Bombyx mandarina
Encyclopedia
Bombyx mandarina, the Wild Silkmoth, is an insect from the moth
family
Bombycidae
. It is the closest relative of Bombyx mori
the Domesticated Silkmoth or "silkworm" (properly, this refers to the caterpillar
s only). Unlike the domesticated relative which is unable to fly or indeed persist outside human care, the Wild Silkmoth is a fairly ordinary lepidoptera
n. Its main difference from the domesticated taxon
is the more slender body with well-developed wings in males, and the dull greyish-brown color.
Bombyx, the true or mulberry silkmoths. The origin of the Domesticated Silkmoth is enigmatic. It has been suggested that it is the survivor of an extinct species
which diverged from the ancestors of Bombyx mandarina millions of years ago. However, this is based on an untenable molecular clock
hypothesis that assumes that wild and domestic silkmoths evolve
d equally fast after their lineages diverged. Rather, the effects of artificial selection
have accelerated evolution in the domestic form to a point where it is hard to trace the origin of the numerous breeds of domestic silkworms even with the most modern molecular phylogeny
methods. (Yukuhiro et al. 2002)
It is not inconceivable that today's domestic silkworms are all descended from an initial stock of B. mandarina collected as late as 5000 years ago (Yoshitake 1968). While wild silk
could have been collected and used as threads etc., since much earlier, the technology to breed and utilize silkworms from a domesticated stock did not exist before the late Neolithic
.
However, it has been possible to trace the geographical origin of the domestic silkmoth. The wild species occurs over a considerable range from inland China
to Korea
and Japan
, and shows much (albeit subtle) variation. The populations from the northeastern end of the range
, for example, differ in karyotype
from those of inland China. Domestic silkmoths are closer to the latter regarding mtDNA sequence data, and especially lack some genetic apomorphies of the northeastern B. mandarina. Thus, it has been concluded that the initial domestic stock came from China. (Yukuhiro et al. 2002, Arunkumar et al. 2006)
Bombyx mandarina is able to hybridize with B. mori. Both in the wild and in a domesticated environment, females release pheromone
s and wait for males to be attracted and fly to them. However, B. mori males cannot fly. Hybridisation therefore inevitably means breeding between domestic (B. mori) females and wild (B. mandarina) males. Here it will be referred to as Bombyx Hybrid
.
Consequently, the two silkmoths have been united as subspecies
of a single species; in this case the name Bombyx mori which was published first applies for both. However, today it is usually recognized that the Domestic Silkmoth is entirely dependent on human care for its survival and thus has a level of reproductive isolation
from its wild relatives.
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Bombycidae
Bombycidae
Bombycidae is a family of moths. The best-known species is Bombyx mori or silkworm, native to northern China and domesticated for millennia...
. It is the closest relative of Bombyx mori
Bombyx mori
The silkworm is the larva or caterpillar of the domesticated silkmoth, Bombyx mori . It is an economically important insect, being a primary producer of silk...
the Domesticated Silkmoth or "silkworm" (properly, this refers to the caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s only). Unlike the domesticated relative which is unable to fly or indeed persist outside human care, the Wild Silkmoth is a fairly ordinary lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
n. Its main difference from the domesticated taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
is the more slender body with well-developed wings in males, and the dull greyish-brown color.
Phylogeny and systematics
Together, the two species constitute the genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Bombyx, the true or mulberry silkmoths. The origin of the Domesticated Silkmoth is enigmatic. It has been suggested that it is the survivor of an extinct species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
which diverged from the ancestors of Bombyx mandarina millions of years ago. However, this is based on an untenable molecular clock
Molecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
hypothesis that assumes that wild and domestic silkmoths evolve
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
d equally fast after their lineages diverged. Rather, the effects of artificial selection
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
have accelerated evolution in the domestic form to a point where it is hard to trace the origin of the numerous breeds of domestic silkworms even with the most modern molecular phylogeny
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
methods. (Yukuhiro et al. 2002)
It is not inconceivable that today's domestic silkworms are all descended from an initial stock of B. mandarina collected as late as 5000 years ago (Yoshitake 1968). While wild silk
Wild silk
Wild silks have been known and used in many countries from early times, although the scale of production is far smaller than that from cultivated silkworms.-Background:...
could have been collected and used as threads etc., since much earlier, the technology to breed and utilize silkworms from a domesticated stock did not exist before the late Neolithic
Neolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...
.
However, it has been possible to trace the geographical origin of the domestic silkmoth. The wild species occurs over a considerable range from inland China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
to Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and shows much (albeit subtle) variation. The populations from the northeastern end of the range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
, for example, differ in karyotype
Karyotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
from those of inland China. Domestic silkmoths are closer to the latter regarding mtDNA sequence data, and especially lack some genetic apomorphies of the northeastern B. mandarina. Thus, it has been concluded that the initial domestic stock came from China. (Yukuhiro et al. 2002, Arunkumar et al. 2006)
Bombyx mandarina is able to hybridize with B. mori. Both in the wild and in a domesticated environment, females release pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s and wait for males to be attracted and fly to them. However, B. mori males cannot fly. Hybridisation therefore inevitably means breeding between domestic (B. mori) females and wild (B. mandarina) males. Here it will be referred to as Bombyx Hybrid
Bombyx Hybrid
The Bombyx hybrid is a hybrid between a Bombyx mori female and a male Bombyx mandarina moth. They produce Silkworm larvae like all species of Bombyx. The larvae look a lot like the other variation, they are brown and the first half and gray at the bottom half, but they get larger black spots than...
.
Consequently, the two silkmoths have been united as subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
of a single species; in this case the name Bombyx mori which was published first applies for both. However, today it is usually recognized that the Domestic Silkmoth is entirely dependent on human care for its survival and thus has a level of reproductive isolation
Reproductive isolation
The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...
from its wild relatives.
External links
- Japanese moths: Bombyx mandarina. Contains many photos. Retrieved 2007-JUL-18.
- Copulation between female B. mandarina (left) and male B. mori in captivity. Note stunted wings of male. Retrieved 2007-JUL-18.
