Since the mid-1970s, most investigators have agreed that the 'bizarre'structures (here referred t... more Since the mid-1970s, most investigators have agreed that the 'bizarre'structures (here referred to as 'exaggerated'structures) of dinosaurs–for example, the horns and frills of ceratopsids, the crests of lambeosaurine hadrosaurids, the domes of pachycephalosaurs–functioned first and foremost as signalling and combat structures used in mate competition (Farlow & Dodson, 1975; Hopson, 1975; Molnar, 1977; Spassov, 1979; Ostrom & Wellnhoffer, 1986; Sampson, 1997, 2001; Dodson, Forster & Sampson, 2004).
Many host-parasite models assume that transmission increases linearly with host population densit... more Many host-parasite models assume that transmission increases linearly with host population density ('densitydependent transmission'), but various alternative transmission functions have been proposed in an effort to capture the complexity of real biological systems. The most common alternative (usually applied to sexually transmitted parasites) assumes instead that the rate at which hosts contact one another is independent of population density, leading to 'frequency-dependent'transmission.
Abstract The persistence of genetic variability in performance traits such as strength is surpris... more Abstract The persistence of genetic variability in performance traits such as strength is surprising given the directional selection that such traits experience, which should cause the fixation of the best genetic variants. One possible explanation is 'genic capture'which is usually considered as a candidate mechanism for the maintenance of high genetic variability in sexual signalling traits.
Summary 1. Animals raised in good environmental conditions are expected to have more resources to... more Summary 1. Animals raised in good environmental conditions are expected to have more resources to invest in immunity than those raised in poor conditions. Variation in immune activity and parasite resistance in response to changes in environmental temperature, population density and food quality have been shown in many invertebrate species.
1. Transgenerational effects of immune stimulation on offspring immunity are widely reported from... more 1. Transgenerational effects of immune stimulation on offspring immunity are widely reported from insects, but we know very little of how other aspects of the parental environment affect offspring immune reactivity. 2. We reared male and female moths Plodia interpunctella on either good-or poor-quality food and then also raised their offspring on one of the two diet qualities. We found strong transgenerational effects on immunity: in general, if only one parent received the poor diet, reductions in immunity were observed whether that parent was the mother or the father, and the lowest offspring immune reactivity was observed when both parents received the poor diet. 3. The mechanism behind these effects is not known, but they could be caused either by imprinting, whereby the parent gives the offspring a cue such as an epigenetic mark that changes the offspring phenotype, or by the mother allocating fewer resources to their offspring when the diet was poor. Two lines of evidence point towards imprinting: the strong paternal effects and the observation that the size of these effects was either unchanged or increased when the offspring were fed a good-quality diet themselves. 4. Weight was also reduced when either parent was fed a poor diet, except when both parents had a poor diet and the offspring were raised on good food, contrasting with the increased rates of obesity seen in vertebrates when either parent is raised on a restricted diet. 5. Overall, the effects of parental diet on offspring weight and immune reactivity are substantial and in some cases are equivalent to that of the diet that the offspring itself consumes.
Abstract In some cases male animals engage in aggressive contests for access to females, in other... more Abstract In some cases male animals engage in aggressive contests for access to females, in others they adopt more passive strategies and invest in traits that assist them in detecting females or in competing with rivals in other ways, such as sperm competition. One possible factor determining the fitness of these different strategies is population density. Theoretically, aggressive tactics should be found at intermediate population densities.
Geographic profiling (GP) was originally developed as a statistical tool in criminology, where it... more Geographic profiling (GP) was originally developed as a statistical tool in criminology, where it uses the spatial locations of linked crimes (for example murder, rape or arson) to identify areas that are most likely to include the offender's residence. The technique has been successful in this field, and is now widely used by police forces and investigative agencies around the world.
Abstract Sexually selected ornaments and weapons are exceptionally variable, even between closely... more Abstract Sexually selected ornaments and weapons are exceptionally variable, even between closely related species. It has long been recognized that some of this diversity can be explained by differences in mating systems between species, but there remains substantial variation between species with similar mating systems.
Abstract Ball rolling in dung beetles is an energy expensive activity associated with elevated th... more Abstract Ball rolling in dung beetles is an energy expensive activity associated with elevated thoracic temperatures. The ability of individuals to engage in such energetically costly behaviour may be dependent on their body condition. Bilateral asymmetries arising from the interaction between an individual's genes and its environment have been hypothesized to reflect an organism's quality. A number of studies have shown that individuals with elevated levels of asymmetry perform less well under stress.
History is filled with examples of novel infectious diseases suddenly appearing, and the origin o... more History is filled with examples of novel infectious diseases suddenly appearing, and the origin of many of these is controversial, as in the case of the sudden emergence of syphilis in Europe in 1496 (Quétel, 1990). Biologists and historians studying these diseases usually pay little attention to the possibility that the infectious agent may have arisen de novo, preferring (often correctly, it should be said) to look for explanations in terms of transfer of pathogens between species or from other host populations.
Abstract Changes in female reproductive investment can have large effects on offspring quality an... more Abstract Changes in female reproductive investment can have large effects on offspring quality and thus maternal fitness. An immune activation is often expected to lead to a reduction in reproductive effort in order to release resources necessary for costly resistance to infection. Alternatively, an increase in investment in current reproduction may occur in order to maximize lifetime reproductive success: the so-called “terminal investment” effect.
Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have... more Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have important effects on host population dynamics, but we know almost nothing for such parasites about constraints on fecundity and transmission. In this study, we have examined the effect of two potentially important constraints in one of the few empirically well-studied animal-STD systems, the ladybird, Adalia bipunctata, and its sexually transmitted mite, Coccipolipus hippodamiae.
Abstract Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bu... more Abstract Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bulbs, showing a remarkable variety of form. It is unlikely that their primary function was for protection or in hydrodynamics. A case is made that they were secondary sexual features, by comparison with similar morphological structures developed on rhinoceros beetles and other arthropods.
Humans and animals alike are exposed to a variety of parasites at any one time and mixed infectio... more Humans and animals alike are exposed to a variety of parasites at any one time and mixed infections, when the host harbors two or more infections at the same time, are frequent and can be considered the norm in nature (Cox 2001; Read and Taylor 2001). As with other ecological systems where organisms share habitat, mixed infections can mean that parasites interact with each other within the host.
It is widely recognized that male animals frequently exhibit extravagant traits such as long tail... more It is widely recognized that male animals frequently exhibit extravagant traits such as long tails, bright coloration, or aural displays. Explaining the presence of these traits in terms of their selective benefit has been an important focus of behavioral ecology over the last few decades, and we now have a broad and successful body of theory and observation dealing with these features of male animals (Andersson, 1994).
Abstract Sexually transmitted diseases (STDs) are widespread in nature, often sterilizing their h... more Abstract Sexually transmitted diseases (STDs) are widespread in nature, often sterilizing their hosts or causing other pathogenic effects. Despite this, there is a widespread occurrence of behaviours that are likely to increase the risk to an individual of contracting an STD. Here, we examine the evolution of behaviours such as promiscuity or mate choice that increase the risk of contracting an STD, but also provide a fitness benefit.
Abstract Central to theoretical studies of host-pathogen population dynamics is a term describing... more Abstract Central to theoretical studies of host-pathogen population dynamics is a term describing transmission of the pathogen. This usually assumes that transmission is proportional to the density of infectious hosts or particles and of susceptible individuals. We tested this assumption with the bacterial pathogen Bacillus thuringiensis infecting larvae of Plodia interpunctella, the Indian meal moth. Transmission was found to increase in a more than linear way with host density in fourth and fifth instar P.
Abstract Resource-based trade-offs are known to be important in determining investment in both se... more Abstract Resource-based trade-offs are known to be important in determining investment in both sexual ornamentation and immunity in insects. Because of the strict resource limitation experienced during metamorphosis, we predict that if insects are trading off ornament size and immunity this should be most apparent immediately after eclosion and that the relationship between sexual ornament size and immunity should change with maturation feeding because of the changing patterns of resource availability during this process.
Since the mid-1970s, most investigators have agreed that the 'bizarre'structures (here referred t... more Since the mid-1970s, most investigators have agreed that the 'bizarre'structures (here referred to as 'exaggerated'structures) of dinosaurs–for example, the horns and frills of ceratopsids, the crests of lambeosaurine hadrosaurids, the domes of pachycephalosaurs–functioned first and foremost as signalling and combat structures used in mate competition (Farlow & Dodson, 1975; Hopson, 1975; Molnar, 1977; Spassov, 1979; Ostrom & Wellnhoffer, 1986; Sampson, 1997, 2001; Dodson, Forster & Sampson, 2004).
Many host-parasite models assume that transmission increases linearly with host population densit... more Many host-parasite models assume that transmission increases linearly with host population density ('densitydependent transmission'), but various alternative transmission functions have been proposed in an effort to capture the complexity of real biological systems. The most common alternative (usually applied to sexually transmitted parasites) assumes instead that the rate at which hosts contact one another is independent of population density, leading to 'frequency-dependent'transmission.
Abstract The persistence of genetic variability in performance traits such as strength is surpris... more Abstract The persistence of genetic variability in performance traits such as strength is surprising given the directional selection that such traits experience, which should cause the fixation of the best genetic variants. One possible explanation is 'genic capture'which is usually considered as a candidate mechanism for the maintenance of high genetic variability in sexual signalling traits.
Summary 1. Animals raised in good environmental conditions are expected to have more resources to... more Summary 1. Animals raised in good environmental conditions are expected to have more resources to invest in immunity than those raised in poor conditions. Variation in immune activity and parasite resistance in response to changes in environmental temperature, population density and food quality have been shown in many invertebrate species.
1. Transgenerational effects of immune stimulation on offspring immunity are widely reported from... more 1. Transgenerational effects of immune stimulation on offspring immunity are widely reported from insects, but we know very little of how other aspects of the parental environment affect offspring immune reactivity. 2. We reared male and female moths Plodia interpunctella on either good-or poor-quality food and then also raised their offspring on one of the two diet qualities. We found strong transgenerational effects on immunity: in general, if only one parent received the poor diet, reductions in immunity were observed whether that parent was the mother or the father, and the lowest offspring immune reactivity was observed when both parents received the poor diet. 3. The mechanism behind these effects is not known, but they could be caused either by imprinting, whereby the parent gives the offspring a cue such as an epigenetic mark that changes the offspring phenotype, or by the mother allocating fewer resources to their offspring when the diet was poor. Two lines of evidence point towards imprinting: the strong paternal effects and the observation that the size of these effects was either unchanged or increased when the offspring were fed a good-quality diet themselves. 4. Weight was also reduced when either parent was fed a poor diet, except when both parents had a poor diet and the offspring were raised on good food, contrasting with the increased rates of obesity seen in vertebrates when either parent is raised on a restricted diet. 5. Overall, the effects of parental diet on offspring weight and immune reactivity are substantial and in some cases are equivalent to that of the diet that the offspring itself consumes.
Abstract In some cases male animals engage in aggressive contests for access to females, in other... more Abstract In some cases male animals engage in aggressive contests for access to females, in others they adopt more passive strategies and invest in traits that assist them in detecting females or in competing with rivals in other ways, such as sperm competition. One possible factor determining the fitness of these different strategies is population density. Theoretically, aggressive tactics should be found at intermediate population densities.
Geographic profiling (GP) was originally developed as a statistical tool in criminology, where it... more Geographic profiling (GP) was originally developed as a statistical tool in criminology, where it uses the spatial locations of linked crimes (for example murder, rape or arson) to identify areas that are most likely to include the offender's residence. The technique has been successful in this field, and is now widely used by police forces and investigative agencies around the world.
Abstract Sexually selected ornaments and weapons are exceptionally variable, even between closely... more Abstract Sexually selected ornaments and weapons are exceptionally variable, even between closely related species. It has long been recognized that some of this diversity can be explained by differences in mating systems between species, but there remains substantial variation between species with similar mating systems.
Abstract Ball rolling in dung beetles is an energy expensive activity associated with elevated th... more Abstract Ball rolling in dung beetles is an energy expensive activity associated with elevated thoracic temperatures. The ability of individuals to engage in such energetically costly behaviour may be dependent on their body condition. Bilateral asymmetries arising from the interaction between an individual's genes and its environment have been hypothesized to reflect an organism's quality. A number of studies have shown that individuals with elevated levels of asymmetry perform less well under stress.
History is filled with examples of novel infectious diseases suddenly appearing, and the origin o... more History is filled with examples of novel infectious diseases suddenly appearing, and the origin of many of these is controversial, as in the case of the sudden emergence of syphilis in Europe in 1496 (Quétel, 1990). Biologists and historians studying these diseases usually pay little attention to the possibility that the infectious agent may have arisen de novo, preferring (often correctly, it should be said) to look for explanations in terms of transfer of pathogens between species or from other host populations.
Abstract Changes in female reproductive investment can have large effects on offspring quality an... more Abstract Changes in female reproductive investment can have large effects on offspring quality and thus maternal fitness. An immune activation is often expected to lead to a reduction in reproductive effort in order to release resources necessary for costly resistance to infection. Alternatively, an increase in investment in current reproduction may occur in order to maximize lifetime reproductive success: the so-called “terminal investment” effect.
Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have... more Parasites that are sexually transmitted (causing sexually transmitted diseases, or STDs) can have important effects on host population dynamics, but we know almost nothing for such parasites about constraints on fecundity and transmission. In this study, we have examined the effect of two potentially important constraints in one of the few empirically well-studied animal-STD systems, the ladybird, Adalia bipunctata, and its sexually transmitted mite, Coccipolipus hippodamiae.
Abstract Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bu... more Abstract Raphiophorid trilobites commonly bore median cephalic protuberances such as spines or bulbs, showing a remarkable variety of form. It is unlikely that their primary function was for protection or in hydrodynamics. A case is made that they were secondary sexual features, by comparison with similar morphological structures developed on rhinoceros beetles and other arthropods.
Humans and animals alike are exposed to a variety of parasites at any one time and mixed infectio... more Humans and animals alike are exposed to a variety of parasites at any one time and mixed infections, when the host harbors two or more infections at the same time, are frequent and can be considered the norm in nature (Cox 2001; Read and Taylor 2001). As with other ecological systems where organisms share habitat, mixed infections can mean that parasites interact with each other within the host.
It is widely recognized that male animals frequently exhibit extravagant traits such as long tail... more It is widely recognized that male animals frequently exhibit extravagant traits such as long tails, bright coloration, or aural displays. Explaining the presence of these traits in terms of their selective benefit has been an important focus of behavioral ecology over the last few decades, and we now have a broad and successful body of theory and observation dealing with these features of male animals (Andersson, 1994).
Abstract Sexually transmitted diseases (STDs) are widespread in nature, often sterilizing their h... more Abstract Sexually transmitted diseases (STDs) are widespread in nature, often sterilizing their hosts or causing other pathogenic effects. Despite this, there is a widespread occurrence of behaviours that are likely to increase the risk to an individual of contracting an STD. Here, we examine the evolution of behaviours such as promiscuity or mate choice that increase the risk of contracting an STD, but also provide a fitness benefit.
Abstract Central to theoretical studies of host-pathogen population dynamics is a term describing... more Abstract Central to theoretical studies of host-pathogen population dynamics is a term describing transmission of the pathogen. This usually assumes that transmission is proportional to the density of infectious hosts or particles and of susceptible individuals. We tested this assumption with the bacterial pathogen Bacillus thuringiensis infecting larvae of Plodia interpunctella, the Indian meal moth. Transmission was found to increase in a more than linear way with host density in fourth and fifth instar P.
Abstract Resource-based trade-offs are known to be important in determining investment in both se... more Abstract Resource-based trade-offs are known to be important in determining investment in both sexual ornamentation and immunity in insects. Because of the strict resource limitation experienced during metamorphosis, we predict that if insects are trading off ornament size and immunity this should be most apparent immediately after eclosion and that the relationship between sexual ornament size and immunity should change with maturation feeding because of the changing patterns of resource availability during this process.
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Papers by Rob Knell