Den Finkenbach wieder besucht – wie lange dauert das Larvalstadium des Bachneunauges Lampetra planeri (Bloch, 1784)?

Im November 1989 und von März bis November 1990 wurden im Finkenbach im hessischen Odenwald monatlich Larven des Bachneunauges Lampetra planeri gefangen und vermessen. Ziel war es, anhand von Längenfrequenzen die Anzahl von Altersklassen und damit die Dauer des Larvalstadiums bestimmen zu können. Anhand einer visuellen Analyse der Längenverteilungen wurde 1990 auf eine Dauer des Larvalstadiums von etwas über sechs Jahren, in einigen Fällen vielleicht auch ein Jahr länger, geschlossen. Die 1989/90 erhobenen Daten wurden 2020 mittels generalisierter additiver Modelle erneut ausgewertet. Anhand des Akaike-Informationskriteriums wurde für jeden Monat das Modell bestimmt, das die Anzahl vorhandener Größenklassen am besten beschrieb. Mit diesen Modellen konnten die Einschätzungen von 1990 im Wesentlichen bestätigt werden. Allerdings ist die Annahme, dass das Larvalstadium etwas über sechs Jahre dauert, mit großen Unsicherheiten behaftet. Die Anzahl von Larven in den höheren Längenbereichen ist zu gering, um hier robuste Schlüsse zur Anzahl von Größen- und damit Altersklassen zuzulassen. Weiterhin ist bei anderen Neunaugenarten auch experimentell nachgewiesen, dass die Metamorphose in einem unterschiedlichen Alter einsetzen kann. Das Wachstum von Neunaugenlarven und damit das Alter, in dem die Metamorphose einsetzt, ist von den Verhältnissen in den Gewässern abhängig. Daher wäre es interessanter, den Einfluss von Umweltbedingungen auf das Wachstum in einer Zeit des Klimawandels zu untersuchen, anstatt sich nur auf die Frage des Zeitpunkts der Metamorphose zu beschränken. Finkenbach revisited – how long is the duration of larval life in the Brook Lamprey? Abstract: In November 1989 and from March to November 1990, larvae of the brook lamprey Lampetra planeri were caught and measured monthly in the Finkenbach-River in the Hessian Odenwald in Germany. The aim was to analyse length frequencies to determine the number of age cohorts and thus the duration of the larval life. Based on a purely visual analysis of the length distributions, it was concluded that the larval life lasted a little over six years, and in some cases perhaps a year longer. The data collected in 1989/90 were re-analysed in 2020 with generalized additive models. Using the Akaike information criterion, the model that best described the number of existing size classes was determined for each month. With these models, the assessment was similar compared to the visual analysis in 1990. However, the assumption that the larval stage lasts a little over six years includes a high degree of uncertainty. The number of larvae in the higher length ranges is too low to allow robust conclusions about the numbers of size-cohorts and thus age groups. Furthermore, it has been experimentally shown in other lamprey species that metamorphosis can begin at different ages. The growth of lamprey larvae and thus the age at which they enter metamorphosis depends on environmental conditions. Therefore, it would be more interesting to examine the influence of these conditions on growth in a time of global warming, instead of restricting analyses to the question of the exact age of metamorphosis.

Insulin signaling and osmotic stress response regulate arousal and developmental progression of C. elegans at hatching

The progression of animal development from embryonic to juvenile life depends on the coordination of organism-wide responses with environmental conditions. We found that two transcription factors that function in interneuron differentiation in Caenorhabditis elegans, fax-1 and unc-42, are required for arousal and progression from embryogenesis to larval life by potentiating insulin signaling. The combination of mutations in either transcription factor and a mutation in daf-2 insulin receptor results in a novel peri-hatching arrest phenotype; embryos are fully-developed but inactive, often remaining trapped within the eggshell, and fail to initiate pharyngeal pumping. This pathway is opposed by an osmotic sensory response pathway that promotes developmental arrest and a sleep state at the end of embryogenesis in response to elevated salt concentration. The quiescent state induced by loss of insulin signaling or by osmotic stress can be reversed by mutations in genes that are required for sleep. Therefore, countervailing signals regulate late embryonic arousal and developmental progression to larval life, mechanistically linking the two responses. Our findings demonstrate a role for insulin signaling in an arousal circuit, consistent with evidence that insulin-related regulation may function in control of sleep states in many animals. The opposing quiescent arrest state may serve as an adaptive response to the osmotic threat from high salinity environments.

Duox generated reactive oxygen species activate ATR/Chk1 to induce G2 arrest in Drosophila tracheoblasts

Progenitors of the thoracic tracheal system of adult Drosophila (tracheoblasts) arrest in G2 during larval life and rekindle a mitotic program subsequently. G2 arrest is dependent on ATR-dependent phosphorylation of Chk1 that is actuated in the absence of detectable DNA damage. We are interested in the mechanisms that activate ATR/Chk1 (Kizhedathu et al., 2018, 2020). Here we report that levels of reactive oxygen species (ROS) are high in arrested tracheoblasts and decrease upon mitotic re-entry. High ROS is dependent on expression of Duox, an H2O2 generating-Dual Oxidase. ROS quenching by overexpression of Superoxide Dismutase 1, or by knockdown of Duox, abolishes Chk1 phosphorylation and results in precocious proliferation. Tracheae deficient in Duox, or deficient in both Duox and regulators of DNA damage-dependent ATR/Chk1 activation (ATRIP/TOPBP1/ Claspin), can induce phosphorylation of Chk1 in response to micromolar concentrations of H2O2 in minutes. The findings presented reveal that H2O2 activates ATR/Chk1 in tracheoblasts by a non-canonical, potentially direct, mechanism.

Fish-Released Kairomones Affect Mosquito Oviposition and Larval Life History

Several species of mosquitoes respond to the presence of kairomones released by larvivorous predators during oviposition habitat selection and larval development. These responses may differ among mosquito species and do not always correlate with larval survival. This study examined the responses of the mosquito Culiseta longiareolata Macquart (Diptera: Culicidae) to kairomones released by three species of fish, Gambusia affinis (Cyprinodontiformes: Poeciliidae), Aphanius mento (Cyprinodontiformes: Cyprinodontidae) and Garra rufa (Cypriniformes: Cyprinidae) during oviposition. In addition, the study examined the effects of kairomones released by Gm. affinis on larval development and survival. Results show that ovipositing female avoided cues from the two larvivorous fish species but not the algivorous Gr. rufa. In addition, developing larvae metamorphosed slower and showed increased mortality when exposed to fish-released kairomones. Culiseta longiareolata larvae are known as dominant competitors, and the straightforward responses of both larvae and adult female to fish-released kairomones may be explained by the lack of additional sources of larval stress other than the presence of predators.

Diversity and evolution of amphibian pupil shapes

Pupil constriction has important functional consequences for animal vision, yet the evolutionary mechanisms underlying diverse pupil sizes and shapes, often among animals that occupy optically similar environments, are poorly understood. We aimed to quantify the diversity and evolution of pupil shapes among amphibians and test for potential correlations to ecology based on functional hypotheses. Using photographs, we surveyed pupil shape and the orientation of the constricted pupil across adults of 1293 amphibian species, 72 families, and 3 orders, and additionally for larval life stages for all families of frogs and salamanders with a biphasic ontogeny. Pupil shape is exceptionally diverse in amphibians with evolutionary transitions throughout the amphibian tree of life. For amphibians with a biphasic life history, we found that pupils change in many species that occupy distinct habitats before and after metamorphosis. Finally, we found that non-elongated (round or diamond) constricted pupils were correlated with species inhabiting consistently dim light environments (burrowing and aquatic species) and that elongated pupils (vertical and horizontal) were more common in species with larger absolute eye sizes. We propose that amphibians provide a valuable group within which to explore the anatomical, physiological, optical, and ecological mechanisms underlying the evolution of pupil shape.

Duox generated reactive oxygen species activate ATR/Chk1 to induce G2 arrest in Drosophila tracheoblasts

ABSTRACTProgenitors of the thoracic tracheal system of adult Drosophila (tracheoblasts) arrest in G2 during larval life and rekindle a mitotic program subsequently. G2 arrest is dependent on ATR-dependent phosphorylation of Chk1 that is actuated in the absence of detectable DNA damage. We are interested in the mechanisms that activate ATR/Chk1 (Kizhedathu et al., 2018, 2020). Here we report that levels of reactive oxygen species (ROS) are high in arrested tracheoblasts and decrease upon mitotic re-entry. High ROS is dependent on expression of Duox, an H2O2 generating-Dual Oxidase. ROS quenching by overexpression of Superoxide Dismutase 1, or by knockdown of Duox, abolishes Chk1 phosphorylation and results in precocious proliferation. Tracheae deficient in Duox, or deficient in both Duox and regulators of DNA damage-dependent ATR/Chk1 activation (Claspin/ATRIP/TOPBP1), can induce phosphorylation of Chk1 in response to micromolar concentrations of H2O2 in minutes. The findings presented reveal that H2O2 activates ATR/Chk1 in tracheoblasts by a non-canonical, potentially direct, mechanism.

The life cycle of Orthemis ferruginea (Fabricius, 1775) (Odonata: Libellulidae)

The complete life cycle of O. ferruginea is described for the first time, represent the first complete life cycle described for an odonate in Mexico. The 17 larval instars obtained are described and illustrated in detail, from prolarva through F-0. Two egg batches of different females were obtained in the field and were subsequently reared in the laboratory. Eggs and larvae of the batches were raised under 26°C controlled temperature conditions until they reached instars F-6 and F-5. An extra collection of wild organisms was made in order to complete the life cycle from F-5. Only four of the wild larvae managed to complete the last five missing larval instars at 30°C. Larvae of the youngest instars (F-15 to F-8) were fed nauplii of Artemia franciscana, while F-7 to F-0 were fed larvae of Culicidae and Chironomidae. Larval life cycle from F-0 to F-16 lasted average of 186 days.

Fish-released kairomones affect Culiseta longiareolata oviposition and larval life history

Several species of mosquitoes respond to the presence of kairomones released by larval predators during oviposition habitat selection and larval development. These responses may differ among mosquito species and do not always correlate with larval survival. This study examined the responses of the mosquito Culiseta longiareolata Macquart to kairomones released by three species of fish during oviposition, Gambusia affinis Baird and Girard, Aphanius mento Heckel and Garra rufa Heckel. In addition, the study examined the effects of kairomones released by G. affinis on larval development. Results show that ovipositing female avoided cues from larvivorous, but not algivorous fish. In addition, developing larvae metamorphosed slower and showed increased mortality when exposed to fish-released kairomones. Results suggest that the responses of this mosquito species to fish-released kairomones may be explained by its competitive ability.

Oxygen limitation fails to explain upper chronic thermal limits and the temperature size rule in mayflies

An inability to adequately meet tissue oxygen demands has been proposed as an important factor setting upper thermal limits in ectothermic invertebrates (especially aquatic species) as well as explaining the observed decline in adult size with increased rearing temperature during the immature stages (a phenomenon known as the Temperature Size Rule, or TSR). We tested this by rearing three aquatic insects (the mayflies Neocloeon triangulifer and two species of the Cloeon dipterum complex) through their entire larval life under a range of temperature and oxygen concentrations. Hyperoxia did not extend upper thermal limits, nor did it prevent the loss of size or fertility experienced near upper chronic thermal limits. At moderate temperatures, the TSR pattern was observed under conditions of hyperoxia, normoxia, and hypoxia, suggesting little or no influence of oxygen on this trend. However, for a given rearing temperature, adults were smaller and less fecund under hypoxia due to a lowering of growth rates. These mayflies greatly increased the size of their gills in response to lower dissolved oxygen concentrations but not under oxygen-saturated conditions over a temperature range yielding the classic TSR response. Using ommatidium diameter as a proxy for cell size we found the classic TSR pattern observed under moderate temperature conditions was due primarily to a change in the number of cells rather than cell size. We conclude overall that a failure to meet tissue oxygen demands is not a viable hypothesis for explaining either the chronic thermal limit or TSR pattern in these species.