Here we compare the two evolutionary scenarios,
sympatric speciation and ecological specialization via reproductive interference, that have been proposed to explain the current niche partitioning between sibling lacewing species.
Ectatomma parasiticum might have evolved by
sympatric speciation from its host species in Apazapan, due to a previous evolution of E.
Host races in plant-feeding insects and their importance in
sympatric speciation. Phil.
However, mtDNA and allozyme evidence conflict over whether species pairs could have evolved within each lake after a single colonization (i.e., via
sympatric speciation) or are instead derived from two successive invasions of each lake (Taylor et al.
Branching is a form of "phenotypic speciation," and it could be a fundamental mechanism underlying
sympatric speciation. In sexual populations, however, recombination and segregation would lead to the constant production of phenotypes that are intermediate between the branches, which would prevent speciation.
This question has been chiefly raised in other systems with reference to
sympatric speciation (Diehl and Bush 1989, Grant and Grant 1989, Wilson 1989), which may be unlikely in the sticklebacks (Schluter and McPhail 1992, McPhail 1993).
Sympatric speciation is a process in which reproductive isolation between the incipient species evolves gradually in the absence of physical barriers to gene flow, that is, in a population that is initially panmictic or nearly panmictic.
If the current dearth of examples is an accurate reflection of nature, then
sympatric speciation via host shifts is an uncommon mode of divergence (Butlin 1987).
Other authorities (Mayr 1988; Carson 1989) maintain that all proposed cases of
sympatric speciation can be explained by allopatric models.
Trophic polymorphisms may, in addition, be especially useful in determining the ecological conditions under which
sympatric speciation might occur.
Under allopatric and parapatric speciation models only a subset of the mt-haplotype variation would be captured by the incipient species; an even smaller subset would be captured under stasipatric and
sympatric speciation models - although in the latter two models the effective population size for nuclear autosomes would also be reduced.