how copepod chemical signals affect marine heterotrophic and mixotrophic species’ diel feeding patterns
A Sample Answer For the Assignment: how copepod chemical signals affect marine heterotrophic and mixotrophic species’ diel feeding patterns
Title: how copepod chemical signals affect marine heterotrophic and mixotrophic species’ diel feeding patterns
Summary
The study evaluates how copepod chemical signals affect marine heterotrophic and mixotrophic species’ diel feeding patterns. Copepods were used in the research as predators and a reservoir of chemical signals for different Microzooplankton species, including dinoflagellates and ciliates. These dinoflagellate and ciliate were kept in a laboratory environment without predation and studied (Arias et al., 2021). Several preparations were made before the research to assure the validity of the results, including fasting the predatory insects for 48 hours to ensure that previously consumed food had been entirely utilized. To eliminate size disparities between day and night, salina was employed as the usual prey. All the examined phagotrophic protists had relatively high diurnal eating rates. Strengths The study’s well-defined goal is its first significant strength. The study aims to elaborate on how copepod chemical signals affect the diel-eating rhythms of marine protists that are heterotrophic and mixotrophic. Having a well-defined research question, allowed them to progress toward confirming or disproving their ideas. The supported experimental design is another strength, this design’s high effectiveness is a result of the use of a standardized process.
The study shows precise control of unnecessary extra and independent variables which allowed a causal relation to be proven. There are enough justifications for the experimental design and all the methods that were applied to create a successful experiment. All the factors are well considered, and the right specimens were used. These two aspects of the article make up the framework of the study in order for the reader to understand the basis of the argument and how important it is to follow the scientific process in conducting studies as such. Weaknesses Low realism is one of the research’s flaws. Other external factors that are not considered in the research study could impact the observation in this investigation. There may be additional environmental elements that have an impact on the research. In terms of ecology, the experiment was not valid, due to the fact that the conditions of each analyzed species’-soaked prey were used for the grazing tests. Two suspensions were made for the experiment: one with just the prey to act as a growth inhibition for the prey and the other with the same quantity of prey and the appropriate number of grazers. The effects of the external environment were not appropriately considered. The statistical analysis of the experimental results is another flaw in this study. The statistical analyses were performed to investigate whether changes in grazers’ ingestion rates during the day and the night are ineffective. The researchers used only t-tests to compare the outcomes from the triplicate bottles of each therapy throughout the day and at night. In addition, used t-tests to evaluate how copepodamides affected the grazers’ diel feeding cycle in connection to the cycle manifested in the absence of chemical stimuli.
However, a t-test is essentially unreliable in giving accurate information due to its direct dependence on sample size. Failure to apply proper controls is another flaw. Accurate experimental designs must also include controlled trials which is an essential component that the researchers failed to do effectively. The conditions of the control experiment are not clear. It may be challenging to discern valid findings from the study if a control group was not adequately included or if the control group was chosen improperly. Researchers can verify that research findings result from manipulating independent variables instead of unrelated variables when control samples are present. These control groups support the research’s internal validity. Decision Due to the strengths outweighing the weaknesses, I recommend accepting this study, but with minor alterations. The clear focus of the aim of the study (how copepod chemical signals affect the diel-eating rhythms of marine protists that are heterotrophic and mixotrophic) is a major strength that adds direction to the research. The only revisions that should be made is the lack of a proper control experiment, which can be easily rectified by ensuring that the control is put under similar conditions as the main experiment.
Finally, the research can also be improved by supplementing the t-tests. Confidence intervals or effect size can address t-inadequacies tests by providing a supplement or a replacement of the t-test. A reminder about Arias et al. Key Findings From Arias et al. 2. Copepodamides had species-specific effect with concentrations. 1. Day-night differences in feeding decreased with time since isolation. Key Findings From Arias et al. 3. Diurnal feeding could be restored in old cultures by exposing to copepodamides. TIPS: The following may be THE most important advice I can give you for writing an impactful analysis (that receives a higher grade)…Be specific. Provide evidence of your claims. Do not be vague. If your analysis does not guide the reader/teacher/editor through the evidence behind your decisions, it will not be convincing. If your review sounds like it is just a list of general strengths and weaknesses without evidence to back them up, it will not be convincing. I dislike single sentence claims that aren’t backed up like “The hypothesis was clear.” For that matter, I would avoid any mention of things being clear. When you make statements, think about why you’re making them and then include some of that why. I would MUCH, MUCH, MUCH rather have you focus on a few major items and spend some space on each one, rather than have a surficial review of too many items. RUBRIC: Evidence-BasedPlease, please, please. Provide evidence of your claims. Vague statements about aspects being “nice” or “good” or “bad” are uniformative.
If something was nice, WHY was it nice? If something was bad, HOW/WHY was it bad? Major weaknesses would lead us to question these key findings (e.g. we would expect a different result in the absence of the weakness). It’s good to look for red flags, but convince us that those matter. A paper analysis is persuasive writing. It’s not just about observing these potential weaknesses. You need to convince the reader that those red flags matter. Examples of arguments that needed better evidence • Differences in prey species fed to the microzooplankton • Differences in prey concentration fed to the microzooplankton • Differences in source from which cultures were isolated • Saturated prey conditions I will model the analysis of the top two. You will work in groups to model the analysis of the bottom two. Evidence needed PAPER: ANALYSIS: “The first weakness is the materials and methods of the experiment, specifically the food given to the grazers. The food provided to the protists was all the same except for one, Mesodinium rubrum. This species was fed Teleaulax amphioxeia every other day while the rest of the protists were fed Rhodomonas salina daily, and the authors never clarified why. I feel as though this difference in feeding would result in different feeding behaviors and possibly different rhythms, and an explanation would’ve cleared up why they still decided to use this protist in the experiment and maybe what significance this would have to the overall experiment.”
I’m especially concerned about vague predictions like “different behaviors” and “different rhythms”. Do you see how this is vague? Decide if this is important • How might prey affect diurnal feeding of microzooplankton, or their responses to predators? • If it is unlikely to matter, then this is a MINOR weakness that can be quickly addressed. • If this may matter, then this is potentially a MAJOR weakness. How might prey affect diurnal feeding of microzooplankton, or their responses to predators? • Prey differ in nutritional quality. • Microzooplankton fed higher quality prey may be more responsive to predator cues. Microzooplankton fed higher quality prey may be more responsive to predator cues. NO CUES IN THIS EXPERIMENT Mesodinium was unresponsive to copepodamide. This would be consistent with it’s prey being lower quality. 2. Copepodamides had species-specific effect with concentrations. 1. Day-night differences in feeding decreased with time since isolation. Microzooplankton fed higher quality prey may be more responsive to predator cues. Mesodinium wasn’t even used in this experiment. 3. Diurnal feeding could be restored in old cultures by exposing to copepodamides. Microzooplankton fed higher quality prey may be more responsive to predator cues. Mesodinium was unresponsive to copepodamide. This would be consistent with it’s prey being lower quality. 2. Copepodamides had species-specific effect with concentrations. Okay, so we have a justified reason of concern for this experiment. A good next step is to determine what would happen if part of the experiment were removed.
In this case, what if they deleted Mesodinium data. What would happen to the conclusion? If removing these data wouldn’t affect the conclusion/story, then you could just ask them to delete these data. If it affects the conclusion/story, then they need to address nutritional differences between prey. If they can’t, then you could consider whether removing this entire experiment would affect your decision. How might prey affect diurnal feeding of microzooplankton, or their responses to predators? • Prey differ in nutritional quality. • Microzooplankton fed higher quality prey may be more responsive to predator cues. • Prey differ in susceptibility to predation in day versus night. • Microzooplankton fed prey that are more susceptible during day will have a higher day:night ingestion quotient. Microzooplankton fed higher quality prey may be more responsive to predator cues. If Mesodinium was fed prey that were more/less susceptible to grazing during the day, then that may be more important than the years since isolation. Same approach as before… Okay, so we have a justified reason of concern for this experiment. 1. Day-night differences in feeding decreased with time since isolation. What would happen if we took out the Mesodinium data? It would weaken the relationship, but it would still be a trend for a negative relationship between years since isolation and ingestion quotient. So, it wouldn’t qualitatively change the conclusions. ANALYSIS: “The first weakness is the materials and methods of the experiment, specifically the food given to the grazers. The food provided to the protists was all the same except for one, Mesodinium rubrum.
This species was fed Teleaulax amphioxeia every other day while the rest of the protists were fed Rhodomonas salina daily, and the authors never clarified why. I feel as though this difference in feeding would result in different feeding behaviors and possibly different rhythms, and an explanation would’ve cleared up why they still decided to use this protist in the experiment and maybe what significance this would have to the overall experiment.” ”…If Teleaulax and Rhodomonas differ in nutritional quality, it could affect how microzooplankton fed these different prey respond to predator cues. I am uncertain if the lack of response of Mesodinium to copepodamides was because Teleaulax is an inferior food. Prey responses to predator cues can be weakened when prey eat lower quality foods. This is problematic in this study because Mesodinium did not respond to copepodamides like the three other microzooplankton tested. As a result, the authors are unable to rule out prey quality as a confounding variable. This prevents an adequate test of the hypothesis that microzooplankton responses to copepod cues are species-specific.” Relevent part of Decision….”…Because the comparison of microzooplankton to copepodamides is confounded by prey species that could affect the author’s conclusions, the authors need to provide evidence that Teleaulax was not nutritionally inferior to Rhodomonas. It is appropriate to provide data from other studies. If the authors can’t provide these data, then the Mesodinium data in Fig. # and any subsequent comparisons of them need to be omitted.” (and you would have some compelling reason for publishing it despite this edit)…” • First, In the methods section, I would like to have known why there was an increase in prey concentration as ‘time since isolation’ increased as well.
This would help the reader understand why the grazers are being fed that amount per species Diurnal feeding behaviors disappear rapidly. Remember They did a feeding experiment in day, and then an experiment with a separate batch at night. I can’t think of an obvious reason that the confounding variable of prey density might affect this pattern. So I’m not worried about it. Perhaps a minor sentence adding why this difference was present. For me, it’s not a big deal so my decision is not based on their ability to provide any compelling reason for this decision. The 3 E’s (a helpful framework for better evidence-based arguments) • EVIDENCE • Make an observation and provide evidence of it. • EXPLAIN • Explain why this observation is a strength or weakness. Theory or ecological common sense would be good here. • ELABORATE • Elaborate on specifically how the results and conclusions were impacted by this observation • Remember, if these aren’t impacted by this observation, it’s probably not a major issue PAPER: A REMINDER AND A NEW PERSPECTIVE… ANALYSIS: “The first weakness is the materials and methods of the experiment, specifically the food given to the grazers. The food provided to the protists was all the same except for one, Mesodinium rubrum. This species was fed Teleaulax amphioxeia every other day while the rest of the protists were fed Rhodomonas salina daily, and the authors never clarified why. I feel as though this difference in feeding would result in different feeding behaviors and possibly different rhythms, and an explanation would’ve cleared up why they still decided to use this protist in the experiment and maybe what significance this would have to the overall experiment.”
This is the evidence. It’s fine. The student observed that there were differences in the prey fed to the protists and their feeding frequency. This is the explain and elaborate. It needs help. First, you need to clearly explain your concern for this observation and why it was a strength/weakness. In this case, why might prey and feeding frequency matter (generally). And then, how might it specifically impacted their results? • EVIDENCE • I observed that grazers were fed different prey and at different frequencies. • EXPLAIN • I am concerned about this because both issues could create grazers with lower nutritional levels or satiation and such grazers may be less responsive to predation risk. For example, some of the grazers may have been fed a nutritionally poorer food. Also, because M. rubrum was not fed daily, it may have been more starved/hungry. Remember, this was the only comparison of these protists so we need to focus the elaborate section on these data… We ask what was the key conclusion? 2. Copepodamides had species-specific effect with concentrations. Then, could the observation have affected the conclusion? Yes, the one protist fed different prey and at a different frequency was unresponsive. So the entire argument about species-specificity requires Mesodinium. The species-specificity pattern is confounded by prey type and feeding frequency. Mesodinium was unresponsive to copepodamide. This would be consistent with it’s prey being lower quality. Last part is key. • EVIDENCE • I observed that grazers were fed different prey and at different frequencies. • EXPLAIN • I am concerned about this because both issues could create grazers with lower nutritional levels or satiation and such grazers may be less responsive to predation risk. For example, some of the grazers may have been fed a nutritionally poorer food. Also, because M. rubrum was not fed daily, it may have been more starved/hungry. • ELABORATE • This could have affected their conclusion about species-specificity of grazer responses to copepod cues (all species but M. rubrum responded). The lack of response of M. rubrum to copepod cues may have been caused by it being fed a low quality food or being fed less frequently. Feeding M. rubrum Rhodomonas or daily could have allowed them to respond to copepod cues. As a result, the claim about species-specific responses is not wellsupported. • “there are many inconsistencies and absences of explanations or reasons for the choices made in experimental setup. For example, there is no explanation given for retrieval of study organisms from two separate locations…” Group Activity • Identify which (if any experiments) could have been impacted by the red flag of using microzooplankton from two sites (mostly Mediterranean, one isolate from Danish waters). • Determine how this might have affected the results and conclusions • Consider what would happen if the Danish water isolate (Mesodinium) data were excluded. Microzooplankton isolated from Danish waters behave differently. Mesodinium was unresponsive to copepodamide. Perhaps this is a general finding for Danish isolates (and is unrelated to species). 2. Copepodamides had species-specific effect with concentrations. 1. Day-night differences in feeding decreased with time since isolation. Isolation source could affect this. For Mesodinium, it’s ingestion quotient may be unrelated to time since isolation. For example, maybe these populations just have a lower ingestion quotient than Mediterranean Sea isolates. And then we would determine what to do… • “Secondly, their first experiment regarding diel grazing rhythm had some areas that were not ecologically realistic. The authors mentioned that grazing experiments were conducted under saturated prey conditions. However, in the real world, predators do not have an abundance of prey in front of them ready for consumption. Not all communities are saturated, and it is unrealistic to conduct an experiment under those conditions.” Remember, I’m trying to get you beyond just seeing red flags and commenting that this could have mattered. Be specific. How would this have affected results? Group Activity • Identify which (if any experiments) could have been impacted by the use of saturating prey conditions. • Determine how this might have affected the results and conclusions I can’t think of a specific direction saturating prey would have on Day/night Ingestion quotients. Yes, absolute ingestion could be affected, but that’s not the focus of this paper. As a result, this isn’t a major concern. 2. Copepodamides had species-specific effect with concentrations. 1. Day-night differences in feeding decreased with time since isolation. Add to decision • Although it is unlikely to have influenced the results and conclusions of this study, running these experiments under saturating conditions was unrealistic because microzooplankton rarely/never encounter such conditions in nature. Thus, please include a statement about why you ran these experiments at saturating prey conditions. (Note: microzooplankton feeding experiments often use saturating prey levels). Consider using an ABT to write a strong summary paragraph • “Previous studies have proposed a predation-avoidance strategy that has caused larger zooplankton to have diel feeding rhythms. This study observed the feeding behaviors of marine protists in the presence and absence of copepod amides in a novel attempt to determine whether predation threats have an effect on the diel feeding rhythms of heterotrophic and mixotrophic microzooplankton (marine protists). However, each of the marine protist species studied reacted differently to the copepod amides. Therefore, this study suggests that in regards to marine protist species, their response to predation threats is species-specific. This paper will be read by mainly chemical ecologists as well as those who study predator-prey interactions.” Evidence for Novelty Strength • WEAK • “Second, the research of diel feeding rhythm among protists is novel and dissects a topic that opens the door towards further research in the field.” • STRONG • “First, I found this research had novelty in the fact that it investigates and tests the idea that predatory copepod chemical cues (copepodamides) have the potential to reinstate the diurnal feeding pattern in protists after the behavior was lost due to being held in a long term predator free environment. The introduction section states that other studies have confirmed a diurnal feeding pattern in protists but not that the behavior may be retained in the organism after years of no use. This result leads to the consideration of the idea that the behavior may be instinctual and may not require constant reinforcement by exposure.” • “First, this paper is novel and addresses a topic that has not been looked at previously. As stated in the introduction, behavioral responses to chemical cues have not previously been examined in microzooplankton. It is known that microzooplankton feed more during the day to avoid predation, however the authors aimed to show how diel feeding behavior would change based on predator cues. Behavioral studies such as this are necessary for understanding trophic links between species and determining the role of microzooplankton in planktonic food webs.” Good Evidence for ecological realism (STRENGTH) “First, there is a strong ecological relevance between the protists and copepods used. Most protists samples were collected in the Mediterranean Sea and the freeze-dried copepods used, Calanus finmarchicus, can be found near the same waters in the Atlantic ocean. There is also ecological relevance between the copepodamine concentrations used as chemical cues in this study, as all concentrations were kept within the natural range (0.4-2pM). A higher concentration (6pM) was also used to include the variation of natural concentrations based on density of copepods and/or proximity to the source. ” • Word Count • Note that for Paper Analysis II, it is 900 word max. Flow • Topic sentences • Numbering strengths/weaknesses • Transition sentences (e.g. start of weaknesses section) Transition sentences into weaknesses section • STRONG • Although the study exhibited certain strengths, there were some key components that raised concerns. • Although despite the strengths of this paper, there were some limitations to the paper that should be addressed before I recommend accepting to publish. • Despite the strengths, the manuscript also presented some weaknesses. • While the study has exceptionally shown great strengths, it is not short of weaknesses. • Nevertheless, I do have some issues regarding the experimental design. • WEAK • Some weaknesses are that the analysis approach is inadequate as that experiment had a smaller sample size. • Low realism is one of the research’s flaws. • There are two weaknesses in this manuscript. Overall, decisions were clearly stated. • As a result of the weaknesses being a major concern, and outweighing the strengths, I am going to reject this paper. • Due to the strengths outweighing the weaknesses, I recommend accepting this study, but with minor alterations. • As a result, my verdict is to reject the paper. • The strengths of this paper outweigh my weaknesses noted, which is why I recommend accepting this paper with minor revisions. If you ask for revisions, clearly state what those revisions are. “I recommend that the paper be accepted with minor corrections because, as evident in the introduction through the conclusion phase, it fills a dearth of knowledge tied to understanding how plants react when predisposed to insect vibrations. Thus far, existing literature only touches on the reaction between single pairs [an interaction between a specific herbivore species and a single plant species. This study has embraced an uncommon approach that will demonstrate the frequency of plant-insect interactions, especially because single plants likely have a lot of predatory insects to contend with. Finally, the article’s weaknesses may be evident, but they are good starting points to further research. They point out knowledge gaps that other scientists can start working on.” Requiring additional experiments should be a decision of REJECT. • “Because there is a balanced amount of strengths to weaknesses, I recommend accepting the experiment with major revisions. This study is important in determining the response of a prey’s feeding pattern to the presence of a predator and is an essential study in the emerging research of predation. For further experiments, I recommend choosing to study species of protist gazers that were isolated at closer times prior to the experiment to prevent the variation in results after the introduction of the predator chemical cue. I also recommend studying a group of protists that are introduced to the predator and not just chemical cues to serve as a control group and identify how physical presence can affect the study. Finally, further studies can be done to identify what causes the different reactions of differing variants to the cue.” Minor revisions to how the experiment was conducted is not a small request. Requiring additional experiments should be a decision of REJECT. • “I accept the article with minor revisions. The article addresses an important issue that can help scientists in conserving marine life. Additionally, the relevance of the study in the current ecological environment is palatable. As a result, the article significantly contributes to the existing marine science literature. However, I would recommend minor revisions to how the experiment was conducted to improve the accuracy of the results. Possibly, a more representative sample could be used by drawing more species in other regions of the world. ” Requiring additional experiments should be a decision of REJECT. • Due to the strengths outweighing the weaknesses, I recommend accepting this study, but with minor alterations. The clear focus of the aim of the study (how copepod chemical signals affect the diel-eating rhythms of marine protists that are heterotrophic and mixotrophic) is a major strength that adds direction to the research. The only revisions that should be made is the lack of a proper control experiment, which can be easily rectified by ensuring that the control is put under similar conditions as the main experiment. Finally, the research can also be improved by supplementing the t-tests. Confidence intervals or effect size can address t-inadequacies tests by providing a supplement or a replacement of the t-test. A strong decision paragraph • “For this paper, I recommend accepting with major revisions. Although this experiment is novel and has a good experimental design, it is hard for me to look past the fact that this experiment is not entirely realistic. I think that a significant rewrite needs to be done in order for this paper to be accepted outright. First, I think that it is necessary for a thorough explanation to be included into this paper about why the protist strains were collected over a prolonged period of 22 years. This is something that caused a lot of confusion for me and I can guarantee that many others will also be confused about this. Additionally, I think that M. rubrum can be excluded entirely from this paper. There is a lack of data presented in this paper on mixotrophic marine protists and I do not think that it is fair to say that M. rubrum is representative of all the mixotrophic protist species. The exclusion of M. rubrum would make the study more ecologically realistic because the remaining species of protists would all come from the NW Mediterranean Sea. The focus of this study would instead be on the effect that copepod chemical cues have on the diel feeding rhythms of solely heterotrophic marine protists.” A couple of students were concerned about the analysis “The statistical analysis of the experimental results is another flaw in this study…The researchers used only t-tests to compare the outcomes from the triplicate bottles of each therapy throughout the day and at night. In addition, used t-tests to evaluate how copepodamides affected the grazers’ diel feeding cycle in connection to the cycle manifested in the absence of chemical stimuli. However, a t-test is essentially unreliable in giving accurate information due to its direct dependence on sample size.” A couple of students were concerned about the analysis “Some weaknesses are that the analysis approach is inadequate as that experiment had a smaller sample size. T-tests alone are insufficient to compare the results obtained from the triplicate bottles of each treatment during the day and nighttime. First, the triplicate bottles’ results may not represent the entire population. Second, the t-test assumes that the data are normally distributed, but this may not be the case for the data from the triplicate bottles. Finally, the t-test does not consider comparing two different groups. Besides, there are no significant differences between treatments in day or night. The results are all within the same 95% confidence interval. If the study found no significant differences between treatments, then there is none between day and nighttime and if that is the case, the study should attempt to the outcome by comparing day with night.” My response to t-test concerns… Your concerns about the t-test were 1) sample size (i.e. replicates will be less representative of the population), 2) the assumptions of the test could not be evaluated (e.g. because assessing normality is difficult/impossible with only three replicates), and 3) the test does not consider comparing two different groups. Regarding sample size, that’s a hard one to challenge without providing a statistical power analysis. Would 4 have been okay? Regarding meeting the assumptions of the test, I agree with you about that challenge. My issue with that weakness as you worded it, is that it isn’t about whether the data are normally distributed, but rather that assessing normality with small sample sizes is difficult/impossible. Regarding the test comparing groups, your statement is incorrect. The t-test being described is a two-sample t-test, so it does indeed compare the groups. If you call them out on proper controls, you should highlight what you mean AND describe why their controls didn’t meet this standard. “Failure to apply proper controls is another flaw. Accurate experimental designs must also include controlled trials which is an essential component that the researchers failed to do effectively.” For the copepodamide experiments, there were controls “No Copepodamide”. It isn’t clear from the analysis what was not “proper” about these controls. Summary Tips from Paper Analysis I • It’s good to look for red flags, but not all red flags are problematic. • Try the 3 E’s (Evidence, Explain, Elaborate) • I observed that… • This was problematic (or strong) because… • This could have affected their conclusion… • If all you want is a sentence with more details or a quick justification, that’s a MINOR edit. • Remember to be just as persuasive when arguing for strengths. • Be clear about what revisions you are asking for. • If you want more experiments, that’s a REJECT. • Use numbered lists. • Use transition sentences. • Abide by word count rules. • Consider an ABT for summary paragraph. • Criticisms on stats are usually really technical and require a higher level of evidence. Dixson et al. 3Es Group Activity • EVIDENCE • We observed that the larvae previously exposed to CO2 water were acclimated to control water for only two minutes. • EXPLAIN • We are concerned about this because the short acclimation time would result in the sensory receptors of the larvae being shocked. • ELABORATE • The results would be different because the larvae having the ability to acclimate for longer would make them less sensitive to predator cues.