The Milwaukee Public Museum (MPM) is a natural and human history museum in downtown Milwaukee, Wisconsin. The museum was chartered in 1882 and opened to the public in 1884; it is a not-for-profit organization operated by the Milwaukee Public Museum, Inc. MPM has three floors of exhibits and the first Dome Theater in Wisconsin.
In most animal species, the sex-determining pathway is typically initiated by the presence/absence of a primary genetic cue at a critical point during development. This primary genetic cue is often located on a single locus-referred to as sex chromosomes-and can be limited to females (in a ZZ/ZW system) or males (in an XX/XY system). One trademark of sex chromosomes is a restriction or cessation of recombination surrounding the sex-limited region (to prevent its inheritance in the homogametic sex). This may lead to-through a variety of mechanisms-higher amounts of genetic divergence within this region, ie between the X/Z and Y/W chromosomes, especially when compared with their autosomal counterparts. Recent advances in genome sequencing and computation have brought with them the ability to resolve haplotypes within a diploid individual, permitting assembly of previously challenging genomic regions like sex chromosomes. Leveraging these advances, we identified replicable diagnostic characteristics between typical autosomes and sex chromosomes (within a single genome assembly). Under this framework, we can use this information to identify putative sex chromosome linkage groups across divergent vertebrate taxa and simultaneously curate misassembled regions on autosomes. Here, we present this conceptual framework and associated tool for identifying candidate sex chromosome linkage groups from a single, diploid individual dubbed Sex Chromosome Identification by Negating Kmer Densities.
Evolutionary transitions to diurnality are often associated with specialized ocular morphology, such as pits (foveae) in the retina. Foveae are required for high visual acuity and are found primarily in diurnal vertebrate taxa, including lizards. Geckos have undergone repeated evolutionary transitions between nocturnality and diurnality. Aristelliger is a nocturnal lineage embedded within a largely diurnal clade and represents a putative reversal to nocturnality. We investigated eye development and morphology of Aristelliger geckos. Despite sharing a most recent common ancestor with its diurnal sister lineage over 60 million years ago, Aristelliger exhibits a fovea. Fovea development is coordinated by dynamic changes in eye shape-such as ocular elongation and retraction-during embryonic development. In Aristelliger embryos, these elongation and retraction phases occur in the same region where the fovea forms, closely resembling the pattern seen in Anolis, a diurnal lizard with two foveae. Given the retention of a fovea in Aristelliger, we hypothesize that the transition to nocturnality is relatively recent. Incorporating these results into comparative phylogenetic methods results in a hypothesized diurnal ancestral temporal niche for sphaerodactylid geckos. We illustrate, similar to some nocturnal primates, that developmental data and robust morphological investigation can provide unique insights into macroevolutionary studies.
Small carpenter bees (Ceratina) are a morphologically diverse group of bees with a cosmopolitan distribution. The ~370 species of this group have been further classified in 25 different recognized subgenera. Here, a distinct new subgenus from Indomalaya, Scuticeratina subgen. nov., with two new species, Ceratina ferruginea sp. nov. and Ceratina phukhaensis sp. nov., are described. Two described species of previously uncertain subgeneric status, C. muscatella Nurse, 1902 stat. rev. and C. splendida Shiokawa, 2008 stat. rev. are also included within Scuticeratina. The monophyly of this group is supported by both morphological characters and molecular data, including phylogenetic analyses based on targeted genes and ultraconserved elements. Additionally, a third new species is tentatively placed in the nominate subgenus Ceratina Latreille, 1802, C. sirikitae sp. nov., distinct from other known species of this subgenus with unusual red abdominal coloration. Finally, an updated key to the Ceratina subgenera of the eastern hemisphere incorporating the new subgenus is provided.
Sex chromosome evolution is among the most dynamic genomic innovations in vertebrates, yet why some lineages evolve XY while others evolve ZW remains unclear. Using chromosome-level genomes from 19 geckos, we found that gecko sex chromosomes originated independently from 16 ancestral chromosomes. Their origins are nonrandom in both time and direction. Five of 11 datable origins coincide near the Middle Miocene Climatic Transition (~10 million years ago). Ancestral gene content is associated with the direction of evolution, with testis-enriched regions tending to evolve into ZW and testis-depleted regions into XY, a pattern observed across multiple amniote sex chromosome origins. Geckos with genetic sex determination repeatedly evolve partial dosage balance through up-regulation in the heterogametic sex. Sex chromosome evolution thus follows constraints from ancestral genomic predisposition and environmental context.
