Range shifts are among the most conspicuous effects of global warming. Marked changes in distribution are recorded both for highly mobile species of insects, which are capable of flight, and wing-dimorphic species with predominantly short-winged individuals. One of these species is the bush-cricket Metrioptera roeselii, which occasionally produces long-winged individuals. However, there is little known about the locomotory behaviour of wing-dimorphic insects. Yet to be able to predict potential range shifts it is necessary to know the dispersal potential of macropters. Therefore, an experiment was conducted in which individually marked M. roeselii were released at four sites. Different movement parameters, such as daily movement, activity radius, dispersal range, net displacement and crowding rate, were calculated. The statistical analyses showed that the movement of long-winged and short-winged individuals did not differ, but the percentage of individuals that were not seen again was twice as high for long-winged bush-crickets. These results suggest that most of the long-winged individuals that were seen again did not fly; i.e., they had the same basic mobility as the short-winged individuals. However, the comparatively low number of long-winged individuals that were seen again suggests that at least some macropters are long-distance dispersers, which is relevant for the dispersal process. The comparison of sexes showed that males were significantly more mobile than females. This sex-specific locomotory behaviour in M. roeselii might depend on a complex series of social interactions and physiological conditions. and Dominik Poniatowski, Thomas Fartmann.
Mechanisms of the suppression of gonadotropic activity of the corpus allatum (CA) in macropterous females were compared with those previously reported for either diapause or starving non-diapause brachypterous females by reciprocal transplantations of the neuroendocrine complexes (comprising the brain-suboesophageal ganglion-corpora cardiaca-CA). The denervated CA stimulated reproduction in most females of all experimental groups suggesting an inhibition of the CA via nervous connections with the brain. The inhibition of the CA within the transplanted neuroendocrine complex was measured by the reproductive performance of feeding recipient females deprived of their own CA. The complex from starving non-diapause brachypterous females stimulated reproduction in 58.3-78.9% of recipients suggesting that the inhibition of the CA was mostly overcome by the stimulating internal milieu of feeding females. In contrast, the "macropterous" complex stimulated reproduction in only 18.8-37.5% of recipients, similar to the "diapause brachypterous" complex (32.0%). The results indicate that the "macropterism", similar to the diapause, is associated with a considerably lower responsiveness of the neuroendocrine complex to humoral stimulation by feeding compared to the responsivenes of the "starving" complex from brachypterous non-diapause females. On the other hand, the CA of macropterous females is of intermediate size between that of the feeding non-diapause and diapause brachypterous females, similar to the CA of the non-diapause brachypterous females deprived of food. Overall, the data suggest that the suppression of the CA activity results from a combination of the diapause-like refractoriness of the neuroendocrine complex with the starvation-like inhibition of the CA growth. Regulation of the CA activity is discussed in relation to the "oogenesis-flight syndrome" recorded for flying wing-polymorphic species of insects.
Macroptery is common in many species of Orthoptera, but the causes are still discussed. Besides the assumption that macroptery is genetically determined, there is evidence that wing dimorphism is induced by environmental factors, particularly population density. However, most of the research is on pest species. In contrast, knowledge of wing dimorphism in species that occur at low population densites is still poor. Our study aims to test how density actually affects macroptery. As model organisms we chose two bush-cricket species of the genus Metrioptera (Ensifera: Tettigoniidae): While long-winged M. roeselii (Hagenbach, 1822) occur regularly, macropterous M. brachyptera (Linnaeus, 1761) are rare and are never observed outside their mating habitat. Nymphs of populations from the range core of both species (340 individuals each) were reared in groups of three and six individuals per 500 cm3 box, and individually. Our analyses revealed that development of macropters was mainly affected by the initial rearing densities. Compared with those reared individually the number of macropters was significantly higher among individuals reared at medium and high densities. The percentage of macropterous individuals was about twice as high in M. brachyptera as in M. roeselii, and the development of macropters significantly differed between the two species. These findings lead to the conclusion that macropterism is mainly influenced by density stress in both bush-crickets. Genetically determined wing dimorphism is unlikely, otherwise the observed high numbers of long-winged individuals of M. brachyptera, which are very rare under natural conditions, would never have developed in the laboratory. Macropterous M. brachyptera may rarely be found in the field, but we argue that this is due to low natural densities and, accordingly, to rare exposure to density stress.
The aim of this study was to determine if there is a latitudinal gradient in the photoperiodic regulation of wing dimorphism in the flightless bug, Pyrrhocoris apterus (L.). For this purpose individuals from three geographical populations (Israel, Spain and Czech Republic) were reared under different photoperiods and the wing length of the adults analyzed. The highest percentage of long-winged (macropterous) specimens was found in the population from Israel (35.3%), whereas percentages of macroptery were lower in the cultures from Spain (9.5%) and Czech Republic (8.6%). A higher proportion of macropterous specimens was recorded in the northern population of P. apterus kept under long daylengths (Czech Republic, 16 h) than in the southern populations (Spain, 14-15 h; Israel, 12 h). The results indicate that there is a latitudinal gradient in the critical photoperiod determining wing length in P. apterus.
This review considers factors affecting the flight capacity of carabid beetles and the implications of flight for carabids. Studies from the Dutch polders in particular show that young populations of carabids consist predominantly of macropterous species and macropterous individuals of wing-dimorphic species. Also populations of wing-dimorphic carabid species at the periphery of their geographical range contain high proportions of macropterous individuals. However, studies from Baltic archipelagos show that older populations of even highly isolated island habitats contain considerable proportions of brachypterous species and individuals. This suggests that macroptery is primarily an adaptation for dispersal and that there exists a mechanism for subsequently reducing the ratio of macropterous to brachypterous species under stable conditions, due to the competitive advantage of brachyptery. Populations in isolated habitats, such as islands and mountains, have high proportions of brachypterous species. Many macropterous species do not possess functional flight muscles. Species of unstable habitats, such as tree canopies and wet habitats, are mostly macropterous. Brachypterous species tend to disappear from disturbed habitats. There is uncertainty regarding the extent to which carabid dispersal is directed and how much passive. Both Den Boer and Lindroth recognized that mostly macropterous individuals of macropterous and wing-dimorphic species disperse and found new populations, after which brachyptery tends to rapidly appear and proliferate in the newly founded population. It is most likely that the allele for brachyptery would arrive via the dispersal of gravid females which had mated with brachypterous males prior to emigration. Whilst many studies consider wing morphology traits of carabid beetles to be species-specific and permanent, a number of studies have shown that the oogenesis flight syndrome, whereby females undertake migration and subsequently lose their flight muscles by histolysis before eventually regenerating them after reproducing, has been reported for a growing number of carabid species. Wing morphology of carabid beetles clearly offers strong potential for the study of population dynamics. This field of study flourished during the 1940's to the late 1980's. Whilst a considerable amount of valuable research has been performed and published, the topic clearly holds considerable potential for future study., Stephen Venn., and Obsahuje bibliografii