Site author Richard Steane
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Sympatric speciation

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Sympatric speciation differs from allopatric speciation in that: In fact it is the concept of reproductive isolation that is key to this form of speciation. Specifically this refers to sexual reproduction, which involves genetic interchange and generates variation.

For example, animals may need particular courtship behaviour before they will mate, or may have specifically shaped sexual organs. So an animal with different markings or making different mating calls than usual will not find a partner, but there may be exceptions to this!

Plants need to be in flower at the same time. However plants may reproduce asexually and effectively exist in isolation for years.

There are several possible categories of reproductive isolation:
Temporal: different breeding seasons/feeding times
Behavioural: different courtship displays / different niches /habitats / feeding areas
Mechanical: mismatch in reproductive parts
Gamete incompatibility: sperm killed in female’s reproductive tract
Post fertilisation factors: Hybrid inviability / hybrid infertility

Different species may reproduce together and produce offspring which are unable to breed - usually as a result of incompatibility in chromosome numbers. This is clearly an evolutionary dead end.

Plants may get round this problem as a result of a fortuitous change. Polyploidy - increase in chromosome number - allows cross fertilisation with other polyploids, (and prevents it with the parental types) and so it can give rise to a new species in a very short time-frame. See below

In fact many plant species have been shown to have multiple sets of chromosomes (tetraploid, hexaploid, etc), presumably as a result of this process, and the consequent gene duplication may contribute to greater genetic diversity. Several crop plants of economic significance to Man have resulted from polyploidy, and been selected as a result of increased vigour. Wheat and several members of the Brassicaceae (cabbage 'family') are examples.

Not quite a new species

Examples of sympatric speciation in animals are rare.

Rhagoletis_on_apple (208K)
This is Rhagoletis pomonella, the apple maggot fly - on an apple
Rhagoletis_on_haw (63K) This is Rhagoletis pomonella, the apple maggot fly- but on a haw
In America Rhagoletis pomonella, the apple maggot fly, originally fed on and its larval stage lived within fruits of hawthorn which is also a member of the Rosaceae. However soon after apple trees were introduced - apparently in about 1800 - some of these flies laid eggs on and lived in apple fruits.
There are now two separate races of Rhagoletis pomonella: the apple race sticks to infesting apples, and the hawthorn race still prefers the original hawthorn.

Christmas cactus and Easter cactus

220px-Distribution_of_Schlumbergera (24K) These plants originate from south-eastern Brazil. They grow in high altitude moist tropical rainforest, mostly as epiphytes (on other plants - moss-covered tree branches) or as lithophytes, (on or in rock crevices in small pockets of substrate formed from decayed leaves and other vegetation).

Their stems have have a flattened form and are green and leafless, as they act as photosynthetic organs. They have a distinctive tubular floral structure with red or pinkish tepals (petals and sepals not being distinguished). They are specialised for pollination by hummingbirds.

There are 6 species within the main Genus Schlumbergera and it has been a popular housplant. In cultivation (in Europe) hybrids have been formed, with intermediate forms. These fall into 4 main categories. Schlumbergera × buckleyi is a hybrid between S. russelliana and S. truncata , first produced in 1852
The easter cactus, aka whitsun cactus, Hatiora gaertneri, used to be classified as Schlumbergera but was moved into a separate genus based on differences in floral structure.

christmas-cactus-2-300x244 (10K)
This is the Christmas Cactus Schlumbergera truncata

Easter_cactus_plant (16K) This is the Easter cactus Hatiora gaertneri
The different species must have evolved from a common ancestor. As a result of a mutation, some plants acquired either a new gene or an alternative allele of an existing gene which gave it the ability to flower at a different time. Possibly the earlier ones were pollinated by a different species of hummingbird, perhaps one which bred earlier.
Then because these species did not interbreed with the other as a consequence of different flowering time, each species had a separate gene pool. There are minor differences in flower colour and shape, as well as growth habit and shape of stem segments.

Spartina cordgrass

Spartina is a genus of plants in the grass family, found in coastal salt marshes at many places around the world. Its photosynthesis uses C4 carbon fixation which may be more efficient than the normal C3 version and this allows it to resist conditions of water stress.
Spartima maritima (16K) Spartina maritima, the small cordgrass
Spartina-alterniflora (175K)
Spartina alterniflora, smooth cordgrass, showing its growth habit along the edges of a saltmarsh creek

In Southampton water (UK) in about 1870 the native species Spartina maritima (S. stricta) hybridised with the introduced American species Spartina alterniflora (possibly originally introduced in ships' ballast water).

The resulting plants were given the name Spartina × townsendii. These plants were infertile, and could not cross with either parent. However they could reproduce asexually and established a colony that is still visible today near Hythe.

It was found that in about 1890 (some of) the hybrid had doubled its chromosome number, possibly as a result of problems in cell division, with the result that a new ('allotetraploid') species Spartina anglica had been formed. This is fertile, as each chromosome can pair with the extra copy of itself when undergoing meiosis to produce gametes. Spartina anglica can set seed and has established itself naturally at several locations along the coast. It has also been introduced by Man at various sites around the world, mostly in schemes to stabilise coastland against tidal erosion.

Spartina anglica is much more vigorous than the parental types and has developed into an invasive species in several parts of the world. It grows densely and does not support much invertebrate life, nor does it lend itself as a habitat to wildfowl.

Spartina alterniflora has hybridised with other species of Spartina and has been studied extensively to determine the genetic basis for its competitiveness. It has been found that its genome has been significantly epigenetically modified by methylation.

A recent discovery

Monkeyflowers is the name given to a number of plant species which are quite popular garden flowers. They used to be placed in the genus Mimulus, but they have been reclassified into the genus Erythranthe. They mostly originate from North America, but several ('escaped') populations have become established in the United Kingdom, mainly in Northern England and Scotland.

2012_06_30_MimulusXrobertsii_MelHardy_ThorpeCloud_Dovedale_IMG_6156_EMSp0 (123K) This is a colony of hybrid monkeyflower Erythranthe × robertsii growing alongside a stream in Dovedale, Derbyshire
Erythranthe_peregrina (9K) This is the flower of Erythranthe peregrina

In 2011 a new species was recorded (although it might have formed in the last 140 years): Erythranthe peregrina originated from E. × robertsii, a sterile hybrid between E. guttata and E. lutea.

Palms of Lord Howe Island

220px-Lord_Howe_Island (8K) Lord Howe Island (600km east of western Australia, and 1880 km north west of New Zealand North Island) has a subtropical climate. This island - with an area of 14.55 km2 - formed 6.9 million years ago as a result of volcanic activity. It has two raised rocky peaks, the remnants of a volcano crater, and well vegetated lower ground.

Four species of palm tree are endemic to it.
These include two closely related species : Howea forsteriana and H. belmoreana - also known as Kentia palms - which have been studied and found to result from sympatric speciation.

Howea_forsteriana (67K) Howea forsteriana (Kentia Palm or Thatch palm) - up to 10 m tall by 6 m wide. Its fronds can reach 3 m long
220px-Howea-belmoreana (37K) Howea belmoreana (Belmore sentry palm) - canopy 2–3 m in diameter, containing roughly 36 leaves.

These have evolved from a common ancestor, which presumably must have originated from another island. The initial colonisation may have resulted from a seed washed up on the beach which germinated and grew into a mature tree, and was self-fertile and so could reproduce sexually. This could then give rise to a number of similar but genetically variable palm trees along the shoreline. Seed dispersal by animals (birds?) or weather action would extend the distribution inland.

It is conceivable that a gene/allele causing later flowering could have occurred as a result of a mutation. Several examples of epistatic late-flowering genes are known in well-studied plants such as Arabidopsis thaliana.

There are areas of the island with different soil types and microclimates and it has been suggested that these differences could act as drivers of parapatric speciation..
Plants growing on calcareous sandy soils - derived from weathered corals - in the lower regions of the island are more likely to experience shortage of certain minerals whereas those growing on richer basaltic soils resulting from volcanic lava flows of the higher regions do not suffer from this disadvantage. This tends to favour earlier flowering on the lower parts of the island, whereas the plants growing in higher regions can grow more steadily and flower later. As late-flowering plants are at a disadvantage in the lower regions, and early-flowering plants are not at an advantage in the higher regions, a form of disruptive natural selection takes place.

Although both species do exist alongside one another in places, H. forsteriana is more common in the lowland which has sandy calcareous soil. It flowers six or seven weeks earlier than H. belmoreana which is quite abundant at higher elevations (up to 450 metres) where the soil is neutral/acidic. Numerically there are more specimens of H. belmoreana on the island, competing with a variety of other plants in the inland forest, and more young plants, so the popuation has not yet climaxed.

These palms are wind pollinated and produce large amounts of pollen at different times of the year, which causes genetic isolation, so that allele frequencies can be expected to differ in the two populations. The two species differ in height and the shape of their leaf fronds, H. forsteriana being more droopy and H. belmoreana more upturned.
A few examples of hybrids between the two Howea species exist, but it is not known if they set seed.

These palm trees have been exported to other parts of the world and have been quite popular horticulturally in Europe - originally in Palm Courts of Victorian and Georgian hotels, and commercial plantations have been established on other islands e.g. Norfolk Island. They are also popular as smaller plants in modern houses. In previous times, their seeds/fruit were used as a food by passing sailors.

Pipistrelle bats - cryptic species

pipistrelle (111K) soprano (113K) Pipistrelles are the most common species of bats in the UK. They are also the smallest. In 1999 it was discovered that there are in fact two species. The Common Pipistrelle Pipistrellus pipistrellus emits its main echolocation calls at 45kHz, and the Soprano Pipistrelle Pipistrellus pygmaeus uses a higher frequency: 55kHz. Their other vital statistics seem to be fairly similar, though. Perhaps Sopranos have a more pointed nose and a more uniform light brown colour. Some (bat people) even say that they smell different!

For reference, the range of frequencies heard by the human ear is often given as 20Hz-20kHz, although as we get older the top frequency falls - perhaps to 10 kHz (a loss of one octave - the sort of notes given by a triangle).

Soprano Pipistrelles gather in larger numbers (hundreds) in maternity roosts in the Summer, but Common Pipistrelles' maternity roosts average about 75.

Male bats defend territories around mating roosts and they make "songflights" around them, presumably 'singing' in different keys.

In fact both species are fairly widespread in Europe although Soprano Pipistrelles tend to favour more wetland habitats, for example over lakes and rivers, and also around woodland edges, although they are not found in northern Scotland.

There is clearly no real geographical isolation between the two species and the two separate gene pools appear to be maintained by behavioural differences.

However studies in Poland suggest that both pipistrelle species are more migratory in central Europe than those in the UK - especially P. pygmaeus - and interspecific hybridization is fairly common.

In one investigation the standard deviation of repeated echolocation frequencies recorded from individual bats was <2kHz.

What is the significance of that finding?

> not much variation, so not likely to overlap with the other form, so the difference is significant.

Other related topics on this site

(also accessible from the drop-down menu above)

Similar level
Allopatric speciation - A different evolutionary process?
Evolution processes - General principles
Species and taxonomy - Putting a name to to a species

Web references

Schlumbergera From Wikipedia, the free encyclopedia

Hatiora gaertneri From Wikipedia, the free encyclopedia

Why is my Christmas Cactus blooming in March?

Sympatric speciation in palms on an oceanic island Letter to Nature

How sympatric is speciation in the Howea palms of Lord Howe Island? - might be described as parapatric

Evidence for sympatric speciation Studies bolster empirical evidence for speciation without geographical barriers, but some experts remain unconvinced - more doubts about cichlid fish

Lord Howe Island From Wikipedia, the free encyclopedia

Howea forsteriana From Wikipedia, the free encyclopedia

Howea forsteriana - great pictures

Evolution in Spartina (Gramineae) I. The history and morphology of the Genus in Britain by C. J. Marchant originally from Journal of the Linnean Society of London, Botany

Hybridization, polyploidy and speciation in Spartina (Poaceae)

Extent and degree of hybridization between exotic (Spartina alterniflora) and native (S. foliosa) cordgrass (Poaceae) in California, USA determined by random amplified polymorphic DNA (RAPDs).

Spartina anglica Joint Nature Conservation Committee

Origin and genetic diversity of Spartina anglica (Poaceae) using nuclear DNA markers.

Erythranthe peregrina From Wikipedia, the free encyclopedia

Mimulus peregrinus (Phrymaceae): A new British allopolyploid species

Hybrid monkeyflower Mimulus × robertsi

UK Bats The Bat Conservation Trust is 'the leading non-governmental organisation in the United Kingdom solely devoted to the conservation of bats and the landscapes on which they rely'.

Bimodal echolocation in pipistrelle bats: are cryptic species present? 1993 paper

Population genetics study of common (Pipistrellus pipistrellus) and soprano (Pipistrellus pygmaeus) pipistrelle bats from central Europe suggests interspecific hybridization

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