Semelparity and iteroparity are two contrasting reproductive strategies available to living organisms. A species is considered semelparous if it is characterized by a single reproductive episode before death, and iteroparous if it is characterized by multiple reproductive cycles over the course of its lifetime. Iteroparity can be further divided into continuous iteroparity (primates including humans and chimpanzees) and seasonal iteroparity (birds, dogs, etc.) Some
botanists
This is a list of botanists who have Wikipedia articles, in alphabetical order by surname. The List of botanists by author abbreviation is mostly a list of plant taxonomists because an author receives a standard abbreviation only when that auth ...
use the parallel terms
monocarpy
Monocarpic plants are those that flower and set seeds only once, and then die.
The term is derived from Greek (''mono'', "single" + ''karpos'', "fruit" or "grain"), and was first used by Alphonse de Candolle. Other terms with the same meaning are ...
and
polycarpy. (See also
plietesials
Plietesials are plants that grow for a number of years, flower gregariously (synchronously), set seed and then die.
The length of the cycle can vary between 8 and 16 years. For example, the neelakurinji plant flowers every 12 years and
bloomed ...
.)
In truly semelparous species, death after reproduction is part of an overall strategy that includes putting all available resources into maximizing reproduction, at the expense of future life (see
§ Trade-offs). In any iteroparous population there will be some individuals who die between their first and second reproductive episodes, but unless this is part of a syndrome of programmed death after reproduction, this would not be called semelparity.
This distinction is also related to the difference between
annual
Annual may refer to:
*Annual publication, periodical publications appearing regularly once per year
** Yearbook
** Literary annual
*Annual plant
*Annual report
*Annual giving
*Annual, Morocco, a settlement in northeastern Morocco
*Annuals (band), ...
and
perennial
A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...
plants. An annual is a plant that completes its life cycle in a single season, and is usually semelparous. Perennials live for more than one season and are usually (but not always) iteroparous.
Semelparity and iteroparity are not, strictly speaking, alternative strategies, but extremes along a continuum of possible modes of reproduction. Many organisms considered to be semelparous can, under certain conditions, separate their single bout of reproduction into two or more episodes.
Overview
Semelparity
![Oncorhynchus nerka 2](https://upload.wikimedia.org/wikipedia/commons/4/4b/Oncorhynchus_nerka_2.jpg)
The word semelparity was coined by evolutionary biologist Lamont Cole, and comes from the Latin ''semel'' 'once, a single time' and ''pario'' 'to beget'. This differs from iteroparity in that iteroparous species are able to have multiple reproductive cycles and therefore can mate more than once in their lifetime. Semelparity is also known as "big bang" reproduction, since the single reproductive event of semelparous organisms is usually large as well as fatal. A classic example of a semelparous organism is Pacific salmon (''
Oncorhynchus
''Oncorhynchus'' is a genus of fish in the family Salmonidae; it contains the Pacific salmon and Pacific trout. The name of the genus is derived from the Greek ὄγκος (ónkos, “lump, bend”) + ῥύγχος (rhúnkhos, “snout”), in r ...
'' spp.), which lives for many years in the ocean before swimming to the freshwater stream of its birth, spawning, and dying. Other semelparous animals include many insects, including some species of butterflies, cicadas, and
mayflies
Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order ...
, many
arachnids
Arachnida () is a Class (biology), class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, came ...
, and some molluscs such as some species of
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
and
octopus
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
.
Semelparity also occurs in
smelt
Smelt may refer to:
* Smelting, chemical process
* The common name of various fish:
** Smelt (fish), a family of small fish, Osmeridae
** Australian smelt in the family Retropinnidae and species ''Retropinna semoni''
** Big-scale sand smelt ''At ...
and
capelin
The capelin or caplin (''Mallotus villosus'') is a small forage fish of the smelt family found in the North Atlantic, North Pacific and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin ...
, but is very rare in vertebrates other than bony fish. In
amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...
s, it is known only among some ''
Hyla
''Hyla'' is a genus of frogs in the tree frog family Hylidae. As traditionally defined, it was a wastebasket genus with more than 300 species found in Europe, Asia, Africa, and across the Americas. After a major revision of the family most of th ...
'' frogs including the
gladiator frog; in reptiles only a few lizards such as
Labord's chameleon
Labord's chameleon (''Furcifer labordi'') is a semelparous species of chameleon, a lizard in the family Chamaeleonidae. The species is endemic to Madagascar.
Etymology
The specific name, ''labordi'', is in honor of French adventurer Jean Labo ...
of southwestern
Madagascar
Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...
, ''
Sceloporus bicanthalis
''Sceloporus bicanthalis'', the trans volcanic bunchgrass lizard, is a species of lizard in the family Phrynosomatidae, first described by Hobart Muir Smith as a subspecies of ''Sceloporus aeneus'' in 1937. It is endemic to Mexico. It was clas ...
'' of the high mountains of Mexico, and some species of ''
Ichnotropis'' from dry savanna areas of Africa.
Among mammals, it exists only in a few
didelphid and
dasyurid
The Dasyuridae are a family of marsupials native to Australia and New Guinea, including 71 extant species divided into 17 genera. Many are small and mouse-like or shrew-like, giving some of them the name marsupial mice or marsupial shrews, but th ...
marsupials.
Annual plants, including all grain crops and most domestic vegetables, are semelparous. Long-lived semelparous plants include century plant (
agave
''Agave'' (; ; ) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some ''Agave'' species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for ...
), ''
Lobelia telekii
''Lobelia telekii'' is a species of flowering plant in the family Campanulaceae, that is found only in the alpine zones of Mount Kenya, Mount Elgon, and the Aberdare Mountains of East Africa. It occurs at higher altitudes on well-drained slop ...
'', and some species of
bamboo
Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, bu ...
.
[
]
This form of lifestyle is consistent with
r-selected
In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individ ...
strategies as many offspring are produced and there is low parental input, as one or both parents die after mating. All of the male's energy is diverting into mating and the immune system is repressed. High levels of
corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...
s are sustained over long periods of time. This triggers immune and inflammatory system failure and
gastrointestinal hemorrhage
Gastrointestinal bleeding (GI bleed), also called gastrointestinal hemorrhage (GIB), is all forms of bleeding in the gastrointestinal tract, from the mouth to the rectum. When there is significant blood loss over a short time, symptoms may includ ...
, which eventually leads to death.
Iteroparity
![Sow with piglet](https://upload.wikimedia.org/wikipedia/commons/5/59/Sow_with_piglet.jpg)
The term iteroparity comes from the Latin ''itero'', to repeat, and ''pario'', to beget. An example of an iteroparous organism is a human—humans are biologically capable of having offspring many times over the course of their lives.
Iteroparous vertebrates include all birds, most reptiles, virtually all mammals, and most fish. Among invertebrates, most mollusca and many insects (for example, mosquitoes and cockroaches) are iteroparous. Most perennial plants are iteroparous.
Models
Trade-offs
It is a biological precept that within its lifetime an organism has a limited amount of energy/resources available to it, and must always partition it among various functions such as collecting food and finding a mate. Of relevance here is the trade-off between
fecundity
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...
, growth, and survivorship in its
life history strategy. These trade-offs come into play in the evolution of iteroparity and semelparity. It has been repeatedly demonstrated that semelparous species produce more offspring in their single fatal reproductive episode than do closely related iteroparous species in any one of theirs. However, the opportunity to reproduce more than once in a lifetime, and possibly with greater care for the development of offspring produced, can offset this strictly numerical benefit.
Models based on non-linear trade-offs
One class of models that tries to explain the differential evolution of semelparity and iteroparity examines the shape of the trade-off between offspring produced and offspring forgone. In
economic
An economy is an area of the Production (economics), production, Distribution (economics), distribution and trade, as well as Consumption (economics), consumption of Goods (economics), goods and Service (economics), services. In general, it is ...
terms, offspring produced is equivalent to a
benefit function, while offspring forgone is comparable to a
cost
In production, research, retail, and accounting, a cost is the value of money that has been used up to produce something or deliver a service, and hence is not available for use anymore. In business, the cost may be one of acquisition, in which ...
function. The reproductive effort of an organism—the proportion of energy that it puts into reproducing, as opposed to growth or survivorship—occurs at the point where the distance between offspring produced and offspring forgone is the greatest.
![reproductive effort iteroparous](https://upload.wikimedia.org/wikipedia/commons/1/11/Reproductive_effort_iteroparous.svg)
In some situations, the
marginal cost
In economics, the marginal cost is the change in the total cost that arises when the quantity produced is incremented, the cost of producing additional quantity. In some contexts, it refers to an increment of one unit of output, and in others it r ...
of offspring produced decreases over time (each additional offspring is less "expensive" than the average of all previous offspring) and the marginal cost of offspring forgone increases. In these cases, the organism only devotes a portion of its resources to reproduction and uses the rest for growth and survivorship so that it can reproduce again in the future.
In other situations, the marginal cost of offspring produced ''increases'' while the marginal cost of offspring forgone decreases. When this is the case, it is favorable for the organism to reproduce a single time. The individual devotes all of its resources to that one episode of reproduction, then dies as it has not reserved enough resources to meet its own ongoing survival needs.
Empirical, quantitative support for this mathematical mode is limited.
Bet-hedging models
A second set of models examines the possibility that iteroparity is a
hedge
A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoini ...
against unpredictable juvenile survivorship (avoiding putting all one's eggs in one basket). Again, mathematical models have not found empirical support from real-world systems. In fact, many semelparous species live in habitats characterized by high (not low) environmental unpredictability, such as deserts and early successional habitats.
Cole's paradox and demographic models
The models that have the strongest support from living systems are demographic. In Lamont Cole's classic 1954 paper, he came to the conclusion that:
For example, imagine two species—an iteroparous species that has annual litters averaging three offspring each, and a semelparous species that has one litter of four, and then dies. These two species have the same rate of population growth, which suggests that even a tiny fecundity advantage of one additional offspring would favor the evolution of semelparity. This is known as Cole's paradox.
In his analysis, Cole assumed that there was no mortality of individuals of the iteroparous species, even seedlings. Twenty years later, Charnov and Schaffer showed that reasonable differences in adult and juvenile mortality yield much more reasonable costs of semelparity, essentially solving Cole's paradox. An even more general demographic model was produced by Young.
These demographic models have been more successful than the other models when tested with real-world systems. It has been shown that semelparous species have higher expected adult mortality, making it more economical to put all reproductive effort into the first (and therefore final) reproductive episode.
Semelparity
Semelparity in mammals
In Dasyuridae
= Small Dasyuridae
=
![Phascogale calura close](https://upload.wikimedia.org/wikipedia/commons/a/ab/Phascogale_calura_close.jpg)
Semelparous species of
Dasyuridae
The Dasyuridae are a family of marsupials native to Australia and New Guinea, including 71 extant species divided into 17 genera. Many are small and mouse-like or shrew-like, giving some of them the name marsupial mice or marsupial shrews, but th ...
are typically small and carnivorous, with the exception of the northern quoll (''
Dasyurus hallucatus
The northern quoll (''Dasyurus hallucatus''), also known as the northern native cat, the North Australian native cat or the satanellus is a carnivorous marsupial native to Australia.
Taxonomy
The northern quoll is a member of the family Das ...
''), which is large. Species with this reproductive strategy include members of the genus ''
Antechinus,
Phascogale tapoatafa
The brush-tailed phascogale (''Phascogale tapoatafa''), also known by its Australian native name tuan, the common wambenger, the black-tailed mousesack or the black-tailed phascogale, is a rat-sized arboreal carnivorous marsupial of the family D ...
'' and ''
Phascogale culura''. The males of all three groups exhibit similar characteristics that classify them as semelparous. First, all of the males of each species disappear immediately after the mating season. Also, males that are captured and isolated from others live for 2 to 3 years.
If these captured males are allowed to mate, they die immediately after the mating season, like those in the wild. Their behaviour also changes drastically before and after the mating season. Before mating, males are extremely aggressive and will fight with other males if placed close together. Males that are captured before they are allowed to mate remain aggressive through the winter months. After the mating season, if allowed to mate, males become extremely lethargic and never regain their aggressiveness even if they survive to the next mating season.
Other changes that occur post-mating include fur degradation and testicular degeneration. During adolescence, male fur is thick and becomes dull and thin after mating, but regains its original condition if the individual manages to survive past the mating season. The fur on the scrotum completely falls off and does not grow back, even if the male survives months after the first mating season. As the marsupial ages, its testicles grow until they reach a peak size and weight at the beginning of the mating season. After the individual mates, the weight and size of the testes and scrotum decrease. They remain small and do not produce
spermatozoa
A spermatozoon (; also spelled spermatozoön; ; ) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote. (A zygote is a single cell, with a complete set of chromosomes, ...
later in life, if maintained in a laboratory.
The 1966 Woolley study on ''Antechinus spp.'' noticed that males were only able to be maintained past mating in the laboratory and no senile males were found in the wild, suggesting that all males die shortly after mating.
= Corticosteroid concentration and increased male mortality
=
![Antechinus stuartii](https://upload.wikimedia.org/wikipedia/commons/9/96/Antechinus_stuartii.jpg)
Studies on ''
Antechinus stuartii
The brown antechinus (''Antechinus stuartii''), also known as Stuart's antechinus and Macleay's marsupial mouse, is a species of small carnivorous marsupial of the family Dasyuridae. The males die after their first breeding season, and the speci ...
'' reveal that male mortality is highly correlated to stress and
andrenocortical activity. The study measured the
corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...
concentration in males in the wild, males injected with cortisol, males injected with saline, and females in the wild. While both males and females exhibit high levels of corticosteroid concentration in the wild, this proves fatal only to males due to females having a higher maximum high affinity corticosteroid binding capacity (MCBC).
Thus, free corticosteroid in the
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
of male ''A. stuartii'' rises sharply, while it remains constant in females. High levels of free corticosteroid, resulting from mating in wild males and injected cortisol in laboratory males, resulted in
stomach ulcers
Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines ...
,
gastrointestinal hemorrhaging, and
liver abscess
A liver abscess is a mass filled with pus inside the liver. Common causes are abdominal conditions such as appendicitis or diverticulitis due to haematogenous spread through the portal vein. It can also develop as a complication of a liver injury.
...
es, all of which increased mortality. These side effects were not found in the males that were injected with saline,
strengthening the hypothesis that high free corticosteroids results in higher mortality in male ''Dasyurids''. A similar study on ''Phascogale calura'' showed that similar
endocrine system
The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neu ...
changes happen in ''P. calura'' as ''A. stuartii''. This supports stress-induced mortality as a characteristic of small ''Dasyurid'' semelparity.
= Large Dasyuridae
=
![Dasyurus hallucatus -Queensland-8](https://upload.wikimedia.org/wikipedia/commons/c/c0/Dasyurus_hallucatus_-Queensland-8.jpg)
''
Dasyurus hallucatus
The northern quoll (''Dasyurus hallucatus''), also known as the northern native cat, the North Australian native cat or the satanellus is a carnivorous marsupial native to Australia.
Taxonomy
The northern quoll is a member of the family Das ...
'', the northern quoll, is a large dasyurid and exhibits increased male mortality after the mating season. Unlike smaller dasyurids, male die-off in ''D. hallucatus'' is not due to endocrine system changes and there was no
spermatogenic failure after the mating season ended.
If male ''D. hallucatus'' survive past their first mating season, they may be able to engage in a second mating season. While the individuals in a 2001 study mostly died from vehicles or predation, researchers found evidence of physiological degradation in males, similar to the physiological degradation in small dasyurids. This includes fur loss, parasite infestations, and weight loss. As the mating period went on, males became increasingly
anemic
Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
, but the anemia was not due to
ulcer
An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...
ation or gastrointestinal bleeding.
Lack of elevated cortisol levels during mating periods in ''D. hallucatus'' means that there is no current universal explanation for the mechanism behind increased male mortality in Dasyuridae. Post-reproductive
senescence
Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...
has also been proposed as an explanation.
In opossums
= Grey slender mouse opossum (''Marmosops incanus'')
=
![Flickr - ggallice - Mouse opossum](https://upload.wikimedia.org/wikipedia/commons/8/87/Flickr_-_ggallice_-_Mouse_opossum.jpg)
The
grey slender mouse opossum exhibits a semelparous reproductive strategy in both males and females. Males disappear from their
endemic area after the reproductive season (February–May). Males found months later (June–August) are of lighter body weight and the molar teeth are less worn down, suggesting these males belong to a different generation. There is a drop off in the female population, but during the months of July and August, evidence of a gap between generations like the male gap. There is also lower body weight and less molar wear observed in females found after August. This is further supported by the evidence that females that reproduce are not observed the following year.
[Lucia, Maria. "Annual age structure and reproductive patterns in Marmosa incana (Lund, 1841)(Didelphidae, Marsupialia)." (1994).] This species has been compared to a related species, ''
Marmosa robinsoni
Robinson's mouse opossum (''Marmosa robinsoni'') is a species of opossum in the family Didelphidae. It is found in Belize, Colombia, Ecuador, Grenada, Honduras, Panama, Peru, Trinidad and Tobago, and Venezuela.
Robinson's mouse opossums mov ...
'', in order to answer what would happen if a female that has reproduced were to survive to the next mating season. ''M. robinsoni'' has a
monoestrus reproductive cycle, like ''M. incanus'', and females are no longer fertile after 17 months so it is unlikely that females that survive past the drop off in female populations would be able to reproduce a second time.
= Other mouse opossums
=
''
Gracilinanus microtarsus
The Brazilian gracile opossum (''Gracilinanus microtarsus'') is a species of small opossum from Brazil.
Description
Brazilian gracile opossums are relatively small opossums, with males ranging from and females from in head-body length. The tai ...
'', or the Brazilian gracile opossum, is considered to be partially semelparous because male mortality increases significantly after the mating season, but some males survive to mate again in the next reproductive cycle. The males also exhibit similar physiological degradation demonstrated in ''Antechinus'' and other semelparous
marsupial
Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
s such as fur loss and increase of infection from parasites.
Semelparity in fish
Pacific salmon
Highly elevated cortisol levels mediate the post-spawning death of semelparous ''
Oncorhynchus
''Oncorhynchus'' is a genus of fish in the family Salmonidae; it contains the Pacific salmon and Pacific trout. The name of the genus is derived from the Greek ὄγκος (ónkos, “lump, bend”) + ῥύγχος (rhúnkhos, “snout”), in r ...
'' Pacific salmon by causing tissue degeneration, suppressing the immune system, and impairing various homeostatic mechanisms. After swimming for such a long distance, salmon expend all of their energy on reproduction. One of the key factors in salmon rapid
senescence
Senescence () or biological aging is the gradual deterioration of functional characteristics in living organisms. The word ''senescence'' can refer to either cellular senescence or to senescence of the whole organism. Organismal senescence inv ...
is that these fish do not feed during reproduction so body weight is extremely reduced. In addition to physiological degradation, pacific salmon become more lethargic as mating goes on, which makes some individuals more susceptible to predation because they have less energy to avoid predators. This also increases mortality rates of adults post-mating.
Semelparity in insects
![Gypsy Moth (35955436354)](https://upload.wikimedia.org/wikipedia/commons/3/33/Gypsy_Moth_%2835955436354%29.jpg)
Traditionally, semelparity was usually defined within the time frame of a year. Critics of this criterion note that this scale is inappropriate in discussing patterns of insect reproduction because many insects breed more than once within one annual period, but generation times of less than one year. Under the traditional definition, insects are considered semelparous as a consequence of time scale rather than the distribution of reproductive effort over their adult life span.
In order to resolve this inconsistency, Fritz ''et al.'' define semelparous insects as "Insects that lay a single
clutch of eggs in their lifetime and deposit them at one place are clearly semelparous or big bang reproducers. Their entire reproductive effort is committed at one time and they die shortly after
oviposition
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typical ...
".
Semelparous insects are found in
Lepidoptera
Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...
,
Ephemeroptera,
Dermaptera
Earwigs make up the insect order Dermaptera. With about 2,000 species in 12 families, they are one of the smaller insect orders. Earwigs have characteristic cerci, a pair of forcep-like pincers on their abdomen, and membranous wings folded ...
,
Plecoptera,
Strepsiptera
The Strepsiptera are an order of insects with eleven extant families that include about 600 described species. They are endoparasites in other insects, such as bees, wasps, leafhoppers, silverfish, and cockroaches. Females of most species never ...
,
Trichoptera
The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the b ...
, and
Hemiptera
Hemiptera (; ) is an order (biology), order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, Reduviidae, assassin bugs, Cimex, bed bugs, and shield bugs. ...
.
Examples in Lepidoptera
Females of certain families of Lepidoptera, like the
Gypsy Moth
''Lymantria dispar'', also known as the gypsy moth or the spongy moth, is a species of moth in the family Erebidae. ''Lymantria dispar'' is subdivided into several subspecies, with subspecies such as ''L. d. dispar'' and ''L. d. japonica'' bei ...
of ''
Psychidae
The Psychidae (bagworm moths, also simply bagworms or bagmoths) are a family of the Lepidoptera ( butterflies and moths). The bagworm family is fairly small, with about 1,350 species described. Bagworm species are found globally, with some, ...
,'' have reduced mobility or
apterous
Aptery is the anatomical condition of an animal completely lacking any kind of wings. An animal with this condition is said to be apterous.
Most animal species belong to and are phylogenetic descendants of apterous taxa. These groups are said to ...
so the insects' dispersal is in the larval stage, as opposed to in the adult stage. In iteroparous insects, major dispersal occurs in the adult stage. All semelparous Lepidopterans share similar characteristics: Larva only feed in restricted periods of the year because of the nutritional state of their host plants (as a result, they are
univoltine
Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism.
...
), initial food supply is predictably abundant, and larval host plants are abundant and adjacent.
Death most commonly occurs by starvation. In the case of the gypsy moth, adults do not possess an active digestive system and cannot feed, but can drink moisture. Mating occurs fairly rapidly after adults emerge from their
pupa
A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their ...
l form and, without a way to digest food, the adult moths die after about a week.
Evolutionary advantages to semelparity
Current evolutionary advantages hypothesis
![Agile Antechinus (Antechinus agilis) showing offspring inside](https://upload.wikimedia.org/wikipedia/commons/0/07/Agile_Antechinus_%28Antechinus_agilis%29_showing_offspring_inside.jpg)
The evolution for semelparity in both sexes has occurred many times in plants, invertebrates, and fish. It is rare in mammals because mammals have obligate maternal care due to
internal fertilization
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inter ...
and incubation of offspring and nursing young after birth, which requires high maternal survival rate after fertilization and offspring
weaning
Weaning is the process of gradually introducing an infant human or another mammal to what will be its adult diet while withdrawing the supply of its mother's milk.
The process takes place only in mammals, as only mammals produce milk. The infan ...
. Also, female mammals have relatively low reproductive rates compared to invertebrates or fish because they invest a lot of energy in maternal care. However, male reproductive rate is much less constrained in mammals because only females bear young. A male that dies after one mating season can still produce a large number of offspring if he invests all of his energy in mating with many females.
Evolution in mammals
Scientists have hypothesized that natural selection has allowed semelparity to evolve in Dasyuridae and Didelphidae because of certain ecological constraints. Female mammals ancestral to these groups may have shortened their mating period to coincide with peak prey abundance. Because this window is so small, the females of these species exhibit a reproduction pattern where the
estrous
The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous p ...
of all females occurs simultaneously. Selection would then favor aggressive males due to increased competition between males for access to females. Since the mating period is so short, it is more beneficial for males to expend all their energy on mating, even more so if they are unlikely to survive to the next mating season.
Evolution in fish
![Dead salmon in spawning season](https://upload.wikimedia.org/wikipedia/commons/5/50/Dead_salmon_in_spawning_season.jpg)
Reproduction is costly for
anadromous
Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousan ...
salmonids
Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whit ...
because their life history requires transition from saltwater to freshwater streams and long migrations, which can be physiologically taxing. The transition between cold oceanic water to warm freshwater and steep elevation changes in Northern Pacific rivers could explain the evolution of semelparity because it would be extremely difficult to return to the ocean. A noticeable difference between semelparous fish and iteroparous salmonids is that egg size varies between the two types of reproductive strategies. Studies show that egg size is also affected by migration and body size. Egg number, however, shows little variation between semelparous and iteroparous populations or between resident and anadromous populations for females of the same body size. The current hypothesis behind this reason is that iteroparous species reduce the size of their eggs in order to improve the mother's chances of survival, since she invests less energy in gamete formation. Semelparous species do not expect to live past one mating season, so females invest a lot more energy in gamete formation resulting in large eggs. Anadromous salmonids may also have evolved semelparity to boost the nutrition density of the
spawning grounds
A spawning bed is an underwater solid surface on which fish spawn to reproduce themselves.
In fishery management, a spawning bed is an artificial bed constructed by wildlife professionals in order to improve the ability of desired game fish to r ...
. The most productive Pacific salmon spawning grounds contain the most carcasses of spawned adults. The dead bodies of the adult salmon decompose and provide nitrogen and phosphorus for
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
to grow in the nutrient-poor water.
Zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
then feed on the algae, and newly hatched salmon feed on the zooplankton.
Evolution in insects
![Earwig guarding eggs](https://upload.wikimedia.org/wikipedia/commons/8/8c/Earwig_guarding_eggs.jpg)
An interesting trait has evolved in semelparous insects, especially in those that have evolved from
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
ancestors, like in all subsocial and
eusocial
Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
aculeate
Aculeata is a subclade of Hymenoptera containing ants, bees, and stinging wasps. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger. However, many members of the group cannot ...
Hymenoptera
Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
. This is because larvae are morphologically specialized for development within a host's innards and thus are entirely helpless outside of that environment. Females would need to invest a lot of energy in protecting their eggs and hatched offspring. They do this through such behaviours as egg guarding. Mothers that actively defend offspring, for example, risk injury or death by doing so.
This is not beneficial in an iteroparous species because the female risks dying and not reaching her full reproductive potential by not being able to reproduce in all reproductive periods in her lifetime. Since semelparous insects only live for one reproductive cycle, they can afford to expend energy on maternal care because those offspring are her only offspring. An iteroparous insect does not need to expend energy on the eggs of one mating period because it is likely that she will mate again. There is ongoing research in maternal care in semelparous insects from lineages not descended from parasites to further understand this relationship between semelparity and maternal care.
See also
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References
Further reading
(peer-reviewed) Nature Education Knowledge entry on Semelparity*De Wreede, R.E, and T. Klinger. Reproductive strategies in algae. pp. 267–276 in: Plant Reproductive Ecology: Patterns and Strategies. J.L Lovett-Doust & L.L Lovett-Doust (eds). Oxford University Press.
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*{{cite journal , last1 = Ranta , first1 = E. , last2 = Tesar , first2 = D. , last3 = Kaitala , first3 = V. , year = 2002 , title = Environmental variability and semelparity vs. iteroparity as life histories , journal = Journal of Theoretical Biology , volume = 217 , issue = 3, pages = 391–398 , doi=10.1006/jtbi.2002.3029, pmid = 12270282 , bibcode = 2002JThBi.217..391R
Reproduction