First survey of the ants (Hymenoptera, Formicidae) of Piauí: filling a major knowledge gap about ant diversity in Brazil

Piauí, a Brazilian Northeast state, has been considered one of the most important regions for the presence of new taxa in ants globally, especially considering the ecosystems’ diversity formed by the transition of the three biomes in the state, the Cerrado, Caatinga and the Atlantic Forest. Despite the recent increase in studies of ant diversity in the Neotropical region, Piauí still represents a major knowledge gap regarding its ant fauna. Therefore, this study aimed to increase the knowledge about the ant fauna of the state by generating a list of species with data obtained from the literature, online repositories and collection expeditions to the Serra da Capivara and Serra das Confusões National Parks. A total of 152 species in 52 genera and nine subfamilies were registered from 24 localities in Piauí. Fifty-eight out the 152 species recorded represent new records for the state, eight are new records for the Brazilian Northeast Region, and one consists of a new record for the country. Eleven species are here recognized as new for science. Considering the field expeditions carried out here, this work represents the first standardized study for the ant fauna of Piauí. The species list presented considerably exceeds the current number of species registered for the state so far. From the present 48 records, the number of species for Piauí raises to more than 150 with a tendency to increase with the accomplishment of future field endeavors and advances in the study of the local ants. Key-Words. Cerrado; Caatinga; Atlantic Forest; Taxonomy; Conservation.


INTRODUCTION
Ants are eusocial insects grouped into a single family (Formicidae), which in turn is classified into 17 subfamilies and 334 genera (Bolton, 2019). Ants occur in great diversity and abundance in most ecosystems (Choe, 2012). In view of this, ants are extremely important ecologically and are key participants in many ecosystem processes (Lamanceau & Blouin, 2018). In addition, these insects are also good indicators of environmental conservation status, since they are very sensitive to environmental stress (Silvestre et al., 2003;Ribas et al., 2012).
In the Brazilian Northeast, anthropic action has led to a deterioration of natural areas and drastic changes in the relief and other characteristics of the soil surface. The state of Piauí, located in this region, has been suffering human disturbances since the 1960s, when tax incentives for agricultural projects were implemented (Lacombe, 1969;Aguiar & Monteiro, 2005). The key location of this state in a transition zone among three Brazilian biomes, the Cerrado, the Caatinga and the Atlantic Forest, makes it a priority for the study of diversity. Despite recent advances, which translate into a 33% reduction in deforestation of the state's Cerrado areas, Piauí remains a leader in the deforestation of that biome (MMA, 2018). Also, since it is one of the last agricultural frontiers in the Cerrado, the southern region of the state is under intense threat (Machado et al., 2004).
The ant fauna of Piauí has remained relatively unstudied compared to other Brazilian states (Camargo, 2011;Prado et al., 2019). One of the few studies involving the state's ant fauna shows that deforestation and loss of diversity by monocultures are very high. In the same study, the anthropic impact on the balance of local ecosystems was highlighted, together with the need for accurate surveys of the local diversity in order to develop more efficient conservation policies, and to promote the documentation of species that are present there before they go locally extinct (Fontes & Almeida Filho, 2002).
Considering the growing need for inventories to fill knowledge gaps about the diversity of places that need to be given conservation prior-ity, regional species lists are an important tool (Castro et al., 2018;Demétrio et al., 2017;Vicente et al., 2018). The primary data generated by the inventory of animal and plant species are very important in decision-making regarding environmental conservation management. Similarly, as predominant and diverse organisms in any terrestrial environment, sampling the local ant fauna is essential. This is especially true when we consider the poorly explored regions of the state of Piauí, which are, on average, suffering more from deforestation than their surrounding areas and therefore deserve special attention regarding conservation and investment in scientific research. In fact, Brazil probably has a widely underestimated number of species and Piauí is where new genera are most likely to be found (Guénard et al., 2012). In this context, the objective of the present study is to increase the knowledge about the ant fauna of the state of Piauí by compiling records from literature, online repositories and field expeditions in two of the state's main National Parks.

MATERIAL AND METHODS
Species records were gathered from a comprehensive independent literature review and consultation of the online repository Antmaps.org. Each species listed here is validated by at least one published reference or data source and the validity of names has been verified in the Antcat.org platform (Bolton, 2019). To confirm the occurrences (Table 1) and to prepare the map (Fig. 1), the geographical coordinates, when not available in the respective reference, were georeferenced based on the Google Earth platform. Figure 1. Areas with ant records in the state of Piauí, Brazil, based on literature review (black circles) and collecting expeditions of the present study to the Serra das Confusões (red circle) and Serra da Capivara (blue circle) National Parks. In addition to the bibliographic survey, two collecting expeditions were made to the Serra da Capivara and Serra das Confusões National Parks. In both parks, ants were collected with three distinct techniques: manual capture, pitfall traps in the soil and vegetation, and Winkler leaf-litter extractors.
Parque Nacional da Serra das Confusões is centered between the coordinates 09°13′22″S and 43°29′23″W and has an average elevation of approximately 700 m. It is located in a transitional area between Caatinga and Cerrado with a predominance of arboreal and shrubby vegetation cover with the presence of semi-deciduous forests in some areas, within the geographic domain of the Atlantic Forest (Gonçalves, 2003).
Serra da Capivara National Park, on the other hand, is centered between the coordinates 08°41′42″S and 42°35′10″W and has an average elevation of approximately 500 m. It has a relief with plateaus and valleys with differences of up to 250 meters. In the high plateau areas, the phytophysiognomy of dense arboreal Caatinga predominates, while in the valleys where humidity is highest, the phytophysiognomy is arboreal Caatinga, with open understory (Barros, et al., 2012).
The specimens were processed at the Laboratory of Ant Systematics and Biology of the Federal University of Paraná, Curitiba, Brazil. Identification to genus was accomplished with the help of the Guide for Ant Genera of Brazil (Baccaro et al., 2015) and for species we used the bibliographies recommended for each genus in this same Guide Kempf, 1951Kempf, , 1973Kugler, 1994;LaPolla & Fisher, 2005;Longino, 2003;Ortiz-Sepulveda et al., 2019;Schmidt & Shattuck, 2014;Watkins, 1976). Vouchers were deposited in the Padre Jesus Santiago Moure Entomological Collection of the Universidade Federal do Paraná (DZUP), Curitiba, Brazil.

RESULTS AND DISCUSSION
A total of 152 ant species/morphospecies were recorded in the state of Piauí in 52 genera and nine subfamilies distributed in 24 locations (Table 1). A total of 96 species were namely identified (63%) and 56 remained as morphospecies due to the lack of taxonomic resolution for their genera. The most diverse subfamilies were Myrmicinae, with 94 species, and Formicinae, with 21 species, represented by 25 and five genera, respectively. Among the genera, Pheidole had the highest number of species, 25, followed by Solenopsis, with 16  The diversity pattern found among the recorded taxa was somewhat expected as the two subfamilies and the most diverse genera in this paper are extremely rich and widely distributed in the Neotropical region (Ward et al., 2015). Myrmicinae can be considered the most successful group among all subfamilies of Formicidae, comprising almost 50% of the diversity of Formicidae (Ward et al., 2015;Bolton, 2019). Their dominance can be explained by the broad feeding and reproductive strategies (Agosti et al., 2000;Hamidi et al., 2017). Thus, the results obtained for this subfamily are within the expectations of the literature, since approximately 62% of the species registered in the state of Piauí belong to this group.
From the eight new ant species firstly recorded for the Northeast Region of Brazil, seven belong to megadiverse genera, including Pheidole, Camponotus, and Strumigenys. This highlights the importance of specific-level identification for an ant inventories, since these new records are both an artifact of the lack of expertise to identify these genera and the lack of data collection in Piauí state. In fact, different ant collections in Brazil probably hold unidentified specimens of Pheidole, Camponotus and similar genera that could be new records in species lists and surveys.
Two exotic species, Monomorium pharaonis (Linnaeus, 1758) and Paratrechina longicornis (Latreille, 1802), were recorded. These species had already been recorded for neighboring states (AntMaps, 2019; Prado et al., 2019). Monomorium pharaonis is considered a species of medical importance in many parts of the world, including Brazil, specifically in hospitals, where it is a potential carrier of pathogens (Wetterer, 2010). Paratrechina longicornis is considered an urban and agricultural pest in most of the tropics and subtropics of the world for infesting buildings and facilitating the multiplication of populations of Hemiptera that feed on plant phloem (Wetterer, 2008).
We recognize at least 11 new ant species (Table 2), of which one belongs to the genus Mycetophylax, one to Mycocepurus and nine to Pheidole. This demonstrates the great potential of this region to reveal taxonomic novelties, as predicted by Guénard et al. (2012), even though these authors referred to potential new genera.
Regarding the relative contribution of each data source (literature and expeditions) to compose the final list of species in Piauí, literature contributed 25% of the registered species (38 species), while the collecting expeditions were responsible for 75% of the species (114 species), 71 collected in Serra da Capivara and 101 in Serra das Confusões. It is noteworthy that all 58 new species records for the state come from these collecting expeditions. From the species collected specifically in the expeditions, 79 were sampled with pitfall traps in the soil, 21 were manually collected, and 27 were exclusively found in leaf-litter samples submitted to the Winkler extractor. This highlights the importance of collecting expeditions  to increase our knowledge of the ant fauna in subsampled areas of the Neotropics, especially when involving multiple collecting techniques.
Regarding the representativity of ants in the different biomes of Piauí, it is not possible to characterize species typical of Cerrado or Caatinga, since these species can be found in both ecosystems and have been classified as "savanna specialists" Vasconcelos et al., 2017). As for the Atlantic Forest ants, they are represented in our dataset by the specimens obtained from leaf-litter samples exclusive of our collection efforts in Parque Nacional da Serra das Confusões ( Table 2).
The list of species presented here considerably increases the number of species previously recorded in the state. From 48 records (AntMaps, 2019), the number of ant species for Piauí went to 152. Nevertheless, these numbers are constantly changing as taxonomic works are published frequently and this process leads to the documentation of new species (Ward, 2007), as well as the establishment of local research groups and field trips. Thus, the list of species presented here is likely to grow with future collecting and advances in ant studies.