Reduced variation among northern deer tick populations at an autosomal microsatellite locus.

To determine whether genes flow freely between populations of the Ixodes ricinus-like ticks of eastern North America, and to determine whether the abundant northerly populations of these vectors of Lyme disease and other zoonotic infections may have arisen recently from a small cohort of ancestral founders, we characterized the nuclear IR27 microsatellite alleles in ticks sampled from the geographic extremes of their ranges. These microsatellite alleles differentiated populations located in the southeastern, northcentral and northeastern United States, respectively. Although evident heterozygous genotypes are about as frequent as would be expected in randomly mating populations, particular microsatellite alleles and diploid genotypes occur more frequently in certain populations than in others. Ticks from the Northeast and upper Midwest are markedly more related to each other than to ticks from the Southeast. Patterns of diversity present in this nuclear microsatellite marker correspond to those evident at a mitochondrial locus and indicate that the deer ticks of the Northeast and upper Midwest are genetically isolated from those in the Southeast. The Ixodes ricinus-like ticks that impose a public health burden in the northeastern and northcentral United States originated recently in a common founder population.     

Sperm precedence in the deer tick Ixodes dammini

ABSTRACT We determined whether female deer ticks Ixodes dammini Spielman, Clifford, Piesman & Corwin (Acari: Ixodidae) can be inseminated repeatedly and whether sperm from first or second matings take precedence in fertilizing eggs. Such information is essential to the design of attempts to reduce the fertility of these vectors of Lyme disease. Although spermatophores are present in about half of questing female ticks, they are present in virtually all those found on deer; the abundance of males on deer exceeds that of females and copulation is common. Females must be inseminated before commencing the rapid engorgement phase of feeding. Males need not be in attendance during feeding, provided that the female has been inseminated preprandially. Thus, preprandial insemination suffices to stimulate rapid engorgement, but less blood is taken than when the female is perprandially inseminated. Both types of insemination effectively fertilize eggs. Eggs from females sequentially inseminated by irradiated and non irradiated males, were fertilized mainly by sperm from the last male. Cobalt-irradiated males mate effectively and their sperm compete with those of non-irradiated males. Sperm from the second two sequential inseminations fertilize most of the eggs. By infesting deer with such irradiated male I.dammini , the abundance of these vector ticks may effectively be reduced.     

The role of migration in mutant dynamics in fragmented populations

Mutant dynamics in fragmented populations have been studied extensively in evolutionary biology. Yet, open questions remain, both experimentally and theoretically. Some of the fundamental properties predicted by models still need to be addressed experimentally. We contribute to this by using a combination of experiments and theory to investigate the role of migration in mutant distribution. In the case of neutral mutants, while the mean frequency of mutants is not influenced by migration, the probability distribution is. To address this empirically, we performed in vitro experiments, where mixtures of GFP-labelled (“mutant”) and non-labelled (“wid-type”) murine cells were grown in wells (demes), and migration was mimicked via cell transfer from well to well. In the presence of migration, we observed a change in the skewedness of the distribution of the mutant frequencies in the wells, consistent with previous and our own model predictions. In the presence of de novo mutant production, we used modelling to investigate the level at which disadvantageous mutants are predicted to exist, which has implications for the adaptive potential of the population in case of an environmental change. In panmictic populations, disadvantageous mutants can persist around a steady state, determined by the rate of mutant production and the selective disadvantage (selection-mutation balance). In a fragmented system that consists of demes connected by migration, a steady-state persistence of disadvantageous mutants is also observed, which, however, is fundamentally different from the mutation-selection balance and characterized by higher mutant levels. The increase in mutant frequencies above the selection-mutation balance can be maintained in small ($N<N_c$) demes as long as the migration rate is sufficiently small. The migration rate above which the mutants approach the selection-mutation balance decays exponentially with $N/N_c$. The observed increase in the mutant numbers is not explained by the change in the effective population size. Implications for evolutionary processes in diseases are discussed, where the pre-existence of disadvantageous drug-resistant mutant cells or pathogens drives the response of the disease to treatments.     

The role of triploid hybrids in the evolutionary dynamics of mixed-ploidy populations

Theory suggests that the evolution of autotetraploids within diploid populations will be opposed by a minority-cytotype mating disadvantage. The role of triploids in promoting autotetraploid establishment is rarely considered, yet triploids are often found in natural populations and are formed in experimental crosses. Here, I evaluate the effects of triploids on autotetraploid evolution using computer simulations and by synthesizing research on the evolutionary dynamics of mixed-ploidy populations in Chamerion angustifolium (Onagraceae). Simulations show that the fate of a tetraploid in a diploid population varies qualitatively depending on the relative fitness of triploids, the ploidy of their gametes and the fitness of diploids relative to tetraploids. In general, even partially fit triploids can increase the likelihood of diploid–tetraploid coexistence and, in some cases, facilitate tetraploid fixation. Within the diploid–tetraploid contact zone of C. angustifolium , mixed populations are common (43%), and often (39%) contain triploids. Greenhouse and field studies indicate that triploid fitness is low (9% of diploids) but variable. Furthermore, euploid gametes produced by triploids can be x , 2 x or 3 x and contribute the majority (62%) of new polyploids formed in each generation (2.3 × 10⁻³). Although triploid bridge, alone, may not account for the evolution of autotetraploidy in C. angustifolium , it probably contributes to the prevalence of mixed-ploidy populations in this species. Therefore, in contrast to hybrids in homoploid species, triploids may actually facilitate rather than diminish the fixation of tetraploids by enhancing the rate of formation.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 537–546.     

The role of food in the dynamics of populations of the landsnail Cepaea nemoralis

Summary The food of the landsnail Cepaea nemoralis has been studied in natural environments.The diet of Cepaea in nature consists predominantly of senescent or dead plant material. Green material of some species, especially Urtica dioica, is also eaten in large quantities and algae, animal remains, fungi and, possibly, living aphids and thripses are included in the diet.The place where a snail is found during the day usually has a great predictive value for the food it ate during the preceding night. There are, however, exceptions. Species such as Aegopodium podagraria, Calystegia sepium and Phragmites communis are used very often to sit on but are hardly ever eaten. On the other hand species such as Urtica dioica and Ranunculus repens were very much favoured as foodplants but much less favoured as resting places. The distribution of the snails over the various components of the vegetation is not random and neither is the selection of food. The snail distribution does not explain the food selection or vice versa.Quantity of food probably is hardly ever limiting for the distribution and abundance of Cepaea. Some essential components may, however, very well be in short supply and thus be limiting.     

Modelling the effect of temperature variation on the seasonal dynamics of Ixodes ricinus tick populations

Seasonal variation in temperature is known to drive annual patterns of tick activity and can influence the dynamics of tick-borne diseases. An age-structured model of the dynamics of Ixodes ricinus populations was developed to explore how changes in average temperature and different levels of temperature variability affect seasonal patterns of tick activity and the transmission of tick-borne diseases. The model produced seasonal patterns of tick emergence that are consistent with those observed throughout Great Britain. Varying average temperature across a continuous spectrum produced a systematic pattern in the times of peak emergence of questing ticks which depends on cumulative temperature over the year. Examination of the effects of between-year stochastic temperature variation on this pattern indicated that peak emergence times are more strongly affected by temperature stochasticity at certain levels of average temperature. Finally the model was extended to give a simple representation of the dynamics of a tick-borne disease. A threshold level of annual cumulative temperature was identified at which disease persistence is sensitive to stochastic temperature variation. In conclusion, the effect of changing patterns of temperature variation on the dynamics of I. ricinus ticks and the diseases they transmit may depend on the cumulative temperature over the year and will therefore vary across different locations. The results also indicate that diapause mechanisms have an important influence on seasonal patterns of tick activity and require further study.     

Effect of deer reduction on abundance of the deer tick (Ixodes dammini)

To evaluate the role of deer in regulating the abundance of the deer tick (Ixodes dammini) we attempted to treat with acaricide, but eventually removed, about 70 percent of deer from Great Island, Cape Cod, Massachusetts. Deer were captured in box traps, a corral, an entanglement net, and with rifle-fired tranquilizer. Failure of these attempts, combined with ineffective acaricides, led us to deer destruction begun in fall 1982. Larval tick abundance on mice was monitored before and after deer removal. We concluded that deer removal, to the extent accomplished, did not markedly reduce the abundance of the tick. Reduced abundance of deer may not result in reduced abundance of immature ticks if deer removal follows the period of adult tick feeding, or if intensity of infestation per deer increases, or if other mammals substitute as suitable hosts. Reduced tick abundance may be delayed if unattached immature ticks survive more than one year.     

The role of pheromones in tick biology

Ticks are important vectors of pathogens that cause human and animal disease. Pheromones play a role of fundamental importance in intraspecies communication. Here, Gordon Hamilton discusses how these chemical messengers play a role in mate location, host location, and survival in adverse conditions, and how manipulation of this chemical communication system may provide a potential method of tick control.     

The role of colonization in the dynamics of patchy populations of a cyclic vole species

The crash phase of vole populations with cyclic dynamics regularly leads to vast areas of uninhabited habitats. Yet although the capacity for cyclic voles to re-colonize such empty space is likely to be large and predicted to have become evolved as a distinct life history trait, the processes of colonization and its effect on the spatio-temporal dynamics have been little studied. Here we report from an experiment with root voles (Microtus oeconomus) specifically targeted at quantifying the process of colonization of empty patches from distant source patches and its resultant effect on local vole deme size variation in a patchy landscape. Three experimental factors: habitat quality, predation risk and inter-patch distance were employed among 24 habitat patches in a 100 × 300-m experimental area. The first-born cohort in the spring efficiently colonized almost all empty patches irrespective of the degree of patch isolation and predation risk, but this was dependent on habitat quality. Just after the initial colonization wave the deme sizes in patches of the same quality were underdispersed relative to Poisson variance, indicating regulated (density-dependent) settlement. Towards the end of the breeding season local demographic processes acted to smooth out the initial post-colonization differences among source and colonization patches, and among patches of initially different quality. However, at this time demographic stochasticity had also given rise to a large (overdispersed) variation in deme sizes that may have contributed to an overshadowing of the effect of other factors. The results of this experiment confirmed our expectation that the space-filling capacity of voles is large. The costs associated with transience appeared to be so low, at least at the spatial scale considered in this experiment, that such costs are not likely to substantially constrain habitat selection and colonization in the increase phase of cyclic patchy populations.     

The role of Chaetogaster limnaei in the dynamics of trematode transmission in natural populations of freshwater snails

Chaetogaster limnaei, an oligochaete was always found infesting Bulinus (Phy.) globosus, B.(B.) forskalii and Lymnaea natalensis in Bo, Sierra Leone, living below the shell or embedded in the mucus of the foot. The worms had no preference for snails with trematode infection. The population was highest in the dry season when fewer snails were infected by trematodes. This is suggested to be a result of the protection the worms give to snails against invading miracidia.     

Reproductive seasonality in female Iberian red deer (Cervus elaphus hispanicus)

This study characterized the seasonal pattern of luteal cyclicity in Iberian red deer (n=16), by measuring plasma progesterone concentrations in hinds (female red deer) twice per week from calving (May and June) 1996 until May 1997. In eight of these hinds we also examined plasma prolactin profiles to assess seasonal responses to photoperiod. Plasma progesterone concentration in the 16 hinds studied indicated that the reproductive pattern is seasonal, and lasts for 5.73 +/- 0.27 months. After calving, progesterone levels remained basal (no luteal activity) for several months, except in a hind that lost her calf just after calving, and thus did not have to suckle it. This hind showed two consecutive estrus cycles in the month following calving, which suggests that suckling has an inhibiting effect on the resumption of ovarian activity. These results also showed that as long as the hinds do not become pregnant, they show between 5 and 10 estrus cycles per reproductive season (8.06 +/- 0.35), ranging between 105 and 249 days from onset of the first cycle to end of the last one. Uninterrupted cycling lasted for 3.5-6.4 months (mean, 4.6 +/- 0.24). Cyclic luteal activity was found from October to February in all hinds, with a smaller, but notable proportion in September (56.25%) and March (68.8%), whereas it was negligible in the remaining period. Our results show a reproductive season similar to or longer than that recorded by other authors. Prolactin plasma concentrations showed a yearly trend following that of photoperiod, with peak concentrations from April to July, a decrease in August, minimal concentrations from September to February and a sharp increase in March.     

Aqueous humor dynamics in the enucleated deer eye

Facility of outflow of aqueous humor was determined in ten deer (Odocoileus virginianus) eyes enucleated within 1 hr post-mortem. Although both outflow facility and anterior chamber volume were much greater than values reported in the literature for a variety of other species, calculated values for aqueous humor turnover were within the reported range for other animals as well as for man. These results strengthen the hypothesis that the rate of turnover of aqueous humor is quite similar in eyes of vastly differing dimensions.     

Changes in marriage seasonality among some european rural populations

The preservation or the change of the population structure is often strictly related to the acquisition or loss of behavioural models: the choice of the wedding period is among them. Analysing the period in which people marry, it is possible to point out modifications in the economy, in the work calendar and it also can be helpful to determine the importance of religious traditions. In this work, the authors study the marriage seasonality of nine rural European populations in France, Spain and Italy and its evolution during the last two centuries. The research has allowed to point out three different patterns of marriage seasonality: the Autumn marriage, the Winter marriage and populations with no remarkable seasonal variations. The first distribution results from the combination of work calendar, harsh climate in winter and religious traditions (the month of May consacrated to Maria, the Lent and Advent period), while the second one is due mostly to summer migrations. The importance of these factors tend to reduce during the XX century, making the distributions more homogeneous.     

Geotropic,hydrokinetic and random walking differ between sympatric tick species: the deer tick Ixodes scapularis and the lone star tick Ambylomma americanum

Journal of Ethology - The black-legged tick –sometimes referred to as the deer tick—Ixodes scapularis&nbsp;and&nbsp;the lone star tick Ambylomma americanum are sympatric species...     

The regulation of the dynamics of human populations

The important aspects of population dynamics are shown in a model along with the changes of population structure, the reasons for these changes and the conditions under which such changes take place. Subsequently, the reasons for these population dynamic processes which can be arranged in a three step scale are shown. Here, it must be differentiated between endogenous processes, due to factors inherent in the population, and exogenous ones caused by external forces effecting structural changes. The population political trends has to be incorporated as a part of the exogenous factors. The questions of regularities in the population dynamics are shown in the examples of important population theories in history. At the same time the theoretically possible borders are described, within which, due to purely physiological reasons, a population dynamic process has to occur. However, these borders will never be reached. Examination of the inertia of the population dynamic processes suggests an examination of the questions about the probability of the self-destructive processes in population dynamics. Considering the strong self-regulatory processes within a population the hypothesis of a population extinction is refuted.     

The dynamics of hierarchical age-structured populations

An age-structured population is considered in which the birth and death rates of an individual of age a is a function of the density of individuals older and/or younger than a. An existence/uniqueness theorem is proved for the McKendrick equation that governs the dynamics of the age distribution function. This proof shows how a decoupled ordinary differential equation for the total population size can be derived. This result makes a study of the population's asymptotic dynamics (indeed, often its global asymptotic dynamics) mathematically tractable. Several applications to models for intra-specific competition and predation are given.