Canid Reproductive Biology: Norm and Unique Aspects in Strategies and Mechanisms

Abstract

The reproductive physiology of canids is unique compared to other mammalian species. Specifically, the reproductive cycle of female canids is characterized by extended periods of proestrus and estrus followed by obligatory diestrus and protracted ovarian inactivity (anestrus). Although canid reproduction follows this general pattern, studies have shown variations in reproductive biology among species and geographic regions. Understanding of these differences is critical to the development of assisted reproductive technologies including estrus induction, gamete rescue, and embryo production techniques for canid conservation efforts. This review summarizes current knowledge of canid reproduction, including estrus cyclicity, seasonality, and seminal traits, with the emphasis on species diversity. The application of reproductive technologies in wild canid conservation will also be discussed.

Keywords: Canidae; assisted reproductive technologies; estrus; seasonality.

Figure 1

(a) Numbers of wild canid species listed as critically endangered (CR), endangered (En), near threatened (NT) or least concern (LC) status according to the IUCN red list of endangered species; (b) Numbers of canid species with decreasing, stable, increasing or unknown population trends.

Figure 2

In vitro growth of isolated ovarian follicles (n = 2 early antral and 3 antral stage) from an African painted dog (SB#2516) over 14 days culture, with representative images of an early antral stage follicle developing to the small antral stage over 7 day culture. Asterisk (*) denotes antral cavity. Black bar = 100 µm. (unpublished data)

Figure 3

Grey wolf testicular tissue preservation, with (a) density germ cell marker DDX4 positive cells in grey wolf tissues following slow freezing in DMSO alone (SF-D), or in ethylene glycol and DMSO (SF-ED), or needle immersion vitrification (NIV) compared with fresh controls (n = 7 wolves), and (b) representative images of DDX4+ cells (green) with nuclear DAPI (blue) counterstain. Yellow line denotes outline of seminiferous tubules, and white bar = 50 µm. Reprinted with the permission from ref. [168]. Copyright 2021 Elsevier.