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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.

The altricial-precocial spectrum describes patterns of variation in avian developmental mode that greatly influence avian life histories. Appraising a given species’ position on this spectrum is therefore fundamental to understanding patterns of avian life history evolution. However, evaluating avian developmental mode remains a relatively subjective task reliant on untested assumptions, including the notion that developmental strategies are distributed along a single dimension of statistical variation. Here, we present a quantitative multivariate framework that objectively discriminates among meaningfully different modes of avian development. We gathered information on seven hatchling and post-hatching traits for up to 4000 extant bird species, and find that most traits related to developmental mode show high phylogenetic signal and little intraclade variation, allowing unknown values to be reliably interpolated. Principal component analyses (PCAs) of these traits illustrate that most variation in hatchling state can be quantified along one dimension of trait space. However, our PCAs also reveal an important second dimension explaining variation in post-hatching behavior, enabling factors related to hatchling state and post-hatching behavior to be disentangled. In order to facilitate future macroevolutionary studies of variation in avian developmental strategies, as well as explorations of covariation between developmental mode and other aspects of avian biology, we present PC scores for 9993 extant avian species.

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.

Root-knot nematodes, known for their broad host range and the challenges associated with their control, cause significant losses in global agricultural productivity. The mitogen-activated protein kinase (MAPK) pathway amplifies signals through a phosphorylation cascade to regulate downstream transcription factors or effector proteins, which is essential for maintaining normal physiological functions in nematodes. This study presents a comprehensive characterization of the MAPK signaling cascade regulatory network in Meloidogyne incognita, elucidating the regulatory roles of Mi-let-60, Mi-lin-45, Mi-mek-2, and Mi-mpk-1 in host chemotaxis and egg hatching behavior. Importantly, RNAi-mediated silencing of Mi-mpk-1 resulted in a 17-fold increase in egg hatching rate and significantly impaired chemotactic responses while silencing of Mi-let-60 led to a marked reduction in root gall formation and egg mass production. These results not only confirmed the evolutionary conservation of this pathway but also identified a feedback regulation mechanism unique to parasitic nematodes. These findings provide valuable insights for future research on signal transduction pathways and the sustainable management of root-knot nematodes.

The biology of Patanga japonica (Bolívar, 1898), including seasonal nymphal growth, host plants, mating, oviposition, hatching, and adult morphology, was studied under outdoor and indoor conditions in central Japan. A field census showed that this grasshopper had a univoltine life cycle and overwintered in the adult stage. Body size was found to increase with a delay in the time of adult emergence in females but not in males, and protandry was observed. The insects were mainly associated with a few plant species. Feeding tests showed that at least one of the 5 test nymphs molted to the second stadium on 37 plant species, and more than 50% did so on 23 plant species. Mating was frequently observed in April and May under outdoor conditions, and the daily maximum number of copulating pairs was positively correlated with air temperature. Copulatory behavior, including stridulation, is described in detail. Oviposition was frequently observed in May and June under outdoor conditions. Larger females produced more eggs per pod, and a negative relationship was observed between egg lengths and the number of eggs per pod, showing a trade-off. On average, female adults had 124 ovarioles. Egg hatching occurred at different times during the daytime, but the eggs from each pod hatched synchronously. Synchronous hatching was also observed in eggs kept in groups of 2, 4, and 10, but hatching occurred earlier in larger group sizes. Eggs achieved synchronous hatching by either delaying or advancing hatching time. Two eggs separated by several millimeters hatched less synchronously than those kept in contact with one another. However, similarly separated eggs restored hatching synchrony when connected by thin wire, suggesting the involvement of vibrational signals in embryo–embryo communication. Morphometric analysis suggested that P. japonica adults change some morphometric ratios in response to crowding. Variation in pronotum shape was not significantly affected by crowding.

Synopsis Arboreal embryos of phyllomedusine treefrogs hatch prematurely to escape snake predation, cued by vibrations in their egg clutches during attacks. However, escape success varies between species, from ∼77% in Agalychnis callidryas to just ∼9% in A. spurrelli at 1 day premature. Both species begin responding to snake attacks at similar developmental stages, when vestibular mechanosensory function begins, suggesting that sensory ability does not limit the hatching response in A. spurrelli. Agalychnis callidryas clutches are thick and gelatinous, while A. spurrelli clutches are thinner and stiffer. We hypothesized that this structural difference alters the egg motion excited by attacks. Since vibrations excited by snakes must propagate through clutches to reach embryos, we hypothesized that the species difference in attack-induced hatching may reflect effects of clutch biomechanics on the cues available to embryos. Mechanics predicts that thinner, stiffer structures have higher free vibration frequencies, greater spatial attenuation, and faster vibration damping than thicker, more flexible structures. We assessed clutch biomechanics by embedding small accelerometers in clutches of both species and recording vibrations during standardized excitation tests at two distances from the accelerometer. Analyses of recorded vibrations showed that A. spurrelli clutches have higher free vibration frequencies and greater vibration damping than A. callidryas clutches. Higher frequencies elicit less hatching in A. callidryas, and greater damping could reduce the amount of vibration embryos can perceive. To directly test if clutch structure affects escape success in snake attacks, we transplanted A. spurrelli eggs into A. callidryas clutches and compared their escape rates with untransplanted, age-matched conspecific controls. We also performed reciprocal transplantation of eggs between pairs of A. callidryas clutches as a method control. Transplanting A. spurrelli embryos into A. callidryas clutches nearly tripled their escape success (44%) compared to conspecific controls (15%), whereas transplanting A. callidryas embryos into different A. callidryas clutches only increased escape success by 10%. At hatching competence, A. callidryas eggs are no longer jelly-encapsulated, while A. spurrelli eggs retain their jelly coat. Therefore, we compared the hatching response and latency of A. spurrelli in de-jellied eggs and their control, jelly-encapsulated siblings using manual egg-jiggling to simulate predation cues. Embryos in de-jellied eggs were more likely to hatch and hatched faster than control siblings. Together, our results suggest that the properties of parentally produced egg-clutch structures, including their vibration biomechanics, constrain the information available to A. spurrelli embryos and contribute to interspecific differences in hatching responses to predator attacks.

The cereal cyst nematode Heterodera avenae has been reported in wheat fields in Egypt; however no information is available on the hatch of second-stage juveniles (J2) from such populations of H. avenae. The aim of this study was to subject five Egyptian populations of H. avenae that were obtained from different regions in the Ismailia Province to different temperatures and storage durations to determine the effects on J2 emergence. The Egyptian populations of H. avenae were compared to a population originating from a different climatic zone in Germany (Grafenreuth, Bavaria). Results showed that the J2 hatching pattern of the Egyptian H. avenae populations did not differ from each other. Although the Egyptian and the German populations of H. avenae hatched primarily between 5 and 20 °C, significant differences in J2 hatching have been observed among them. Highest emergence of J2 of the Egyptian populations was observed between 10 and 15 °C, whereas the highest level of J2 emergence of the German population was between 5 and 10 °C. Storing cysts to 5 °C before incubation at 10 °C stimulated the hatch of the German population of H. avenae significantly compared to the control. Whereas, storing cysts at 20 °C, before incubation at 10 °C, significantly stimulated J2 hatching of the Egyptian populations compared to the control. The J2 hatching behavior of the Egyptian populations of H. avenae was in agreement with reports for Mediterranean ecotypes which have winter activity, while the hatching pattern of the German population was similar to those of the Northern ecotypes with spring activity.

We tested for the first time the efficiency of the use of infra-red (IR) cameras for sea turtle hatchling monitoring. The cameras were installed on one green turtle (Chelonia mydas) and four loggerhead turtle (Caretta caretta) nests during 2014 and 2015 nesting season in the south-east Mediterranean, Turkey. The camera monitoring, even with the limited sample size, have successfully corroborated the previous observations and provided further insights on hatchling emergence behavior. The analysis of the camera recordings revealed that hatchlings emerged from the nests asynchronously in varying numbers of groups and different group sizes, while c. 60% hatchlings emerged during the first 5 days of emergence activity. 98.6% of hatchlings emerged at night with a peak activity between 21:00 and 00:00. The day of first emergence varied between 38 and 64 days since egg deposition, while the day of last emergence varied only between 60 and 65 days. Total emergence activity continued up to maximum of 22 days, which is longer than that of previous records. Overall, the present study showed that IR camera monitoring is a promising tool for sea turtle monitoring and can provide detailed insights on sea turtle hatchling behavior.

The arboreal embryos of red-eyed treefrogs (Agalychnis callidryas) hatch prematurely to escape from egg predators, and escape success increases with age. We assessed developmental changes in the behavior and hatching performance of embryos attacked by wasps (Polybia rejecta) and their contributions to improved embryo survival. We recorded videos of 4- and 5-day-old embryos exposed to wasp attacks and determined each embryo’s fate. For a stratified random sample of embryos that escaped and died, we determined the occurrence, sequence, and timing of events during wasp-embryo interactions. We constructed path diagrams of event sequences, tested for age effects on transition probabilities, and measured the durations of periods between key events. Overall, escape success was 38% higher in older embryos. They were more likely to hatch pre-emptively than younger ones, thus less likely to experience direct attacks, suggesting that developmental gains in mechanosensory sensitivity may increase hatching responses to indirect cues. During direct attacks, embryos were equally likely to be captured by wasps at both ages, and hatching speed was similar, suggesting no relevant difference in escape-hatching performance. After a wasp ruptured their egg capsule, older embryos were more likely to exit, and they did so much sooner; younger embryos remained in ruptured capsules for longer and were more likely to be attacked again. This developmental change in embryo behavior indicates decreased tolerance for egg-stage risk as the chance of tadpole survival increases, suggesting that ontogenetic adaptation to changing risk trade-offs contributes strongly to the developmental increase in escape success.Significance statementAs animals develop, both their abilities and the optimal strategies for antipredator defense change, and some show ontogenetic adaptation of defensive behavior. This is documented in the larval and juvenile stages but rarely examined during the embryonic period, when development is fastest. We document substantial changes in embryo behavior across a 1-day period following the onset of predator-induced hatching in red-eyed treefrogs, with rapidly decreasing tolerance of egg-stage risk contributing to higher survival under wasp predation as the costs of hatching decrease. This provides evidence for ontogenetic adaptation of defensive behavior in a natural predation context and across an earlier developmental period than previously known, thereby strengthening results from prior work with vibration playbacks across later developmental stages. It suggests that even during periods of rapid development of morphology and abilities, understanding behavioral decisions may be crucial to explaining changes in survival.

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.