*5.3. Biogeography*

Our divergence dating results show that Centrolenidae and Allophrynidae separated from each other 25–55 Mya, and centrolenids started to diversify about 25–41 Mya, which are slightly older ages than previous estimates [3]. The most recent estimate of divergence times found an age of ~45 Mya for the split between Centrolenidae and Allophrynidae [328]. The geographic origin of glassfrogs is placed, unambiguously, in South America, originating at mid-elevations or climatically similar habitats [3,28]. From there, glassfrogs have dispersed into Central America multiple times [2,3]. Notably, the lowland clades (e.g., *Hyalinobatrachium*, *Teratohyla*) have colonized Central America, whereas Andean clades with high levels of species richness (e.g., *Nymphargus*, *Centrolene*) are completely absent from Central America [3]. This is likely in part due to climatic-niche conservatism constraining centrolenids from dispersing to lowland regions from the Andes [3,28].

Even though glassfrog diversity thrives in the Andes (Figures 228 and 229), the specific ancestral biogeographic region of centrolenid origins is ambiguous [3]; what we do know, however, is that the most common recent ancestor inhabited mid-elevation mountains (1000–2000 m), and that lower and higher elevation habitats were colonized more recently [3,28]. Also, the Andes facilitated an explosion of species that is best explained by greater time (ancient cradle or montane museum hypothesis; or time-for-speciation e ffect more generally) rather than faster diversification at mid-elevations (montane species pump), despite the recently of the major Andean uplift [3,28,342]. At a broad scale, speciation within the Andes is produced, mainly, by a combination of landscape heterogeneity (e.g., with both longitudinal and transversal barriers) and climatic-niche conservatism in species [28]. There are several examples of niche conservatism at the generic level; most species of *Centrolene*, *Nymphargus*, *Celsiella*, and *Ikakogi* are restricted to mountains, whereas others such as *Hyalinobatrachium*, *Vitreorana*, and *Cochranella* are more prevalent in lowlands.

**Figure 228.** Elevational distribution of glassfrogs found on the Pacific lowlands and western slopes of the Ecuadorian Andes.

**Figure 229.** Elevational distribution of glassfrogs on the Amazonian lowlands and Amazonian slopes of the Ecuadorian Andes.

Glassfrogs have shown to be successful, in terms of species numbers, mostly in tropical montane areas (Figures 230 and 231). There is a clear reduction of species richness as latitude increases, with low temperature and low precipitation being the most likely limiting factors. These two variables also explain the absence (or near absence) of glassfrogs in dry or highly seasonal areas (Cerrado, Llanos, Chaco) and high-elevation regions within the tropics (e.g., Páramo; Figures 230–232).

In Ecuador, glassfrogs also reach their diversity peak in cloud and montane forests (Figure 232). They have a moderate species richness in the Choco and Amazonian Rainforest and are completely absent from xeric and dry areas of southwestern Ecuador, although they can be found in semideciduous

forests (Figure 232). Below, we describe the patterns and diversification mechanisms that are prevalent in Centrolenidae.

**Figure 230.** Biogeographical regions in the Neotropics (sensu Duellman [343]). Each region is followed by its number of glassfrog species. Note that one particular species can occur in more than one biogeographic area. Modified from Castroviejo-Fisher et al. [3].

**Figure 231.** Species richness of glassfrogs per biogeographic region in the Neotropics.

**Figure 232.** Species richness of glassfrogs per biogeographic region in Ecuador.
