Numerous subspecies of Telmatobius culeus have been described based on morphological differences (de la Riva et al 2000). High phenotypic plasticity makes morphological taxonomies unreliable, even when based on osteological characters (de la Riva et al 2010). The most recent analysis based on sequenced mtDNA places T. culeus as a sister taxon to T. marmoratus (de la Riva et al 2010). Although a phylogenetic study using morphometrics and allozyme data did support reciprocal monophyly of these groups (Benavides et al 2002), a different result was obtained by sequencing mitochondrial cytochrome b (Benavides 2005). Benavides (2005) failed to support monophyletic clades for T. marmoratus and T. culeus, and instead found support for separate riverine and lacustrine clades. These discrepancies may be resolved in the future by sequencing nuclear genes from a wider sample of T. culeus.
Phylogenetic studies have also addressed the degree of phenotypic plasticity in this species. Benavides et al. (2002) synonymized several of the subspecies of T. culeus. The implication of this work is that highly divergent ecotypes of T. culeus exist. These ecotypes show divergent resource use and morphology, indicating that the species has a high degree of phenotypic plasticity (especially in terms of body size) and niche polymorphism.
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