I think one of the reasons I like damselflies and their larvae is because they look neat! The adults are so fragile, even more so than dragonflies, and the larvae have three beautiful “tails”, also known as caudal lamellae. In the summer of 2011, I was working in a fisheries lab and we were told to design individual projects. I got the crazy idea that I could raise damselflies, take pictures of them every week, and when they emerged, identify them to species and use the pictures to make a species key for larval damselflies. Little did I know that when I would go to identify my first emerged adult I would stumble across a larval key, get very upset that my project was useless and resign to the fact that raising macroinvertebrates was just too difficult a task for me anyways. The point of this anecdote was that when I originally collected the live damselfly larvae some of them lost their “tails” and I figured they would die within the first week. I knew that their three caudal lamellae were a source for respiration and would probably be able to live with out one, but not two. After stumbling across the following paper, I have reevaluated the main cause of death for may of the larvae to be their lack of interest in the fish food/mosquito larvae diet they were on, not that their gills had fallen off.
The following paper is entitled “Hypoxia and lost gills: Respiratory ecology of a temperate larval damselfly” by Sesterhenn, Reardon, and Chapman. The authors examined the effect of hypoxia (low dissolved oxygen) on the behaviors of an Ischnura (Coenagrionidae) species with respect to the number of caudal lamellae. This is important to understand as many lakes and slow moving systems, the favored habitat of most damselfly species, become eutrophic. Damselfly and dragonfly species are the top predator of aquatic macroinvertebrates in fishless systems and this role in an ecosystem with low dissolved oxygen is one reason that makes them a model organism for a study on hypoxia.
Caudal lamellae have many uses other than their function for respiration. They are also used for ion regulation, locomotion, intraspecific signaling, and weaponry. However, they are most well adapted for the uptake of oxygen. In looking at a close-up picture you will find that they look like a leaf with prominent veins. It is estimated that up to 90% of individuals in a population may lose at least one lamellae in its life just through the harshness of an environment. However, damselflies have other ways of breathing or increasing oxygen intake. One method is through rectal pumping which allows water to move in and out of the organisms back end and absorbing oxygen through specialized cells inside of the organism. Another method is abdomen waves in which the damselfly will “swish” its abdomen side to side to move water across its lamellae. Also, some damselflies (actually, most gilled aquatic macroinvertebrates use these methods) will do “pull-downs” or what I think looks more like a push-up. This also helps move water over the gills. Below is a link for a stonefly doing this action. Lastly, aquatic macroinvertebrates may just move to the surface of the water to access the oxygen rich layer right below the surface. Despite these other methods, the researchers hypothesized that the “number of caudal lamellae influences damselfly respiratory ecology, and that the role of lamellae may change at different levels of dissolved oxygen.”
With all of this in mind, Ischnura larvae were collected from low dissolved oxygen ponds in Kentucky. Only specimens with all three lamellae were taken for this experiment. The researchers successfully kept them alive (their methods for that make sense in retrospect as compared to mine) and prepared the larvae for two types of experiments. The first experiment involved measuring metabolic rates of damselfly larvae with either three or one caudal lamellae (yes, that means they pulled two lamellae off of some specimens). Through a complex set-up, the oxygen decline in a closed system in response to damselfly respiration could be measured. The second experiment was to observe behaviors of three and one lamellae damselflies at various levels of dissolved oxygen. Behaviors were recorded with a video camera.
What they learned from all of this is that the metabolic rate of Ischnura larvae was not affected by the number of lamellae. Also, smaller individuals and those with one lamellae spent more time near the surface of the water when the dissolved oxygen was low in the behavioral experiments. In addition, the alternate behaviors I previously described were observed more as the dissolved oxygen level decreased. From this we can understand that Ischnura is well adapted to living in low dissolved oxygen (hypoxic) ecosystems. It can also be noted that one caudal lamellae is sufficient for survival. The loss of all three lamellae would change the larvae’s ability to swim and then it wouldn’t be able to move oxygenated water over its body if needed. Therefore, the loss of all three lamellae is much more lethal.
Knowledge about specific tolerances of macroinvertebrates of environmental conditions will prove to be critical as water systems are degraded. A loss of macroinvertebrates communities will hurt fish populations if the fish aren’t directly affected by the low dissolved oxygen in the first place. It also goes beyond dissolved oxygen. Specific chemical tolerance can be species specific which also makes it that more important to know what is going into our waterways (*cough cough* fracking fluid)!
Stonefly pushups:https://www.youtube.com/watch?v=c06Up7YGkY4
Link to original paper:http://www.sciencedirect.com/science/article/pii/S0022191012002752
More about respiration and caudal lamellae: http://link.springer.com/content/pdf/10.1007%2FBF00323773.pdf
Ischnura being parasitized by mites!:http://www.researchgate.net/publication/232664446_PARASITISM_OF_ISCHNURA_POSITA_%28ODONATA_COENAGRIONIDAE%29_IN_FLORIDA_BY_TWO_SPECIES_OF_WATER_MITES
Thursday, May 23, 2013
Sunday, May 19, 2013
Kick, kick! Who's in There?
Aquatic macroinvertebrates are critical species to understand when conducting biological surveys of aquatic ecosystems. Many times, population changes over long term monitoring schemes serve as indicators of water quality. Typically, samples are collected with a kicknet. I follow Frost and Huni’s procedures outlined in their 1971 paper. The authors say that their method effectively collects 90% of the benthic (bottom-dwelling) fauna. Samples are preserved in 70% ethanol and taken back to the laboratory for identification. Aquatic macroinvertebrates are usually identified to the lowest taxonomic unit possible, which in many cases is the genus level identification. Species keys are not developed for most larvae because of the morphological (physical) differences in instars (stages of development). If individuals in a sample are damaged, identification to the genus level may not be possible. In addition, there is room for human error in the identification process.
Therefore, there may be a need for other methods of identifying the specimens in a field collection of aquatic macroinvertebrates. One way of doing this is using Next-generation sequencing (NGS). NGS is a new technology that is starting to be applied to the biological sciences. NGS is similar to other DNA sequencing technologies; however, NGS is able to analyze mixtures of DNA. Therefore, the theory is that biologists can collect aquatic macroinvertebrates in the same manner they have in the past, but can analyze a mixture of DNA to get species level identification. DNA can be sequenced from one of three ways although only two are ideal. The first method is to blend the entire sample and analyze the smoothie of aquatic macroinvertebrates. However, this is the least ideal method because it is quite destructive. The other two methods allow the specimens to have minimal damage done to them. One method is for researcher to take a tissue sample from each individual specimen (usually a leg but not all macro invertebrates have those) and add that to the blend of DNA. The second, and least destructive, method is to use the ethanol the aquatic macroinvertebrates have been preserved in; as specimens sit in ethanol, some of their DNA ends up in the liquid ethanol. This is called “free DNA”.
Without getting too technical, the DNA is amplified (copies are made through chemical processes) and sequenced (think of each DNA strand having its own barcode) and then matched against known sequences (barcodes in a library). These known sequences are species specific. This sounds great; however, there are several biases that may prove to be problematic for at least the near future. The greatest issue is that some strands of DNA may get copied more than others and therefore the abundance of individual species will be skewed. Remember that biomonitoring tends of look at changes in populations over time so if there is no accurate indication of population size, this information may be useless. In addition, it may obscure the presence of some species. Also, this bias makes DNA copying not replicable since there is no consistency in which strands will be amplified more than others. There have been attempts to avoid this bias by using different types of amplifiers (copiers) and different combinations of DNA sources. The highest detection rate has been 91.3% in a combined “free DNA” and tissue DNAs along with multiple types of amplifiers.
It should be noted that this is different than eDNA (environmental DNA), which would involve testing pieces of the environment for traces of DNA. An example, and increasing application of eDNA technology, would be taking a water sample and testing for the DNA of invasive fishes to test for presence/absence data. For NGS it is required to have a collected and preserved specimen.
This type of technology could be applied to the monitoring of terrestrial invertebrates such as a collection from a malaise trap. However, the same biases still apply. NGS technology needs to be refined, and if easy to use, I would be happy to try using it in the monitoring programs I am involved in.
This article this post is based on can be found at: http://www.biomedcentral.com/content/pdf/1472-6785-12-28.pdf
Therefore, there may be a need for other methods of identifying the specimens in a field collection of aquatic macroinvertebrates. One way of doing this is using Next-generation sequencing (NGS). NGS is a new technology that is starting to be applied to the biological sciences. NGS is similar to other DNA sequencing technologies; however, NGS is able to analyze mixtures of DNA. Therefore, the theory is that biologists can collect aquatic macroinvertebrates in the same manner they have in the past, but can analyze a mixture of DNA to get species level identification. DNA can be sequenced from one of three ways although only two are ideal. The first method is to blend the entire sample and analyze the smoothie of aquatic macroinvertebrates. However, this is the least ideal method because it is quite destructive. The other two methods allow the specimens to have minimal damage done to them. One method is for researcher to take a tissue sample from each individual specimen (usually a leg but not all macro invertebrates have those) and add that to the blend of DNA. The second, and least destructive, method is to use the ethanol the aquatic macroinvertebrates have been preserved in; as specimens sit in ethanol, some of their DNA ends up in the liquid ethanol. This is called “free DNA”.
Without getting too technical, the DNA is amplified (copies are made through chemical processes) and sequenced (think of each DNA strand having its own barcode) and then matched against known sequences (barcodes in a library). These known sequences are species specific. This sounds great; however, there are several biases that may prove to be problematic for at least the near future. The greatest issue is that some strands of DNA may get copied more than others and therefore the abundance of individual species will be skewed. Remember that biomonitoring tends of look at changes in populations over time so if there is no accurate indication of population size, this information may be useless. In addition, it may obscure the presence of some species. Also, this bias makes DNA copying not replicable since there is no consistency in which strands will be amplified more than others. There have been attempts to avoid this bias by using different types of amplifiers (copiers) and different combinations of DNA sources. The highest detection rate has been 91.3% in a combined “free DNA” and tissue DNAs along with multiple types of amplifiers.
It should be noted that this is different than eDNA (environmental DNA), which would involve testing pieces of the environment for traces of DNA. An example, and increasing application of eDNA technology, would be taking a water sample and testing for the DNA of invasive fishes to test for presence/absence data. For NGS it is required to have a collected and preserved specimen.
This type of technology could be applied to the monitoring of terrestrial invertebrates such as a collection from a malaise trap. However, the same biases still apply. NGS technology needs to be refined, and if easy to use, I would be happy to try using it in the monitoring programs I am involved in.
This article this post is based on can be found at: http://www.biomedcentral.com/content/pdf/1472-6785-12-28.pdf
Thursday, May 9, 2013
Looking at the Little Guys
Insect behavior is a curious thing. Those that are terrestrial are easily observed by the average person such as ants on the ground, bees buzzing around flowers, crickets chirping at night or the pesky house fly sitting on the window. However, there are many insects whose behaviors go unnoticed. One such group of insects is a group that lives in water also referred to as aquatic macroinvertebrates.
Aquatic macroinvertebrates exhibit a behavior called drift. A scientist by the name of Mueller (no known relation but I am looking into it) described a phenomenon where some, not all, species of macroinvertebrates release themselves from the substrate and float downstream in the current until they choose to grab ahold again. The macroinvertebrates continue this process of moving farther and farther downstream until they emerge and the adult fly upstream to lay their eggs. Once the eggs hatch the process of drifting repeats itself. Without going into further detail of when, why, types and other patterns, simply put there is still limited knowledge about this behavior.
An increasing number of studies have been done to look at various factors influencing insect drift. One particular study looked at the impact of suspended solids (sediment) on macroinvertebrates drift behavior in an Indiana Creek (USA). Sediment is considered a pollutant, which comes from activities such as mining, farming, and logging. Previous studies have shown that when there has been an observed increase in sediment in water there has been an observed decrease in macroinvertebrate numbers because sediment decreases the amount of light that comes through the water column as well as smothers habitat. This particular study wanted to consider the impact of sediment runoff of a rock quarry. In this study, controlled amounts of sediment (collected from the bottom of the quarry’s settling ponds) were released into the stream from a modified garbage can dispenser. Holes in the bottom of the can allowed water to flow through the garbage can and a known amount of sediment was placed inside therefore they could calculate the total suspended solids released.
Collecting drifting macroinvertebrates is done by using an appropriately named drift net. These nets were placed in the water downstream of the garbage can for 15 minutes during the time the sediment was being added. After 15 minutes, nets were removed from the water and the insects and debris captured were preserved in 70% ethanol. In the laboratory, macroinvertebrates were identified and counted. Water samples were also taken to be checked in the laboratory for the total suspended solids in order to compare the numbers to what was being released. The researchers were responsible and stopped the experiment on a particular day when they noticed sediment starting to collect on rocks in the study site. Lastly, a substrate sample was also taken, on non-experiment days, with a Surber sampler to determine what the natural benthic macroinvertebrate community structure was.
The results of this study were not particularly surprising. There was a linear relationship between the number of macroinvertebrates drifting and the amount of sediment put into the stream. They found that midge, blackfly, caddisfly, and mayfly larvae were the most common drifting species. Riffle beetles were observed in the substrate but did drift and were therefore not as effected by the sediment entering the water. The researchers cannot be sure, but they believe this drifting behavior could be classified as active-behavioral drift. This means that the macroinvertebrates chose to move away from something happening in their environment as opposed to being carried away by a high flow after a heavy rain. Based on their observations, short term re-population of the study area was successful but high levels of suspended solids could be detrimental in the long term.
So even though an impact like dumping sediment into a stream is a pretty drastic situation, it can have further implications on an ecosystem than just making some insects change habitat. Fish rely on macroinvertebrates as a food source. No macroinvertebrates will mean no fish. Therefore, it is critical that more studies like this one occur to find our what human activities have what level of effect on macroinvertebrate behaviors. The same applies for the dumping of chemicals or excess water into streams. What are the part per million or part per billion tolerances of macroinvertebrates? How tightly can they hang onto the substrate when there is an increased flow? There is also limited knowledge of the time scales of which these changes in macroinvertebrate behaviors occur. Therefore, as more an more industry waste is created it is important to remember the little guys even if we don't see them every day.
To see the original paper visit: https://journals.iupui.edu/index.php/ias/article/viewFile/8310/8461
To read more about the original research on drift, locate the paper:
Müller, K. 1954. Investigations on the organic drift in North Swedish streams. Rep. Inst. Freshw. Res. Drottning. 35:133-148.
Aquatic macroinvertebrates exhibit a behavior called drift. A scientist by the name of Mueller (no known relation but I am looking into it) described a phenomenon where some, not all, species of macroinvertebrates release themselves from the substrate and float downstream in the current until they choose to grab ahold again. The macroinvertebrates continue this process of moving farther and farther downstream until they emerge and the adult fly upstream to lay their eggs. Once the eggs hatch the process of drifting repeats itself. Without going into further detail of when, why, types and other patterns, simply put there is still limited knowledge about this behavior.
An increasing number of studies have been done to look at various factors influencing insect drift. One particular study looked at the impact of suspended solids (sediment) on macroinvertebrates drift behavior in an Indiana Creek (USA). Sediment is considered a pollutant, which comes from activities such as mining, farming, and logging. Previous studies have shown that when there has been an observed increase in sediment in water there has been an observed decrease in macroinvertebrate numbers because sediment decreases the amount of light that comes through the water column as well as smothers habitat. This particular study wanted to consider the impact of sediment runoff of a rock quarry. In this study, controlled amounts of sediment (collected from the bottom of the quarry’s settling ponds) were released into the stream from a modified garbage can dispenser. Holes in the bottom of the can allowed water to flow through the garbage can and a known amount of sediment was placed inside therefore they could calculate the total suspended solids released.
Collecting drifting macroinvertebrates is done by using an appropriately named drift net. These nets were placed in the water downstream of the garbage can for 15 minutes during the time the sediment was being added. After 15 minutes, nets were removed from the water and the insects and debris captured were preserved in 70% ethanol. In the laboratory, macroinvertebrates were identified and counted. Water samples were also taken to be checked in the laboratory for the total suspended solids in order to compare the numbers to what was being released. The researchers were responsible and stopped the experiment on a particular day when they noticed sediment starting to collect on rocks in the study site. Lastly, a substrate sample was also taken, on non-experiment days, with a Surber sampler to determine what the natural benthic macroinvertebrate community structure was.
The results of this study were not particularly surprising. There was a linear relationship between the number of macroinvertebrates drifting and the amount of sediment put into the stream. They found that midge, blackfly, caddisfly, and mayfly larvae were the most common drifting species. Riffle beetles were observed in the substrate but did drift and were therefore not as effected by the sediment entering the water. The researchers cannot be sure, but they believe this drifting behavior could be classified as active-behavioral drift. This means that the macroinvertebrates chose to move away from something happening in their environment as opposed to being carried away by a high flow after a heavy rain. Based on their observations, short term re-population of the study area was successful but high levels of suspended solids could be detrimental in the long term.
So even though an impact like dumping sediment into a stream is a pretty drastic situation, it can have further implications on an ecosystem than just making some insects change habitat. Fish rely on macroinvertebrates as a food source. No macroinvertebrates will mean no fish. Therefore, it is critical that more studies like this one occur to find our what human activities have what level of effect on macroinvertebrate behaviors. The same applies for the dumping of chemicals or excess water into streams. What are the part per million or part per billion tolerances of macroinvertebrates? How tightly can they hang onto the substrate when there is an increased flow? There is also limited knowledge of the time scales of which these changes in macroinvertebrate behaviors occur. Therefore, as more an more industry waste is created it is important to remember the little guys even if we don't see them every day.
To see the original paper visit: https://journals.iupui.edu/index.php/ias/article/viewFile/8310/8461
To read more about the original research on drift, locate the paper:
Müller, K. 1954. Investigations on the organic drift in North Swedish streams. Rep. Inst. Freshw. Res. Drottning. 35:133-148.
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