Metrioxenini

Metrioxenini
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Belidae
Subfamily:	Oxycoryninae
Tribe:	Metrioxenini; Voss, 1953
Genera
	Afrocorynus ; Hispodes ; Metrioxena ; and see text
Synonyms
	Metrioxeninae Zherikhin & Gratshev, 1995 [1]

Last updated July 11, 2019

Metrioxenini (metrioxenines) are a tribe of belids, primitive weevils of the family Belidae, containing about 30 species. They are only found in two widely separated areas, Southeast Asia extending to Indonesia, and South Africa. In the Paleogene, they were found at least in North America and Europe also, occurring perhaps across the entire Northern Hemisphere.^[1]

In biology, a tribe is a taxonomic rank above genus, but below family and subfamily. It is sometimes subdivided into subtribes. By convention, all taxonomic ranks above genus are capitalized, including both tribe and subtribe.

Belidae is a family of weevils, called belids or primitive weevils because they have straight antennae, unlike the "true weevils" or Curculionidae which have elbowed antennae. They are sometimes known as "cycad weevils", but this properly refers to a few species from the genera Parallocorynus and Rhopalotria.

Weevils are a type of beetle belonging to the superfamily Curculionoidea. They are usually small, less than 6 mm (0.24 in), and herbivorous. About 97,000 species of weevils are known. They belong to several families, with most of them in the family Curculionidae. Some other beetles, although not closely related, bear the name "weevil", such as the biscuit weevil, which belongs to the family Ptinidae.

As in other belids, their antennae are straight, not elbowed as in the true weevils (Curculionidae). They are far less characteristic than their presumed closest living relatives, the Aglycyderini. They can be recognized by the sharp-sided rostrum ("snout"). Also, their eyes are bordered by a wide and ridged groove. Metrioxena shows two sharp ribs on each elytron, which are absent in the other genera. These, by contrast, have their tarsal claws fused together at the base (they are unfused in Metrioxena) and grooves on the pygidium which are absent in Metrioxena.^[1]

Antennae, sometimes referred to as "feelers", are paired appendages used for sensing in arthropods.

The Curculionidae are the family of the "true" weevils. They are one of the largest animal families, with 6,800 genera and 83,000 species described worldwide.

Aglycyderini are a tribe of belids, primitive weevils of the family Belidae. Like in other belids, their antennae are straight, not elbowed as in the true weevils (Curculionidae). They occur only on the Pacific Islands and in the Macaronesian region.

Distribution and ecology

The type genus Metrioxena contains twelve described species apart from the fossil ones mentioned below. They are today restricted to parts Southeast Asia, extending into the Indonesian archipelago. Roughly, they occur between Thailand and the Philippines and from Malaysia to the Tanimbar Islands. They have been found on Sumatra, Java, Sulawesi and offshore Ternate but are hitherto unknown from Borneo and the Lesser Sunda Islands where they conceivably might also occur. Considering that in the Paleogene the genus (or very close relatives) were found in North America and Europe, it may well be that the present distribution is a relict of a formerly Holarctic range. The Paleogene was warmer than our time, and the climate in today's temperate latitudes was by then indeed more like that in today's Southeast Asia.^[1]

In biological classification, especially zoology, the type genus is the genus which defines a biological family and the root of the family name.

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.

A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. The totality of fossils is known as the fossil record.

Afrocorynus contains presently two described species, which are only known to occur in the mountains and hills that extend on the southern coast of South Africa, between Mosselbay in the west, Grahamstown in the east, and the Karoo inland. Hispodes occurs in similar habitat extending eastwards and inland, with the single described species (H. spicatus) found hitherto only in the Katberg region, and an undescribed species known from the Drakensberg escarpment south of Tzaneen.^[1]

South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres (1,739 mi) of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans; to the north by the neighbouring countries of Namibia, Botswana, and Zimbabwe; and to the east and northeast by Mozambique and Eswatini (Swaziland); and it surrounds the enclaved country of Lesotho. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation. It is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Bantu ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status. The remaining population consists of Africa's largest communities of European, Asian (Indian), and multiracial (Coloured) ancestry.

The Karoo is a semi desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is also not precisely defined. The Karoo is partly defined by its topography, geology and climate, and above all, its low rainfall, arid air, cloudless skies, and extremes of heat and cold. The Karoo also hosted a well-preserved ecosystem hundreds of million years ago which is now represented by many fossils.

In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both physical and biological features. A species' habitat is those places where it can find food, shelter, protection and mates for reproduction.

Larval host plants

Metrioxena apparently feed only on Arenga sugar palms (Arecaceae). Larvae, though little is known about them, are probably eating the wood of dead or dying trees, while the adults eat pollen. The Paleogene fossil Metrioxena electrica was found in conifer amber from the Baltic region, where palms are known to have grown some 50 million years ago.^[1]

Arenga is a genus of palms, native to Southeast Asia, southern China, New Guinea, and northern Australia. They are small to medium-sized palms, growing to 2–20 m tall, with pinnate leaves 2–12 m long. Arenga palms can grow in areas with little sunlight and relatively infertile soil.

Sugar palm is a common name for several species of palms used to produce sugar.

The Arecaceae are a botanical family of perennial plants. Their growth form can be climbers, shrubs, trees and stemless plants, all commonly known as palms. Those having a tree form are colloquially called palm trees. They are flowering plants, a family in the monocot order Arecales. Currently 181 genera with around 2600 species are known, most of them restricted to tropical and subtropical climates. Most palms are distinguished by their large, compound, evergreen leaves, known as fronds, arranged at the top of an unbranched stem. However, palms exhibit an enormous diversity in physical characteristics and inhabit nearly every type of habitat within their range, from rainforests to deserts.

The South African species seem to be dependent on the Knysna-Amatole montane forests biome. Very little is known about their host plants. The first specimen of Afrocorynus asparagi was found on "wild asparagus" but this seems a most unlikely host plant for Belidae; in any case it has never again been found on an Asparagus species but only on Putterlickia pyracantha (Celastraceae). Hispodes spicatus has not been recorded from any other plant than Rhoicissus tridentata (Vitaceae). And though the Knysna-Amatole montane forests hold the conifers Podocarpus and African cypress (Widdringtonia), which seem plausible host plants considering what other Belidae feed on, the Rosidae P. pyracantha and R. tridentata actually grown in shrubby habitat interspersed with the actual montane forest. It may be that H. spicatus larvae feed - atypically for the family - on flower buds, as they have not been found in immature fruits which, apart from wood, are the other known food-type of Belidae larvae. More probably, they feed on the decaying wood like most of their relatives.^[1]

The Knysna-Amatole montane forests ecoregion, of the Tropical and subtropical moist broadleaf forests Biome, is in South Africa. It covers an Afromontane area of 3,100 square kilometres (1,200 sq mi) in South Africa's Eastern Cape and Western Cape provinces.

Biome Distinct biological communities that have formed in response to a shared physical climate

A biome is a community of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.

Asparagus, or garden asparagus, folk name sparrow grass, scientific name Asparagus officinalis, is a perennial flowering plant species in the genus Asparagus. Its young shoots are used as a spring vegetable.

Presumably, the original host plants of belid larvae were conifers, namely Araucariaceae. From there the Metrioxenini shifted to palms. The African lineages might have host-shifted to the Rosidae shrubs directly (from conifers) or indirectly (via palms, which used to occur in their present range but eventually disappeared). This issue could be resolved by checking whether the Pondoland Palm (Jubaeopsis caffra), the only survivor from the original palmtree flora of Southern Africa, is host to a metrioxenine.^[1]

Systematics and evolution

The three currently recognized living genera of Metrioxenini are occasionally assigned to subtribes, that seem almost superfluous, as it seems that the presently monotypic Metrioxenina simply represent a more basal lineage and the Afrocorynina ( Afrocorynus and Hispodes ) a more advanced one. But the relationship among the genera is not resolved with complete certainty. Indeed, Metrioxena was sometimes placed in the Oxycoryninae and the Afrocorynina elevated to full tribe status, but this seems to be in error. It is possible that Metrioxena iwill eventually be split up into several genera (e.g. Prometrioxena).Hispodes on the other hand is occasionally separated in a subtribe of Hispodini, which Marvaldi and co-writers 2006 find to be an unwarranted arrangement, since it would render all subtribes monotypic and thus redundant.^[1]

The fossil record shows that the Metrioxenini were well distinct by the mid-Paleogene, about 50 million years ago (mya). The belids as a whole are of Jurassic origin,^[2] and the Metrioxenini must thus have evolved in the Late Cretaceous or perhaps Paleocene, roughly some 100-60 mya.^[1]

There are three fossil species of Metrioxenini known to date: Paltorhynchus bisulcatus of the Early Eocene Green River Formation and "Paltorhynchus" narwhal from the latest Eocene or earliest Oligocene of the Florissant Fossil Beds are both from North America. If the latter species actually belongs in the modern genus Metrioxena , since it is the type species of Paltorhynchus , that name would become a junior synonym of Metrioxena and a new genus would have to be established for the more primitive "P." bisulcatus. That species might represent another genus of the Metrioxenina or a still more basal member of the tribe. Metrioxena electrica known from Baltic amber and of comparable age to the North American fossils, is sometimes separated in Archimetrioxena.^[1]

Footnotes

1 2 3 4 5 6 7 8 9 10 11 Marvaldi et al. (2006)
↑ Ming et al. (2006)

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References

Marvaldi, A.E.; Oberprieler, R.G.; Lyal, C.H.C.; Bradbury, T. & Anderson, R.S. (2006): Phylogeny of the Oxycoryninae sensu lato (Coleoptera: Belidae) and evolution of host-plant associations. Invertebrate Systematics20: 447–476. doi : 10.1071/IS05059 (HTML abstract)
Ming, Liu; Dong, Ren & Chungkun, Shi (2006): A new fossil weevil (Coleoptera, Curculionoidea, Belidae) from the Yixian Formation of western Liaoning, China. Progress in Natural Science16 (8): 885-888. doi : 10.1080/10020070612330084 (HTML abstract)

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[marvaldietal2006-1] 1 2 3 4 5 6 7 8 9 10 11 Marvaldi et al. (2006)

[2] Ming et al. (2006)