Fitness consequences of targeted gene flow to counter impacts of drying climates on terrestrial-breeding frogs

Rudin-Bitterli et al. created pure and reciprocal crosses of the Australian crawling frog Pseudophryne guentheri among geographically distant populations to investigate fitness impacts of targeted gene flow in counteracting a drying environment. When reared on wet and dry soils, embryonic survival depended on the origin of gametes from each sex, highlighting the need to experimentally evaluate the outcomes of TGF prior to implementing management actions. Targeted gene flow (TGF) could bolster the adaptive potential of isolated populations threatened by climate change, but could also lead to outbreeding depression. Here, we explore these possibilities by creating mixed- and within-population crosses in a terrestrial-breeding frog species threatened by a drying climate. We reared embryos of the crawling frog (Pseudophryne guentheri) on wet and dry soils and quantified fitness-related traits upon hatching. TGF produced mixed outcomes in hybrids, which depended on crossing direction (origin of gametes from each sex). North-south crosses led to low embryonic survival if eggs were of a southern origin, and high malformation rates when eggs were from a northern population. Conversely, east-west crosses led to one instance of hybrid vigour, evident by increased fitness and desiccation tolerance of hybrid offspring relative to offspring produced from within-population crosses. These contrasting results highlight the need to experimentally evaluate the outcomes of TGF for focal species across generations prior to implementing management actions.

Automated summary

The study found that implementing targeted gene flow in populations of the Australian crawling frog may have an impact on combating dry environments, but the results depend on the origin of gametes from each sex. North-south crosses could result in low survival rates and high malformation rates, while east-west crosses could lead to hybrid vigor.