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キーワード:
life cycle; larval development; seasonality; inundation; submersion resistance; dormancy; Megacephala; Phaeoxantha; Tetracha; Pentacomia; Cylindera
要旨:
Terrestrial organisms living in the Central Amazon floodplain have to cope with an annual inundation period of several months. Life cycles, habitats, behavior, and other parameters were investigated in the eight tiger beetle species inhabiting open areas in white- and blackwater floodplains near Manaus. Populations of larvae and adult beetles were observed during monthly field excursions during 1997-1999 to follow larval and adult phenology and to determine habitats and other parameters. Adult beetles were regularly taken to the laboratory for examination of gonad maturity, occasionally also for submersion experiments and to obtain eggs for rearing larvae to the adult beetle under controlled conditions. Larvae, too, were collected in the field and taken to the laboratory for submersion experiments and for rearing to the adult beetle. Submersion tolerance/resistance in the field was estimated by calculating the longest duration of inundation survived (using water gauge data) and from other observations. In the laboratory, maximum survival in water (without sediment) was tested in adult beetles of five species, in active larvae of four species, and in dormant larvae of one species. In addition, maximum survival in larvae submerged in sediment (simulating natural flooding conditions) was tested in two species. Here we complete information from previous contributions on life cycles in the four Phaeoxantha species, as well as on habitats and activity patterns of all eight species. Data are given on the life cycle of Tetracha sobrina punctata, Pentacomia cribrata (both field and laboratory data), Tetracha spinosa, and Cylindera suturalis (field observations). These four species have annual life cycles with a short larval phase (3-4 months) during low water periods and with adult beetles surviving the inundation period. Adult life span was long (>9 months) and is likely to involve a gonad dormancy in both sexes. This type of life cycle contrasts with findings in Phaeoxantha species. These also showed annual life cycles, but the larval phase was long (>7-10 months), including submersion resistance in larvae (shown for P. klugii and P. lindemannae, presumed for P. aequinoctialis bifasciata), and adult life span is either short or long. Submersion resistance in the field and when being submerged in sediment in the laboratory was >3-4 months in larval P. klugii and P. lindemannae. However, submersion resistance of active larvae in water without sediment was only a few days (P. klugii, P. lindemannae, P. a. bifasciata, and T. s. punctata) and >15 days in dormant larvae of P. klugii. Hence, submersion resistance in active larvae was low in species representing both life cycle types. Resistance is apparently enhanced by dormancy, although further factors are likely to be involved, as field data show a much higher resistance still. Adult beetles were not resistant to submersion (maximum survival <15 or <10 h, Phaeoxantha klugii, P. lindemannae, P. limata, P. aequinoctialis ssp., and Tetracha spinosa). Data on egg numbers, sex ratio, prey spectrum, predators and parasites, and on behavior are given and discussed for several of the species. Based on their life cycle, two different types of survival strategy can be assigned to the tiger beetle species inhabiting open habitats: Phaeoxantha species show a non-migratory type with flood resistant larvae, whereas P. cribrata, C. suturalis, and Tetracha species exhibit a migratory type with adults passing the inundation period. The specific sets of phenological, physiological, and ethological adaptations characterizing these two types of survival strategy are discussed.
