# Morphological, Histochemical and Immunohistochemical Characterisation of the Penis in Free‐Ranging Giant Anteaters (Myrmecophaga tridactyla)

## TL;DR

This study describes the structure and composition of the penis in giant anteaters to better understand their reproductive biology.

## Contribution

It provides the first detailed morphological and histochemical analysis of the giant anteater's penis.

## Key findings

- The giant anteater's penis contains two erectile bodies and specific collagen fibers.
- Epithelial cells in the penile urethra show sensitivity to estrogen and progesterone.
- PAS-positive staining was found in epithelial cells at the base of hair follicles.

## Abstract

The giant anteater (
Myrmecophaga tridactyla
) belongs to the superorder Xenarthra and is distributed throughout Central and South America. This animal is listed as ‘vulnerable’ on the International Union for Conservation of Nature's Red List of Threatened Species. Studies on the reproduction of this species are essential because of its peculiarities; however, there is a lack of information on its reproductive aspects and the biotechnologies that can be applied to it. Morphological and histopathological descriptions of the reproductive organs of
Myrmecophaga tridactyla
are fundamental for determining the general characteristics that could improve our understanding of reproductive disorders in this species. Therefore, this study aimed to perform morphological and histochemical characterisation of the penis of
Myrmecophaga tridactyla
. For this purpose, we collected six postmortem samples of giant anteater penises. The penis of the giant anteater has no foreskin, two erectile bodies, a paired corpora cavernosa, corpus spongiosum and urethra. Type I (red) and type III (yellow‐green) collagen fibres were distributed throughout the stroma and erectile bodies of the penis. Periodic acid‐Schiff (PAS)‐positive staining was observed in the epithelial cells at the base of the hair follicles, and immunohistochemical immunolabelling for androgen receptors (AR) and oestrogen receptors (ER) was detected in all cells of the transitional epithelium of the penile urethra. These findings suggest that penile urethra cells are sensitive to oestrogen and progesterone.