Which of the following is an example of an event that could lead to sympatric speciation?

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.

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.

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

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.

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

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.

Which of the following can lead to sympatric speciation?

What are the two examples of sympatric speciation?

Which is an example of sympatric speciation quizlet?

Which of the events can result in sympatric speciation quizlet?