Living the Scientific Life (Scientist, Interrupted)

SICB Posters

I also managed to see a lot of posters today — some of which I will tell you about below the fold (I primarily focused on those posters that discussed birds or molecular evolution of certain characters);

  • Albers. The mosquito larvae of the genus Ochlerotatus actively regulate of the osmotic pressure of their body fluids so as to maintain homeostasis of the body’s water content, a process known as osmoregulation. For this reason, some species are restricted to freshwater habitats while others can successfully osmoregulate in saline waters that greatly exceed the concentration of seawater. This physiological difference between the freshwater and saline-tolerant forms is associated with a morphological difference in the larval rectum, an organ that serves an osmoregulatory function. Albers is interested in identifying when saline-tolerance evolved in this lineage. To do this, Albers and Bradley characterized the physiological and morphological aspects of larval osmoregulatory capabilities for several mosquito species. Albers and Bradley used freshwater and saline-tolerant Ochlerotatus mosquitoes to construct a phylogenetic tree using molecular data. These molecular data were obtained by PCR amplifying and sequencing mitochondrial and ribosomal DNA genes. When Albers and Bradley superimposed saline-tolerance characteristics of the larval stages onto this tree, they found that the evolution of saline-tolerance within the Ochlerotatus genus suggest that saline-tolerance evolved independently multiple times in this genus. It appears that saline-tolerance may also have been lost in some lineages.
  • Vaughn. A central assumption of life history theory is that reproduction is costly so therefore, it is important to choose a mate based on his overall quality. This requires the presence of an honest signal that reveals the fitness of a potential mate. Recent studies have shown that susceptibility to oxidative damage might be a mechanism by which the cost of reproduction is conferred. In order to measure the cost of reproduction in terms of oxidative damage, Vaughn and colleagues measured lipid peroxidation (LPO) and catalase activity in a population of wild birds, black guillemots, Cepphus grylle. They hypothesized that if higher metabolic rates generate more reactive oxygen species (ROS), they would see more oxidative damage in individuals with better body condition. Alternatively, it was possible that individuals in poorer body condition might show high levels of oxidative damage due to a decreased ability to scavenge ROS. They collected samples from adult black guillemots, a black and white seabird with red feet, during the breeding season. Their results revealed a positive correlation between LPO and catalase activity, and variation in LPO was correlated by a combination of body condition and date such that LPO increased with body condition and decreased during the course of the study. They also discovered that catalase activity increased with date but did not correlate with body condition. Vaughn and colleagues’ results suggest that intracellular antioxidant activity responds to increased amounts of damage and that breeding individuals in better body condition experience higher levels of oxidative damage, which causes their feet to have a more intense red color. Vaughn and colleagues are investigating the possibility that the redness of guillemot feet is an honest signal of oxidative stress.
  • Bird. Cypriniform fishes (minnows, carps, loaches, algae-eaters, and suckers) represent one of the most diverse orders of fishes in the world. They have a number of evolutionary innovations that are key to improved hearing and feeding that have probably played an important role in their invasion and dominance of freshwater niches in North America, Europe, and Asia. One such innovation, the Weberian apparatus, is a novel assemblage of vertebral elements that relay and amplify sound and pressure changes from the gas bladder to the inner ear. Although not unique to Cypriniformes, the Weberian apparatus has undergone dramatic morphological changes within Cypriniformes. As one of the most complex skeletal adaptations in fishes, Bird and colleagues are interested in the mechanisms that are responsible for the origin, development, and subsequent evolution of the Weberian apparatus within Cypriniformes. Using cleared and stained specimens, they assembled a detailed morphological comparison of the Weberian apparatus of Cypriniformes. They presented data of the morphological variations within and among all major cypriniform families. Their comparative study identified diverse morphologies as well as evidence of convergent evolution. For example, many divergent benthic fishes inhabiting swift-moving waters have encapsulated gas bladders. Additionally, variation within the families Balitoridae, Gyrinocheilidae, and Catostomidae was minimal, whereas variation within the subfamilies Cyprinidae and Cobitidae was far more significant. Large-scale variation was found among families, with each family exhibiting unique structural adaptations. This variation and morphological divergence provide insight into how ancestral vertebral structures have evolved and adapted to produce a functional Weberian apparatus in these fishes.
  • Hopkins. Some ecomorphological specializations create an evolutionary “ratchet”, a term used to describe irreversible morphological evolution. The phenomenon of an evolutionary ratchet occurs because the evolutionary specialization creates an evolutionary character such that it is much easier for the species to become increasingly specialized than for it to become less so. Fossoriality, or burrowing behavior, may provide an example of such an evolutionary ratchet. Fossorial adaptations, such as long, curved digging claws, short, powerful limbs, and reduced eyes, all make it much more difficult for mammals acquiring these features to escape predators using the behaviors of their ancestors. Hence, adaptation to a burrowing lifestyle provides a selective regime likely to produce an evolutionary ratchet. However, recognizing the pattern of an evolutionary ratchet requires tracing the evolution of morphology across phylogeny. For this study, Hopkins used measurements of limb bone proportions and craniodental morphology, as well as published behavioral data to determine degrees of morphological adaptation for fossoriality. By examining the morphological patterns of fossoriality across phylogenies of a number of extant and extinct burrowing mammalian lineages, it is possible to reconstruct the history of morphological evolution related to burrowing behavior. Preliminary results predict burrowing is an evolutionary ratchet, although defensive adaptations to deter predation may release the pressure to become more and more fossorial through time.
  • Bei. According to Hennig, one goal of phylogenetic systematics is to express the relationships of all organisms in a form that cannot be misunderstood. Cladograms are unambiguous diagrams of hypothetical relationships among select taxa. Unfortunately, interpreting cladograms can be difficult for biology students and can lead to general misunderstandings of evolutionary relationships between described taxa. Bei and Hoese investigated their introductory college biology students’ understanding of cladograms both before and after instruction. They used open-ended interviews to uncover major trends in conceptual difficulties and based on these interviews, they developed a written survey and a directed interview to investigate student difficulties. Before instruction most students had seen cladograms in textbooks, but few had interpreted them. In fact, several students interpreted a cladogram of vertebrate diversity as a food web diagram. Bei and Hoese found that most students read from left to right at the tips of the diagram, and that many students interpreted closeness of relationships by taxon proximity at the tips of the cladogram. Many students labeled the direction of time differently, depending on the style and orientation of the cladogram. Additionally, after instruction, many students shared new misconceptions. These included “ladder” thinking in which extant animals evolve into other extant animals as they progress up the “main branch.” Many students also thought that any given taxon is most closely related to the previous taxon on this “ladder.” In addition, this study shows that many pre-instruction conceptions were unchanged after instruction. Many students still had incorrect ideas about the direction of time on a cladogram, and thought that proximity at the tips implies closeness of relationships. Addressing both pre- and post-instruction misconceptions should allow scientists to teach cladogram interpretation more effectively, and to hopefully take one step closer to accomplishing Hennig’s goal.

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Comments

  1. #1 RPM
    January 6, 2007

    Did you happen to write down any citations on the Bei poster? I notice a lot of my students tend to be confused by cladograms, and I’m always looking for new ways to explain the basics.

  2. #2 GrrlScientist
    January 7, 2007

    no, i did not write down the references, but i did draw their figures on my notepad, if that helps you.

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