Trait-mediated effects of non-consumptive predation on Daphnia dentifera

Kristina Amato Author

04/04/2021 Added

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This research was completed through UCARE and looks at how indirect predation affects reproduction, foraging, and growth in Daphnia dentifera.

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[00:00:01.860]Hi,
[00:00:02.370]my name is Kristina Amato and I'm a junior fisheries and wildlife major here at
[00:00:06.030]UNL. Today. I'll be discussing my independent research project,
[00:00:09.900]over trait-mediated effects of indirect predation on Daphne dentifera. To begin.
[00:00:14.580]I do want to briefly touch on the background and development of my research
[00:00:17.820]question. When we think of predation,
[00:00:20.580]we often think of direct consumption of a prey by a predator. However,
[00:00:24.330]a predator also has the ability to indirectly affect prey by just being in the
[00:00:28.200]vicinity of the prey. This may be seen and prey,
[00:00:31.380]detecting a predator's presence through visual, acoustic, mechanical,
[00:00:35.070]and or chemical cues. And when these cues are detected,
[00:00:38.580]pray may allocate their energy differently to things like foraging,
[00:00:41.460]reproduction and growth. From this information,
[00:00:44.700]I wanted to figure out how indirect predation may affect Daphnia.
[00:00:47.970]dentifera my model organism in this study,
[00:00:51.870]Daphnia denifera are algae-eating invertebrates that reproduced quickly
[00:00:55.650]asexually, and clonally and they are preyed upon by small fish among other
[00:00:59.430]predators.
[00:01:00.720]I ultimately wanted to see how Daphnia dentifera may alter their energy
[00:01:04.170]allocation for forging reproduction and growth in the presence of predatory
[00:01:07.830]fish. To do this,
[00:01:10.080]I had the help from Jamielynn Polettos's lab on East campus to obtain water from a
[00:01:13.800]tank housing, a predatory fish to Daphnia,
[00:01:16.050]which were bluegill in this case before harvesting the water,
[00:01:19.710]I allowed the blue to swim in a small tank for about 24 hours so that the fish
[00:01:23.790]could eat and excrete waste to make the water as fishy as possible.
[00:01:27.240]For lack of a better term. And debris was also continuously filtered this time.
[00:01:32.460]After the 24 hours,
[00:01:33.930]the fish water was then transported back to the lab where I work in and frozen,
[00:01:37.740]so that the same water could be used throughout the entirety of the experiment.
[00:01:41.130]I then separated 72, one day old Daphnia into three groups.
[00:01:45.480]One group would be chronically exposed to fish water throughout the whole
[00:01:48.270]experiment. Another group would only be acutely exposed to fish water,
[00:01:51.930]meaning it would only be put in fish water on the days I collected feeding rate
[00:01:55.140]data and the last group would be the control group.
[00:01:58.320]This group would not be exposed to fish water at all.
[00:02:00.510]They were just put in normal filtered water.
[00:02:03.750]Foraging data was then collected when the Daphnia were 11,
[00:02:06.480]16 and 21 days old using a microplate fluorescence reader and offsprings
[00:02:11.400]and deaths were counted daily for each group as well.
[00:02:16.230]I originally hypothesized that constant exposure to fish cue would reduce
[00:02:19.980]feeding rate and increase reproduction leading to less energy attributed to
[00:02:24.030]growth. I also hypothesized that acute exposure to fish cue
[00:02:27.930]would not have a drastic effect on Daphnia at younger ages,
[00:02:31.650]as they will put more energy toward growth at the beginning,
[00:02:33.840]so that reproduction can eventually become a priority.
[00:02:36.720]I figured that these Daphnia would eventually see a decrease in feeding as well
[00:02:39.990]as a reduction in growth and reproduction as they aged.
[00:02:44.310]after analyzing my data,
[00:02:45.660]I realized my hypotheses were somewhat in line with the results,
[00:02:48.300]but there were a couple of surprises. In figure one,
[00:02:51.240]We see Daphnia chronically exposed to fish cue experience,
[00:02:54.340]lower feeding rate on each feeding rate day,
[00:02:56.610]compared to the controls with the feeding rates being similar on each of these
[00:02:59.680]days,
[00:03:00.850]these same animals yielded the most offspring as seen in figure two and began
[00:03:04.810]having offspring the earliest out of the three treatments as seen in figure three
[00:03:09.370]and in the acutely exposed group.
[00:03:10.900]We not only see lower feeding rates than the controls on the feeding rate days,
[00:03:14.620]but we also see a steady decline in feeding rate as age increases.
[00:03:19.840]And this makes sense because just like the control group, feeding rate decreases
[00:03:24.010]with age,
[00:03:25.420]because we assume that less energy is being put toward reproduction and growth
[00:03:28.930]at this time
[00:03:31.330]the acute exposed group also has similar total offspring to the control as seen
[00:03:35.590]in figure two,
[00:03:36.520]but begins having offspring at a point between the controls and chronically
[00:03:39.940]exposed animals. Due to the high variability and reproduction and forging between
[00:03:44.830]the three groups.
[00:03:45.550]I actually initially thought there would be a difference in growth between the
[00:03:48.400]groups to account for this difference in energy allocation that we see,
[00:03:51.820]for example, I've figured that at the chronically exposed group,
[00:03:54.640]where to experience high reproduction and decreased foraging,
[00:03:57.670]they would not have grown as much. However,
[00:03:59.560]growth was quite similar between the three groups from beginning to end and in
[00:04:03.190]between each feeding right day, because of this,
[00:04:06.850]I hypothesized that the trade off for high reproduction would be seen in
[00:04:10.060]survival potentially,
[00:04:11.650]but my project did not go along enough to record the death of each sample
[00:04:17.160]Based off of these results,
[00:04:18.210]We can attribute high reproduction and decreased feeding as an effect to fish
[00:04:21.870]cue exposure, which is a form of indirect predation.
[00:04:26.730]It seems that a constant state of stress occurs when in constant presence of a
[00:04:30.630]predator, this causes a need to reproduce as rapidly and abundantly as possible.
[00:04:34.920]In case the predator were to consume the prey constant exposure to the presence
[00:04:39.420]of a predator also causes a decrease in foraging because putting energy toward
[00:04:43.560]eating is not a priority when under stress. In the chronically exposed group,
[00:04:47.970]we also see hardly any change in between feeding rates between ages.
[00:04:52.320]This is because these animals are under constant stress,
[00:04:55.020]their top priority is to reproduce and eat just enough to survive,
[00:04:58.590]and consistenty yield offspring,
[00:05:01.110]Their feeding should also not be changing one day from the next,
[00:05:04.230]which it isn't because they are in the same environment every day,
[00:05:08.760]the Daphnia acutely exposed to fish cue also decrease their feeding,
[00:05:12.090]but they're decreased follows a similar slope to the control.
[00:05:15.240]This shows us that short occurrences of the presence of a predator cause
[00:05:18.760]short-term effects in feeding,
[00:05:20.700]but the effects are not lasting enough to cause any reproductive changes and
[00:05:25.350]because acute exposure does not cause a major difference in offspring yield,
[00:05:28.920]we would expect feeding to decrease with age as reproduction is no longer a top
[00:05:32.520]priority. As mentioned previously,
[00:05:35.850]growth was not seen as an energy trade-off for the high reproduction seen in
[00:05:39.360]chronically exposed daphnia. However,
[00:05:41.520]this opens up an opportunity for future research to see if survival is the
[00:05:45.120]trade-off of high reproduction throughout an entire lifespan.
[00:05:48.330]This research also raises questions on how indirect predation effects other
[00:05:52.380]predator prey systems and provides insight into the complex yet strategic
[00:05:56.550]choices prey make when in the presence of a predator. Lastly,
[00:06:00.290]I want to thank you for your time and also thank my advisor, Dr.
[00:06:03.440]Clay Cressler and his graduate student,
[00:06:06.140]Alaina Pfenning for the support and guidance throughout the entire project.
[00:06:09.980]There are many roadblocks along the way,
[00:06:11.630]but I do hope you all enjoy the final product. Thanks again.

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Trait-mediated effects of non-consumptive predation on Daphnia dentifera

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