Extensive Uncharted Biodiversity: The Parasite Dimension

Abstract

Parasites are often hidden in their hosts and exhibit patchy spatial distributions. This makes them relatively difficult to detect and sample. Consequently we have poor knowledge of parasite diversities, distributions and extinction. We evaluate our general understanding of parasite diversity and highlight the enormous bias in research on parasites such as helminths and arthropods that infect vertebrate hosts. We then focus on Myxozoa as an exemplary case for demonstrating uncharted parasite diversity. Myxozoans are a poorly recognised but speciose clade of endoparasitic cnidarians with complex life cycles that have radiated to exploit freshwater, marine and terrestrial hosts by adopting strategies convergent to those of parasitic protists. Myxozoans are estimated to represent some 20% of described cnidarian species - greatly outnumbering the combined species richness of scyphozoans, cubozoans, and staurozoans. We summarise limited understanding of myxozoan diversification and geographical distributions, and highlight gaps in knowledge and approaches for measuring myxozoan diversity. We close by reviewing methods and problems in estimating parasite extinction and concerns about extinction risks in view of the fundamental roles parasites play in ecosystem dynamics and in driving host evolutionary trajectories.

What would it take to describe the global diversity of parasites?

“…The lack of slowing down in those linear trends is a strong indicator that we remain a long way from a complete catalog of helminth diversity. 4…”

“…Helminth parasites exhibit immense diversity, tremendous ecological and epidemiological significance, and a wide host range across vertebrates, invertebrates, and plants. Estimates of helminth diversity remain controversial (1; 2; 15), especially given uncertainties arising from the small fraction of total diversity described so far (4). Though the task of describing parasite diversity has been called a "testimony to human inquisitiveness" (1), it also has practical consequences for the global task of cataloging life; one recent study proposed there could be 80 million or more species of nematode parasites of arthropods, easily reaffirming the Nematoda as a contender for the most diverse phylum on Earth.…”

Mechanisms and Drivers for the Establishment of Life Cycle Complexity in Myxozoan Parasites

“…Myxozoans are intriguing group of obligate parasites that evolved at the base of metazoans, showing extremely derived genomes [8] and complex life histories (summarized in [3]). Given that it is likely that the vast majority of myxozoan diversity has not yet been sampled and molecular data are only available for approximately 30% of described species [40], our approach represents only a first step for strengthening the base of the tree by adding evolutionary ancient parasite sequence data from some of the first fish hosts available on Earth for secondary host acquisition. While broader sampling is certainly required, we hoped to characterize at least some isolates that pre-date the epoch of within teleost mass-diversification.…”

A review of the role of parasites in the ecology of reptiles and amphibians

“…Comprehensive ecological studies detailing prevalence and effects in wild populations are lacking (Okamura et al . ), though myxosporean parasites can reach high loads and cause disease in captive frogs (Hartigan et al . ), and they may have emerged in distribution recently (Hartigan et al .…”