Historical morphometrics of the European bison skulls and its association with species inbreeding increase

The summary and objectives of the project:

European bison is a species of unique demographic history. It has been through an extremely severe bottleneck in the 1920s. The whole contemporary population originates from a meager group of founders. Just two of them turned out to be predominant, and their share in the contemporary gene pool is above 80%. The effects are extremely low genetic variation (Wójcik et al., 2009; Tokarska et al., 2009; Tokarska et al., 2011) and highly increased inbreeding level, reaching 75% (Pertoldi et al., unpublished). Although increased inbreeding is regarded as an important factor affecting the viability of a population, resulting in lowered genetic differentiation and decreased fitness, its impact on the European bison seems milder than might be expected. Long term fertility coefficients are stable and satisfactory (Krasińska i Krasiński, 2017) and no indisputable inbreeding depression symptoms are observed (Tokarska et al., 2011). The reported potential inbreeding depression symptoms are related to skeleton conformation. Baranov et al. (1997) reported signs of developmental instability of skull morphology in the European bison skulls and indicated developmental instability as essential for characterizing the condition of the population. Analyses of fluctuating  symmetry of the European bison, associated with genetic diversity (Makowiecka, 1994) suggest that the Białowieża line of the European bison had the lowest, unbeneficial, developmental instability as the result of inbreeding. Until recently, the only method of estimating inbreeding level was pedigree analysis – a rough and inaccurate method. The development of genomic techniques enables precise calculation of inbreeding level using high density SNP (single nucleotide polymorphism) set. This method has been successfully used in the European bison studies and allowed for the first, accurate inbreeding calculations, using ROH (Runs of Homozygosity) analyses (Iacolina et al., 2016, Pertoldi et al., unpublished) This project enables the actual effect of extreme inbreeding on skull conformation in a historical context to be estimated, by association of genomic and morphometric data in one of the most inbred mammals known – the European bison.
We will use hundreds of 3D skull scans from European collections and museums and juxtaposition them with their inbreeding level information based on SNP markers. The objective of the project is to specify whether and in what extent inbreeding level shaped the skull conformation of European bison individuals by answering three questions:
Has the morphometry of the skull fluctuated over time? Has the growing inbreeding of the European bison influenced its skull morphometry? If yes, what morphometric skull features have been affected by growing inbreeding?