preferences of _elaeochroa_ and
_staufferi_ depend on the climatic changes that took place during the
Pleistocene. On this basis it may be proposed that when the original
prototype broke up into the two incipient species, the _staufferi_
stock became physiologically and behaviorally adapted to subhumid
conditions and dispersed into dry areas of the lowlands of Middle
America. The tropical evergreen forests on the Caribbean side of lower
Central America and the uplift of the Talamanca range in the Pliocene
were barriers to the dispersal of _staufferi_. Consequently, this frog
dispersed along the Pacific lowlands.

At the present time _staufferi_ occupies the length of the Pacific
lowlands in Central America, except in the rainforest of the Golfo Duce
region, which apparently is a relict stand and now separates the ranges
of two subspecies of _Hyla staufferi_. This species crossed the central
Nicaraguan lowlands and reached the Caribbean lowlands of Nicaragua and
nuclear Central America. The species migrated through the subhumid
corridor in northern Honduras and eastern Guatemala (Comayagua Valley
in Honduras and the Motagua Valley of Guatemala) to the Isthmus of
Tehuantepec. Duellman (1960) hypothesized "that during the times of
glacial advances (Pleistocene) the lowlands of the Isthmus probably
were more extensive and had more semiarid tropical environments than at
the present" and that when semiarid environments were continuous from
the Pacific slope across the isthmus to the Gulf lowlands _staufferi_
and other amphibians migrated northward to southeastern Tamaulipas,
Mexico.

_Hyla elaeochroa_ dispersed along Caribbean lowland routes. This
species not only occurs in the wet forests of the Golfo Dulce region
but also in Guanacaste. It is possible that _elaeochroa_ entered
Guanacaste and moved to the Golfo Dulce region when the intervening
area was less xeric than now (Duellman, 1966b). _Hyla elaeochroa_
extended its range to eastern Nicaragua, but even though northeastern
Nicaragua has over 2,000 mm. of precipitation annually (Vivo Escoto,
1964), this species has not spread into Honduras and Guatemala.

_Hyla boulengeri_ is widespread in Amazonian and northern South
America, whereas _foliamorta_ occurs only in eastern Panama and in
north-central Colombia. The ancestral _boulengeri-foliamorta_ stock
probably invaded Central America in the late Pliocene and dispersed
through humid forested environments to Nicaragua.