Parameters of ontogeny and population dynamics modeling of Panagrolaimus detritophagus (Nematoda: Rhabditida) in vitro

The parameters of individual development and population cycle in in vitro nematodes Panagrolaimus detritophagus were revealed. The nematodes are bacterial feeders and commensals of the cerambycid Monochamus galloprovincialis from the pine Pinus sylvestris; nematodes use beetles as vectors. Mean development time (T) from egg to juvenile is 1–2 days for J2, 3–4 days for J3, and 4–7 days for J4; to adults (G, generation) 7 (6–8) days. In vitro the population cycle is equal to 4 generations and ends with 90% of survival juveniles (J3, day 34). In the growth phase of the population, the proportion of eggs exceeds the proportion of other stages of the developmental cycle: 39±11% for 7 days; 53±10% for 21 days. The average oviposition rate of females is 4.5±1.3/day and only 56±12% of eggs proceed to immediate development (hatching and molting of juveniles). The remaining mass of eggs enter development only after 27 days (4 individual generations). This feature may be considered as a form of delay or a brief diapause at the egg stage. Individual females may accumulate up to 4 synchronous eggs in the body and lay them simultaneously. The average life span of an adult female is 13–20 days. Formulas for the exponential growth of the number of females and the total nematode population have been developed.

Identification of Spruce Budworm Natural Enemies Using a qPCR-Based Molecular Sorting Approach

Annual monitoring of mortality agents in the course of a spruce budworm (Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae)) population cycle is essential to understanding the factors governing the rise and collapse of outbreaks. To date, assessments of causes of budworm mortality have relied on laboratory rearing of field-collected larvae, followed by visual identification of emerging parasitoids and/or microscopic analysis of pathogens in larval carcasses. Although this approach has provided vital information on the abundance and identity of mortality agents, the procedure is labor-intensive and has limits in terms of accuracy. To overcome these shortcomings, we developed a molecular identification tool that makes use of real-time quantitative PCR (qPCR) and TaqMan® technologies. The tool relies on taxon-specific molecular variants (single nucleotide polymorphism [SNP] markers) found in mitochondrial (COI) and nuclear (28S rDNA) genes, for parasitoids, and in the nuclear SSU rDNA gene for microsporidian pathogens; these are then used as molecular signatures targeted by qPCR primers and TaqMan probes. Thus, the design of several sets of primers and probes deployed in multiplex format enables the identification of natural enemies via a molecular sorting process, bypassing barcode sequencing. Crude budworm DNA extracts are processed through a first module that detects dipteran and hymenopteran parasitoids, and microsporidian infections. Positive samples are then processed for species determination using three additional modules, enabling the identification of 20 common natural enemies of the spruce budworm. The tool has been fully validated using DNA samples from all comprised taxa, and both its sensitivity and accuracy compared favorably with the rearing-based method in an analysis of field-collected budworms. Using this tool, sample processing can be completed within two days, does not require larval rearing, provides accurate species identification, and can be conducted by technical staff without extensive molecular biology or insect taxonomy training.

Relating the 4-year lemming (Lemmus spp. and Dicrostonyx spp.) population cycle to a 3.8-year lunar cycle and ENSO

Reported peak years of lemming (Lemmus spp. and Dicrostonyx spp.) and Arctic fox (Vulpes lagopus (Linnaeus, 1758)) abundance were compiled from the literature for 12 locations spanning 127 years. The mean period of the 34 reported lemming and Arctic fox cycles from 1868 to 1994 was 3.8 years, suggesting that the period of the 4-year cycle is actually 3.8 years. Peak population years were predicted using a simple model based on a 3.8-year lunar cycle. For nearly 130 years, reported years of peak abundance of lemmings and Arctic foxes were significantly correlated with and have persistently stayed in phase with predicted peak years of abundance. Over the same period, predicted peak years of lemming abundance have been closely aligned with peak (i.e., La Niña) years of the January–March Southern Oscillation Index (SOI). From 1952 to 1995, peak flowering in Norway tended to occur close to trough June–August SOI (El Niño) years. The hypothesis proposed is that the 3.8-year lunar cycle governs the timing of the lemming cycle, but it does not cause the population cycling itself. If this hypothesis is true, then the heretofore unexplained source of the persistent periodicity and quasi-metronomic regularity of the lemming cycle is identified.

Inadequate Sampling Rates Can Undermine the Reliability of Ecological Interaction Estimation

Cycles in population dynamics are abundant in nature and are understood as emerging from the interaction among coupled species. When sampling is conducted at a slow rate compared to the population cycle period (aliasing effect), one is prone to misinterpretations. However, aliasing has been poorly addressed in coupled population dynamics. To illustrate the aliasing effect, the Lotka–Volterra model oscillatory regime is numerically sampled, creating prey–predator cycles. We show that inadequate sampling rates may produce inversions in the cause-effect relationship among other artifacts. More generally, slow acquisition rates may distort data interpretation and produce deceptive patterns and eventually leading to misinterpretations, as predators becoming preys. Experiments in coupled population dynamics should be designed that address the eventual aliasing effect.

Changes in abundance and reproductive activity of small arid-zone murid rodents on an active cattle station in central Australia

Context Boom and bust population cycles are characteristic of many arid-zone rodents, but it is unknown to what extent these dynamics might be influenced by the presence of invasive rodents, such as the house mouse (Mus musculus) in Australia. Aim To determine whether the presence of M. musculus can have negative consequences on the population abundance and reproduction of two old Australian endemic rodents (the spinifex hopping mouse, Notomys alexis, and sandy inland mouse, Pseudomys hermannsburgensis). Methods The study took place on the sand dunes of a cattle station in central Australia. Population abundance was estimated as the number of individuals caught in small mammal traps, and female reproductive condition by external examination and, in a few cases, euthanasia and inspection of the reproductive tract. Key results Two synchronous periods of high abundance of N. alexis and M. musculus occurred several months after significant rainfall events, whereas the abundance of P. hermannsburgensis was consistently low. No reproduction took place in N. alexis or M. musculus when populations had reached high abundance. During low-rainfall periods, M. musculus was not detected on the sand dunes, and the two endemic species were sparsely distributed, with reproduction occasionally being evident. Conclusions During dry periods, M. musculus contracted back to refuges around the homestead and, after significant rainfall, it expanded onto the sand dunes and became abundant at the same time as did N. alexis. In contrast, and unlike in areas where M. musculus was generally rare, P. hermannsburgensis always remained at a low abundance. These patterns suggest that in areas of the natural environment close to human-modified sites, populations of at least one species of an old endemic rodent are supressed by the presence of M. musculus. Reproduction did not occur in the old endemics at times of high M. musculus abundance, but did take place in spring/early summer, even in some dry years. Implications The spread of M. musculus into the Australian arid zone may have had negative impacts on the population dynamics of P. hermannsburgensis. These findings suggest that the presence of human settlements has resulted in refuges for house mice, which periodically spread out into the natural environment during ‘boom’ times and adversely affect the natural population cycle of ecologically similar species such as P. hermannsburgensis.

Reproductive activity of male edible dormice (Glis glis L., 1766) in the peripheral population

The edible dormouse is a dendrobiont hibernating rodent breeding once a year. A peculiarity of the species biology is regular reproduction failure in non-mast years. In the center of the area it occurs due to the lack of male reproductive activity. In the studied population on the eastern periphery of the dormouse area previous studies proved the decisive role of mass resorption of embryos at females in the process. The dynamics of males reproductive activity and its impact on the reproduction were not considered previously in detail. In this work the periodicity and intensity of reproductive activity of males, depending on the age and phase of population cycle, was studied. Reproductive activity of the overwhelming majority of males was annually observed, the proportion of individuals not involved in reproduction did not exceed 6,7%. The age differences in the timing of beginning of the reproduction were revealed: yearlings came the first in the activity state and after them two-year and three-year and older individuals became active. The minimal duration of the mating period was observed in yearling males, the maximal - in two-year, which were also characterized by the longest individual periods of reproductive activity. As a result of sharp fluctuations in the population age structure two-year males are the most important group in reproduction, but the three-year and older individuals in mast years are also able to ensure the reproduction of the population. The characteristic feature of reproduction was noted at yearling males: they began reproduction depending on body weight. Fluctuations in the male reproductive activity during the active period do not play a significant role in the regulation of reproduction. Shorter duration of reproductive activity of yearling animals in the years of reproduction failure is compensated by the later beginning of reproduction of three-year and older individuals. Nonsynchronous participation in breeding of males of different age groups provides the involvement in reproduction of maximal number of animals.