Aphids are one of the affected organisms and are the subject of a number of ..... Dynamics of Soybean Aphid (Hemiptera: Aphididae).â Biological Control, 2017,.
Toluwalope Toluhi Principles of Ecology Biology 261 Professor Emily Mohl
Effects of Crowding on Aphid Alate Frequency (Hemiptera: Aphididae) Introduction The phenomena of global warming is one that has been extensively discussed in recent times as the world seems to come unglued with melting glaciers, erratic weather patterns and overall higher average temperatures(Karl, 2003). While there are two sides to the debate, a major undeniable fact is the rise of CO2 and greenhouse gases in recent years and the corresponding rise in factors such as temperature and drought conditions around the world. These observable, largely quantifiable phenomena have far reaching effects that we are yet to fully comprehend, one being the effect on the life cycle of a vast number of organisms on the planet. Aphids are one of the affected organisms and are the subject of a number of studies(Hulle, 2010). These inquiries examine factors such as temperature, precipitation, seasonal changes and duration of daytime light. Many effects have been uncovered such as the increased migration of aphids from their local populations to previously unoccupied locations by these species, which in some cases presents with the symptoms of a serious pest invasion(Watson et al., 1999). There are many facets to this development that have far reaching implications to public health and ecology. One of these is the spread of diseases and viruses by aphid vectors(Escriu et al., 2003). While in their natural habitats we can assume the parasitized organisms had sufficient defences so as not to be decimated by aphid parasitoids. We can also assume predators that acted as a population control and reduced carrying capacity of the aphid populations(Bannerman, 2017). However in the event of migrations, aphid populations might arrive at locations where they effectively had no predatorial control(Ehler Toluhi 1
& Kinsley, 1995) and in high densities virus transmission even to local aphids is an event that might occur(Betancourt et al., 2016). A counter argument is that events that cause such migration will sometimes result in the same effect in the predator species, but this has only been noticed in specific species(Conti et al., 2018; Baaren, 2010). Another possibility is the lack of defences or adaptation by the organisms that would become parasitized by the aphids. Such a situation could decimate a certain niche of the biome and effectively remove a key player in that ecosystem from the trophic level(Bertness, 1984). In the event that the decimated organism were not vital to the survival of other organisms, the effect would be minimal and the aphid migration would have done little to no damage. If it is the case that the decimated organisms are important to the new system, we would then have a breakdown of the system and a possible reorganization of the trophic levels, possibly causing some extinctions. The aphids status as disease or virus vectors could be one that compounds their effect in a new habitat. The various species of aphids are known to be able to transmit viruses to their hosts. While the virus might have had a certain negative effect on a former population, a new habitat might be unprepared for the virus. A study on the swine flu virus showed how the reintroduction of even formerly familiar viruses can have catastrophic effects due to mutation and reassortment(Neumann et al., 2009). Therefore, the similarity of the habitats being migrated from and to is more relevant in terms of how easily the new habitat would be occupied and less relevant in regards to the possible similarity of viral load of the symbiont vectors present in the biomes. Hence we are aware that depending on the new habitat and the virus that the specific aphid is a vector to, the effects of migration might present a health risk to the habitat and any populations nearby. Aphid migration is made possible by the alates who develop in response to crowding on a host plant, temperature changes, precipitation, lower food quality and longer nights. Alates are winged aphids who enable migration after the aforementioned factors precipitate their presence(Mehrparvar et al., 2013). There have been studies on the specific rates at
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which alates have been produced for the Cereal Aphid, Sitobion avenae, with formulaic methods:Percentage alates = 2.603 × Aphid density + 0.847 × GS − 27.189(Carter et al., 1982). There is the assumption of a max flight time of 2 hours serving as a limiting factor to how far they may emigrate(Duffy et al., 2017). However the progression towards earlier migratory dates might enable more intense niche carving by aphids(Hughes, 2000; Hulle, 2010). Continuing advancement in this vein, this paper focuses on how the aphid populations of the particular species Aphis Nerii g row and aims to quantify the effect of crowdedness on the development of alates who are perfect migrants and serve as virus vectors. The viruses infect the plants mostly and the expurgation of unsuspecting plant hosts might have unforeseen negative impacts on the inhabitants of the biome. We hypothesize that the effects of density are sufficient enough to cause a significant increase in alate frequency. Since high alate frequency may result in increased migration attempts, this would lead to successfully established populations of aphids in non native areas that may be less beneficial to the particular biome. Among other effects, new plant viruses from the migrant aphids would present a challenge the new host plant and population might be unprepared for.
Materials and Methods Data for this project was gathered from a experiment run by students of an Ecological Principles Class taught by Professor Emily Mohl at St. Olaf College in the Fall Semester of 2017. The experiment consisted of 148 milkweed plants that were housed in netted cages(n = 18) in the greenhouse at St. Olaf with an average of 8 plants to a cage. There were 67 control plants and 71 damaged plants in the final pool of milkweed. The damage criteria was included because the original study was interested in the effects of damaged leaves on the parasite-host interaction between the plant and a parasite we would introduce. Of the 8 plants, 4 of them had the top half of their leaves damaged by cutting off Toluhi 3
half the leaf along the midrib which reduces overall photosynthesis and gas exchange(Delaney & Leon, 2006). So if a plant had 12 leaves, the top 6 leaves would be damaged in this manner and the bottom 6 would be untouched. Plants were distributed randomly into the cages by genotype(samples were collected from various locations with varying genotypes). Aphids(n = 5) of the Aphis nerii species, the milkweed aphid, were then put on the plants and allowed to grow for 14 days. This number was used to simulate migration of aphids when overcrowding happens on a host plant. The A. nerii were used because they are the native parasites of the milkweed plant. In order to obtain useful data we tried to replicate the organisms and conditions as they would occur in the world, hence the use of the natural parasite and its natural host. Counts were taken daily of winged and unwinged aphids on 1 damaged and one control milkweed plant. On day = 1 and day = 14 the following measurements were taken from the host plant: Height(cm), nodes(n), leaves(n), Largest leaf width(cm), largest leaf length(cm), and stem width(mm). This analysis takes the counts from day 14 of the control plants(n = 581) to select for ideal conditions and performs regressions to search for any correlation between population number and alates. The regression plots the number of unwinged aphids against the winged aphids(alates) and gives an R-squared value to indicate correlation. In trying to quantify the extent to which alate production is dependent on or correlated to aphid population, a regression test is a helpful tool. A higher R-squared number signifies greater correlation. R, a statistical modeling freeware was used for all analyses. P values were taken into account in deciding how significant any values were. P values of ≤0.05 were considered significant. All the conditions for regressions and were satisfied as the graphs included show.
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A number of plants had unusable date and had to be excluded from the analyses in order to obtain trustworthy results
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Results The experiments went smoothly as students came in to do counts of aphid numbers on assigned days. No plant casualties were recorded and plants with abnormalities in counts were excluded from analyses. The counts that were used in this analysis were collected on the 14th day. A range in unwinged aphids was observed from 74 to 1400. Winged ranges were more conservative and went from 0 to 80. A regression done resulted in multiple R-squared of 0.02766, adjusted R-squared of 0.0103 and p-value of 0.2121
Figure 1. Each dot represents a milkweed plant and its winged and unwinged population. A line of best fit has been drawn to show a trend and supply us with R-squared values. Adjusted R-squared = 0.0103 and p-value = 0.2121
There would seem to be a slight correlation from the graph however they actually only indicate that only 1% of the data points can be predicted based on the data supplied and alongside that, the p value is >0.05(Hence our F-statistic is also insignificant). These give us insignificant results.
Discussion In regards to populations grow and and the quantification of the effect of crowdedness on alate frequency who are perfect migrants and serve as virus vectors, the data Toluhi 5
available is inadequate to support or dispute the idea that an increase in aphid density per plant results in higher alate frequency. The p-value does not meet the maximum 0.05 rendering the results from the analyses insignificant. This might be due to a number of factors: (i) difference in counts among various students. It could be that there were some conservative counters and some more liberal counters of a proportion and to an extent that did not even out. That could be an aspect that is more standardized in a sequel of this study. (ii) difference in densities. Because not all milkweed plants grew at the same rate, some were larger than others, giving more room to reproduce to the aphids. In this case, there might have been some populations that reached carrying capacity(a function of available resources), which would stimulate alate production, while others were still below the line at which reproduction would begin to slow down. (iii) difference in genotypes. The project utilized a number of different phenotypes collected from different regions of the US. Because they were now all in a common garden study due to the similar conditions, they grew at different rates as some of them were better suited for the environment provided. Based on these, it would be necessary to conduct more experiments in order to obtain significant data. More consistency with the data collection would be needed. More uniform numbers would help to solidify trends wherein confidence can be couched. It would also be beneficial to use a single genotype for the plants to give more uniform growth indices and food quality. While the effect of different plants on aphid population size has been studied(Wu et al., 2013; Zhang et al., 2016), intraspecies, genotype specific comparisons have not been carried out and these various genotypes could be used in a study that explored the response of aphids to the quality or robustness of the host. However, for the purpose of quantifying how population quantity relates to proportion of alates the study would need to be as uniform as possible. Another aspect that might be related to genotype in some studies is plant height. Height dictates amount of space available for aphid growth before carrying capacity is reached. If this were to be studied, plants would need to be selected for specific heights for the desired study as aphid habitation of plants has been shown to affect
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phenotypic traits which could impact resource availability and quality for the aphid populations(Park & Blossey, 2008). In this particular study plant height could definitely have affected the rate at which aphid populations grew and an improved analysis could normalize for plant height to observe whether predictability increased once this variable was removed. This paper will not go into how to identify potential migration destinations, but studies have shown how to predict aphid migration patterns using factors such as time of year, precipitation, uplift at the source, wind velocity, etc.(Sands, 1965; Parry, 2013). Niche construction theory helps in understanding the various options aphids may take advantage of inhabiting new areas(Laland et al., 2016; Laland et al., 2017), though conditions would need to be extremely favorable as aphids seem unlikely to be able to exert these changes except due to sheer number and intensity of grazing. Since these are all factors that have been mentioned previously in respect of the likelihood of their increase in response to symptoms of global warming, it follows that there should be concern about how they might further impact systems affected by global warming. There seems to have been a diversity of thought in academia about the effects of global warming on parasitoids and their hosts(Bezemer et al., 1998; Romo & Tylianakis, 2013), but newer studies tend to state that their results are limited based on region, even though functionally aphids would respond similarly(Newman, 2005; Tekle, 2016). They already are finding significant correlations between winged aphids migrating and the effects of global warming(Newman, 2005; Tekle, 2016). Further research should then examine more micro influences of the effects of global warming on aphid-milkweed interaction as there is an abundance of big picture reasoning. These micro effects might be a clue into localized solutions for their mitigation. Additionally, in future studies, temperature could be manipulated in order to examine how the proportions of alates differ at different levels. While it is known that determinants such as drought and rises in temperature enhance aphid fitness on trees(Dale & Frank, 2017; Doherty, 2017) and other plants with varying results(Bezemer et al., 1998; Romo & Tylianakis, 2013), it is unknown how the same or similar conditions would impact aphid
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fitness on milkweed. This quantification would also further the field in understanding the rates at which alates as migratory vectors are produced and how specific stimuli affect their noxiousness.
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References Bannerman, J.a., et al. “Predators and Alate Immigration Influence the Season-Long Dynamics of Soybean Aphid (Hemiptera: Aphididae).” Biological Control, 2017, doi:10.1016/j.biocontrol.2017.10.011. Baaren, Joan Van, et al. “Consequences of Climate Change for Aphid-Based Multi-Trophic Systems.” Aphid Biodiversity under Environmental Change, 2010, pp. 55–68., doi:10.1007/978-90-481-8601-3_4. Bertness, M. D. “Habitat and Community Modification by An Introduced Herbivorous Snail.” Ecology, vol. 65, no. 2, 1984, pp. 370–381., doi:10.2307/1941400. Betancourt, M., et al. “Aphid Vector Population Density Determines the Emergence of Necrogenic Satellite RNAs in Populations of Cucumber Mosaic Virus.” Journal of General Virology, vol. 97, no. 6, Jan. 2016, pp. 1453–1457., doi:10.1099/jgv.0.000435. Bezemer, T. Martijn, et al. “Long-Term Effects of Elevated CO 2 and Temperature on Populations of the Peach Potato Aphid Myzus Persicae and Its Parasitoid Aphidius Matricariae.” Oecologia, vol. 116, no. 1-2, Oct. 1998, pp. 128–135., doi:10.1007/s004420050571. Carter, N., et al. Cereal Aphid Populations: Biology, Simulation and Prediction. Centre for Agricultural Pub. and Documentation, 1982.
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Dale, A. G., and Steven D. Frank. “Warming and Drought Combine to Increase Pest Insect Fitness on Urban Trees.” Plos One, vol. 12, no. 3, Sept. 2017, doi:10.1371/journal.pone.0173844. Delaney, K. J., and Leon G. Higley. “An Insect Countermeasure Impacts Plant Physiology: Midrib Vein Cutting, Defoliation and Leaf Photosynthesis.” Plant, Cell and Environment, vol. 29, no. 7, 2006, pp. 1245–1258., doi:10.1111/j.1365-3040.2006.01504.x. Doherty, J., et al. “Temperature-Manipulated Dynamics and Phenology of Mindarus Abietinus (Hemiptera: Aphididae) in Commercial Christmas Tree Plantations in Quebec, Canada.” The Canadian Entomologist, vol. 149, no. 06, July 2017, pp. 801–812., doi:10.4039/tce.2017.41. Driesche, R. G. Van, et al. “Classical Biological Control for the Protection of Natural Ecosystems.” Biological Control, vol. 54, 2010, doi:10.1016/j.biocontrol.2010.03.003. Duffy, Catriona, et al. “An Improved Simulation Model to Describe the Temperature-Dependent Population Dynamics of the Grain Aphid, Sitobion Avenae.” Ecological Modelling, vol. 354, 2017, pp. 140–171., doi:10.1016/j.ecolmodel.2017.03.011. Ehler, L. E., and M. G. Kinsey. “Ecology and Management Of Mindarus Kinseyi Voegtlin (Aphidoidea: Mindaridae) on White-Fir Seedlings at a California Forest Nursery.”Hilgardia, vol. 62, no. 1, 1995, pp. 1–62., doi:10.3733/hilg.v62n01p006. Escriu, F., et al. “The Evolution Of Virulence In A Plant Virus.” Evolution, vol. 57, no. 4, 2003, p. 755., doi:10.1554/0014-3820(2003)057[0755:teovia]2.0.co;2.
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Hulle, M., et al. “Aphids in the Face of Global Changes.” Comptes Rendus Biologies, vol. 333, no. 6-7, 2010, pp. 497–503., doi:10.1016/j.crvi.2010.03.005. Hughes, L. “Biological Consequences of Global Warming: Is the Signal Already Apparent?” Trends in Ecology & Evolution, vol. 15, no. 2, 2000, pp. 56–61., doi:10.1016/s0169-5347(99)01764-4. Karl, T. R. “Modern Global Climate Change.” Science, vol. 302, no. 5651, May 2003, pp. 1719–1723., doi:10.1126/science.1090228. Kurane, I. “The Effect of Global Warming on Infectious Diseases.” Osong Public Health and Research Perspectives, vol. 1, no. 1, 2010, pp. 4–9., doi:10.1016/j.phrp.2010.12.004. Laland, K, et al. “An Introduction to Niche Construction Theory.” Evolutionary Ecology, vol. 30, no. 2, Mar. 2016, pp. 191–202., doi:10.1007/s10682-016-9821-z. Laland, K, et al. “Niche Construction, Sources of Selection and Trait Coevolution.”Interface Focus, vol. 7, no. 5, 2017, p. 20160147., doi:10.1098/rsfs.2016.0147. Mehrparvar, M, et al. “Multiple Cues for Winged Morph Production in an Aphid Metacommunity.” PLoS ONE, vol. 8, no. 3, May 2013, doi:10.1371/journal.pone.0058323. Neumann, G, et al. “Emergence and Pandemic Potential of Swine-Origin H1N1 Influenza Virus.” Nature, vol. 459, no. 7249, 2009, pp. 931–939., doi:10.1038/nature08157. Newman, J. A. “Climate Change and the Fate of Cereal Aphids in Southern Britain.” Global Change Biology, vol. 11, no. 6, 2005, pp. 940–944., doi:10.1111/j.1365-2486.2005.00946.x.
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Park, M. G., and B. Blossey. “Importance of Plant Traits and Herbivory for Invasiveness of Phragmites Australis (Poaceae).” American Journal of Botany, vol. 95, no. 12, Jan. 2008, pp. 1557–1568., doi:10.3732/ajb.0800023. Parry, H. R. “Cereal Aphid Movement: General Principles and Simulation Modelling.” Movement Ecology, vol. 1, no. 1, 2013, p. 14., doi:10.1186/2051-3933-1-14. Romo, C. M., and Jason M. Tylianakis. “Elevated Temperature and Drought Interact to Reduce Parasitoid Effectiveness in Suppressing Hosts.” PLoS ONE, vol. 8, no. 3, May 2013, doi:10.1371/journal.pone.0058136. Sands, W. A. “Alate Development and Colony Foundation in Five Species Of Trinervitermes (Isoptera, Nasutitermitinæ) in Nigeria, West Africa.” Insectes Sociaux, vol. 12, no. 2, 1965, pp. 117–130., doi:10.1007/bf02223758. Tekle, M. B.. “Impacts of Climate Change, Biodiversity Loss and Population on Sustainable Development in Ethiopia.” Biodiversity and Climate Change, Dec. 2016, pp. 94–121., doi:10.4337/9781782546894.00014. Watson, G. W., et al. “Biogeography of the Cinara Cupressi Complex (Hemiptera: Aphididae) on Cupressaceae, with Description of a Pest Species Introduced into Africa.” Bulletin of Entomological Research, vol. 89, no. 03, 1999, doi:10.1017/s0007485399000395. Wu, W., et al. “Special Plant Species Determines Diet Breadth of Phytophagous Insects: A Study on Host Plant Expansion of the Host-Specialized Aphis Gossypii Glover.” PLoS ONE, vol. 8, no. 4, Aug. 2013, doi:10.1371/journal.pone.0060832.
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Zhang, Y., et al. “Host Plant Determines the Population Size of an Obligate Symbiont (Buchnera Aphidicola) in Aphids.” Applied and Environmental Microbiology, vol. 82, no. 8, May 2016, pp. 2336–2346., doi:10.1128/aem.04131-15.
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