Neglected giant Neotropical snakes: assessing worldwide research on anacondas (Boidae: Eunectes)

Anacondas (Squamata: Boidae: Eunectes) are emblematic snakes and are composed of four living species. Despite popular appeal, its structural role in ecosystems and industrial use, several aspects of its biology are still misunderstood. The lack of studies is worrisome because there is a global trend of population decline for reptiles, especially in the tropics. To date, no work has provided a quantitative and comprehensive assessment of anaconda research and its trends. This work aims to conduct a bibliometric and scientometric analysis on anacondas, the largest snakes in the world. Our search resulted in 218 papers between 1861 and 2022. This search was conducted in two different databases: The Web of Science database that returned 60 articles, plus the author's personal library of 98 articles. Although the number of publications on anacondas has doubled every 20 years.

  

For this scientometric study regarding anacondas, we used two independent databases. We exhaustively researched for papers on Web of Science (WoS) and included the personal authors’ library, who are anaconda researchers and own an extensive literature collection about these snakes. For WoS research we used the keywords “((Eunect* OR sucuri* OR anaconda*)) on title, abstract and keywords selecting the research mode “Topic” (TS) until 2022. This search provided us 104 publications, however, after screening and excluding articles not related to our focal group, our base data counted with 60 articles. The authors library added 158 new articles to our database. The authors’ library (AL) was built over years of research and is based on an exhaustive search for the literature on anacondas obtained by contact with other researchers in the area and historical works scanned from physical journals belonging to collections of museums and biological collections in Brazil.

We aimed to evaluate trends, biases, and gaps in knowledge about the anaconda species. We selected only papers that addressed some biological aspects (ecological, veterinary, zoological, ethnobiological, etc.), in wild or captive animals, in natural or anthropogenic environments. Selection criteria were applied to refine the database, such as the exclusion of all articles that did not address some biological aspect, or exclusively bibliographic review papers. We include works that address other taxonomic groups (which anacondas were included), such as fauna inventories. All geographic, taxonomic, and biological data present in our database were obtained from the texts, figures and tables presented in the articles.

After applying the selection criteria, our database was structured with the following items (see Supporting Information Table S1): (1) year of publication; (2) country(-ies) where the work was conducted; (3) funding country of the research; (4) species studied; (5) if the work was conducted in outdoor (natural areas/rural areas/urban areas) or indoor (laboratory/museum/zoo, etc.); (6) research field involved in the studies (see below).

To identify researches trends, we classified the papers into four general research fields partitioned into subcategories (Magle et al. 2012; Brum et al. 2022): Ecology (5): Behavior (home range, habitat use, defensive/escape behavior, etc.), Community (works with more than one species involving interactions between two or more species, faunal inventories), Population (population dynamics, abundance, density, and viability), Diet (foraging and prey description), and Reproduction (reproductive cycles, parthenogenesis, reproductive behavior). Zoology (5): Morphology (morphometry and morphological features description, even in fossil pieces), Taxonomy (diagnoses and phylogenetics studies), Genetics (we fitted here all works that used some type of molecular technique, e.g. DNA sequencing, cytogenetics, etc.), Biogeography (studies regarding anacondas distribution across time and geographic space), and Paleontology (fossil record—because we were looking for the knowledge about living anacondas. Here we include only fossil records to Eunectes sp. and E. murinus and excluded papers regarding extinct species, as Eunectes stirtoni. We included records of Eunectes sp. because it is possibly related to any living species, but the fossil records were so incomplete that they did not allow the for specific identification). Veterinary (5): Anatomy (morphological description of organs), Physiology (evaluations of the functioning and maintenance of the animal's body system), Biochemistry (description and evaluation of biochemical parameters such as blood counts, enzymatic action, chemical analysis of tissues or products from the animal), Parasitology (endo and/or ectoparasite infection), and Pathology (description of diseases, etiological agents, injuries, anomalies, and their medical treatment). Conservation (4): Conflicts (situations of interaction between humans and anacondas that cause harm to either party such as injury, death and/or economic loss), Management (animal management acts such as population/commercial control, relocation, slaughter, and handling and containment techniques), Commercial use (Commercial use of the animal, pet or international trades, or its parts, as meat, fat and skin), Conservation status (the assessment of risk extinction of the species). Ethnobiology (2): Ethnopharmacology (studies of animal parts, products and by-products for medicinal purposes used by traditional communities), and Ethnography (folk tales, myths, and beliefs). 

Some studies reported data associated with multiple species, diverse research fields and/or different countries/locations. Thus, we name each case within a study for a given species. A specific research topic was a unique case, and it was given as a unit in our database. As each paper in our database can contain multiple lines of information, the number of papers (N= 218) do not match with the total number of cases (N= 336). The lines constituted our basic unit of our database (SUPP MAT XX). Some papers brought international studies, covering several countries and locations, and with animals traded and/or bred in captivity such as zoos, natural parks and serpentariums. Papers addressing the species Eunectes barbouri or the subspecies E. murinus murinus and E. murinus gigas were regarded as E. murinus following the current zoological nomenclature (Strimple 1997; Dirksen & Böhme, 1998a).