Genetic distinctiveness of an endangered falcon: Implications for conservation in Europe

Abstract

In the Falconidae, the genus Falco comprises species of large birds of prey with wide distribution worldwide. However, the European lanner falcon Falco biarmicus feldeggii is rapidly heading for global extinction following a dramatic decline caused by anthropogenic interference. Conservation projects are currently underway with the main purpose of increasing its population size in the Mediterranean basin through captive breeding and release of birds into the wild. To support the projects, and strengthen the legitimacy of conservation efforts consistently with the Evolutionary Significant Unit concept, we explored the possibility of characterising the gene pool of the European lanner and reliably distinguishing it from other falcon taxa inhabiting the Mediterranean area, which show morphological and genetic similarities. To address the issue, we examined genetic variability at the nuclear level through the analysis of 12 neutral Short Tandem Repeat loci, and, for the first time in these taxa, two single-copy functional genes, coding for the brain-derived neurotrophic factor precursor and the oocyte maturation factor, respectively. The second exon of the major histocompatibility complex class II B gene was also investigated. Additionally, to frame our data with previously published data, we assess variation at the mitochondrial level by sequencing portions of the cytochrome b, 12S rRNA gene, and the control region. Our results showed that the European lanner is highly distinct from other falcon taxa, as revealed by nuclear, but not by mitochondrial DNA. We discuss our findings focusing on their implications for the preservation of this highly endangered European bird, and highlighted the critical role of genetic information in planning and monitoring concrete interventions.

Fig 1. Distribution of F. biarmicus and F. cherrug in the Mediterranean area.

Only areas where the species occur as resident and breeding native are indicated (redrawn from BirdLife International 2022, public domain, web site http://datazone.birdlife.org/species/requestdis). The individual ranges for subspecies of F. biarmicus are not indicated because it is not clear exactly which areas they cover and where they meet. Map layout was freely available online from Natural Earth at https://www.naturalearthdata.com/.

Fig 2. DAPC scatterplot based on a 15-locus panel describing the genetic variability in the sampled falcon taxa, identified by first (X-axis) and second (Y-axis) principal components.

The graph features single individuals as dots and groups as inertia ellipses.

Fig 3. Bar plotting of the results from a Bayesian analysis conducted with STRUCTURE, showing five genetic clusters (K = 5).

Each vertical bar represents one individual and the length of the different coloured sections is proportional to membership (q-values) in the inferred genetic clusters. Membership of F. b. feldeggii is distributed into two private clusters (see also Table 4). The star indicates one specimen of tanypterus that fell into the erlangeri group, as also revealed by DAPC. The bar plot was drawn using STRUCTURE PLOT [39] (http://omicsspeaks.com/strplot2/).

Fig 4. Median-joining networks based on the mitochondrial haplotypes of Falco taxa.

Networks obtained using: a) a 985-bp alignment of concatenated sequences from our samples of F. biarmicus ssp. and F. cherrug; b) a trimmed 295-bp CR alignment including our and published sequences from several falcon (sub)species. Circles represent single haplotypes; the size of the circles is proportional to the haplotype frequency; colours represent the proportion of individuals from each (sub)species; ticks on connecting lines indicate mutational steps between haplotypes; small black nodes mark inferred (unsampled) sequences. Hatched lines separate two major haplogroups (I and II).