Browsing by Subject "natural-selection"
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Item A Common, Non-Optimal Phenotypic Endpoint in Experimental Adaptations of Bacteriophage Lysis Time(2012-03) Chantranupong, Lynne; Heineman, Richard H.; Chantranupong, LynneOptimality models of evolution, which ignore genetic details and focus on natural selection, are widely used but sometimes criticized as oversimplifications. Their utility for quantitatively predicting phenotypic evolution can be tested experimentally. One such model predicts optimal bacteriophage lysis interval, how long a virus should produce progeny before lysing its host bacterium to release them. The genetic basis of this life history trait is well studied in many easily propagated phages, making it possible to test the model across a variety of environments and taxa. Results: We adapted two related small single-stranded DNA phages, Phi X174 and ST-1, to various conditions. The model predicted the evolution of the lysis interval in response to host density and other environmental factors. In all cases the initial phages lysed later than predicted. The FX174 lysis interval did not evolve detectably when the phage was adapted to normal hosts, indicating complete failure of optimality predictions. Phi X174 grown on slyD defective hosts which initially entirely prevented lysis readily recovered to a lysis interval similar to that attained on normal hosts. Finally, the lysis interval still evolved to the same endpoint when the environment was altered to delay optimal lysis interval. ST-1 lysis interval evolved to be similar to 2 min shorter, qualitatively in accord with predictions. However, there were no changes in the single known lysis gene. Part of ST-1's total lysis time evolution consisted of an earlier start to progeny production, an unpredicted phenotypic response outside the boundaries of the optimality model. Conclusions: The consistent failure of the optimality model suggests that constraint and genetic details affect quantitative and even qualitative success of optimality predictions. Several features of ST-1 adaptation show that lysis time is best understood as an output of multiple traits, rather than in isolation.Item The Cost Of Reinforcement: Selection On Flower Color In Allopatric Populations Of Phlox Drummondii*(2014-05) Hopkins, Robin; Rausher, Mark D.; Hopkins, RobinReinforcement is the process by which increased reproductive isolation between incipient species evolves due to selection against maladaptive hybrids or costly hybrid mating. Reinforcement is predicted to create a pattern of greater prezygotic reproductive isolation in regions where the two species co-occur, sympatry, than in allopatry. Although most research on reinforcement focuses on understanding the evolutionary forces acting in sympatry, here we consider what prevents the alleles conferring greater reproductive isolation from spreading into allopatry. We investigate flower color divergence in the wildflower Phlox drummondii, which is caused by reinforcement in the regions sympatric with its congener Phlox cuspidata. Specifically, we performed common garden field experiments and pollinator observations to estimate selection acting on flower color variation in allopatry. We combine our estimates of maternal and paternal fitness using simulations and predict how flower color alleles migrating from sympatry will evolve in allopatry. Our results suggest that strong pollinator preference for the ancestral flower color in allopatry can maintain divergence between allopatric and sympatric populations.Item Thermoregulation As An Alternate Function Of The Sexually Dimorphic Fiddler Crab Claw(2011-09) Darnell, M. Zachary; Munguia, Pablo; Darnell, M. Zachary; Munguia, PabloFiddler crabs are highly sexually dimorphic. Males possess one small (minor) feeding claw and one greatly enlarged (major) claw; females possess two small claws. The major claw is used to attract mates and for burrow defense, but it is costly for the male to possess. We tested the hypothesis that the major claw also functions as a thermoregulatory structure, a function that would allow males to spend a greater amount of time at the surface, foraging and attracting potential mates. Fiddler crabs Uca panacea were exposed to a source of radiant heat and body temperatures were monitored. Four groups of crabs were tested: intact males, males with the minor claw removed, males with the major claw removed, and females. The body temperatures of males without the major claw increased more rapidly and reached higher values than did those of males with the major claw intact, but the results from these animals were similar to those of females. These results support the hypothesized thermoregulatory function of the major claw. The major claw may function as a heat sink, transferring heat away from the body and dissipating it into the air. Enhanced thermoregulatory ability provided by the major claw may partially ameliorate the energetic costs of possessing such a large claw.