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Lorenzo Sacconi - One of the best experts on this subject based on the ideXlab platform.
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corporate social responsibility csr as a model of extended corporate governance an explanation based on the economic theories of social contract reputation and reciprocal Conformism
LIUC Papers in Ethics Law and Economics, 2004Co-Authors: Lorenzo SacconiAbstract:This paper first sets a definition of corporate social responsibility (CSR) as an extended model of corporate governance and then accounts for a voluntary approach to CSR, meant as voluntary compliance with CSR strategic management standards, in terms of an economic theory of self-regulation based on the concepts of social contract, reputation and reciprocal Conformism. The paper argues that extended fiduciary duties toward all the firm's stakeholders are needed because of the same neo-institutional analysis of the firm that justifies it as a unified system of governance of economic transactions based on authority relations and residual rights of control. The key concept here is that of abuse of firm's authority vis-a-vis the stakeholders who hold incomplete contracts with the firm. Extended fiduciary duties are singled out from the model of a Social Contract amongst the firm's stakeholders. This provide for a clear cut and calculable criterion of strategic management no less able to set a bottom-line to the firm management than the profit maximisation principle, while being able of answering legitimate claims of fair treatment from all the firm's stakeholders. Such a task is accomplished by an application of the theory of bargaining games to the Social Contract of the firm, which employs the Nash-Harsanyi bargaining solution as a normative criterion for strategic management and corporate governance, providing an answer to the deficit of uniqueness problem raised by Michael Jensen (2001) against the notion of stakeholders value. Then, the paper distinguishes two models of self regulation (the discretionary one, and the explicit-norms-cum-self-enforcement one) and argues that while incomplete contracts and imperfect knowledge debar form resorting to reputation effects in order to support discretional self-regulation, on the contrary an explicit standard for CSR strategic management, based on general and abstract business ethics principles and precautionary protocols and rules of behaviour - both publicly shared by stakeholders and firms through social dialog - make possible to put again at work the reputation mechanism inducing endogenous incentives of compliance with a voluntary standard. The paper here suggests how (by both fuzzy logic and default reasoning ) a CSR Strategic Management Standard may work as a cognitive gap filling tool with respect to the firm's commitments and the stakeholders' expectations in presence of incomplete information. Moreover recent developments in the theory of conformist non-purely-self-interested preferences add motivational force to the basic result about self-enforcement of a CSR management standard. Hence, conformist preferences solve the problem of optimal mixed strategies that otherwise could enable the firm inducing the stakeholders to “trust” it without really conforming to a CSR standard. This result is given a formal proof in sec.11. The paper concludes with a collusion-proof design of intermediate social bodies (civil society institutions) that may answer the demand for assurance and external verifiability of CSR standards compliance by independent third-parties.
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corporate social responsibility csr as a model of extended corporate governance an explanation based on the economic theories of social contract reputation and reciprocal Conformism
Social Science Research Network, 2004Co-Authors: Lorenzo SacconiAbstract:This paper first sets a definition of corporate social responsibility (CSR) as an extended model of corporate governance and then accounts for a voluntary approach to CSR, meant as voluntary compliance with CSR strategic management standards, in terms of an economic theory of self-regulation based on the concepts of social contract, reputation and reciprocal Conformism. The paper argues that extended fiduciary duties toward all the firm's stakeholders are needed because of the same neo-institutional analysis of the firm that justifies it as a unified system of governance of economic transactions based on authority relations and residual rights of control. The key concept here is that of abuse of firm's authority vis-a-vis the stakeholders who hold incomplete contracts with the firm. Extended fiduciary duties are singled out from the model of a Social Contract amongst the firm's stakeholders. This provide for a clear cut and calculable criterion of strategic management no less able to set a bottom-line to the firm management than the profit maximisation principle, while being able of answering legitimate claims of fair treatment from all the firm's stakeholders. Such a task is accomplished by an application of the theory of bargaining games to the Social Contract of the firm, which employs the Nash-Harsanyi bargaining solution as a normative criterion for strategic management and corporate governance, providing an answer to the deficit of uniqueness problem raised by Michael Jensen (2001) against the notion of stakeholders value. Then, the paper distinguishes two models of self regulation (the discretionary one, and the explicit-norms-cum-self-enforcement one) and argues that while incomplete contracts and imperfect knowledge debar form resorting to reputation effects in order to support discretional self-regulation, on the contrary an explicit standard for CSR strategic management, based on general and abstract business ethics principles and precautionary protocols and rules of behaviour - both publicly shared by stakeholders and firms through social dialog - make possible to put again at work the reputation mechanism inducing endogenous incentives of compliance with a voluntary standard. The paper here suggests how (by both fuzzy logic and default reasoning) a CSR Strategic Management Standard may work as a cognitive gap filling tool with respect to the firm's commitments and the stakeholders' expectations in presence of incomplete information. Moreover recent developments in the theory of conformist non-purely-self-interested preferences add motivational force to the basic result about self-enforcement of a CSR management standard. Hence, conformist preferences solve the problem of optimal mixed strategies that otherwise could enable the firm inducing the stakeholders to "trust" it without really conforming to a CSR standard. This result is given a formal proof in sec.11. The paper concludes with a collusion-proof design of intermediate social bodies (civil society institutions) that may answer the demand for assurance and external verifiability of CSR standards compliance by independent third.
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the constitution of the nonprofit enterprise ideals Conformism and reciprocity
LIUC Papers in Ethics Law and Economics, 2002Co-Authors: Gianluca Grimalda, Lorenzo SacconiAbstract:We provide an account of the non profit enterprise based on the motivations of the agents involved. Our main idea is that these are ex -post motivated by both self-interest and a conditional willingness to conform to their ex ante accepted constitutional ideology, which are weighed up in a comprehensive utility function. Ideology is shaped as the result of a hypothetical ‘social' contract between the relevant figures participating in the venture, in particular an entrepreneur, a worker, and a consumer who acts as a dummy beneficiary in the ex-post stage. It can thus be defined as a normative principle of fairness that boils down to a distributive social welfare function defined over the outcomes of a game, which permits to order them according to their conformity to the constitutional ideology. For conformist preferences depend upon expectations of reciprocal conformity to a normative principle, defined on social states described in as much they conform to an ideal, then the agents' model of choice asks for the adoption of the psychological games approach, where payoff functions range over not only the players' strategies but also their beliefs. If the conformist prompt to action is sufficiently strong then the outcome in which both the active agents perform an action improving the quality of the good with respect to the free market standard, thus maximising the surplus of the consumers, results in a psychological Nash equilibrium of the game. We associate this outcome, and the corresponding norm of behaviour, with the constitution of the non profit enterprise. We also show that the structure of the interaction is a coordination game, thus calling for the necessity of devices such as codes of ethics to solve the coordination problem. Keywords: Nonprofit, non-self-interested motivations, Conformism, reciprocity, ideology.
Boris R Krasnov - One of the best experts on this subject based on the ideXlab platform.
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evidence for a negative fitness density relationship between parent density and offspring quality for two xenopsylla spp parasitic on desert mammals
Medical and Veterinary Entomology, 2008Co-Authors: Boris R Krasnov, A Hovhanyan, Irina S. Khokhlova, Allan A DegenAbstract:: We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.
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fitness consequences of host selection in ectoparasites testing reproductive patterns predicted by isodar theory in fleas parasitizing rodents
Journal of Animal Ecology, 2004Co-Authors: Boris R Krasnov, Nadezhda V Burdelova, Irina S. Khokhlova, Natella Mirzoyan, Allan A DegenAbstract:Summary 1 Fleas Xenopsylla conformis and Xenopsylla ramesis parasitize the rodents Meriones crassus and Gerbillus dasyurus. Previously reported isodar analysis of host selection suggested that at low density, X. conformis parasitizes M. crassus only, but with an increase in flea density, G. dasyurus is also parasitized. Xenopsylla ramesis at low density parasitizes both hosts equally, whereas at high density prefers M. crassus. The ultimate cause of underlying these patterns was suggested to be differential fitness reward of parasitism on a particular host species, while the mechanism can be adaptive host selection by fleas. 2 To justify the suggested fitness–density relations, we studied reproductive success in X. conformis and X. ramesis feeding on either M. crassus or G. dasyurus. We hypothesized that reproductive success would differ between two host species for each flea species. 3 Xenopsylla conformis parasitizing M. crassus produced more eggs than when parasitizing G. dasyurus, whereas time of oviposition and larval hatching did not depend on host species. In contrast, egg production in X. ramesis did not differ between host species. However, fleas fed on M. crassus needed fewer bloodmeals, oviposited earlier and hatching of their larvae took less time than those of fleas fed on G. dasyurus. 4 Patterns of egg production and development time in both fleas were consistent with the hypothesis that their between-host distribution arose from adaptive host selection strategy.
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water balance in two species of desert fleas xenopsylla ramesis and x conformis siphonaptera pulicidae
Journal of Medical Entomology, 2002Co-Authors: Laura J Fielden, Boris R Krasnov, Kelly M Still, Irina S. KhokhlovaAbstract:The role of water balance capabilities of seas was examined in desert habitats. The seas studied were Xenopsylla ramesis Rothschild and Xenopsylla conformis Wagner. Both seas occur on SundevallOs jird, Meriones crassus, in the Negev Highlands of Israel but in different macro- and microhabitats. Because M. crassus occurs in several habitats of the highlands, it was used as a model for investigating the effect of habitat parameters on species composition of seas within a host species. Water balance parameters investigated were the range of humidities over which active water uptake occurs in the larvae and prepupae of X. ramesis and X. conformis. Critical equilibrium humidity estimates were close to 65% RH for larvae and prepupae of both species. Water loss rates were determined for each life stage, except eggs, and represented water loss from cuticular, respiratory, and other body openings) under conditions of little or no bulk air movement. When converted to a proportional rate (1.44 Ð2.37% mass loss h 1 ) water loss rates did not differ signiÞcantly between stages or species. Thus, geographic separation of X. ramesis and X. conformis could not be explained by any difference in water uptake capabilities or water loss rates. Other factors that may be important include interspeciÞc competition for resource availability among larval seas and effect of soil texture on cocoon construction.
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time of survival under starvation in two flea species siphonaptera pulicidae at different air temperatures and relative humidities
Journal of Vector Ecology, 2002Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:We studied the effect of air temperature and RH on the survival time of adult Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904 fleas during starvation to explain the paratopic habitat distribution of these species on opposite ends of a precipitation and temperature gradient in the Negev Highlands, Israel. We hypothesized that the pattern of distribution of the two flea species is caused by differential microclimatic preferences of imagoes and predicted that (1) the resistance to starvation would differ between the two flea species at different air temperatures (10 o C-38 o C) and relative humidities (RH) (40%-92%) and (2) survival time of starving X. conformis would be longer than that of starving X. ramesis at high air temperatures and low RHs. Survival time of newly emerged X. conformis was dependent on air temperature but not on RH, whereas in newly emerged X. ramesis it was affected by both air temperature and RH. Generally, survival time of newly emerged fleas was longer at lower air temperatures and higher humidities than at higher air temperatures and lower humidities. No significant difference in survival time between species in dependence on either air temperature or RH were found for newly emerged fleas. Fed fleas of both species responded similarly to changes in air temperature and RH in terms of survival time. Survival time at lower temperatures was longer than that at higher temperatures. Females survived longer than males at all air temperatures except for the highest temperature when the survival time of both sexes was similarly low. In both species, the effect of RH on survival time was significant at the highest RH only, with a decrease in survival time at 92% RH. In contrast, survival times at lower RHs did not differ. Males of both species survived for less time than females at all RHs. X. conformis generally survived for less time than X. ramesis, all else being equal. The only regime at which X. conformis survived longer than X. ramesis was 38 o C
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development rates of two xenopsylla flea species in relation to air temperature and humidity
Medical and Veterinary Entomology, 2001Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:Abstract. The rate of development of immature fleas, Xenopsylla conformisWagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) wasstudied in the laboratory at 25°C and 28°C with 40, 55, 75 and 92% relativehumidity (RH). These fleas are separately associated with the host jird Merionescrassus Sundevall in different microhabitats of the Ramon erosion cirque, NegevHighlands, Israel. This study of basic climatic factors in relation to flea bionomicsprovides the basis for ecological investigations to interpret reasons for paratopiclocal distributions of these two species of congeneric fleas on the same host. Bothair temperature and RH were positively correlated with duration of egg and larvalstages in both species. Change of humidity between egg and larval environmentsdid not affect duration of larval development at any temperature. At eachtemperature and RH, the eggs and larvae of X. ramesis did not differ betweenmales and females in the duration of their development, whereas female eggs andlarvae of X. conformis usually developed significantly faster than those of males.For both species, male pupae developed slower than female pupae at the same airtemperature and RH. Air temperature, but not RH, affected the duration of pupaldevelopment. At each humidity, duration of the pupal stage was significantly longerat 25°C than at 28°C: 15.3 6 1.7 vs. 11.7 6 1.2 days in X. conformis; 14.1 6 2.0vs. 11.5 6 1.7 days in X. ramesis, with a significantly shorter pupal period of thelatter species at 25°C. These limited interspecific bionomic contrasts in relation tobasic climatic factors appear insufficient to explain the differential habitatdistributions of X. conformis and X. ramesisKey words. Meriones crassus, Xenopsylla conformis, X. ramesis, developmentrate, eggs, females, jird, larvae, males, pupae, relative humidity, temperature,Negev, Israel.
Pierre M. Picard - One of the best experts on this subject based on the ideXlab platform.
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Effect of Conformism on firm selection, product quality and home bias
Journal of Economic Behavior & Organization, 2021Co-Authors: Sergey Kichko, Pierre M. PicardAbstract:Abstract This paper discusses the effect of Conformism on the demand for products that differ in quality and studies its implications for firm selection, entry, average quality, and trade patterns. Demand for each variety is shown to fall when consumers have a lower degree of Conformism or when the distribution of Conformism becomes more concentrated. This induces firms facing lower demand and of lower quality to exit the market, which raises average quality and diminishes product diversity. In an international trade context, home consumption bias is amplified when there is a lower degree of Conformism. Home consumption bias is mitigated by the presence of global Conformism, in which individuals tend to conform to people across the world rather than within their own country.
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heterogeneity in Conformism firm selection and home bias
Social Science Research Network, 2018Co-Authors: Sergey Kichko, Pierre M. PicardAbstract:This paper discusses the impact of Conformism on product quality, firm selection, and trade patterns. It shows that when consumers have a higher degree of Conformism and/or their distribution of Conformism becomes more concentrated, the equilibrium average demand falls while product quality rises in a closed economy. In an international trade context, this strengthens the home consumption bias when consumers conform to the behavior of local people. The home bias is mitigated under globalization where individuals tend to conform to people worldwide. The paper also discusses the conditions under which Conformism and conspicuousness are reconciled.
Irina S. Khokhlova - One of the best experts on this subject based on the ideXlab platform.
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evidence for a negative fitness density relationship between parent density and offspring quality for two xenopsylla spp parasitic on desert mammals
Medical and Veterinary Entomology, 2008Co-Authors: Boris R Krasnov, A Hovhanyan, Irina S. Khokhlova, Allan A DegenAbstract:: We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.
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fitness consequences of host selection in ectoparasites testing reproductive patterns predicted by isodar theory in fleas parasitizing rodents
Journal of Animal Ecology, 2004Co-Authors: Boris R Krasnov, Nadezhda V Burdelova, Irina S. Khokhlova, Natella Mirzoyan, Allan A DegenAbstract:Summary 1 Fleas Xenopsylla conformis and Xenopsylla ramesis parasitize the rodents Meriones crassus and Gerbillus dasyurus. Previously reported isodar analysis of host selection suggested that at low density, X. conformis parasitizes M. crassus only, but with an increase in flea density, G. dasyurus is also parasitized. Xenopsylla ramesis at low density parasitizes both hosts equally, whereas at high density prefers M. crassus. The ultimate cause of underlying these patterns was suggested to be differential fitness reward of parasitism on a particular host species, while the mechanism can be adaptive host selection by fleas. 2 To justify the suggested fitness–density relations, we studied reproductive success in X. conformis and X. ramesis feeding on either M. crassus or G. dasyurus. We hypothesized that reproductive success would differ between two host species for each flea species. 3 Xenopsylla conformis parasitizing M. crassus produced more eggs than when parasitizing G. dasyurus, whereas time of oviposition and larval hatching did not depend on host species. In contrast, egg production in X. ramesis did not differ between host species. However, fleas fed on M. crassus needed fewer bloodmeals, oviposited earlier and hatching of their larvae took less time than those of fleas fed on G. dasyurus. 4 Patterns of egg production and development time in both fleas were consistent with the hypothesis that their between-host distribution arose from adaptive host selection strategy.
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water balance in two species of desert fleas xenopsylla ramesis and x conformis siphonaptera pulicidae
Journal of Medical Entomology, 2002Co-Authors: Laura J Fielden, Boris R Krasnov, Kelly M Still, Irina S. KhokhlovaAbstract:The role of water balance capabilities of seas was examined in desert habitats. The seas studied were Xenopsylla ramesis Rothschild and Xenopsylla conformis Wagner. Both seas occur on SundevallOs jird, Meriones crassus, in the Negev Highlands of Israel but in different macro- and microhabitats. Because M. crassus occurs in several habitats of the highlands, it was used as a model for investigating the effect of habitat parameters on species composition of seas within a host species. Water balance parameters investigated were the range of humidities over which active water uptake occurs in the larvae and prepupae of X. ramesis and X. conformis. Critical equilibrium humidity estimates were close to 65% RH for larvae and prepupae of both species. Water loss rates were determined for each life stage, except eggs, and represented water loss from cuticular, respiratory, and other body openings) under conditions of little or no bulk air movement. When converted to a proportional rate (1.44 Ð2.37% mass loss h 1 ) water loss rates did not differ signiÞcantly between stages or species. Thus, geographic separation of X. ramesis and X. conformis could not be explained by any difference in water uptake capabilities or water loss rates. Other factors that may be important include interspeciÞc competition for resource availability among larval seas and effect of soil texture on cocoon construction.
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time of survival under starvation in two flea species siphonaptera pulicidae at different air temperatures and relative humidities
Journal of Vector Ecology, 2002Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:We studied the effect of air temperature and RH on the survival time of adult Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904 fleas during starvation to explain the paratopic habitat distribution of these species on opposite ends of a precipitation and temperature gradient in the Negev Highlands, Israel. We hypothesized that the pattern of distribution of the two flea species is caused by differential microclimatic preferences of imagoes and predicted that (1) the resistance to starvation would differ between the two flea species at different air temperatures (10 o C-38 o C) and relative humidities (RH) (40%-92%) and (2) survival time of starving X. conformis would be longer than that of starving X. ramesis at high air temperatures and low RHs. Survival time of newly emerged X. conformis was dependent on air temperature but not on RH, whereas in newly emerged X. ramesis it was affected by both air temperature and RH. Generally, survival time of newly emerged fleas was longer at lower air temperatures and higher humidities than at higher air temperatures and lower humidities. No significant difference in survival time between species in dependence on either air temperature or RH were found for newly emerged fleas. Fed fleas of both species responded similarly to changes in air temperature and RH in terms of survival time. Survival time at lower temperatures was longer than that at higher temperatures. Females survived longer than males at all air temperatures except for the highest temperature when the survival time of both sexes was similarly low. In both species, the effect of RH on survival time was significant at the highest RH only, with a decrease in survival time at 92% RH. In contrast, survival times at lower RHs did not differ. Males of both species survived for less time than females at all RHs. X. conformis generally survived for less time than X. ramesis, all else being equal. The only regime at which X. conformis survived longer than X. ramesis was 38 o C
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development rates of two xenopsylla flea species in relation to air temperature and humidity
Medical and Veterinary Entomology, 2001Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:Abstract. The rate of development of immature fleas, Xenopsylla conformisWagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) wasstudied in the laboratory at 25°C and 28°C with 40, 55, 75 and 92% relativehumidity (RH). These fleas are separately associated with the host jird Merionescrassus Sundevall in different microhabitats of the Ramon erosion cirque, NegevHighlands, Israel. This study of basic climatic factors in relation to flea bionomicsprovides the basis for ecological investigations to interpret reasons for paratopiclocal distributions of these two species of congeneric fleas on the same host. Bothair temperature and RH were positively correlated with duration of egg and larvalstages in both species. Change of humidity between egg and larval environmentsdid not affect duration of larval development at any temperature. At eachtemperature and RH, the eggs and larvae of X. ramesis did not differ betweenmales and females in the duration of their development, whereas female eggs andlarvae of X. conformis usually developed significantly faster than those of males.For both species, male pupae developed slower than female pupae at the same airtemperature and RH. Air temperature, but not RH, affected the duration of pupaldevelopment. At each humidity, duration of the pupal stage was significantly longerat 25°C than at 28°C: 15.3 6 1.7 vs. 11.7 6 1.2 days in X. conformis; 14.1 6 2.0vs. 11.5 6 1.7 days in X. ramesis, with a significantly shorter pupal period of thelatter species at 25°C. These limited interspecific bionomic contrasts in relation tobasic climatic factors appear insufficient to explain the differential habitatdistributions of X. conformis and X. ramesisKey words. Meriones crassus, Xenopsylla conformis, X. ramesis, developmentrate, eggs, females, jird, larvae, males, pupae, relative humidity, temperature,Negev, Israel.
Nadezhda V Burdelova - One of the best experts on this subject based on the ideXlab platform.
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fitness consequences of host selection in ectoparasites testing reproductive patterns predicted by isodar theory in fleas parasitizing rodents
Journal of Animal Ecology, 2004Co-Authors: Boris R Krasnov, Nadezhda V Burdelova, Irina S. Khokhlova, Natella Mirzoyan, Allan A DegenAbstract:Summary 1 Fleas Xenopsylla conformis and Xenopsylla ramesis parasitize the rodents Meriones crassus and Gerbillus dasyurus. Previously reported isodar analysis of host selection suggested that at low density, X. conformis parasitizes M. crassus only, but with an increase in flea density, G. dasyurus is also parasitized. Xenopsylla ramesis at low density parasitizes both hosts equally, whereas at high density prefers M. crassus. The ultimate cause of underlying these patterns was suggested to be differential fitness reward of parasitism on a particular host species, while the mechanism can be adaptive host selection by fleas. 2 To justify the suggested fitness–density relations, we studied reproductive success in X. conformis and X. ramesis feeding on either M. crassus or G. dasyurus. We hypothesized that reproductive success would differ between two host species for each flea species. 3 Xenopsylla conformis parasitizing M. crassus produced more eggs than when parasitizing G. dasyurus, whereas time of oviposition and larval hatching did not depend on host species. In contrast, egg production in X. ramesis did not differ between host species. However, fleas fed on M. crassus needed fewer bloodmeals, oviposited earlier and hatching of their larvae took less time than those of fleas fed on G. dasyurus. 4 Patterns of egg production and development time in both fleas were consistent with the hypothesis that their between-host distribution arose from adaptive host selection strategy.
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time of survival under starvation in two flea species siphonaptera pulicidae at different air temperatures and relative humidities
Journal of Vector Ecology, 2002Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:We studied the effect of air temperature and RH on the survival time of adult Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904 fleas during starvation to explain the paratopic habitat distribution of these species on opposite ends of a precipitation and temperature gradient in the Negev Highlands, Israel. We hypothesized that the pattern of distribution of the two flea species is caused by differential microclimatic preferences of imagoes and predicted that (1) the resistance to starvation would differ between the two flea species at different air temperatures (10 o C-38 o C) and relative humidities (RH) (40%-92%) and (2) survival time of starving X. conformis would be longer than that of starving X. ramesis at high air temperatures and low RHs. Survival time of newly emerged X. conformis was dependent on air temperature but not on RH, whereas in newly emerged X. ramesis it was affected by both air temperature and RH. Generally, survival time of newly emerged fleas was longer at lower air temperatures and higher humidities than at higher air temperatures and lower humidities. No significant difference in survival time between species in dependence on either air temperature or RH were found for newly emerged fleas. Fed fleas of both species responded similarly to changes in air temperature and RH in terms of survival time. Survival time at lower temperatures was longer than that at higher temperatures. Females survived longer than males at all air temperatures except for the highest temperature when the survival time of both sexes was similarly low. In both species, the effect of RH on survival time was significant at the highest RH only, with a decrease in survival time at 92% RH. In contrast, survival times at lower RHs did not differ. Males of both species survived for less time than females at all RHs. X. conformis generally survived for less time than X. ramesis, all else being equal. The only regime at which X. conformis survived longer than X. ramesis was 38 o C
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development rates of two xenopsylla flea species in relation to air temperature and humidity
Medical and Veterinary Entomology, 2001Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:Abstract. The rate of development of immature fleas, Xenopsylla conformisWagner and Xenopsylla ramesis Rothschild (Siphonaptera: Xenopsyllidae) wasstudied in the laboratory at 25°C and 28°C with 40, 55, 75 and 92% relativehumidity (RH). These fleas are separately associated with the host jird Merionescrassus Sundevall in different microhabitats of the Ramon erosion cirque, NegevHighlands, Israel. This study of basic climatic factors in relation to flea bionomicsprovides the basis for ecological investigations to interpret reasons for paratopiclocal distributions of these two species of congeneric fleas on the same host. Bothair temperature and RH were positively correlated with duration of egg and larvalstages in both species. Change of humidity between egg and larval environmentsdid not affect duration of larval development at any temperature. At eachtemperature and RH, the eggs and larvae of X. ramesis did not differ betweenmales and females in the duration of their development, whereas female eggs andlarvae of X. conformis usually developed significantly faster than those of males.For both species, male pupae developed slower than female pupae at the same airtemperature and RH. Air temperature, but not RH, affected the duration of pupaldevelopment. At each humidity, duration of the pupal stage was significantly longerat 25°C than at 28°C: 15.3 6 1.7 vs. 11.7 6 1.2 days in X. conformis; 14.1 6 2.0vs. 11.5 6 1.7 days in X. ramesis, with a significantly shorter pupal period of thelatter species at 25°C. These limited interspecific bionomic contrasts in relation tobasic climatic factors appear insufficient to explain the differential habitatdistributions of X. conformis and X. ramesisKey words. Meriones crassus, Xenopsylla conformis, X. ramesis, developmentrate, eggs, females, jird, larvae, males, pupae, relative humidity, temperature,Negev, Israel.
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effect of air temperature and humidity on the survival of pre imaginal stages of two flea species siphonaptera pulicidae
Journal of Medical Entomology, 2001Co-Authors: Boris R Krasnov, Laura J Fielden, Irina S. Khokhlova, Nadezhda V BurdelovaAbstract:The survival of immature fleas at 25 and 28°C and 40, 55, 75, and 92% RH was studied to test the hypothesis that the difference in microclimatic preferences determines habitat distribution of Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904. Survival of X. conformis eggs did not depend on either temperature or humidity or both, whereas eggs of X. ramesis survived significantly less at 40% RH than at higher humidities. No larva of either species survived at 40% RH at either temperature. Larval survival of both species at both temperature regimes was significantly lower at 55% humidity than at higher humidities. Maximal survival time of larvae that died before pupation depended on both temperature and humidity in both species. Change of humidity during early stages of the life cycle (from egg to larva) increased the maximal survival time in X. conformis larvae but decreased that in X. ramesis larvae. Pupal survival was higher at higher humidities independent of temperature. Survival of X. conformis pupae was lower than that of X. ramesis pupae when the relative humidity was low. Humidity change on later stages (from larva to cocoon) decreased X. conformis pupal survival and had no effect on X. ramesis pupal survival. The sex ratio of emerged adults was not affected by either temperature or humidity in both species. Changes in humidity between egg and larval environments significantly decreased the percentage of females in X. conformis emergence at 28°C.