Postnatal development of franciscana's (Pontoporia blainvillei) biosonar relevant structures with potential implications for function, life history, and bycatch

Abstract

Franciscana dolphins (Pontoporia blainvillei) are the most endangered species of the western South Atlantic Ocean. The major cause of their vulnerability is incidental bycatch in fishery gill nets. Ontogenetic changes of biosonar relevant structures in Pontoporia were analyzed in five specimens (one female neonate, two male neonates and two male adults) using digital imaging technology (MRI, CT) and macroscopic dissections to compare structures involved in sound production and reception. These data were compared to an ontogenetic series of 69 macerated skulls of Pontoporia in order to elucidate the correlation between soft tissue structures and bones of the epicranial complex and to describe the development‐related changes in the mandible. Postnatal developmental shape changes of the posterior part of the right vestibular air sac followed bone formation and the melon with its right branch elongated, paralleling the flatter facial depression of adults. Minor postnatal developmental modifications were verified in the tympano‐periotic complex but a shape change of the mandible was visible by a ventral deviation of the posterior part of the mandible in adults. These results reveal postnatal changes in allometry and shape of biosonar relevant structures that may be one of the causes that increase bycatch of neonate and young Pontoporia individuals.

Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications

“…Rauschmann et al () noted that the nasal area of perinatal Stenella attenuata is similar to that of adults in terms of structure, and del Castillo et al (, in press) observed a development of premaxillae and external nares in P. blainvillei and C. commersonii . In addition, Frainer et al () found that the sound generating structures and auditory sense of P. blainvillei might already be functional at birth. Thus, the observed trends suggest that the development of the external nares and the posterior portion of the premaxilla are common features among odontocetes, probably associated with the early development of breathing and sound production apparatuses, albeit they have a continuous postnatal maturation (Rauschmann et al, ; Cozzi et al, ).…”

Towards understanding the ontogeny of echolocation in franciscana dolphins (Pontoporia blainvillei)

“…Once the sound arrives at the melon, this structure would be responsible for focusing the sound energy (Norris and Harvey 1974, Harper et al 2008, McKenna et al 2012. Recent findings by Frainer et al (2015) show that the vestibular air sac is less developed in neonates of franciscana dolphin, such that it does not cover the dorsal area of the melon. This result may explain the broader bandwidth of the acoustic signals (probably accompanied by wider beam, even though this hypothesis should be tested) emitted by the neonate of franciscana dolphin analyzed in this study.…”

Franciscana dolphin (Pontoporia blainvillei) phonic lips: Correction about fused phonic lips

“…, Frainer et al . ), we found an error in the paper of Frainer et al . , regarding the description of fused phonic lips.…”

“…), we found an error in the paper of Frainer et al . , regarding the description of fused phonic lips. The aim of this letter is to correct this description and to illustrate the correct location of phonic lips in franciscana dolphin.…”

“…Based on our dissections we believe that Frainer et al . (; see fig. 2D) incorrectly identified the phonic lips, showing the “fused phonic lips” in the midline, when the phonic lips are lateral (see Fig.…”