Diapause is a common dormancy strategy exhibited by many species of invertebrates and insects to temporarily avoid seasonally recurring unfavourable conditions for their development, most usually in winter. Less frequently, a prolonged diapause lasting two or more years is described in species living in unpredictable environments where it is adaptive, but with significant costs. In this paper we examine the occurrence of prolonged diapause in the lycaenid butterfly Tomares ballus. Pupae of this species undergo an obligate diapause from mid-May to late January the following year. However, during our rearing experiments (from 2009 to 2016) the emergence of adults occurred sequentially and a fraction of the pupae remained in diapause for up to seven years. The annual percentage emergence after the first year of diapause was 45.6%, and only barely exceeded 50.0% in 2015. Remarkably, 12 pupae (11.4% of the initial brood) remained in diapause in their eighth year. The negative exponential equation fitted to the emergence data suggests that further emergences may occur within the next five years. Therefore, the potential for successful prolonged diapause of T. ballus pupae may be more than 10 years. The adaptive value of this strategy is discussed in relation to the effects of adverse and unpredictable weather during the flight period of the butterfly, intra-guild competition, parasitoids and changes in habitat quality. We suggest that this strategy may also be exhibited by other species of Mediterranean lycaenids., Rafael Obregón, Juan Fernández Haeger, Diego Jordano., and Obsahuje bibliografii
Competition plays an important role in the replacement of native species by alien plants. A greenhouse experiment was conducted to investigate whether the competition pattern of alien Robinia pseudoacacia L. and native Quercus acutissima Carr. is affected by soil sterilization. Physiological traits, such as gas-exchange parameters and chlorophyll (Chl) content, and growth traits, such as the biomass accumulation of the two species, were examined in natural soil or in soil sterilized with benomyl. The results show that native Q. acutissima inhibits the growth of R. pseudoacacia in natural soil. When the two plants coexisted and competed under sterilization treatment, R. pseudoacacia was less inhibited by Q. acutissima and the competition of R. pseudoacacia decreased the growth of Q. acutissima in terms of biomass, Chl a, Chl b, total Chl, and Chl a/b. These results suggest that soil sterilization benefits the growth of R. pseudoacacia and changes the competition pattern by the changed soil biota. Soil sterilization increased the biomass of root nodules, which ultimately benefits the growth of R. pseudoacacia and root nodule bacteria may be important in the dispersal and invasion process of nitrogen-fixing alien plants such as R. pseudoacacia., H. Chen ... [et al.]., and Obsahuje bibliografii
The natural diet of goitred gazelle (Gazella subgutturosa) was studied over the period of a year in northern Xinjiang, China using microhistological analysis. The winter food habits of the goitred gazelle and domestic sheep were also compared. The microhistological analysis method demonstrated that gazelle ate 47 species of plants during the year. Chenopodiaceae and Poaceae were major foods, and ephemeral plants were used mostly during spring. Stipa glareosa was a major food item of gazelle throughout the year, Ceratoides latens was mainly used in spring and summer, whereas in autumn and winter, gazelles consumed a large amount of Haloxylon ammodendron. Because of the extremely warm and dry weather during summer and autumn, succulent plants like Allium polyrhizum, Zygophyllum rosovii, Salsola subcrassa were favored by gazelles. In winter, goitred gazelle and domestic sheep in Kalamaili reserve had strong food competition; with an overlap in diet of 0.77. The number of sheep in the reserve should be reduced to lessen the pressure of competition.
In forest ecosystems in the temperate and boreal zones in Europe, red wood ants (RWA, Formica rufa group) have a significant affect as predators and competitors in communities of ground-dwelling arthropods. Therefore, the spatiotemporal distribution and abundance of RWA affect the distribution of many other species. The hypothesis that a reduction in the abundance of RWA in clear-cut areas enables other arthropods to increase in abundance was tested. The study was conducted in NW Poland in 2007 and 2008. A total of 276 1×1 m plots were sampled and 1,696 individuals recorded. The probability of the occurrence of RWA decreased significantly towards the center of clear-cut areas and increased with increasing plant cover. The frequency of Lasius platythorax, Formica fusca and spiders in the plots significantly increased towards the edge of a clear-cut area. Moreover, the occurrence of L. platythorax was negatively associated with the presence of RWA, while that of the Myrmica species was positively associated. The effect of the distance to the edge of a clear-cut area seems to be much more pronounced than the effect of RWA. This suggests that the arthropods studied prefer habitats close to the edge that are utilized by RWA than RWA-free sites located in the centre of clear-cut areas. and Michal Zmihorski.
An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.
This study determined the effect of larval density-dependent competition for food on development and adult fitness in Sesamia nonagriodes Lef. (Lepidoptera: Noctuidae). Different numbers (5, 10, 15, 20 and 30 individuals) of larvae of the pink stalk borer were reared on a constant amount of food. Although crowding during the immature stages did not significantly increase mortality, it prolonged the larval developmental period and resulted in reduced pupal weight. Females were more adversely affected by high density than males, resulting in lighter females, indicating that female growth is more sensitive to density. The fecundity of the adults reared in the various larval crowding treatments was analysed. Total female fecundity was correlated negatively with increasing larval density. The effects of crowding on fecundity were not caused by the reduced pupal weight, indicating that food shortage during larval development may affect adult traits. Female longevity was negatively affected by density and positively related to pupal weight. Thus, larval density may affect the allocation of food resources and adult fitness. We conclude that crowding related changes during larval development directly affect larval life and reduce female fitness.
The importance of interspecific competition as a force promoting specialization in phytophagous insects has been long debated. Myzus persicae sensu stricto (Hemiptera: Aphididae) is one of the most polyphagous aphids. Its subspecies, M. persicae nicotianae, is found mainly on tobacco, although it can survive and reproduce on a relatively wide range of plant species in the laboratory. Since life history traits of these taxa make competitive interactions likely, we hypothesize that asymmetrical competition occurs between M. p. nicotianae and M. persicae s.s., and accounts for the exclusion of the former when they share a common resource. This hypothesis was tested in laboratory experiments, which examined the population growth of colonies of both taxa coexisting on sweet pepper. A replacement series experiment was set up with both aphid taxa on sweet pepper plants, and the rates of population growth (RPG) evaluated at 5 day intervals for 25 days. M. p. nicotianae showed a significantly lower RPG when interacting with M. persicae s.s. than when in monotypic colonies, while M. persicae s.s. RPG was unaffected by competition. The relative population growth from the second census onwards of M. persicae s.s. was consistently higher than that of M. p. nicotianae. Finally, the RPG of M. p. nicotianae was significantly reduced when the plant was infested with M. persicae s.s. The results suggest that the absence of M. p. nicotianae from sweet pepper in the field in Chile can be partly explained by competitive exclusion by M. persicae s.s.
Parasitoid females may adjust offspring sex allocation according to the number and quality of hosts available. Because in solitary species only one offspring survives per host, already parasitized hosts are of low quality and generally rejected. Superparasitism (i.e., sequential oviposition by the same or different females) results in aggressive interactions and competition for nutritional resources among larvae. We examined variations in the offspring sex ratio of Dendrocerus carpenteri (Curtis) (Hymenoptera: Megaspilidae), a solitary ectoparasitoid developing as a hyperparasitoid on the prepupae and pupae of primary aphid parasitoids inside mummified aphids. Mated females produced a female-biased sex ratio of 0.433 (proportion of sons) when caged singly and provided with 12 mummies for 2 h; they parasitized an average of four mummies/h and rarely superparasitized. Superparasitism increased when two females were caged together and provided with 12 mummies, from 1.18 to 1.24 and 1.38 eggs/host parasitized in 1, 2 and 3 h, respectively. The offspring sex ratio became increasingly more female-biased with increase in superparasitism; however, sex ratio variations were not correlated with cohort size. One mated and one unmated female provided with 12 mummies and caged together for 1 h produced a mean cohort sex ratio of 0.645, which differed from the one predicted (0.717) by an algebraic model incorporating the assumptions that both females contribute equal numbers of offspring and that the mated female does not change her offspring-sex allocation strategy. The observed shift in the cohort sex ratio to an increased female-bias indicates that mated females of D. carpenteri change their behaviour when encountering parasitized mummies or a conspecific competitor in the same patch. By depositing fertilized rather than unfertilized eggs, a female can increase the proportion of her daughters among parasitoids competing for a diminishing host supply., Manfred Mackauer, Andrew Chow., and Obsahuje bibliografii
In this study, we questioned whether ground-level ozone (O3) induces hormesis in Japanese larch (Larix kaempferi) and its hybrid F1 (L. gmelinii var. japonica × L. kaempferi). In order to answer the question, we exposed seedlings of both taxa to four O3 treatments [ranging from ≈10 to 60 nmol(O3) mol-1] in open-top chambers for two consecutive growing seasons. We found a hormetic response in maximum photosynthetic rate (PNmax) at 1700 μmol(CO2) mol-1 and maximum rates of carboxylation (Vcmax) and electron transport (Jmax) in both larches. Stimulation of PNmax, Vcmax, and Jmax did not lead to suppressed plant productivity in Japanese larch, which followed a stress-tolerant strategy, but it did lead to suppressed plant productivity in hybrid larch which followed a competitive strategy. These findings are the first to suggest that stimulation of physiological functions by low O3 exposures may have negative consequences for larch reproduction., T. Sugai, D.-G. Kam, E. Agathokleous, M. Watanabe, K. Kita, T. Koike., and Obsahuje bibliografii
In the parthenogenetic monogeneans of the genus Gyrodactylus Nordmann, 1832, the genetic diversity within or between hosts is determined by the relative roles of lateral transmission and clonal propagation. Clonality and limited transmission lead to high-amplitude metapopulation dynamics and strong genetic drift. In Baltic populations of the three-spined stickleback Gasterosteus aculeatus Linnaeus, the local mitochondrial diversity of Gyrodactylus arcuatus Bychowsky, 1933 is very high, and spatial differentiation weak. To understand the transmission dynamics in a single location, the transmission of the parasite from adults to next generation sticklebacks was investigated in a northern Baltic brackish water location. By sequencing 777 nt of cox1, as many as 38 separate mitochondrial haplotypes were identified. In August, the intensity of gyrodactylid infection on adult hosts was high, the haplotype diversity (h) was extreme and differentiation between fish was negligible (total h = 0.926, mean h = 0.938). In October, only 46% of the juvenile sticklebacks carried G. arcuatus. The number of parasites per young fish followed a Poisson distribution 0.92 ± 1.04 (mean ± SD) on October 2, and was clearly overdispersed 2.38 ± 5.00 on October 25. The total haplotype diversity of parasites on juveniles was nearly as high as in adults (h = 0.916), but the mean per fish was only h = 0.364 (FST = 0.60), due to low intensity of infection and rapid clonal propagation of early arrivals. The initial first come first served advantage of the first gyrodactylid colonisers will be lost during the host adulthood via continuous transmission. Nesting and polygamy are suggested as factors maintaining the high genetic diversity of the parasite population. The transmission dynamics and, consequently, the population structure of Baltic G. arcuatus is fundamentally different from that of G. salaris Malmberg, 1957, on the Baltic salmon Salmo salar Linnaeus., Jaakko Lumme, Marek S. Ziętara., and Obsahuje bibliografii