A test for Allee effects in the self-incompatible wasp-pollinated milkweed Gomphocarpus physocarpus
- Coombs, Gareth, Peter, Craig I, Johnson, Steven D
- Authors: Coombs, Gareth , Peter, Craig I , Johnson, Steven D
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6511 , http://hdl.handle.net/10962/d1005938 , http://dx.doi.org/10.1111/j.1442-9993.2009.01976.x
- Description: It has been suggested that plants which are good colonizers will generally have either an ability to self-fertilize or a generalist pollination system. This prediction is based on the idea that these reproductive traits should confer resistance to Allee effects in founder populations and was tested using Gomphocarpus physocarpus (Asclepiadoideae; Apocynaceae), a species native to South Africa that is invasive in other parts of the world. We found no significant relationships between the size of G. physocarpus populations and various measures of pollination success (pollen deposition, pollen removal, and pollen transfer efficiency) and fruit set. A breeding system experiment showed that plants in a South African population are genetically self-incompatible and thus obligate outcrossers. Out-crossing is further enhanced by mechanical reconfiguration of removed pollinaria before the pollinia can be deposited. Selfpollination is reduced when such reconfiguration exceeds the average duration of pollinator visits to a plant. Observations suggest that a wide variety of wasp species in the genera Belonogaster and Polistes (Vespidae) are the primary pollinators. We conclude that efficient pollination of plants in small founding populations, resulting from their generalist wasp-pollination system, contributes in part to the colonizing success of G. physocarpus. The presence of similar wasps in other parts of the world has evidently facilitated the expansion of the range of this milkweed.
- Full Text:
- Authors: Coombs, Gareth , Peter, Craig I , Johnson, Steven D
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6511 , http://hdl.handle.net/10962/d1005938 , http://dx.doi.org/10.1111/j.1442-9993.2009.01976.x
- Description: It has been suggested that plants which are good colonizers will generally have either an ability to self-fertilize or a generalist pollination system. This prediction is based on the idea that these reproductive traits should confer resistance to Allee effects in founder populations and was tested using Gomphocarpus physocarpus (Asclepiadoideae; Apocynaceae), a species native to South Africa that is invasive in other parts of the world. We found no significant relationships between the size of G. physocarpus populations and various measures of pollination success (pollen deposition, pollen removal, and pollen transfer efficiency) and fruit set. A breeding system experiment showed that plants in a South African population are genetically self-incompatible and thus obligate outcrossers. Out-crossing is further enhanced by mechanical reconfiguration of removed pollinaria before the pollinia can be deposited. Selfpollination is reduced when such reconfiguration exceeds the average duration of pollinator visits to a plant. Observations suggest that a wide variety of wasp species in the genera Belonogaster and Polistes (Vespidae) are the primary pollinators. We conclude that efficient pollination of plants in small founding populations, resulting from their generalist wasp-pollination system, contributes in part to the colonizing success of G. physocarpus. The presence of similar wasps in other parts of the world has evidently facilitated the expansion of the range of this milkweed.
- Full Text:
Pollinators, “mustard oil” volatiles, and fruit production in flowers of the dioecious tree Drypetes natalensis (Putranjivaceae)
- Johnson, Steven D, Griffiths, Megan E, Peter, Craig I, Lawes, Michael J
- Authors: Johnson, Steven D , Griffiths, Megan E , Peter, Craig I , Lawes, Michael J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6519 , http://hdl.handle.net/10962/d1005948
- Description: The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the “ mustard oil bomb ” ). We investigated the pollination biology and fl oral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with fl owers borne on the stem (caulifl ory). Flowering male trees were more abundant than female ones and produced about 10-fold more fl owers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main fl ower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fi delity to D. natalensis fl owers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female fl owers developing fruits with viable seeds. Cetoniid beetles showed signifi cant orientation toward the scent of D. natalensis fl owers in a Y-maze olfactometer. The scents of male and female fl owers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.
- Full Text:
- Authors: Johnson, Steven D , Griffiths, Megan E , Peter, Craig I , Lawes, Michael J
- Date: 2009
- Language: English
- Type: Article
- Identifier: vital:6519 , http://hdl.handle.net/10962/d1005948
- Description: The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the “ mustard oil bomb ” ). We investigated the pollination biology and fl oral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with fl owers borne on the stem (caulifl ory). Flowering male trees were more abundant than female ones and produced about 10-fold more fl owers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main fl ower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fi delity to D. natalensis fl owers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female fl owers developing fruits with viable seeds. Cetoniid beetles showed signifi cant orientation toward the scent of D. natalensis fl owers in a Y-maze olfactometer. The scents of male and female fl owers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.
- Full Text:
- «
- ‹
- 1
- ›
- »