Nematodes (roundworms) are distributed worldwide in almost all habitats. Mermithidae, a family of nematodes larger than others, are obligate invertebrate parasites that occur in insects, millipedes, crustaceans, spiders, mollusks and earthworms. It can affect the morphology, physiology, and even behavior of their hosts.
Fossils of mermithid nematodes have mostly been discovered from Eocene Baltic amber (11 species) and Miocene Dominican amber (nine species), but only four pre-Cenozoic species have been previously recorded. Therefore, little is known about their early evolution of parasitism.
Recently, researchers led by Prof. Wang Bo from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS), in collaboration with colleagues from the US and the UK, discovered 16 new mermithids that associate with their insect hosts from in the middle. -Cretaceous (about 100 million years ago) Kachin amber.
The study was published in eLife on July 14. It revealed the seemingly lost history of nematodes that parasitized Cretaceous insects.
In this study, 16 new mermithids associated with their insect hosts were described, including nine new species, tripling the diversity of the Cretaceous Mermithidae (from four to 13 species). Meanwhile, according to the new records of this study, nine insect orders are now known to be infected by mermithid nematodes in Kachin amber and this number is higher than Baltic amber and Dominican amber (six and three insect orders, respectively).
“This result suggests that mermithid parasitism of insects was widespread during the mid-Cretaceous period, and may have played an important role in regulating insect populations in Cretaceous terrestrial ecosystems,” said Prof. . Wang, corresponding author of the study.
The researchers found that 12 of these 16 mermithids in Kachin amber included previously unknown hosts, such as bristletails (Archaeognatha), barklice (Psocodea), and planthoppers (Perforissidae). This study also provides the first fossil records of mermithids parasitizing dragonflies (Odonata), earwigs (Dermaptera), crickets (Orthoptera) and cockroaches (Blattodea), four host associations predicted from existing records but without fossil evidence.
Furthermore, among the insect populations of mermithids preserved in Kachin amber, only one of nine orders (Diptera) is holometabolous, while it is four of six in Baltic amber and three in Dominican amber.
The situation is similar when referring to the number of nematode parasitism. In Kachin amber, only about 40% of hosts are holometabolous, while this percentage increases to 80% in Baltic and Dominican ambers. Holometabola is the most important group of extant mermithids as well as all invertebrate-parasitizing nematodes and this hexapod subgroup dominated the insect fauna during the Cretaceous.
This study shows that nematodes have not yet fully exploited Holometabola as hosts, and non-holometabolous insects were more available as hosts in the mid-Cretaceous. The widespread association between nematodes and Holometabola may have formed later.
“This study provides a glimpse into the structure of ancient parasitic nematode-host associations and their evolution over the past 100 million years,” said Luo Cihang, Ph.D. candidate from NIGPAS and first author of the study. “It also brings new opportunities to study the evolution of parasitism through the amber medium and provides direct evidence for the reconstruction of Cretaceous terrestrial ecosystems.”
This research provides a good example to study the coevolution of nematodes and their host and helps scientists to better estimate the extinction risk of modern species, according to a commentary published in same journal.
Cihang Luo et al, Widespread mermithid nematode parasitism in Cretaceous insects, eLife (2023). DOI: 10.7554/eLife.86283
Kenneth De Baets et al, Trapped in time, eLife (2023). DOI: 10.7554/eLife.90008
Awarded by the Chinese Academy of Sciences
Citation: Amber reveals evolution of parasitism in nematodes (2023, July 18) retrieved on July 18, 2023 from https://phys.org/news/2023-07-amber-reveals-evolution-parasitism-nematodes.html
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