The structure and importance of nest mounds in a tropical ant Diacamma indicum

Abstract

1. Nest mounds are an integral part of many subterranean insect species, and they aid in thermoregulation, gaseous exchange, and flood prevention. Ants living in subterranean nests are prone to nest flooding particularly during monsoons and this will impact the colonies' fitness. 2. Diacamma indicum is a tropical Ponerine ant species that lives in simple, single‐chambered nests with a single entrance. In this study, we characterised the mound architecture and performed field experiments to check functional significance of mounds. 3. On examining mound architecture (n = 19 nests), we found that mounds not only elevated the nest entrance by 3.39 cm on average, but they also made the entrance at the top of the mound significantly smaller than the nest entrance at the base of the mound. Both these features are likely to reduce rainwater from falling directly into the nest's entrance tunnel. 4. Upon performing partial (n = 18 nests) and complete destruction (n = 20 nests) in two different seasons, colonies were observed to actively rebuilt mounds to pre‐destruction levels within 3 days in all cases. 5. Furthermore, examining the amount of water that entered the nest upon flooding in the presence and absence of mounds (n = 18 colonies) revealed that mounds prevented a minimum of 29.2% of water from seeping into the nest from the surrounding area, as mounds could act as a levee. This study highlights the active architectural adaptations to flooding by an organism that dwells in subterranean nests in a tropical habitat.

Cryptic functional diversity in ant tandem runs

“…1B); this has rarely been observed in Temnothorax , possibly due to its potential interference with route-learning. Furthermore, although emigrating Diacamma colonies prefer better nest sites (Sahu et al, 2019), they can excavate their own underground nests from pre-existing openings on the ground (Bhattacharyya et al, 2021; Kaur et al, 2012), and thus are less limited by nest site availability than Temnothorax .…”

Construction of nest mound and preference for it during relocation in an Indian ant Diacamma indicum

“…The Building index (BI) was used to measure the modifications of the nest at the nest entrance like placement of decorative materials, building of mounds and scores that ranged from 0 to 5 were assigned to each colony. A bare open nest entrance without any modification is scored 0 and a nest entrance which has a consolidated mound and decorative materials receives a score of 5 (for details see Kolay & Annagiri, 2015;Bhattacharyya & Annagiri, 2019;Bhattacharyya et al, 2021). Scores were assigned to nests in a double-blind manner in order to remove a potential source of experimenter's bias.…”

“…On day 6 all the treatment colonies made nest mounds and some of the control colonies had mounds as well (Figure 2b). Mounds built inside the laboratory were qualitatively similar in its architecture to the mounds found in nature (Bhattacharyya et al, 2021). These mounds were made of heaps of soil at nest entrance and it incorporated chips of plaster of Paris (collected by the ants by digging the wet nest floor) and pieces of paper.…”

“…Cataulacus muticus, another tropical ant living in Malaysian rainforests, frequently experience heavy rainfall and are known to use two methods to reduce the risk of flooding inside their nests: (i) workers block the nest entrance with their workers' heads to prevent water seepage through the entrance and, (ii) they drink up the excess of water that enters the nest and thereafter excrete it out; a behaviour known as "communal peeing" (Maschwitz & Moog, 2000). The tropical Indian ant Diacamma indicum, use two methods to combat nest flooding; they occupy nests at higher elevations, and they also modify the nest entrance by building clay mounds which on one hand act as a levee and on the other elevate the nest entrance from the ground level (Kolay & Annagiri, 2015;Bhattacharyya et al, 2021).…”

“…They typically occupy pre-existing cavities in their natural habitat and perform some modification to the interiors if needed (Viginier et al, 2004;Kaur & Sumana, 2014;Kolay & Annagiri, 2015;Bhattacharyya & Annagiri, 2019). In their natural habitat, during monsoons they are known to construct mounds at the entrance of their nest and rebuild these mounds upon damage or destruction (Bhattacharyya et al, 2021). These ants often relocate to new nest locations and their choice of nests is influenced by factors like presence of conspecific nest odour, presence of nestmates at the new nest location (Kaur & Annagiri, 2015).…”