Calling frogs usually are on vegetation adjacent to or overhanging streams; some calling males of P. spinipollex were on rocks in or by streams. Clasping pairs of P. euthysanota and P. schmidtorum were observed on vegetation by streams. Despite intensive search, no eggs were found. It is doubtful if Ptychohyla deposit eggs on vegetation overhanging streams, as do centrolenids and Phyllomedusa, for egg-clutches of these frogs are easily found. Possibly the eggs are laid separately on vegetation above the stream, in which case they could be overlooked easily. In streams where Ptychohyla and other hylid tadpoles occur, empty egg capsules have been found on the lee sides of rocks, but there is no way to determine which species laid the eggs.
Numbers of eggs were counted in gravid females; the largest eggs have diameters ranging from 2.5 to 3.0 mm. The smaller species, comprising the Ptychohyla schmidtorum group, have fewer eggs than do the larger species. Numbers of eggs found in females of the various species are: P. euthysanota euthysanota, 108; P. euthysanota macrotympanum, 136, 160; P. leonhardschultzei, 141; P. spinipollex, 119, 134, 143; P. schmidtorum schmidtorum, 59, 61, 90; P. schmidtorum chamulae, 60, 71, 89.
Duration of the larval stage is unknown. Metamorphosing young have been found from May through August. From two to six completely metamorphosed young are available for each of the species, except for P. ignicolor of which none is available. The smallest young frog is a P. euthysanota having a snout-vent length of 14.2 mm.; the largest young frog is a P. schmidtorum schmidtorum having a snout-vent length of 17.0 mm.
PHYLOGENY OF PTYCHOHYLA
The preceding data on morphology, life histories, and behavior form the basis for the following interpretation of the phylogeny of Ptychohyla. Additional data are needed to support some of the ideas discussed below; many of the data that are available for Ptychohyla are lacking for other, possibly related, hylids. The family Hylidae is composed of several hundred species, and most of the species are poorly known. Consequently, any attempt to place Ptychohyla in the over-all scheme of hylid phylogeny would be premature at this time. But, as between the five species of two species-groups here recognized as constituting the genus Ptychohyla, some estimate of relationships can be made. First, it is necessary to determine the validity of the genus itself.
Ptychohyla as a Natural Assemblage
As stated in the diagnosis of the genus, the only character that sets this group of species apart from other hylids is the presence of ventrolateral glands in the breeding males. To many systematists the thought of being able to identify to genus only breeding males is sufficiently disturbing to cause them to view with disfavor the recognition of the genus. Nonetheless, the question is raised: Do the five species herein placed in the genus Ptychohyla constitute a natural assemblage? If the genus is considered to be more than a category of convenience, that is to say, a group of related species having a common origin, the primary problem is to determine whether or not the five species form a phylogenetic unit.
The species of Ptychohyla are divided into two groups on the basis of external morphology, breeding calls, and tadpoles. The Ptychohyla euthysanota group seems to be a natural group composed of three species, all of which are more closely related to one another than to any other hylid. Likewise, the species comprising the Ptychohyla schmidtorum group seem to represent a natural unit. If the presence of ventrolateral glands in breeding males is ignored, a student of salientian systematics might derive the Ptychohyla euthysanota group from a hylid stock containing Hyla miotympanum and Hyla mixomaculata. Likewise, Ptychohyla schmidtorum could be placed with Hyla uranochroa and related species in Costa Rica. Nonetheless, the fact remains that all of the species assigned to the genus Ptychohyla have ventrolateral glands in the breeding males; furthermore, ventrolateral glands are unknown in other hylids. If the P. schmidtorum group and the P. euthysanota group each evolved from separate hylid stocks, then the ventrolateral glands must have developed independently in both groups. That ventrolateral glands developed independently in five species of frogs in southern México and northern Central America and not in any of the other approximately 500 species of hylids in the world is untenable. It is more logical to assume that the development of the glands took place only once in a stock of hylids that gave rise to the five species herein recognized as members of the genus Ptychohyla.