Occurrence and natural history of Myrmelachista Roger ( Formicidae : Formicinae ) in the Atlantic Forest of southeastern Brazil

Information on the biology of the species in Myrmelachista remains notably scarce. The objective of this study was to report the occurrence, analyze the infl uence of canopy cover on the number of nests in twigs in the litter describe behavioral characteristics of this genus. Hand sampling was performed on trees and twigs deposited in the litter. A total of 84 nests and seven species were found. Myrmelachista ruszkii and M. catharinae were the most frequent and abundant species. In trees, most of the nests were located at the ti ps of dry twigs, and these nests were probably the source of the nests found in the litter of fragments of Atlantic Forest of southeastern Brazil. Canopy cover is associated with the number of nests that were in twigs.


INTRODUCTION
T h e g e n u s M y r m e l a c h i s t a i s t y p i c a l l y neotropical wit h 69 species described from southern Mexico to northern Argentina (Kempf 1972, Fernández & Sendoya 2004, Bolton et al. 2006, Longino 2006).The species of this genus forage on trees, nesting inside live stems (Lo ngino 2006) and may develop mutualistic interactions with host plants, specialized domatia or feeding on extrafloral nectaries (Frederickson 2005, McNett et al. 2010) and/ or coccids (Stout 1979, Ketterl et al. 2003).Data regarding the ecology and behavior of species in the genus have been reported by Renner & Ricklefs (1998), Frederickson (2005Frederickson ( , 2006)), Frederickson & Gordon (2009), Edwards et al. (2009) and McNett et a l. (2010).Information regarding the biology of cer tain species, specifi cally from Costa Rica, is summarized in the review by Longino (2006).
Despite the information mentioned above, the biology of the genus Myrmelachista is still considered to be poorly known in comparative terms (Longino 2006).The objective of this study was to (1) repor t the occurrence of Myrmelachista species in Atlantic Forest remnants of southeastern Brazil, (2) analyze the association between canopy cover and the number of nests in twigs in the litter and (3) d escribe behavioral characteristics obser ved during the fi eldwork.

Study sites and sampling of the species in vegetation
Colonies were recorded and collected from the vegetation and twigs found in the litter of Atlantic Forest remnants located in southeastern São Paulo state, Brazil (Fig. 1).

Sampling of the species in vegetation
The sampling was performed on a weekly basis from September 2008 to September 2009, covering all seasons of the region (Minuzzi et al. 2007), along the sunny trails.The colonies were collected from three areas of the Brazilian Atlantic forest.The sampling effort was kept constant, in terms of the number of fi eld expeditions, length of stay (≥ 4 h) and number of collectors (3).Worker ants that were exiting holes in tree trunks, or foraging until fi ve centimeters from the hole, and tips of dry twigs on alive trees were collected by hand and were transferred to vials with 70 % ethanol.The presence of winged reproductive was recorded.

Sampling of the nests in twigs and canopy cover
The colonies were collected from six areas of the Brazilian Atlantic forest.The sampling was performed on a weekly basis from September to December 2010 in areas without trails and not sunny.In these months, rainfall is more intense (Minuzzi et al. 2007), and results in higher deposit twigs in the leaf litter.In each area, six 16 m 2 sampling points, which were separated from one another by 50 m, were delineated.All of the twigs of 10-30 cm in length were opened; those with colonies that were found on the litter surface were individually placed in plas tic bags for subsequent identifi cation.Twigs with Myrmelachista nests, workers, winged and immature individuals were counted and transferred to vials with 70 % ethanol.
The canopy cover was recorded at the center and corners of each 16 m 2 plot using a Nikon D80 digital camera with a fi sheye lens.The images were analyzed using the Gap Light Analyzer (GLA) software, version 2.0 (Frazer et al. 1999).

Species identifi cation
The identification of the ant species was performed through comparison with specimens deposited in the reference collection of the Museum of Zoology, University of São Paulo (Museu de Zoologia da Universidade de São Paulo, MZUSP).Type specimens were deposited in the collection of the Laboratory of Myrmecology, University of Mogi das Cruzes (Universidade de Mogi das Cruzes, UMC) and in the MZUSP.
The identification of the plants where the Myrmelachista workers were found was performed through comparison with the collection of the Upper Tietê flora in the Herbarium Mogiense (Herbário Mogiense, HUMC) at the University of Mogi das Cruzes.For that purpose, fertile or sterile branches were collected.Type specimens were deposited in the HUMC.

Data analysis
The abundances of adults and immature individuals in the twigs were compared using Mann-Whitney test.The association between canopy cover and the number of nests was determined using scatter plots and Spearman correlation.The level of signifi cance was α = 0.05.

RESULTS
Seven Myrmelachista species were recorded in a total of 41 nests in 20 species of live trees   2).Nests were also found in small dead trees (diameter at breast height < 15 cm).These nests belonged to the species M. ruszkii (n = 3), M. catharinae (n = 3), M. gallicola (n = 2) and M. nodigera (n = 1).Two M. arthuri nests were found in dead trees fallen in the trail.One nest was located in a 30 cm diameter T. mutabilis (Melastoma taceae) trunk, and the length of the trunk region that was occupied by the colony was approximately 50 cm.This trunk was maintained in the laboratory (28 ± 2 °C; 70 ± 10 %) to determine the time of emergence of winged individuals (Table 2; Fig. 3).The other nest remained in the forest, and the tree species in which it was located could not be identifi ed.Moreover, the presence of a single M. nodigera nest in a partially dry Psychotria sp.1 (Rubiaceae) trunk fallen in the litter was also recorded.Approximately 300 workers, several immature individuals and a single queen were collected in this nest.
The presence of winged individuals in live tree was recorded for some Myrmelachista species, and the reproductive period mainly occurred fr om August to December (Table 3).The number of winged individuals could only be counted for Myrmelachista sp.7; 109 unfertilized queens and 11 males were found in one nest, while 113 unfertilized queens and only one male were found in the other nest.
A total of 33 nests, 19 of M. ruszkii and 14 of M. catharinae, were collected in twigs in    Angiosperm families and species observed to associate with Myrmelachista species according to the literature.
Familias y especies de angiosperma observadas y asociadas con especies de Myrmelachista de acuerdo con la literatura.Asociación entre cobertura del dosel y el número de nidos en ramas pequeñas en la Floresta Atlántica del sudeste de Brasil the litter (Table 4), all of which were with a single queen.Winged ants were recorded only in four colonies, three of M. ruszkii and one of M. catharinae.The populations of workers and immature individuals in the M. ruszkii and M. catharinae colonies were not signifi cantly different (Table 3).The canopy openness was associated with the number of nests in the leaf litter (r S = -0.4151;P = 0.02) (Fig. 4)

DISCUSSION
The seven Myrmelachista species recorded in the studied Atlantic Forest remnants c o m p l e m e n t t h e e x i s t i n g d a t a o n a n t biodiversity in the region (Suguituru et al. 2011(Suguituru et al. , 2013) ) and the tree species in which nests of this ant genus can be found (Table 4).The species richness that was found is rel evant for biodiversity studies because workers are rarely obser ved foraging on the surfaces of plants (Longino 2006); as a consequence, species records are rare or even absent in studies on arboreal ants (Silvestre et al. 2003, Morini et al. 2006, Delabie et al. 2007).
Most of the nests found in the vegetation were located in the tips of dry twigs of live trees or in dead trunks of trees; few nests were found in live stems.Nevertheless, most Myrmelachista species nest in cavities or live stems of trees (Stout 1979, Brown 2000, Longino 2006, Edwards et al. 2009).
Myrmelachista nests are also found in dry twigs fallen in the litter but are more abundant in areas with open canopies.For other ant sp ecies recorded in dry twigs in the Atlantic Forest, the abundance of nests increases with canopy cover (Fernandes et al. 2012), as there is a greater supply of resources (Philpott & Foster 2005).Most nests in dr y twigs recorded by Nakano et al. (2012) in sunny trials belonged to M. catharinae and M. ruzkii, which corroborates the present work.In addition, fi ve species that occur at the tips of dry twigs of live in the case of Myrmelachista (Pfeif fer & Linsenmair 1998).Myrmelachista also uses other food sources external to the host plant (McNett et al. 2010).M. ramulorum Wheeler workers, for example, were observed carrying plant and animal par ts (eggs, feces and larvae), and even fungi, into their nest (Torres 1984).The workers of M. arthuri kept in the laboratory collected insect pieces (cockroaches and termites) and carried them into the nest (Nakano MA personal obs.).
When The natural histor y of most ant species is still poorly understood, preventing broad generalizations (Del-Claro et al. 2009).This study par tly fills the gap in the body of knowledge regarding the biology of the genus Myrmelachista by repor ting obser vations concer ning a number of its species, such as the ability of colonies to emergence winged reproductives especially during rainy season, that is an important stimulus for the synchronized release of winged ants (Torres et al. 2001;Santos & Del Claro 2009) 1, which housed the colony with the queen and winged individuals at the time at which the twigs fell to the ground.This fact is supported (1) by the observation made in this study for M. gallicola and also by Ketterl et al. (2003), who found the presence of three Myrmelachista species in Araucaria angustifolia (Ber tol.)Kuntze, both in trees and nearby fallen twigs, and (2) because the most frequently observed Myrmelachista species in tips of dry twigs of live trees are the same as those found nesting in twigs on the litter surface.Conversely, the fact that only M. catharinae and M. ruszkii nests were found in dead twigs fallen in the litter is interesting because other species (Myrmelachista sp.4; Myrmelachista sp.7; M. nodigera and M. gallicola) were recorded in the tips of dry twigs.Morever, Nakano et al. (2012) reported Myrmelachista sp. 4, M. catharinae, M. ruszkii, M. nodigera, M. gallicola, and M. reticulata in fallen twigs in the leaf litter of the sunny Atlantic Forest.
Specifi cally for M. gallicola, the 14 nests found in a single plant suggest a possible case of polydomy because all of the nests had workers, immature individuals and one fertilized queen (Debout et al. 2007, Lanan et al. 2011).However, no connection was found among them, cor roborating the results of Carvalho & Vasconcelos (2002), Santos & Del Claro (2009) and Lanan et al. (2011).Polydomy is relatively common among ants, occurring in over 150 species (Debout et al. 2007).
The occur rence of polydomy may be an alter native for Myrmelachista colonies possessing growth that may be limited by the space available for nesting, but polydomy may also be related to polygyny (Walin et al. 2001), increased foraging area (Santos & Del Claro 2009, Schmolke 2009, Lanan et al. 2011), of fspring ther moregulation (Pedersen & Boomsma 1999) and type of food source, such as extrafloral nectaries and insect exudates

Fig. 1 :
Fig.1: Sampling sites.Fragments of the Atlantic Rainforest where the study was conducted.Sitios de muestreo.Fragmentos de la Mata Atlántica donde se realizó el estudio.

Fig. 2 :
Fig.2: Total number of tree species associated with each studied Myrmelachista species in the Atlantic Forest of southeastern Brazil.Número total de especies arbóreas asociadas a cada especie estudiada de Myrmelachista en la Floresta Atlántica del sudeste de Brasil.

Fig. 4 :
Fig.4: Association between canopy cover and the number of nests in twigs in the Atlantic Forest of southeastern Brazil.

TABLE 1
Number of nests of Myrmelachista species present in the different species of trees.Número de nidos de especies de Myrmelachista presentes en diferentes especies arbóreas.Reproductive winged forms of Myrmelachista observed over a year in the live trees.*Datafrom one nest kept in the laboratory.Formas aladas reproductivas de Myrmelachista observadas a lo largo de un año en árboles vivos.*Datos de un nido mantenido en el laboratorio.
December(Table2).Myrmelachista ruszkii Forel and M. catharinae Mayr were found on the greatest number of tree species followed by M. nodigera Mayr and M. arthuri Forel (Fig.2).Only M. arthuri nests (n = 6; Table1) were recorded in live twigs of live trees.Nests of the other species were found only in the tips of dry twigs in live trees (nests = 35; Table1).Surprisingly, M. gallicola nests were found in 14 twigs of a single Schinus terebinthifolius Raddi plant with dr y tips.These colonies consisted of a queen, workers and immature individuals.

TABLE 3
Total number of nests, workers and immature individuals of Myrmelachista in dry twigs.The data are reported as medians with the range in parentheses.Número total de nidos, obreras e individuos inmaduros de Myrmelachista en ramas secas.Los datos corresponden a las medianas, los intervalos se muestran entre paréntesis.

TABLE 4 .
Continuation disturbed, due to a more abr upt motion of the researcher, while foraging or at the nest entrance, individuals of M. ruszkii, M. catharinae, M. arthuri and Myrmelachista sp.7 responded aggressively, immediately elevating their gaster.Conversely, individuals of M. nodigera, M. gallicola and Myrmelachista sp. 4 quickly hid in nest holes.The aggressive behavior of gaster elevation has been previously obser ved for M. zeledoni Emer y (Longino 2006) and Myrmelachista sp.(Espírito Santo 2008).Davidson et al. (1989) described a less aggressive behavior for another unidentifi ed species.
. This result complements the work ofNakano et al.  (2012)that reported the emergence of males and females of Myrmelachista during rainy season and the confirmation of M. ruszkii and M. catharinae as common species in Atlantic Forest remnants of southeastern Brazil.Furthermore, this study reports the preference of these species for sites with opener canopies.arefound in dry twigs fallen on the litter(Nakano et al. 2012).Exception is made for M. arthuri that was recorded in this work only in live stems, but not in fallen twigs on the litter(Nakano et al. 2012). trees