Neuropeptides in the desert ant : Mass spectrometric analysis, localization, and age‐related changesCataglyphis fortis: Mass spectrometric analysis, localization, and age‐related changes

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Division of labor is one of the key processes underlying the enormous ecological success of eusocial insects. Organization of behavioral diversity (polyethism) promoting division of labor among the worker caste may be phenotype related, age related, or both. Although crucial for the success of many ant species, the underlying intrinsic mechanisms of age‐related polyethism are only poorly understood (for review see Hölldobler and Wilson, 1990; Mersch, 2016). Cataglyphis ants have very distinct interior phases inside the dark nest for ∼4 weeks: After the callow phase (∼24 hours after eclosion), ants start their in‐nest work as interior I animals, which serve primarily in food storage (repletes) and minimize energy consumption by low activity levels. The interior I to interior II transition occurs after ∼14 days and is accompanied by a higher locomotor activity and increased walking distance as the ants now care for the brood and queen and are involed in nest construction. After ∼28 days, the ants transition from the interior to the forager stage. This goes along with not only greater walking distances and higher activity levels but also an increase in positive phototaxis as the ants leave the dark nest and enter the open field to start foraging (Wehner et al., 1972; Schmid‐Hempel and Schmid‐Hempel, 1984; Wehner and Rössler, 2013). Previous work has focused mainly on the interior–forager transition and has shown that it is associated with changes at the behavioral and neuronal levels (see, e.g., Wehner et al., 1972; Kühn‐Bühlmann and Wehner, 2006; Stieb et al., 2010; Schmitt et al., 2016).
It has been shown that the transition between interior workers and foragers in insect societies is codetermined by external factors, such as variable numbers of brood, food, and foragers (Kolmes, 1985; Gordon, 1989; for review see Robinson, 1992; Mersch, 2016). Juvenile hormone (JH) levels, in concert with vitellogenin (Vg) and ecdysteroids, were shown to change with the interior–forager transition in honeybees (Jassim et al., 2000, Elekonich et al., 2001) and in ants (Dolezal et al., 2012). JH and its analogue methoprene were shown to influence the onset of the interior–forager transition and several aspects associated with it, such as the expression of genes related to the transition or biogenic amine levels (for review see Pandey and Bloch, 2015). However, it appears unlikely that JH alone orchestrates the species‐specific sequence of distinct changes in behavioral patterns at various stages of age‐related polyethism and the neuronal changes associated with the transitions. For example, it was shown that disturbance of the JH/Vg system did not affect neuroplasticity in the mushroom bodies (Scholl et al., 2014). Recent studies in the honeybee therefore have started to focus on neuropeptides, in particular their potential roles in orchestrating behavioral plasticity in social insects (Brockmann et al., 2009; Pratavieira et al., 2014). Candidates suggested by these studies are neuropeptides of the allatostatin (Ast), short neuropeptide F (sNPF), and tachykinin (TK) families. In Hymenoptera genomes three functionally distinct Ast families, AstA, C, and CC, have been identified (Hummon et al., 2006; Hauser et al., 2010; Nygaard et al., 2011), but only AstA could be biochemically identified bona fide in bees and ants (Hummon et al., 2006; Boerjan et al., 2010; Schmitt et al., 2015). In ants and bees, all peptide families listed above were shown to be present in the brain, the main center for the integration and processing of sensory information and decision making (for reviews see Ritzmann and Büschges, 2007; Niven et al., 2008), suggesting their neuromodulatory roles in behavior (Zitnan et al., 1993; Boerjan et al., 2010; Schmitt et al., 2015).
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