Evidence of adoption, monozygotic twinning, and low inbreeding rates in a large genetic pedigree of polar bears

Abstract

Multigenerational pedigrees have been developed for free-ranging populations of many species, are frequently used to describe mating systems, and are used in studies of quantitative genetics. Here, we document the development of a 4449-individual pedigree for the Western Hudson Bay subpopulation of polar bears (Ursus maritimus), created from relationships inferred from field and genetic data collected over six generations of bears sampled between 1966 and 2011. Microsatellite genotypes for 22-25 loci were obtained for 2945 individuals, and parentage analysis was performed using the program FRANZ, including additional offspring-dam associations known only from capture data. Parentage assignments for a subset of 859 individuals were confirmed using an independent high-density set of single nucleotide polymorphisms. To account for unsampled males in our population, we performed half-sib-full-sib analysis to reconstruct males using the program COLONY, resulting in a final pedigree containing 2957 assigned maternities and 1861 assigned paternities with only one observed case of inbreeding between close relatives. During genotyping, we identified two independently captured two-yearold males with identical genotypes at all 25 loci, showing-for the first time-a case of monozygotic twinning among polar bears. In addition, we documented six new cases of cub adoption, which we attribute to cub misidentification or misdirected maternal care by a female bereaved of her young. Importantly, none of these adoptions could be attributed to reduced female vigilance caused by immobilization to facilitate scientific handling, as has previously been suggested.

Quantitative analysis of connectivity in populations of a semi‐aquatic mammal using kinship categories and network assortativity

“…The use of genetic methods to infer kinship categories and multigenerational pedigrees has been applied to relatively few studies of wild animals considering the high potential they have to analyse fundamental aspects of species such as the reproductive biology, mating systems, cooperative breeding, inbreeding avoidance or the characterization of the abundance of populations, to name a few (Carpenter et al, ; Carroll et al, ; DeWoody, ; Garrigue, Dodemont, Steel, & Baker, ; Rioux‐Paquette, Festa‐Bianchet, & Coltman, ; Vigilant et al, ); this is due to the large quantities of genetic data necessary to obtain robust pedigrees together with the fact that the most powerful techniques for drawing such inferences have only been recently developed (Eggert et al, ; Malenfant et al, ; Pemberton, ; Städele & Vigilant, ; Stenglein, Waits, Ausband, Zager, & Mack, ). Parent–offspring relationships have classically been easier to determine, even with microsatellite markers (Cercueil, Bellemain, & Manel, ; Kalinowski, Taper, & Marshall, ).…”

Climate change, age acceleration, and the erosion of fitness in polar bears

“…Fitness benefits associated with early reproduction declined with warming, and today, bears have similar lifetime reproductive success regardless of when they first reproduce. Finally, using a large pedigree 5 , we found no evidence for genetic variation associated with reproductive success in this population—the population is not evolving in response to the changing environment. The physiological costs of climate change accumulate across lifetimes to degrade cellular function and, ultimately, adaptive capacity.…”

“…This means that population persistence will depend on a population’s overall capacity to adapt genetically to the changing environment. We used our estimates of lifetime reproductive success and a population pedigree that spanned the 40-year study 5 to test for genetic differences among individuals in their ability to reproduce (i.e., the contribution of selection to the genetically based increase in population mean fitness). We did so by estimating the additive genetic variance in individual relative fitness, which can be thought of as an estimate of the overall effect of selection on the ability of individuals to reproduce 45 .…”

Estimating reproductive costs in marine mammal bioenergetic models: a review of current knowledge and data availability

“…misidentification by the mother) or milk theft by the pup, although there are isolated examples of extended fostering, such as when a female has lost her own pup. Fostering has also been observed in polar bears (Malenfant et al, 2016) and sea otters (Staedler and Riedman, 1989), while allonursing and fostering have been observed in manatees (Bonde, 2009). Allonursing is less common in cetaceans, having been observed in sperm whales (Physeter macrocephalus) and captive beluga whales (Delphinapterus leucas) (Leung et al, 2010;Konrad et al, 2019), although this may be because it is difficult to observe in the wild and not because it does not occur in other species.…”