Vetufebrus ovatus n. gen., n. sp. (Haemospororida: Plasmodiidae) vectored by a streblid bat fly (Diptera: Streblidae) in Dominican amber.

BACKGROUND: Both sexes of bat flies in the families Nycteribiidae and Streblidae (Diptera: Hippoboscoidea) reside in the hair or on the wing membranes of bats and feed on blood. Members of the Nycteribiidae transmit bat malaria globally however extant streblids have never been implemented as vectors of bat malaria. The present study shows that during the Tertiary, streblids also were vectors of bat malaria.
RESULTS: A new haemospororidan, Vetufebrus ovatus, n. gen., n. sp., (Haemospororida: Plasmodiidae) is described from two oocysts attached to the midgut wall and sporozoites in salivary glands and ducts of a fossil bat fly (Diptera: Streblidae) in Dominican amber. The new genus is characterized by ovoid oocysts, short, stubby sporozoites with rounded ends and its occurrence in a fossil streblid. This is the first haemosporidian reported from a streblid bat fly and shows that representatives of the Hippoboscoidea were vectoring bat malaria in the New World by the mid-Tertiary.
CONCLUSIONS: This report is the first evidence of an extant or extinct streblid bat fly transmitting malaria. Discovering a mid-tertiary malarial parasite in a fossil streblid that closely resembles members of a malarial genus found in nycteribiid bat flies today shows how little we know about the vector associations of streblids. While no malaria parasites have been found in extant streblids, they probably occur and it is possible that streblids were the earliest lineage of flies that transmitted bat malaria to Chiroptera.

Background

Amber is known for its ability to preserve vertebrate microbial pathogens. Thus far, there are records of malaria, leishmaniasis and trypanosomiasis associated with insect vectors in amber deposits ranging from 20 to 100 million years of age [1]. Sporogonic stages of the bird malaria, Plasmodium dominicana, occurred in Culex malariager in Dominican amber [2] and developmental stages of Paleohaemoproteus burmacis (Haemospororida: Plasmodiidae) were reported from an Early Cretaceous Burmese amber biting midge (Diptera: Ceratopogonidae) [3]. The present study describes the sporogonic stages of a new genus of bat malaria in a Dominican amber fossil streblid [4]. Extant streblids have never been implicated as vectors of bat malaria, however members of the closely related family Nycteribiidae transmit bat malaria globally [5,6] (Table 1). Since both sexes of streblid bat flies (Diptera: Hippoboscoidea: Streblidae) feed on the blood of bats and reside in the hair or on the wing membranes [7-9], they would be excellent vectors of bat malaria.

Table 1

Hippoboscoidea vectors of malaria

Vector	Malaria type	Vertebrate	Reference
Hippoboscidae
Icosta hirsuta	Haemoproteus lophortyx	birds	[8]
I. rufiventris	H. lophortyx	birds	[8]
Lynchia hirsuta	H. lophortyx	birds	[20]
Microlynchia pusilla	H. columbae	birds	[21]
M. pusulla	H. maccallumi	birds	[22]
M. pusilla	H. sacherovi	birds	[22]
Ornithomyia avicularia	H. mansoni	birds	[23]
Ornithomyia lagopodia	H. mansoni	birds	[24]
Pseudolynchia brunnea	H. columbae	birds	[21]
P. canariensis	H. columbae	birds	[25]
P. canariensis	H. maccallumi	birds	[22]
P. capensis	H. columbae	birds	[21]
P. maura	H. columbae	birds	[21]
Stilbometopa impressa	H. lophortyx	birds	[26]
Nycteribiidae
Basilia sp.	Polychromophilus deanei	bats	[12]
Listropoda sp.	?	bats	[27]
Nycteribia dentata	Polychromophilus sp.	bats	[28]
N. kolenatii	P. murinus	bats	[10]
N. parvula	P. melanipherus	bats	[29]
Penicillidia fulvida	Polychromophilus sp.	bats	[11]
Penicillidia spp.	Polychromophilus sp.	bats	[13]

Methods

Specimen

The fossil streblid is in a piece of amber 5 mm long by 4 mm wide by 4 mm deep (Figure 1). Observations, drawings, and photographs were made with a Nikon SMZ-10 R stereoscopic microscope and Nikon Optiphot compound microscope with magnifications up to 600×.

Figure 1

Two oocysts. Two oocysts (arrows) of Vetufebrus ovatus n. gen., n. sp. on the gut wall of a Dominican amber streblid bat fly. Bar = 272 μm.

Since it was not possible to photograph the malarial organisms without polishing away portions of the fly, photographs had to be taken through the thickness of the amber matrix as well as the width of the body wall of the vector. Adobe Photoshop was used to enlarge the photos and obtain the clearest images.

Locality

The amber with the bat fly came from La Búcara mine in the Cordillera Septentrional of the Dominican Republic. Dating of Dominican amber is still controversial with the latest purposed age of 20-15 mya based on foraminifera [10] and the earliest as 45-30 mya based on coccoliths [11]. In addition, Dominican amber is secondarily deposited in sedimentary rocks, which makes a definite age determination difficult [12]. A range of ages for Dominican amber is possible since the amber is associated with turbiditic sandstones of the Upper Eocene to Lower Miocene Mamey Group [13]. Dominican amber was produced by the leguminous tree, Hymenaea protera Poinar [14] and a re-construction of the Dominican amber forest based on amber fossils indicated that the environment was similar to that of a present day tropical moist forest [15].

Results and Discussion

Description of malarial pathogen

Phylum Apicomplexa Levine, 1970

Class Aconoidasida Mehlhorn, Peters & Haberkorn, 1980

Order Haemospororida Danilewsky, 1885

The description is based on two oocysts and sporozoites in the oocysts and salivary glands/secretions of a fossil streblid bat fly [4].

Vetufebrus Poinar n. gen. (Figures 1, 2, 3 and 4)

Figure 2

Oocysts A and B of . Oocysts A and B of Vetufebrus ovatus n. gen., n. sp. attached to the gut wall of a Dominican amber streblid bat fly. Arrows show developing sporozoites inside oocysts. Bar = 33 μm.

Figure 3

Sporozoites (arrows) of . Sporozoites (arrows) of Vetufebrus ovatus n. gen., n. sp. in salivary glands and ducts of a Dominican amber streblid bat fly. Bar = 20 μm.

Figure 4

Oocysts of . A and B. Oocysts of Vetufebrus ovatus n. gen., n. sp. containing nucleated cells and developing sporozoites in a Dominican amber streblid bat fly. C. Sporozoites of Vetufebrus ovatus n. gen., n. sp. in a salivary gland secretion of a Dominican amber streblid bat fly. Bar = 27 μm.

Description. Oocysts small, oval, with nucleated cells 3-5 μm in diameter and developing sporozoites 7-10 μm in length; sporozoites in salivary glands and ducts stubby, with rounded ends, 8-10 μm in length; occurs in a Dominican amber streblid bat fly [4].

Type species: Vetufebrus ovatus Poinar

Vetufebrus ovatus Poinar, n. sp.

Description: Oocysts brown; oocyst A, 32 μm × 15 μm; surrounding membrane 1.2 -1.4 μm wide, containing dark nucleated cells 3-5 μm in diameter and developing sporozoites 7-10 μm in length; oocyst B, 29 μm × 17 μm, containing dark nucleated cells 3-5 μm in diameter and developing sporozoites 7-10 μm in length; surrounding membrane 1.2-1.4 μm wide; sporozoites in salivary glands/secretions short, stubby, with rounded ends, 8-10 μm in length.

Etymology: The generic name is from the Latin "vetus" for old and the Latin "febris" for fever. The specific epithet is from the Latin "ovatus" for ovate, referring to the shape of the oocysts.

Holotype. Specimen (accession # D-7-239) deposited in the Poinar amber collection maintained at Oregon State University, Corvallis, Oregon.

Locality: La Búcara amber mine (19°13' × 70°40') in the northern portion of the Dominican Republic.

Conclusions

The present study represents the first description of a haemosporidian reported from a streblid bat fly and shows that representatives of the Hippoboscoidea were vectoring bat malaria in the mid-Tertiary. The presence of sporozoites in salivary glands and ducts indicates that the streblid was a successful vector of Vetufebrus.

Bats are infected with four genera of malaria: Plasmodium, Hepatocystis, Nycteria and Polychromophilus [5,6]. Species of the former three genera infect Old World bats while Polychromophilus occurs globally and is the only bat malaria reported from the New World [16]. All known strains of Polychromophilus are vectored by nycteriibid flies of the genera Nycteribia, Penicillidia and Basilia (Table 2).

Table 2

Sporogonic stages of bat malaria in Hippoboscoidea (all Nycteriibidae except for Vetufebrus in a fossil streblid).

Malaria	Vector	Oocyst	Sporozoite	Reference
Vetufebrus ovatus	Fossil streblid	35 × 15,29 × 17oval	7-10, stubbyends rounded	Present study
P. deanei	Basilia sp.	60, round	8, thick	[12]
P. melanipherus	Nycteribia parvula	?	?	[29]
P. murinus	Nycteribia kolenatii	57-71, round	7.4	[10]
Polychromophilus sp.	Nycteribia dentata	?	7, stubbyends rounded	[28]
Polychromophilus sp.	Penicillidia fulvida	oval, 31 × 1057 × 47	13, thick,blunt ends	[11]
Polychromophilus sp.	P. dufouriP. conspicua	?	stubby,blunt ends	[5,13]
Polychromophilus ?	Listropoda sp.	?	6.3, stubby,blunt ends	[5,27]

All measurements in microns.

The sporogonic stages of Polychromophilus are characterized by round, slow growing oocysts attached to the midgut of the vector and short, stubby sporozoites with rounded ends [5]. The mature round oocysts of Polychromophilus spp. contrast with the small oval oocysts of Vetufebrus (Table 2)(Figures 2, 4A, B). However, Adam and Landau [17] noted a small (31 × 10 μm), oval Polychromophilus oocyst in the nycteribiid fly, Penicillidia fulvida Bigot, 1889. It is likely that this oval oocyst in the nycteribiid was still developing, which could be the case with the two oocysts of Vetufebrus. While the sporozoites noted in the two oocysts of Vetufebrus are similar in size and shape to those in the salivary glands, it is possible that some of the salivary gland sporozoites originated from an earlier infection.

Short and stubby sporozoites with rounded ends as reported here for Vetufebrus (Figures 3, 4C) are characteristic of Polychromophilus infections [17-19](Table 2) and the dimensions of Vetufebrus sporozoites fall within the range of some Polychromophilus spp. (Table 2). While Vetufebrus could represent an early lineage of Polychromophilus, this is unclear due to the small size of the oocysts. Also bat malaria has not been found in extant streblids even though species of the closely related Nycteribiidae carry bat malaria (Table 1). Adam & Landau [17] found no malarial stages in the streblids, Raymondia simplex Jobling 1954, R. seminuda Jobling, 1954 and R. leleupi Jobling 1954 while searching for vectors of Polychromophilus in the Congo Republic. Also, Garnham [5] found no sporogonic stages of malaria in African streblids.

In accordance with section 8.6 of the ICZN's International Code of Zoological

Nomenclature, copies of this article are deposited at the following five publicly accessible libraries: Natural History Museum, London, UK; American Museum of Natural History, New York, USA; Museum National d'Histoire Naturelle, Paris, France; Russian Academy of Sciences, Moscow, Russia; Academia Sinica, Taipei, Taiwan.

Competing interests

The author declares that they have no competing interests.

Authors' contributions

GP discovered the haemosporidian, designed and wrote the paper and supplied the figures.