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Biology Postdoc Seminar

N. Gownaris, C. Lahondère, T. Pham, E. Theobald
University of Washington, Department of Biology
Seminar date:
Friday, February 17, 2017 - 12:00
HCK 132

Bachelor Birds: Why Models Should Consider Seabird Sex

By: Natasha Gownaris

Punta Tombo, Argentina is the world’s largest colony (~200,000 breeding pairs) of Magellanic penguins (Spheniscus magellanicus) and has declined an average of 1%/year since 1987, with lack of food believed to be a major cause. Using 33 years of banding data on 45,000 known-age penguins, we developed a mark-recapture model with two levels of uncertainty in state assignment (breeding state and sex). We had two goals, to: 1) understand the drivers of the colony’s decline, and 2) show the importance of including sex in demographic studies. Only 20% of mark-recapture studies over the past decade consider sex, despite existing methodological solutions to sex assignment uncertainty. Sex was a major driver of variability in survival, with males showing annual juvenile survival rates as high as 1.7 times that of females. The sex survival gap was smaller in older birds, but female survival was lower than male survival over 80% of the time. These results help to explain our findings that the sex ratio at Punta Tombo has increased significantly over time, from 1.2 (M:F) in 1987 to 2.5 in 2015, and has been coupled with a significant decline in male breeding propensity. Population trajectory simulations show that assuming average survival provides misleading information on population health. We argue that female-biased mortality relates to the smaller size of females relative to males, which influences energetics and diet. Consequently, periods of low resource availability may have disproportionate effects on the smaller sex in species with sexual size dimorphism. 

Effect of temperature on olfactory behavior in mosquitoes

By: Chloé Lahondère 

In order to obtain a blood meal, disease vector insects need to accurately identify and locate mobile vertebrate hosts using a wide range of cues, in particular olfactory signals, which are key mediator of the vector-host interaction. While the physiological processes regulating food-seeking behavior have been well studied in these insects, comparatively less is understood about how environmental temperature might affect the performance of their sensory system. This project aims at contributing closing the knowledge gaps in our understanding of thermal sensitivity in disease vector mosquitoes.

The mechanome of asymmetric cell division

Tri Pham

Asymmetric cell division (ACD) generates cellular diversity and is an important process during development. Stem cells in particular utilize ACD in order to self-renew the stem cell yet generate differentiating siblings. Some stem cells undergo both physical and molecular ACD and it is unknown how biophysical parameters, such as cortical tension, stiffness or osmotic pressure generate physical asymmetry. We use Drosophila neural stem cells (neuroblasts) to study the contribution of biophysical parameters on ACD. We are combining fluorescence microscopy with atomic force microscopy (AFM) to measure the dynamics of the actomyosin network and cortical stiffness of cultured neuroblasts. Our measurements indicate that cortical stiffness gradually increases during metaphase before it suddenly drops at early anaphase and then quickly increases to a maximum value at mid anaphase. Interestingly, we detect high stiffness values on the apical cortex at anaphase although Myosin is barely detectable in this region. Since our results suggest that cortical stiffness does not necessarily correlate with Myosin levels, we then use Particle image velocimetry (PIV) and FRET biosensors to measure both cytoplasmic streaming and active cortical tension during ACD. Our FRET data shows that the apical cortex is compressed at early metaphase and is being stretched from anaphase onward. The combination of these measurements allow us to propose a model, explaining how changes in physical parameters contribute to the establishment of sibling cell size differences during mitosis.

Group experience impacts individual performance

By: Elli Theobald

Active learning in college STEM classes as well as productive participation in the workforce frequently hinges on small, informal groups. However, these groups can vary in functionality, ranging from true collaboration and cooperation to a single individual dominating and instructing the other group members. We asked whether this variation in group interaction impacts certain undergraduate students more than others. Does group inequity, comfort, or working with a friend help or hinder content mastery, and can an intentionally constructed, high-structure group activities mitigate some of the impacts? In a large-enrollment introductory biology course, we asked students pre-validated questions about group function after two types of in-class group activities: 1) working through an assignment together for an entire class period, or 2) a ‘jigsaw’ activity wherein students first independently mastered content, then joined “mixed-expertise groups” to teach peers specific parts of the assignment. We analyzed the impact of declaring the presence of a dominator, the feeling of comfort, or working with a friend on course performance, as well as the impact of activity type and demographic characteristics on those declarations. Students who report a dominator in their group are more likely to score lower on a post-test assessing content mastery than students who did not report a dominator. Similarly, being comfortable in their group was strongly correlated with increased performance, and working with a friend was the single biggest predictor of reporting comfort. There was no performance impact of working with a friend. Finally, we found that students experiencing a ‘jigsaw’ activity were less likely to report a dominator. Group activities that rely on positive interdependence, and include turn-taking and explicit prompts for students to explain their reasoning, may help reduce the negative impact of inequitable groups. 

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