# Habitat Loss and Other Threats to the Survival of _Parnasius apollo_ ([PERSON], 1758) in Serbia
## 1 Introduction
### Conservation Challenges and Genetic Perspectives  
A recent study in the Sierra Nevada revealed that populations of _Parnussius apollo_ are highly spatially fragmented, with limited gene flow between the western and eastern sectors of the mountain range. Notably, the formerly occupied Puerto de la Ragua pass has been entirely depopulated, most likely due to a decline in host and nectar plant availability at lower elevations [59]. This case underscores the crucial role of microhabitat continuity in sustaining viable metapopulations. In Poland's Pienny National Park, reintroduction efforts also highlight key conservation dilemmas. Excessive supplementation using captive-bred individuals--without parallel habitat restoration--resulted in a reduced carrying capacity and disrupted natural population dynamics [60]. This study emphasized the risks of poorly coordinated reintroduction initiatives and the need for integrated ecological planning to avoid so-called \"overload effects.\"A geometric morphometric analysis involving 20 _P. apollo_ subspecies across the Carpathian-Pannonian region found negligible morphological divergence. The authors recommend treating these lineages as a single conservation unit pending further genetic resolution [61], potentially streamlining resource allocation and management strategies. In parallel, mark-release-recapture experiments have shown that variation in terrain and vegetation structure significantly influences capture success and estimates of population size [62], suggesting that microtopographic features should be integrated into future monitoring protocols. Although once widespread, _P. apollo_ is now classified as endangered, its survival jeopardized by a convergence of genetic, ecological, and climatic threats. While reintroduction projects have been met with partial success, novel challenges have emerged, such as a higher incidence of wing malformations among semi-captive individuals. Recent research has implicated several underlying causes: mutations in the _wingless_ gene, disruption of key enzymes like lacase 1 and 2, absence of _Wolbachia_ symbionts, and the presence of pathogenic bacteria including _Yersinia pseudotuberculosisis_ and _Serratia_ spp. [63]. On a broader scale, macroevolutionary studies on the genus _Parnassius_ in the Himalayan-Tibetan region indicate that diversification is driven not by clade age or speciation rate, but by ecological opportunity--i.e., niche saturation in isolated mountain environments [64]. Supporting this, a recent reference genome for _P. apollo_--among the most complete for Lepidoptera--has revealed a highly conserved chromosomal structure and notable genome expansion due to repetitive element accumulation. This provides a foundational tool for future conservation genomics [65]. Morphological responses to environmental stress have also been documented. A longitudinal study based on historical specimens from the Streeno pass in Slovakia identified notable changes in forewing shape, attributed more to anthropogenic disturbance--such as road construction--than to climatic extremes [66]. Ecological investigations further reveal that _P. apollo_ exhibits relatively high mobility (up to 6.4 km), though dispersal is density-dependent: emigration increases with population density, while immigration declines, reinforcing the need for finely tuned interventions in fragmented landscapes [67]. Population genetics of _P. apollo_ in the French Alps and Auvergne indicate a complex demographic trajectory. While populations diverged prior to the Last Glacial Maximum, gene flow persisted until the mid-Holocene. Today's metapopulation structure reflects pulsating patterns of contraction and expansion, complicating conservation planning [68]. Moreover, contemporary landscape models predict that ongoing succession from open grassland to forest will lead to the loss of over 45% of suitable _P. apollo_ habitats on the island of Gotland--emphasizing the need for active, long-term management of successional processes to retain habitat heterogeneity [69].