Rodent malaria-resistant strains of the mosquito, Anopheles gambiae, have slower population growth than -susceptible strains

<p>Abstract</p> <p>Background</p> <p>Trade-offs between anti-parasite defence mechanisms and other life history traits limit the evolution of host resistance to parasites and have important implications for understanding diseases such as malaria. Mosquitoes have not evolved complete resistance to malaria parasites and one hypothesis is that anti-malaria defence mechanisms are costly.</p> <p>Results</p> <p>We used matrix population models to compare the population growth rates among lines of <it>Anopheles gambiae </it>that had been selected for resistance or high susceptibility to the rodent malaria parasite, <it>Plasmodium yoelii nigeriensis</it>. The population growth rate of the resistant line was significantly lower than that of the highly susceptible and the unselected control lines, regardless of whether mosquitoes were infected with <it>Plasmodium </it>or not. The lower population growth of malaria-resistant mosquitoes was caused by reduced post blood-feeding survival of females and poor egg hatching.</p> <p>Conclusion</p> <p>With respect to eradicating malaria, the strategy of releasing <it>Plasmodium</it>-resistant <it>Anopheles </it>mosquitoes is unlikely to be successful if the costs of <it>Plasmodium</it>-resistance in the field are as great as the ones measured in this study. High densities of malaria-resistant mosquitoes would have to be maintained by continuous release from captive breeding facilities.</p

Prevalence of the pathogenic chytrid fungus, Batrachochytrium dendrobatidis, in an endangered population of northern leopard frogs, Rana pipiens

Background Emerging infectious diseases threaten naïve host populations with extinction. Chytridiomycosis, an emerging infectious disease of amphibians, is caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd) and has been linked to global declines in amphibians. Results We monitored the prevalence of Bd for four years in the Northern leopard frog, Rana pipiens, which is critically imperiled in British Columbia (BC), Canada. The prevalence of Bd initially increased and then remained constant over the last three years of the study. Young of the year emerging from breeding ponds in summer were rarely infected with Bd. Some individuals cleared their Bd infections and the return rate between infected and uninfected individuals was not significantly different. Conclusions The BC population of R. pipiens appears to have evolved a level of resistance that allows it to co-exist with Bd. However, this small population of R. pipiens remains vulnerable to extinction

The Land — An Unused Opportunity for the Return and Production Reactivization of External Migrants

Autor članka ukazuje da se povratnici s privremenog rada u inostranstvu nedovoljno uključuju u sektor individualne poljoprivrede gdje bi na sopstveekonomski institut, nom gazdinstvu razvili modernu i masovnu proizsarajevo, jugoslavija vodnju za potrebe tržišta. Ni aktuelni vanjski migranti, oni koji su još uvijek na radu u inostranstvu ne planiraju svoju reaktivizaciju u agraru, odnosno ne vežu svoj povratak za poljoprivredu iz koje su najvećim dijelom krenuli u tuđinu. Razloga za takvo njihovo ponašanje veoma je mnogo i oni su razliičite prirode. Autor identifikuje, kako one koji su eksterne, tako i one koji su interne naravi. Nakon identifikacije činilaca koji nepovoljno utiču na obim i intenzitet povratka u agrar daju se prijedlozi mjera i akcija koje bi pomogle i podstakle povratak migranata (njihovih znanja, vještina i, naravno njihovog novčanog kapitala) u agrar.The author of the article shows that returnees from temporary work abroad are not adequately included in the sector of private farming, where they would on their own farms develop modern, mass and market production. The current external migrants, those who are still at work abroad, do not plan reactivization on the land, i.e. they do not intend to return to farming, which most of them left to go abroad. There are many and very varied reasons for this. The author identifies both external reasons, and also those of an internal nature. After showing which factors influence unfavourably the volume and intensity of the return to farming, he proposes measures and actions that would aid and influence the return of the migrants (their knowledge, their skill and, of course, their capital) into farming

Intra-specific variation of sperm length in the malaria vector Anopheles gambiae: males with shorter sperm have higher reproductive success

<p>Abstract</p> <p>Background</p> <p>Intra-specific variation in sperm length influences male reproductive success in several species of insects. In males of the malaria vector <it>Anopheles gambiae</it>, sperm length is highly variable but the significance of this variation is unknown. Understanding what determines the reproductive success of male mosquitoes is critical for controlling malaria, and in particular for replacing natural populations with transgenic, malaria-resistant mosquitoes.</p> <p>Methods</p> <p>A laboratory population of <it>A. gambiae </it>males was tested for intra-specific variation in sperm length. A full-sib quantitative genetic design was used to test for a genetic component of sperm length in <it>A. gambiae </it>males and estimate its heritability. This study also tested for a relationship between sperm length and male reproductive success in <it>A. gambiae</it>. Male reproductive success was measured as the proportions of inseminated and ovipositing females.</p> <p>Results</p> <p>There was intra-specific variation of sperm length in <it>A. gambiae</it>. There was no significant genetic variation in sperm length and its heritability was low (h²= 0.18) compared to other insects. Sperm length was correlated with male body size (measured as wing length). Males with short sperm had significantly higher reproductive success than males with long sperm and this was independent of body size.</p> <p>Conclusion</p> <p>This is the first study to demonstrate intra-specific variation in sperm length in <it>A. gambiae </it>and that males with short sperm have higher reproductive success. That sperm length influences female oviposition is important for any strategy considering the release of transgenic males.</p

Comparison of male reproductive success in malaria-refractory and susceptible strains of Anopheles gambiae

<p>Abstract</p> <p>Background</p> <p>In female mosquitoes that transmit malaria, the benefits of being refractory to the <it>Plasmodium </it>parasite are balanced by the immunity costs in the absence of infection. Male mosquitoes, however, gain no advantage from being refractory to blood-transmitted parasites, so that any costs associated with an enhanced immune system in the males limit the evolution of female refractoriness and has practical implications for the release of transgenic males.</p> <p>Methods</p> <p>Aspects of the male cost of carrying <it>Plasmodium</it>-refractory genes were estimated by comparing the males' immune response and reproductive success among strains of <it>Anopheles gambiae </it>that had been selected for refractoriness or extreme susceptibility to the rodent malaria parasite, <it>Plasmodium yoelii nigeriensis</it>. The refractory males had a stronger melanization response than males from the susceptible line. Four traits were used as correlates of a male's reproductive success: the proportion of females that were inseminated by a fixed number of males in a cage within a fixed time frame, the proportion of females with motile sperm in their spermathecae, the proportion of ovipositing females, and the mean number of eggs per batch.</p> <p>Results</p> <p>Although there were significant differences among groups of males in sperm motility and oviposition success, these differences in male reproductive success were not associated with the refractory or susceptible male genotypes. Contrary to expectation, females mated to early emerging refractory males laid significantly more eggs per batch than females mated to later emerging susceptible males. Sperm motility and oviposition success were strongly correlated suggesting that variation in sperm motility influences female oviposition and ultimately male reproductive success.</p> <p>Conclusion</p> <p>An increased melanization response in male <it>A. gambiae </it>does not diminish male reproductive success under the experimental protocol used in this study. That refractory males induced ovipositing females to lay more eggs than susceptible males is an interesting result for any strategy considering the release of transgenic males. That sperm motility influences female oviposition is also important for the release of transgenic males.</p

Genetic variation of male reproductive success in a laboratory population of Anopheles gambiae

<p>Abstract</p> <p>Background</p> <p>For Anopheline mosquitoes, the vectors of human malaria, genetic variation in male reproductive success can have important consequences for any control strategy based on the release of transgenic or sterile males.</p> <p>Methods</p> <p>A quantitative genetics approach was used to test whether there was a genetic component to variation in male reproductive success in a laboratory population of <it>Anopheles gambiae</it>. Swarms of full sibling brothers were mated with a fixed number of females and their reproductive success was measured as (1) proportion of ovipositing females, (2) proportion of ovipositing females that produced larvae, (3) proportion of females that produced larvae, (4) number of eggs laid per female, (5) number of larvae per ovipositing female and (6) number of larvae per female.</p> <p>Results</p> <p>The proportion of ovipositing females (trait 1) and the proportion of ovipositing females that produced larvae (trait 2) differed among full sib families, suggesting a genetic basis of mating success. In contrast, the other measures of male reproductive success showed little variation due to the full sib families, as their variation are probably mostly due to differences among females. While age at emergence and wing length of the males were also heritable, they were not associated with reproductive success. Larger females produced more eggs, but males did not prefer such partners.</p> <p>Conclusion</p> <p>The first study to quantify genetic variation for male reproductive success in <it>A. gambiae </it>found that while the initial stages of male reproduction (i.e. the proportion of ovipositing females and the proportion of ovipositing females that produced larvae) had a genetic basis, the overall reproductive success (i.e. the mean number of larvae per female) did not.</p