Backyard evolutionary biology: Investigating local flowers brings learning to life.

Inquiry-based learning allows students to actively engage in and appreciate the process of science. As college courses transition to online instruction in response to COVID-19, incorporating inquiry-based learning is all the more essential for student engagement. However, with the cancelation of in-person laboratory courses, implementing inquiry can prove challenging for instructors. Here, I describe a case that exemplifies a strategy for inquiry-based learning and can be adapted for use in various course modalities, from traditional face-to-face laboratory courses to asynchronous and synchronous online courses. I detail an assignment where students explore the developmental basis of morphological evolution. Flowers offer an excellent example to address this concept and are easy for students to access and describe. Students research local flowering plants, collect and dissect flower specimens to determine their whorl patterns, and generate hypotheses to explain the developmental genetic basis of the patterns identified. This task allows students to apply their scientific thinking skills, conduct guided exploration in nature, and connect their understanding of the developmental basis of evolutionary change to everyday life. Incorporating inquiry using readily available, tangible, tractable real-world examples represents a pragmatic and effective model that can be applied in a variety of disciplines during and beyond COVID-19.

Rotation of sex combs in Drosophila melanogaster requires precise and coordinated spatio-temporal dynamics from forces generated by epithelial cells.

The morphogenesis of sex combs (SCs), a male trait in many species of fruit flies, is an excellent system in which to study the cell biology, genetics and evolution of a trait. In Drosophila melanogaster, where the incipient SC rotates from horizontal to a vertical position, three signal comb properties have been documented: length, final angle and shape (linearity). During SC rotation, in which many cellular processes are occurring both spatially and temporally, it is difficult to distinguish which processes are crucial for which attributes of the comb. We have used a novel approach combining simulations and experiments to uncover the spatio-temporal dynamics underlying SC rotation. Our results indicate that 1) the final SC shape is primarily controlled by the inhomogeneity of initial cell size in cells close to the immature comb, 2) the final angle is primarily controlled by later cell expansion and 3) a temporal sequence of cell expansion mitigates the malformations generally associated with longer rotated SCs. Overall, our work has linked together the morphological diversity of SCs and the cellular dynamics behind such diversity, thus providing important insights on how evolution may affect SC development via the behaviours of surrounding epithelial cells.

Evolutionary Consequences of Male Driven Sexual Selection and Sex-Biased Fitness Modifications in Drosophila melanogaster and Members of the simulans Clade.

Males have evolved a variety of behavioral, morphological, and physiological traits to manipulate their mates in order to maximize their chances of success. These traits are bound to influence how females respond to male behaviors and influence the nature of sexual selection/conflict. A common consequence of aggressive male mating strategies in Drosophila melanogaster is the reduction of female lifespan. Our study shows that this is common across members of the simulans clade. Reduced life expectancy of females implies that female contribution to a population is less than that of males per generation. Fitness differences between the sexes in every generation will invariably affect overall population fitness. How natural selection responds to the female deaths and thereby the unequal fitness of the sexes has rarely been addressed. We shed light on this issue and provide evidence, which suggests that additional gains of fitness by males due to their longevity and continued mating may provide one explanation as to why the loss of female fitness may be "invisible" (effectively neutral) to natural selection. Male driven sexual selection and additional, transgenerational gains of male fitness can be an important force of evolutionary change and need to be tested with other organisms.

Evolution of Drosophila sex comb length illustrates the inextricable interplay between selection and variation.

In spite of the diversity of possible biological forms observed in nature, a limited range of morphospace is frequently occupied for a given trait. Several mechanisms have been proposed to explain this bias in the distribution of phenotypes including selection, drift, and developmental constraints. Despite extensive work on phenotypic bias, the underlying developmental mechanisms explaining why particular regions of morphological space remain unoccupied are poorly understood. To address this issue, we studied the sex comb, a group of modified bristles used in courtship that shows marked morphological diversity among Drosophila species. In many Drosophila species including Drosophila melanogaster, the sex comb rotates 90° to a vertical position during development. Here we analyze the effect of changing D. melanogaster sex comb length on the process of rotation. We find that artificial selection changes the number of bristles per comb without a proportional change in the space available for rotation. As a result, when increasing sex comb length, rather than displaying a similar straight vertical shape observed in other Drosophila species, long sex combs bend because rotation is blocked by a neighboring row of bristles. Our results show ways in which morphologies that would be favored by natural selection are apparently impossible to achieve developmentally. These findings highlight the potential role of development in modifying selectable variation in the evolution of Drosophila sex comb length.

Patterns of molecular evolution of the germ line specification gene oskar suggest that a novel domain may contribute to functional divergence in Drosophila.

In several metazoans including flies of the genus Drosophila, germ line specification occurs through the inheritance of maternally deposited cytoplasmic determinants, collectively called germ plasm. The novel insect gene oskar is at the top of the Drosophila germ line specification pathway, and also plays an important role in posterior patterning. A novel N-terminal domain of oskar (the Long Oskar domain) evolved in Drosophilids, but the role of this domain in oskar functional evolution is unknown. Trans-species transgenesis experiments have shown that oskar orthologs from different Drosophila species have functionally diverged, but the underlying selective pressures and molecular changes have not been investigated. As a first step toward understanding how Oskar function could have evolved, we applied molecular evolution analysis to oskar sequences from the completely sequenced genomes of 16 Drosophila species from the Sophophora subgenus, Drosophila virilis and Drosophila immigrans. We show that overall, this gene is subject to purifying selection, but that individual predicted structural and functional domains are subject to heterogeneous selection pressures. Specifically, two domains, the Drosophila-specific Long Osk domain and the region that interacts with the germ plasm protein Lasp, are evolving at a faster rate than other regions of oskar. Further, we provide evidence that positive selection may have acted on specific sites within these two domains on the D. virilis branch. Our domain-based analysis suggests that changes in the Long Osk and Lasp-binding domains are strong candidates for the molecular basis of functional divergence between the Oskar proteins of D. melanogaster and D. virilis. This molecular evolutionary analysis thus represents an important step towards understanding the role of an evolutionarily and developmentally critical gene in germ plasm evolution and assembly.

The roles of cell size and cell number in determining ovariole number in Drosophila.

All insect ovaries are composed of functional units called ovarioles, which contain sequentially developing egg chambers. The number of ovarioles varies between and within species. Ovariole number is an important determinant of fecundity and thus affects individual fitness. Although Drosophila oogenesis has been intensively studied, the genetic and cellular basis for determination of ovariole number remains unknown. Ovariole formation begins during larval development with the morphogenesis of terminal filament cells (TFCs) into stacks called terminal filaments (TFs). We induced changes in ovariole number in Drosophila melanogaster by genetically altering cell size and cell number in the TFC population, and analyzed TF morphogenesis in these ovaries to understand the cellular basis for the changes in ovariole number. Increasing TFC size contributed to higher ovariole number by increasing TF number. Similarly, increasing total TFC number led to higher ovariole number via an increase in TF number. By analyzing ovarian morphogenesis in another Drosophila species we showed that TFC number regulation is a target of evolutionary change that affects ovariole number. In contrast, temperature-dependent plasticity in ovariole number was due to changes in cell-cell sorting during TF morphogenesis, rather than changes in cell size or cell number. We have thus identified two distinct developmental processes that regulate ovariole number: establishment of total TFC number, and TFC sorting during TF morphogenesis. Our data suggest that the genetic changes underlying species-specific ovariole number may alter the total number of TFCs available to contribute to TF formation. This work provides for the first time specific and quantitative developmental tools to investigate the evolution of a highly conserved reproductive structure.

Condition dependence and the nature of genetic variation for male sex comb bristle number in Drosophila melanogaster.

Genetic architecture of variation underlying male sex comb bristle number, a rapidly evolving secondary sexual character of Drosophila, was examined. First, in order to test for condition dependence, diet was manipulated in a set of ten Drosophila melanogaster full-sib families. We confirmed heightened condition dependent expression of sex comb bristle number and its female homologue (distal transverse row bristles) as compared to non-sex sternopleural bristles. Significant genotype by environment effects were detected for the sex traits indicating a genetic basis for condition dependence. Next we measured sex comb bristle number and sternopleural bristle number, as well as residual mass, a commonly used condition index, in a set of thirty half-sib families. Sire effect was not significant for sex comb and sternopleural bristle number, and we detected a strong dominance and/or maternal effect or X chromosome effect for both traits. A strong sire effect was detected for condition and its heritability was the highest as compared to sex comb and sternopleural bristles. We discuss our results in light of the rapid response to divergent artificial selection for sex comb bristle number reported previously. The nature of genetic variation for male sex traits continues to be an important unresolved issue in evolutionary biology.

Variation and evolution of male sex combs in Drosophila: nature of selection response and theories of genetic variation for sexual traits.

We investigated the genetic architecture of variation in male sex comb bristle number, a rapidly evolving secondary sexual character of Drosophila. Twenty-four generations of divergent artificial selection for sex comb bristle number in a heterogeneous population of Drosophila melanogaster resulted in a significant response that was more pronounced in the direction of low bristle numbers. We observed a strong positive correlated response to selection in the corresponding female transverse bristle row. The correlated response in male abdominal and sternopleural bristle numbers, on the other hand, did not follow the same pattern as sex comb bristle number differences between selection lines. Relaxation-of-selection experiments along with mate choice and fecundity assays using the selection lines developed demonstrated the action of stabilizing selection on sex comb bristle number. Our results show (1) substantial genetic variation underlying sex comb bristle number variation; (2) a weak relationship between the sex comb and developmentally related, non-sex bristle systems; and (3) that sexual selection may be a driving force in sex comb evolution, indicating the potential of sex combs to diversify rapidly during population differentiation and speciation. We discuss the implications of these results for theories of genetic variation in display and nondisplay male sex traits.

Coiling versus clipping for the treatment of aneurysmal subarachnoid hemorrhage: a longitudinal investigation into cognitive outcome.

OBJECTIVE: Endovascular coiling has been used increasingly as an alternative to neurosurgical clipping for treating subarachnoid hemorrhage secondary to aneurysm rupture. The aim of the present study was to provide a prospective, longitudinal investigation into cognitive function in patients with aneurysmal subarachnoid hemorrhage treated with either neurosurgical clipping or endovascular coiling. METHODS: Twenty-three patients who were treated for aneurysmal subarachnoid hemorrhage at the National Hospital for Neurology and Neurosurgery in London, England, were recruited prospectively. Twelve patients who underwent surgical clipping were compared with a group of 11 patients who underwent endovascular coiling. All patients underwent a comprehensive, standardized neuropsychological assessment using the same battery of tests at the acute stage (within 2 wk after treatment). All patients who underwent coiling and 11 of the 12 patients who underwent clipping were reassessed at the post-acute long-term follow-up (6 mo) stage. RESULTS: Group comparisons at the acute assessment revealed a significant difference favoring coiling patients on only one measure of verbal recall. However, there were no other significant differences between the groups at this stage. At the post-acute assessment, the clipped group performed better than the coiled group on measures of intellectual functioning (P < 0.05), although no other differences were found on a range of cognitive tests. Intragroup comparisons between the acute and post-acute assessments found equivocal, significant improvements in measures of intellectual functioning, memory, executive functions, and speed of information processing in both groups of patients. CONCLUSION: We argue that there are minimal differences in the long-term cognitive outcome between endovascular coiling and surgical clipping. In the acute phase after treatment, we suggest that coiled patients, having been spared neurosurgical intervention, may have a slightly better cognitive outcome than clipped patients. However, these differences level off and both groups of patients ultimately experience widespread improvement in cognitive functioning by the post-acute stage of recovery.