Reproductive coevolution in Ficus

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The genus Ficus is composed of 800 species of vines, shrubs, and trees, defined by their syconiums, the fruit-like vessels that either hold female flowers or pollen on the inside. In addition to being cultivated by humans for thousands of years, Ficus is also known for their reproductive mutualism with the fig wasp. [1]

Contents

A common fig exposing its many tiny matured, seed-bearing gynoecia. These are pollinated by the fig wasp, Blastophaga psenes. In the cultivated fig, there are also asexual mutants. Ficus plant.jpg
A common fig exposing its many tiny matured, seed-bearing gynoecia. These are pollinated by the fig wasp, Blastophaga psenes . In the cultivated fig, there are also asexual mutants.

Fig trees either produce hermaphrodite fruit known as caprifigs, or female figs; only the female figs are palatable to humans. In exchange for a safe place for their eggs and larvae, fig wasps help pollinate the ficus by crawling inside the tiny hole in the apex of the fig, called the ostiole, without knowing whether they crawled into a caprifig or a fig. If the female wasp crawls into the caprifig, she can successfully lay her eggs and die. The males hatch first, mate with the females, dig tunnels out of the caprifig, and die. The females, now covered in fig pollen from the caprifig, fly out to begin the cycle again. If the female wasp crawls into a female fig, she will not be able to successfully lay her eggs despite pollinating the fig with pollen from the caprifig she hatched in. The fig will absorb her body and her eggs as the fruit develops. [2]

History

Aristotle noted in Historia animalium that wild figs contain psenes that begin as grubs, but whose skin splits allowing the psen to fly out. The psen flies into a cultivated fig, and stops it from falling. He noted further that Greek farmers planted wild figs next to cultivated figs, and tied wild fig fruits on to the cultivated trees. [3]

Mechanisms and outcomes

Overall, the coevolution of Ficus and wasps features Ficus being very specific as a host, combined with the tendency of the wasp species to frequent plant species different from that of their specific Ficus host.

Ficus domination in mutualism

Ficus typically control the reproductive mutualism with fig wasps by being highly selective in their choice of pollinator. [4] This high host specificity is proven by the low pollinator sharing ratios found in fig pollinators, especially in the wasp genera Ceratosolen and Kradibia . [5] Contributing to the evolution of Ficus, pollinator specificity in Ficus is a pre-zygotic mechanism of reproductive isolation, in other words, the fig can control which pollen it gets by physically controlling which wasps pollinate it. Morphologically, one way the fig can specify the pollinator it wants includes the diameters of ostioles compared to the head widths of the respective wasp species. While the fig species F. wassa have a diameter of 1.0-1.5 mm, its pollinator K. wassae had an average head width of 0.58 mm. [5]

Pollinator sharing

Mutualism between figs and their wasps is not always strictly one on one: in Neotropical monoecious Ficus (among a few examples with the genus Ficus alone), different plant species may share the same species of pollinator wasp, and in a number of Ficus species, a few species of wasps are able to pollinate the figs (to various degrees) of a single fig species. [5]

Clearly, sharing of pollinators could allow interspecific hybrids to occur more easily, which would threaten the integrity of specific species of both plant or wasp, or allow new species to develop from the hybrids. [5] Hybridization does not appear to have played a major role in the evolution of fig and pollinator lineages, based on a maximum likelihood test. [6]

Sharing of pollinators has implications for the evolutionary history of the fig-wasp mutualism, because this means specific wasps may have switched hosts, perhaps to new fig species rather unrelated to the original host species -this, along with possible hybridisation, can thus mean that the phylogenies of the figs and their wasp pollinators do not strictly correspond one on one. [5] Due to this shifting of hosts, wasp species which share the same fig species as hosts may not be sister species, but quite unrelated. [6] The process whereby pollinating wasps switch fig host species, known as a host switch, has been identified as an important process in leading to coevolutionary patterns in a community of strangler figs and pollinating wasps in Panama. [7]

Another possibility is the evolution of cheating. Where a single fig species is able to use multiple wasp species to pollinate itself, and some wasp species may be better at this than others, a certain wasp species may not need to end up evolving to become a better pollinator, as opposed to simply using the fig as a brood chamber. Wasp species which share the same fig species compete for resources. Where wasp species may visit numerous hosts, if one fig species evolves to be a better host, the wasp may shift hosts, rendering its other shared fig hosts incidentally visited, and thus improperly pollinated, and the wasp a 'cheat' when it visits them. [6]

Cospeciation

Cospeciation, where the evolution of one of a pair (or more) of species is influenced by the evolution of the other of the pair, appears to have occurred in the history of the Ficus-wasp mutualism, despite some significant differences in the fig and pollinator phylogenies. [6]

Related Research Articles

<i>Ficus</i> Genus of flowering plants in the mulberry family Moraceae

Ficus is a genus of about 850 species of woody trees, shrubs, vines, epiphytes and hemiepiphytes in the family Moraceae. Collectively known as fig trees or figs, they are native throughout the tropics with a few species extending into the semi-warm temperate zone. The common fig (F. carica) is a temperate species native to southwest Asia and the Mediterranean region, which has been widely cultivated from ancient times for its fruit, also referred to as figs. The fruit of most other species are also edible though they are usually of only local economic importance or eaten as bushfood. However, they are extremely important food resources for wildlife. Figs are also of considerable cultural importance throughout the tropics, both as objects of worship and for their many practical uses.

<span class="mw-page-title-main">Fig wasp</span> Group of mostly pollinating insects whose larvae live in figs.

Fig wasps are wasps of the superfamily Chalcidoidea which spend their larval stage inside figs. Most are pollinators but others simply feed off the plant. The non-pollinators belong to several groups within the superfamily Chalcidoidea, while the pollinators are in the family Agaonidae. While pollinating fig wasps are gall-makers, the remaining types either make their own galls or usurp the galls of other fig wasps; reports of their being parasitoids are considered dubious.

<span class="mw-page-title-main">Coevolution</span> Two or more species influencing each others evolution

In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well as gene-culture coevolution.

<i>Ficus macrophylla</i> Species of banyan tree

Ficus macrophylla, commonly known as the Moreton Bay fig or Australian banyan, is a large evergreen banyan tree of the family Moraceae native to eastern Australia, from the Wide Bay–Burnett region in the north to the Illawarra in New South Wales, as well as Lord Howe Island. Its common name is derived from Moreton Bay in Queensland, Australia. It is best known for its imposing buttress roots.

<i>Ficus rubiginosa</i> Species of flowering plant in the family Moraceaea native to eastern Australia

Ficus rubiginosa, the rusty fig or Port Jackson fig, is a species of flowering plant native to eastern Australia in the genus Ficus. Beginning as a seedling that grows on other plants (hemiepiphyte) or rocks (lithophyte), F. rubiginosa matures into a tree 30 m (100 ft) high and nearly as wide with a yellow-brown buttressed trunk. The leaves are oval and glossy green and measure from 4 to 19.3 cm long and 1.25 to 13.2 cm wide.

<span class="mw-page-title-main">Agaonidae</span> Family of wasps

The family Agaonidae is a group of pollinating and nonpollinating fig wasps. They spend their larval stage inside the fruits of figs. The pollinating wasps are the mutualistic partners of the fig trees. The non-pollinating fig wasps are parasitoids. Extinct forms from the Eocene and Miocene are nearly identical to modern forms, suggesting that the niche has been stable over geologic time.

<span class="mw-page-title-main">Syconium</span> Technical name for a type of plant fruit

Syconium is the type of inflorescence borne by figs, formed by an enlarged, fleshy, hollow receptacle with multiple ovaries on the inside surface. In essence, it is really a fleshy stem with a number of flowers, so it is considered both a multiple and accessory fruit.

<i>Ficus aurea</i> Species of strangler fig

Ficus aurea, commonly known as the Florida strangler fig, golden fig, or higuerón, is a tree in the family Moraceae that is native to the U.S. state of Florida, the northern and western Caribbean, southern Mexico and Central America south to Panama. The specific epithet aurea was applied by English botanist Thomas Nuttall who described the species in 1846.

Ficus maxima is a fig tree which is native to Mexico, Central America, the Caribbean and South America south to Paraguay. Figs belong to the family Moraceae. The specific epithet maxima was coined by Scottish botanist Philip Miller in 1768; Miller's name was applied to this species in the Flora of Jamaica, but it was later determined that Miller's description was actually of the species now known as Ficus aurea. To avoid confusion, Cornelis Berg proposed that the name should be conserved for this species. Berg's proposal was accepted in 2005.

<i>Ficus insipida</i> Species of fig tree from the Neotropics

Ficus insipida is a common tropical tree in the fig genus of the family Moraceae growing in forest habitats along rivers. It ranges from Mexico to northern South America.

<i>Ficus americana</i> Species of fig tree native to the Neotropics

Ficus americana, commonly known as the West Indian laurel fig or Jamaican cherry fig, is a tree in the family Moraceae which is native to the Caribbean, Mexico in the north, through Central and South America south to southern Brazil. It is an introduced species in Florida, USA. The species is variable; the five recognised subspecies were previously placed in a large number of other species.

<i>Ficus pleurocarpa</i> Species of epiphyte

Ficus pleurocarpa, commonly known as the banana fig, karpe fig or gabi fig, is a fig that is endemic to the wet tropical rainforests of northeastern Queensland, Australia. It has characteristic ribbed orange and red cylindrical syconia. It begins life as a hemiepiphyte, later becoming a tree up to 25 m (82 ft) tall. F. pleurocarpa is one of the few figs known to be pollinated by more than one species of fig wasp.

<i>Ficus watkinsiana</i> Species of epiphyte

Ficus watkinsiana, commonly known as strangler fig, Watkins' fig, nipple fig or the green-leaved Moreton Bay fig is a hemiepiphytic fig that is endemic to Australia. The species exists in three populations—one in northeast Queensland and the others in southeast Queensland and northeast New South Wales. It also has been introduced to Kauai island (Hawaiʻi).

<i>Ficus obliqua</i> A tree, the small-leaved fig

Ficus obliqua, commonly known as the small-leaved fig, is a tree in the family Moraceae, native to eastern Australia, New Guinea, eastern Indonesia to Sulawesi and islands in the southwestern Pacific Ocean. Previously known for many years as Ficus eugenioides, it is a banyan of the genus Ficus, which contains around 750 species worldwide in warm climates, including the edible fig. Beginning life as a seedling, which grows on other plants (epiphyte) or on rocks (lithophyte), F. obliqua can grow to 60 m (200 ft) high and nearly as wide with a pale grey buttressed trunk, and glossy green leaves.

<span class="mw-page-title-main">Fig</span> Species of flowering plant known as the common fig

The fig is the edible fruit of Ficus carica, a species of small tree in the flowering plant family Moraceae. Native to the Mediterranean and western Asia, it has been cultivated since ancient times and is now widely grown throughout the world, both for its fruit and as an ornamental plant. Ficus carica is the type species of the genus Ficus, containing over 800 tropical and subtropical plant species.

<i>Ficus septica</i> Species of fig

Ficus septica is a shrub or tree of the family Moraceae living at low altitudes from northeast India to north Australia (Queensland), and throughout Malesia. It lives on the edge of the vegetation, often in degraded environments. The seeds of this species are dispersed by numerous species, including fruit bats (Megachiroptera) when present.

<i>Blastophaga psenes</i> Species of wasp

Blastophaga psenes is a wasp species in the genus Blastophaga. It pollinates the common fig Ficus carica and the closely related Ficus palmata. Without a colony or nest, these wasps breed in figs and the adults live for only a few days or weeks. They locate the fig they wish to pollinate through olfactory senses.

<i>Ceratosolen</i> Genus of wasps

Ceratosolen is an Old World wasp genus in the family Agaonidae. They are pollinators of the monoecious fig subsections Sycomorus and Sycocarpus, and the section Neomorphe, all belonging to the subgenus Sycomorus. The genus is native to the Palearctic, Afrotropical, Indomalayan and Australasian realms.

<i>Ficus amplissima</i> Species of fig tree

Ficus amplissima, also known as the Indian Bat tree, Indian Bat fig, Pimpri, Pipri (Piparee), Pipali or Bilibasari mara is a tree species of flowering plants that belongs to Moraceae, the fig or mulberry family. It is native to Central and southern Peninsular India, Sri Lanka and Maldives, having a significant distribution throughout Western Ghats of India. It is most commonly planted to provide shade in coffee plantations due to its dense and wide foliage. The ripened figs attract many birds, especially during the spring.

A tree in the Moraceae family, Ficus bernaysii is found from New Guinea to the Solomon Islands, growing in lowland rainforest. It is dioecious, and grows cauliflorous fruit. It is fed on by a wide range of animals.

References

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  3. Aristotle. Historia animalium. p. 557b25.
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