Evolution & Development最新文献

Evolutionary novelties often arise through complex interactions among genetic, developmental, and ecological processes, yet their origins remain poorly understood. Here, we investigate the germline capsule in Camponotus (Carpenter ants) as a case of an evolutionary novelty. Using an integrated framework combining transcriptomic, morphological, and comparative developmental approaches, we characterize its molecular signatures, cellular architecture, and ontogeny. We show that germline gene–expressing cells adjacent to bacteriocytes fuse to form a multinucleated germline capsule, which subsequently contributes to the presumptive gonads, as revealed by label tracing. Despite harboring endosymbiotic bacteria like bacteriocytes, germline capsules exhibit distinct gene expression profiles. Furthermore, their phenotypic variation is developmentally modulated by bacterial presence. By examining the expression profile of germ-line specific gene (oskar) across multiple Camponotus species, we test the germline function of the capsule and its evolutionary conservation. Based on these findings, we propose a model in which the germline capsule evolved through cell fusion events enabled by developmental plasticity and shaped by interactions between host germline determinants and endosymbiotic bacteria. This study illustrates how integrating molecular, developmental, and ecological perspectives can illuminate the mechanisms underlying evolutionary innovation.

Modularity is an inherent property of organismal design where organisms are subdivided into quasi-independent units. Studies have shown that patterns of modularity can dramatically shift during the ontogenies of direct developing organisms. However, it is unclear how modularity patterns shift in organisms that undergo metamorphosis which is a dynamic period of development where organisms undergo morphological changes in response to ecological or physiological cues. Here we examined the ontogenetic modularity of the skull in the Red Sea anemonefish, Amphiprion bicinctus, across four larval stages, preflexion, flexion, postflexion, and metamorphosis, using micro-CT scanning and 3D geometric morphometrics to assess ontogenetic allometry and modularity. We hypothesized that skull modularity reorganizes during developmental transitions, and that oral jaw elements exhibit strong allometric growth and integration linked to functional demands during larval stages. The mandible, premaxilla, and maxilla exhibited strong size–shape relationships while the lower pharyngeal jaw and parasphenoid were isometric. Morphological disparity peaked at preflexion, suggesting high developmental plasticity early in ontogeny. We tested modularity hypotheses based on developmental and functional interactions and found that the developmental hypotheses were favored across most stages. However, during flexion, a stage characterized by structural reorganization, support shifted to functional hypotheses and then reverted back to developmental hypothesis. This suggests that modular reorganization coincides with key functional transitions. Across all stages, the premaxilla and mandible remained highly integrated, underscoring the need for coordinated oral jaw development during early feeding. Our findings reveal how allometry, modularity, and integration interact during early skull development in a species undergoing rapid developmental and ecological transitions and highlight the functional importance of oral jaw coordination during early feeding.

Segmentation is one of the most striking features of bilaterians, and understanding its mechanisms provides insights into the evolution of body plans. In annelids, segmentation occurs at different developmental stages through a variety of processes, yet the molecular pathways remain underexplored. Aiming to compare segmentation patterns in ontogeny and phylogeny, we analysed the expression of Avi-en (homologous to engrailed) and Avi-wnt1 in the nereidid polychaete Alitta virens. Using in situ hybridization, immunofluorescence, and cell proliferation assays, we mapped the spatiotemporal expression of these genes across embryonic, larval, and postlarval stages. We found that Avi-en was expressed in solid lateral domains early in the unsegmented protrochophore stage and progressed through a metameric pattern, while Avi-wnt1 expression appeared later, also aligning with segmental boundaries. At the nectochaete stage, the posterior domain of Avi-en expression in the growth zone expanded and split into two due to increased cell proliferation. The postlarval segment primordium then developed progressively, culminating in the activation of Avi-wnt1 at the posterior border. According to available published data, the revealed pattern of gradual segment formation is unique to nereidids. The observed divergence in gene expression and cell proliferation across annelids suggests that segmentation in bilaterians did not arise from a common ancestral mechanism. Our study enhances future progress in understanding the evolution of body patterning by providing a foundation for future comparisons.

A fundamental focus of evolutionary developmental biology is uncovering the genetic mechanisms responsible for the gain and loss of characters. One approach to this question is to investigate changes in the coordinated expression of a group of genes important for the development of a character of interest (a gene regulatory network). Here we consider the possibility that modifications to the wing gene regulatory network (wGRN), as defined by work primarily done in Drosophila melanogaster, were involved in the evolution of wing dimorphisms of the pea aphid (Acyrthosiphon pisum). We hypothesize that this may have occurred via changes in expression levels or by duplication followed by divergence of wGRN components. To test this, we annotated members of the wGRN in the pea aphid genome and assessed their expression levels in first and third nymphal instars of winged and wingless morphs of males and asexual females. We find that only 2 of the 32 assessed genes exhibit morph-biased expression. We also find that three wing genes (apterous (ap), warts (wts), and decapentaplegic (dpp)) have undergone gene duplication. In each case, the resulting paralogs show signs consistent with functional divergence, exhibiting either sex-, morph-, or stage-specific expression. Two gene duplicates, wts2 and dpp3, are of particular interest with respect to wing dimorphism, as they exhibit male morph-specific isoforms and wingless male-biased expression, respectively. These gene expression results provide an important first step toward identifying members of the pea aphid wGRN that may play a causative role in differentiating winged from wingless morphs. These findings supplement our understanding of trends in developmental gene network evolution, such as side-stepping pleiotropic constraint via duplication and sub-functionalization, underlying the emergence of novel phenotypes.

Embryos are vulnerable. Rapid development decreases the period of vulnerability. Parents’ protections also decrease vulnerability and may decrease selection for rapid development. A previous study showed that invertebrate embryos with more protection had slower early cell cycles. The slowing varied greatly among species. Hypotheses for the slowing include genetic drift and selection for developmental improvements. Here, published data on teleost fish indicated that (1) guarded and hidden embryos exhibit a similar pattern of varied slowing and (2) the pattern of slowing is similar for early cell cycles (mostly dependent on times for DNA replication and cell division) and somite formation (which also involves transcription and cell signaling). Times for early cell cycles and somite formation were more uniformly fast for teleosts with scattered nonadhesive eggs than for those with guarded or hidden eggs. Some species with adhesive eggs that were not reported to be guarded or hidden also developed slowly, as expected if parents select safe sites for egg attachment. Slower development is expected to increase bias against evolutionary reversals to less protection of embryos. Differences in egg size did not account for slower development of protected embryos. Slow development increased age at hatching but did not account for all the increase in age at hatching of protected embryos. Greater protection of embryos was associated with an evolutionary slowing of developmental processes as simple as early cell multiplication and complex as somite formation, in fish with disparate protections of embryos, in habitats ranging from the ocean to temporary ponds.