Fecundity-Longevity Trade-Off, Vertical Transmission, and Evolution of Virulence in Sterilizing Pathogens

SUMMARYUnderstanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. This study therefore examined variation between parasite isolates (the bacterium Pasteuria ramosa) from the crustacean Daphnia magna. From a single wild-caught infected host we obtained 2 P. ramosa isolates that differed substantially in the mortality they caused. Surprisingly, the isolate causing higher early mortality was, on average, less successful at establishing infections and had a slower growth rate within hosts. The observation that within-host replication rate was negatively correlated with mortality could violate a central assumption of the trade-off hypothesis for the evolution of virulence, but we discuss a number of caveats which caution against premature rejection of the trade-off hypothesis. We sought to test if the characteristics of these parasite isolates were constant across host genotypes in a second experiment that included 2 Daphnia host clones. The relative growth rates of the two parasite isolates did indeed depend on the host genotype (although the rank order did not change). We suggest that testing evolutionary hypotheses for virulence may require substantial sampling of both host and parasite genetic variation, and discuss how selection for virulence may change with the epidemiological state of natural populations and how this can promote genetic variation for virulence.

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Detection, not mortality, constrains the evolution of virulence

10.1101/2021.11.14.468516 ◽

2021 ◽

Author(s):

David A Kennedy

Keyword(s):

Mathematical Model ◽

Disease Severity ◽

Behavioral Change ◽

Scientific Literature ◽

Empirical Support ◽

Infectious Period ◽

Trade Off ◽

Evolution Of Virulence ◽

Host Mortality

Why would a pathogen evolve to kill its hosts when killing a host ends a pathogen's own opportunity for transmission? A vast body of scientific literature has attempted to answer this question using "trade-off theory," which posits that host mortality persists due to its cost being balanced by benefits of other traits that correlate with host mortality. The most commonly invoked trade-off is the mortality-transmission trade-off, where increasingly harmful pathogens are assumed to transmit at higher rates from hosts while the hosts are alive, but the pathogens truncate their infectious period by killing their hosts. Here I show that costs of mortality are too small to plausibly constrain the evolution of disease severity except in systems where survival is rare. I alternatively propose that disease severity can be much more readily constrained by a cost of behavioral change due to the detection of infection, whereby increasingly harmful pathogens have increasing likelihood of detection and behavioral change following detection, thereby limiting opportunities for transmission. Using a mathematical model, I show the conditions under which detection can limit disease severity. Ultimately, this argument may explain why empirical support for trade-off theory has been limited and mixed.

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WITHIN-HOST PARASITE DYNAMICS, EMERGING TRADE-OFF, AND EVOLUTION OF VIRULENCE WITH IMMUNE SYSTEM

Evolution ◽

10.1554/02-667 ◽

2003 ◽

Vol 57 (7) ◽

pp. 1489 ◽

Cited By ~ 4

Author(s):

Jean-Baptiste André ◽

Jean-Baptiste Ferdy ◽

Bernard Godelle

Keyword(s):

Immune System ◽

Trade Off ◽

Evolution Of Virulence ◽

Host Parasite ◽

Parasite Dynamics

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Evolution of symbiont transmission in conditional mutualisms in spatially and temporally variable environments

10.1101/2020.05.05.079103 ◽

2020 ◽

Author(s):

Alexandra Brown ◽

Erol Akçay

Keyword(s):

Vertical Transmission ◽

Horizontal Transmission ◽

Environmental Variation ◽

Transmission Mode ◽

Trade Off ◽

Symbiotic Relationships ◽

Physiological Constraints ◽

Fitness Effects ◽

Variable Environments ◽

Symbiont Transmission

AbstractSymbiotic relationships affect the fitness and organismal function of virtually all organisms. In many cases, the fitness effects of symbiosis may be beneficial or harmful depending on the environment. The hosts of such symbionts are favored to acquire them only when the symbiont is beneficial. However, it is not clear whether such selection favors vertical or horizontal transmission, both, or neither. To address this question, we model the evolution of transmission mode in a conditional mutualism experiencing spatial and temporal environmental variation. We find that when symbionts affect host lifespan, but not fecundity, horizontal transmission can contain them to beneficial environments. Vertical transmission can produce symbiont containment when the environmental state is synchronized across locations. We also find an emergent trade-off between horizontal and vertical transmission, suggesting that physiological constraints are not required for the evolution of limits on the total amount of transmission.

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Challenging the trade-off model for the evolution of virulence: is virulence management feasible?

Trends in Microbiology ◽

10.1016/s0966-842x(02)00003-3 ◽

2003 ◽

Vol 11 (1) ◽

pp. 15-20 ◽

Cited By ~ 203

Author(s):

Dieter Ebert ◽

James J. Bull

Keyword(s):

Trade Off ◽

Evolution Of Virulence

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Competition–colonization trade-off promotes coexistence of low-virulence viral strains

Journal of The Royal Society Interface ◽

10.1098/rsif.2012.0160 ◽

2012 ◽

Vol 9 (74) ◽

pp. 2244-2254 ◽

Cited By ~ 4

Author(s):

Samuel Ojosnegros ◽

Edgar Delgado-Eckert ◽

Niko Beerenwinkel

Keyword(s):

Rna Viruses ◽

Rna Virus ◽

Diverse Populations ◽

Trade Off ◽

Virulent Strains ◽

Evolution Of Virulence ◽

Virulence Attenuation ◽

Fast Spreading ◽

Infected Cells ◽

Virus Clone

RNA viruses exist as genetically diverse populations displaying a range of virulence degrees. The evolution of virulence in viral populations is, however, poorly understood. On the basis of the experimental observation of an RNA virus clone in cell culture diversifying into two subpopulations of different virulence, we study the dynamics of mutating virus populations with varying virulence. We introduce a competition–colonization trade-off into standard mathematical models of intra-host viral infection. Colonizers are fast-spreading virulent strains, whereas the competitors are less-virulent variants but more successful within co-infected cells. We observe a two-step dynamics of the population. Early in the infection, the population is dominated by colonizers, which later are outcompeted by competitors. Our simulations suggest the existence of steady state in which all virulence classes coexist but are dominated by the most competitive ones. This equilibrium implies collective virulence attenuation in the population, in contrast to previous models predicting evolution of the population towards increased virulence.

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