A Generalist Feeding on Brassicaceae: It Does Not Get Any Better with Selection

Brassicaceae (Cruciferae) are ostensibly defended in part against generalist insect herbivores by toxic isothiocyanates formed when protoxic glucosinolates are hydrolysed. Based on an analysis of published host records, feeding on Brassicas is widespread by both specialist and generalists in the Lepidoptera. The polyphagous noctuid moth Helicoverpa armigera is recorded as a pest on some Brassicas and we attempted to improve performance by artificial selection to, in part, determine if this contributes to pest status. Assays on cabbage and kale versus an artificial diet showed no difference in larval growth rate, development times and pupal weights between the parental and the selected strain after 2, 21 and 29 rounds of selection, nor in behaviour assays after 50 generations. There were large differences between the two Brassicas: performance was better on kale than cabbage, although both were comparable to records for other crop hosts, on which the species is a major pest. We discuss what determines “pest” status.

Pelagic larval growth rate impacts benthic settlement and survival of a temperate reef fish

Larvae of marine reef organisms settling into benthic habitats may vary greatly in individual quality. We evaluated potential effects of variation in larval growth rate (1 metric of quality) on larval duration, size-at-settlement, and post-settlement survival of recently settled kelp bass Paralabrax clathratus. We sampled kelp bass daily and weekly from standardized collectors located near the Wrigley Institute for Environmental Studies, Santa Catalina Island, to characterize larval traits of settlers and surviving recruits. Using growth models to fit trajectories of larval otolith growth, we estimated instantaneous larval growth rates and found that these values were good predictors of larval duration and juvenile survival. Kelp bass that grew rapidly as larvae settled ∼8.5 d sooner than the slowest growing individuals; both groups had similar sized individuals at settlement, but fast growing larvae experienced enhanced survival during the first 5 d after settlement relative to slower growing larvae. There is growing evidence suggesting that larval experience continues to exert demographic consequences on subsequent life stages. This helps to explain some of the spatial and temporal variability that characterizes recruitment in marine systems.

Pelagic larval growth rate impacts benthic settlement and survival of a temperate reef fish

Larvae of marine reef organisms settling into benthic habitats may vary greatly in individual quality. We evaluated potential effects of variation in larval growth rate (1 metric of quality) on larval duration, size-at-settlement, and post-settlement survival of recently settled kelp bass Paralabrax clathratus. We sampled kelp bass daily and weekly from standardized collectors located near the Wrigley Institute for Environmental Studies, Santa Catalina Island, to characterize larval traits of settlers and surviving recruits. Using growth models to fit trajectories of larval otolith growth, we estimated instantaneous larval growth rates and found that these values were good predictors of larval duration and juvenile survival. Kelp bass that grew rapidly as larvae settled ∼8.5 d sooner than the slowest growing individuals; both groups had similar sized individuals at settlement, but fast growing larvae experienced enhanced survival during the first 5 d after settlement relative to slower growing larvae. There is growing evidence suggesting that larval experience continues to exert demographic consequences on subsequent life stages. This helps to explain some of the spatial and temporal variability that characterizes recruitment in marine systems.

Dipteran diversity and succession pattern on carcass of rabbits treated with opium dross: Implication in forensic medicine

Keshavarz D, Rassi Y, Oshaghi MA, Azizi K, Rafizadeh S, Shahriarinamadi M. 2020. Dipteran diversity and succession pattern on carcass of rabbits treated with opium: Implication in forensic medicine. Biodiversitas 21: 3135-3141. The present study aimed to investigate the effect of opium on the succession pattern and diversity of Diptera on rabbit carcasses. In the present experimental study, dipteran species were collected from rabbit carcasses during the decay process. During this study, two replicates were performed, and four rabbits were used in each. Rabbits divided equally into two groups. In the first group, animals were received 25 mg opium dross orally via a gastric tube and then gradually increased the dose to 100 mg/case/day, while the second group were used as controls and received distilled water. The most frequent species on both carcass types were Chrysomya albiceps (26.2%), Lucilia sericata (15.9%), and Musca domestica (13.9%). Diversity analysis indicates high species richness on untreated carcasses (Shannon: 2.1; Margalef: 1.7). However, a significant difference was not detected for the Shannon index between the treated and untreated carcasses (P: 0.56). The taxa similarity values for sampling intervals ranged from 0.20-0.46 for both untreated and treated carcasses. Permutation analysis showed that successional patterns of dipteran species were similar between opium dross-treated and untreated carcasses. Therefore, in the case of opioid (opium) abused cadaver, this substance could not have an effect on the PMI estimation based on the pattern of succession. But it seems that the PMI should be corrected when the estimate is based on larval growth rate.

Insulin-Like Signalling Influences the Coordination of Larval Hemocyte Number with Body Size in Drosophila melanogaster

Blood cells, known as hemocytes in invertebrates, play important and conserved roles in immunity, wound healing and tissue remodelling. The control of hemocyte number is therefore critical to ensure these functions are not compromised, and studies using Drosophila melanogaster are proving useful for understanding how this occurs. Recently, the embryonic patterning gene, torso-like (tsl), was identified as being required both for normal hemocyte development and for providing immunity against certain pathogens. Here, we report that Tsl is required specifically during the larval phase of hematopoiesis, and that tsl mutant larvae likely have reduced hemocyte numbers due to a reduced larval growth rate and compromised insulin signaling. Consistent with this, we find that impairing insulin-mediated growth, either by nutrient deprivation or genetically, results in fewer hemocytes. This is likely the result of impaired insulin-like signaling in the hemocytes themselves, since modulation of Insulin-like Receptor (InR) activity specifically in hemocytes causes concomitant changes to their population size in developing larvae. Taken together, our work reveals the strong relationship that exists between body size and hemocyte number, and suggests that insulin-like signaling contributes to, but is not solely responsible for, keeping these tightly aligned during larval development.

Insulin-like signalling influences the coordination of Drosophila larval hemocyte number with body size

Blood cells, known as hemocytes in invertebrates, play important and conserved roles in immunity, wound healing and tissue remodelling. The control of hemocyte number is therefore critical to ensure these functions are not compromised, and studies using Drosophila are proving useful for understanding how this occurs. Recently, the well characterised embryonic patterning gene, torso-like (tsl), was identified as being required both for normal hemocyte number and for providing immunity against certain pathogens. Here, we report that Tsl is required specifically during the larval phase of hematopoiesis, and that the reduced hemocyte number found in tsl mutant larvae is likely the result of a reduced larval growth rate and compromised insulin signalling. Consistent with this, we find that impairing insulin-mediated growth, either by nutrient deprivation or genetically, results in fewer hemocytes. This is likely the result of impaired insulin-like signalling in the hemocytes themselves since modulation of Insulin-like Receptor (InR) activity specifically in hemocytes causes concomitant changes to their population size in developing larvae. Taken together, our work reveals the strong relationship that exists between body size and hemocyte number, and suggests that insulin-like signalling contributes to, but is not solely responsible for, keeping these tightly aligned during larval development.

Field study suggests that sex determination in sea lamprey is directly influenced by larval growth rate

Sex determination mechanisms in fishes lie along a genetic-environmental continuum and thereby offer opportunities to understand how physiology and environment interact to determine sex. Mechanisms and ecological consequences of sex determination in fishes are primarily garnered from teleosts, with little investigation into basal fishes. We tagged and released larval sea lamprey ( Petromyzon marinus ) into unproductive lake and productive stream environments. Sex ratios produced from these environments were quantified by recapturing tagged individuals as adults. Sex ratios from unproductive and productive environments were initially similar. However, sex ratios soon diverged, with unproductive environments becoming increasingly male-skewed and productive environments becoming less male-skewed with time. We hypothesize that slower growth in unproductive environments contributed to the sex ratio differences by directly influencing sex determination. To the best of our knowledge, this is the first study suggesting that growth rate in a fish species directly influences sex determination; other studies have suggested that the environmental variables to which sex determination is sensitive (e.g. density, temperature) act as cues for favourable or unfavourable growth conditions. Understanding mechanisms of sex determination in lampreys may provide unique insight into the underlying principles of sex determination in other vertebrates and provide innovative approaches for their management where valued and invasive.