Is Wide Outcrossing Beneficial for the Translocation of Tetratheca erubescens?

Melissa-Rose Blake

Investigation of the mating system of plant species is key information for effectively managing population fitness and species conservation of rare plants at risk of extinction from anthropogenic habitat disturbance. Fragmentation from habitat clearing can change mating systems by decreasing the population outcrossing rate and increasing the rate of selfing. Together with a reduction in population size, these changes may result in the need for intervention to conserve the species. Specifically, translocation is an intervention used to increase the population size, improve, or maintain genetic diversity and to provide opportunities for outcrossing among populations of the species. In 2017, a translocation project was completed for the threatened endemic species Tetratheca erubescens. Since this study, the population has been reduced by 22% due to habitat clearing for mining. Prior to construction commencement, it was agreed that 313 individuals would be planted to conserve the species. One year after the translocation, the seedlings and propagated cuttings had failed. An investigation into the population genetic structure revealed the population is at risk of suffering inbreeding depression, and to prevent it, the genetic diversity must be increased. In an effort to introduce new genetic material, in this study, I asked if wide outcrossing would produce offspring with an increased fitness to improve the success of future translocations. Here I show T. erubescens has a mixed mating system with partial self-incompatibility. Pollen acceptance did not vary significantly between populations separated by at least 1000m (and likely genetically diverged) or near neighbours. Among all seedlings produced, the self-group showed a decline in fitness both in proportion of emergence and seedling survivorship. Seedling emergence from wide-outcrossing was lower than those from the neighbour mating and from seeds sourced from natural populations (wild). The neighbour seeds had 56.5% seedling emergence, the wild had 47%, self, 42%, and the wide outcross had 37%. There was a consistent indication of genetic divergence affecting fitness, regarding offspring survival among the sample population. While the treatment groups also showed little variation in fitness between distantly related matings and neighbour matings, assessing the mating pairs highlighted information that will assist future propagation of in situ individuals. While one mating pair is often similar to or superior to the wild population, another is consistently inferior to all, and similar to self-produced offspring. The wild population is in need of intervention as further habitat loss and population reduction will continue to negatively affect the species future generations. The failed translocation only highlights the level of investigation required of the genetic structure and environmental requirements at various life stages. In conclusion, I have determined wide outcrossing to not be beneficial to Tetratheca erubescens in the early life stages, therefore not likely to improve translocation success. However, I have presented potential alternate research avenues that may lead to the production of offspring fit enough to survive to maturity and to contribute to the population growth for generations to come.

Is Wide Outcrossing Beneficial for the Translocation of Tetratheca erubescens?

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