The development of the electroreceptors of the platypus ( Ornithorhynchus anatinus )

Abstract

A series of developmental stages of the platypus were examined to obtain an anatomical description of the development of the periphery of the electroreceptive system. Putative electroreceptors, composed of modified mucous glands, were observed to appear at 10 days post hatching (p.h.). The typical striped arrangement of peripheral electroreceptors in the platypus was seen at 12 days p.h. The arrangement of the stripes was modified during development with a range of additions and divisions of stripes occurring until the adult pattern is obtained, approximately 6 months p.h. After appearing at 10 days p.h., the number of electroreceptors increases rapidly until sometime between 24 and 28 days p.h. when there is massive death of electroreceptors, the number present at 28 days p.h. being 60% of the number present at 24 days p.h. This massive death of receptors is coincident with the appearance of other sensory structures in the epidermis of the bill skin, the push–rod mechanoreceptors and the sensory serous glands. Histological examination of a range of developmental stages demonstrated poorly differentiated innervation at 28 days p.h., which became differentiated and reached the adult configuration between 11 weeks p.h. and 6 months p.h., the time at which nestling platypus leave the burrow. Lamination of the cells lining the duct of the electroreceptors showed a similar developmental profile. This study indicates that the electroreceptive system of the developing platypus is not functional, in a similar manner to the adult, until it is time for the platypus to leave the nesting burrow. However, the system may be functional in the developing platypus, and may be used speculatively in the location of the mammary region for suckling.

Distinct Development of Peripheral Trigeminal Pathways in the Platypus <i>(Ornithorhynchus anatinus)</i> and Short-Beaked Echidna <i>(Tachyglossus aculeatus)</i>

“…1 d-f), these ridges break up into individual epidermal pegs penetrat- ing 50-100 m into the dermis, predominantly along the dorsal surface of the upper bill, but also on the ventral surface of the lower bill. These are identical in appearance to those structures identified as the developing ducts of mucous electroreceptors [Manger et al, 1998a]. The specializations are loosely clustered into longitudinal domains in the 33-mm CRL platypus ( fig.…”

“…It should be emphasized that although the early appearance of these epidermal specializations is broadly similar to developing hair follicles, at no time during the life of the platypus do hair follicles appear on this region of the body. The subsequent development of these specializations over the next 6 weeks involves a rapid increase in their number, their alignment into longitudinal stripes and their elongation/further penetration of the dermis as described by Manger et al [1998a]. The development of epidermal specializations in the beak of the short-beaked echidna follows a rather different pattern from that seen in the platypus.…”

“…Manger et al [1998a] identified putative mucous electroreceptors in sections through the platypus bill at post-hatching day 28, but they did not examine any sectioned material from an age younger than this. However, they did claim to be able to identify putative mucous gland electroreceptors from post-hatching day 10 on the basis of external duct pits seen by stereomicroscopic examination of the bill surface in undissected specimens.…”

“…By studying this system we hoped to determine whether the developmental trajectories of the trigeminal pathway in these two species show early divergence with features characteristic of the respective adult, or whether there are early similarities (with a bias towards the modern platypus) followed by subsequent structural divergence. A previous study has examined the development of electroreceptors in posthatching platypus [Manger et al, 1998a], but no study has yet examined receptor or trigeminal pathway development in the embryos of either species or in post-hatching echidnas.…”

Distinct Development of the Trigeminal Sensory Nuclei in Platypus and Echidna

“…Our observations are most consistent with the contention of that the two monotreme clades diverged before the late Cretaceous. Manger et al [1998b] have reported that electroreceptors begin to emerge on the surface of the platypus bill around 10 days after hatching, but they did not have the opportunity to examine sections of pre-hatching platypus. We recently showed that the peripheral trigeminal pathways of platypus and echidna are morphologically distinct from the earliest stages of the skin receptor, trigeminal nerve and ganglion differentiation, even before hatching [Ashwell et al, 2012].…”