Invasive ant (Hymenoptera: Formicidae) Paratrechina longicornis along elevational gradients on Mount Marapi, West Sumatera

The diversity of ants along elevational gradients has become a topic in many scientific types of research, while the information regarding patterns of, and processes that shapes, ant community structure across different elevations is still considerably lacking. Therefore, the study about ants (Hymenoptera: Formicidae) at Mount Marapi, Agam Regency, West Sumatra, was conducted at three elevations (low elevation at 0-1200 m, mid-elevation at 1200-2100m and high elevation at 2100-3000 m) and by applying Quadra Protocol (honey bait trapping, soil sampling, leaf litter sifting and hand collecting). It focused on Paratrechina longicornis, renowned as an invasive species. A total of 144 individuals from this species were collected; 13 individuals from low elevation, 144 individuals from mid-elevation and 127 individuals from the high elevation. Paratrechina longicornis, also named as ‘longhorn crazy ant’, became the only species observed to be present along the whole study transects. Its ability to adapt to many artificial environments could explain its success as an invasive species. P. longicornis distributions at the elevational gradients of Mount Marapi were discussed in this paper.


Introduction
As part of the insect kingdoms, ants are abundant in the terrestrial ecosystem [1], asplayers in various ecological functions such as predator [2], decomposer [3] and herbivore [4].Some species occupy specific microhabitats; hence they can serve as a bioindicator for environmental changes [5].On the other hand, some species negatively affect the ecosystem by being invasive or becoming pests that adversely impacts the agricultural sector, public health and social infrastructures [6,7].
Invasive alien species are animals or plants that have been introduced accidentally or deliberately into a natural environment where they do not normally exist [8].Despite their small size and innocuous look, some ant species, known as "tramp ants" can cause serious damage once introduced to a new habitat.The invasive ants impose such damage that the native species could be pushed to the brink of extinction [9,10,11].Paratrechina longicornis, the 'Longhorn crazy ants' as of its swift, jerky movements [12], can be found in urbanized and garden areas all over the tropics as well as in greenhouses or other manmade structures during cold climates [13,14].This species can also be a significant agricultural pest, promoting the growth of populations of the phloem-feeding hemipterans [12,15].Notably, P. longicornis has been vastly distributed around the globe since centuries ago, and its native range remains unclear [14], although some evidences might refer P. longicornis as native to Southeast Asia and Melanesia [16,17].This ant is not as aggressive as other invasive species, such as the red imported fire ant Solenopsis invicta, it still has the potential to disrupt local ecosystems and lead to the localized extinction of the indigenous ant and other invertebrate species [12].
Despite its worldwide distribution, this invasive species was still understudied within the highaltitude setting.This study, therefore, aims to add a novel perspective regarding the existence of P. longicornis along the elevational gradients of Mount Marapi in West Sumatra.It also provides information on ant species composition at three different elevations in the mountain.

Study Site and Sampling Method
The research was conducted from May 2019 to August 2020 at Mount Marapi (2891 m elevation), in Agam Regency, West Sumatra, Indonesia.The study chose to use the hiking trail from Koto Baru village, among several available hiking paths.The sampling sites were selected at low elevation (up to 1200 m), mid-elevation (between 1200-2100 m) and high elevation (between 2100-3000 m).At low elevations, the habitat was dominated by horticulture areas such as onion, sweet potato (Ipomoea batatas), chilli (Capsicum annuum) and tomato (Solanum lycopersicum); this site was mostly affected by frequent human interferences.At mid-elevation, the habitat was a moist tropical mountainous forest consisting of the standings of Macropanax dispermus, Brassaiopsis polyacantha, Schefflera simulans, Antidesma montanum, Aporosa prainiana, Aporosa sp, Baccaurea sp, Bridelia sp, Actinodaphne sp, Litsea sp, Pinus merkusii, Ficus glandulifera, Ficus ampelas, Ardisia laevigata, Polygala venenosa and Pterygota alata.The habitat in this area had lower human interference.At high elevations, which included the summit, no prominent tall trees or any vegetation standing observed.This area was dominated by limestone covered with lichen, and moss and interspersed with dense grass and wildflowers such as Vaccinium spp., Rhododendron retusum and Anaphalis sp.
Ant sampling was conducted by using Quadra Protocol, in which only three collection techniques were applied simultaneously; hand collecting, soil core sampling, and honey bait trap.The leaf litter sifting that also part of Quadra Protocol was also used but intermittently due to some technical difficulties and time constraints during the field survey.This study deployed a 180 m transect in each elevation, each transect was divided into three sub-transects of 60 m to accommodate the sampling on rough mountainous terrain.Hand collecting was applied for 30 minutes in each transect.In the soil core technique, five soil core masses (dimension 20 x 20 x 15 cm) were drilled from the ground at equal intervals along each sub transect.The soil core masses were sorted with hand-sieve onto the white tray where ants were detected and collected.Honey baited traps used 15 traps for each transect, prepared using honey drops placed on a piece of paper and set on the forest floor at four meters intervals along the transect.Attracted ants were then collected with forceps.All samples were separately put into vials filled with 96 % ethanol.

Ant identification
Ant samples were processed at the Animal Taxonomy Laboratory, Department of Biology, Universitas Andalas, Padang.The identification process was guided with proper references [18,19,20,21].This process was also assisted by comparing studied specimens with curated specimens stored in the lab.Documented images of samples were compared with online databases and shared with some international experts for their advice and confirmation on species identification [22].

Data Analysis
Identified ants were grouped according to their taxonomical orders; individual and species numbers were counted, so then the simple statistic could be used to see the tendency of data.The findings were then descriptively explained.

Results and Discussion
A total of 144 individuals of P. longicornis were recorded from all elevations.This ant is a member of Formicinae, the second-largest and most widely distributed ant subfamily in the world.Formicinae retains 3,700 species and 49 genera that were identified only from Australia [23,24].As many as 13 individuals of this ant were collected at low elevation, four individuals at mid-elevation and 127 individuals at high elevation.These individual records were in line with the fact that human activities provide pathways for the movement of non-native species [25].The habitats, such as horticultural area at the low elevation or area with high hiking traffic such as one at mount summit, were fitted to this description.The invasive P. longicornis is a ubiquitous household and garden pest throughout the tropics and subtropics, while in temperate, they act as a pervasive indoor pest.The ants can become pests when they are able to adapt to the variability of environment types, from dry to moist.Aside from its adaptability, P. longicornis enhance the population of phloem-feeding Hemiptera (including mealybugs, scale insects, and aphids), which in turn highlights its potent destructiveness.These Hemipterans impose damage on plants by sucking essential nutrients from plants while increasing their vulnerability to diseases induced by viral and fungal infections.The honeydew cared for by P. longicornis in Madagascar outcompeted the local stingless bees and discouraged any ecological service provided by the stingless bees [26].The invasive P. longicornis is known to be rare or absent in pristine environments, yet abundant in disturbed and semi-natural habitats.They nest in rotten wood, rock bottom or even under fallen trees.The nest can be easily spotted by following the workers.Paratrechina longicornis was observed to be present along all research transects.Its ability to adapt to many artificial and impacted environments may explain its success as invasive species.The nests of this ant can be accidentally transported, while they can move to another environment if urged.It can also live within the indoor setting, sharing the same place with humans.It has no restrictions on the latitude or altitude where it can thrive.In the case of Mount Marapi, the extension of the agricultural area and increasing traffic of mountain hikers could heighten the possibility for many exotic species, including ants, to be introduced into the area.In fact, the current survey recorded many other invasive ants, including Pheidole sp., Monomorium floricola, Tapinoma melanocephalum, Cardiocondyla sp., Lophomyrmex bedoti, Solenopsis geminata, Nylanderia sp 2 of HH and Odontoponera denticulata.Tapinoma and Mononomorium are the two indicator genera for ongoing disturbances in the habitats [27,28,29].
Despite these invasion records above, only P. longicornis persisted at all surveyed elevations.For example, Nylanderia sp 2 of HH was recorded with 308 individuals, exceeding the record for P. longicornis.Nylanderia is known for its wide distribution across geographic boundaries and elevations and for inhabiting a variety of habitats [28,30].However, this species and other invasive ants were absent in one or more survey sites.The mid-elevation site, which was observed to be the least disturbed area in this study as well as had more vegetation standings, seemed to be less favourable for the infestation of invasive ants.It might hint that the more natural a habitat, the lower the invasive ant species infest it.According to the collecting techniques applied in this study, hand collection sampled 54 individuals of P. longicornis.On the other hand, the gaining from the soil sampling, honey bait traps and leaf lifter sifting were respectively 39, 36 and 15 individuals.The result from soil sampling technique was lower than what has been gained through the hand collection technique in sampling this invasive species.In a previous study in Sabah, Malaysian Borneo, the soil sampling technique showed the most optimal result [19].The hand collection was deemed to be more proactive in searching and collecting ants within the study transects compared to the other three techniques, which seemed to be more passive.Hence, it explains the optimal gaining in this study.Quadra protocol is indeed the effective procedure to study the diversity and species composition of ants, as observed from many previous studies [31,32,33].Each technique in this protocol has specifications for collecting ants with typical habitus, yet every technique complements each other's shortage.Due to the adaptability of invasive ant species to various habitats, by adjusting their behaviour and other biological aspects, thus Quadra Protocol fits to do an inventory survey on this kind of ant.This study, at least, gives a glance at the ecological dynamics in the mountainous ant community as well as the existence of invasive species that were more adaptive to various elevation in Mount Marapi, West Sumatra.It also provides important insights as the baseline in working on natural habitat conservation and restoration, especially in the specific mountainous ecosystem.

Conclusion
A total of 144 individuals of invasive longhorn crazy ant P. longicornis were collected.Thirteen individuals were recorded from low elevation, four individuals from mid-elevation and 127 individuals from the high elevation.This result confirmed that these ants are more in high elevation and the adaptability of Paratrechina longicornis across mountain elevational gradient and artificial or humanimpacted environments.

Figure 2 .
Figure 2. Habitat at the sampling sites in Mount Marapi West Sumatra: (A) Low elevation with horticultural area, (B) Mid-elevation with forested area, (C) High elevation with rocky areaThe invasive P. longicornis is a ubiquitous household and garden pest throughout the tropics and subtropics, while in temperate, they act as a pervasive indoor pest.The ants can become pests when they are able to adapt to the variability of environment types, from dry to moist.Aside from its adaptability,