FILE: <bc-15.htm> Pooled References GENERAL INDEX [Navigate to MAIN MENU ]
PARTHENOGENESIS
In Arthropods
(Contacts)
---- Please CLICK on desired underlined categories [ to search for Subject Matter, depress
Ctrl/F ]:
[Please refer also to Related Research #1; #2 & Detailed Research ]
|
Overview The
production of animals from fertilized eggs has been called zygogenesis as distinguished from parthenogenesis which refers to the development of
an egg without fertilization. In
parthenogenesis eggs may develop in any of three ways: (1) they may begin as
tetraploid or diploid bodies which undergo reduction in chromosome number as
if in preparation for fertilization; but if fertilization is lacking, the
males developing from them have the reduced or haploid set of hereditary
factors; (2) unfertilized eggs may start as haploids and subsequently acquire
the diploid number of chromosomes in some stage of cleavage, or (3)
unfertilized eggs may start and end as diploids. In Hymenoptera diploids are
usually females, all normal males originate as haploids. There are some
exceptions, which will be discussed later. (Also see Gordh et al. 1999). The end
result of all parthenogenetic ontogeny (development) is a fatherless or impaternate animal. These, of course have grandfathers!
In Types 2 and 3 parthenogenesis above such animals are diploid. In Type 1 we
have impaternate haploids which pose several problems such as (a) their
survival with a reduced chromosome number, (b) sex determination and (c)
spermatogenesis in the haploid male. Except for
those haploid males regularly produced in six or seven groups of invertebrates,
there have been very few known haploid adult animals. On the other hand,
diploid and polyploid impaternates are known to occur with some frequency and
as independent events in most of the larger groups of Metazoa. Sex
determination in these larger Metazoan groups is entirely orthodox, while
that of haploid males involves an entirely different genetic mechanism.
Different kinds of animals combine different types of parthenogenesis with
bisexual reproduction in their life cycles in various complicated ways.
Parthenogenesis may be natural or it may be artificial, induced by
some artificial stimulus. It may be incomplete (rudimentary), the embryo
dying before maturity, or it may be complete, leading to viability as adults.
It may be obligatory, occurring from a type of egg that cannot normally be
fertilized, or it may be facultative if the egg can develop with or without
fertilization. Considering
the sex of the impaternate offspring, parthenogenesis includes arrhenotoky (production of impaternate males), thelytoky
(production of impaternate females) and deuterotoky (production of both sexes
parthenogenetically).
Parthenogenesis may be constant, occurring in each successive
generation, or it may be cyclic in which case one or more parthenogenetic
generations alternates with a bisexual. In cyclic parthenogenesis
(heterogony), the agamic (or parthenogenetic) generation consists almost
entirely of females. Individuals of the bisexual generation, both males and
gamic females, are impaternate.
Parthenogenesis may occur as a general condition throughout the range
of the species, or it may be geographic in which case the parthenogenetic
form occupies a different area from the bisexual. Males may be absent or rare
(spanandry) within the range of the parthenogenetic
form. There are two main cytological processes
involved in parthenogenesis, apomictic and automictic. In apomixis there is one maturation division in
the egg that is equational. There is no reduction in chromosomes so that the
diploid number is maintained. Apomixis is considered the simplest type of
parthenogenesis. Heterozygosity steadily increases in these species because
when gene mutations and structural rearrangements occur, the heterozygosity is
maintained in the following generation. Mutation cannot be homozygous and
elimination of recessive mutations is impossible. This continued increase in
heterozygosity allows for greater adaptiveness and dispersal through
heterosis (White 1954, Smith 1955, Suomalinen 1962). Apomixis is a common
name for uniparental procreation in which the sexual structures are retained
(Dobzhansky 1941). In automixis, the early stages of meiosis
are similar to biparental species in the production of a haploid oocyte
through reduction; however, a third division occurs resulting in a diploid.
This restoration of the diploid number is accomplished in different ways in
different species (Onions 1912, Whiting 1935, Speicher & Speicher 1938,
Flanders 1945, Doutt & Smith 1950, S. G. Smith 1955, Tucker 1958, Bacci
1965). Arrhenotoky
vs Thelytoky In arrhenotoky males are impaternate and
females paternate. This is the most common type of parthenogenesis found in
Hymenoptera. Actually female production is generally regarded as zygogenetic
and not parthenogenetic. Fertilized eggs result in diploid females, while
unfertilized eggs yield haploid males (Flanders 1939, White 1954, Bacci
1965). Several animal groups showing arrhenotoky are the Thysanoptera,
rotifers, Coleoptera (Micromalthus),
Acarina (all except the suborder Mesostigmata), Iceryini (cottony-cushion
scale), and the Aleurodidae. Thelytoky results in the production of
impaternate females. Males are rare and are considered usually nonfunctional in
reproduction, although in the laboratory they have been observed to function
(Legner 1969, Rossler &
DeBach 1972). Cytological processes may be either apomictic or automictic. Deuterotoky does not differ from thelytoky other than males are more
common. Some workers favor the elimination of this category entirely. By 1940 Clausen listed 30 or more genera of
parasitic Hymenoptera that were known with one or more species that
reproduced uniparentally
(by thelytoky). Today the number is much larger. Flanders (1945) regarded
any biparental (arrhenotokous) population to be capable of thelytokous
reproduction at times. He indicated the difficulties in distinguishing one
from the other. He observed that the Cynipidae showed bisexuality most often,
although the family usually reproduced unisexually. Speicher & Speicher
(1938) noted that uniparental females of Bracon
hebetor were obtained almost
entirely from biparental females that resulted from crossing certain strains. The difference between thelytoky and
deuterotoky is sometimes confusing. Some parasitoids that were initially
classified as thelytokous, have been found on detailed examination to produce
an occasional son, although such sons are though to be nonfunctional (White
1984), which may be based on insufficient evidence (Marchal 1936, Flanders
1942, Wilson & Woolcock 1960, Bowen & Stern 1966, Birova 1970, Eskafi
& Legner 1974, Laraichi 1978, Jardak et al. 1979, Stile & Davring
1980, Sorakina 1987). Males are often found in laboratory populations of
thelytokous species and their frequency usually depends on the temperature at
which their thelytokous mothers develop (Flanders 1942, Schlinger & Hall
1959, Flanders 1965, Eskafi & Legner 1974, Gordh & Lacey 1976,
Laraichi 1978, Jardak et al. 1979, Cabello & Vargas 1985, Sorakina 1987,
Luck et al. 1996). Exercise
15.1--Distinguish zygogenesis from parthenogenesis. Exercise
15.2--What are three possible fates of eggs in parthenogenesis? Exercise
15.3--Discuss different manifestations of parthenogenesis. Exercise
15.4--What principal cytological processes are involved in
parthenogenesis? Discuss each. Exercise
15.5--Distinguish arrhenotoky and thelytoky. REFERENCES: [Additional references may be found at
MELVYL Library ] Bacci,
G. 1965. Sex Determination. Pergamon Press. 306 p. Bellows,
T. S., Jr. & T. W. Fisher, (eds) 1999. Handbook of Biological Control:
Principles and Applications. Academic Press, San Diego, CA. 1046.p. Birova,
H. 1970. A contribution to the knowledge of the reproduction of Trichogramma embryophagum. Acta Ent. Bohemoslov. 67: 70-82. Bowen, W. R. & V. M. Stern. 1966.
Effect of temperature on the production of males and sexual mosaics in a
uniparental race of Trichogramma
semifumatum. Ann. Ent. Soc. Amer. 59: 823-34. Cabello, G. T. & P. P. Vargas. 1985.
Temperature as a factor influencing the form of reproduction of Trichogramma cordubensis. Z. angew. Ent. 100: 434-41. Clausen, C. P. 1940. Entomophagous
Insects. McGraw-Hill Book Co., Inc., New York & London. 688 p. Dobzhansky, T. 1941. Genetics
and the Origin of Species. 2nd
ed. Columbia Univ. Press, New York. Doutt,
R. L. & R. A. Smith. 1950. Males and intersexes in a normally thelytokous
insect, Tropidophryne melvillei Comp. Canad. Ent. 82: 165-70. Eskafi, F. M. & E. F. Legner. 1974.
parthenogenetic reproduction in Hexacola
sp. near websteri, a
parasite of Hippelates eye
gnats. Ann.
Ent. Soc. Amer. 67: 767-68. 264. Etzel, L. K. & E. F. Legner. 1999. Culture and Colonization. In: T. W. Fisher & T. S. Bellows, Jr.
(eds.), Chapter 15, p. 125-197, Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, CA 1046 p. Flanders, S. E. 1942. The
sex-ratio in the Hymenoptera: a function of the environment. Ecology 23:
120-21. Flanders,
S. E. 1945. Uniparentalism in the Hymenoptera and its relation to polyploidy.
Science 100(2591): 168-69. Gordh,
G. & L. Lacey. 1976. Biological studies of Plagiomerus diaspidis,
a primary internal parasite of diaspidid scale insects. Proc. Ent. Soc. Wash.
78: 132-44. 265. Gordh, G., E. F. Legner & L. E.
Caltagirone. 1999. Biology of parasitic Hymenoptera. In: T. W. Fisher & T. S. Bellows, Jr.
(eds.), Chapter 15, p. 355-381, Handbook
of Biological Control: Principles and
Applications. Academic Press, San
Diego, CA 1046 p. Jardak, T., B. Pintureau & J.
Voegele. 1979.
Mise en evidence d'une nouvelle espece de Trichogramma.
Phenomene
d'intersexualite, etude enzymatique. Ann. Soc. Ent. France 15: 635-42. Laraichi, M. 1978. L'effect de hautes
temperatures sur le taux sexuel de Ooencyrtus
fecundus (Hym: Encyrtidae). Ent.
Exp. Appl. 23: 237-42. 58.
Legner, E. F. 1969. Reproductive isolation and size variation
in the Muscidifurax raptor Girault & Sanders
complex. Ann. Entomol. Soc. Amer.
62(2): 382-385. 255. Legner, E. F. 1991b. Recombinant
males in the parasitic wasp Muscidifurax
raptorellus [Hymenoptera: Pteromalidae]. Entomophaga 36(2): 173-81. Luck,
R. F., L. Nunney & R. Stouthamer. 1996. Evolutionary Ecology of
Parasitoids and Invertebrate Predators, Chapter 9, In: Theories & Mechanisms of Biological Control.
University of California Press, Berkeley. (in press). Marchal,
P. 1936. Recherches
sur la biologie et le developpement des Hymenopteres parasites. Les
Trichogrammes. Ann.
Ephiphytes 2: 447-50. Onion,
G. W. 1912. South African fertile worker bees. Agr. J. Union S. Africa 3:
720-28. Onion,
G. W. 1914. South African fertile worker bees. Agr. J. Union S. Africa 7:
44-46. Rössler, Y & P. DeBach. 1972.
The biosystematic relations between a thelytokous and an arrhenotokous form
of Aphytis mytilaspidis (LeBarron)
([Hymenoptera: Aphelinidae]. I. The reproductive relations. Entomophaga 17: 391-423. Schlinger, E. I. & J. C. Hall. 1959. A
synopsis of the biologies of three imported parasites of the spotted alfalfa
aphid. J.
Econ. Ent. 52: 154-57. Slobodchikoff,
C. N. & H. V. Daly. 1971. Systematic and evolutionary implications of
parthenogenesis in the Hymenoptera. Amer. Zool. 11: 273-82. Sorakina,
A. P. 1987. Biological and morphological substantiation of the specific
distinctness of Trichogramma
telengai spp. Ent. Rev. 66:
20-34. Smith,
S. G. 1955. Cytogenetics of obligatory parthenogenesis. Canad. Ent. 87: 131-35. Speicher, K. G. & B. R. Speicher. 1938.
Diploids from unfertilized eggs in Habrobracon.
Biol. Bull. 74: 247-52. Stille,
B. & L. Davring. 1980. Meiosis and reproductive strategy in the
parthenogenetic gall wasp Diplolepis
rosae. Heredity 92: 353-62. Suomalinen,
E. 1962. Significance of parthenogenesis in the evolution of insects. Ann.
Rev. Ent. 7: 349-66. Tucker,
K. W. 1958. Automictic parthenogenesis in the honey bee. Genetics 43:
299-316. White,
M. J. D. 1954. Animal Cytology and Evolution. 2nd. ed. Cambridge Univ. Press,
Cambridge. 454 p. White,
M. J. D. 1984. Chromosomal mechanisms in animal reproduction. Bull. Zool. 51:
1-23. Whiting, P. W. 1935. Sex determination in bees and wasps. J.
Heredity 26: 263-78. |