Resident-invader dynamics of similar strategies in fluctuating environments

We study resident-invader dynamics in fluctuating environments when the invader and the resident have close but distinct strategies. First we focus on a class of continuous-time models of unstructured populations of multi-dimensional strategies, which incorporates environmental feedback and environmental stochasticity. Then we generalize our results to a class of structured population models. We classify the generic population dynamical outcomes of an invasion event when the resident population in a given environment is non-growing on the long-run and stochastically persistent. Our approach is based on the series expansion of a model with respect to the small strategy difference, and on the analysis of a stochastic fast-slow system induced by time-scale separation. Theoretical and numerical analyses show that the total size of the resident and invader population varies stochastically and dramatically in time, while the relative size of the invader population changes slowly and asymptotically in time. Thereby the classification is based on the asymptotic behavior of the relative population size, and which is shown to be fully determined by invasion criteria (i.e., without having to study the full generic dynamical system). Our results extend and generalize previous results for a stable resident equilibrium (particularly, Geritz in J Math Biol 50(1):67–82, 2005; Dercole and Geritz in J Theor Biol 394:231-254, 2016) to non-equilibrium resident population dynamics as well as resident dynamics with stochastic (or deterministic) drivers.

Cestode species Khawia sinensis as indicator of epizootic state of rivers of Dagestan and test of microelement composition in fish meat

Caviosis in the waters of the south of the Russian Federation is a poorly studied problem. Indicators of the extent of invasion were in the range of slightly moderate registration with extent of invasion (9.00-15.00%) with an abundance index of cestodes Khawia sinensis (1.40-2.18 ind./piece) in fish of different species (bighead carp, grass carp, black carp (black Chinese roach), spirlin, Sabanejewia caucasica, Krinitsky char, Tersk nase, Tersk barbel, silver Prussian carp, rutilus, Tersky gudgeon) in the basin of the Terek river, and a high level of detection of cestodes in the intestine of fish of 6 species (common carp, European carp, Tersk barbel, crucian carp, rutilus, Tersky gudgeon) was registered with extent of invasion criteria (21.00-37.00%) and an epizootic degree of abundance index of the cestode species Khawia sinensis (4.16-6.13 ind./piece). As a result of biochemical studies of 20-30 fish muscle samples within the boundaries of Dagestan authors found that the intensity of infection of fish of 14 species in Terek river basin with intestinal cestodes Khawia sinensis reduces the content of iodine, cobalt and iron in the muscles, that affect the nutritional value of fish. The content of biogenic microelements in the muscles of fish infected with cestodes Khawia sinensis was 2-5.9 times less than in fish free from helminths, which confirms the fact that the biological qualities of fish decrease with intensive cestode invasion. The most intensive infection with intestinal cestodes Khawia sinensis in comparison with fish populations free from helminths caused the marked reduction in the content of biogenic micronutrients in the muscles of trout, common carp, European carp, grass carp, black Chinese roach.

Body size and meta-community structure: the allometric scaling of parasitic worm communities in their mammalian hosts

SUMMARYIn this paper we derive from first principles the expected body sizes of the parasite communities that can coexist in a mammal of given body size. We use a mixture of mathematical models and known allometric relationships to examine whether host and parasite life histories constrain the diversity of parasite species that can coexist in the population of any host species. The model consists of one differential equation for each parasite species and a single density-dependent nonlinear equation for the affected host under the assumption of exploitation competition. We derive threshold conditions for the coexistence and competitive exclusion of parasite species using invasion criteria and stability analysis of the resulting equilibria. These results are then used to evaluate the range of parasites species that can invade and establish in a target host and identify the ‘optimal’ size of a parasite species for a host of a given body size; ‘optimal’ is defined as the body size of a parasite species that cannot be outcompeted by any other parasite species. The expected distributions of parasites body sizes in hosts of different sizes are then compared with those observed in empirical studies. Our analysis predicts the relative abundance of parasites of different size that establish in the host and suggests that increasing the ratio of parasite body size to host body size above a minimum threshold increases the persistence of the parasite population.

Maternal-Zygotic Gene Conflict Over Sex Determination: Effects of Inbreeding

There is growing evidence that sex determination in a wide range of organisms is determined by interactions between maternal-effect genes and zygotically expressing genes. Maternal-effect genes typically produce products (e.g., mRNA or proteins) that are placed into the egg during oogenesis and therefore depend upon maternal genotype. Here it is shown that maternal-effect and zygotic genes are subject to conflicting selective pressures over sex determination in species with partial inbreeding or subdivided populations. The optimal sex ratios for maternal-effect genes and zygotically expressing genes are derived for two models: partial inbreeding (sibmating) and subdivided populations with local mating in temporary demes (local mate competition). In both cases, maternal-effect genes are selected to bias sex determination more toward females than are zygotically expressed genes. By investigating the invasion criteria for zygotic genes in a population producing the maternal optimum (and vice versa), it is shown that genetic conflict occurs between these genes. Even relatively low levels of inbreeding or subdivision can result in maternalzygotic gene conflict over sex determination. The generality of maternal-zygotic gene conflict to sex determination evolution is discussed; such conflict should be considered in genetic studies of sex-determining mechanisms.