Reproductive parasites such as Wolbachia are extremely widespread amongst the arthropods and can have a large influence over the reproduction and fitness of their hosts. Undetected infections could thus confound the r...Reproductive parasites such as Wolbachia are extremely widespread amongst the arthropods and can have a large influence over the reproduction and fitness of their hosts. Undetected infections could thus confound the results of a wide range of studies that focus on aspects of host behavior, reproduction, fitness, and degrees of reproductive isolation. This potential problem has already been underlined by work investigating the in- cidence of Wolbachia infections in stocks of the model system Drosophila melanogaster. Here we survey a range of lab stocks of further commonly used model arthropods, fo- cusing especially on the flour beetles Tribolium castaneum and Tribolium confusum, the cowpea weevil Callosobruchus maculatus and related species （Coleoptera： Tenebrionidae and Bruchidae）. These species are widespread stored product pests so knowledge of infec- tions with symbionts further has potential use in informing biocontrol measures. Beetles were assessed for infection with 3 known microbial reproductive parasites： Wolbachia, Rickettsia, Spiroplasma. Infections with some of these microbes were found in some of the lab stocks studied, although overall infections were relatively rare. The consequences of finding infections in these or other species and the type of previous studies likely to be affected most are discussed.展开更多
Rensch＇s rule proposes a universal allometric scaling phenomenon across species where sexual size dimorphism （SSD） has evolved： in taxa with male-biased dimorphism, degree of SSD should increase with overall body ...Rensch＇s rule proposes a universal allometric scaling phenomenon across species where sexual size dimorphism （SSD） has evolved： in taxa with male-biased dimorphism, degree of SSD should increase with overall body size, and in taxa with female-biased dimorphism, degree of SSD should decrease with increasing average body size. Rensch＇s rule appears to hold widely across taxa where SSD is male-biased, but not consistently when SSD is female-biased. Furthermore, studies addressing this question within species are rare, so it remains unclear whether this rule applies at the intraspecific level. We assess body size and SSD within Tribolium castaneum （Herbst）, a species where females are larger than males, using 21 populations derived from separate locations across the world, and maintained in isolated laboratory culture for at least 20 years. Body size, and hence SSD patterns, are highly susceptible to variations in temperature, diet quality and other environmental factors. Crucially, here we nullify interference of such confounds as all populations were maintained under identical conditions （similar densities, standard diet and exposed to identical temperature, relative humidity and photoperiod）. We measured thirty beetles of each sex for all populations, and found body size variation across populations, and （as expected） female-biased SSD in all populations. We test whether Rensch＇s rule holds for our populations, but find isometry, i.e. no allometry for SSD. Our results thus show that Rensch＇s rule does not hold across populations within this species. Our intraspecific test matches previous interspecific studies showing that Rensch＇s rule fails in species with female-biased SSD.展开更多
文摘Reproductive parasites such as Wolbachia are extremely widespread amongst the arthropods and can have a large influence over the reproduction and fitness of their hosts. Undetected infections could thus confound the results of a wide range of studies that focus on aspects of host behavior, reproduction, fitness, and degrees of reproductive isolation. This potential problem has already been underlined by work investigating the in- cidence of Wolbachia infections in stocks of the model system Drosophila melanogaster. Here we survey a range of lab stocks of further commonly used model arthropods, fo- cusing especially on the flour beetles Tribolium castaneum and Tribolium confusum, the cowpea weevil Callosobruchus maculatus and related species （Coleoptera： Tenebrionidae and Bruchidae）. These species are widespread stored product pests so knowledge of infec- tions with symbionts further has potential use in informing biocontrol measures. Beetles were assessed for infection with 3 known microbial reproductive parasites： Wolbachia, Rickettsia, Spiroplasma. Infections with some of these microbes were found in some of the lab stocks studied, although overall infections were relatively rare. The consequences of finding infections in these or other species and the type of previous studies likely to be affected most are discussed.
基金Acknowledgments The authors thank Richard Beeman （USDA） for generously sending us the beetles used to start our lab stocks, and Wolf Blanckenhorn for kindly providing a copy of an Excel spreadsheet designed for calculation of RMA and MA slopes. The authors further thank NERC （Standard research grant to MJGG, BCE and OYM）, Swiss National Science Foundation （postdoctoral fellowships and Ambizione grants to OYM）, the University of East Anglia and ETH Zurich for support, and the anonymous reviewers for comments on the manuscript.
文摘Rensch＇s rule proposes a universal allometric scaling phenomenon across species where sexual size dimorphism （SSD） has evolved： in taxa with male-biased dimorphism, degree of SSD should increase with overall body size, and in taxa with female-biased dimorphism, degree of SSD should decrease with increasing average body size. Rensch＇s rule appears to hold widely across taxa where SSD is male-biased, but not consistently when SSD is female-biased. Furthermore, studies addressing this question within species are rare, so it remains unclear whether this rule applies at the intraspecific level. We assess body size and SSD within Tribolium castaneum （Herbst）, a species where females are larger than males, using 21 populations derived from separate locations across the world, and maintained in isolated laboratory culture for at least 20 years. Body size, and hence SSD patterns, are highly susceptible to variations in temperature, diet quality and other environmental factors. Crucially, here we nullify interference of such confounds as all populations were maintained under identical conditions （similar densities, standard diet and exposed to identical temperature, relative humidity and photoperiod）. We measured thirty beetles of each sex for all populations, and found body size variation across populations, and （as expected） female-biased SSD in all populations. We test whether Rensch＇s rule holds for our populations, but find isometry, i.e. no allometry for SSD. Our results thus show that Rensch＇s rule does not hold across populations within this species. Our intraspecific test matches previous interspecific studies showing that Rensch＇s rule fails in species with female-biased SSD.
