Many insects experience a decrease in reproductive output when parasitised. We are investigating ... more Many insects experience a decrease in reproductive output when parasitised. We are investigating mechanisms underlying this fecundity reduction using the rat tapeworm, Hymenolepis diminuta infection of Tenebrio molitor beetles. These include an increase in the resorption of developing ovarian follicles and a decrease in fat body synthesis of vitellogenin. The latter is the direct effect of a molecule produced by the parasite. Here we report a study to determine whether vitellogenin synthesis and follicle resorption are the result of parasite-induced apoptosis in the respective tissues and whether the parasite molecule acts directly on the fat body by inducing apoptosis. In vivo, the number of fat body cell nuclei with chromatin condensation are significantly elevated in parasitised females at all days examined and peaked at day 7 post-infection. A TUNEL assay to detect DNA fragmentation confirmed these observations of apoptosis. However, when fat body from uninfected females was co-cultured with live metacestodes they did not cause cells to die by apoptosis, showing that the induction signal does not come directly from the parasite. The follicle resorption observed in the ovaries of infected beetles was not associated with apoptosis of the epithelial cells. The possibility of several mechanisms underlying fecundity reduction is discussed.
It is probably a truism to say that what seems to be a single organism is, in fact, an assemblage... more It is probably a truism to say that what seems to be a single organism is, in fact, an assemblage of organisms – for there can hardly be an individual living outside a specialized laboratory that does not have commensals or parasites living within. The insects, the most diverse and numerous group of organisms on earth are no exception, and with micro- and macro-parasites from a wide range of taxa generate a remarkable range of interspecific associations. In some cases the insect is the sole host, in others it is an intermediate host or vector. It is the latter relationship which attracts much attention when insects and arachnids transmit infectious agents to humans, their animals or crops. Knowledge of the parasites of insects provides us with an opportunity to develop novel control methods for pests. Despite the diverse and widespread nature of insect infections, their impact on human well-being and the opportunity they give us to understand the complexity of the natural world, the...
It has been shown previously that infection with Plasmodium yoelii nigeriensis reduces the number... more It has been shown previously that infection with Plasmodium yoelii nigeriensis reduces the number of eggs produced by female Anopheles stephensi. Here we examine the mechanism underlying fecundity reduction. Ovaries from infected and uninfected (control) female mosquitoes were examined 12, 24 or 36 h after blood-feeding during the first gonotrophic cycle (replicated) or the second gonotrophic cycle (unreplicated). Follicular development was assessed according to Christophers' stages and the proportions of developing and resorbing follicles per ovary were determined. Resorption of some follicles commenced within 12 h of blood-feeding, affecting significantly more follicles in the infected females: 1.1% v. 3.2%. The difference was greatest 36 h after blood-feeding: 25% reduction (10 v. 35%) in the first cycle; 16% reduction (9 v. 25%) in the second gonotrophic cycle. The mean speed of oogenesis was also found to be significantly retarded in infected mosquitoes. During the second gonotrophic cycle, for example, only 92-94% of follicles reached stage III by 24 h and stage IV by 36 h in infected females, whereas all the developing follicles of uninfected females reached these stages more or less synchronously in the time specified.
Many insects experience a decrease in reproductive output when parasitised. We are investigating ... more Many insects experience a decrease in reproductive output when parasitised. We are investigating mechanisms underlying this fecundity reduction using the rat tapeworm, Hymenolepis diminuta infection of Tenebrio molitor beetles. These include an increase in the resorption of developing ovarian follicles and a decrease in fat body synthesis of vitellogenin. The latter is the direct effect of a molecule produced by the parasite. Here we report a study to determine whether vitellogenin synthesis and follicle resorption are the result of parasite-induced apoptosis in the respective tissues and whether the parasite molecule acts directly on the fat body by inducing apoptosis. In vivo, the number of fat body cell nuclei with chromatin condensation are significantly elevated in parasitised females at all days examined and peaked at day 7 post-infection. A TUNEL assay to detect DNA fragmentation confirmed these observations of apoptosis. However, when fat body from uninfected females was co-cultured with live metacestodes they did not cause cells to die by apoptosis, showing that the induction signal does not come directly from the parasite. The follicle resorption observed in the ovaries of infected beetles was not associated with apoptosis of the epithelial cells. The possibility of several mechanisms underlying fecundity reduction is discussed.
It is probably a truism to say that what seems to be a single organism is, in fact, an assemblage... more It is probably a truism to say that what seems to be a single organism is, in fact, an assemblage of organisms – for there can hardly be an individual living outside a specialized laboratory that does not have commensals or parasites living within. The insects, the most diverse and numerous group of organisms on earth are no exception, and with micro- and macro-parasites from a wide range of taxa generate a remarkable range of interspecific associations. In some cases the insect is the sole host, in others it is an intermediate host or vector. It is the latter relationship which attracts much attention when insects and arachnids transmit infectious agents to humans, their animals or crops. Knowledge of the parasites of insects provides us with an opportunity to develop novel control methods for pests. Despite the diverse and widespread nature of insect infections, their impact on human well-being and the opportunity they give us to understand the complexity of the natural world, the...
It has been shown previously that infection with Plasmodium yoelii nigeriensis reduces the number... more It has been shown previously that infection with Plasmodium yoelii nigeriensis reduces the number of eggs produced by female Anopheles stephensi. Here we examine the mechanism underlying fecundity reduction. Ovaries from infected and uninfected (control) female mosquitoes were examined 12, 24 or 36 h after blood-feeding during the first gonotrophic cycle (replicated) or the second gonotrophic cycle (unreplicated). Follicular development was assessed according to Christophers' stages and the proportions of developing and resorbing follicles per ovary were determined. Resorption of some follicles commenced within 12 h of blood-feeding, affecting significantly more follicles in the infected females: 1.1% v. 3.2%. The difference was greatest 36 h after blood-feeding: 25% reduction (10 v. 35%) in the first cycle; 16% reduction (9 v. 25%) in the second gonotrophic cycle. The mean speed of oogenesis was also found to be significantly retarded in infected mosquitoes. During the second gonotrophic cycle, for example, only 92-94% of follicles reached stage III by 24 h and stage IV by 36 h in infected females, whereas all the developing follicles of uninfected females reached these stages more or less synchronously in the time specified.
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Papers by Hilary Hurd