The ant genus Cardiocondyla is characterized by wingless, ergatoid males, which in some species replace the typical winged male. Depending on species, ergatoid males engage in lethal fighting for access to sexual females, establish territories within their nests, or are mutually tolerant. Here we investigate, whether the morphology of ergatoid males and in particular the shape of their mandibles reflect phylogeny or male behaviour. In contrast to the worker mandible, which is relatively similar in shape in the ten species examined, mandibles of ergatoid males show a great variation in size and shape not only between the two clades of Cardiocondyla but also among species belonging to Cardiocondyla clade A. This diversity appears to reflect the diverse reproductive tactics of ergatoid males of different species, with extremely long, anteriorly oriented mandibles associated with indirect killing of adult competitors, while particularly short mandibles possibly constitute an adaptation to a tactic in which ergatoid males crush the cuticle of young rivals., Christine V. Schmidt, Jürgen Heinze., and Obsahuje bibliografii
In insects, allometries of exaggerated traits such as horns or mandibles are often considered species specific and constant during a season. However, given that constraints imposed by the advancing season affect the developmental processes of organisms, these allometries may not be fixed, and the switch point between morphs may vary between populations and within populations during a season. The hypothesis of such a seasonal variation in exaggerated traits was tested using the dimorphic males of the beetle Lucanus cervus. The remains of specimens killed by predators were collected along forest tracks from mid May to late August 2008 in a protected lowland forest in northern Italy. The largest beetles were collected in mid May and average size thereafter decreased. Males collected early in the season mostly had large mandibles (i.e. they belonged to the major morph). In contrast, late in the season the probability of finding males with large mandibles was very low. The threshold body size determining morph expression also shifted during the season. Early in the season, the threshold pronotum width for a 50% chance of developing into the major morph was 1.74 cm, whereas later in the season it was 1.90 cm. This shift in the threshold body size was interpreted as the effect of phenotypic plasticity in a population exposed to constraints imposed by the advancing season. and Sönke Hardersen, Anna L.M. Macagno, Roberto Sacchi, Ilaria Toni.
A comparative study of mitotic activities and haemolymph ecdysteroid levels was performed in the phasmid Clitumnus extradentatus. Temporal correlation was found between increases in mitotic frequency in mandibular and general epidermis, and variations of ecdysteroid levels in the haemolymph of the insects. Whereas, mitotic waves occurring in the fat body cells or in the basal cells of the midgut did not appear to be strictly correlated with these hormonal variations. During the fourth larval instar of this phasma; an accurate study of mitotic figures, monitored from histological sections, indicated a time-lag in their stimulation according to the studied area, with a peak on day 2 in the mandible tips, on day 5 in the mandible bases and on day 7 in the head capsule, thorax and abdomen epidermis: namely a five-day delay with respect to the 12 days of the fourth instar. Simultaneously, the evolution of ecdysteroid levels in the haemolymph showed three increases of different importance. Each hormonal increase occurred 24 h before the triggering of each increase in the mitotic activity, whereas a fourth and very high peak, occurring on day 8, corresponded to the sudden fall in the number of epidermal mitoses.