Abstract
Paussus favieri Fairmaire is one of only two species of the myrmecophilous carabid tribe Paussini known from Europe. Larvae are known from only 10 of the 580 paussine species. As in many beetles with considerably modified later instar larvae, the first instars represent a valuable source of informative characters for taxonomy and phylogenetic analyses (primary chaetotaxy, egg-bursters, etc.). Therefore, the discovery of the first instar larva of P. favieri is particularly important, as it represents only the second species for which this larval stage is known. In this paper we describe the behavior and morphology of the larval first instar of P. favieri (subtribe Paussina of Paussini) and compare it with that of Arthropterus sp. (subtribe Cerapterina), which is the only other 1st instar described in the Paussini. Most surprisingly, we found that the 1st instar of P. favieri lacks a prostheca, which was previously thought to be a synapomorphy of Paussina + Platyrhopalina. Rather, P. favieri has a unique mandibular structure that seems to be functionally analogous to the protheca. It is a long, broadly lanceolate, distinctly flattened structure apparently homologous to the medial mandibular seta (MN2*), which arises from an area behind the cutting edge of mandible. We predict that the function of the protheca and this similar structure in P. favieri are involved in a specialized feeding strategy that may include soliciting trophallaxis from their host ants. We also report some observations of the first instar hatching from the egg, feeding on liquid and a behaviour we interpret as a "calling behavior," all of which were videotaped and posted on the Tree of Life Web Project.
Highlights
IntroductionMyrmecophiles (obligate symbionts of ants) are challenging to study because they are rare, they live in concealed environments (ant nests), and they have complex but little understood interactions with their hosts
Myrmecophiles are challenging to study because they are rare, they live in concealed environments, and they have complex but little understood interactions with their hosts
We predict that the function of the protheca and this similar structure in P. favieri are involved in a specialized feeding strategy that may include soliciting trophallaxis from their host ants
Summary
Myrmecophiles (obligate symbionts of ants) are challenging to study because they are rare, they live in concealed environments (ant nests), and they have complex but little understood interactions with their hosts. While it is difficult to study their behavior and life cycle in nature, there are challenges rearing them in laboratory conditions Because these difficulties hamper direct observations, the nature of most interactions between myrmecophiles and ants, and the function of many structural adaptations, remain a mystery or a matter of speculation (e.g., Di Giulio & Moore, 2004). Myrmecophiles possess specialized adaptations in order to be accepted by ants and to survive and develop within their nests. Such adaptations include: chemical and morphological mimicry; specialized behaviors to feed on and/or be fed by ants; and structural and chemical modifications to avoid ant attacks. Adults can freely enter and leave the nests, but the larvae (and pupae) must remain in the nest full-time and they are completely dependent upon the ants for survival
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