Angiosperms Flowering plants

Transcription

1 Pollination

2 Angiosperms Flowering plants Flowering plants (250k sp) comprise the dominant plant life form on earth Evolved ~ mya a modest beginning but million years later increased in diversity

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5 Insects Become Modern the Cretaceous and Tertiary times The Cretaceous ( MYA) is one of the most significant geological periods for insect evolution 1. Devonian Hexapods 2. Carboniferous Winged insects 3. Permian to Triassic earliest members of most modern orders 4. Cretaceous Nascent modern biota (amidst unprecedented geological and evolutionarily change)

6 Insects Become Modern the Cretaceous During Cretaceous period many modern families 1 st appeared (some as early as Jurassic or Triassic), others like schizophoran flies & ditrysian leps evolved in the Tertiary 65 million to 1.8 mya Estimated that perhaps half or more of recent families appeared in Cretaceous Appears to be related (both cause and effect) to the radiation of the angiosperms

7 The Cretaceous Earth was geologically more active than at most times Dramatic climate change and Tectonic activity which resulted in widespread volcanism, splitting and drifting of the continents Fragmentation of Gondwana into the present southern continents is often invoked for contemporary distributions of various plant and animals

8 The Cretaceous Appear to be little affected by KT boundary events (at gross scale) Geologic record from this time forward better preserved than earlier periods

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11 Evolved from Pollinivory in early seed plants MYA (late Paleozoic, Mesozoic) e.g. Cycadales, seed ferns Probably Beetles Pollination perhaps inadvertent initially, but floral traits that increased chances of pollination and encouraged visits by most efficient pollinators were favored by selection Beetles also can destroy ovules-this may have promoted carpel closure and possibly evolution of inferior ovary

12 Basal Angiosperms e.g. Apetalous magnolias insect pollinated, probably Diptera, Coleoptera (early Cretaceous ~ 150 MYA) (Anemophily wind pollination derived later)

13 Taxonomic Distribution 2/3 + of Angiosperms are animal pollinated + a small proportion of Gymnosperms (e.g. Ephedra, cycads) Pollinators include: Flies (Diptera), Ants, bees, and wasps (Hymenoptera), Beetles (Coleoptera), Butterflies and moths (Lepidoptera) Hummingbirds, sunbirds, honey eaters Bats, rodents, small marsupials Oddities: Frogs, slugs, earthworms

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15 Insect Pollination Entomophily

16 Cantharophily

17 Myophily

18 Sphecophily

19 Myrmecophily

20 Melitophily

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23 Phalaenophily

24 Psycophily

25 Traditional Pollinator syndromes suggest some degree of coevolution Faegri and van der Pijl (1979)

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28 Alison Brody: effects of pollinators, herbivores, and seed predators on flowering phenology. Competition for pollinator services has often been suggested as the primary selective force molding flowering schedules. Flowering and reproductive characters are likely to reflect an evolutionary compromise of responses to various selective forces. Apparent competition or associational resistance may be important to the composition and flowering patterns of plant communities.

29 Two Big Ideas - Evolution has tended towards specialization of pollinator plant interactions, which has led to tight coevolution (not just diffuse) between these groups and.. - Coevolutionary interactions between insect pollinators and angiosperms are responsible (at least in part) for the incredible diversification of these two groups

30 Early Angiosperms Generalized flowers Many pollinators Open Sturdy (beetles) Recent Angiosperms Specialized flowers Rosidae few pollinators Zygomorphic-complex Nectaries Bees (50 MYA)

31 Should specialized plant-pollinator associations evolve? Plant Animal Benefits -Avoid pollen loading -Minimize pollen & nectar theft -Efficient movement of gametes -Neurological efficiency? -Shorter Handling time -Rewards large? -Reduced Competition Costs -Rewards large? -Risk of pollinator extinction & Dependence on pollinator populations -Reduced foraging efficiency -Longer travel times -Phenological dependence -Dependence on plant populations

32 Are plant-pollinator associations tightly co-evolved? Are plant-pollinator associations largely specialized?

33 Some are: Fig wasps Figs Expect specialized plants if long-lived, many reproductive episodes (continuous), pollinators whose populations fluctuate slightly

34 Tegeticula yuccasella Local host Specificity Oviposition into flower Limited seed destruction Pollination causing behavior 40 MYA!

35 But many apparently coevolved pollinator mutualisms are asymmetric - antagonistic exploitation E.g. the Orchidaceae At least 8-10,000 species offer no reward, only deception and fraud - capture pollinators - intoxicate them - Prostitution - mimicry (rivals, enemies, prey) Basically parasitism of insect by plants

36 Robbers Thieves Unfaithful Cheaters

37 Most plants are visited by a variety of potential pollinators Robertson Illinois Clements & Long 1923 Pikes Peak, CO

38 Pollinating animals tend to visit many plant species Clements & Long 1923 Pikes Peak CO

39 Ranunculaceae Even advanced, presumably specialized, plant families tend to be moderate generalists Orchidaceae Polemonianceae

40 Bees, most of which rely obligately and solely on floral resources, also tend to be moderate generalists Andrenidae Halictidae Apidae

41 Geographic ranges of plants and pollinators rarely correspond closely Plants often successful in new geographic areas, despite leaving their mutualists behind - Hawaiian ieie (Freycinetia arborea) formerly pollinated by extinct honeycreepers - In New Zealand Freycinetia baueriana lost bat pollinator

42 Why are pollination syndromes so weak? or What prevents coevolution? Thompson 1999: Geographic mosaic theory of coevolution dynamics of coevolution occur at a geographic scale above the level of local populations and below the level of the fixed traits of interacting species.

43 Did insect pollination cause increased seedplant diversity? Root Gorelick, Biological Journal of the Linnean Society (2001) 74: Poaceae (grasses) diverse (10,000 sp.), almost all wind pollinated Ants diverse, generally not pollinators Cycads, Gnetales other groups of insect pollinated plants were either never diverse, or diversified and became extinct Insect diversity decreased when angiosperms originated

44 However, these are rather poor arguments - Orchidaceae -25,000 species, almost exclusively insect pollinated, many specialized (Fabaceae, Asteraceae,Rubiaceae, Euphorbiaceae) - Bees: 20,000 species, few of which could exist without angiosperm flowers. - Rhopalocera = butterflies + skippers, almost all visit flowers: 20,000 species - Large families of Diptera (e.g. Syrphidae, Bombyliidae) rely heavily on floral resources

45 Most of the species diversity of angiosperms originated < 50 MYA e.g. major eudicot families Orchidaceae

46 and insect groups did diversify coincident with the angiosperms in the cenozoic Families

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48 Angiosperms Flowering plants Insects were original partners of angiosperms as pollinators and herbivores Undoubtedly pollinating insects facilitate and can control gene flow in most angiosperms and must effect speciation

49 Questions?