Abstract
The carabid subfamily Paussinae contains many species known to be obligately associated with ants during at least one stage of their life history. Myrmecophilous larvae have been documented for members of the tribe Paussini as well as several genera in the tribes Ozaenini, including Physea and Eustra. Here we describe the first instar larva of Ozaena lemoulti, and find it to be the most highly modified ozaenine larva that we have examined to date. Many structures of the larva suggest that it is a myrmecophile. Unlike all other described ozaenine larvae, which live in burrows that they construct and seal with their terminal disk, the completely unique larval morphology suggests Ozaena has adapted to living without the protection of a burrow and therefore must have a completely different feeding strategy than the typical ambush strategy of burrow dwelling larvae. We hypothesize that Ozaena larvae live in association with ants and use their long legs for running within the nest, and modifications of the mouthparts suggest the larva feeds on soft lightly sclerotized prey, such as ant brood. Our findings support an earlier hypothesis that Ozaena is mymecophilous during the adult stage. Comparisons of the functional anatomy of the eggs, larvae and adult between Ozaena lemoulti and the closely related, non-myrmecophilous general arthropod predator, Goniotropis kuntzeni, provide complementary, yet independent, evidence suggestive of this shift in lifestyle. We also examine and molecularly identify gut contents, providing direct evidence that adult Ozaena exclusively eat Camponotus ants. We conclude that Ozaena represents an independent shift to adopting a life of myrmecophily among beetles classified within the carabid subfamily Paussinae and document the morphological changes at each life history stage associated with the shift to a nest parasite lifestyle.
Highlights
Many non-ant species have evolved adaptations to avoid ant attacks in order to exploit the rich, well-protected resources of ant nests
Functional anatomy reveals an obligate life with ants transitioned from being free-living to being either partially or completely dependent on ant colonies for their survival [1]
Comparative anatomy of three life history stages reveals that Ozaena species have adopted a new, obligate nest parasite strategy for living with and exploiting ants as their sole source of food
Summary
Many non-ant species have evolved adaptations to avoid ant attacks in order to exploit the rich, well-protected resources of ant nests. Female Paussus lay their eggs inside their host ant’s nest and the beetle larvae develop alongside the ant brood [14, 15] These larvae are highly modified, rendering them nearly immobile. The trochanter, femur, tibia and tarsus of their legs are fused [14, 21], and they become physogastric after the first instar [15, 21] These nearly immobile larvae feed by sucking the juices from their neighboring ant brood, and they solicit trophallaxis from worker ants. Paussus species are among the most integrated myrmecophiles documented to date They are completely dependent upon their ant hosts during their egg, larval and adult life history stages and the safety of the nest for protection during development
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