Atsushi Miyashita | Dalhousie University (original) (raw)

Papers by Atsushi Miyashita

Research paper thumbnail of Serum apolipoprotein A-I potentiates the therapeutic efficacy of lysocin E against Staphylococcus aureus

Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus ... more Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. For unclear reasons, the antibacterial activity of lysocin E in a mouse systemic infection model is higher than expected from in vitro results, and the in vitro activity is enhanced by addition of bovine serum. Here, we confirm that serum from various species, including humans, increases lysocin E antimicrobial activity, and identify apolipoprotein A-I (ApoA-I) as an enhancing factor. ApoA-I increases the antibacterial activity of lysocin E when added in vitro, and the antibiotic displays reduced activity in ApoA-I gene knockout mice. Binding of ApoA-I to lysocin E is enhanced by lipid II, a cell-wall synthesis precursor found in the bacterial membrane. Thus, the antimicrobial activity of lysocin E is potentiated through interactions with host serum proteins and microbial components.

Research paper thumbnail of Using silkworms to search for lactic acid bacteria that contribute to infection prevention and improvement of hyperglycemia

Bombyx mori, the silkworm, has biological functions in common with mammals, including humans. Sin... more Bombyx mori, the silkworm, has biological functions in common with mammals, including humans. Since the molecular design of silkworm's innate immune system is analogous to that of mammals, understanding the silkworm's innate immunity is expected to contribute to the control of infection in humans. It is also possible to use silkworms to explore foodstuffs that activate innate immunity. Lactic acid bacteria have long been used in the production of fermented foods, and in recent years, their use as supplements has been attracting attention. Using silkworms, which are laboratory animals, functional lactic acid bacteria can be explored and isolated at low cost. Fermented foods produced by this method are expected to contribute to the maintenance of human health. In addition to the immune system, humans and silkworms share a common mechanism for maintaining blood glucose homeostasis, and it is possible to construct a pathological model of diabetes and search for therapeutic substances using silkworms. Taken together, we propose that the silkworm is useful for assessing the functions of lactic acid bacterial for health purposes.

Research paper thumbnail of Applying the silkworm model for the search of immunosuppressants

Silkworm model, immunosuppressants, screening system, natural products Various stresses (high tem... more Silkworm model, immunosuppressants, screening system, natural products Various stresses (high temperature, starvation, or sublethal Cryptococcal infection) increased the susceptibility of silkworms to bacterial infection by up to 100-fold, confirming the stressinduced immunosuppression reported in a range of species. When the silkworm was injected with a steroidal drug, betamethasone (1 mg/larva), the susceptibility of the silkworm to bacterial infection increased about 100-fold. This indicates that the immune function of the silkworm can be suppressed by a known compound that shows immunosuppressive effects in humans. We further tested the immunosuppressive effect of the culture supernatants (acetone extracts) of soil bacteria, and 24 out of 193 isolates showed the immunosuppressive activity. These results suggest that it is possible to search for immunosuppressive agents targeting innate immunity by using a silkworm bacterial infection model as a screening system, and that there may be candidate compounds for immunosuppressive agents among the substances produced by soil bacteria.

Research paper thumbnail of A digital scheme of human trials for the evaluation of functional foods

human trial, personal devices, functional food, natural food In this study, we designed a method ... more human trial, personal devices, functional food, natural food In this study, we designed a method for conducting a human study by the following process. (1) The host computer stores the subject information. (2) The sample preparer prepares a food sample. (3) The subject (healthy human volunteer) sends the information of an intake of the food sample to the host computer, which creates an event entry for the event. (4) The medical professional (typically a physician) collects and stores the subject's blood sample in a container with the subject's identification (e.g., ID number). (5) The sample analyst analyzes the blood biochemical profiles. (6) The host computer stores the blood biochemical data, and by matching the blood biochemical data with the subject IDs, a final analysis report will automatically be created. In this study, we also run a test case, based on this design, where we obtained a blood biochemical dataset from healthy volunteers. This scheme can reduce the cost of human trials for functional foods and will help acquiring the scientific basis of functional foods.

Research paper thumbnail of -Advances in Invertebrate (Neuro) Endocrinology Vol 2 author copy

Research paper thumbnail of Table of Contents

Research paper thumbnail of A novel application of bubble‑eyestrain of Carassius auratus  for ex vivo fish immunologicalstudies

Research paper thumbnail of High-Stakes Decision-Making by Female Crickets (Gryllus texensis): When to Trade In Wing Muscles for Eggs

Resource-intensive traits, such as dispersal and reproduction, can be difficult to express simult... more Resource-intensive traits, such as dispersal and reproduction, can be difficult to express simultaneously because of resource limitations. One solution is to switch between resource-intensive behaviors. Such phenotypic plasticity is one strategy that organisms use to funnel resources from one expensive trait to another. In crickets (Gryllus texensis), the development and maintenance of flight muscles reduce resource availability for reproduction, leading to physiological trade-offs between the two traits. Longwinged female G. texensis can histolyze their wing muscles, resulting in increased egg production, but they can then no longer fly. Using a diet that mimics food availability in the field, we found that long-winged females adopted one of the three following strategies: early reproduction, intermediate reproduction, and late reproduction. Some late reproducers maintained their flight capability until the end of their natural life span and laid few eggs. If females lost the ability to fly (i.e., their hind wings are removed), they laid eggs earlier, leading to increased reproductive output. However, other environmental cues (e.g., an increased number of mates, increased oviposition substrate quality, or a bout of dispersal flight) had no effect. Late-reproducing females laid 96% fewer eggs than early reproducers, suggesting that late reproduction exacts a huge fitness cost. Nevertheless, some females maintain their flight muscles to the end of their natural life span in both the lab and the field. We suggest that the ability to fly allows for bet hedging against an environmental catastrophe (e.g., drought or flood). This benefit may help explain the persistence of latereproducing long-winged females, despite the cost of this choice. As climate change increases drought and flood in Texas, late dispersal may be one factor that helps this species survive in the future. An increased understanding of factors that maintain seemingly low fitness strategies can help us predict the resilience of species under climate change.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis)

PLOS ONE, 2019

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis

PLOS ONE, 2019

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of No Effect of Body Size on the Frequency of Calling and Courtship Song in the Two- Spotted Cricket, Gryllus bimaculatus

PLOS ONE, 2016

The relationship between body size and vocalization parameters has been studied in many animal sp... more The relationship between body size and vocalization parameters has been studied in many animal species. In insect species, however, the effect of body size on song frequency has remained unclear. Here we analyzed the effect of body size on the frequency spectra of mating songs produced by the two-spotted cricket, Gryllus bimaculatus. We recorded the calling songs and courtship songs of male crickets of different body sizes. The calling songs contained a frequency component that peaked at 5.7 kHz. On the other hand, courtship songs contained two frequency components that peaked at 5.8 and 14.7 kHz. The dominant frequency of each component in both the calling and courtship songs was constant regardless of body size. The size of the harp and mirror regions in the cricket forewings, which are the acoustic sources of the songs, correlated positively with body size. These findings suggest that the frequency contents of both the calling and courtship songs of the cricket are unaffected by whole body, harp, or mirror size.

Research paper thumbnail of Body-enlarging effect of royal jelly in a non-holometabolous insect species, Gryllus bimaculatus

Biology Open, 2016

Honeybee royal jelly is reported to have body-enlarging effects in holometabolous insects such as... more Honeybee royal jelly is reported to have body-enlarging effects in holometabolous insects such as the honeybee, fly and silkmoth, but its effect in non-holometabolous insect species has not yet been examined. The present study confirmed the body-enlarging effect in silkmoths fed an artificial diet instead of mulberry leaves used in the previous literature. Administration of honeybee royal jelly to silkmoth from early larval stage increased the size of female pupae and adult moths, but not larvae (at the late larval stage) or male pupae. We further examined the body-enlarging effect of royal jelly in a non-holometabolous species, the two-spotted cricket Gryllus bimaculatus, which belongs to the evolutionarily primitive group Polyneoptera. Administration of royal jelly to G. bimaculatus from its early nymph stage enlarged both males and females at the mid-nymph and adult stages. In the cricket, the body parts were uniformly enlarged in both males and females; whereas the enlarged female silkmoths had swollen abdomens. Administration of royal jelly increased the number, but not the size, of eggs loaded in the abdomen of silkmoth females. In addition, fat body cells were enlarged by royal jelly in the silkmoth, but not in the cricket. These findings suggest that the body-enlarging effect of royal jelly is common in non-holometabolous species, G. bimaculatus, but it acts in a different manner than in holometabolous species.

Research paper thumbnail of Primed Immune Responses Triggered by Ingested Bacteria Lead to Systemic Infection Tolerance in Silkworms

PLOS ONE, 2015

In the present study, we examined whether microorganisms collaterally ingested by insects with th... more In the present study, we examined whether microorganisms collaterally ingested by insects with their food activate the innate immune system to confer systemic resistance against subsequent bacterial invasion. Silkworms orally administered heat-killed Pseudomonas aeruginosa cells showed resistance against intra-hemolymph infection by P. aeruginosa. Oral administration of peptidoglycans, cell wall components of P. aeruginosa, conferred protective effects against P. aeruginosa infection, whereas oral administration of lipopolysac-charides, bacterial surface components, did not. In silkworms orally administered heat-killed P. aeruginosa cells, P. aeruginosa growth was inhibited in the hemolymph, and mRNA amounts of the antimicrobial peptides cecropin A and moricin were increased in the hemo-cytes and fat body. Furthermore, the amount of paralytic peptide, an insect cytokine that activates innate immune reactions, was increased in the hemolymph of silkworms orally administered heat-killed P. aeruginosa cells. These findings suggest that insects sense bacteria present in their food by peptidoglycan recognition, which activates systemic immune reactions to defend the insects against a second round of infection.

Research paper thumbnail of Lipopolysaccharide O-antigen of enterohemorrhagic Escherichia coli O157:H7 is required for killing both insects and mammals

FEMS Microbiology Letters, 2012

Studies of enterohemorrhagic Escherichia coli (EHEC) infection mechanisms using mammals require l... more Studies of enterohemorrhagic Escherichia coli (EHEC) infection mechanisms using mammals require large numbers of animals and are both costly and associated with ethical problems. Here, we evaluated the pathogenic mechanisms of EHEC in the silkworm model.

Research paper thumbnail of Primed Immune Responses to Gram-negative Peptidoglycans Confer Infection Resistance in Silkworms

Journal of Biological Chemistry, 2014

Background: Primed immune responses contribute to vertebrate host defense. Results: Silkworms acq... more Background: Primed immune responses contribute to vertebrate host defense. Results: Silkworms acquire resistance to a pathogen by a preinjection of its heat-killed cells or its cell surface peptidoglycans. The amount of antimicrobial peptides is increased at the second round of infection. Conclusion: Invertebrates acquire infection resistance by peptidoglycan recognition and antimicrobial peptide increase. Significance: Molecular mechanisms of invertebrate primed immunity were revealed.

Research paper thumbnail of Serum apolipoprotein A-I potentiates the therapeutic efficacy of lysocin E against Staphylococcus aureus

Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus ... more Lysocin E is a lipopeptide with antibiotic activity against methicillin-resistant Staphylococcus aureus. For unclear reasons, the antibacterial activity of lysocin E in a mouse systemic infection model is higher than expected from in vitro results, and the in vitro activity is enhanced by addition of bovine serum. Here, we confirm that serum from various species, including humans, increases lysocin E antimicrobial activity, and identify apolipoprotein A-I (ApoA-I) as an enhancing factor. ApoA-I increases the antibacterial activity of lysocin E when added in vitro, and the antibiotic displays reduced activity in ApoA-I gene knockout mice. Binding of ApoA-I to lysocin E is enhanced by lipid II, a cell-wall synthesis precursor found in the bacterial membrane. Thus, the antimicrobial activity of lysocin E is potentiated through interactions with host serum proteins and microbial components.

Research paper thumbnail of Using silkworms to search for lactic acid bacteria that contribute to infection prevention and improvement of hyperglycemia

Bombyx mori, the silkworm, has biological functions in common with mammals, including humans. Sin... more Bombyx mori, the silkworm, has biological functions in common with mammals, including humans. Since the molecular design of silkworm's innate immune system is analogous to that of mammals, understanding the silkworm's innate immunity is expected to contribute to the control of infection in humans. It is also possible to use silkworms to explore foodstuffs that activate innate immunity. Lactic acid bacteria have long been used in the production of fermented foods, and in recent years, their use as supplements has been attracting attention. Using silkworms, which are laboratory animals, functional lactic acid bacteria can be explored and isolated at low cost. Fermented foods produced by this method are expected to contribute to the maintenance of human health. In addition to the immune system, humans and silkworms share a common mechanism for maintaining blood glucose homeostasis, and it is possible to construct a pathological model of diabetes and search for therapeutic substances using silkworms. Taken together, we propose that the silkworm is useful for assessing the functions of lactic acid bacterial for health purposes.

Research paper thumbnail of Applying the silkworm model for the search of immunosuppressants

Silkworm model, immunosuppressants, screening system, natural products Various stresses (high tem... more Silkworm model, immunosuppressants, screening system, natural products Various stresses (high temperature, starvation, or sublethal Cryptococcal infection) increased the susceptibility of silkworms to bacterial infection by up to 100-fold, confirming the stressinduced immunosuppression reported in a range of species. When the silkworm was injected with a steroidal drug, betamethasone (1 mg/larva), the susceptibility of the silkworm to bacterial infection increased about 100-fold. This indicates that the immune function of the silkworm can be suppressed by a known compound that shows immunosuppressive effects in humans. We further tested the immunosuppressive effect of the culture supernatants (acetone extracts) of soil bacteria, and 24 out of 193 isolates showed the immunosuppressive activity. These results suggest that it is possible to search for immunosuppressive agents targeting innate immunity by using a silkworm bacterial infection model as a screening system, and that there may be candidate compounds for immunosuppressive agents among the substances produced by soil bacteria.

Research paper thumbnail of A digital scheme of human trials for the evaluation of functional foods

human trial, personal devices, functional food, natural food In this study, we designed a method ... more human trial, personal devices, functional food, natural food In this study, we designed a method for conducting a human study by the following process. (1) The host computer stores the subject information. (2) The sample preparer prepares a food sample. (3) The subject (healthy human volunteer) sends the information of an intake of the food sample to the host computer, which creates an event entry for the event. (4) The medical professional (typically a physician) collects and stores the subject's blood sample in a container with the subject's identification (e.g., ID number). (5) The sample analyst analyzes the blood biochemical profiles. (6) The host computer stores the blood biochemical data, and by matching the blood biochemical data with the subject IDs, a final analysis report will automatically be created. In this study, we also run a test case, based on this design, where we obtained a blood biochemical dataset from healthy volunteers. This scheme can reduce the cost of human trials for functional foods and will help acquiring the scientific basis of functional foods.

Research paper thumbnail of -Advances in Invertebrate (Neuro) Endocrinology Vol 2 author copy

Research paper thumbnail of Table of Contents

Research paper thumbnail of A novel application of bubble‑eyestrain of Carassius auratus  for ex vivo fish immunologicalstudies

Research paper thumbnail of High-Stakes Decision-Making by Female Crickets (Gryllus texensis): When to Trade In Wing Muscles for Eggs

Resource-intensive traits, such as dispersal and reproduction, can be difficult to express simult... more Resource-intensive traits, such as dispersal and reproduction, can be difficult to express simultaneously because of resource limitations. One solution is to switch between resource-intensive behaviors. Such phenotypic plasticity is one strategy that organisms use to funnel resources from one expensive trait to another. In crickets (Gryllus texensis), the development and maintenance of flight muscles reduce resource availability for reproduction, leading to physiological trade-offs between the two traits. Longwinged female G. texensis can histolyze their wing muscles, resulting in increased egg production, but they can then no longer fly. Using a diet that mimics food availability in the field, we found that long-winged females adopted one of the three following strategies: early reproduction, intermediate reproduction, and late reproduction. Some late reproducers maintained their flight capability until the end of their natural life span and laid few eggs. If females lost the ability to fly (i.e., their hind wings are removed), they laid eggs earlier, leading to increased reproductive output. However, other environmental cues (e.g., an increased number of mates, increased oviposition substrate quality, or a bout of dispersal flight) had no effect. Late-reproducing females laid 96% fewer eggs than early reproducers, suggesting that late reproduction exacts a huge fitness cost. Nevertheless, some females maintain their flight muscles to the end of their natural life span in both the lab and the field. We suggest that the ability to fly allows for bet hedging against an environmental catastrophe (e.g., drought or flood). This benefit may help explain the persistence of latereproducing long-winged females, despite the cost of this choice. As climate change increases drought and flood in Texas, late dispersal may be one factor that helps this species survive in the future. An increased understanding of factors that maintain seemingly low fitness strategies can help us predict the resilience of species under climate change.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis)

PLOS ONE, 2019

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of Immunity for nothing and the eggs for free: Apparent lack of both physiological trade-offs and terminal reproductive investment in female crickets (Gryllus texensis

PLOS ONE, 2019

Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provi... more Should females alter their reproductive strategy when attacked by pathogens? Two hypotheses provide opposite predictions. Terminal reproductive investment theory predicts that reproduction should increase when the risk of death increases. However, physiological trade-offs between reproduction and immune function might be expected to produce a decrease in reproduction during a robust immune response. There is evidence for both hypotheses. We examine whether age determines the effect of an immune challenge on reproductive strategy in long-winged females of the Texas field cricket, Gryllus texensis, when fed an ecologically valid (i.e. limited) diet. The limited diet reduced reproductive output. However, even under resource-limited conditions, immune challenge had no effect on the reproductive output of young or middle-aged females. Both reproductive output and immune function (lysozyme-like activity and phenoloxidase (PO) activity) increased with age, which is contrary to both hypotheses. We hypothesize that PO activity is pleiotropic and represents an investment in both reproduction and immune function. Three proPO genes (identified in a published RNA-seq dataset (transcriptome)) were expressed either in the fat body or the ovaries (supporting the hypothesis that PO is bifunctional). The possible bifunctionality of PO suggests that it may not be an appropriate immune measure for studies on immune/ reproductive trade-offs. This study also suggests that the threshold for terminal reproductive investment may not decrease prior to senescence in some species.

Research paper thumbnail of No Effect of Body Size on the Frequency of Calling and Courtship Song in the Two- Spotted Cricket, Gryllus bimaculatus

PLOS ONE, 2016

The relationship between body size and vocalization parameters has been studied in many animal sp... more The relationship between body size and vocalization parameters has been studied in many animal species. In insect species, however, the effect of body size on song frequency has remained unclear. Here we analyzed the effect of body size on the frequency spectra of mating songs produced by the two-spotted cricket, Gryllus bimaculatus. We recorded the calling songs and courtship songs of male crickets of different body sizes. The calling songs contained a frequency component that peaked at 5.7 kHz. On the other hand, courtship songs contained two frequency components that peaked at 5.8 and 14.7 kHz. The dominant frequency of each component in both the calling and courtship songs was constant regardless of body size. The size of the harp and mirror regions in the cricket forewings, which are the acoustic sources of the songs, correlated positively with body size. These findings suggest that the frequency contents of both the calling and courtship songs of the cricket are unaffected by whole body, harp, or mirror size.

Research paper thumbnail of Body-enlarging effect of royal jelly in a non-holometabolous insect species, Gryllus bimaculatus

Biology Open, 2016

Honeybee royal jelly is reported to have body-enlarging effects in holometabolous insects such as... more Honeybee royal jelly is reported to have body-enlarging effects in holometabolous insects such as the honeybee, fly and silkmoth, but its effect in non-holometabolous insect species has not yet been examined. The present study confirmed the body-enlarging effect in silkmoths fed an artificial diet instead of mulberry leaves used in the previous literature. Administration of honeybee royal jelly to silkmoth from early larval stage increased the size of female pupae and adult moths, but not larvae (at the late larval stage) or male pupae. We further examined the body-enlarging effect of royal jelly in a non-holometabolous species, the two-spotted cricket Gryllus bimaculatus, which belongs to the evolutionarily primitive group Polyneoptera. Administration of royal jelly to G. bimaculatus from its early nymph stage enlarged both males and females at the mid-nymph and adult stages. In the cricket, the body parts were uniformly enlarged in both males and females; whereas the enlarged female silkmoths had swollen abdomens. Administration of royal jelly increased the number, but not the size, of eggs loaded in the abdomen of silkmoth females. In addition, fat body cells were enlarged by royal jelly in the silkmoth, but not in the cricket. These findings suggest that the body-enlarging effect of royal jelly is common in non-holometabolous species, G. bimaculatus, but it acts in a different manner than in holometabolous species.

Research paper thumbnail of Primed Immune Responses Triggered by Ingested Bacteria Lead to Systemic Infection Tolerance in Silkworms

PLOS ONE, 2015

In the present study, we examined whether microorganisms collaterally ingested by insects with th... more In the present study, we examined whether microorganisms collaterally ingested by insects with their food activate the innate immune system to confer systemic resistance against subsequent bacterial invasion. Silkworms orally administered heat-killed Pseudomonas aeruginosa cells showed resistance against intra-hemolymph infection by P. aeruginosa. Oral administration of peptidoglycans, cell wall components of P. aeruginosa, conferred protective effects against P. aeruginosa infection, whereas oral administration of lipopolysac-charides, bacterial surface components, did not. In silkworms orally administered heat-killed P. aeruginosa cells, P. aeruginosa growth was inhibited in the hemolymph, and mRNA amounts of the antimicrobial peptides cecropin A and moricin were increased in the hemo-cytes and fat body. Furthermore, the amount of paralytic peptide, an insect cytokine that activates innate immune reactions, was increased in the hemolymph of silkworms orally administered heat-killed P. aeruginosa cells. These findings suggest that insects sense bacteria present in their food by peptidoglycan recognition, which activates systemic immune reactions to defend the insects against a second round of infection.

Research paper thumbnail of Lipopolysaccharide O-antigen of enterohemorrhagic Escherichia coli O157:H7 is required for killing both insects and mammals

FEMS Microbiology Letters, 2012

Studies of enterohemorrhagic Escherichia coli (EHEC) infection mechanisms using mammals require l... more Studies of enterohemorrhagic Escherichia coli (EHEC) infection mechanisms using mammals require large numbers of animals and are both costly and associated with ethical problems. Here, we evaluated the pathogenic mechanisms of EHEC in the silkworm model.

Research paper thumbnail of Primed Immune Responses to Gram-negative Peptidoglycans Confer Infection Resistance in Silkworms

Journal of Biological Chemistry, 2014

Background: Primed immune responses contribute to vertebrate host defense. Results: Silkworms acq... more Background: Primed immune responses contribute to vertebrate host defense. Results: Silkworms acquire resistance to a pathogen by a preinjection of its heat-killed cells or its cell surface peptidoglycans. The amount of antimicrobial peptides is increased at the second round of infection. Conclusion: Invertebrates acquire infection resistance by peptidoglycan recognition and antimicrobial peptide increase. Significance: Molecular mechanisms of invertebrate primed immunity were revealed.