Download Macroevolutionary processes

Macroevolutionary Processes—
Radiations
Major Speciation Models
Ancestor
B
A
A
Allopatric
C
B (island)
A’
A
A’ A” B
(ancestor dies out)
Founder
Phyletic gradualism
Concepts Involving Radiations
• Definition of “radiation”—relatively rapid
diversification of an initial ancestral
population into several derivatives (species)
• Often associated with opening of a new
geographic area or set of new niches (e.g.,
ecological, behavioral, nutritional)
• Often accompanied or provoked by one or
more novelties/innovations
Concepts Involving Radiations
• Character displacement—one species
affects direction of evolution or at least
local behavior, in one or more competitors,
not often explicitly demonstrated but often
implicitly invoked in studies of radiations
• Parallelisms—multiple independent origins
of similar traits within lineages or among
closely related lineages is often compelling
evidence of a radiation
Coevolutionary Radiation
• Intimate association with and parallel speciation in
different organismal lineages
• Must demonstrate closely correspondent
diversification patterns between organism groups;
often revealed by congruent molecular
phylogenies and tight host-user relationships
• Generally demands sole utilization of one host by
an organism (no generalist behavior)
• e.g., figs and fig wasps
• e.g., yuccas and yucca moths
Adaptive Radiation
• “The rise of a diversity of ecological roles
and attendant adaptations in different
species within a lineage" (Givnish and
Sytsma)
• Term “adaptive radiation” has been recently
loosely applied to all bursts of
diversification; attempts being made to
restrict definition
• Does not always result in large species
numbers or depend on a key innovation
Adaptive Radiation
• Correctly defined examples require empirical
evidence:
– Adaptive value of phenotypic traits
• Comparative methods—distantly related, ecologically similar
species show convergent form, physiology or behavior
• Functional analyses—functional significance of traits (e.g.,
stomata)
• Populational studies—phenotypic traits linked to survivorship
and reproduction
– Environmental sorting of different phenotypic forms,
tracking of multiple new niches/adaptive zones by sister
taxa; similar phenotypic traits and occupation of
“equivalent” habitats by non-sister taxa
Adaptive Radiation
• Examined (or at least postulated) most
intensively in oceanic islands
• Could further subdivide examples
– Diversification within one habitat—e.g.,
pollinator exploitation
– Diversification across habitats—e.g., classic
AR
• Examples later on
Adaptive Radiation
• Adaptive radiation still commonly assumed
prior to investigation; results then used to
characterize “an example of adaptive
radiation”—circular reasoning!!
• Few studies have adequately demonstrated
divergence in both phenotypic (e.g.,
morphological, anatomical) traits and
ecological differentiation among sister taxa
Adaptive Radiation
• Few studies have adequately investigated the
evolution of derivative taxa relative to the sister
group (nearest relative[s])
• Extraordinarily few groups have been investigated
intensively for comprehensive information on
evolutionary processes, relevant speciation models,
isolation mechanisms, microevolutionary (genetic)
processes, etc.
• Most studies have focused on island groups—easier
to work with and get funded, sexier; but many of the
same processes should hold for continental groups
•
Molecular Data in AR
Studies
Use of phenotypic traits to reconstruct phylogeny of a
group and to interpret phenotypic changes is
controversial, considered by many to be circular
reasoning
• Molecular markers provide a more "neutral" data set
from which to generate a phylogeny
• Molecular phylogeny can be used to infer relationship
of morphological traits, ecological diversification,
divergence in feeding behavior, etc., and can be used
as starting point for investigating
molecular/developmental basis of traits
Evolution in African Cichlids
• Several distinctive groups, many very different
looking species in each, with divergent feeding
strategies within lakes
• Several hundred cichlid species in each lake, most
endemic to one lake
• Extreme phenotypic features among species within
groups make interpretation of relationships difficult
• Similar forms with similar mouth structures, feeding
behavior and ecological niche grow in different lakes;
are they related? Or parallel products of adaptive
radiation?
Evolution in African Cichlids
Evolution in African Cichlids
• mtDNA phylogeny reveals
that cichlid species in
different African lakes with
equivalent body form and
mouth-feeding structures
are NOT sister species 
rampant parallelism
• phenotypically and
ecologically divergent
species typically are sisters
extensive divergence in
relatives
Reinthal & Meyer (1997)
Evolution in African Cichlids
• Evolution in African cichlid fishes
(cont.)
– Ecologically equivalent species in different
lakes occupy similar microhabitats, eat same
food items  strong selection for similar
phenotypes
– Suggestion of sympatric speciation within
individual lakes, accompanied by adaptive
radiation based on mouthparts for feeding
 reinforcement by competitive exclusion?
Diversification in Brocchinia
• e.g., “pitcher plants”
(Brocchinia) on
Venezuelan tepuis
– About 20 species on tall,
nutrient-poor (often boggy)
sandstone mesas (tepuis)
jutting up out of the
Venezuelan lowland
rainforest
– Several growth habits and
feeding strategies--"tank"
habit and carnivory,
epiphytes, tree forms, antplants
Givnish et al. (1997)
Diversification in Brocchinia
Diversification in Brocchinia
• “pitcher plants” (Brocchinia) on Venezuelan
tepuis (cont.)
– Morphological and anatomical traits related
intimately to growth form and nutrition; tank habit
found only at higher elevations
– Divergent growth forms and feeding strategies
obscure the relationships  chloroplast DNA
phylogeny used to interpret morphological and
ecological evolution
– Two sister lineages occur primarily on tepuis in
different geographic areas
Diversification in Brocchinia
•“pitcher plants” (Brocchinia) on Venezuelan
tepuis (cont.)—parallelism of carnivorous traits
Givnish et al. (199
Diversification in Brocchinia
stepwise evolution of traits for carnivorous habit
Givnish et al. (1997)
Evolution in Hawaiian Viola
• Nine taxa, seven species distributed over most islands
• Species occupy several different habitats across five
islands
–
–
–
–
–
dry forest
dry cliff
mesic streambank
swamp (cloud) forest
open bog
• Species growing in same habitat on different islands
are almost identical morphologically, anatomically
Evolution in Hawaiian Viola
Hawaiian Islands
Price, J. P. a. W. W. L. (2004).
Evolution in Hawaiian Viola
•Phylogenetic tree of
Internal Transcribed
Spacer (nrDNA)
shows that Hawaiian
taxa highly derived
(i.e., advanced) in
the genus
• Nearest sister is an
Arctic tundra bog
violet, Viola
langsdorffii, NOT
tropical species
Ballard & Sytsma (2000)
Evolution in Hawaiian Viola
•Arctic-breeding birds
probably dispersed
seeds to Hawaii
•ca. 75 bird species
breed in Arctic,
overwinter in central
or
south Pacific
•some (e.g., golden
plover) arrive in
Hawaii by the
millions, feed in
areas near tundra
bogs before migration
Range of Viola langsdorffii
Ballard & Sytsma (2000)
Evolution
in
Hawaiian
Viola
Bog (reclining herb
or shrub)
Dry Forest (treelet)
Swamp forest (shrub)
V. maviensis (Maui, Molokai,
Hawaii)
V. wailenalenae (Kauai)
V. kauaensis (Kauai,
Oahu)
V. tracheliifolia (Kauai,
Oahu, Maui, Molokai)
V. robusta (Molokai)
Evolution in Hawaiian
Viola
Bog
Swamp Forest
Wet
(Swamp Forest)
Dry
(Dry Forest)
Very Wet
(Bog)
Prevailing Trade Winds
Dry Forest
Havran (unpublished data)
Evolution in Hawaiian Viola
• Phylogenetic tree of ITS
sequences, and mapping of
islands and habitats onto it:
– Modest radiation from Arctic
tundra bog ancestor
– Colonization first on Kauai,
subsequent diversification and
dispersal eastward
– Parallel evolution in growth
form, leaf morphology, leaf
anatomy
– Morphologically “analogous”
species on different islands not
close relatives
Evolution in Hawaiian Viola
Phylogenetic Tree
Showing Leaf Traits
of Hawaiian Viola
Comparative Ecological Studies of
“Evolutionary Replicates” Across Islands
•Replicate sublineages studied
intensively on two different islands,
Kaui and Molokai
•Replicates include:
-1 dry forest species (V.
tracheliifolia) across islands
-2 swamp forest species
(V. robusta or V.
waialenalenae)
-2 bog species (V. kauaensis or
V. maviensis)
Evolution in Hawaiian Viola
Ecological research
• Microhabitat parameters
– Soil
– Climate
– Light Availability
• Physiological Traits
– Leaf Anatomy
– Photosynthetic
Physiology
– Leaf Water Potential
Kauai
V. kauaensis
Molokai
Bog
V. wailenalenae
V. robusta
Swamp Forest
V. tracheliifolia
• Reproductive Biology
– Breeding Systems
– Isolation Mechanisms
• Ethological
• Temporal
V. maviensis
V. tracheliifolia
Dry Forest
Havran (unpublished data)
V. waialenalenae
V. kauaensis
Evolution in Hawaiian Viola
Examined % canopy openness, soil moisture, pH, N, C &
several micronutrients in populations of 4 spp.
• Soil moisture & related
traits (e.g., C)
differentiate spp.
• N & pH also important,
Ca not very important
(distinguish bog
species)
• Light etc. contribute
little
• WATER IS KEY!
Havran (unpublished data)
Evolution in Hawaiian Viola
Climate - Humidity
Kauai
Molokai
Havran (unpublished data)
Evolution in Hawaiian Viola
Soil Water
Kauai
Molokai
Bog
Swamp
Dry Forest
Havran (unpublished data)
Evolution in Hawaiian Viola
Photosynthetic Efficiency in
V. robusta and V. maviensis
Swamp forest
violet
outperforms
bog violet at all
light levels!?
Havran (unpublished data)
Evolution in Hawaiian Viola
Leaf Anatomy - Bog Violets
V. maviensis
•Thick upper
and lower
epidermis
•Palisade cells 1
layer thick
V. kauaensis
Havran (unpublished data)
Evolution in Hawaiian Viola
Leaf Anatomy - Swamp Violets
V. robusta
•Thick upper
epidermis, thin
lower epidermis
•Palisade cells 2
layers thick
•Druses present
V. wailenalenae
Havran (unpublished data)
Evolution in Hawaiian Viola
•Morphologically and anatomically similar species on
different islands are not phylogenetic “sister” species
•Morphologically and anatomically similar species on
different islands occupy similar ecological niches
•soil moisture mainly drives local species distributions in different
habitats; anatomy linked to habitats
•Surprisingly, Swamp Violet (V. wailenalenae) is more
photosynthetically efficient at high light levels than Bog Violet (V.
kauaensis), but restriction to lower soil moisture prevents it from
invading bog!
•Leaf anatomy appears linked to habitat
 Hawaiian violets = adaptive radiation
Review
• A “radiation” is a relatively rapid burst of
speciation, producing multiple species from
a recent common ancestor
• Not all lineage radiations are adaptive;
researchers must demonstrate a link
between environmental selection (habitat)
and phenotypes (morphology)
• Molecular data are valuable to provide a
basis for inferring morphological evolution
Review
• Adaptive radiations common on oceanic
islands but probably overlooked on
continents
• Two consequences of AR are common and
often concurrent:
– Non-sister species inhabiting similar ecological
zones are phenotypically convergent
– Sister species in different adjacent habitats are
phenotypically divergent
Bibliography
• Ballard, H. E., Jr. and K. J. Sytsma. 2000. Evolution and
biogeography of the woody Hawaiian violets (Viola, Violaceae):
Arctic origins, herbaceous ancestry, and bird dispersal. Evolution
54:1521-1532.
• Givnish, T. J. and K. J. Sytsma (eds.). 1997. Molecular evolution and
adaptive radiation. Cambridge University Press, Cambridge, United
Kingdom. 621 pp.
• Givnish, T. J., K. J. Sytsma, J. F. Smith, W. J. Hahn, D. H. Benzing,
and E. M. Burkhardt. 1997. Molecular evolution and adaptive
radiation in Brocchinia (Bromeliaceae: Pitcairnioideae) atop tepuis of
the Guayana shield. In: Givnish, T. J. and K. J. Sytsma (eds.),
Molecular evolution and adaptive radiation. Cambridge University
Press, Cambridge, United Kingdom. pp. 259-311.
• Niklas, K. J. 1997. The evolutionary biology of plants. University of
Chicago Press, Chicago, Illinois. 449 pp.
Bibliography
• Nitecki, M. H. (ed.). 1990. Evolutionary innovations.
University of Chicago Press, Chicago, Illinois. 304 pp.
• Reinthal, P. N. and A. Meyer. 1997. Molecular phylogenetic
tests of speciation models in Lake Malawi cichlid fishes. In:
Givnish, T. J. and K. J. Sytsma (eds.), Molecular evolution
and adaptive radiation. Cambridge University Press,
Cambridge, United Kingdom. pp. 376-390.
• Schluter, D. and J. D. McPhail. 1993. Character
displacement and replicate adaptive radiation. Trends in
Ecology and Evolution 8:197-200.