Crocodilian Parasites: the mysterious frontier unfolded

A Load of Croc started out as a blog describing Dr. Marisa Tellez’s journey as she explored the unique relationship between crocodilians and their parasites.  Her journey has not ended and the Crocodile Research Coalition continues to lead investigations, as well as collaborate with other interested scientists internationally to further pursue this unique relationship.  So, let us guide you through this journey of unfolding the mysteries between crocodilians and their parasites, beginning with a brief intro, where we are now, and then back to the future of where we are going! 

Crocodilians are the sole surviving reptilian archosaurs of an ancient phylogenetic lineage, evolving into the keystone and apex predators of their habitat within the tropics and sub-tropics.  Unlike other reptiles, crocodilians have a four-chambered heart, and are capable of a rapid innate and anamnestic immune response as a result of a robust complement system eradicating various viruses and bacteria.  This is beneficial as crocodilians are more likely to be pre-exposed to pathogens as a result of conspecific inflicted injuries in parallel with their preferred (bacteria-infested) habitat .  However, climate change, habitat loss, and increasing environmental pollution can intensify susceptibility to pathogens as a result of external factors impairing immune function.  Therefore it is pertinent to create a foundation of information on the relationship of host and pathogen in order to prevent epidemic host mortality and/or morbidity due to environmental alterations negatively affecting the dynamic.

The complex interaction and fundamental dependence parasites have with their host and environment are two significant factors that designate them as key biological indicators of environmental disturbance.  Siddall et al. (1994) and Marcogliese and Cone (1996) discovered that studying the prevalence of digene cercariae and miracidiae in an area affected by increase sewadge sludge and water acidity was more effective in determining the negative impact on the ecosystem than assessing intermediate host abundance.   In addition, the higher heavy metal accumulation and extreme concentration difference by helminth parasites in comparison to their host make them superior bio-indicators of heavy pollutants in the geographic area of study, which allows investigators to determine the cause of a negative factor that was otherwise detectable in a host or environment.  Exploring the consequences of ecosystem perturbation, habitat alteration, and pollution on the symbiotic relationship between hosts and its parasites can provide the information needed to protect the productivity and biodiversity of an ecosystem.  In particular, such information can be highly beneficial in protecting keystone predators of a locality that are under environmental and anthropogenic pressure.

Continual stress to survive in a rapidly changing habitat with decreased or changing resources is negatively affecting crocodilian physiology and immunity, enhancing susceptibility to parasites.  This may have serious consequences as the disruption of a potentially coevolved relationship can lead to disease dispersal, irregular host population fluctuations, and parasitism of feeble hosts.  This cascade of events has resulted in epidemic mortality of crocodilian species in the past, pushing many to the brink of extinction.  In order to take the proper action to ensure future existence of the crocodilian species, it is essential that information be gathered on the interaction of this host-parasite system.

Dr. Tellez’s Research

Crocodilian parasites have been well-documented since the early 1800s, but few have attempted to understand the unique, and possibly prehistoric, association between crocodilians and their parasites.  Investigating the dynamic between crocodilians and their parasites proposes new insight on coevolution, parasite roles’ in food webs, parasite adaptations, and parasite ecology.  My PhD research entailed:  1)  Looking at the Spatio-Temporal dynamic of alligators and their parasites over a three year period.  This could indicate which  anthropogenic and environmental perturbations may alter the system. 2) Analyzing and comparing and contrasting infracommunities (parasites within the host) to component communities (host population of parasites).  This could give us information on the correlation of ontogeny to parasitism, as well as heavy metals and innate immune function.  3)  Compare and Contrast Florida and Louisiana alligators.  And finally 4) create a niche model to predict parasite species distribution.  

So, what cool information did Dr. Tellez find from her PhD at UCLA?  Check out her thesis- Alligator Parasitism- the mysterious frontier unfolded: exploration of the ecological interaction between an archaic predator (Alligator mississippiensis) and its parasites

Current CRC Crocodilian-Parasite Research

Dr. Tellez received the National Science Foundation Postdoctoral Fellow,  investigating the health and biodiversity of wildlife within crocodilian habitat in Belize utilizing parasites as a bio-indicator of environmental health and species richness.  Here’s a summary of her proposed project, in which the CRC continues To-Date as this has become a long-term monitoring project:

“Extinction of a substantial fraction of the tropical biota of Latin America is inevitable if present trends of deforestation, poaching, environmental pollution, and current careless attitudes of the natural world continue. Implementation of suitable conservation tactics and education programs are hindered in part due to the lack of data on local biodiversity. Quantifying the species richness of a community is time consuming and costly, particularly in low socio-economic regions. It is therefore paramount to generate feasible actions that can assess the biodiversity promptly, in order to ameliorate impact of human activities.

A particular cost-effective approach to evaluate community species richness is the identification and use of indicator species or taxa. Because of the complex interactions and the fundamental dependence parasites have with their hosts, parasites are considered significant bioindicators of the animal community. Simply, species richness of parasites directly parallels the richness of hosts in a community. Stressors affecting host abundance should induce a change in parasitism, which could revel cryptic information about environmental disturbances. For example, pollution can alter parasite abundance directly and indirectly by altering host diversity and population density, in addition to interfering with their parasite free-living transmission stages. The superiority of parasites as pollutant indicators is directly due to their ability to absorb and accumulate pollutants in their tissues more readily than in their hosts. Concentrations of heavy metals are revealed in parasites that may be undetectable in the hosts or in environmental samples. Therefore, parasites could be used as a proxy for determining ecosystem health in addition to quantifying the biodiversity of the extensive community.

In an effort to maximize the protection of biodiversity, keystone species have been used for the conservation management of whole communities. Top predators, such as crocodilians, often fit the criteria of a keystone species. The stabilization of biodiversity through landscape modification, nutrient recycling, and top-down regulation have all been attributed to the presence of crocodilians within their environments. Crocodilians are also effective health indicator species due to their bioaccumulation of toxins, and sensitivity to anthropogenic perturbations. Given the crucial ecological role of crocodilians, it seems justifiable to assume that the preservation of lower trophic levels is dependent on the integrity of crocodilian populations.

Research objectives

Conservation efforts for ecosystems depends on the scientific discoveries of field studies, and the translation of these findings to policy makers. The paradigm of “translational ecology” could be a beneficial approach in understanding the potential threat human impacts have on the biodiversity of crocodilian habitats, particularly through the involvement of various scientific disciplines. Translational ecology is the application of translating scientific data to further enhance research and policy making (Schlesinger, 2010). This study will examine how anthropogenic alteration has affected the biodiversity of crocodilian ecosystems in Belize through an interdisciplinary approach that incorporates parasitology, community ecology, ecotoxicology, and conservation biology. Moreover, it is anticipated that this study will reflect the standards of translational ecology as data will assist in habitat and wildlife management. The goals of this research will be accomplished by 1) assessing parasites as bioindicators for ecosystem diversity by examining the species richness of metazoan parasites at local and regional scales, and I will integrate this with the knowledge of community diversity, 2) quantifying the biodiversity of the free-living community of pristine, semi-pristine, and no-pristine habitats, 3) perform an analysis of heavy metal concentrations of hosts and parasites representing three different trophic levels will be performed to evaluate human impact via environmental contamination, and 4) examine if the above analyses are applicable to other similar crocodilian environments in Central America.”

The future?

So what’s to come of Crocodilian-Parasite research?  Well, follow our monthly updates as we highlight some of the cool research!



9 comments on “Crocodilian Parasites: the mysterious frontier unfolded

  1. I have been obsessed with crocodiles and alligators since I was five. What is your degree in and where were you with the baby croc?

    • I have my BA and BS, my MA in science, and currently getting my PhD. The croc was in Mexico. Crocodiles and alligators are such a passion of mine, I can’t think of anything else I would want to do!

      • Its great working with them. I have worked in Mexico before with crocodiles in the Yucatan and Chiapas- can’t wait to go back!

    • I apologize for the delay reply as I’ve been traveling and finishing up my PhD! My BS was in Zoology, and I got a MA in Biology, writing up a croc-parasite book that is now available on Amazon. Crocodiles are fantastic!

  2. Good day! Thank you for your information. I’m a graduate school student taking up MS Biological Science in the Philippines. I would like to study parasites on farm crocodiles as my thesis, would it be possible?

    • Crocodiles in farms usually don’t have a lot of macroparasites in farms because farms won’t feed crocs “natural” food usually. However, you may be able to study bacteria, virus, or blood parasites. What I would do is examine the organs of sacrificed crocs at the farms (maybe about 10) and see what you fine. If you are finding a lot of parasites, then you can go forward with doing a study. Hopefully that helps?

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