Evolution & Development最新文献

During their development, fish pass through a series of developmental processes advancing, for example, their physiological and locomotive abilities. In particular, many marine fish larvae often hatch at an (semi-) embryonic developmental stage, and existential processes, such as digestion and respiration, and structures, such as muscle and skeleton, must form and/or change during the larval development. In this study, we analyzed the gene expression of factors associated with myogenesis, skeletogenesis, and growth within the different larval life stages of Atlantic herring. We evaluated these results in relation to length and stage ratio and performed histological analysis of cross-sections of herring larvae in different stages. Overall, the length per stage ratios showed that there are two major growth periods in larval herring development, the first occurring during the dorsal fin development phase and the second during the transition from caudal fin to pelvic fin development phase. This is consistent with the histological analysis, as an increase in muscle fibers was observed in both phases. The gene expression data also showed that factors responsible for muscle cell lineage determination and fiber development were highest before a period with increased growth. Combining our results with other studies on skeletogenesis, organogenesis, and the development of neural and sensory systems in herring, it becomes evident that other energetically costly developmental processes tend to occur in periods when growth is less prominent. It can therefore be concluded that growth and developmental priority periods alternate during larval development.

Telomeres (repeat-DNA-protein structures primarily located at the ends of chromosomes) protect coding DNA against attacks by reactive molecules and the cells’ own DNA repair systems. If that capacity is costly, but enhances an individual's viability, we might expect to see natural selection acting on telomere length: that is, individuals with optimal telomere lengths should have higher lifetime reproductive success than conspecifics with shorter or longer telomeres. Some recent studies on humans broadly support that prediction, but no data are available for free-ranging ectothermic vertebrates that, unlike mammals, can facultatively adjust telomere length during an individual's lifetime. In our decade-long study of a natural population of sand lizards (Lacerta agilis), including measurement of 2736 telomeres across > 1700 hatchling lizards and their > 500 parents, but with a very high hatchling mortality reducing later-life sample sizes, we found that lifespan, lifetime reproductive success and offspring recruitment rate were highest for hatchlings with “average-length” telomeres. Hatchlings with shorter-than-average telomeres elongated their telomeres during juvenile life, attaining the population-average telomere length by the time of sexual maturity; but that compensatory telomere growth was associated with lower body condition.

The early development of Cryptoheros spilurus, a substrate-breeding Middle American cichlid, was studied from hatching to 16 days post-hatching (dph), to document for the first time, the sequence of key ontogenetic changes. Eggs, deposited on rocky substrates, measured 1.65 ± 0.05 mm in diameter, with asynchronous hatching occurring at 52–54 h post-fertilization. Hatchlings (TL = 4.739 ± 0.27 mm) showed a large yolk sacs, finfold, straight notochord, and undeveloped eyes. Scanning electron microscopy revealed early differentiation of structures, including cement glands, olfactory pits, and optic primordia. Cement glands, previously reported in other cichlids, were documented here in their full developmental chronology, including their regression by 7 dph. Cranial development proceeded rapidly, with pigmentation and eye formation initiating by 1 dph and oral cavity, dentition, and taste buds forming by 6 dph. Fin development followed a sequential pattern: early pectoral fin formation supported initial mobility, while caudal, dorsal, anal, and pelvic fins emerged progressively, with full formation completed by 16 dph. Pigmentation evolved from a ventral melanophore stripe to a distinct species-specific pattern involving xanthophores and iridophores. By 16 dph, C. spilurus had completed metamorphosis (TL = 13.168 ± 0.55 mm). Allometric analysis revealed biphasic growth trajectories. Structures involved in feeding and sensory input, such as head length, snout length, and gape size, exhibited prolonged positive allometry, while trunk and tail traits showed delayed or negative allometry. These patterns reflect functional prioritization during the shift to active foraging. This study highlights C. spilurus as a valuable model for examining heterochrony, morphological modularity, and ecological adaptation during early development. Our findings provide essential baseline data for future comparative work on developmental plasticity and diversification in Neotropical cichlids.

Diverse regulatory mechanisms enable precise spatio-temporal control of gene expression across developmental stages, tissues, and sexes, contributing to the proper development of the organism. Evolutionary divergence leads to species-specific gene expression patterns, even in preserved developmental structures, due to regulatory changes that can disproportionately influence subsets of developmental genetic networks. Here, we quantify the evolution of sex-biased and tissue-biased transcriptomes from two tissue types (gonad and soma) for each of two sexes (male and female) from two of the closest known sister species of Caenorhabditis nematodes (C. remanei and C. latens). Differential gene expression and co-expression network analyses identify gene sets with distinct transcriptomic profiles, revealing widespread divergence between these morphologically and developmentally cryptic sister species. The transcriptomic divergence occurs despite most genes showing conserved expression across tissues and sexes. These observations implicate shared selection pressures related to tissue and sex differences as outweighing species-specific selection and developmental system drift in shaping overall transcriptome profiles. Although developmentally plastic tissue-biased expression profiles are mostly conserved between species, we find that sex-biased genes, particularly male-biased genes, contribute disproportionately to species-differences in gene expression, consistent with a disproportionate role for male-biased selection driving gene expression divergence.

Developmental changes in animals reflect important behavioral, biological, and ecological shifts. Allometric adjustments in arthropods, specifically, are associated with changes in sexual maturity or alterations in life mode. Examining post-embryological allometry of the American horseshoe crab—Limulus polyphemus—here evidences early shifts in prosomal development, later changes in thoracetronic size, and possible modularity across exoskeletal sections. Modifications in prosomal allometry reflect transitions from living above the substrate to primarily burrowing. This change occurs at the 3–4 moult stage and is associated with a 70% mortality rate in both natural settings and under aquaculture conditions. Thoracetron allometry changes record the fusion of opisthosomal tergites into a plate, where tergal development drives shifts in thoracetron morphology. Allometric changes between main body sections present possible evidence for modularity within the horseshoe crab exoskeleton that manifest across moulting events. These allometric shifts reflect the complex evolutionary history of the group, especially changes from surface dwelling and enrollment to burrowing, likely in response to increased predation pressures.

Sulfidic caves are harsh and extreme environments characterized by limited oxygen, low pH, and the presence of hydrogen sulfide. Amazingly, animals can live in sulfidic caves, one such animal being Asellus infernus, a representative of the Asellus aquaticus species complex, originating from Movile Cave and from old wells that represent windows of access to a sulfidic groundwater ecosystem located in southeast Romania. Little previous work has been done on lab-reared populations of A. infernus as they have been historically difficult to raise in the lab. Here, we develop resources for A. infernus, examining questions of timing of morphological differences in cave versus surface individuals, whether the environment (lab-bred vs. wild-caught) influenced size characteristics, and the genes and pathways showing differential expression between cave and surface samples. We found that A. infernus did not develop pigmentation embryonically, and juveniles had increased body length and longer antenna II as compared to surface individuals. Furthermore, we found that some of these measures differed between wild-caught and lab-reared juveniles for a given population, indicating that environmental differences can also influence these size characteristics. In addition, differential expression between cave and surface samples and allele-specific expression studies within F1 hybrids identified multiple genes, including those involved in sulfide metabolism and phototransduction. Strikingly, molecular convergence of genes involved in sulfide detoxification was observed between A. infernus and previous work on a fish that lives in both cave and sulfidic environments, Poecilia mexicana. In sum, we were able to develop embryonic and genomic tools for A. infernus, a model for understanding cave adaptation and adaptation to sulfidic environments.

The biological processes underlying the wide phenotypic mammal diversity are still not thoroughly understood. In this study, we examined how major stages in the life history of the common hippopotamus (Hippopotamus Amphibius) influence its craniomandibular morphology throughout ontogeny. Using geometric morphometrics and life-history meta-analysis correlations, we characterized skulls from 198 individuals spanning 20 developmental stages. The most significant morphological changes were observed during early infancy (0–3 years), coinciding with lactation and weaning, and during puberty (10–15 years), coinciding with reproductive maturation. These findings align with growth patterns typical of social mammals exhibiting high sexual dimorphism. Notably, we identified a pattern previously undocumented in any other vertebrate: cranial morphology stabilizes earlier than the mandibular one. Specifically, late-stage (20–25 years) shape modification in the mandibles indicates progressive reconfiguration of masticatory biomechanics as well as a continuous change of dental occlusion throughout life. This pattern is common in both male and female individuals and may be related to shifts in diet rather than sexual selection. This study provides the most comprehensive ontogenetic dataset for a semi-aquatic, large semigraviportal mammal with a polygynous social structure, offering a valuable foundation for future evolutionary studies based on comparative analyses.