes with a wide distribution in South Americ... more Anacondas, genus Eunectes, are a group of aquatic snakes with a wide distribution in South America. The taxonomic status of several species has been uncertain and/or controversial. Using genetic data from four recognized anaconda species across nine countries, this study investigates the phylogenetic relationships within the genus Eunectes. A key finding was the identification of two distinct clades within Eunectes murinus, revealing two species as cryptic yet genetically deeply divergent. This has led to the recognition of the Northern Green Anaconda as a separate species (Eunectes akayima sp. nov), distinct from its southern counterpart (E. murinus), the Southern Green Anaconda. Additionally, our data challenge the current understanding of Yellow Anaconda species by proposing the unification of Eunectes deschauenseei and Eunectes beniensis into a single species with Eunectes notaeus. This reclassification is based on comprehensive genetic and phylogeographic analyses, suggesting closer relationships than previously recognized and the realization that our understanding of their geographic ranges is insufficient to justify its use as a separation criterion. We also present a phylogeographic hypothesis that traces the Miocene diversification of anacondas in western South America. Beyond its academic significance, this study has vital implications for the conservation of these iconic reptile species, highlighting our lack of knowledge about
Introduction: Trophic cascades can produce important effects on a community where some species ma... more Introduction: Trophic cascades can produce important effects on a community where some species may have strong effects on other parts of the community up, down the food chain, or both. Top predators are often controlled from the bottom-up by the abundance of their prey base while prey animals are often controlled from the top-down. Studies of trophic interactions in the tropics suggest that the trophic chains are longer because of the high productivity; and because of the high diversity there is abundant intraguild redundancy which results in weak interactions. Methods: We studied the effect of bottom-up forces affecting the population of green Anaconda (Eunectes murinus) in the Venezuelan llanos; looking at net primary productivity, precipitation, and the abundance of an important prey item, Capybara (Hydrochaeris hydrochaeris). Results: Our data show a strong interaction of these variables on the percentage of Anacondas that reproduce in a given year (here forth breeding ratio). In particular Capybara abundance has a strong effect. Capybara abundance itself is also under strong bottom-up influence determined by precipitation and Net Primary Productivity. Discussion: These strong interactions are not what is expected from a tropical ecosystem. We also found an unexpected strong influence of precipitation and primary productivity on Anaconda breeding ratio not related to the abundance of Capybara, likely affecting abundance of other prey or affecting non-trophic variables. This later evidence supports the notion that there is redundancy in tropical food chains and, strong as the effect of Capybara abundance might be, Anacondas do not entirely rely on them.
Capital breeders are animals that breed with the stored energy they have gathered prior to the re... more Capital breeders are animals that breed with the stored energy they have gathered prior to the reproductive event. The amount of energy stored by a given individual can be quantified using morphological measurements and estimating a condition index that can help study the reproductive biology of wild-caught animals. Several condition indices have been used to study the biology and natural history of snakes, with the residual of the log-transformed data being one of the most popular. Here, I develop a simple condition index that assumes that the animals do not change shape throughout life except for changes in condition. This condition with isometry assumption (CIA) is unbiased for all size classes and simple to calculate. With data of animals whose breeding condition was known, I determine a cutoff of 0.875. Animals with a higher condition had a high chance of breeding, while those with lower condition did not. This method correctly predicts the breeding status of 94% of the observations. Using the same data set, I tested the residuals of the log-transformed regression and found far worse results. The CIA was also able to predict breeding status in other snakes opportunistically found in the study. The fact that it is possible to reliably predict the breeding status of anacondas based on their condition confirms that anacondas are capital breeders.
Article provide evidence that the Pebas system was the result of the damming of the original Pale... more Article provide evidence that the Pebas system was the result of the damming of the original Paleo Amazon/Orinoco River
The maximum size that snakes can reach has been a mater of long held debate until the discovery o... more The maximum size that snakes can reach has been a mater of long held debate until the discovery of Titanoboa cerrejonensis (Boidae). It was an aquatic predator that lived 60–58 million years ago in what is currently eastern Colombia, occupying tropical swamps. It was calculated to measure 12.82 meters and it was speculated that it grew so much due to a warmer planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas Eunectes murinus, this study makes inferences about aspects of the natural history of T. cerrejonensis that perhaps will not be easily available by studying the fossil record. Drawing parallels with anaconda's biology, I estmate that a non-breeding female T. cerrejonensis weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born Titanoboa were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that Titanoboa had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like.
Movement ecology is an important tool for understanding animal behaviour toward basic needs, as w... more Movement ecology is an important tool for understanding animal behaviour toward basic needs, as well as to design conservation and management priorities. Animals usually do not move randomly and may prefer certain types of habitats over others. The yellow anaconda (Eunectes notaeus) is one of the largest snakes in South America. However, little is known about its natural history. Here, we present results from a telemetry study to quantify movement patterns and habitat use of eight yellow anacondas in a protected, seasonally flooded area in Midwestern Brazil. Yellow anacondas were associated to small channels with macrophyte stands and bushy vegetation. They moved relatively little (188 m monthly) and had small home range (mean 6.2 ha); they used native pastures and abandoned farmlands with forest patches more than expected by chance. Our results contribute to the understanding of dispersal patterns, habitat choices, and life history of this large aquatic snake and to the body of knowledge needed for management and conservation of its populations and habitats.
Understanding the origin of South America's diversity is of great importance especially consideri... more Understanding the origin of South America's diversity is of great importance especially considering our current extinction crisis in the face of climate change. While great debate exists about the sources of Amazonian diversity, there is no consensus about an overarching process that explains the Amazon's uniquely high diversity. In this contribution, I present the following model considering the impact of tectonics on the hydrology of the continent. When the Andes rose, it dammed the paleo-Amazon, which ran west at the time. This produced generalized flooding with a mosaic of forest in the more elevated areas surrounded by flooded habitats. Because of the flat relief of the Amazon basin, small changes in water level produced forest expansion and contraction, resulting in speciation pulses. Using data from the literature on species distribution, as well as the age of new lineages from molecular studies, I show that the space and timing of speciation process in the South America was consistent with the predictions of this model. This model also posits that there were no marine incursions on the continent. Rather, marine conditions developed in situ, might be a better explanation for the marine conditions found in paleo-history of the region. This model provides a theoretical framework for evolutionary processes in South America that explains its uniquely high diversity. K E Y W O R D S Amazon, biodiversity, macroevolution, paleo-ecology, speciation.
Opportunitic encounter of P trigonatus nest in the Ecuatorian amazon describes the nest's locatio... more Opportunitic encounter of P trigonatus nest in the Ecuatorian amazon describes the nest's location and success.
osteomyelitis is frequently reported in turtles, lizards and snakes and Salmonellae are increasin... more osteomyelitis is frequently reported in turtles, lizards and snakes and Salmonellae are increasingly reported as the causative organism. however, very little is known of this disease occurring in crocodilians. crocodilians are shy, robust animals and often hide clinical symptoms, especially when submerged in water. Knowledge of disease in crocodilians is important, especially in zoos and farms where they are often kept in high densities. here we report the first known case of trunk vertebrae osteomyelitis in the order Crocodilia. A six year old, captive raised spectacled caiman (Caiman crocodilus) was admitted for veterinary examination after developing a postural abnormality in the vertebral region, including spinal curvature and dorsal indentation. radiographic and computed tomographic studies showed muscle wastage and multifocal vertebral osteolytic changes suggestive of osteomyelitis. the caiman was euthanized and post-mortem examination revealed coelomic serosanguinous effusion and a diffuse severe fibrinous coelomitis with firm visceral adhesions involving the liver and spleen. a 15 cm irregular mass was found within and greatly expanding a major blood vessel ventral to the trunk vertebrae. examination of the mass revealed an organized thrombus and examination of the affected trunk vertebrae revealed severe osteolytic changes with extensive remodeling. Salmonella enterica houtenae was isolated from the vertebral lesions. Salmonellae, a common constituent of the reptilian gut microbiota, are potentially pathogenic and can become clinically important in times of stress. Salmonella enterica houtenae was previously isolated from reptiles and humans with pathological symptoms. However, this appears to be the first documented case in association with osteomyelitis in vertebrates.
Opportunistic encounter of wild nest of reintroduced Orinoco crocodiles allows to determine the a... more Opportunistic encounter of wild nest of reintroduced Orinoco crocodiles allows to determine the age at which the start reproducing in the wild
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Papers by Jesus Rivas
planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas Eunectes murinus, this study makes inferences about aspects of the natural history of T. cerrejonensis that perhaps will not be easily available by studying the fossil record. Drawing
parallels with anaconda's biology, I estmate that a non-breeding female T. cerrejonensis weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born Titanoboa were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that Titanoboa had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like.
planetary weather. Its life history and ecology are speculated to be very similar to that of current day anacondas. Using data from a long-term study involving hundreds of green anacondas Eunectes murinus, this study makes inferences about aspects of the natural history of T. cerrejonensis that perhaps will not be easily available by studying the fossil record. Drawing
parallels with anaconda's biology, I estmate that a non-breeding female T. cerrejonensis weighed approximately 1,232 kg, and 1,465 kg when pregnant. It would have started breeding at 480 cm SVL, weighing 95 kg. New-born Titanoboa were between 181 and 215 cm. Its average meal was estimated to be 505 kg, with a potential maximum of 1,799 kg. I estimate that Titanoboa had a growth rate of 0.046 mm/day compared with 0.036 in anacondas; which does not support the notion that it grew more due to a warmer planet. Although the results are largely speculative, they help give a better idea of what the life of an extinct snake was like.