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"Rollo, David"
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The effects of rearing density on growth, survival, and starvation resistance of the house cricket Acheta domesticus
Alternative food sources have become an important focus of research due to increased food demand coupled with reductions in traditional food productivity. In particular, substitutes for protein sources have been of increasing interest due to the unsustainability of traditional protein sources. Insects have been identified as a sustainable alternative to traditional protein sources, as they are easy to produce and contain essential proteins, fats, and minerals. However, mass-rearing insects requires similar considerations as farming traditional protein sources. To increase productively, growth and survival must be maximized at the highest possible densities while minimizing disease and food requirements. Here, we use the house cricket Acheta domesticus, a highly cultivated insect species, to investigate optimal densities for mass rearing at 14 days of age (4th instar). Nymphs were separated into density groups of 0.09, 0.19, 0.47, and 0.93 cricket/cm² and monitored for growth and survival. Multiple regression revealed sex (p < 0.0001), density (p < 0.0001), and sex*density interaction (p = 0.0345) as predictors of growth rate. Survival to maturation was significantly reduced in both 0.47 (31%) and 0.93 (45%) cricket/cm² groups compared to the controls. A second experiment was then conducted to investigate the starvation resistance of adult crickets reared from 14 days of age at 0.09, 0.19, 0.93, and 1.86 cricket/cm². A second multiple regression analysis revealed only density (p < 0.0001) and to a lesser extent sex (p = 0.0005) to be predictors of starvation resistance. These results indicate that mass-rearing house crickets is most optimal at densities < 0.93 cricket/cm², where impacts on survival and starvation are minimal. Although these results have implications for cricket mass rearing, research on other endpoints, including reproduction and the synergistic effects of other environmental factors, such as temperature and humidity, should be conducted.
Journal Article
Necromone Death Cues and Risk Avoidance by the Cricket Acheta domesticus: Effects of Sex and Duration of Exposure
We document that the cricket,
Acheta domesticus,
avoids “necromone” chemical cues of death associated with treated surfaces and shelters (i.e., ethanol extracts of cricket bodies, oleic acid or linoleic acid). Initially we tested male responses to male body extract, oleic acid, or linoleic acid associated with shelters. Body extract was more repellent than either oleic or linoleic acid at a dose of 10 body equivalents per shelter. At 15 or 20 body equivalents/shelter extract and oleic acid were similarly repellent but linoleic acid was weaker. We next tested responses of males or females to shelters and surfaces treated with body extracts of males, females, a male-female mixture, or oleic acid. Repellency was evaluated at 1, 16, and 22 h following introduction. Body extracts elicited more immediate aversion than did authentic oleic acid (1 h). Females showed declining aversion with time (1, 16, 22 h), especially with regard to male extract. Alternatively, males showed increasing aversion with time, particularly to female extract. Both sexes showed weak responses to oleic acid at 1 h, but significant aversion at 16 and 22 h. We suggest that females may be less risk aversive as they seek out singing males holding established territories (i.e., mobility makes risk transient). Alternatively, males may respond more strongly to female necromone as this would reduce attraction of females to their territory. Finally, we consider a classic paper that documents a strong cricket repellent associated with tissue-covered perches. We provide new evidence that this repellent was likely an unsaturated fatty acid.
Journal Article
Trans-Generational Impacts of Paternal Irradiation in a Cricket: Damage, Life-History Features and Hormesis in F1 Offspring
Animals exposed to significant stress express multi-modal responses to buffer negative impacts. Trans-generational impacts have been mainly studied in maternal lines, with paternal lines having received less attention. Here, we assessed paternal generational effects using irradiated male crickets (Acheta domesticus), and their F1 offspring (irradiated males mated to unirradiated females). Paternal transmission of radiation impacts emerged in multiple life history traits when compared to controls. Irradiated males and their F1 offspring expressed hormetic responses in survivorship and median longevity at mid-range doses. For F0 males, 7 Gy & 10 Gy doses extended F0 longevity by 39% and 34.2% respectively. F1 offspring of 7 Gy and 10 Gy sires had median lifespans 71.3% and 110.9% longer, respectively. Survivorship for both F0 7 Gy (p < 0.0001) and 10 Gy (p = 0.0055) males and F1 7 Gy and 10 Gy (p < 0.0001) offspring significantly surpassed that of controls. Irradiated F0 males and F1 offspring had significantly reduced growth rates. For F0 males, significant reductions were evident in 4Gy-12 Gy males and F1 offspring in 4 Gy (p < 0.0001), 7 Gy (p < 0.0001), and 10 Gy (p = 0.017). Our results indicate paternal effects; that irradiation directly impacted males but also mediated diverse alterations in the life history features (particularly longevity and survivorship) of F1 offspring.
Journal Article
Hormetic Effects of Early Juvenile Radiation Exposure on Adult Reproduction and Offspring Performance in the Cricket (Acheta domesticus)
Exposure to low-dose ionizing radiation can have positive impacts on biological performance—a concept known as hormesis. Although radiation hormesis is well-documented, the predominant focus has been medical. In comparison, little research has examined potential effects of early life radiation stress on organismal investment in life history traits that closely influence evolutionary fitness (eg, patterns of growth, survival, and reproduction). Evaluating the fitness consequences of radiation stress is important, given that low-level radiation pollution from anthropogenic sources is considered a major threat to natural ecosystems. Using the cricket (Acheta domesticus), we tested a wide range of doses to assess whether a single juvenile exposure to radiation could induce hormetic benefits on lifetime fitness measures. Consistent with hormesis, we found that low-dose juvenile radiation positively impacted female fecundity, offspring size, and offspring performance. Remarkably, even a single low dose of radiation in early juvenile development can elicit a range of positive fitness effects emerging over the life span and even into the next generation.
Journal Article
Conspecific mortality cues mediate associative learning in crickets, Acheta domesticus (Orthoptera: Gryllidae)
Many terrestrial and aquatic animals learn associations between environmental features and chemical cues of mortality risk (e.g. conspecific alarm pheromones or predator-derived cues), but the chemical nature of the cues that mediate this type of learning are rarely considered. Fatty acid necromones (particularly oleic and linoleic acids) are well established as cues associated with dead or injured conspecifics. Necromones elicit risk aversive behavior across diverse arthropod phylogenies, yet they have not been linked to associative learning. Here, we provide evidence that necromones can mediate associative olfactory learning in an insect by acting as an aversive reinforcement. When house crickets (Acheta domesticus) were forced to inhabit an environment containing an initially attractive odor along with a necromone cue, they subsequently avoided the previously attractive odor and displayed tolerance for an initially unattractive odor. This occurred when crickets were conditioned with linoleic acid but not when they were conditioned with oleic acid. Similar aversive learning occurred when crickets were conditioned with ethanol body extracts composed of male and female corpses combined, as well as extracts composed of female corpses alone. Conditioning with male body extract did not elicit learned aversion in either sex, even though we detected no notable differences in fatty acid composition between male and female body extracts. We suggest that necromone-mediated learning responses might vary depending on synergistic or antagonistic interactions with sex or species-specific recognition cues.
Journal Article
Trojan Genes and Transparent Genomes: Sexual Selection, Regulatory Evolution and the Real Hopeful Monsters
Potential impacts of genetically modified (GM) animals in natural environments are explored in a framework of regulatory evolution. Transgenic growth hormone animals express remarkable alterations and plasticity in development, physiology and behavior in response to environmental factors (nutrition, temperature, photoperiod), suggesting that standard laboratory assessments are likely to underestimate their evolutionary potential. Sexual selection is examined in the context of female self-referent appraisal of male fitness that reflects performance in the species-specific niche. Wild-type females may recognize and discriminate against GM males (the Transparent Genome Hypothesis) but if accepted as mates, pleiotropic disruption associated with GMs may reduce fitness of the natural population (the Trojan Gene Hypothesis). Alternatively, facilitation of regulatory evolution by sexual reproduction (recombination and segregation) may derive modifier selection, masking, integration, or niche shifts. Other aspects explored include mutation theory, purging, pleiotropy, epigenetics and plasticity, behavior and the Bruce effect, and mismatch of genetic or epigenetic background between GM stock and natural populations.
Journal Article
Glamorous Sorcery
Through the analysis of magic as a metaphor for the mysterious workings of writing, Glamorous Sorcery sheds light on the power attributed to language in shaping perceptions of the world and conferring status.
eBook
Venerating nature’s deviance in the Roman de la Rose
The Roman de la Rose ends with an allegory of foreplay and intercourse: Amant first venerates relics that figuratively represent testicles and then penetrates his beloved only to find entry hampered by a barrier signifying the hymen. The hermaphroditism of the body here penetrated incarnates a hermaphroditic hermeneutics. The reader must engage the body of the beloved with an attention to detail that is at least as rapt as the adoring gaze of the lover and must, in the process, attempt to separate the literal and figurative registers of the text. The task is frustrated, however, by the fact that the body in question is both literally male and figuratively female. Frustration, nonetheless, brings a pleasure of its own, the delight that accrues for the very act of interpretation.
Journal Article
Metabolic flexibility revealed in the genome of the cyst-forming α-1 proteobacterium Rhodospirillum centenum
Background
Rhodospirillum centenum
is a photosynthetic non-sulfur purple bacterium that favors growth in an anoxygenic, photosynthetic N
2
-fixing environment. It is emerging as a genetically amenable model organism for molecular genetic analysis of cyst formation, photosynthesis, phototaxis, and cellular development. Here, we present an analysis of the genome of this bacterium.
Results
R. centenum
contains a singular circular chromosome of 4,355,548 base pairs in size harboring 4,105 genes. It has an intact Calvin cycle with two forms of Rubisco, as well as a gene encoding phosphoenolpyruvate carboxylase (PEPC) for mixotrophic CO
2
fixation. This dual carbon-fixation system may be required for regulating internal carbon flux to facilitate bacterial nitrogen assimilation. Enzymatic reactions associated with arsenate and mercuric detoxification are rare or unique compared to other purple bacteria. Among numerous newly identified signal transduction proteins, of particular interest is a putative bacteriophytochrome that is phylogenetically distinct from a previously characterized
R. centenum
phytochrome, Ppr. Genes encoding proteins involved in chemotaxis as well as a sophisticated dual flagellar system have also been mapped.
Conclusions
Remarkable metabolic versatility and a superior capability for photoautotrophic carbon assimilation is evident in
R. centenum
.
Journal Article