Non-feeding and feeding tadpoles in hemiphractine frogs: larval head morphology, heterochrony, and systematics of Flectonotus goeldii (Amphibia: Anura: Hylidae)

Abstract

The Hemiphractinae (Hylidae) is group of neotropical egg-brooding frogs. It comprises species with different larval life history strategies. The larvae of Flectonotus hatch in an advanced stage of development. They are free-living but non-feeding. The putative sister taxon Gastrotheca includes species with feeding and free-living larvae, and others that undergo direct development. This study gives the first description of the skull of premetamorphic Flectonotus goeldii. Results are compared to the skulls of free-living Gastrotheca larvae. Some of the differences between the skulls can be explained as structural reductions of the larval feeding system in F. goeldii, due to the non-feeding mode of life: small and shallow branchial basket: simple ceratobranchialia; absence of branchial food traps, filter rows, ciliary cushions; only two open gill clefts; some branchial muscles weakly developed or missing. Many cranial structures appear to stop their differentiation and growth precociously in F. goeldii, compared to Gastrotheca: lack of commissura quadratoorbiialis anterior; short cornu trabeculae; persisting fenestrae parietales; and crista parotica without pronounced processus. The simplified feeding apparatus and the retarded features of the neurocranium can be accounted for by a heterochronic truncation of the larval developmental program in F. goeldii. Despite many structural differences, larvae of F. goeldii and Gastrotheca also share cranial features: similar eihmoidal region: lack of processus oticus; high cartilago orbitalis; intermediate suspensorium; large processus pterygoideus; copula anterior absent; musculus levator mandibulae externus and m. branchiohyoideus externus missing; m. levator mandibulae anterior lateralis not functionally differentiated before metamorphosis: ramus mandibularis (N.V) perforates m. levator mandibulae subexternus: rostral end of cornu trabeculae not conspicuously projecting laterally beyond cartilago labialis superior; and lateral rim of palatoquadrate curved dorsally and smooth. However, none of these shared character states is unique to the two taxa. They are also found in larvae of some other species of the Hylidae and Hyloidea and are probably symplesiomorphic for Gastrotheca and Flectonotus.