Inbreeding increases genome homozygosity within populations, which can exacerbate inbreeding depression by exposing homozygous deleterious alleles that are responsible for declines in fitness traits. In small populations, genetic purging that occurs under pressure of natural selection acts as an opposing force, contributing to a reduction of deleterious alleles. Both inbreeding and genetic purging are paramount in the field of conservation genomics. The Amur tiger (Panthera tigris altaica) lives in small populations in the forests of Northeast Asia and is among the most endangered animals on the planet. Using genome-wide assessment and comparison, we reveal substantially higher and more extensive inbreeding in wild Amur tigers (F_ROH = 0.50) than in captive individuals (F_ROH = 0.24). However, a relatively reduced number of loss-of-function mutations in wild Amur tigers was observed when compared with captive individuals, indicating a genetic purging of relatively large-effect inbreeding load. The higher ratio of homozygous mutation load and number of fixed damaging alleles in the wild population indicate a less-efficient genetic purging, with purifying selection also contributing to this process. These findings provide valuable insights for future conservation of Amur tigers.

This study aimed to determine whether the fetuses experienced hypoxic distress or intra-partum death due to compromised oxygen supply by quantitatively analyzing the lung structures of deceased captive South China Tiger (Panthera tigris amoyensis, SCT) cubs. Furthermore, it investigated the etiology and mechanisms of asphyxia in the deceased cubs and explored potential factors contributing to the high mortality rate of SCT cubs. The research focused on three deceased SCT cubs, using three deceased neonatal Amur Tigers (P. t. altaica, AT) with no inbreeding background as controls. Histological analysis of the cubs’ lungs was conducted using hematoxylin–eosin (H&E) and special staining techniques. The possible causes of death in SCT cubs were evaluated by comparing pulmonary pathological changes and morphological parameters, including alveolar space (P(ASP)) values, mean alveolar linear intercept (L_m), and mean thickness of alveolar septa (Tas). Our research reveals that hypoxia is one of the most significant factors contributing to the mortality of tiger cubs. Additionally, we hypothesize that inbreeding depression may lead to abnormal lung development (e.g., thickening of lung tissue) in SCT cubs. This study lays the foundation for comprehensive investigations into the mortality of highly inbred SCT cubs.