Mating systems and reproductive success inferred via PBT
Results from parentage-based tagging identified a total of 934 unique parent-pairs from a combinations of 373 male and 486 female Yellowstone Cutthroat trout. The number of mates per adult was right skewed, with no offspring contributions detected from 37.9% of females and 48.9% (Figure 2A ). Of the adults that were assigned at least one offspring, the most common number of mates per adult was one for both females (27.7%) and males (24.2%). Individual females mated with up to five different males, whereas males mated with up to 16 different females (Figure 2A ). The mean number of mates was 1.19 (SD: 1.25) for females and 1.28 (SD: 2.02) for males. The median number of mates was one for both males and females. Based on the reproductive profiles of individual adults we identified evidence of monogamy, polygyny, and polyandry.
Similar to the number of mates per adult, the distribution of relative reproductive success was right skewed. Among adults that contributed to reproduction, the most frequent number of offspring produced was one for both females (13.3%) and males (11.9%; Figure 2B ). The maximum number of offspring attributed to a female was 22, whereas one male produced 57 offspring. The mean number of offspring produced per female was 2.95 (SD: 3.89) and 3.16 (SD: 6.22) for males.
A positive relationship was identified between the number of mates and the relative number of offspring produced (Figure 2C ). For both females and males, the average number of offspring per adult increased as a function of the number of mates acquired but the strength of this correlation differed by sex. Specifically, Pearson’s correlation coefficient between the number of offspring produced and number of mates acquired was 0.77 and 0.89 for females and males, respectively.
The same set of 3,862 full-sibling pairs were identified by both sibship assignment and parentage analysis. Seventeen full-sib pairs were detected by sibship assignment only, and 35 full-sib pairs were detected exclusively by parentage analysis. Discordance between methods (52 pairs differed of 3,914 total pairs) was 1.3% indicating that both methods produced highly similar results. Both analyses identified 410 offspring that were ‘only children’ (i.e., had no full siblings) and an additional 33 ‘only children’ were detected by sibship assignment and not PBT. Three ‘only children’ were detected by PBT but not sibship analysis.