A Worker-Like Female of Myrmica sabuleti (Meinert, 1861) (Hymenoptera: Formicidae: Myrmicinae) in a Pitfall Trap with Five Mermithids (Nematoda: Mermithidae) Protruding from the Gaster

Abstract

A worker-like female of Myrmica sabuleti (Meinert, 1861), pitfall-trapped near Jena, Germany, in late summer 2016, was infested by five postparasitic juvenile mermithids. They poked out of the ant´s gaster as a trail of seven filaments of various lengths. Apart from its swollen gaster, the ant differed from conspecifics in several morphometric parameters. Using both morphological and molecular techniques, the parasite family Mermithidae was confirmed. Our stray find raises multiple questions concerning the genus and species identity of the parasite, its biology, and the infestation rate of the host ant population. More mermithid awareness by the various researchers working with Myrmica will help, but directed fieldwork, experimental life-history research, and molecular studies are needed to emancipate progress in ant-mermithid research from serendipity.

Among the shapeshifters: parasite-induced morphologies in ants (Hymenoptera, Formicidae) and their relevance within the EcoEvoDevo framework

“…The case of ant–parasitic mermithid nematodes (“ Mermithidae ” section) represents a good example of a system with an immensely rich body of case reports, but deficient in empirical investigations of developmental processes: apart from the vast diversity of aberrant host phenotypes, one of the most pressing obstacles to researching ant–mermithid systems is the unresolved taxonomy and diversity of the involved parasites [ 74 ]. Morphologically, mermithids are only reliably identifiable in their mature stage—and even then, only by expert nematologists [ 84 , 85 ]—and their complex life-cycles are very difficult to recreate under controlled laboratory conditions [ 69 ].…”

“…Studies from the past decade focussing on DNA-barcoding of parasitic nematodes have yielded promising results for species identification [ 85 , 184 – 186 ]. However, genetic sequences of ant–parasitic mermithids deposited in accessible databases are still extremely scarce, hampering identification and comparability even in cases where barcodes have been obtained [ 51 , 74 ]. The same is true for methods of 3D imaging to assess the extent of internal and external changes in ant hosts (Fig.…”

“…Many studies have investigated parasitogenic effects in the Formicinae and Myrmicinae, especially the genera Lasius (e.g., [ 30 , 37 , 51 , 55 , 64 , 65 , 68 , 69 ]) and Myrmica (e.g., [ 33 , 70 – 74 ]). While these taxa may be among the most ubiquitous and commonly infected, other accounts report mermithid infections of Ponerinae, Ectatomminae and Dorylinae [ 50 , 57 , 60 , 66 , 75 ] as well as of charismatic groups like the Southeast-Asian “exploding ants” ( Colob-opsis spp., [ 52 , 53 ]) or invasive species like Solenopsis invicta [ 76 , 77 ].…”

“…In comparison to the respective original host caste, characteristic changes may include altered body size, elongated or shortened extremities, physogastry (enlarged gaster, distended by the parasite), reduced size of head, deviations in pilosity and sculpture, as well as reduction of all sexual characters (wings, thoracic sclerites, ovaries, and ocelli; Fig. 1 a, b) (e.g., [ 31 , 33 , 42 , 50 – 52 , 55 , 67 – 71 , 74 ]).…”

“…In contrast, newer studies on Myrmica spp. have proposed a common origin of all aberrant morphologies from larvae destined to become gynes or males [ 33 ] or opted to omit caste assignment of the host in light of unclear morphology [ 74 ]. Accounts of “workers” and “soldiers” exhibiting gigantism or gyne-like traits [ 32 , 36 , 83 ] or infection of adult ants [ 63 , 67 ] are currently considered doubtful and are in need of further investigation.…”