How Low Oxygen Stress affects Host- Parasite Interactions in Daphnia dentifera

Allyson Schmitz Author

03/31/2021 Added

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This research study looks at how low oxygen stress affects the reproduction and immune function of Daphnia dentifera

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[00:00:00.900]Hello everyone. My name is Allyson Schmitz.
[00:00:03.390]I'm a senior undergraduate student at UNL,
[00:00:06.600]and my study is looking at how low oxygen stress affects host parasite
[00:00:10.500]interactions in Daphnia dentifera
[00:00:13.110]And I wanted to say thank you to everyone for coming out and watching my video
[00:00:19.140]Daphnia are small freshwater crustaceans,
[00:00:22.020]and they're typically used in microbiome research and research on
[00:00:26.700]host parasite interactions and circadian rhythms.
[00:00:30.660]They're an ideal study species because they're very small and easy to take care
[00:00:35.340]of.
[00:00:36.720]They also have a short life cycle and it's six to eight days until they reach
[00:00:41.670]maturity.
[00:00:42.240]So it's very easy to take them from the start to end in their life cycle.
[00:00:47.730]There are key species and the ecosystems that they live in,
[00:00:51.390]they live in ponds and lakes in the United States and in other countries.
[00:00:56.340]And so the purpose of looking at different oxygen levels and how it would affect
[00:01:00.510]them is because these animals go through migration patterns and
[00:01:05.490]climate change can also lower at the oxygen levels in ponds and lakes.
[00:01:10.320]And so during the day,
[00:01:12.450]Daphnia are deeper in these lakes and ponds
[00:01:17.130]because it's dark. And so they do this to avoid predation.
[00:01:21.240]And then at night they swim up to the top in order to feed on algae.
[00:01:25.950]And so when they are in those deep waters, there's less oxygen there.
[00:01:30.150]So I wanted to see how this might affect their ability to fight off infection.
[00:01:36.240]The objectives for my study were to determine how this low oxygen
[00:01:40.920]stress would affect their ability to reproduce and then their
[00:01:45.630]infection rates and severity, and then their pehnoloxidase levels.
[00:01:50.100]So I wanted to look at phenol oxidase because one acts as
[00:01:55.080]a key part of their immune system in invertebrates.
[00:01:58.950]And also phenoloxidase acts as an oxygen transport enzyme.
[00:02:04.920]And so its prevalence may change depending on the oxygen levels in the water,
[00:02:10.260]and also may change depending on how infected
[00:02:13.130]They are.
[00:02:16.670]And so the methods that I used in this study were 12 different
[00:02:21.260]groups were established. So they were split up between two different genotypes,
[00:02:26.510]three oxygen levels and whether or not they were infected and each
[00:02:31.340]group had 16 individuals in it.
[00:02:34.160]And so the three oxygen levels were normal,
[00:02:38.750]which was the control group and then low and hypoxic.
[00:02:42.890]And these were made the combo that the Daphnia live in.
[00:02:47.420]It's a combo media. It was bubbled with a nitrogen bumbler,
[00:02:51.410]which got the oxygen out.
[00:02:53.390]And then a probe was used to measure the oxygen levels to make sure it was
[00:02:57.290]correct. And
[00:03:00.400]after they reach maturity,
[00:03:02.590]the six experimental groups were exposed to Metschnikowia
[00:03:07.660]spores.
[00:03:09.010]And the infection's severity was measured after they were infected by counting
[00:03:13.990]the spores and phenoloxidase levels were measured by
[00:03:18.310]extracting hemolymph from their hearts.
[00:03:20.710]And I used a fluorescence essay that was established by one of their
[00:03:25.270]graduate students and the Cressler lab
[00:03:30.190]for results. This is the infection rates.
[00:03:32.500]This is rates right here and infection severity.
[00:03:36.340]So this was measured by their spore counts.
[00:03:40.210]And this was measured by how many animals in each group were actually
[00:03:44.740]infected. So as we can see from these figures,
[00:03:49.000]there was some variance between the two genotypes and infection rates and between
[00:03:52.810]the oxygen levels,
[00:03:54.370]which was the purpose of using two different genotypes to see how they would
[00:03:57.940]vary.
[00:03:58.930]And so the C back genotype actually seemed to be more susceptible
[00:04:03.880]to infection than the standards, except for in the hypoxic conditions
[00:04:09.550]and the results from this graph.
[00:04:11.230]Aren't exactly what we expected to see because it looks like the C back were
[00:04:15.760]actually less infected.
[00:04:19.000]in the water that had less oxygen in the low and
[00:04:23.470]hypoxic groups,
[00:04:26.860]these are the results from the phenol oxidase assay
[00:04:30.340]And so this is measuring total phenol oxidase instead,
[00:04:34.420]or active phenol oxidase instead of total. And so, as you can see,
[00:04:39.550]the phenoloxidase levels were much higher in the groups that were infected,
[00:04:43.780]which is the light green,
[00:04:45.670]and they were also much higher in the hypoxic group than in the normal group.
[00:04:51.640]And so this makes sense because if phenoloxidase
[00:04:54.640]acts as an oxygen transporter,
[00:04:57.430]and so these animals upregulated phenoloxidase in order to pull in
[00:05:02.380]as much oxygen as possible when they were in these hypoxic conditions.
[00:05:07.930]And it also makes sense that the infected animals had higher phenoloxidase
[00:05:12.760]levels since it plays such a key role in their immune system.
[00:05:16.630]And phenoloxidase actually is an enzyme that can help to synthesize
[00:05:21.610]some of the intermediate chemicals that are used in their
[00:05:26.230]defense against pathogens in their immune system.
[00:05:30.700]This is the data from the reproduction.
[00:05:34.030]And so the bottom left figure here shows the animals that were exposed to the
[00:05:38.920]fungus had higher total reproduction rates.
[00:05:41.470]And so these striped ones are the infected
[00:05:46.150]animals and the bottom right figure shows that the
[00:05:51.070]infected animals also had a larger average brood size.
[00:05:55.540]And so this goes back to the life history trade-off idea that I was talking
[00:05:58.850]about.
[00:05:59.240]So the animals that were infected may have put more energy into
[00:06:04.070]reproduction since they knew that they were sick and might not have had the time
[00:06:08.300]to reproduce it later.
[00:06:11.090]these were tested with an ANOVA test in R software.
[00:06:16.730]And so it confirmed the idea that the exposed
[00:06:21.530]groups had significantly higher total reproduction rates and average
[00:06:26.420]brood sizes. Both of those P values were less than 0.05.
[00:06:33.310]In conclusion,
[00:06:34.210]the Daphnia that were exposed to these fungal spores had higher reproduction
[00:06:38.500]rates and average brood sizes,
[00:06:41.710]which goes back to the energy allocation into reproduction rather than
[00:06:45.520]survival.
[00:06:47.590]And then the Daphnia that were exposed also at higher phenaloxidase levels
[00:06:53.140]because they needed phenoloxidase in order to transport oxygen
[00:06:56.650]And because it plays a role in their immune system
[00:07:01.480]and the two different genotypes had different susceptibilities to infection.
[00:07:05.980]The C back had higher infection rates and infection severity,
[00:07:10.240]which is why two different Genotypes were used to see how the results could
[00:07:14.650]differ. So I wanted to say,
[00:07:18.700]thank you to Dr. Cressler,
[00:07:20.590]who is the head of the Daphnia lab at UNL and
[00:07:25.270]Alaina is the graduate student.
[00:07:27.220]She helped me with infections and spore counting and Reilly is the other
[00:07:31.810]graduate student.
[00:07:32.680]He focuses on microbiome research and I wanted to thank all of the
[00:07:37.480]other undergraduate researchers in the Cresser lab who helped me out along the
[00:07:41.350]way. Thank you for coming to my presentation.

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How Low Oxygen Stress affects Host- Parasite Interactions in Daphnia dentifera

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