Parasitism in aquatic ecosystems

Many of us wonder why our ancestors drained so many beautiful meadows. We will stop wondering when we remember the invasive diseases associated with wetlands and flooded areas. Water is a reservoir of parasites dangerous to humans, from lamblia to blood flukes to vandellates. Among aquatic and marsh organisms, we will meet intermediate hosts and vectors of a host of parasites dangerous to humans, from malarial spores to tapeworms. Parasitism in aquatic ecosystems is a vast but fascinating topic.

To choose from, to color!

Examples from aquatic ecosystems can illustrate almost all types of parasitism. Hyperparasitoids (parasites of other parasites) are not only mistletoes growing on twigs, but also microsporidia from flukes in fish. Micro-predation as an intermediate link between parasitism and predation? To choose from, to color: leeches, spittlebugs, larvae of Gnathidae , female mosquitoes and cucurbits, lampreys. Parasitoids for breeding (dropping off their own offspring for others to feed on) are not only cuckoos and buzzards, but also parasitic ducks Heteronetta atricapilla, and most importantly, some fish, such as benthic fish to cichlids.

The model kleptoparasites (resource thieves) remain the otter Skua spp. Sexual parasitism (when males are much smaller than females and develop on them) is even a specialty of marine organisms, especially the invertebrate green bonela Boneliia viridis and deep-sea fish of the order Lophiiformes. Hybridogenesis(stealing the gametesof a second, related species) as a special case of sexual parasitism is the domain of the beaked fish Poeciliopsis and the green frog Pelophylax spp. Adelphoparasitism (when the host and the parasite are sister species)? There you go! Examples of this life strategy can be found among crayfish. The uncanny nature of these systems prompted early naturalists to look for the ancestors of fungi, including insectivores, among the adelphoparasitic red algae.

In the seas and freshwaters we will not find only examples of social parasitism, as there are no potential hosts, i.e. eusocial insects, although there are eusocial Synalpheus shrimps. It is noteworthy that, among the insects, a similar lifestyle inside sponges is led by perchids, aquatic networms, native to and for Poland [1, 2, 3, 9, 12].

Each rake to itself?

A typical biologist is certain that every living being pursues its own personal interest. A parasitologist would counter that each biological system primarily pursues the interests of its parasites. The ecology and evolution of parasites are topics that are little known even to many naturalists. As phenomena of great importance to human, animal and human health, they remain the domain of physicians, veterinarians and phytopathologists. It is widely accepted that parasites are ubiquitous agents of natural selection, and much of artificial selection (the creation of new varieties) is the search for resistance to their invasions.

Nevertheless, the long-standing separation between the applied sciences (biomedical, agricultural and forestry) and the basic sciences (ecology and evolutionism) has limited the exchange of ideas between researchers of this impact. Parasitologists and non-parasitologists not only attend separate conferences and publish in different journals, but quite literally speak different languages. They adhere to different philosophies of biology – for old-school parasitologists, evolution always reduces virulence for hosts, while modern evolutionary theories allow for many more equally optimal solutions, including an increase in virulence [2].

You do the cleanup, you’ll lose a lot of time

An important problem is the location of parasites in food webs . For example, flukes and tapeworms that change hosts at successive stages of the development cycle simultaneously occupy a multitude of positions in the same trophic network, creating countless loops of energy flow and circulation of matter. This makes bioenergetic analysis difficult. Since almost every living organism (including parasites themselves) acts as a host for parasites from the most diverse kingdoms, parasites should be placed at the apex of any trophic pyramid (the highest level of the network) [2, 8, 10].

His own or a stranger’s?

The presence of parasites determines the invasion of alien species, including free-living ones (non-parasites). Marine and freshwater ecosystems provide many examples of this phenomenon. The edible crayfish Carcinus maenas has become invasive on the US Atlantic coast because it is more resistant than the native crabs:, the Atlantic pocket crab Cancer irroratus and the northern pocket crab Cancer borealis,to Atlantic parasites [8, 10].

The exchange of results between practitioners (veterinarians, doctors) and theoreticians (ecologists) can determine the success of the fight against parasites spread by water. The history of the fight against Dracunculus medinensis rickettsia will be very instructive here. The complete eradication of this disease among humans and dogs has been delayed because the role of fish and frogs as paratenic hosts, in which rishtas can lurk when they are not in mesh, has been overlooked [4, 10].

You don’t have to be a naturalist to know that certain parasites change the behavior of their hosts. This is especially true for intermediate hosts. For the development cycle to close successfully for the parasite, its intermediate host must fall prey to a suitable predator. Videos by the Valencians show swamp snails – amberjack, with feelers like pulsating neon lights, attracting birds. Borrowed fish are easier prey for fish-eaters. They are so dulled by both the California fluke Euhaplorchis californiensis and the tapeworms of our waters: the ventriloquist broadhead Diphyllobothrium latum or the thong Ligula intestinalis. The motile pest Plasmodium vivax alters the scent of human skin, intensifying its attractiveness to mosquitoes – in this case, Homo sapiens is the intermediate host, while the female fork-worm is the final one [10].

And who is in charge? How can parasitism affect reproduction?

There is also increasing talk of changes in the behavior of definitive hosts. Until recently, it was thought (and in some universities it is still taught this way…) that European waterbirds undergo tapeworm infestations asymptomatically, without suffering measurable damage to their health. Today we know that they also undergo a kind of castration. This is because the parasites prefer the host to invest in feeding them, rather than in their own reproduction. Such a phenomenon was previously observed in crabs infested by Sacculina sacculina or snails attacked by flukes [10, 11].

Together for eternity

The direct nature of the parasite-host relationship means that the partners evolve together, at the same rate. According to Fahrenholz’s law, the family trees of parasites and hosts begin to mirror each other. Evolutionarily “young” species have modern parasites, while living fossils have old inhabitants. For example, the chimeras, as a group of strange chondrichthyans, are the only hosts of the equally peculiar and evolutionarily old flatworms Gyrocotylidae, which are a mixture of features typical of today’s spiders and tapeworms with their own peculiar ones.

Studying the shared evolutionary history of hosts and parasites sheds new light on the affinities of certain host taxa, especially when we have little paleontological and genetic data. Since the 19th century. Evolutionists have argued over whether flamingos are more closely related to ducks or storks. The former possibility is indicated by feeding by filtering water with their beaks, and the latter by their general body structure. Parasites shared by redstarts and ducks were considered conclusive evidence of closer affinity to the paleflies. However, it was later found that flamingos share their unwanted guests with grebes rather than ducks, so grebes, not ducks and not storks, would be their closest family. Lice have expanded their host range to include ducks, after all, sharing the same environments with grebes [5].

That’s the biggest embarrassment, so that two can at once

Long-term coevolution of parasites with their hosts, both on the scale of individuals and entire species and orders, stabilizes their relationships. It is often assumed that parasitism always tends toward commensalism or mutualism, but we know the opposite situations. In mammals, including humans, the presence of certain organisms harms on many levels, but protects against autoimmune diseases [11]. Certain nematodes and insects (themselves often parasites of plants, such as aphids) cannot reproduce or become defenseless without infection by Wolbachia or Spiroplasma bacteria.

Moreover, it is not so much the presence of any Wolbachia itself that is decisive, but specific strains infected with “appropriate” transposons, phages or plasmids. The latter factor enables or prevents reproduction, determining the reproductive isolation (interspecies barrier) between otherwise similar individuals. This is nicely seen in the protected EU and Swiss praying mantids: alcono and rebelle. The dry- and thermophilic forms, feeding on the crossbill gentian, traditionally included as P. rebelii prairie rebel, arose repeatedly, independently from the swampy, moist- and cold-hardy ancestors, feeding in the caterpillar stage on the narrow-leaved gentian, traditionally classified as Phengaris alkon [2, 6, 7].

Perhaps it’s not surprising that Peter Kropotkin, and after him Lynn Margulis, thought that natural selection would always turn parasitism into mutualism, especially when resources are increasingly limited. This was the path that archeons and bacteria in the ancient oceans were supposed to take. Over time, their relationship proved so durable that it ushered in a new common quality: the first eukaryotic cells [8, 13].

In the article, I used, among other things. z:

1. Berec, L.; Schembri, P.; Boukal, D. (2005). Sex determination in Bonellia viridis (Echiura: Bonelliidae): population dynamics and evolution. Oikos. 108 (3): 473-484.
2. Combes, C. (1999). Ecology and evolution of parasitism. Long-term interactions. Published. Naukowe PWN, Warsaw.
3. Duffy, E.; MacDonald, K. (2009). Kin structure, ecology and the evolution of social organization in shrimp: a comparative analysis. Proceedings of the Royal Society B: Biological Sciences. 277 (1681): 575-584.
4. Eberhard, M. L. (2016). Possible Role of Fish and Frogs as Paratenic Hosts of Dracunculus medinensis, Chad. Emerging Infectious Diseases. 22 (8): 1428-1430.
5. Johnson, K. P.; Kennedy, M.; McCracken, K. G (2006). Reinterpreting the origins of flamingo lice: cospeciation or host-switching? Biology Letters. 2 (2): 275-278.
6. Kaur, R.; Shropshire, J; Cross, KL, Leigh; B, Mansueto, A.; Stewart, V. (2021) Living in the endosymbiotic world of Wolbachia: a centennial review. Cell Host Microbe 29:879-893.
7. Lucek, K.; Blattner, L.; Cornet, C.; Chittaro, Y.; … Dušej, G. (2024). Towards a genomic resolution of the Phengaris alcon species complex. Conservation Genetics, 1-12.
8. Margulis, L.; Sagan, D.; Eldredge, N. (1995). What Is Life? Simon and Schuster.
9. Podbielkowski, Z.; Rejment-Grochowska, I.; Skirgiello, A. (1979). Spore plants. PWN, Warsaw.
10. Poulin, R. (2007). Evolutionary Ecology of Parasites. Princeton University Press.
11. Rook, G. A. (2007). The hygiene hypothesis and the increasing prevalence of chronic inflammatory disorders. Transactions of the Royal Society of Tropical Medicine and Hygiene. 101 (11): 1072-1074.
12. Rios, R.; Duffy, E., (2007). A review of the sponge-dwelling snapping shrimp from Carrie Bow Cay, Belize, with description of Zuzalpheus, a new genus, and six new species (Crustacea: Decapoda: Alpheidae). Zootaxa. 1602: 1-89.
13. Ryszkiewicz, M. (1994). Mother Earth in the friendly cosmos. Gaia and the anthropic principle in the history of natural thought. Published. Naukowe PWN, Warsaw.