Heterochrony in Growth and Development in Anurans from the Chaco of South America

Abstract

Heterochrony refers to those permutations in timing of differentiation events, and those changes in rates of growth and development through which morphological changes and novelties originate during phyletic evolution. This research analyzes morphological variation during the ontogeny of 18 different anuran species that inhabit semiarid environments of the Chaco in South America. I use field data, collection samples, and anatomical methods to compare larval growth, and sequences of ontogenetic events. Most species present a similar pattern of larval development, with a size at metamorphosis related to the duration of larval period, and disappearance and transformations of larval features that occur in a short period between forelimb emergence and tail loss. Among these 18 species, Pseudis paradoxa has giant tadpole and long larval development that are the results of deviations of rates of growth. In this species events of differentiation that usually occur at postmetamorphic stages have an offset when tail is still present. Tadpoles of Lepidobatrachus spp. reach large sizes at metamorphosis by accelerate developmental rates and exhibit an early onset of metamorphic features. The uniqueness of the ontogeny of Lepidobatrachus indicates that evolution of anuran larval development may occasionally involve mid-metamorphic morphologies conserving a free feeding tadpole and reduction of the morphological-ecological differences between tadpoles and adults.

The Development ofDermatonotus muelleri(Anura: Microhylidae: Gastrophryninae)

“…6F-J). This fact is different from other anurans in which the metamorphic lengthening of the infrarostrals contributes to form up to the 30% of the adult cartilaginous jaw (Fabrezi, 2011: fig. 6).…”

“…Disappearance of Larval Traits.-Among the larval structures that disappear are the oral structures, vent tube, spiracle, and tail; these structures have been described in other studies (e.g., Gosner, 1960;Duellman and Trueb, 1986;Fabrezi, 2011). Herein, we focus on the lateral line system.…”

“…The period between stages 41 and 46 corresponds to metamorphic climax and at a maximum, lasts 3 days. By stage 37, tadpoles have attained their metamorphic snout-vent size; this seems to distinguish larvae of D. muelleri from other Type-IV tadpoles in which the snout-vent size increases until the forelimbs emerge (Hall et al, 1997;Quinzio et al, 2006;Fabrezi, 2011). Larval somatic growth and metamorphic development seem to parallel each other in most anurans; thus, one might expect that any negative external factor (e.g., diet, temperature, competence, and predation) might affect the rate of development and modify somatic growth or vice versa (Wilbur and Collins, 1973).…”

“…During the development of Dermatonotus muelleri, as well as that of H. boliviana (de Sá and Trueb, 1991), transformations of larval jaws reflect a low developmental rate in which the offset of the palatoquadrate/infrarostal-Meckel's cartilages lengthening at the end of metamorphosis exhibits the condition that most anurans reach at the middle of metamorphosis (stage 44) (Fabrezi, 2011). Paedomorphic features of cartilaginous jaws impact the development of the associated bones that are either reduced (e.g.…”

“…Within this context, the developmental sequences in D. muelleri, as well as that of other anurans, such as Pseudis spp. (Fabrezi et al, , 2010Fabrezi, 2011), ceratophryines (Fabrezi and Quinzio, 2008;Fabrezi, 2011), and Sphaenorhynchus bromelicola (Bokermann, 1974), suggest that the onset of metamorphic changes varies and is not fixed as might be inferred from standard anuran developmental tables. However, the end of larval development is marked by the complete loss of the tail, an ontogenetic event in which changes in larval developmental modules undergo integration with those of the adult stages to converge in the unique adult body plan that seems to be independent with larval growth.…”