Популяционно-генетическая структура степного орла: есть ли надежда на сохранение вида?

Abstract

For centuries, Steppe Eagle (Aquila nipalensis) had been the most numerous Palearctic Aquila species, but nowadays it has been decreasing in numbers progressively, so in 2015 the IUCN changed the species status to “endangered”. The decrease is evidently related to Steppe Eagles’ electrocution at nesting areas and during migration, poisoning by veterinarian drugs when feeding on agricultural animal carcasses at wintering grounds, steppe fires and total habitat loss combined with loss of prey like susliks. To the contrary, the sister Aquila species, the Imperial Eagle (Aquila heliaca), which exhibits similar biological traits and lives simpatrically to the Steppe Eagle at some parts of areas, shows local increase in numbers and even substitutes the decreasing Steppe Eagle in steppe biomes. In the 1960s, many Palearctic birds of prey came through population decline due to so-called “DDT crisis” – massive pesticide poisoning. To restore the species numbers, specific conservation actions were initiated in Europe to support population numbers and genetic diversity of raptors. Regarding the Steppe Eagle with its nesting area located mostly at Kazakhstan, Russian, Mongolian and Chinese territories, the implications of DDT and electrocution impacts on the population numbers stayed poorly investigated. Meanwhile, loss of genetic stability can be a reason for lasting population decline. Genetic threats like population fragmentation, genetic erosion, and inbreeding depression are believed more prolonged in comparison to anthropogenic impacts and more rarely come under increasing scrutiny of conservation practitioners. However, if exist, they can lead to species extinction regardless of removal of all other threats. The Steppe Eagle population structure stays poorly investigated. In 2018, during the 1st Steppe Eagle conservation international workshop, this problem was highlighted with recommendations for filling this gap. Our presented study was conducted following this recommendation and focused on genetic structure, fragmentation, and effective number comparison of the Steppe Eagle population at the individual samples) and sympatric populations of the Imperial Eagle (over 100 samples). For conservation criteria estimation, we used widespread genetic markers like nuclear microsatellites (9 loci) and mitochondrial control region (D-loop). Also we performed molecular individual tagging and parentage analysis to study the population structure using samples from the numerous Western Kazakhstan population. We also used GIS methods to study geographic fragmentation of populations. The genetic analysis showed that the Steppe Eagle population structure is highly similar to that of the Imperial Eagle but with less genetic diversity and has traces of repeated survival of “population bottlenecks” with huge decline in the number and genetic diversity. Fragmentation analysis showed no genetic isolation of geographically fragmented nesting groups despite the presumed natal phylopatry in accordance with our Steppe Eagle parentage data. Preliminary estimation of the Steppe Eagle population effective numbers by linkage disequilibrium method showed rather high values inspite of the lasting population decline. The molecular coancestry estimation showed more serious decline during the latest bottleneck which was also far below the ancestral Imperial Eagle population at the studied areas. The inbreeding rate for the Steppe Eagle population at the most part of the species areas turned out to outnumber one for the local population of the Imperial Eagle. Our data showed no immediate genetic threats for the Steppe Eagle population restoration and also demonstrated traces of multiple bottlenecks in the species evolution. Still the genetic structure of the species population keeps some traits of modern decline and should be monitored permanently according to the species numbers. Unique population structure patterns of the Steppe Eagle between other Aquilinae species and their conservation aspects are directions for future Aquila nipalensis genetic research.