Too Hot to Nest? In a Hot Summer the Tortoise Chersina angulata Can Switch From Nesting to Facultative Viviparity

In a captive colony of Chersina angulata in Cape Town, South Africa, we observed in 2015/16 retention of the last egg clutch inside the female until the hatching stage was reached, conforming to the generally accepted definition of viviparity. Retrospective climatic analysis indicates egg retention until the hatching stage co-occurred with unusually hot summer weather: the average air temperatures in December 2015 and January and February 2016 were higher than during the preceding five and the following 5 years when facultative viviparity could not be observed. Late December and January appears to be the critical period for females to either deposit their last clutch of the nesting season into a nest, or to retain the last clutch for embryonic development inside the female. Over the 28 December to 24 January period the minimum, average and maximum air temperatures in 2015–16 were about 3°C higher than in the five following years. This association of facultative viviparity with unusual summer heat suggests that hot ambient temperatures at the end of the nesting season may cue females to switch from oviposition to facultative viviparity. Compared to incubation in a nest this phenotypic plasticity of the reproductive mode—to retain during hot summers the season’s last clutch inside the female—may buffer the developing embryos from excessive heat exposure: females can thermo-regulate by moving among microhabitats whereas sun exposed shallow nests cannot escape high ground temperatures. This novel reproductive strategy has the potential to enhance the resilience of species to global warming.

Aquatain® Causes Anti-Oviposition, Egg Retention, Oocyte Melanization and Triggers Female Death in Ae. Aegypti

Background: In arboviral disease systems where the virus can be transmitted from male to female and from one generation to the next, targeting the female (especially when she is pregnant) can help alter the persistence of the virus in nature and its transmission. This is typical of Ae. aegypti, which has been unmanageable due to the development of insecticide resistance. Despite evidence that monomolecular surface films prevent the selection of genetic resistance, their potential in Aedes vector control remains largely unexplored. Methods: We examined the oviposition, egg retention, oocyte melanization, and female mortality of the Cayman Islands strain of Ae. aegypti, using choice and no-choice bioassays involving Aquatain® Mosquito Formulation (AMF). Results: When presented with similar opportunities to oviposit in two sites treated with AMF and two others with water (control), egg deposition rates were significantly higher in water than in oil presence. We also observed a matching pattern of egg deposition preference in arenas with more options in AMF-treated sites. Females laid appreciably more eggs when water was the only available medium than when all sites were treated with AMF. Also, considerably more mature eggs were withheld in the AMF no-choice arena than in the no-choice test involving only water. Internal oocyte melanization was not observed in females from the oviposition arenas with the lowest oil presence (equal-choice and water-based no-choice); in contrast, this physiological response intensified as the number of AMF-treated sites increased. Female death occurred at high rates in AMF-treated environments, and this response increased with the increasing presence of such egg deposition sites. Conclusions: This study demonstrated that AMF acted as a deterrent signal to ovipositing Ae. aegypti and an indirect adulticide. Referring to its previously reported direct toxicity on the aquatic stages of this mosquito and its biodegradability, AMF should be incorporated as a critical component in integrated control strategies for dengue and related diseases.

End-of-life targeted degradation of DAF-2 insulin/IGF-1 receptor promotes longevity free from growth-related pathologies

Preferably, lifespan-extending therapies should work when applied late in life without causing undesired pathologies. Reducing insulin/insulin-like growth factor (IGF)-1 signaling (IIS) increases lifespan across species, but the effects of reduced IIS interventions in extreme geriatric ages remains unknown. Using the nematode Caenorhabditis elegans, we engineered the conditional depletion of the DAF-2/insulin/IGF-1 transmembrane receptor using an auxin-inducible degradation (AID) system. This allowed for the temporal and spatial reduction in DAF-2 protein levels at time points after which interventions such as RNAi become ineffective. Using this system, we found that AID-mediated depletion of DAF-2 protein surpasses the longevity of daf-2 mutants. Depletion of DAF-2 during early adulthood resulted in multiple adverse phenotypes, including growth retardation, germline shrinkage, egg retention, and reduced brood size. By contrast, AID-mediated depletion of DAF-2 post-reproduction, or specifically in the intestine in early adulthood, resulted in an extension of lifespan without these deleterious effects. Strikingly, at geriatric ages, when 75% of the population had died, AID-mediated depletion of DAF-2 protein resulted in a doubling in lifespan. Thus, we provide a proof-of-concept that even close to the end of an individual’s lifespan, it is possible to slow aging and promote longevity.

Impact of seasonal adult emergence period on reproductive performance of tasar silkmoth Antherea mylitta Drury (Lepidoptera: Saturnidae)

Influence of adult emergence period and prevailing weather parameters on reproductive biology of tasar silkmoth Antherea mylitta was studied under grainage (indoor) condition. There was a significant difference of fecundity was observed on different days of adult emergence. Maximum fecundity was observed on 10th day (219 eggs/female) during first grainage (diapause cocoons) while same has been observed on 13th day (224.30 eggs/female) of emergence during second grainage (nondiapause cocoons). With respect to hatching percentage, during first grainage maximum hatching was observed on 1st, 6th, 7th and 12th days of emergence (93.32, 90.14, 90.96 and 90.18 % respectively). In the case of second grainage maximum hatching was on 12th and 2nd day of emergence. Data on per cent egg retention during first grainage ranged between 6.46 to 29.25 % and it was between 6.49 to 14.39 % during second grainage. Retained eggs were unfertile and could observe less than 2 % of hatching across all the days of emergence in first and second grainage together. Despite of significant difference in the reproductive parameters it was not clear about which phase or days of seasonal emergence period yields better layings. Better reproductive performance was scattered randomly across the days of emergence and it also indicates that adult emergence period don’t have any influence over reproductive biology of A. mylitta. Prevailing temperature and relative humidity during emergence period found to have no major influence over fecundity, hatching percentage and egg retention.

End-of-life targeted auxin-mediated degradation of DAF-2 Insulin/IGF-1 receptor promotes longevity free from growth-related pathologies

Preferably, lifespan-extending therapies should work when applied late in life without causing undesired pathologies. However, identifying lifespan-extending interventions that are effective late in life and which avoid undesired secondary pathologies remains elusive. Reducing Insulin/IGF-1 signaling (IIS) increases lifespan across species, but the effects of reduced IIS interventions in extreme geriatric ages remains unknown. Using the nematode C. elegans, we engineered the conditional depletion of the DAF-2/insulin/IGF-1 transmembrane receptor using an auxin-inducible degradation (AID) system that allows for the temporal and spatial reduction in DAF-2 protein levels at time points after which interventions such as RNAi may lose efficacy. Using this system, we found that AID-mediated depletion of DAF-2 protein efficiently extends animal lifespan. Depletion of DAF-2 during early adulthood resulted in multiple adverse phenotypes, including growth retardation, germline shrinkage, egg-retention, and reducing offspring. By contrast, however, AID-mediated depletion of DAF-2 specifically in the intestine resulted in an extension of lifespan without these deleterious effects. Importantly, AID-mediated depletion of DAF-2 protein in animals past their median lifespan allowed for an extension of lifespan without affecting growth or behavioral capacity. Thus, both late-in-life targeting and tissue-specific targeting of IIS minimize the deleterious effects typically seen with interventions that reduced IIS, suggesting potential therapeutic methods by which longevity and healthspan can be increased in even geriatric populations.

Behavioural adaptations in egg laying ancestors facilitate evolutionary transitions to live birth

Live birth is a key innovation that has evolved from egg laying over 100 times in reptiles. One significant feature in this transition is the thermal conditions experienced by developing embryos. Adult lizards and snakes often have preferred body temperatures that can be lethal to developing embryos and should prevent egg retention: how has viviparity repeatedly evolved in the face of this pervasive mismatch? Here we resolve this paradox by conducting phylogenetic analyses using data on thermal preference from 224 species. Thermal mismatches between mothers and offspring are widespread but resolved by gravid females behaviourally down-regulating their body temperature towards the thermal optimum of embryos. Importantly, this thermoregulatory behaviour evolved in ancestral egg-laying species before the evolutionary emergence of live birth. Maternal thermoregulatory behaviour therefore bypasses constraints imposed by a slowly evolving thermal physiology and is likely to have been a key requirement for repeated transitions to live birth.

Modelling grass carp egg transport using a 3-D hydrodynamic river model: the role of egg retention in dead zones on spawning success

Invasive grass carp (Ctenopharyngodon idella) are known to spawn in the Sandusky River, Ohio, USA, within the Great Lakes Basin, and are threatening to expand throughout the Great Lakes. Successful spawning is thought to require that eggs remain in suspension until hatching, which depends on river hydrodynamics and temperature-dependent egg development. Previous modelling efforts used one-dimensional hydrodynamic models that simplify egg movement by not simulating low-velocity zones within the river. To examine the effect of low-velocity zones on egg transit times and hatching rates, we developed a novel coupling of a biophysical Lagrangian particle tracker and three-dimensional hydrodynamic model on the Sandusky River during a high-flow event. The model successfully predicted egg-capture data for a range of developmental stages and revealed a mechanism that resuspends eggs trapped in low-velocity zones. The resuspension mechanism increases the residence time of grass carp eggs in spawning tributaries and can lead to successful hatching occurring in shorter distances than previously estimated. Grass carp potentially spawning in shorter tributary lengths has widespread implications for efforts preventing establishment in the Great Lakes Basin.