Variance in Reproductive Success is Driven by Environmental Factors, not Mating System, in Bonytails

Abstract

Studying the reproductive ecology of aggregate broadcast spawning fishes is difficult because it generally is not feasible to sample all potential parents and unambiguously assign their offspring. We used molecular-based parentage analysis to gain insights into the reproductive ecology of the endangered Bonytail, and to evaluate whether protected off-channel habitats could be used as an alternative to hatchery production. By genotyping adults and offspring stocked (n = 4130) into two experimental backwaters across three years, we determined that most adults (82–97%) contributed to progeny production across years and backwaters, with one exception. Both sexes mated multiply and the number of mates and family size were positively correlated. There was also a positive correlation between adult size and metrics of reproductive success. There were strong interactions between sample years and backwaters suggesting that environmental factors are the primary driver of variance in reproductive success. Knowledge of mating systems and sources of variance in reproductive success is important for management of endangered fish because high variance in reproductive success leads to substantial losses of genetic variation when few individuals reproduce successfully. Although variance in reproductive success was observed, most adults contributed to genetically diverse progeny in experimental backwaters. These results support the use of predator-free, but otherwise natural, backwaters as an effective conservation tool for reintroducing Bonytail to its native habitat.

Rapid Molecular Determination of Sex for Western North American Chub (Gila spp.)

“…We collected fin clips from six species but were only able to make determinations of sex by using phenotypic characteristics for five species. Unless otherwise noted, all of the phenotypic determinations of sex were made according to the sex-specific morphology of the urogenital opening and by secondary sexual characteristics (i.e., tuberculation in males) if present (Osborne et al 2018). The hatchery samples were sourced from either SNARRC (Bonytail, Chihuahua Chub, Virgin Chub, and White River Chub) or the John W. Mumma Native Aquatic Species Restoration Facility (Rio Grande Chub).…”

“…Fish and Wildlife Service (USFWS) propagation program at Southwestern Native Aquatic Resources and Recovery Center (SNARRC; Dexter, New Mexico) and multiple state and federal grow-out programs have since been established for Bonytail restoration and recovery. However, wild reproduction remains exceptionally rare and natural recruitment has never been documented (Bestgen et al 2017;Osborne et al 2018;Diver et al 2019).…”

“…A common theme emerges for all threatened and endangered Gila despite the species-specific variability in their life history traits: propagation and recovery programs are in place for several Gila species, and thus the ability to accurately sex wild populations and hatchery stocks would prove useful for these programs. For example, given the conservation reliance of Bonytail on hatcheries and the influence of sex ratios on N e , the ability to identify sex could promote conservation and propagation efforts by allowing fisheries managers to ensure equal sex ratios in broodstock populations (Osborne et al 2018), thus reducing potential adverse effects of genetic drift and inbreeding on genetic diversity. To aid the aforementioned conservation goals, we identified a locus that correlated with sex in Bonytail by using genomic sequencing methods.…”

Size Sorting in Bonytail Skews the Sex Ratio of Stocked Fish

“…More recently, genetic work on semi‐natural populations has suggested that (1) most adults in a population spawn annually, (2) both males and females have multiple mates, and (3) reproductive success is correlated with body size (Osborne et al. ).…”

“…Historical accounts suggested that in May-July, Bonytail formed large spawning aggregates consisting of hundreds of fish, with three to five males attending a single female as she released eggs onto gravel (Jonez and Sumner 1954;Vanicek and Kramer 1969;McKinley 1973;Marsh 2004;Mueller 2006). More recently, genetic work on semi-natural populations has suggested that (1) most adults in a population spawn annually, (2) both males and females have multiple mates, and (3) reproductive success is correlated with body size (Osborne et al 2018).…”