Differences In Development Time Research Articles

Notch pathway mutants do not equivalently perturb mouse embryonic retinal development.

In the vertebrate eye, Notch ligands, receptors, and ternary complex components determine the destiny of retinal progenitor cells in part by regulating Hes effector gene activity. There are multiple paralogues for nearly every node in this pathway, which results in numerous instances of redundancy and compensation during development. To dissect such complexity at the earliest stages of eye development, we used seven germline or conditional mutant mice and two spatiotemporally distinct Cre drivers. We perturbed the Notch ternary complex and multiple Hes genes to understand if Notch regulates optic stalk/nerve head development; and to test intracellular pathway components for their Notch-dependent versus -independent roles during retinal ganglion cell and cone photoreceptor competence and fate acquisition. We confirmed that disrupting Notch signaling universally blocks progenitor cell growth, but delineated specific pathway components that can act independently, such as sustained Hes1 expression in the optic stalk/nerve head. In retinal progenitor cells, we found that among the genes tested, they do not uniformly suppress retinal ganglion cell or cone differentiation; which is not due differences in developmental timing. We discovered that shifts in the earliest cell fates correlate with expression changes for the early photoreceptor factor Otx2, but not with Atoh7, a factor required for retinal ganglion cell formation. During photoreceptor genesis we also better defined multiple and simultaneous activities for Rbpj and Hes1 and identify redundant activities that occur downstream of Notch. Given its unique roles at the retina-optic stalk boundary and cone photoreceptor genesis, our data suggest Hes1 as a hub where Notch-dependent and -independent inputs converge.

The destinies of human embryos reaching blastocyst stage between Day 4 and Day 7 diverge as early as fertilization.

What clinical and laboratory differences emerge from parallel direct comparison of embryos reaching the blastocyst stage between Days 4, 5, 6, and 7 (Days 4-7)? Increasing times to blastocyst formation are associated with a worse clinical outcome and perturbations in developmental patterns appear as early as the fertilization stage. Previous evidence indicates that later times to blastocyst development are associated with a worse clinical outcome. However, the vast majority of these data concern Day 5 and Day 6 blastocysts, while Day 4 and Day 7 blastocysts remain less thoroughly investigated. In addition, studies comparing in parallel the developmental patterns and trajectories of Day 4-7 blastocysts are lacking. This leaves unanswered the question of when and how differences among such embryos emerge. Acquisition of such knowledge would significantly contribute to understanding the relative impact of intrinsic and extrinsic causes of embryo developmental kinetics and competence. This retrospective study involved time-lapse technology (TLT) monitoring of Day 4 (N = 70), Day 5 (N = 6147), Day 6 (N = 3243), and Day 7 (N = 149) blastocysts generated in 9450 ICSI cycles. Oocyte retrievals were carried out after clomiphene citrate-based minimal ovarian stimulation, between January 2020 and April 2021. Couples included in the study presented with different diagnoses, mainly male factor and unexplained infertility. Cases involving cryopreserved gametes or surgically retrieved sperm were excluded. Microinjected oocytes were assessed by a combined TLT-culture system. Day 4-7 blastocyst groups were compared in terms of morphokinetics (pronuclear dynamics, cleavage patterns and timings, and embryo quality) and clinical outcome. Clinically usable blastocysts were cryopreserved and transferred in single vitrified-warmed blastocyst transfers (SVBT). From 19846 microinjected oocytes, 17144 zygotes (86.4%) were obtained. Overall, the blastocyst development rate was 56.0%. Rates of blastocysts formation on Days 4, 5, 6, and 7 were 0.7%, 64.0%, 33.8%, and 1.6%, respectively. The average expanded blastocyst development times were 98.4 ± 0.4, 112.4 ± 0.1, 131.6 ± 0.1, and 151.2 ± 0.5 h in the Day 4-7 groups, respectively. Female age was positively associated with longer times to blastocyst development. Rates of both inner cell mass (ICM) and trophectoderm (TE) morphological grade A blastocysts were negatively associated with the day of blastocyst development (P < 0.0001). The differences in development times and intervals increased progressively until blastocyst expansion (P < 0.0001 for all development times). Strikingly, such differences were already markedly evident as early as the time of pronuclear fading (tPNf) (20.6 ± 0.3, 22.5 ± 0.0, 24.0 ± 0.0, 25.5 ± 0.3; Days 4-7, respectively; P < 0.0001). Rates of cleavage anomalies (tri-/multi-chotomous mitosis or rapid cleavage) occurring at the first or second/third division cycles were also positively associated with longer times to blastocyst development. Implantation, ongoing pregnancy, and live birth rates were progressively reduced with increasing blastocyst development times (P < 0.0001), even after stratification for maternal age. When controlled for female age, male age, number of previous embryo transfer cycles, morphological grade of the ICM and TE, and progesterone supplementation, the probabilities of implantation, clinical, and ongoing pregnancy and live birth were significantly decreased in Day 6 blastocysts in comparison to Day 5 blastocysts. Follow-up data on birth length, weight, and malformations were comparable among the four blastocyst groups. The study is limited by its retrospective design. Having been obtained from a single centre, the data require independent validation. This study extends previous data on the relation between time of blastocyst formation and clinical outcome. It also indicates that differences in developmental times and patterns of Day 4-7 blastocysts occur as early as the fertilization stage, possibly dictated by intrinsic gamete-derived factors. This study was supported by the participating institutions. The authors have no conflict of interest to declare. N/A.

P-261 Embryo compaction based on time-lapse imaging is a valuable parameter for selecting blastocysts with the highest developmental potency and associated with a ploidy state

Abstract Study question Does embryo compaction positively correlate with blastocyst development and further embryonic ploidy status? Summary answer Fully compacted embryos develop into good-quality blastocysts, have shorter developmental times, and are related to ploidy status. What is known already To succeed in assisted reproduction technique (ART), it is necessary to select embryos that have the highest potential. So, numerous studies make an effort to establish parameters for selecting embryos. A Time-lapse system (TLS) allows embryologists to understand dynamic embryo change through continuous monitoring. In development, embryos undergo dynamic functional changes during compaction, which play a crucial role in blastocyst formation. It is also known that embryonic genome activation can be seen with compaction. Incomplete compaction leads to blastocyst developmental failure. Nevertheless, the details about the compaction of human embryos have not been paid sufficient attention, so still rarely known. Study design, size, duration This was a retrospective cohort study including couples that underwent an IVF cycle at the CHA Fertility Center, Gangnam, between January 2019 to October 2022. A total of 371 reached the blastocyst from 113 patients cultured in the TLS were analyzed. Among these, 94 blastocysts were analyzed by preimplantation genetic testing for aneuploidy (PGT-A). Statistical analysis was performed by prism9 using a t-test and chi-square test. P values &amp;lt;0.05 were regarded as statistically significant. Participants/materials, setting, methods Embryos were classified into two categories by compaction pattern: fully compacted (Group1, N = 194) and partially compacted (Group2, N = 177). Blastocyst quality was determined by morphology and divided into three groups (Good, Average, and Poor). The developmental time ranging from morula to blastocyst was annotated based on the embryo scope image. The surface of the blastocyst was measured every hour starting at blastocyst formation (tB) by using the ellipse tool of the Embryo Viewer software. Main results and the role of chance Good and average quality blastocysts are significantly higher in Group 1 than in Group 2 (21.6% vs. 3.4%, p &amp;lt; 0.01; 47.9% vs. 26.6%, p &amp;lt; 0.01, respectively). In contrast, poor-quality blastocysts are lower in Group 1 than in Group 2 (30.4% vs. 70.1%, p &amp;lt; 0.01). The beginning and completion of compaction, and blastocyst formation times of embryos from Group 1 were significantly shorter than those of embryos that Group 2(78.6h vs. 82.4, p &amp;lt; 0.01; 87.0h vs. 92.2h, p &amp;lt; 0.01; 100.2h vs. 103.7, p &amp;lt; 0.01, respectively). Also, there is a significant difference in longitudinal surface area at 3, 6, and 12h from the time of tB between the two groups. Consequently, the average expansion rate in Group 1 was significantly faster than in Group 2 (653.6 μm2/hour vs. 499.2μm2/hour, p &amp;lt; 0.05). According to the result of PGT-A, Group 1 had statistically significantly higher euploid and lower aneuploidy rates compared to Group 2 (47.2% vs. 36.2%, p &amp;lt; 0.001; 52.8% vs. 63.8%, p &amp;lt; 0.001, respectively). However, in the PGT-A group, there was no significant difference in developmental time between the two groups, regardless of fully or partial compaction. Meanwhile, the average expansion rate in euploidy blastocyst was significantly faster than in aneuploidy blastocyst (747.8 μm2/hour vs. 564.3 μm2/hour, p &amp;lt; 0.05). Limitations, reasons for caution The main limitation is the single-center retrospective approach. Therefore future prospective research is needed to verify and extend our findings. Another one, in the PGT-A there was no difference in developmental time regardless of fully or partially compaction. The reason is that we selected blastocysts of sufficient quality for biopsy. Wider implications of the findings Using the TLS, we have observed the dynamics of compaction in detail. We found a positive relationship between compaction and blastocyst quality and its association with embryo ploidy. The assessment of compaction is a significant parameter for predicting competent embryos and should be given priority when selecting blastocysts. Trial registration number Not applicable

Life history responses of the small brown planthopper Laodelphax striatellus to temperature change

Temperature is a key environmental factor in ectotherms and influences many life history traits. In the present study, the nymphal development time, sex ratio and wing dimorphism of the small brown planthopper Laodelphax striatellus were examined under the conditions of constant temperatures, naturally varying temperatures (or different generations), and different temperatures combined with different photoperiod. The results showed that from 18 to 28 °C, the developmental time of nymphs was gradually shortened with the increase of temperature, whereas the high temperatures of 30 and 32 °C in the third to fifth instar nymphal stages and high summer temperature of 28.8 and 29.7 °C significantly delayed developmental time and resulted in higher mortality of nymphs. In all treatments, the developmental time was longer in females than males. The nymphs took significantly longer time to develop in the short daylength of 12 h than in longer daylengths of 13, 14, 15 and 16. Differences in developmental time were also found between wing morph, with long-winged individuals being significantly longer than the short-winged individuals at lower temperatures and significantly shorter than the short-winged individuals at higher temperatures. In all treatments, the sex ratio was stable, approaching 1:1, without being affected by temperature, generations and photoperiod. Photoperiod and temperature had significantly influence on the wing dimorphism. Long daylength combined with different temperatures resulted in significantly higher proportions of long-winged morph, whereas the low temperatures combined with the short daylengths in autumn and winter resulted in significantly high proportion of short-winged morph.This study broadens our understanding of the life-history traits of this planthopper and provides basic data for analyzing the effects of climate change on the planthopper reproduction.

Effects of population variations and temperature on Chrysomya megacephala (Diptera: Calliphoridae) development: implications for estimating the postmortem interval.

Forensic entomology requires knowledge of the developmental rates of the species that colonize a body after death to estimate the postmortem interval (PMI). These developmental rates may vary depending not only on the species but also on the geographic location due to population differences. Therefore, the objectives of this work were to determine the developmental duration of the forensically important fly Chrysomya megacephala under constant controlled and field condition temperatures and to compare these results, through a meta-analysis, with data reported by other authors on populations from different localities. For this, C. megacephala colonies were established in the laboratory, and the duration of the life cycle was studied at two controlled temperatures (25°C and 27°C) and field conditions (27.5 ± 3.2°C). Analysis of variance was performed to determine differences in developmental time and larval length between constant laboratory temperatures and field conditions. A generalized linear model was performed with predictor variables extracted from the literature (diet, relative humidity, latitude, longitude) to evaluate the effect of population variation on developmental times. The results showed significant differences in developmental times between 25 and 27°C. As expected, the complete life cycle of C. megacephala was shorter at 27°C. Finally, the meta-analysis suggested differences between the developmental times of different populations, based on temperature and geographic location. The results of this study provide fundamental developmental data to use C. megacephala in PMI estimations. Finally, we suggest that, when making expert reports, information from local populations should be used to determine a more accurate and reliable PMI.

Cell time: How cells control developmental timetables

An overview on the molecular and metabolic mechanisms behind individual cell differences in developmental timing in the segmentation clock and the central nervous system.

Fitness differences between parthenogenetic litters of the synanthropic scorpion Tityus stigmurus (Scorpiones: Buthidae)

Abstract Clonal lineages in similar environments may be influenced by non-Mendelian inheritance, such as maternal age effects and developmental instabilities. These mechanisms may affect the developmental fitness of parthenogenetic litters. In this study, the scorpion Tityus stigmurus (Thorell, 1876) was used to analyze the effects of non-Mendelian variation on parthenogenetic litters. A total of 75 juveniles from five females were reared under the same controlled conditions, while their development was observed and evaluated through differences in offspring fitness traits (litter size, prosoma size, developmental time, and mortality) between the litters. First and second litters had a similar litter size, although second litters exhibited longer developmental time in the early instar stages (second and third) than first litters. These results indicate that T. stigmurus females allocated nutrient resources to maximize litter size rather than developmental fitness in subsequent litters. Differences in developmental time found in early instars but not in late instars may have occurred as a result of stochastic developmental variations in young individuals. Such variation in duration of development has the potential to influence survival of juveniles in natural environments because individuals that grow faster may avoid large predators and consume larger prey, compared to those that do not.

Impact of Host Plant Resistance on Emergence, Body Parameters, and Supercooling Point of Cylas formicarius elegantulus (Coleoptera: Brentidae)

Sweetpotato weevil, Cylas formicarius elegantulus (Summers) (Coleoptera: Brentidae), an in-field and storage pest of sweetpotato, is the primary insect constraint to sweetpotato production in tropical and subtropical regions. Feeding by adult and larval sweetpotato weevil induces terpenes, rendering storage roots unmarketable. To reduce storage root damage and sweetpotato weevil populations, the present experiment tested the impact of sweetpotato cultivar on developmental time, adult emergence, body length, weight, and supercooling point of sweetpotato weevil. The cultivars tested were ‘Beauregard’ and ‘Evangeline,’ both orange fleshed cultivars susceptible to sweetpotato weevil, and ‘Murasaki,’ a white fleshed cultivar known to be resistant to sweetpotato weevil. There were no differences in developmental time with most adult sweetpotato weevils emerging 34 to 44 d after oviposition. However, the number of adult sweetpotato weevil that emerged from Beauregard (38.9 ± 3.3) and Evangeline (48.4 ± 6.2) roots were greater than numbers emerging from Murasaki (11.1 ± 3.5), indicating resistance is due to antixenosis. Although fewer in number, adults (male and female) emerging from Murasaki were heavier than males and females emerging from Beauregard and males from Evangeline. Supercooling points of sweetpotato weevil males emerging from Murasaki (–17.9 ± 0.4 °C) were significantly lower than Beauregard (–16.3 ± 0.5 °C) but similar to Evangeline (–17.1 ± 0.4 °C). Host plant resistance expressed by Murasaki may reduce sweetpotato weevil populations significantly, but those that emerge may be better suited to survive the cold.

Susceptibility of sixteen strawberry (Fragaria × ananassa) cultivars to Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) in Southwestern Spain

The susceptibility of the newest and most used strawberry cultivars to the Spotted Wing Drosophila (SWD) in southwestern Spain was evaluated. Sixteen strawberry cultivarswere selected (‘Calderón’, ‘Calinda’, ‘Charlene’, ‘Flaminia’, ‘Flavia’, ‘Fortuna’, ‘Marisol’,‘Marquis’, ‘Melissa’, ‘Palmeritas’, ‘Petaluma’, ‘Plared0955’, ‘Primoris’, ‘Rábida’, ‘Rociera’and ‘Sabrina’) and no-choice tests were carried out under laboratory conditions. In addition, fruit weight, fruit firmness, °Brix, pH, protein content and total phenolic content were recorded in order to assess what influence these variables had on SWD infestation. The sixteen strawberry cultivars tested in this study were susceptible to SWD, although significant differences have been found among them. The mean number of emerged adults in ‘Calderon’ and ‘Plared0955’ were significantly higher than in the other tested cultivars. Significant differences in developmental time were also detected among these cultivars and both sexes but these were unrelated to the level of infestation. No correlation between fruit quality and chemical traits and infestation parameters was found. Our results detected significant differences in the susceptibility of strawberry cultivars in southwestern Spain to SWD; these may help to design IPM programs and to make recommendations for strawberry production, one of the most important crops in southern Europe.

Transgenerational effects on development following microplastic exposure in Drosophila melanogaster.

BackgroundPlastic pollution affects all ecosystems, and detrimental effects to animals have been reported in a growing number of studies. However, there is a paucity of evidence for effects on terrestrial animals in comparison to those in the marine realm.MethodsWe used the fly Drosophila melanogaster to study the effects that exposure to plastics may have on life history traits and immune response. We reared flies in four conditions: In media containing 1% virgin polyethylene, with no chemical additives; in media supplemented with 1% or 4% polyvinyl chloride, known to have a high content of added chemicals; and control flies in non-supplemented media. Plastic particle size ranged from 23–500 µm. We studied fly survival to viral infection, the length of the larval and pupal stage, sex ratios, fertility and the size of the resultant adult flies. We then performed crossings of F1 flies in non-supplemented media and looked at the life history traits of the F2.ResultsFlies treated with plastics in the food media showed changes in fertility and sex ratio, but showed no differences in developmental times, adult size or the capacity to fight infections in comparison with controls. However, the offspring of treated flies reared in non-supplemented food had shorter life cycles, and those coming from both polyvinyl chloride treatments were smaller than those offspring of controls.

Characterizing the diverse cells that associate with the developing commissures of the zebrafish forebrain.

During embryonic development of bilaterally symmetrical organisms, neurons send axons across the midline at specific points to connect the two halves of the nervous system with a commissure. Little is known about the cells at the midline that facilitate this tightly regulated process. We exploit the conserved process of vertebrate embryonic development in the zebrafish model system to elucidate the identity of cells at the midline that may facilitate postoptic (POC) and anterior commissure (AC) development. We have discovered that three different gfap+ astroglial cell morphologies persist in contact with pathfinding axons throughout commissure formation. Similarly, olig2+ progenitor cells occupy delineated portions of the postoptic and anterior commissures where they act as multipotent, neural progenitors. Moreover, we conclude that both gfap+ and olig2+ progenitor cells give rise to neuronal populations in both the telencephalon and diencephalon; however, these varied cell populations showed significant developmental timing differences between the telencephalon and diencephalon. Lastly, we also showed that fli1a+ mesenchymal cells migrate along the presumptive commissure regions before and during midline axon crossing. Furthermore, following commissure maturation, specific blood vessels formed at the midline of the POC and immediately ventral and parallel to the AC. This comprehensive account of the cellular populations that correlate with the timing and position of commissural axon pathfinding has supported the conceptual modeling and identification of the early forebrain architecture that may be necessary for proper commissure development.

Primate cell fusion disentangles gene regulatory divergence in neurodevelopment.

Among primates, humans display a unique trajectory of development that is responsible for the many traits specific to our species. However, the inaccessibility of primary human and chimpanzee tissues has limited our ability to study human evolution. Comparative in vitro approaches using primate-derived induced pluripotent stem cells have begun to reveal species differences on the cellular and molecular levels1,2. In particular, brain organoids have emerged as a promising platform to study primate neural development in vitro3-5, although cross-species comparisons of organoids are complicated by differences in developmental timing and variability of differentiation6,7. Here we develop a new platform to address these limitations by fusing human and chimpanzee induced pluripotent stem cells to generate a panel of tetraploid hybrid stem cells. We applied this approach to study species divergence in cerebral cortical development by differentiating these cells into neural organoids. We found that hybrid organoids provide a controlled system for disentangling cis- and trans-acting gene-expression divergence across cell types and developmental stages, revealing a signature of selection on astrocyte-related genes. In addition, we identified an upregulation of the human somatostatin receptor 2 gene (SSTR2), which regulates neuronal calcium signalling and is associated with neuropsychiatric disorders8,9. We reveal a human-specific response to modulation of SSTR2 function in cortical neurons, underscoring the potential of this platform for elucidating the molecular basis of human evolution.

Gene introgression in assessing fitness costs associated with phosphine resistance in the rusty grain beetle

The current study investigates the fitness cost associated with phosphine resistance in the rusty grain beetle, Cryptolestes ferrugineus (Stephens), a problematic pest in the stored commodities that has developed strong resistance to fumigant phosphine. Three characterised insect strains: the susceptible (Ref-S), the strongly resistant (Ref-R), the introgressed resistant (Intro-R) and a segregating population (F25) derived from crossing the Ref-S and Ref-R strains were used in this study. Intro-R was developed by introgressing two phosphine resistance genes, cf_rph1 and cf_rph2 into Ref-S, aimed to reduce the influence of background genetic factors. Intro-R exhibited 592 × resistance to phosphine and homozygous for strong resistance allele, cf_rph2 (L73N). Two key fitness cost criteria, developmental time and fecundity, were assessed under optimal and suboptimal conditions (less favourable diet and low temperature). There was no significant difference in developmental time and fecundity between Ref-S and either Intro-R strain or F25 under optimal conditions. When challenged with a less favourable diet, cracked wheat + cracked sorghum (CW + CS), or exposed to a low temperature (22 °C), both Intro-R and Ref-S had similar developmental time and total numbers of F1 progeny, confirming the absence of significant fitness effects expressed in these conditions. Therefore, we conclude that strongly phosphine resistant C. ferrugineus are unlikely to incur potential fitness costs. This finding will have implications towards developing strategies to manage this pest.

Tempus fugit: How time flies during development

Developmental-timing differences between species are linked to protein turnover

Virus-virus interactions in a plant host and in a hemipteran vector: Implications for vector fitness and virus epidemics

Mixed virus infection in host plants can differentially alter the plant phenotype, influence vector fitness, and affect virus acquisition and inoculation by vectors than single-virus infection. Vector acquisition of multiple viruses from multiple host plants could also differentially affect vector fitness and virus inoculation than acquisition of one virus. Whitefly-virus pathosystems in the southern United States include both the above-stated facets. For the first facet, this study examined the effects of single and mixed infection of cucurbit leaf crumple virus (CuLCrV, a begomovirus) and cucurbit yellow stunting disorder virus (CYSDV, a crinivirus) infecting squash on whitefly (Bemisia tabaci Gennadius MEAM1) host preference and fitness. Mixed infection of CuLCrV and CYSDV in squash plants severely altered their phenotype than single infection. The CYSDV load was reduced in mixed-infected squash plants than in singly-infected plants. Consequently, whiteflies acquired reduced amounts of CYSDV from mixed-infected plants than singly-infected plants. No differences in CuLCrV load were found between singly- and mixed-infected squash plants, and acquisition of CuLCrV by whiteflies did not vary between singly- and mixed-infected squash plants. Both singly- and mixed-infected plants similarly affected whitefly preference, wherein non-viruliferous and viruliferous (CuLCrV and/or CYSDV) whiteflies preferred non-infected plants over infected plants. The fitness study involving viruliferous and non-viruliferous whiteflies revealed no differences in developmental time and fecundity. For the second facet, this study evaluated the effects of individual or combined acquisition of tomato-infecting tomato yellow leaf curl virus (TYLCV, a begomovirus) and squash-infecting CuLCrV on whitefly host preference and fitness. Whiteflies that acquired both CuLCrV and TYLCV had significantly lower CuLCrV load than whiteflies that acquired CuLCrV alone, whereas TYLCV load remained unaltered when acquired individually or in conjunction with CuLCrV. Whitefly preference was not affected following individual or combined virus acquisition. Viruliferous (CuLCrV and/or TYLCV) whiteflies preferred to settle on non-infected tomato and squash plants. The mere presence of CuLCrV and/or TYLCV in whiteflies did not affect their fitness. Taken together, these results indicate that mixed infection of viruses in host plants and acquisition of multiple viruses by the vector could have implications for virus accumulation, virus acquisition, vector preference, and epidemics that sometimes are different from single-virus infection or acquisition.

A maturing view of cochlear calcium.

Charles Darwin was exercised to explain how a structure as complex as the human eye could have evolved. Had he been conversant with the mammalian cochlea, in his time just starting to be examined by the microscope, he would have had an even harder time. The cochlea contains an intricate arrangement of sensory hair cells that detect and encode the amplitude, the frequency and the timing of sound entering the ear for more or less the whole lifetime of the animal. The taxing question is how such a complex structure develops embryologically. Our inner ear is more less completely developed by 25 weeks in utero. But in the mouse the whole process takes only 30 days from conception. Of these 12 days proceed postnatally. Such a timetable has its advantages. The newborn cells are accessible. The soft tissues can be cultured. The signals they generate can be recorded and imaged. The downside is that the developmental processes often involve temporary structures and the steps that build the final cochlear cells must be demarcated from the final adult result. Once such transient structure is Kolliker's organ, a ridge of cells that transforms into the lining cells of the cochlear sulcus before maturation and provides synchronization signals for the auditory wiring. A second example is the sound transducing channel of hair cells where gene expression (Kawashima et al. 2011) and the channels themselves (Beurg et al. 2018) show conversion from a pair, TMC1 and TMC2, in the immature cell to TMC1 alone in the mature cell. A further confound is that cells along the length of the cochlea do not develop at the same time. A wave of cells exiting the cell cycle, judged by a marker protein p27KIP1, progresses from the cochlear apex to the cochlear base (the future high frequency end) prenatally, and then the cells differentiate over the next few days around birth (P0 in the mouse) in the opposite direction, from base to apex. Thus basal cells express many of their identifying markers before apical cells but at least ten distinct types of cell can be recognised in the cochlea, two of which are the hair cells: inner hair cells (IHCs), making the sensory input to the nerve, and the outer hair cells (OHCs), part of the sound amplification process. The paper by Jeng et al. (2020) describes a further orchestration of cell maturation and identifies another developmental prerequisite for the distinction between these two hair cell types. They have used a mouse deficient in a cochlear calcium channel CaV1.3 – which accounts for the majority of the Ca2+ channels in hair cells – and where it is known that the OHCs degenerate progressively from apex to base from the onset of hearing (around postnatal day P12). Indeed, the CaV1.3 knockout mouse is deaf (Platzer et al. 2000). The surprise is that that there is an intimate connection between Ca2+ signalling in the first week (P0–P7) and the loss of K+ channels (Fig. 1). The most overt early sign of any deficiency is that the OHCs lose spontaneous Ca2+ action potentials, a necessary but not sufficient signal which is thought to contribute to the correct neural wiring of the cochlea to the brain. Other markers of the OHC maturation, in particular the motor protein prestin, seem to be unaffected and IHCs, although surviving, never quite form their adult quota of K+ channels. Why should a Ca2+ signal determine K+ channel expression in the hair cells? Although other critical factors are required, including the serine protease Tmprss3 (Molina et al. 2013), the hair cells’ Ca2+ dependent K+ channels are certainly affected. These include the BK/KCNMA1 and the SK2/KCNN2 channels, the latter being involved in the efferent innervation of the OHCs. But the most prominent result of the CaV1.3 deletion is to remove a hair cell K+ channel, KCNQ4, from basal cochlear cells but leaving a residual expression further along towards the apical end, a distinction which may partly reflect the developmental timing differences along the cochlea. KCNQ4, which underpins a characteristic hair cell current IKn, is certainly required for OHC survival as it forms the pathway for intracellular K+ homeostasis; without it the cells depolarise and die. But perhaps equally puzzling is that the Ca2+ entry is determined by a voltage gated channel. Could it be that cell potential plays a critical role in protein translocation to membrane? Or is the temporal patterning of the early Ca2+ signals the trigger for gene translation? Unravelling all the causal links is a challenging problem for the future. None declared. Sole author. None applicable.

The development of the osteocranium in the snake Psammophis sibilans (Serpentes: Lamprophiidae).

Non-avian reptiles are good models to investigate structural and developmental differences between amniotes. Investigations of craniofacial development in a complete series of embryos from oviposition up to hatching are still relatively rare. Consideration of a complete series can reveal developmental events that were previously missed, and thus correct or confirm theories about developmental events. The Egyptian Sand snake, Psammophis sibilans, has been a key species in descriptions of the snake skull development. However, published work was based on a limited sample of specimens collected from the wild. Here, we supplement previous descriptions with an illustrated account of skull development in P.sibilans based on a staged series of embryos and histological sections. Our findings largely agree with those of previous authors, although we record differences in developmental timing, confirming the presence of an egg tooth in this species. We add further observations on the enigmatic fenestra X, showing that it closes rather than merging with the prootic notch. Our observations revealed the likely contribution of the tectum posterius to the occipital roof, the presence of an internal carotid foramen (possibly transitory or variable), and the formation of the initial laterosphenoid pillar.

A large close relative of C. elegans is slow-developing but not long-lived

BackgroundVariation in body size is thought to be a major driver of a wide variety of ecological and evolutionary patterns, including changes in development, reproduction, and longevity. Additionally, drastic changes in natural context often have profound effects on multiple fitness-related traits. Caenorhabditis inopinata is a recently-discovered fig-associated nematode that is unusually large relative to other members of the genus, including the closely related model system C. elegans. Here we test whether the dramatic increase in body size and shift in ecological context has led to correlated changes in key life history and developmental parameters within this species.ResultsUsing four developmental milestones, C. inopinata was found to have a slower rate of development than C. elegans across a range of temperatures. Despite this, C. inopinata did not reveal any differences in adult lifespan from C. elegans after accounting for differences in developmental timing and reproductive mode. C. inopinata fecundity was generally lower than that of C. elegans, but fitness improved under continuous-mating, consistent with sperm-limitation under gonochoristic (male/female) reproduction. C. inopinata also revealed greater fecundity and viability at higher temperatures.ConclusionConsistent with observations in other ectotherms, slower growth in C. inopinata indicates a potential trade-off between body size and developmental timing, whereas its unchanged lifespan suggests that longevity is largely uncoupled from its increase in body size. Additionally, temperature-dependent patterns of fitness in C. inopinata are consistent with its geographic origins in subtropical Okinawa. Overall, these results underscore the extent to which changes in ecological context and body size can shape life history traits.

Hidden complexity in the ontogeny of sexual size dimorphism in male-larger beetles

Sexual size dimorphism (SSD) is widespread among animals, but its developmental mechanisms are not fully undestood. We investigated the proximate causes of SSD in three male-larger and one monomorphic scarab beetles using detailed monitoring of growth in individual instars. Apart from the finding that SSD in all three male-larger species started to develop already in the first larval instar, we generally found a high variability in SSD formation among the species as well as among instars. Overall, sexual differences in developmental time, average growth rate, as well as in the shape of the growth trajectory seem to be the mechanisms responsible for SSD ontogeny in scarab beetles. In the third instar, when the larvae attain most of their mass, the males had a similar or even lower instantaneous growth rate than females and SSD largely developed as a consequence of a longer period of rapid growth in males even in cases when the sexes did not differ in the total duration of this instar. Our results demonstrate that a detailed approach, examining not only the average growth rate and developmental time, but also the shape of the growth trajectory, is necessary to elucidate the complex development of SSD.

Variation is the universal: making cultural evolution work in developmental psychology.

Culture is a human universal, yet it is a source of variation in human psychology, behaviour and development. Developmental researchers are now expanding the geographical scope of research to include populations beyond relatively wealthy Western communities. However, culture and context still play a secondary role in the theoretical grounding of developmental psychology research, far too often. In this paper, we highlight four false assumptions that are common in psychology, and that detract from the quality of both standard and cross-cultural research in development. These assumptions are: (i) the universality assumption, that empirical uniformity is evidence for universality, while any variation is evidence for culturally derived variation; (ii) the Western centrality assumption, that Western populations represent a normal and/or healthy standard against which development in all societies can be compared; (iii) the deficit assumption, that population-level differences in developmental timing or outcomes are necessarily due to something lacking among non-Western populations; and (iv) the equivalency assumption, that using identical research methods will necessarily produce equivalent and externally valid data, across disparate cultural contexts. For each assumption, we draw on cultural evolutionary theory to critique and replace the assumption with a theoretically grounded approach to culture in development. We support these suggestions with positive examples drawn from research in development. Finally, we conclude with a call for researchers to take reasonable steps towards more fully incorporating culture and context into studies of development, by expanding their participant pools in strategic ways. This will lead to a more inclusive and therefore more accurate description of human development.This article is part of the theme issue 'Bridging cultural gaps: interdisciplinary studies in human cultural evolution'.