Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree

The success of invasive species relies heavily on the production, dispersal and genetic composition of propagules. For range expanding species, breeding strategy and level of reproductive investment will strongly influence their capacity to establish and invade new areas. A hermaphroditic lifestyle provides the advantage of increasing the number of seed bearing individuals within a population while a dioecious habit may enable more rapid adaptation to new environments, improve resource use efficiency, fecundity and dispersal. Pittosporum undulatum, a tree native to coastal areas of southeastern Australia, has many characteristics of an invasive species within and beyond its native range. A previous study detected a male bias within invasive populations, with a high proportion of fruit deriving from female-only trees, leading to recommendations for the removal of ‘matriarch’ trees as a simple management technique. We expanded that study and investigated breeding systems of different populations of P. undulatum by assessing tree density, gender, resource availability and fruit load of 871 individuals in seven native and seven invasive populations. All populations comprised either females (47%) or hermaphrodites. No male-only trees were observed within the study. More females produced more fruit than hermaphrodites, especially in the native site. This could not be attributed to environmental differences between sites. These data support the current management practices of targeting the removal of females as a simple method for containing invasions given the benefits of reducing the workload and spreading limited management resource. Our work highlights the value in understanding the breeding strategy employed by focal invasive species as a means of developing improved and more targeted control methods.