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A large proportion of lake-Daphnia ephippia which are shed by females in the water column sink to the bottom, where they form an assemblage of dormant stages known as an egg bank. Although the quantity of zooplankton eggs in such assemblages may exceed tens of thousands per square meter, the annual hatch from this bank is usually extremely low (from zero to a few dozens animals per square meter per year). This low-hatching phenomenon may be caused by isolation from hatching stimuli by water or sediment layers, a mechanical barrier formed by sediment that does not allow hatchlings to reach the water, or by a bet-hedging strategy of the resting eggs. The aim of our study was to determine the extent to which coverage by lake sediment may affect the hatching of Daphnia dormant eggs. The ephippia of lake-Daphnia (longispina species complex), covered by sterilized lake sediment of different thicknesses (0, 0.25, 0.5, 1, 2 and 4 cm; 4 replicates per treatment), were incubated for 8 weeks in lab controlled conditions. The results indicate that even the thinnest tested layer (0.25 cm) may completely inhibit hatching of ephippial eggs. A few Daphnia neonates were observed in two (of five) sediment treatments, while dozens of animals hatched in the control one. In the second experiment we determined that the sediment sterilization process did not affect the hatching proportion of ephippial eggs (when compared to the treatment with unsterilized sediments). We hypothesize that the observed inhibition of Daphnia hatching in the main experiment, which may cause a serious problem for Cladoceran populations in lakes where no sediment mixing occurs, may be caused by low light intensity, anoxic conditions or a physical barrier created by the sediment.

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

The resting eggs of large branchiopods do not hatch all at once during a hydroperiod; instead, a fraction of the eggs are left dormant to cope with unstable conditions in temporary wetlands. In order to maximize fitness, the fraction that terminates diapause is modified by signals indicating habitat suitability and biotic interactions. Here, in a laboratory experiment, we investigate the effect of conspecific cues on the hatching time and hatching rate of resting eggs from Triops cancriformis (Bosc, 1801). While hatching time was not significantly affected by conspecific cues, the effect of these cues on hatching rate was highly significant, with hatching rate increasing with increasing concentration of conspecific cues. This indicates that alongside environmental factors, conspecific cues also have the power to terminate the diapause of Triops resting eggs. In addition to indicating suitable conditions, such cues could also act as a mechanism for reducing egg cannibalism by adults, which are predominantly benthic feeders. As such, our results suggest that the response of large branchiopod encysted embryos to conspecific chemical cues could have evolved as a response to the feeding strategy of their adult stages; however, more research will be needed to fully understand the mechanism(s) behind this response.

Organisms living in intermittent wetlands present adaptations to cope with the inundation-desiccation process. Microcrustaceans are commonly found in intermittent wetlands because they present reproductive strategies able to synchronize with the hydroperiod. To know the dynamic of the microcrustaceans, that inhabit these wetlands of the subtropical coastal plain, which predominate the Pampas biome in Brazil, we analyzed the influence of hydration time and temperature on the hatching of microcrustaceans, comparing in situ and ex situ approaches. We followed hatching 34 days after in situ flooding and tested three temperatures (10, 15, and 20°C) 30 days after laboratory flooding. In both approaches, we classified the hydration time as the beginning, middle, and end of the hydroperiod. We recorded a total of 41 taxa distributed in Cladocera (26 taxa), Ostracoda (8), Copepoda (3), Anostraca (1), and Conchostraca (1). We observed that in situ hydration time was the most important factor for hatching. Ex situ hydration time was also important, but the increase in temperature positively affected the hatching of organisms. We also found that in both approaches, the beginning of hydration time is the most important period for the hatching of microcrustaceans.

The soundscape experienced by animals early in life can affect their behaviour later in life. For birds, sounds experienced in the egg can influence how individuals learn to respond to specific calls post-hatching. However, how early acoustic experiences affect subsequent social behaviour remains unknown. Here, we investigate how exposure to maternal ‘cluck’ calls pre-hatching affects the behaviour of domestic chickens ( Gallus gallus domesticus ) at 3–5 days and 17–21 days old. We incubated eggs and played cluck calls to half of them. After hatching, we raised chicks in small groups occupying different enclosures. At 3–5 days old, we tested chicks’ responses to three stimuli: (i) background sound, (ii) chick calls and (iii) cluck calls. We found that the pre-hatching experience of cluck calls reduced the likelihood of moving in response to all three stimuli. At 17–21 days old, some chicks explored beyond their own enclosure and ‘visited’ other groups. Chicks exposed to cluck calls before hatching were three times more likely to enter another group’s enclosure than control chicks, and this was unaffected by the chicks’ social connectedness. Our results indicate age- and context-dependent responses of chicks to pre-hatching cluck-call playbacks, with potential long-term effects on individual social behaviour.

Expansion of anthropogenic noise and night lighting across our planet 1 , 2 is of increasing conservation concern 3 – 6 . Despite growing knowledge of physiological and behavioural responses to these stimuli from single-species and local-scale studies, whether these pollutants affect fitness is less clear, as is how and why species vary in their sensitivity to these anthropic stressors. Here we leverage a large citizen science dataset paired with high-resolution noise and light data from across the contiguous United States to assess how these stimuli affect reproductive success in 142 bird species. We find responses to both sensory pollutants linked to the functional traits and habitat affiliations of species. For example, overall nest success was negatively correlated with noise among birds in closed environments. Species-specific changes in reproductive timing and hatching success in response to noise exposure were explained by vocalization frequency, nesting location and diet. Additionally, increased light-gathering ability of species’ eyes was associated with stronger advancements in reproductive timing in response to light exposure, potentially creating phenological mismatches 7 . Unexpectedly, better light-gathering ability was linked to reduced clutch failure and increased overall nest success in response to light exposure, raising important questions about how responses to sensory pollutants counteract or exacerbate responses to other aspects of global change, such as climate warming. These findings demonstrate that anthropogenic noise and light can substantially affect breeding bird phenology and fitness, and underscore the need to consider sensory pollutants alongside traditional dimensions of the environment that typically inform biodiversity conservation. Human-generated noise and night lighting affect breeding habits and fitness in birds, implying that sensory pollutants must be considered alongside other environmental factors in assessing biodiversity conservation.

As animals develop, their capacities to sense cues, assess threats, and perform actions change, as do the relative costs and benefits that underlie behavioural decisions. We presented ambiguous cues to test if hatching decisions of red-eyed treefrogs, Agalychnis callidryas, change developmentally following adaptive predictions based on changing costs of decision errors. These arboreal embryos hatch prematurely to escape from egg predators, cued by vibrations in attacks. Young embryos modulate hatching based on the frequency and temporal properties of cues, reducing false alarms that unnecessarily expose them to risk in the water. Since the cost of false alarms decreases developmentally, we hypothesized that hatching responses to ambiguous cues would increase. We tested this using vibration playbacks at two ages, with two sets of 3 stimuli. We matched sampling costs and varied ambiguity in either temporal or frequency properties, so one stimulus elicited high hatching (positive control) and two elicited low hatching but differed in ambiguity, based on prior results with younger embryos. Older embryos hatched faster, indicating reduced cue sampling. They responded strongly to both clear threat cues and ambiguous stimuli but little when either property clearly indicated low risk. In both experiments, we saw the greatest ontogenetic change in response to the more ambiguous stimulus. These playback experiments improve our understanding of how embryos facing risk tradeoffs make adaptive decisions based on incidental cues from predators. Ambiguity in incidental cues is ubiquitous and developmental changes in behaviour due to ontogenetic adaptation of decision processes are likely to be widespread.

This laboratory study examined the stimuli involved in controlling egg hatching in the desert locust Schistocerca gregaria. We found that eggs that were kept in their egg pods hatched in synchrony, whereas those that were kept individually hatched over an extended period of time and took significantly longer to hatch. Synchronous hatching was also observed in pairs of eggs that were kept in contact with each other in the same plastic wells, but not in those that were kept individually in separate wells. This demonstrates that the eggs needed to be placed in contact with each other to achieve synchronous hatching and suggests that a hatching individual stimulates adjacent eggs to hatch via some unknown stimulus. Additional experiments suggested that neither auditory nor pheromonal stimuli were important in this process, but rather some sort of vibratory stimulus. This inference was supported by the results of another experiment, which demonstrated that when isolated eggs were vibrated with a vortex mixer, most of them hatched shortly after the stimulation. Our results suggest the possibility that direct mechanical stimulation caused by the first egg to hatch stimulates adjacent eggs to also hatch, thus producing synchronous hatching in the entire egg pod. However, the exact nature of this stimulus remains to be determined.

Repetition of the same vocal stimulus during vocal learning may result in habituation. Therefore, selection may favor vocal tutors that produce vocal stimuli with characteristics that reduce the risk of habituation. Superb fairywren Malurus cyaneus mothers produce a two‐element (A and signature B) call to embryos, but embryos only produce one element type (B) after hatching. Why do mothers use the A element to embryos? We broadcast calls with one (B) or two (AB) element types and measured embryo response. Embryos habituated to calls with one element type and remained responsive to calls with both. We conclude that signal characteristics in tutors may guide learning to retain pupil attention during learning.

1. Behavioural consistency within and across behaviours (animal personality and behavioural syndrome, respectively) has been vigorously studied in the last decade, leading to the emergence of \"animal personality\" research. It has been proposed recently that not only mean behaviour (behavioural type), but the environmentally induced behavioural change (behavioural plasticity) might also differ between individuals within populations. 2. While case studies presenting between-individual variation in behavioural plasticity have started to accumulate, the mechanisms behind its emergence are virtually unknown. We have recently demonstrated that ecologically relevant environmental stimuli during ontogeny are necessary for the development of animal personality and behavioural syndromes. However, it is unknown whether between-individual variation in behavioural plasticity is hard-wired or induced. 3. Here, we tested whether experience with predation during development affected predator-induced behavioural plasticity in Rana dalmatina tadpoles. We ran a common garden experiment with two ontogenetic predation treatments: tadpoles developed from hatching in either the presence or absence of olfactory predator stimuli. Then, we assayed all tadpoles repeatedly for activity and risk-taking both in the absence and presence of olfactory predator stimuli. 4. We found that (a) between-individual variation in predator-induced behavioural plasticity was present only in the group that developed in the presence of olfactory stimuli from predators and (b) previous experience with predatory stimuli resulted in lower plastic response at the group level. The latter pattern resulted from increased between-individual variation and not from universally lower individual responses. We also found that experience with predation during development increased the predictability (i.e. decreased the within-individual variation unrelated to environmental change) of activity, but not risk-taking. In line with this, tadpoles developing under perceived predatory risk expressed their activity with higher repeatability. 5. We suggest that ecologically relevant environmental stimuli are not only fundamental for the development of animal personality and behavioural syndromes, but also for individual variation in behavioural plasticity. Thus, experience is of central importance for the emergence of individual behavioural variation at many levels.