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INTRODUCTION
Formicidae (Hymenoptera) is one of the most abundant groups of insects in terrestrial eco systems (Mason et al., 2006; Schultheiss et al., 2022). They are distributed in practically all environments, from arid deserts to riverside forests subjected to long periods of flooding (Fernández, 2003) and from sea level to an altitude that ex ceeds 4,000 meters (Beutel et al., 2013).
The Neotropical region is recognized for har boring high species richness of ants, with around 3,400 taxa (Fernández et al., 2021), representing about 23% of the total number of current species registered worldwide. In addition to their biolog ical diversity, ants exhibit a wide variety of be haviors, food habits, and interactions with other organisms, intervening in important processes such as seed dispersal and soil dynamics (Arcila & Lozano-Zambrano, 2003; Kaspari, 2003).
Due to its geographical location, longitudi nal extension, and topography, Argentina has a great variety of ecoregions, from the extensive Patagonian Steppes to the high rain forests of the Yungas (Matteucci, 2007; Arana et al., 2017, 2021). These conditions favor the establishment of rich ant fauna, with a total of 697 species dis tributed among 82 genera and 10 subfamilies recognized in the country, many of which are en demic (Cuezzo & Larrea, 2022). The richness of ant species in Argentina has intermediate values if compared with those of other countries in the region, such as Chile (84 species), Uruguay (104 species), Bolivia (441 species), Paraguay (445 species), Colombia (1,200 species), and Brazil (1,521 species) (Fernández & Sendoya, 2004; Wild, 2007a; Baccaro et al., 2015; Fernández et al., 2019, 2021). However, several areas, such as the Chaco Region, are poorly inventoried.
The Humid Chaco is one of the three ecore gions into which the Chaco region is divided (Arana et al., 2021). This ecoregion comprises central Paraguay, northeast Argentina, and a small area of Brazil (Morrone 2014). The vegeta tion unit of this ecoregion is characterized by a mosaic composed of various plant communities, namely mesophyte forest, semi-open xerophyte forest, riverside forest, Copernicia alba palm sa vanna, tall hygrophyte grassland, and marshy herbaceous formations (Oyarzabal et al., 2018). Argentina is one of the ten countries in the world with the highest loss of forest extensions (FAO, 2016), the Humid Chaco being one of the most de forested ecoregions in the last three decades (Zak et al., 2008; Hoyos et al., 2012). The ecosystems of this ecoregion are threatened by conversion pro cesses caused by anthropic activities (Dinerstein et al., 1995; Volante & Seghezzo, 2018). These processes reduce the recovery capacity of the en vironments and cause irreversible effects on the biodiversity of the flora and fauna, affecting the provision of ecosystem services (Sanderson et al., 2002; Pavlacky et al., 2012; Correa Ayram et al., 2017). There is no accurate data on the diversity of ants in this ecoregion because many species inventories are made using political divisions (i.e., country/province/state) that lack biological meaning (Whittaker et al., 2005; Diniz-Filho et al., 2010). Therefore, the distribution range of most insect species in the tropical and subtropi cal ecoregions of Asia, America, and Africa is un known (Diniz-Filho et al., 2010).
Given the limited knowledge of ant assem blages in many ecosystems of the Humid Chaco ecoregion, it is essential to conduct studies that make it possible to inventory and map the biodiversity in this area and evaluate the crucial role that these insects play in the structure and function of these terrestrial ecosystems (Cuezzo, 1998; Calcaterra et al., 2021). Inventories pro vide valuable information on the biodiversity, structure, and function of the different hierar chical levels of species in different environments, and such information is essential for decision-making in ecosystem management and conser vation programs (Villarreal et al., 2006). This study aimed to inventory the ants inhabiting the Humid Chaco ecoregion and update the species distribution for this area given new records. In addition, pictorial keys are included to aid in the taxonomic identification of subfamilies and gen era of Formicidae occurring in this ecoregion of South America.
MATERIAL AND METHODS
Inventory and data sources
This inventory was created based on a) cen suses carried out in gallery forests in the prov inces of Chaco and Corrientes (Argentina) and b) bibliographic records corresponding to speci mens collected in different environments of the Humid Chaco ecoregion. All localities providing a reference are included and detailed in Figure 1 and Table 1.
Fig. 1 Map of the Humid Chaco ecoregion and localities where Formicidae species are registered (for references see Table 1).
Table 1 Localities in the Humid Chaco ecoregion where species of Formicidae were registered. Abbreviations: a, censuses; b, bibliographic record.
The bibliographic information was obtained and georeferenced using the antmaps.org page (Janicki et al., 2016), which displays the infor mation from the GABI database (Guénard et al., 2017). This database is an important tool and represents a starting point for characterizing and understanding the geographic distribution of a species or group of ants. The georeferenced data in this system were verified by searching for the scientific articles referenced in the database for each point and species and by corroborating the coordinates provided by the antmap website.
Study área
New material was collected from gallery forests located in the following departments of the province of Chaco, Argentina: Primero de Mayo (Antequera, Los Chaguares), Bermejo (El Bagual, San Carlos, Vedia), General San Martín (Pampa del Indio Provincial Park) and Sargento Cabral (Quintana, and Chaco National Park). In addition, new material was collected from gallery forests, grasslands (Larrea et al., 2022), and palm forests located in the following depart ments of the province of Corrientes, Argentina: Mburucuyá (Mburucuyá National Park), San Miguel (San Miguel, San Nicolás), Santo Tome (Galarza), and Ituzaingó (Cambyreta).
Trapping methodology
Ant censuses were taken by following the rec ommendations of the ALL protocol, developed as a proposal for a rapid and standardized survey of ants in a humid and wooded environment (Agosti et al., 2000). Censuses in Chaco were carried out from October to March in 2017 and 2018, whereas in Corrientes they were conducted from October to March in 2013, 2014, and 2017. At each site, two transects (200 m long) were drawn, 100 m apart from each other. In each transect, 20 points separated by 10 m were selected. The following census methods were used: a) collection of 1 m2 of litter, b) foliage pattering, c) manual catch, and d) pitfall.
All the captured specimens were kept in plas tic containers with 70% alcohol, labeled with information on the locality, date, collector, and capture technique, until their subsequent puri fication and taxonomic identification.
Inventory format
To organize the inventory, the classification of subfamilies and genera proposed in AntCat (www.antcat.org) was followed. This website compiles all the changes in the relationships between the different groups of Formicidae (Bolton, 2022). The subfamilies, genera, and species were placed in alphabetical order, with their valid name, author, and year of publication.
For new records in the Humid Chaco ecore gion and Argentina, the inventory was prepared according to this structure: family, subfamily, valid species name with author and year of publi cation, country, province, department, locality in brackets, date of collection, collector, number and caste of specimens, and depository with collection number in brackets of the pinned specimens and/or glass vials (for specimens of the same species from the same locality). For departments in the same province, information is separated by semi colons. General species distribution at the coun try level for the Neotropical region is presented according to Cuezzo (1998), Lattke (2003), De Andrade (2004), Fernández & Sendoya (2004), Wild (2007b), Vittar & Cuezzo (2008), Lattke (2012), and Longino (2013). Detailed informa tion for species distribution in the Humid Chaco ecoregion is also provided as follows: country and province, department, and locality in brackets. Localities in the same province are separated by a comma.
Pictorial keys for subfamily and genera of ants inhabiting the Humid Chaco ecore gion
The pictorial keys presented are based on Bolton (1994), Palacio & Fernández (2003), and Baccaro et al. (2015). We followed the classifica tion proposed by Ward (2005, 2007), Brady et al. (2014), Schmidt & Shattuck (2014), Ward et al. (2014), Camacho et al. (2022), and Hanisch et al. (2022). Illustrations were made on a Wacom Intuos Art tablet and Adobe Photoshop editing software.
RESULTS
Herein we present the inventory of Formicidae species recorded in the Humid Chaco ecoregion. Ten subfamilies distributed among 77 genera and 462 species are listed (supp. Table 1). Eight species have been recorded for the first time in this ecoregion. In addition, and six species have been recorded for the first time in Argentina. We highlight out seven species that could be endemic species of Humid Chaco (Table S1).
New records for the Humid Chaco ecore gion
Family Formicidae (Latreille, 1809)
Subfamily Ectatomminae Emery, 1895
Acanthoponera mucronata (Roger, 1860)
Material examined. Argentina, Chaco, Sargento Cabral (Estancia El Bagual), 20-III-2018, Larrea leg, 15 Workers, (CARTROUNNE 9603); Primero de Mayo (Reserva Los Chaguares), 21-X-2017, Larrea leg, 4 Workers, (CARTROUNNE 9604).
Distribution. Neotropical: Argentina, Brazil, Bolivia, Colombia, Ecuador, Paraguay, Peru and Venezuela.
Distribution in the Humid Chaco ecoregion. Argentina (Chaco: Sargento Cabral, Primero de Mayo).
Comments. Workers were collected in galler ies forests. These ants were found nesting in the trees with nocturnal habits.
Subfamily Myrmicinae Lepeletier de Saint-Fargeau, 1835
Pheidole capillataEmery, 1906
Material examined. Argentina, Chaco, Primero de Mayo (Reserva Los Chaguares), 21-X-2017, Larrea leg, 8 Workers (CARTROUNNE 9684).
Distribution. Neotropical: Argentina, Brazil and Peru.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Primero de Mayo).
Comments. Wilson (2003) mentions that this species forage on cloudy days at dawn or dusk.
Pheidole synarmataWilson, 2003
Material examined. Argentina, Chaco, Bermejo (Estancia San Carlos), 20-III-2018, Larrea leg, 5 Workers, (CARTROUNNE 9654).
Distribution. Neotropical: Argentina, Brazil, Colombia, Costa Rica, El Salvador, French Guiana, Guyana, Honduras, Nicaragua, Panama, Peru and Venezuela.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Bermejo).
Comments. This species was reported as asso ciated with pig carcasses (Andrade-Silva et al. 2015).
Procryptocerus goeldiiForel 1899.
Material examined. Argentina, Chaco, Bermejo (Estancia San Carlos), 15-XI-2013, Larrea leg, 11 Workers, (CARTROUNNE 9656); Sargento Cabral (Chaco National Park 1), 10-II-2018, Larrea leg, 7 Workers, (CARTROUNNE 9684).
Distribution. Neotropical: Argentina, Brazil, French Guiana, Guyana and Paraguay.Revista del Museo Argentino de Ciencias Naturales, n. s. 25(2), 2023 182
Distribution in the Humid Chaco ecoregion. Argentina (Chaco: Bermejo, Capitán Solari).
Procryptocerus hylaeusKempf 1951.
Material examined. Argentina, Chaco, Primero de Mayo (Puerto Antequera), 30-X-2017, Larrea leg, 3 Workers, (CARTROUNNE 9685).
Distribution. Neotropical: Argentina, Brazil, Bolivia, Colombia, Costa Rica, French Guiana, Guyana, Panama, Paraguay, Peru and Venezuela.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Primero de Mayo).
Comments. Longino & Snelling (2002) reported to P. goeldii and P. hylaeus as species with sym patric distribution.
Strumigenys dyseides Bolton, 2000.
Material examined. Argentina, Chaco, Sargento Cabral (Estancia El Bagual), 20-III-2018, Larrea leg, 19 Workers, (CARTROUNNE 9686); Sargento Cabral (Chaco National Park 1), 14-II-2018, Larrea leg, 7 Workers, (CARTROUNNE 9687).
Distribution. Neotropical: Argentina, Brazil, Colombia, French Guiana and Guyana.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Sargento Cabral, Capitán Solario).
Strumigenys lilloana (Brown, 1950)
Material examined. Argentina, Chaco, Sargento Cabral (Estancia El Bagual), 20-III-2018, Larrea leg, 2 Workers, (CARTROUNNE 9661).
Distribution. Neotropical: Argentina, Brazil.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Sargento Cabral).
Subfamily Ponerinae Lepeletier de Saint-Fargeau, 1835
Leptogenys pusilla (Emery, 1890)
Material examined. Argentina, Chaco, Sargento Cabral (Estancia El Bagual), 20-III-2018, Larrea leg, 6 Workers, (CARTROUNNE 9675).
Distribution. Neotropical: Argentina, Brazil, Colombia, Costa Rica, Lesser Antilles, Mexico, Panama.
Distribution in the Humid Chaco ecore gion. Argentina (Chaco: Sargento Cabral).
Pictorial keys for Formicidae ants from the Humid Chaco ecoregion
To assist researchers who wish to perform the taxonomic identification of ants, we prepared rel atively simple pictorial keys for identification to the subfamilies (Fig. 2, see Fig. S1 for the Spanish version) and genera for each subfamily inhabit ing the Humid Chaco ecoregion: Amblyoponinae (Fig. 3), Dolichoderinae (Fig. 4), Dorylinae (Fig. 5), Ectatomminae (Fig. 6), Formicinae (Fig. 7), Myrmicinae (Figs. 8-11), Paraponerinae (Fig. 2), Ponerinae (Figs. 12-13), Proceratiinae (Fig. 2), and Pseudomyrmecinae (Fig. 2).
Fig. 3 Pictorial key to the genera of Amblyoponinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 4 Pictorial key to the genera of Dolichoderinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 6 Pictorial key to the genera of Ectatomminae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 7 Pictorial key to the genera of Formicinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 8 First part of the pictorial key to the genera of Myrmicinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 9 Second part of the pictorial key to the genera of Myrmicinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 10 Third part of the pictorial key to the genera of Myrmicinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 11 Fourth part of the pictorial key to the genera of Myrmicinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
Fig. 12 First part of the pictorial key to the genera of Ponerinae (Hymenoptera: Formicidae) from the Humid Chaco ecoregion.
DISCUSSION
This inventory provides valuable information for understanding the distribution of one of the most conspicuous groups of arthropods in the Humid Chaco. This information, added to previ ous studies on other invertebrate taxa (Laffont et al., 2007; Rubio et al., 2008; Dufek et al., 2020), will allow the evaluation of patterns of endemism of arthropods in the region.
Ten subfamilies of ants were re corded for the Humid Chaco ecoregion: Amblyoponinae, Dolichoderinae, Dorylinae, Ectatomminae, Formicinae, Myrmicinae, Paraponerinae, Ponerinae, Proceratiinae, and Pseudomyrmecinae. This represents 77% (10/13) of the total subfamilies registered in the Neotropical region (Fernández & Sendoya, 2004; Guénard et al., 2017; Fernández et al., 2021).
Of the 462 species included in this inventory, 56 were obtained from censuses whereas 398 were only recorded from bibliographical sources. Eight species are new records for the Humid Chaco ecoregion. These species were exclusively obtained from census events carried out in the provinces of Chaco and Corrientes, Argentina.
The most diverse genera recorded in the Humid Chaco ecoregion were Camponotus Mayr, 1961 (46 species) and PheidoleWestwood, 1839 (38 species). These ants represent the most com mon groups in the Neotropical region and are the most hyperdiverse genera of ants worldwide (Wilson, 2003; Pérez-Sánchez et al., 2018).
The species with the most widespread distribution (five or more localities) were Crematogaster crinosaMayr, 1862, Dorymyrmex thoracicusGallardo 1916, Ectatomma brunneumSmith 1858, Linepithema humile (Mayr, 1868), Nesomyrmex spininodis (Mayr, 1887), Nylanderia fulva (Mayr, 1862), Octostruma balzani (Emery, 1894), Pseudomyrmex gracilis (Fabricius, 1804), Solenopsis invictaBuren, 1972, Strumigenys eggersi Emery, 1890, and Wasmannia auro punctata (Roger, 1863). Many of these species (e.g., Solenopsis invicta, Linepithema humile, Nylanderia fulva and Wasmannia auropunctata) are organisms with great adaptation capacity, considered exotic (introduced) species of eco nomic importance in other regions of the planet (Della, 2003).
Several species of this inventory collected in censuses stand out in a forensic and eco nomic context. The species Camponotus blandus (Smith, 1858), Camponotus punctulatusMayr, 1868, Camponotus rufipes (Fabricius, 1775), Ectatomma brunneum, Pheidole radoszkowskii Mayr, 1884, Pheidole synarmata, Pseudomyrmex gracilis, and Solenopsis saevissi were collected associated with pig carcasses in Brazil (Andrade-Silva et al., 2015; Viana et al., 2022). Regarding its economic importance, the genera Acromyrmex spp. Mayr, 1863 and Atta Fabricius, 1804 include several species which are pest for a variety of crops (Nickele et al., 2012; Montoya-Lerma et al., 2012; Diaz Napal et al., 2015). In addition, species like Linepithema humile, Wasmannia auropunc tata, Nylanderia fulva are recognized as house hold pest (Ness & Bronstein, 2004).The follow ing seven taxa were recorded as endemic species for the Humid Chaco ecoregion: Acanthostichus longinodisMackay, 2004, Camponotus fiebrigiForel, 1906, Crematogaster thalia Forel, 1911, Eciton mexicanum argentinumBorgmeier, 1955, Mycetomoellerius fiebrigi (Santschi, 1916), Strumigenys insolita Bolton, 2000 and Strumigenys siagodens (Bolton, 2000). This con tribution provides new groups of useful insects to characterize the biographical ecoregion of the Humid Chaco, which to date has no reported en demic ant species (Morrone, 2000; Arana et al., 2021). It is important to mention that there are few records available for many of these species. This implies that future studies could extend the distribution area of these organisms beyond the Humid Chaco ecoregion. Therefore, new surveys may help to better understand the distribution of some of these species.
CONCLUSIONS
Species inventory, new records, endemic spe cies, and taxonomic keys presented herein repre sent a significant contribution to the knowledge of Formicidae from the Humid Chaco ecoregion. This will allow for a better understanding of the biological value of this ecoregion of South America which is being greatly transformed by human activity. Furthermore, the inventory approach with a biogeographical perspective is essential because it presents true biologi cal implications on organisms, unlike the tra ditional approaches using political boundaries (i.e., countries, states/provinces, departments).
Supplementary information online. http://revista.macn.gob.ar/ojs/index.php/RevMus/rt/suppFiles/792/0
