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HITCHHIKING BEHAVIOR OF A WORKER SUBCASTE IN LEAF-CUTTER ANTS (ATTA CEPHALOTES)

Abstract

The minim worker subcaste of leaf-cutter ants (Atta spp.) exhibits hitchhiking behavior in foraging columns. Minims frequently ride (hitchhike) on cut leaf fragments being transported to the subterranean nest by forager ants. Minims remove fungal contaminants from fragments that might otherwise destroy the mutualistic Leucoagaricus fungi in the nest that nourish the ants. They also guard against parasitoid phorid flies that attempt to lay eggs on the head of laden foragers. In addition to fungal and phorid defense, minims also obtain nourishment from the sap of cut leaves (sap obtention). We observed Atta cephalotes minims in a tropical cloud forest near San Luis, Monteverde, Costa Rica in June 2019 to determine whether their hitchhiking behavior is (a) more consistent with defense or sap obtention and (b) whether this behavior differed in day versus night foraging columns. Hitchhikers in eight foraging columns were monitored during the day (1300-1600 h) and night (1900-2130 h). Hitchhikers were chosen at random in each foraging column and each ant was filmed (iPhone camera) for 30 s. We filmed 209 ants, 94 in day columns and 115 in night columns. During video replay, the ant’s head posture and its position on the leaf fragment was recorded as consistent with either defense or sap obtention. A contingency Chi-square test revealed that posture, position on the leaf fragment, and foraging time (day versus night) were mutually dependent (Χ2 = 9. 49, 0.005 > P > 0.001). Minims in nighttime and daytime foraging columns were most frequently observed in postures and positions consistent with phorid defense. Head posture and position associated with sap obtention were infrequent. The frequency of nighttime hitchhikers exhibiting phorid defense behavior was greater than that of daytime hitchhikers. Because phorid parasitoids are active only at day, defensive postures at night that are consistent with phorid defense is puzzling and warrants further investigation.

Acknowledgements

UNG Dept. of Biology, CIEE-San Luis, Danyelle Aganovic

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