2017 RESEARCH FINDINGS in the School of VETERINARY & LIFE SCIENCES
Total Page：16
File Type：pdf, Size：1020Kb
BULLETIN 5.11 Ecology, People & Environment 2017 RESEARCH FINDINGS in the School of VETERINARY & LIFE SCIENCES EMILY EAKIN-BUSHER, JOSEPH FONTAINE AND PHILIP LADD Fringe festival! How do closely related species stay separate? any flowers have both male and the flower. Heterospecific pollen may Mfemale parts, and produce seeds prevent the right pollen being delivered, or when pollen (male) reaches the ovary could produce sterile offspring. Fringe lily facts (female). Some plants can use their own Some flowers have evolved different ways to Buzz pollinated pollen to make seeds (self-pollination), avoid interference from heterospecific pollen, however many rely on pollen from Fringe lilies (Thysanotus species) are ‘buzz such as attracting different pollinators, another plant (cross-pollination) for pollinated’. Buzz pollination is where flowering at different times, or using successful seed production (Figure 1). pollen is only released by vibration. Only chemical processes. Evolutionary biologists native bees can do this. Because plants stay still, animals are often refer to these mechanisms as pre-mating and required for pollen transfer. These animals post-mating reproductive isolation, and 40 are known as pollinators and include many they are critical mechanisms for species to There are around 40 different fringe lily species of birds and insects. Pollinators maintain their separate identities. species here in the southwest of WA. recognise useful rewards and will be Fringe lilies have showy purple flowers that attracted to flowers by their colour, scent, A few hours are common in the spring and summer and/or shape. When closely related plant in Western Australia. There is a high level Each flower only lasts for a few hours! species have similar flowers and flower at of visual similarity between flowers of the same time, the same set of pollinators different species and most rely on native may visit both species. This could lead Methods and results bees for pollination. This raises questions to negative consequences for both about how these species maintain We investigated two pairs of fringe lily plant species as another species’ pollen reproductive isolation. (Thysanotus) species. Those in each pair (heterospecific pollen) may contaminate are closely related and have similar flowers (Figure 2). We recorded the flowering Self-pollination Cross-pollination Heterospecific pollination of each species in an urban reserve and (between species) recorded the number of pollinators that Same flower Different visited the flowers. flower Different plant Mating system trials: We examined the mating system of each species through hand pollination experiments. All four species had a mixed-mating system i.e. they set fruit from both self- and cross- pollination. However, few fruits were produced by three of the species when Species 1 Species 2 exposed to natural insect visitation. FIGURE 1 Different types of pollination which can occur in fringe lilies A series of bulletins outlining key research in the School of Veterinary & Life Sciences | 2017 Conclusions dependence on native bees means they will A B The long-term survival and reproduction be vulnerable to loss of pollinators. of a plant species relies on the production Flowers with special requirements for of seed. Landscape fragmentation can be pollination may have pre-mating isolation unfavourable for plant populations, as small (structures that require specific visitors land fragments may support few pollinators for successful pollen transfer). These or be difficult for pollinators to reach. In requirements may limit reproduction if addition, small plant populations tend to their pollinator is absent, but this was not C D have lower genetic diversity. the case in our study. Post-mating isolation Fragmentation may influence the is a better strategy than pre-mating evolution of the mating system of plants, isolation if low pollinator visitation is a for example, in the absence of pollinators, regular problem, as overall community self-pollination may increase and this can flowering will ensure that some pollinators lead to inbreeding depression. In cases are present that might visit the flowers. FIGURE 2 Pair 1 A. Thysanotus tenellus. B. where plants cannot self-pollinate, lack Although our Thysanotus flowers received Thysanotus sp. Pair 2 C. Thysanotus triandrus. of pollinators may also lead to local pollen from multiple species, pollen from D. Thysanotus multiflorus species extinctions. one species in each pair did not decrease seed set in the other. Therefore, it is likely Heterospecific pollination trial: We added We found that T. tenellus can self-pollinate that reproductive isolation between the heterospecific pollen to T. tenellus and without animal pollinators and still species occurs after mating, despite their T. triandrus then later added either self- produced abundant fruit. The other lilies rather specialised pollination method. n pollen or cross-pollen. The proportion could also self-pollinate, however they had low fruit production and showed of flowers setting fruit after receiving More information considerable pollen limitation. heterospecific pollen was almost identical Contact Emily Eakin-Busher to the proportion setting fruit in the mating Pollinators are unlikely to distinguish E: [email protected] system investigation (Figure 3). between the almost-identical flower colour References and structure of our fringe lily pairs. 1. Excerpt from: Eakin-Busher, E. L., Fontaine, 1.0 Although pollen is an attractive food J. B., and Ladd, P. G. (2016) The bees don’t reward, buzzing is a rather specialised know and the flowers don’t care: the effect 0.8 method of collecting pollen and only some of heterospecific pollen on reproduction in bee species can do it. We expect that the co-occurring Thysanotus species (Asparagaceae) sequential flowering and consistent flower with similar flowers. Botanical Journal of the 0.6 Linnean Society. 181(4), 640–650. appearance is likely to benefit the fringe lilies overall, as bees that are accustomed to 0.4 the floral form and colour will reliably visit, Terminology even if the flowers are of different species. Reproductive isolation different species live in the same area, but 0.2 Heterospecific pollination may incur a cost properties of individuals prevent them Mean prop. flowers setting fruit to the visited species (i.e. if pollen is lost 43 45 489 474 from interbreeding. 0 to another species, it is no longer available Cross Self HP cross HP self for transfer to a flower of its own species). Inbreeding depression describes Pollination type However, pollen loss is unlikely to have breeding between closely related FIGURE 3 Results of the breeding system a negative impact in fringe lilies because individuals that lowers the population’s trial on mean fruit set in T. triandrus. For the during buzzing, pollen is often scattered. ability to survive and reproduce (i.e., heterospecific pollen trial (light green), T. The bees cannot collect all the pollen fitness). multiflorus pollen was added to T. triandrus, scattered over their bodies, so some will followed by later cross (HP cross) or self (HP Pollen limitation is where flowering always be available for transfer to flowers. self) pollen. Sample sizes are given at the plants produce fewer seeds than they base of each column, and bars are 95% Nevertheless, low visitation is still a problem would if they received more pollen. confidence intervals for three of the lily species, and their If you are interested in our research and would like to know more, then please contact us on [email protected] Our research bulletins can be downloaded from www.murdoch.edu.au/School-of-Veterinary-and-Life-Sciences/Our-research/Our-Bulletins/ Undergraduate or postgraduate degrees, please see www.murdoch.edu.au/School-of-Veterinary-and-Life-Sciences/Our-courses/ CRICOS Code: 00125J A series of bulletins outlining key research in the School of Veterinary & Life Sciences | 2017.