Pollination Ecology Of Two Vincetoxicum Species,V.Hainanense And V.Hirundinaria

Globally,nearly 90 % of flowering plants depend on animals,especially insects for pollination and reproduction.At present,four orders of insects are mostly reported as pollinators: Lepidoptera,Coleoptera,Hymenoptera,and Diptera.In contrast,other polinator groups,such as Blattodea(cockroaches),have scarcely been reported as polinators.Currently,cockroaches are known pollinators of ten plant species from eight families,and this pollination system may be more widespread than we thought.However,the pollination effectiveness and chemical attraction of cockroaches to flowers has not been studied previously.Among flowering plants,the floral structure of species in the subfamily Asclepiadoideae(Apocynaceae)is extremely delicate and complicated,and species in this subfamily represent excellent candidates for pollination ecological studies,especially for the confirmation of effective pollinators and the quantification of polination effectiveness.In addition,previous studies recorded cockroaches and ants as flower visitors in species such as Vincetoxicum spp.,however,their role as pollinators remains unclear.In this thesis,we conducted a comprehensive study of the flowering biology and the chemical ecology of pollination in two Vincetoxicum species(V.hainanense in China and V.hirundinaria in Austria),which both release strong scents and are visited by cockroaches and ants,as determined in preliminary analyses.We addressed the following specific questions:(1)Do cockroaches and ants flower visitors function as pollinators of the two Vincetoxicum species?(2)What's the difference of pollination effectiveness of cockroaches and ants,and other insects that also might visit the flowers?(3)What's the difference of flower scent compounds release of the two species,and which compounds of V.hirundinaria elicit physiological and behavioral responses in pollinators?(4)What's the difference of pollination system of the two species?The main results are as follows:1.The pollination system of the rare and endangered plant V.hainanense was studied for the first time,and we introduce cockroach pollination in Apocynaceae.The floral features of V.hainanense are adapted for cockroach pollination.Flowers were pale green,opened at night(19:00 ? 20:00),and did not produce visible amounts of nectar.The flowers had a heavy,nauseatingly sweet scent,dominated by 3-Methyl-1-butyl acetate,Pyridine and 3-Methylbutan-1-ol.Few insects were visiting the flowers in the 40 h of daytime observations and none of them acted as pollinators.During the40 h of nighttime observations,however,we found seven species of visitors,and three of them were pollinators,i.e.the cockroach Blattella bisignata,the beetle Carabidae sp.,and the ant Tetramorium sp..On average,the corpuscle carrying rate of pollinators were 65.0 %,41.7 %,25.0 %,respectively.The number of corpuscles carried were 3.1± 0.8,1.6 ± 0.8,1.2 ± 0.4,respectively.The pollinaria removal rate of pollinators following a single visit was 87.6 %,63.2 %,and 10.0 %,respectively,and the pollinia insertion rate was 21.9 %,7.9 %,and 5.0 %,respectively.The most effective pollinator was the cockroach B.bisignata,followed by the beetle,and then the ant.The pollination system of V.hainanense is relatively specialized,and the strategy of flower opening reflects adaptation to the most efficient pollinator.The flowers are not autogamous,and with low self-compability.The reproductive success is highly depend on adult of cockroach for cross pollination.Overall,the cockroach Blattella bisignata plays a vital role in the maintenance of population structure of V.hainanense.2.The flower of V.hirundinaria,though morphologically specialized as other Asclepiadoideae,shared abundant and generalized pollinators.The floral features of V.hirundinaria are adapted for daytime and nighttime pollinatiors,such as bees,flies,moths,cockroaches,and ants.Flowers were pale white and opened at the afternoon(16:00 ? 18:00).The nectar was visible in the stigmatic chamber.The flowers released a strong sweet scent during day and night,dominated by Benzaldehyde,Phenylacetaldehyde,Acetophenone,and Methyl benzoate.During the 30 h of daytime and 20 h of nighttime observations,we overall recorded 7 orders,38 families and 81 species of flower visitors.Thereof,5 orders,18 families and 37 species were pollinators.On average,the corpuscle carrying rate of beetle and moth pollinators was 60.0 %,of bees and wasps 50.0 %,of flies 43.3 %,of cockroaches 40.0 %,and of ants 3.5 %.The number of corpuscles carried per individual was 3.2 ± 1.2 in flies,2.0 ± 0.0 in cockroaches,1.5 ± 0.9 in ants,1.4 ± 0.7 in bees and wasps,1.3 ± 0.5 in beetles,and 1.2± 0.4 in moths.We used 18 species of 13 families and five orders of pollinators for GCEAD(gas chromatography coupled to electroantennographic detection)experiments and demonstrated that they are sensitive to the most abundant compounds of V.hirundinaria.Subsequent behavioural field tests proved that these compounds are capable of attracting both flower visitors(4 orders,8 families and 13 species: flies,beetles,ants,and true bugs)and pollinators(4 orders,7 families and 12 species: beetles,flies,cockroaches,and ants).Overall,the strong floral scent of V.hirundinaria plays a significant role in the chemical attraction of both daytime and nighttime visitors and polinators.3.The pollination systems of the two studied Vincetoxicum species are quite different.This is caused by the difference in their flowering biology,i.e.phenology,flower features,nectar amount,and floral scent.While the share of floral features,i.e.flowers open very late,are pale in color,and produce a strong scent,lead to the similarity of pollinator groups.Though both species attract cockroaches,beetles,and ants,their chemical signals are distinct from each other.In conclusion,this thesis evaluated the flowering biology and pollination ecology of two Vincetoxicum species.Our study newly discovered and confirmed that cockroaches and ants are pollinators of both species,but cockroaches are much more effective than ants.The two plant species share some floral features and pollinator groups,but their pollination systems are quite different.We for the first time analysed floral scents in the genus by using chemical analytical and electrophysiological studies,and proved the involvement of scent in both daytime and nighttime visitor and polinator attraction.The results of this thesis advanced our understanding of cockroach polination and pollination of Vincetoxicum species in general.