Infanticide in brown bear: a case-study in the Italian Alps – Genetic identification of perpetrator and implications in small populations

Abstract

Sexually Selected Infanticide (SSI) is thought of as a male reproductive strategy in social mammalian species, because females who lose cubs may quickly re-enter oestrus. SSI has rarely been documented in non-social mammals and, in brown bears, SSI has been studied mainly in an eco-ethological perspective. The authors examined the first genetically documented infanticide case which occurred in May 2015 in brown bears in Italy (Trentino, Central-Eastern Alps). The infanticide killed two cubs and their mother. Hair samples were collected from the corpses as well as saliva, through swabs on mother’s wounds, with the aim of identifying the genotype of the perpetrator. The samples were genotyped by PCR amplification of 15 autosomal microsatellite loci, following the protocol routinely used for individual bear identifications within the Interregional Action Plan for Brown Bear Conservation in the Central-Eastern Alps (PACOBACE). Reliable genotypes were obtained from the mother, cubs and putative perpetrator. The genotypes were matched with those populating the PACOBACE database and genealogies were reconstructed. Both mother and perpetrator genotypes were already present in the database. Kinship analyses confirmed mother-cubs relationships and identified the father of the cubs. In this study, for the first time, the authors used the open-source LRmix STUDIO software, designed to analyse human forensic genetic profiles, to solve a case in wildlife. Through LRmix STUDIO, those alleles that do not belong to the victims were isolated and, finally, the perpetrator was identified. This study presents a method that allows, through the application of different models, the genetic identification of the conspecific perpetrator with the highest probability. The identification of the infanticidal male is relevant for the better management and conservation of wild populations with small effective population size (Ne) and low population growth rate, especially in the case of recently established populations in human-dominated landscapes. This procedure will have predictably wide applications, supplying important data in the monitoring of small and isolated populations.

Microsatellite Characterization and Panel Selection for Brown Bear (Ursus arctos) Population Assessment

“…In fact, we estimated relatively low genetic diversity in the studied Italian bear populations, especially with regard to Uam , with three loci being monomorphic. The Uam population was characterized by an even lower genetic diversity compared to Uaa (uHe = 0.368 vs. 0.627; GD = 0.40 vs. 0.61), confirming the results reported in [ 33 , 34 ]. Since the management of both these small populations depends on regular genetic analyses, the BEST set of identified markers will be critical to keeping the cost-benefit ratio in favor of continued monitoring.…”

“…Polymorphism and genotyping errors of the CURRENT panel were extrapolated from [ 33 ] ( Uam ) and [ 34 ] ( Uaa ) ( Table 3 ).…”

“…Total genomic DNA was isolated from invasive and non-invasive samples with the QIAGEN DNeasy ® Blood & Tissue Kit (QIAGEN, Hilden, Germany), using a robotic workstation for automated purification of DNA (QIAcube, QIAGEN, Hilden, Germany). Since the DNA obtained from non-invasive sampling is often diluted and deteriorated, a multiple-tubes approach, with positive and negative controls at each step, was used to prevent stochastic errors [ 33 , 34 , 39 ]. Multilocus genotypes were obtained by evaluating the results of four independent PCR replicates, following the protocols described in [ 33 ].…”

“…The 20-year monitoring projects of both brown bear populations in Italy are currently using 13 and 15 STRs for individual identification in the Uam [ 33 ] and Uaa [ 34 ] populations, respectively. However, the low genetic variability in Uam and the low discrimination power of the current microsatellite panel will almost certainly reduce the resolution of individual genotyping in the long term.…”

Cannibalism in bears

“…We did come across some lack of clarity that would be helpful to address in future research. There were many reports of infanticide, and although some authors assumed that cannibalism always accompanies infanticide (e.g., Davoli et al 2018), most studies neglected to report whether or not the cubs were consumed after being killed. For the sake of our literature review of cannibalism, we only considered the cases where a conspecific was reported to be consumed, but this means that our literature review may have underestimated cannibalism events by bears, especially cases of sexually selected infanticide, which is the most common form of cannibalism.…”