How different are bird parasite communities between mountain ranges?

Featured Scientist: Dr. Lisa Barrow (she/her/hers), Assistant Professor and Curator, Museum of Southwestern Biology and Department of Biology, University of New Mexico.

A large green Luna Moth perched on the side of Lisa's head while in the forests in the Southeastern United States. She was a graduate student at the time and was hiking through the woods, probably looking for amphibians.
Making friends with a Luna Moth while exploring the Southeastern United States during my Ph.D. fieldwork.

Birthplace:  Tempe, Arizona, USA

My Research: I am interested in understanding the diversityof amphibians and reptiles. I study how species have evolved over time, where they occur, and what leads to the loss of diversity in these species.

Research Goals: My research uses information from museum collections to study how different species change over time. A museum collection is almost like a library, but instead of books, it contains the preserved bones, furs, feathers, and tissues of animals from across the world and throughout time. Part of my work is to make sure that we continue to build our museum collections so that other researchers can use them to ask their own questions. My research moving forward will focus on herpetofauna, or “herps” for short. These are amphibians and reptiles. I have also enjoyed studying birds and mammals in my previous work.

Career Goals: I recently started as an Assistant Professor and Curator of a museum collection – this has been my career goal for a very long time! I now look forward to continuing my research and training students to help them pursue their goals.

Hobbies: I enjoy traveling to new places to see new herps and birds, learn about other cultures, and try different cuisines. I also enjoy baking and trying new recipes at home.

Favorite Thing About Science: Learning never ends! I especially love that science is a team effort, and we can always keep learning from other people with different knowledge and expertise than we each have on our own.

My Team: This project was a huge team effort. At the time of this project (2016-2018), I was a postdoctoral researcher working in Dr. Chris Witt’s lab at the University of New Mexico. We led a team that included three undergraduates, four post-bacs, four graduate students, and four lab associates and former students. Together, we conducted the first community-wide survey of bird blood parasites in New Mexico. I helped with fieldwork, sample collection, specimen preparation, and trained the students who conducted molecular work, the microscopic examination of blood cells, and data analysis. I drafted the manuscript with great input from Dr. Chris Witt and the other co-authors. From the time we finished data collection, it took another few years to finish analyzing and writing!

Organism of Study: Birds and their haemosporidian parasites, including many different lineages in the groups Plasmodium, Parahaemoproteus, and Leucocytozoon.

A three panel image. The top image shows a vireo, a small grey bird on a log. The bottom two images show parasites inside bird blood cells. The Leucocytozoon parasite is larger, more circular, and causes the infected blood cell and its nucleus to change shape. The Parahaemoproteus parasite is wrapped around the nucleus of the blood cell. Both parasites are stained a light purple color and the nuclei of the bird host cells are dark purple.
The vireo (scientific name: Vireo plumbeus) seen in the top image is an example of a bird species sampled in our study. The bottom images show examples of their common haemosporidian parasites, Leucocytozoon and Parahaemoproteus. The arrows point to infected blood cells. Image source: WikiMedia Commons

Field of Study: Community Ecology

What is Community Ecology? Community ecology is the study of groups of species and how they interact with one another. People who study community ecology look at how species compete with each other, how they are organized in space, and how they live together.

Check Out My Original Paper: “Detecting turnover among complex communities using null models: a case study with sky‐island haemosporidian parasites”

A QR code that links to the original publication.
QR code to the original publication

Citation: Barrow, L.N., Bauernfeind, S.M., Cruz, P.A., Williamson, J.L., Wiley, D.L., Ford, J.E., Baumann, M.J., Brady, S.S., Chavez, A.N., Gadek, C.R., Galen, S.C., Johnson, A.B., Mapel, X.M., Marroquin-Flores, R.A., Martinez, T.E., McCullough, J.M., McLaughlin, J.E., Witt, C.C. Detecting turnover among complex communities using null models: a case study with sky-island haemosporidian parasites. Oecologia 195, 435–451 (2021). (doi: 10.1007/s00442-021-04854-6)

Research At A Glance: Haemosporidians are a diverse group of parasites that are found around the world. They can cause diseases, such as malaria, in humans and birds. Only five species of haemosporidians infect humans, but researchers have found over 3,000 lineages of haemosporidian parasites that can infect birds. Like what we see in humans, haemosporidian parasites can make birds sick and some birds are more likely to become infected, and die from that infection, than others. It is important for scientists to know which parasite lineages are likely to encounter and infect different bird species, so they can be prepared to help prevent infections and protect those species. One way to study this is to describe the community of haemosporidian parasites at different locations. However, it is not easy to sample such a diverse group of parasites. Haemosporidian parasites infect blood cells. This means that we needed to catch birds and obtain blood samples before we could determine the identity of their parasites. This is even more difficult because some parasites are very common, while others are rarer and might be easily missed if we do not catch many birds. Some parasites are also host specialists, meaning they may only occur in one or a few closely related birds. Others are host generalists and can infect many types of birds. These challenges needed to be addressed by sampling many birds at our study sites and by using a specific type of statistical analysis.

Our team set out to describe a community of haemosporidian parasites in the sky islands of the Southwestern United States. Sky islands refer to mountain ranges that have forest habitat at high elevations and desert habitat at low elevations. Like true islands separated by oceans, plants and animals that live in forests may not be able to move easily across desert habitats. We wanted to know if the parasite communities were different between these mountain ranges. To do this, we checked birds for parasitesusing two methods. We used molecular methods to isolate parasite DNA from bird blood cells and sequenced the DNA to find out which type of parasite had infected the bird. We also looked at blood samples using a microscope and photographed the parasites.

Once we had identified the parasites, we analyzed our data using a null modeling approach. This statistical approach allowed us to find out if the parasite communities were different between sky islands. This method also helped us to understand how our results were affected by our sampling. At the end of our study, we had sampled 776 birds. We found that 280 of them were infected with parasites and we found that some bird species were more infected than others. We found that parasite communities were different between the mountain ranges, even when the same species of birds were sampled. This result is interesting because it suggests that different populations of the same bird species will encounter different parasites across the area that the bird is found.

Highlights: One of the most important parts of this research was the way that we analyzed our data. The null modeling approach that we used was developed by Dr. Chris Witt and Selina Bauernfeind. Selina is the second author on our paper and was a post-baccalaureate researcher at the time. Our models ask whether the actual communities of parasites that we observed are different than we would expect if the parasites were randomly sampled from a single parasite community. This community represents our expectation under a null model, where there is no difference in the parasite lineages between sky islands. Selina developed this model by writing computer code in R. R is a type of statistical software that scientists often use to analyze data. She used the computer code to simulate 10,000 parasite communities under the null model.The null model statesthat there is no difference between sky islands. She then compared the simulated parasite communities to the observed parasite communities that we sampled during our study.

The main results are shown in Figure 1 and Figure 2. In both figures, the gray curves show the simulated parasitecommunities. The dotted line represents the results from our observed community, the parasites that we sampled. The stars (*) above the dotted line mean that the parasite community that we sampled is different from the community that we would have expected under the null model. Figure 1 shows that 56 parasite lineages were only found in one of the three mountain ranges. This number was higher than expected based on the null model, indicating that there were many unique parasite lineages in each mountain range.Only 19 parasite lineages were found in all three mountain ranges. This number was lower than expected based on the null model, suggesting that few parasites were shared across three mountain ranges. Taken together, our results suggest that the community of parasites was different between mountain ranges.

The figure shows three curves for the parasite lineages expected under the null model. For one mountain, most simulations found fewer lineages (the expected value) than the 56 lineages that the researchers observed. For two mountains, the observed number (25 lineages) was similar to the expected number of lineages. For all three mountain ranges, most simulations found more lineages than the 19 lineages observed.
Figure 1. The observed (dotted line) and expected (grey curve) number of parasite lineages found in one mountain range, two mountain ranges, or in all three mountain ranges studied. The stars (*) above the dotted line show that the parasite community that we sampled is different than the simulated parasite community. Adapted from Barrow et al. 2021.

Figure 2 shows the Jaccard dissimilarity index. It ranges from 0 to 1. Higher values show a greater difference between mountain ranges. As shown by the dotted line with the stars (*), the results show that the parasite community differed between Mount Taylor and the other two mountain ranges, Jemez and Zuni. The observed parasite communities in these mountain ranges had higher dissimilarity index values than expected under the null model.

The figure shows three curves for the parasite community differences between each pair of mountain ranges expected under the null model. A dotted line for each pair shows the observed parasite community differences. The observed difference between Mount Taylor and the Jemez Mountains was higher than expected under the null model. Similarly, the observed value between Mount Taylor and the Zuni Mountains was higher than expected under the null model.
Figure 2. The observed (dotted line) and expected (grey curve) parasite communities at the three mountain ranges studied: Mount Taylor, Zuni Mountains, and Jemez Mountains. The x-axis shows the Jaccard dissimilarity index. Adapted from Barrow et al. 2021.

What My Science Looks Like: Our team spent two years sampling birds in the field for this project. Our field set-up included plenty of supplies to record data, preserve samples for DNA analysis, and prepare blood smears to examine under the microscope.

A picture of six people sitting around two small tables in the piñon-juniper woodlands. There are test tubes on the table and a nitrogen tank in the background.
Here is a picture of some of the people in our field crew processing samples after a morning of collecting data. Pictured clockwise: Moses Michelsohn, Serina Brady, Chauncey Gadek, Jenna McCullough, Lisa Barrow, and John Ford.

Figure 3 shows the number of birds collected and the number of infections that we found at each of our three mountain ranges. “Individuals” refers to the number of birds that we caught, “host species” refers to the number of bird species that we caught, and “infected birds” refers to the number of birds that were infected with at least one haemosporidian parasite. Parahaemoproteus,denoted by “H”,were the most common haemosporidians we found (54 to 70 infections in each mountain range). Plasmodium,denoted by “P”, were theleast common haemosporidians we found (13 to 37 infections in each mountain range). The number of infected birds in each mountain range was similar, ranging from 87 to 93 birds.

An image that shows the state of New Mexico with locations for the three mountain ranges sampled in the northwestern part of the state. Birds were sampled at the transition zone between the piñon-juniper woodlands and the ponderosa pine forests at elevations ranging between 2,100-2,500 meters. The highest number of birds were sampled at Zuni Mountain (n=294) and Zuni also had the highest number of infected birds (n=93). The lowest number of birds were sampled at Jemez Mountain (n=207), which also had the lowest number of infected birds (n=87).
Figure 3. A figure that summarizes the locations for sample collection and the results of our 2-year study. It shows the number of birds and parasites found at the three mountain ranges: “H” stands for Parahaemoproteus,“P” stands forPlasmodium, and “L” stands for Leucocytozoon.Panel (b) shows the region of the United States that the samples were collected from. Panel (c) shows the elevation of the mountain ranges, where darker colors indicate higher elevations. Adapted from Barrow et al. 2021.

The Big Picture: Parasites are everywhere in the natural world. They can cause disease or death to hosts that they infect. It is important for researchers to study where parasites naturally occur, how widespread they are, and which host species they infect. Parasite communities are usually hard to describe because they are so diverse. If we do not sample all the bird species in an area or if we sample a different number of each bird species in each area, we may underestimate the number and type of parasites there. Our research took a new approach that helped to account for these types of problems. Our null modeling approach can be used by other researchers who want to ask similar questions. Our approach helped us understand the community of haemosporidian parasites in an area that has received little attention in the past. We found that the community of parasites can change between areas that are only tens of kilometers apart, even when the bird communities are similar. Our research helps us better understand parasite diversity and how that relates to host diversity.

Decoding the Language:

Fieldwork: Fieldwork is any type of research conducted outdoors. Examples of fieldwork include people who trap birds, measure plants, or collect water samples outside.

Generalists: Generalists are organisms that can use a wide variety of habitats, food sources, or environmental conditions. In the context of this study, generalist parasites can infect a wide variety of bird species.

Haemosporidians: Haemosporidians are microscopic parasites that can infect the blood cells of vertebrate animals (animals with a backbone). They have a unique structure called an apicoplast that allows the parasite to penetrate the blood cells of the host. These parasites are transmitted when the host is bitten by an insect. There are hundreds of described species and thousands of undescribed lineages.

Herpetofauna: Herpetofauna, or “herps”, are amphibians and reptiles.

Jaccard dissimilarity index: The Jaccard dissimilarity index is a metric that describes the difference between two ecological communities. The index ranges from 0 to 1, where low values show that the two communities have similar species and high values show a greater difference between communities.

Lineages: A lineage is a group of organisms descended from a common ancestor. Members of the same lineage are closely related and their genetic sequences are more similar to each other than to other lineages. A lineage can refer to several species, or it can refer to organisms that are not yet described as a species but are known to be closely related. In this study, haemosporidians are considered different lineages if their genetic sequence is different from other haemosporidian parasites.

Leucocytozoon: Leucocytozoon is a genus of haemosporidian parasite that infects birds. They are introduced to their avian host through the bite of an insect, most often a blackfly. More than 100 species of Leucocytozoon have been described.

Malaria: Malaria is an infectious disease caused by Plasmodium parasites that are transmitted by mosquitoes. This disease affects humans and other animals, including birds. Malaria causes tiredness, fever, headaches, and in severe cases, can result in death. Human malaria is most common in the tropics and subtropics, regions near the equator.

Museum collection: A museum collection is a set of objects that is catalogued and cared for by an institution or dedicated set of individuals. Museum collections can include art, historical objects, or scientific collections, like those at natural history museums. Collections can also include living collections of specimens, such as in zoos or seed banks. Natural history museum collections focus on specimens and parts of animals, plants, fungi, and other natural objects. These specimens are collected and cared for so that current and future generations can study, learn from, and have a record of the natural world.

Null model: The null modeling approach that we used is a statistical method. It is a way to analyze data. A null model describes the expectation that a certain process/event has not happened, or there is no difference between groups. It provides a reference point for comparison. In the context of this research, the null model suggests that there is no difference in parasite communities across mountain ranges. When a null modeling approach is used, researchers randomly sample datasets based on the expectations of the null model (that there is no difference between groups) and then compare that to the dataset that was observed in nature. In the context of this research, we randomly sampled from a pool of all the parasites that we found over the course of the study and compared that to the parasite communities that we found at each individual mountain range. If the values from the observed dataset fall outside the range of values from the randomly generated dataset, this suggests that the null model is not supported. In other words, if the parasites that we found at a particular mountain range look different than the parasites from the random dataset, we say that the null model is not supported and that the parasites are different between the mountain ranges.

Parahaemoproteus: Parahaemoproteus is a genus of haemosporidian parasites that primarily infects birds. They are introduced to their vertebrate host through the bite of an insect, most often a biting midge. More than 170 species have been described.

Plasmodium: Plasmodium is a genus of haemosporidian parasites that infects birds, lizards, and mammals. They are introduced to their vertebrate host through the bite of an insect, most often a mosquito. More than 200 species have been described, only five of which are known to infect humans. These parasites cause the disease malaria.

Post-baccalaureate researcher:  A post-baccalaureate researcher, or a “post-bac”, is a person who has completed their bachelor’s degree and has enrolled in a 1–2 year research-intensive program. Post-baccalaureate programs are offered across the country. They are professional development programs that help students transition into PhD programs.

Postdoctoral researcher: A postdoctoral researcher, or a “post-doc”, is a person who has completed their Ph.D., or doctoral degree, and continues to conduct  research. Postdoctoral research is often collaborative where the post-doc will work with other researchers and students, and often they are more independent. Usually, these researchers have significant training and skills, but are still considered to be early in their career stage. They may be continuing their training or gaining additional skills before beginning a more permanent position. A typical post-doc lasts for 2-3 years, and a person may complete more than one post-doc appointment, depending on their career goals.

Simulate: Scientists run simulations using computers. The computer will take a mathematical concept and a set of data to mimic what might happen in nature. In the context of this research, we created simulated datasets to describe what might happen in nature under the null model. In other words, these datasets describe what we expected if all the mountain ranges had similar parasite communities.

Sky island: The term “sky island” refers to a mountain range that has forest habitat at high elevations and is surrounded by desert habitat at low elevations. Like true islands separated by oceans, plants and animals that live in forests may not be able to move as easily across desert habitats. This landscape can result in isolated populations.

Specialists: In general ecology, specialists may use or specialize on a particular habitat, food source, or set of environmental conditions. In the context of this study, a specialist parasite only infects one species or a closely related bird species.

Learn More:

Arctos: Arctos is a museum collection management system where we make specimen data available. More information for each of the birds sampled in this project can be found through specimen links reported in our paper. See an example here.

MalAvi: MalAvi is the avian malaria database. All the haemosporidian parasite lineages that have been identified are reported here, along with their host species, geographic ranges, genetic sequences, and publications. New genetic sequences can be compared to the existing database to determine whether a particular parasite has been found before.

United States Geological Survey (USGS) information on avian malaria

Audubon article on avian malaria

Dr. Chris Witt’s lab webpage for those interested in this type of research

Synopsis edited by Rosario Marroquin-Flores, PhD (Anticipated: August 2022), Illinois State University, School of Biological Sciences and Madison Rittinger, PhD (Anticipated: May 2027), University of Wisconsin-Milwaukee, Department of Biological Sciences.

Download this article here

%d bloggers like this: