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Background Eggs of anopheline mosquitoes hatch within a few days of laying and require high levels of humidity to survive. Assessing natural variation in egg hatching and its environmental and genetic determinants in sibling species of the malaria vector Anopheles gambiae s.l. is important for understanding their adaptation to variable aquatic habitats. Crucially, it can also inform insectary rearing practices toward the optimization of mosquito production for genetic vector control strategies. Methods Hatching rates and timing of egg hatching in long-established and recently colonized strains of An. gambiae s.s, Anopheles arabiensis , and Anopheles coluzzii , were compared under still water conditions (26 ℃) and with cold (4 ℃) and (15 ℃) water agitation regimes. Next, early and late hatching strains of the recently colonized An. coluzzii VK colony were generated through bidirectional selection for 18–23 generations to detect a genetic component for this trait. Results Hatching rates differed significantly between species and treatments. The older An. arabiensis Senn and An. gambiae s.s. Kisumu strains had the highest proportion of hatching and preferred the nonagitation treatment at 26 °C. In contrast, the more recently colonized An. coluzzii VK and An. arabiensis Rufisque strains had lower overall hatching success but responded strongly to agitation at 4 °C, while the An. coluzzii Mopti strain did not significantly respond to water agitation. In all strains, eggs hatching started at day 2 and continued till day 5 in the older strains, whilst it was more staggered and extended up to day 6 in the younger strains. Bidirectional selection for early and late hatching over many generations resulted in early hatching selected strains with eggs hatching 2–3 days earlier than in late hatching ones indicating a significant heritable component for these traits. Conclusions Water agitation and temperature and age of colonization are likely important determinants of egg hatching in natural An. gambiae s.l. populations. Current rearing protocols systematically select for fast hatching and result in the progressive loss of staggered egg hatching in older laboratory strains. The selection of novel slow-hatching strains may prove instrumental to enable the mass production, shipping, and release of Anopheles mosquitoes across Africa as part of genetic vector control programs. Graphical Abstract

Variation in life-history strategies is central to our understanding of population dynamics and how organisms adapt to their environments. Yet we lack consensus regarding the ecological processes that drive variation in traits related to reproduction and survival. For example, we still do not understand the cause of two widespread inter- and intraspecific patterns: (1) the ubiquitous positive association between avian clutch size and latitude; and (2) variation in the extent of asynchronous hatching of eggs within a single clutch. Well-known hypotheses to explain each pattern have largely focused on biotic processes related to food availability and predation risk. However, local adaptation to maintain egg viability could explain both patterns with a single abiotic mechanism. The egg viability hypothesis was initially proposed to explain the cause of asynchronous hatching and suggests that asynchronous hatching results from early incubation onset in response to unfavorable nest microclimatic conditions, which otherwise reduce egg viability. However, allocation of resources to early incubation, prior to clutch completion, may energetically constrain clutch size and help explain the positive association between clutch size and latitude. We measured intraspecific variation in five functionally linked life-history traits of burrowing owls at five study sites spanning a 1,400-km latitudinal transect in western North America: clutch size, the timing of incubation onset, the degree of hatching asynchrony, the probability of hatching failure, and nestling survival. We found that most traits varied clinally with latitude, but all the traits were more strongly associated with individual nest microclimates than with latitude, and all varied with nest microclimate in the directions predicted by the egg viability hypothesis. Furthermore, incubation began earlier, hatching asynchrony increased, and clutch size declined across the breeding season. These results suggest that nest microclimate drives an important life-history trade-off and that thermal gradients are often sufficient to account for observed biogeographic and seasonal patterns in life-history strategies. Furthermore, our results reveal a potentially important indirect mechanism by which reproductive success and recruitment could be affected by climate change.

We assayed the toxicity of polystyrene nanoparticles (PS-NP, 52 nm) to Daphnia galeata . Survival and reproduction were significantly decreased in individuals exposed to 5 mg/L of PS-NP for 5 days, and embryos showed abnormal development, including a low hatching rate. Using fluorescence confocal microscopy, we recorded the transfer of PS-NP from the external surface of the body to the internal organs, including the thoracic appendices, ovaries, caudal appendices, and brood chamber, as well as PS-NP storage in lipid droplets. Although embryos were exposed to PS-NP in the brood chamber, they did not internalize PS-NP. Exposed D . galeata adults that were not pregnant stored significantly fewer lipid droplets than did the control group, and the lipid droplets that they did store were smaller; meanwhile, there were no significant changes in lipid storage in exposed pregnant individuals. Some embryos showed a high level of lipid storage, a response that occurs when embryos experience an abnormal state, and these embryos showed a very low hatching rate. However, the offspring of exposed adults showed normal survival and lipid storage. This study provides visual evidence that confirms the transfer and effects of PS-NP in Daphnia species, and suggests a relationship between toxicity and lipid storage.

Fish have somehow colonized isolated water bodies all over the world without human assistance. It has long been speculated that these colonization events are assisted by waterbirds, transporting fish eggs attached to their feet and feathers, yet empirical support for this is lacking. Recently, it was suggested that endozoochory (i.e., internal transport within the gut) might play a more important role, but only highly resistant diapause eggs of killifish have been found to survive passage through waterbird guts. Here, we performed a controlled feeding experiment, where developing eggs of two cosmopolitan, invasive cyprinids (common carp, Prussian carp) were fed to captive mallards. Live embryos of both species were retrieved from fresh feces and survived beyond hatching. Our study identifies an overlooked dispersal mechanism in fish, providing evidence for bird-mediated dispersal ability of soft-membraned eggs undergoing active development. Only 0.2% of ingested eggs survived gut passage, yet, given the abundance, diet, and movements of ducks in nature, our results have major implications for biodiversity conservation and invasion dynamics in freshwater ecosystems.

The spatial distribution of predators is affected by intra- and interspecific interactions within the predator guild. Studying these interactions under fluctuating food availability, while taking habitat characteristics into account, offers a quasi-experimental setup to determine the relative impact of con- and heterospecifics on reproductive success of predators. We analyzed the settlement decisions and reproductive success of Eurasian Pygmy Owls (Glaucidium passerinum) in the presence of both breeding conspecifics and their competitor and intraguild predator, Tengmalm's Owls (Aegolius funereus), under fluctuating abundance of their primary prey (voles). We used detailed data, collected across 11 years in a large study area (1300 km²), on the spatial and temporal variation of habitat characteristics in all available nesting sites, local densities of both species, and vole abundance. We found that Pygmy Owls strongly avoided breeding close to conspecifics but did not avoid Tengmalm's Owl nests. Nest box occupation of Pygmy Owls was positively correlated to the proportion of old spruce, mature and old pine forests, and farmlands, and occupation probability was higher at high vole abundance and in areas occupied in previous years. Pygmy Owl avoidance of conspecifics decreased when voles were abundant. At high conspecific density, Pygmy Owls showed lower hatching success and delayed hatching date, in agreement with the observed spatial avoidance. Finally, even though breeding Pygmy Owls did not spatially avoid Tengmalm's Owls, the density of heterospecifics correlated with low hatching and fledging success in Pygmy Owls. This suggests short term fitness costs when living close to competitors, even when lethal effects of intraguild interactions are subtle. Our results suggest that joint costs of exploitative and interference competition by Tengmalm's Owls, as well as intraguild predation, were lower than those induced by intraspecific competition only. This result might be due to the similar body size between the species considered, Tengmalm's Owls being only twice as large as Pygmy Owls. Interactions among con- and heterospecifics can therefore modify the spatial settlement and reproductive success of individuals on a landscape scale, also within the predator guild.

Costa Rica hosts two renowned olive ridley (Lepidochelys olivacea) arribada beaches: Nancite and Ostional. In addition, the country hosts a third nascent arribada beach in Corozalito. We documented the frequency of arribada events in Corozalito (9°50′55.40″ N; 85°22′ 47.67″ W) from 2008 to 2021 and the abundance of egg-laying females during 12 arribadas. Moreover, we report on tag recaptures at Corozalito that were initially deployed at other nesting beaches in Costa Rica. Finally, we estimated incubation temperature, and performed quadrat and nest excavations to estimate hatching rates. We registered 29 arribadas at Corozalito since 2008, all between August and January. We estimated more than 150,000 olive ridleys nested during 12 arribadas from 2019 to 2021. Mean hatching success was 65% in quadrats and 59% for in situ marked nests. The mean incubation temperature was 32.3 °C. We found turtles tagged at other locations on the Pacific coast of Costa Rica nesting at Corozalito, providing evidence of philopatric plasticity. We suggest nascent arribada rookeries form rapidly via recruitment from regional turtle aggregations. Our findings show that hatching success is far higher at Corozalito than Ostional or Nancite. Continued monitoring of nesting dynamics at this site may shed light upon the mechanisms that rule how arribada beaches are born and evolve. Corozalito offers a unique opportunity to study and understand the arribada phenomenon and warrants official protection under official National Wildlife Refuge status.

The green sea turtle (Chelonia mydas) is the only sea turtle species that breeds in China, and the largest remaining nesting grounds for green sea turtles in Chinese waters is found on the Qilianyu atoll of the Xisha Islands. Nesting site selection is particularly important for egg survival, and understanding the microhabitat characteristics of green sea turtle nesting sites is crucial for delineating priority conservation areas for nesting grounds. In this study, we aimed to examine the role of several microhabitat ecological factors in the selection of nesting sites and the success of nesting. To this end, we performed differential comparisons, principal component analysis, and generalized linear model analysis. There were significant differences in microhabitat ecological factors, such as surface temperature, humidity, and particle size distribution (0.250–1 mm), between the nesting sites and the surrounding area. Green sea turtle nests were concentrated at a distance of 20.1–30 m from the high tide line, with a preferred distance from vegetation of 0–0.5 m. The vegetation cover of successful nests was concentrated in the range of 0%–25%, and the preferred sand types for successful nests were coarse sand (0.425–1 mm) and medium sand (0.250–0.425 mm). The average hatching success of six green sea turtle nests on North Island was 94.52%. The key microhabitat factors affecting the success of nesting were found to be sand characteristics such as humidity, bulk density, and particle size ratio. Therefore, green sea turtles on the Xisha Islands exhibit preferences for microhabitat ecological factors during nesting site selection, and the ecological characteristics of nesting grounds can affect the hatching success rate of green sea turtles. Therefore, it is recommended to continuously monitor the characteristics of and changes in green sea turtle nesting site selection and take measures to provide high‐quality nesting and hatching environments for sea turtles. The green sea turtles in the Xisha Islands exhibit nest site microhabitat preference. The nesting sites are mainly concentrated at a distance from vegetation zone of 0–0.5 m, with 92% of aborted nests were distributed under dense vegetation. Green turtles tend to choose areas with coarse sand (0.425–1 mm) and medium sand (0.250–0.425 mm) for nesting. The hatching success rate of green sea turtles is positively correlated with microhabitat characteristics.

Most Lophiiformes including Lophius species are considered to spawn egg masses called an “egg veil” or “egg ribbon” composed of numerous mucoid chambers. However, Lophius eggs have been rarely collected in the field and thus little is known about their biological features. Here we examined the embryonic development of Lophius litulon and also the effects of water temperature on the embryonic development of eggs from egg veils collected in the field. Embryonic development was observed from the late cleavage stage to hatching. Low rates of mortality and deformity of embryos and early larvae were observed at 13–21°C. The estimated appropriate water temperature range closely approximated the range of temperatures (12–20°C) at which egg veils of L. litulon have been found in the field. Embryonic development accelerated with increased water temperatures. These results will enable estimation of the origin of and passive movement of egg veils and subsequently larvae and will help to reveal the spatiotemporal distribution of the spawning and nursery grounds of L. litulon.

Predation pressure on vulnerable bird species has made predator control an important issue for international nature conservation. Predator removal by culling or translocation is controversial, expensive, and time-consuming, and results are often temporary. Thus, it is important to assess its effectiveness from all available evidence. We used explicit systematic review methodology to determine the impact of predator removal on four measurable responses in birds: breeding performance (hatching success and fledging success) and population size (breeding and postbreeding). We used meta-analysis to summarize results from 83 predator removal studies from six continents. We also investigated whether characteristics of the prey, predator species, location, and study methodology explained heterogeneity in effect sizes. Removing predators increased hatching success, fledging success, and breeding populations. Removing all predator species achieved a significantly larger increase in breeding population than removing only a subset. Postbreeding population size was not improved on islands, or overall, but did increase on mainlands. Heterogeneity in effect sizes for the four population parameters was not explained by whether predators were native or introduced; prey were declining, migratory, or game species; or by the study methodology. Effect sizes for fledging success were smaller for ground-nesting birds than those that nest elsewhere, but the difference was not significant. We conclude that current evidence indicates that predator removal is an effective strategy for the conservation of vulnerable bird populations. Nevertheless, the ethical and practical problems associated with predator removal may lead managers to favor alternative, nonlethal solutions. Research is needed to provide and synthesize data to determine whether these are effective management practices for future policies on bird conservation.

1. Physiological parameters can give valuable indications about the performance of animals in their environment and the combined deleterious effects of several factors on the individual. The concentration of circulating glucocorticoids is often taken as a measurement of the level of stress an animal is exposed to. As an alternative, the ratio of heterophils (or neutrophils in mammals) to lymphocytes in blood (H/L-ratio) has been proposed. Although laboratory studies with exogenous corticosterone treatment or strong Stressors found a positive correlation between circulating corticosterone and the H/L-ratio, studies in free-living birds did not. 2. In Eurasian kestrel nestlings Falco tinnunculus, we first confirmed that implanting exogenous corticosterone elevated the H/L-ratio and depressed the immune response to PHA in altricial nestlings under field conditions, as found in precocial species. 3. In non-treated, free-living kestrel nestlings we showed that circulating corticosterone concentration and the H/L-ratio were not correlated among each other and that various environmental factors were not correlated with baseline corticosterone concentration to the same degree as with the H/L-ratio. Baseline corticosterone concentrations were only elevated when nestlings had no body fat stores and as a reaction to our presence at the nest. In contrast, the H/L-ratio was increased as a response to five potential natural Stressors: being later-hatched and thus competitively inferior, low body fat stores, ectoparasite infestation, after rain which impaired food delivery of adults and with ongoing season which reflects deteriorating environmental conditions. Baseline corticosterone on day 10 of age was a better predictor of survival until day 13 than the H/L-ratio. 4. In accordance with findings from the literature, it appears that baseline corticosterone concentration and H/L-ratio differ in sensitivity to various Stressors. While the H/L-ratio increases already in response to more subtle Stressors, both measures react to severe, life-threatening Stressors, like starvation in free-living birds, although in our study corticosterone was the better predictor of survival. 5. This study showed that baseline corticosterone and H/L-ratio cannot be used interchangeably as indicators of stress, but together can provide a comprehensive picture about the stressstatus of a bird in ecological studies. If only one measure is to be taken, the choice depends on the questions to be answered, practical issues (speed of blood sampling after first disturbance) and physiological interpretability and amenability to experiments.