The mitochondrial genome (mitogenome or mtDNA), the extrachromosomal genome, is a multicopy circular DNA with high mutation rates due to replication and repair errors. A mitochondrion, cell, tissue, organ, or an individual body may hold multiple variants, both inherited and developed over a lifetime, which make up individual mitogene pools. This phenomenon is also called mtDNA heteroplasmy. MtDNA variants influence cellular and tissular functions and are consequently subjected to selection. Although it has long been recognized that only inheritable germline heteroplasmies have evolutionary significance, non-inheritable somatic heteroplasmies have been overlooked since they directly affect individual fitness and thus indirectly affect the fate of heritable germline variants. This review focuses on the characteristics, dynamics, and functions of mtDNA heteroplasmy and proposes the concept of individual mitogene pools to discuss individual genetic diversity from multiple angles. We provide a unique perspective on the relationship between individual genetic diversity and heritable genetic diversity and guide how the individual mitogene pool with novel genetic markers can be applied to ecological research.

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.