Evolution & Development最新文献

Uncovering mechanisms by which sensory systems evolve is critical for understanding how organisms adapt to a novel environment. Astyanax mexicanus is a species of fish with populations of surface fish, which inhabit rivers and streams, and cavefish, which have adapted to life within caves. Cavefish have evolved sensory system changes relative to their surface fish counterparts, providing an opportunity to investigate mechanisms underlying sensory system evolution. Here, we report the role of the gene retinal homeobox 3 (rx3) in cavefish eye evolution. We generated surface fish with putative loss-of-function mutations in the rx3 gene using CRISPR-Cas9 to determine the role of this gene in eye development in this species. These rx3 mutant surface fish fail to develop eyes, demonstrating that rx3 is required for surface fish eye development. Further, rx3 mutant surface fish exhibit altered behaviors relative to wild-type surface fish, suggesting that the loss of eyes impacts sensory-dependent behaviors. Finally, eye development is altered in cave-surface hybrid fish that inherit the mutant allele of rx3 from surface fish relative to siblings that inherit a wild-type surface fish rx3 allele, suggesting that cis-regulatory variation at the rx3 locus contributes to eye size evolution in cavefish. Together, these findings demonstrate that, as in other species, rx3 is required for eye development in A. mexicanus. Moreover, they suggest that variation at the rx3 locus plays a role in the evolved reduction of eye size in cavefish, shedding light on the genetic mechanisms underlying sensory system evolution in response to extreme environmental changes.

Two growth modes are recognized in colonial pterobranchs (Graptolithina): monopodial growth and sympodial growth. The earliest colonial Graptolithina likely developed through monopodial growth, a mode of colony formation well-documented in the extant graptolite Rhabdopleura normani. This growth involves a permanent terminal zooid and the sequential budding of additional zooids behind it, as the contractile stalk (gymnocaulus) of this terminal zooid elongates. This process is reflected in specific features of the secreted housing structure, the tubarium. Recently, monopodial growth was identified for the first time in a fossil taxon—the Cambrian dithecodendrid Tarnagraptus—based on tubarium characteristics, as no zooids were preserved. Monopodial growth also appears probable in other Cambrian taxa resembling Tarnagraptus, although evidence remains limited due to fragmentary materials. Sympodial growth, characterized by transient terminal zooids that are sequentially replaced as new buds form, is extensively documented in the fossil record of the Graptolithina. This growth mode characterizes the vast majority of Cambrian to Devonian Dendroidea and Graptoloidea. Phylogenetic evidence suggests sympodial growth evolved from monopodial growth in graptolithines, but the mechanisms underlying this evolutionary transition remain unclear.

Prey attraction is an integral component of the carnivorous syndrome, yet its molecular adaptations have remained largely unexplored. Our study utilized tissue-specific transcriptomic data from the South American marsh pitcher plant, Heliamphora tatei, to explore the molecular and developmental basis of prey attraction. Carnivorous plants often present specialized structures associated with prey attraction and in Heliamphora, that function is carried out by the nectar spoon, a colorful extension of the top of the pitcher that is densely covered in nectaries. Through comparisons of gene expression in the nectar spoon with the rest of the pitcher, we identified a suite of differentially expressed genes that likely contribute to prey attraction, including enzymes involved in volatile synthesis and sugar transporters. We found that one lineage of sugar transporters, the 14a clade of SWEETs (Sugars Will Eventually Be Exported Transporters), is highly upregulated in the nectar spoon and has evolved more rapidly in Sarraceniaceae, consistent with specialization for nectar transport as part of prey attraction. Among the genes related to volatile production, we found several enzymes best known for their role in floral scent. These results suggest that, similar to prey digestion, ancient genes are repurposed for novel functions during the transition to carnivory and may facilitate the repeated convergent origins of carnivory across angiosperms.

Variation in shape and size within a lineage, driven by developmental processes, plays a key role in diversification. Here, we explore the effects of allometry and heterochrony on the skull shape evolution during the post-metamorphic period of species within the Boana faber clade, which vary considerably in body size. We analyzed 61 skulls of specimens belonging to eight species of the Boana faber clade, in addition to two outgroups, through 2D geometric morphometric analyses taken from CT-Scan images. Our results demonstrated that skull shape is considerably impacted by the size, represented by centroid size, and this effect can be observed from ontogenetic and evolutionary perspectives. In this way, we accessed the ontogenetic trajectories of analysed species and, in light of the phylogenetic hypothesis of the clade, we discussed the observed variation based on the concept of heterochrony, suggesting that a peramorphic pattern has evolved in the group.

Sex-specific trait expression represents a striking dimension of morphological variation within and across species. The mechanisms instructing sex-specific organ development have been well studied in a small number of insect model systems, suggesting striking conservation in some parts of the somatic sex determination pathway while hinting at possible evolutionary lability in others. However, further resolution of this phenomenon necessitates additional taxon sampling, particularly in groups in which sexual dimorphisms have undergone significant elaboration and diversification. Here, we functionally investigate the somatic sex determination pathway in the gazelle dung beetle Digitonthophagus gazella, an emerging model system in the study of the development and evolution of sexual dimorphisms. We find that RNA interference (RNAi) targeting transformer (tra) caused chromosomal females to develop morphological traits largely indistinguishable from those normally only observed in males, and that tra^RNAi is sufficient to induce splicing of the normally male-specific isoform of doublesex in chromosomal females, while leaving males unaffected. Further, intersex^RNAi was found to phenocopy previously described RNAi phenotypes of doublesex in female but not male beetles. These findings match predictions derived from models of the sex determination cascade as developed largely through studies in Drosophila melanogaster. In contrast, efforts to target transformer2 via RNAi resulted in high juvenile mortality but did not appear to affect doublesex splicing, whereas RNAi targeting Sex-lethal and two putative orthologs of hermaphrodite yielded no obvious phenotypic modifications in either males or females, raising the possibility that the function of a subset of sex determination genes may be derived in select Diptera and thus nonrepresentative of their roles in other holometabolous orders. Our results help illuminate how the differential evolutionary lability of the somatic sex determination pathway has contributed to the extraordinary morphological diversification of sex-specific trait expression found in nature.

The regulation of bone size is a poorly understood and complex developmental process. Evolutionary models can enable insight through interrogation of the developmental and molecular underpinnings of natural variation in bone size and shape. Here, we examine the Mexican tetra (Astyanax mexicanus), a species of teleost fish comprising of an extant river-dwelling surface fish and obligate cave-dwelling fish. These divergent morphs have evolved for thousands of years in drastically different habitats, which have led to diverse phenotypic differences. Among many craniofacial aberrations, cavefish harbor a wider gape, an underbite, and larger jaws compared to surface-dwelling morphs. Morphotypes are inter-fertile, allowing quantitative genetic analyses in F₂ pedigrees derived from surface × cavefish crosses. Here, we used quantitative trait locus (QTL) analysis to determine the genetic basis of jaw size. Strikingly, we discovered a single genomic region associated with several jaw size metrics. Future work identifying genetic lesions that explain differences in jaw development will provide new insight to the mechanisms driving bone size differences across vertebrate taxa.