Revision of Passiflora Subgenus Decaloba ... - Passion Flowers

159
There are two primary types of speciation: allopatric or geographic speciation,
and sympatric speciation. The allopatric model of speciation requires the
geographic isolation of two populations to prevent gene flow and divergence.
Sympatric speciation can occur without geographic separation, but some type of
strong barrier to gene flow is still necessary.
By and large, the species of supersection Cieca are not sympatric. Where the
ranges of two or more species do overlap, the plants are found growing at
different elevations or in different habitats. Passiflora tridactylites, a Galapagos
endemic, seems to be a good example of the peripheral isolation model of
speciation. It seems likely that the progenitor of Passiflora tridactylites originally
arrived on the Galapagos Islands from Ecuador by long distance dispersal and
began to diverge morphologically, in response to new environmental pressures.
The species is very similar to populations of P. suberosa ssp. litoralis both in the
Galapagos and in other areas of western South America, and P. tridactylites
cannot be separated from that entity base upon vegetative morphology alone.
However, the reproductive morphology of these taxa is very different, likely
resulting from a shift in pollinators (see discussion under “Pollination Biology”).
This neospecies has spread to many islands of the Galapagos and occurs in dry
lowland areas, but P. suberosa ssp. litoralis is found in more mesic habitats both
there and on the mainland of South America. Thus, P. tridactylites has
developed a divergent ecological amplitude that has allowed it to invade novel
habitats and exploit a different spectrum of pollinators. It is seems likely that
other members of the supersection fit this model as well.