Differences

This shows you the differences between two versions of the page.

--- 2020:groups:g5:start [2020/01/09 19:15] – [Introduction] prado
+++ 2020:groups:g5:start [2024/01/09 18:45] (current) – external edit 127.0.0.1
@@ Line 2: / Line 2: @@
 **Group 5**
-<html><font size=6 face="Arial">Sex ratio shift as an invasion strategy</font></html>
+<html><font size=6 face="Arial">Third wheeling as an invasion strategy</font></html>
@@ Line 14: / Line 14: @@
 ===== Introduction =====
+{{::silverleaf_whitefly.jpg?nolink&200 |}}
-Between 2000 and 2006, farmers and scientists watched an infection of //Rickettsia bellii//, a symbiotic bacteria, to skyrocket in Sweet-potato whiteflies, //Bemisia tabaci//. Martha Hunter of the University of Arizona in Tucson showed that the proportion of whiteflies infected with the bacterium in Arizona, New Mexico and California soared from 1% in 2000 to 97% in 2006.
+Infestations of the whitefly //Bemisia tabaci// (left image, from Wikipedia) destroy plantations in the South of USA, Australia, China, among other countries. Several mechanisms have been isolated and tested in experimental settings to reveal how they contribute to this plague's success.
-The strategies that //Rickettsia// used to proliferate more quickly are very interesting. We know parasites typically spread in two ways: horizontally – in other words, within a generation – or vertically, from parent to offspring. Experiments ruled out horizontal transmissions of //Rickettsia//, and also show that the bacterium is passed from mother to offspring, whether or not the male population is also infected. Therefore, to increase the proliferation rate, //Rickettsia// helps female whiteflies not only to have more offspring, as well as it changes the sex-ratio of offspring towards female. But the presence of males should not be underestimated since they are important to generate female offspring because the whitefly species is haplodiploid, i.e., fertilized eggs generate diploid females and unfertilized eggs generate haploid males.
+Twelve different biotypes of whitefly have already been distinguished through phylogenetic analysis. One of these biotypes, referred to as 'B biotype', is native from Mediterranean Asia and has been reported rapidly invading worldwide populations of whitefly of other biotypes. For instance, B biotype entered in both China and Australia in the 90s, where the native biotypes are ZHJ1 and AN, respectively.
+Liu //et al.//  detected significant changes in sex ratio in both the indigenous and alien populations in both regions. In China, when populations of either B or ZHJ1 occurred alone, B usually had female
+ratios of 60~70%, which were higher than the 50~60% female ratios in ZHJ1. Very similar results also happened to AN biotype. This difference was even higher when the two different biotypes coexisted during the infestations. Then, the same researchers decided to reproduce this behavior in controlled environments, and observed similar data as in nature, as well as B biotype invasion of indigenous biotypes.
-{{::silverleaf_whitefly.jpg?nolink&200 |}}
+Interestingly, mating experiments between B and ZHJ1 and between B and AN indicated that neither could interbreed, although they could interfere in the frequency of copulation of the other biotype. For instance, in the presence of B biotype indigenous biotype couples could decrease their copulations. Oddly enough,  B-couple increases their frequency copulation in the presence of the indigenous biotype. Measurements of frequency of copulation and some other nice information are reported in the Supporting Online Material of Liu //et al//.
-Himler //et al.// (2011) showed that female whiteflies (left imagem, from Wikipedia) infected by this bacterium produce twice more offspring and its progeny has biased sex-ratios (that is, ca. 3:7 male:female ratio). Uninfected female whiteflies produce unbiased offsprings, as expected by Fisher's principle, since unbalanced sex ratios strongly affect individual fitness.
+This manipulation happens, literally, as a third wheel - the different biotype is able to court the female, but not to copulate with her. Moreover, copulation by indigenous individuals is partly blocked by B males that readily attempt to court with females of either biotype — a behavior not reciprocated by the indigenous males.
-What is suggested is an adaptive shift in sex allocation, which can occur when one of the sexes is more costly than the other. In many insects, including whiteflies, females are larger than males, hence they need more maternal resources to be produced. In this context, //Rickettsia// may provide products that are otherwise limiting for the production of ‘costly’ female offspring (for example, specific products that mediate fertilization, or limiting nutrients required in greater amounts by female than male progeny). This would be the reason that //Rickettsia//-infected whiteflies are able to produce more females.
-In this project we are going to explore this mechanism, a symbiotic relation between bacteria and female whiteflies: //Rickettsia// provides females with more resources to produce more high-costing female progeny, while whiteflies producing more females benefits //Rickettsia// by increasing vertical transmission. But be careful, it’s mutual up to a point: if the sex ratio becomes too skewed, it could become detrimental to the whitefly parents. In a female-abundant scenario, parents that increase the rate of  males in their progeny have fitness (Fisher's Principle, see references).
+===== Assignment =====
+Propose and analyze a mathematical model for whitefly populations to investigate the strategy of changing copulation frequency in whiteflies biotypes.
-===== Assignment =====
+===== Suggested questions =====
-Propose a mathematical model to investigate the strategy of sex-ratio shift in whiteflies caused by //Rickettsia// interference, the possible symbiotic mechanism discussed above. Explore the consequences of it to the bacteria invasion speed and the persistence of whiteflies.
+  - Which conditions of frequency of copulation ensures biotype B's capacity to invade and displace indigenous populations? Under what circumstances do you observe B invasion in your model?
+  - Which conditions verify the sex ratio shifts, given this mating behavior and the fact that whiteflies are haplodiploid?
-===== Questions & Suggestions =====
-  - Can you come up with a quantification of the invasion speed in your model? How does it behave with the biasing of sex? Is there a ratio which provides the highest speed?
-  - What are the consequences of  infection by //Rickettsia// to the persistence of whitefly species? Can high biased sex-ratios extinguish the population of whiteflies?
-  - Can this suggested mechanism explain an equilibrium at an unbalanced sex ratio in the population?
-  - Which parameters (and how) interfere in the population equilibrium sex ratio?
+Further well-grounded questions from the group are welcome.
 ===== References =====
+Shu-Sheng Liu, P. J. De Barro, Jing Xu, Jun-Bo Luan, Lian-Sheng Zang, Yong-Ming Ruan, Fang-Hao Wan. **Asymmetric Mating Interactions Drive Widespread Invasion and Displacement in a Whitefly** Science (2007), Vol. 318, Issue 5857, pp. 1769-1772. [[https://science.sciencemag.org/content/318/5857/1769]].
-Anna G. Himler, Tetsuya Adachi-Hagimori, Jacqueline E. Bergen, Amaranta Kozuch, Suzanne E. Kelly, Bruce E. Tabashnik, Elad Chiel, Victoria E. Duckworth, Timothy J. Dennehy, Einat Zchori-Fein, Martha S. Hunter.**Rapid Spread of a Bacterial Symbiont in an Invasive Whitefly Is Driven by Fitness Benefits and Female Bias**. Science, 2011. Vol. 332, Issue 6026, pp. 254-256. [[https://science.sciencemag.org/content/332/6026/254]].
-A short article about sex-ratio shift in the light of evolution and natural selection:  [[https://evolution.berkeley.edu/evolibrary/news/110401_whiteflies]].