Modes of sex determination are quite variable in vertebrates. The developmental decision to form a testis or an ovary can be influenced by one gene, several genes, environmental variables, or a combination of these factors. Nevertheless, certain morphogenetic aspects of sex determination appear to be conserved in amniotes. Here we clone fragments of nine candidate sex-determining genes from the snapping turtle Chelydra serpentina, a species with temperature-dependent sex determination (TSD). We then analyze expression of these genes during the thermosensitive period of gonad development. In particular, we compare gene expression profiles in gonads from embryos incubated at a male-producing temperature to those from embryos at a female-producing temperature. Expression of Dmrt1 and Sox9 mRNA increased gradually at the male-producing temperature, but was suppressed at the female-producing temperature. This finding suggests that Dmrt1 and Sox9 play a role in testis development. In contrast, expression of aromatase, androgen receptor (Ar), and Foxl2 mRNA was constant at the male-producing temperature, but increased several-fold in embryos at the female-producing temperature. Aromatase, Ar, and Foxl2 may therefore play a role in ovary development. In addition, there was a small temperature effect on ERα expression with lower mRNA levels found in embryos at the female-producing temperature. Finally, Dax1, Fgf9, and SF-1 were not differentially expressed during the sex-determining period, suggesting these genes are not involved in sex determination in the snapping turtle. Comparison of gene expression profiles among amniotes indicates that Dmrt1 and Sox9 are part of a core testis-determining pathway and that Ar, aromatase, ERα, and Foxl2 are part of a core ovary-determining pathway.

Temperature-dependent sex determination (TSD) was described nearly 50 years ago. Researchers have since identified many genes that display differential expression at male-vs. female-producing temperatures. Yet, it is unclear whether these genes (1) are involved in sex determination per se, (2) are downstream effectors involved in differentiation of ovaries and testes, or (3) are thermo-sensitive but unrelated to gonad development. Here we present multiple lines of evidence linking CIRBP to sex determination in the snapping turtle, Chelydra serpentina. We demonstrate significant associations between a single nucleotide polymorphism (SNP) (c63A . C) in CIRBP, transcript levels in embryonic gonads during specification of gonad fate, and sex in hatchlings from a thermal regime that produces mixed sex ratios. The A allele was induced in embryos exposed to a female-producing temperature, while expression of the C allele did not differ between female-and male-producing temperatures. In accord with this pattern of temperaturedependent, allele-specific expression, AA homozygotes were more likely to develop ovaries than AC heterozygotes, which, in turn, were more likely to develop ovaries than CC homozygotes. Multiple regression using SNPs in CIRBP and adjacent loci suggests that c63A . C may be the causal variant or closely linked to it. Differences in CIRBP allele frequencies among turtles from northern Minnesota, southern Minnesota, and Texas reflect small and large-scale latitudinal differences in TSD pattern. Finally, analysis of CIRBP protein localization reveals that CIRBP is in a position to mediate temperature effects on the developing gonads. Together, these studies strongly suggest that CIRBP is involved in determining the fate of the bipotential gonad.KEYWORDS genetics of sex; cold-inducible RNA-binding protein; temperature-dependent sex determination; genetic association S EX determination in vertebrates is divided into two broad categories, either genotypic or environmental. Genotypic sex determination (GSD) occurs at fertilization and is governed by an individual's genotype. GSD species often, but not always, display morphologically distinct sex chromosomes, as observed in mammals, birds, snakes, some lizards, and some turtles. While some GSD systems are monogenic, other GSD systems involve two or more genes (Moore and Roberts 2013; Bachtrog et al. 2014). Environmental sex determination occurs when extrinsic factors influence whether an embryo develops into a female or a male. Various abiotic and biotic factors determine sex in metazoans, but temperature is the only environmental factor known to influence sex determination in amniotes (Bull 1983;Janes et al. 2010;Merchant-Larios and Díaz-Hernández 2013). This phenomenon is referred to as temperature-dependent sex determination (TSD) and is observed in many lizards, numerous turtles, and all crocodilians studied to date (Ewert et al. , 2004Lang and Andrews 1994;Viets et al. 1994;Deeming 2004;Harlow 2004). However, GSD and TSD are not as distinct as ...

Background: Despite the overwhelming agreement among scientists regarding the fundamental importance of evolution to all areas of biology, a lack of evolution understanding and acceptance has been reported in studies of students, educators, and members of society. In the present study, we investigate and report evolution acceptance in a population of undergraduate health sciences students enrolled in a first-year foundational biology course. Two published instruments-The Measure of Acceptance of the Theory of Evolution (MATE) and the Generalized Acceptance of Evolution Evaluation (GAENE)-were used to quantify evolution acceptance. A confirmatory factor analysis (CFA) was performed on both instruments to test whether the items measured the underlying construct sufficiently. Additionally, Rasch scaling was used to investigate fit between the data and the measurement model, and to determine if the MATE should be treated as a unidimensional or bidimensional instrument. Using correlation and regression analysis, we examined the relationships between the two measures of evolution acceptance, and between measures of evolution acceptance with other student variables of interest. Results:The health sciences students in this study demonstrated high acceptance of evolution at the start of term, as well as a significant increase in evolution acceptance from pre-to post-test. CFA and Rasch scaling provided some evidence that the MATE is a bidimensional instrument, but considering MATE as a bidimensional instrument provided little additional insight compared to treating MATE as a unidimensional instrument. Measures of evolution acceptance resulting from the MATE and GAENE instruments were significantly and strongly correlated. Multiple regression modeling identified underrepresented minority status as a demographic variable predictive of evolution acceptance, and provided further evidence of the strong association between the MATE and GAENE instruments. Conclusions:The undergraduate health sciences students in this study demonstrated a significant increase in evolution acceptance from pre-to post-test after one semester of instruction in general biology. Measures of evolution acceptance from the MATE and GAENE instruments were strongly correlated whether MATE was treated as a unidimensional or bidimensional instrument. This work provides initial indications that the MATE and GAENE instruments perform comparably as measures of evolution acceptance. Although the instruments are closely related, this work found more psychometric evidence for interpreting and using GAENE scores than MATE scores as a measure of evolution acceptance. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Psychology researchers have long attempted to identify educational practices that improve student learning. However, experimental research on these practices is often conducted in laboratory contexts or in a single course, which threatens the external validity of the results. In this article, we establish an experimental paradigm for evaluating the benefits of recommended practices across a variety of authentic educational contexts—a model we call ManyClasses. The core feature is that researchers examine the same research question and measure the same experimental effect across many classes spanning a range of topics, institutions, teacher implementations, and student populations. We report the first ManyClasses study, in which we examined how the timing of feedback on class assignments, either immediate or delayed by a few days, affected subsequent performance on class assessments. Across 38 classes, the overall estimate for the effect of feedback timing was 0.002 (95% highest density interval = [−0.05, 0.05]), which indicates that there was no effect of immediate feedback compared with delayed feedback on student learning that generalizes across classes. Furthermore, there were no credibly nonzero effects for 40 preregistered moderators related to class-level and student-level characteristics. Yet our results provide hints that in certain kinds of classes, which were undersampled in the current study, there may be modest advantages for delayed feedback. More broadly, these findings provide insights regarding the feasibility of conducting within-class randomized experiments across a range of naturally occurring learning environments.

BackgroundCC chemokine receptor proteins (CCR1 through CCR10) are seven-transmembrane G-protein coupled receptors whose signaling pathways are known for their important roles coordinating immune system responses through targeted trafficking of white blood cells. In addition, some of these receptors have been identified as fusion proteins for viral pathogens: for example, HIV-1 strains utilize CCR5, CCR2 and CCR3 proteins to obtain cellular entry in humans. The extracellular domains of these receptor proteins are involved in ligand-binding specificity as well as pathogen recognition interactions.In mammals, the majority of chemokine receptor genes are clustered together; in humans, seven of the ten genes are clustered in the 3p21-24 chromosome region. Gene conversion events, or exchange of DNA sequence between genes, have been reported in chemokine receptor paralogs in various mammalian lineages, especially between the cytogenetically closely located pairs CCR2/5 and CCR1/3. Datasets of mammalian orthologs for each gene were analyzed separately to minimize the potential confounding impact of analyzing highly similar sequences resulting from gene conversion events.Molecular evolution approaches and the software package Phylogenetic Analyses by Maximum Likelihood (PAML) were utilized to investigate the signature of selection that has acted on the mammalian CC chemokine receptor (CCR) gene family. The results of neutral vs. adaptive evolution (positive selection) hypothesis testing using Site Models are reported. In general, positive selection is defined by a ratio of nonsynonymous/synonymous nucleotide changes (dN/dS, or ω) >1.ResultsOf the ten mammalian CC motif chemokine receptor sequence datasets analyzed, only CCR2 and CCR3 contain amino acid codon sites that exhibit evidence of positive selection using site based hypothesis testing in PAML. Nineteen of the twenty codon sites putatively indentified as likely to be under positive selection code for amino acid residues located in extracellular domains of the receptor protein products.ConclusionsThese results suggest that amino acid residues present in intracellular and membrane-bound domains are more selectively constrained for functional signal transduction and homo- or heterodimerization, whereas amino acid residues in extracellular domains of these receptor proteins evolve more quickly, perhaps due to heightened selective pressure resulting from ligand-binding and pathogen interactions of extracellular domains.