ectosymbionts (lecture 4) Flashcards
what are ant-plant mutualisms?
- various types of mutualistic relationships between plants and ants that have evolved independently in over 100 tropical genera (Heil and McKey, 2003)
- usually work through plants supplying ants with food &/ shelter
- ants defend plant from herbivores and other plants in return
what is the relationship between the swollen thorn acacia and the ant pseudomyrmex ferruginea?
- the plant produces lipid based energy rich beltian bodies at the end of leaves that are food for ant larvae
- extra floral nectaries on stem provide food for ants, triggered by their presence
- ants live in domatia in swollen thorns
- ants attack herbivores and plants that invade their host plant’s space, providing defence
what is the relationship between chamaecrista and ants?
- extra floral nectaries on petioles and stems provide food for ants in return for defence
- convergent evolution with efn on acacia and other species
- (coutinho et al 2012)
what did baker-meio and marquis (2012) find about chamaecrista?
- removing extra floral nectaries, imp. source of nutrients and water for ants reduced successful fruit
- presence vs exclusion of seed predators = same fruiting success when efns present as ants kill predators
- signif reduction in fruiting success when predators present but no efns
what is the relationship between whistling thorn acacia and ants?
- ants defend whistling thorn against macrofauna in africa, effective deterrent even against animals as big as giraffe
- domatia refuges and efns in return
- mutualistic basis of relationship regulated by large herbivore pressure, in their absence the plant down regulates nectar secretion and domatia production
what did palmer et al (2008) find about different ant species and whistling thorn acacia defense?
- different ant species compete to colonise acacia
- different levels of aggression
e. g. Crematogaster mimosae: very agressive, relies heavily on extra floral nectaries and domatia. does better colonising plant in presence of large predators. more trees survive and grow better when colonised by this good defender. few beetle attacks
e. g. Crematogaster sjostedti: less aggressive, does not rely on domatia but live in wounds from tree-boring longhorned beetle larvae. do better when large predators absent. trees do worse - less growth, more death. facilitate beetle attacks - even more than when no ants at all
what are the ant plants?
- paraphyletic genuses of epiphytes: hydnophytum and mymrecodia
- multichambered tubers (refugia) in swollen stem
- ants defend hosts and also defecate in chambers providing mineral nutrients hard to come by as an epiphyte
what did huxley et al (1978) find out about the chambers in ant plants?
- gave ants radioactive phosphate and traced where it went
- translocated to plants, evidence of nutrient flow
- differential nutrient flow in different chambers
- better uptake in warty chambers
- ants defecate more in warty chambers as host does better
what are aphid-ant mutualisms?
- ants farm aphids, antennating them so they secrete sugary honeydew
- spatially and temporally stable source of carbohydrates and water for ants
- aphids don’t get potentially lethal build up of fungal sugar middents and ants defend them from attacks. ant-attended colonies more stable, persist longer
what are the costs of the mutualism to aphids?
- ants prevent formation of new colonies via dispersal
- bite off aphid wings
- ant mandibular secretions can inhibit wing development
- oliver et al (2007) ants have tranquilising effect on aphids, limiting motor function, so can’t disperse via walking either
- larger, unusually crowded colonies benefit ants as more honeydew
define pollination
- the transfer of pollen from the anther to the sifma of carpels to fertilise ovules
what is the history of pollination mutualisms (bronstein et al 2006)
- insects have consumed pollen since permian, pre evolution of angiosperms
- excess pollen probs evolved as reward for early mutualistic pollinators by late paleozoic (generalist pollinators, flies, wasps beetles etc not specialised)
- nectar evolved some time before the late jurassic, judged by appearance of specialised mouthparts in diptera for nectar feeding
what is an honest signal of floral quality?
- symmetry usually considered honest
- controlled development under unstable environmental and genetic conditions sign of genotypic quality and therefore more nectar
Moller, 1995:
- manipulated symmetry, the more symmetrical, the more visits from pollinators
- symmetry is a signal
when is floral symmetry dishonest?
e. g. in bee orchid
- no nectar
- acts as mimic of female bee to lure male bees in and produces scent like insect pheromones
- even though v symmetrical
