Exam 2
number
(A) Changes in the ______ of Hox genes correlate with changes at the level of phyla; increasing the number of Hox genes enables increased complexity. (B) Broad changes in Hox gene expression can produce different types of structures in body segments that had been identical. In branchiopods (top), the head contains feeding appendages, whereas thoracic segment T1, contains swimming appendages that are like those further back on the thorax (segments T2-T5). In other crustaceans, such as isopods, the first thoracic appendages have been modified into feeding structures called maxillipeds.
expression
(A) Changes in the number of Hox genes correlate with changes at the level of phyla; increasing the number of Hox genes enables increased complexity. (B) Broad changes in Hox gene _____ can produce different types of structures in body segments that had been identical. In branchiopods (top), the head contains feeding appendages, whereas thoracic segment T1, contains swimming appendages that are like those further back on the thorax (segments T2-T5). In other crustaceans, such as isopods, the first thoracic appendages have been modified into feeding structures called maxillipeds.
expression
(C) Specific changes in Hox gene _____ may be important in enabling different groups of animals to evolve different features; e.g., prolegs of butterfly and moth (lepidopteran) caterpillars that are not seen in fly (dipteran) larvae. (D) Changes in the function and/or regulation of downstream genes may allow differences such as those distinguishing the halteres of dipterans from the hindwings of lepidopterans.
downstream
(C) Specific changes in Hox gene expression may be important in enabling different groups of animals to evolve different features; e.g., prolegs of butterfly and moth (lepidopteran) caterpillars that are not seen in fly (dipteran) larvae. (D) Changes in the function and/or regulation of ______ genes may allow differences such as those distinguishing the halteres of dipterans from the hindwings of lepidopterans.
insect
Angraecum sesquipedale, also known as Darwin's orchid or the Star of Bethlehem orchid, is an epiphytic orchid endemic to Madagascar. First discovered in 1798, it was not taxonomically described until 1822. Angraecum sesquipedale has an extraordinarily deep nectary that grows as long as 35 cm (13.8 in). In 1862 Darwin received a box of flowers of these orchids, and in writing to his friend suggested that this orchid must be pollinated by a suitably long-tongued ______ pollinator.
arbuscules
Arbuscular Mycorrhiza (AM) Fungi (Glomeromycota) penetrate the cortical cells of the roots of a vascular plant and form _____/vescicles to aborb nutrients from the soil for growth; fungi are obligate symbionts 80% of vascular plant families contain AM; plants benefit from increased phosphorus uptake
congruent
Co-speciation/coevolution of host and parasite e.g., phylogeny of parasitic feather lice is mostly ______ with that of their dove and pigeon hosts, suggesting a history of co-speciation Eight (8) co-speciation events shown in figure Exceptions shown by crossing of lines between lice and hosts (evidence of host switching?)
co-speciation
Co-speciation/coevolution of host and parasite e.g., phylogeny of parasitic feather lice is mostly congruent with that of their dove and pigeon hosts, suggesting a history of _____-_____ Eight (8) co-speciation events shown in figure Exceptions shown by crossing of lines between lice and hosts (evidence of host switching?)
static
Coevolution - It is important to remember that we are looking at a snapshot of these interactions in evolutionary time; they are not ______ interactions
reciprocal
Coevolution - as one species adapts to another, its partner(s) may evolve as well - this two-way evolution results from ______ selection
parallel
Coevolution and cospeciation When the benefits of mutualism to both species are high and the relationship has been in place over long periods of evolutionary time, the relationship may result in cospeciation, in which speciation in one partner leads to and parallels speciation in the other partner Examples include systems where there is a history of _____ diversification of associated organisms such as hosts and their symbionts or parasites, as revealed by 'concordant' or 'congruent' phylogenies
co-speciation
Coevolution coevolution is often viewed from the perspective of _____-_______ but that is not always the case
reciprocal
Coevolution in narrow sense - _____ genetic change in two or more species resulting from interactions among them, owing to natural selection imposed by each on the other(s)
interspecific
Coevolution in simplest sense - species interact and evolve in response to each other - i.e., _____ interactions
coevolutionary
Coevolution may play out differently in different populations, leading to a diversity of ______ outcomes
identity
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era Homeotic genes are master-switch genes, encode proteins that determine the patterning - _____ and positioning - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a single gene family, and the proteins they encode share a particular 60 amino acid sequence ("homeodomain") that specifically binds to DNA to regulate the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
positioning
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era Homeotic genes are master-switch genes, encode proteins that determine the patterning - identity and _____ - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a single gene family, and the proteins they encode share a particular 60 amino acid sequence ("homeodomain") that specifically binds to DNA to regulate the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
single
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era Homeotic genes are master-switch genes, encode proteins that determine the patterning - identity and positioning - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a _____ gene family, and the proteins they encode share a particular 60 amino acid sequence ("homeodomain") that specifically binds to DNA to regulate the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
homeodomain
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era Homeotic genes are master-switch genes, encode proteins that determine the patterning - identity and positioning - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a single gene family, and the proteins they encode share a particular 60 amino acid sequence ("______") that specifically binds to DNA to regulate the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
regulate
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era Homeotic genes are master-switch genes, encode proteins that determine the patterning - identity and positioning - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a single gene family, and the proteins they encode share a particular 60 amino acid sequence ("homeodomain") that specifically binds to DNA to ______ the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
Homeotic
Discovery & characterization of the "Hox" cluster of homeotic genes in animals in 1970-1980s marked the beginning of modern "evo-devo" era ______ genes are master-switch genes, encode proteins that determine the patterning - identity and positioning - of anatomical structures during development along the anterior-posterior axis in metazoans Hox genes are members of a single gene family, and the proteins they encode share a particular 60 amino acid sequence ("homeodomain") that specifically binds to DNA to regulate the transcription of other genes crucial for development Comparable gene families exist and function in plant development (e.g., MADS-box genes)
Greeks
Evo-Devo, a short history Evo-devo-like ideas date to the ancient _____, who noted a parallel between the stages on the ladder-like Scala Naturae - from "lowest" to "highest" - and the developmental stages of organisms, from simple to complex
higher
Evo-Devo, a short history The evolutionary study of embryonic development reached a peak in the late 1800s thanks primarily to the efforts of one extraordinarily gifted, eminent German scientist named Ernst Haeckel. Haeckel, a physician, was so influenced by Darwin's The Origin of Species that he gave up medicine and devoted himself to comparative anatomy. But he embraced the pre-Darwinian notion that life formed a series of successively "_____ forms", with embryos of higher forms "recapitulating" those of the lower ones (an idea analogous to Russian nested dolls)
Ernst Haeckel
Evo-Devo, a short history The evolutionary study of embryonic development reached a peak in the late 1800s thanks primarily to the efforts of one extraordinarily gifted, eminent German scientist named _____ _____. Haeckel, a physician, was so influenced by Darwin's The Origin of Species that he gave up medicine and devoted himself to comparative anatomy. But he embraced the pre-Darwinian notion that life formed a series of successively "higher forms", with embryos of higher forms "recapitulating" those of the lower ones (an idea analogous to Russian nested dolls)
ontogeny
Evo-Devo, a short history They argued that the development of an individual over its lifetime - its _____- proceeded through simple traits early in development to more complex ones later in development
evo-devo
Evolution and Development Evolutionary developmental biology - "_____-______" - seeks to understand the mechanisms by which developmental patterns have evolved, both in terms of genetic/cellular (gene, cell & tissue) interactions and the evolutionary (selection) processes that drive them Several questions emerge, for example: what role has developmental evolution played in history of life on Earth? do developmental trajectories that produce phenotypes bias the variation & diversity that is produced or in any way constrain evolutionary change?
radiate
Examples of antagonistic coevolutionary associations Escape and _____ coevolution - species evolves a defense against a predator or parasite and is enabled to speciate into a diverse clade e.g., plant species evolve effective chemical defenses against herbivorous insects and subsequently undergo diversification Prey/host species evolve a major new defense, escapes from predator or parasite, and diversifies, only later a different predator/parasite adapts to prey/host and diversifies
Guild
Examples of antagonistic coevolutionary associations _____ coevolution - involves several species & their effects are not independent e.g., genetic variation in resistance of a host to two different species of parasite might be correlated (evolve in parallel) prey species interacts with two or more predators/parasites
Specific
Examples of antagonistic coevolutionary associations _____ coevolution - two species evolve in response to each other e.g., predator - prey relationship; i.e., an "evolutionary arms race"*
evolutionary
Examples of antagonistic coevolutionary associations ______ arms race - the most spectacular form of antagonistic coevolution in which one species invests in defenses, spurring its partner to invest in even greater counter-defenses, and so on
recapitulation
Haeckel believed that, over the course of time, evolution added new stages to produce new life forms, new species. Haeckel sought to explain evolution as a series of stages in which the new characteristics of the next animal to evolve are simply added on to those of the "lower" animal. Thus, embryonic development was seen as a record of evolutionary history. His 1866 biogenetic law stated "ontogeny is a precise and compressed _____ of phylogeny" - i.e., the embryological development of a particular species repeats the evolutionary history of that species.
Modern Synthesis
Haeckel's Biogenetic Law This idea was very attractive to scientists; it's as if development were a time machine that allowed them to look back into the distant past, just by studying early stages of development. Haeckel was so convinced of his law that he manipulated evidence to support it. However, the truth is that the development of embryos does not fit into the strict progression that Haeckel claimed. By the beginning of the 20th century, scientists had discovered many cases that defied Haeckel's so-called law. This was an unfortunate turn for science, because it set evolutionary biologists and developmental biologists down a dead-end. Haeckel's downfall came with the rise of genetics and the _____ _____ in the early 20th century - after all, Haeckel was promoting a basically Lamarckian notion that evolution had a built-in direction towards "higher" forms. Genes, it was soon discovered, controlled the rate and direction of embryonic development.
genetics
Henry Bateson (1861-1926) Naturalist, evolutionary and developmental biologist, and geneticist Translated Mendel's work into English, and named the science of ____ Noted a number of developmental 'abnormalities' in animals in parts of bodies that were either repeated (appendages) or segmented, or both, and called them "homeotic transformations" Bateson was interested in what such developmental transformations revealed about evolutionary change E. Lewis, C. Nüsslein-Volhard, and E. Wieschaus were awarded the the Nobel Prize in Physiology or Medicine in 1995 for their discovery of homeotic and segmentation genes
abnormalities
Henry Bateson (1861-1926) Naturalist, evolutionary and developmental biologist, and geneticist Translated Mendel's work into English, and named the science of genetics Noted a number of developmental '______' in animals in parts of bodies that were either repeated (appendages) or segmented, or both, and called them "homeotic transformations" Bateson was interested in what such developmental transformations revealed about evolutionary change E. Lewis, C. Nüsslein-Volhard, and E. Wieschaus were awarded the the Nobel Prize in Physiology or Medicine in 1995 for their discovery of homeotic and segmentation genes
homeotic
Henry Bateson (1861-1926) Naturalist, evolutionary and developmental biologist, and geneticist Translated Mendel's work into English, and named the science of genetics Noted a number of developmental 'abnormalities' in animals in parts of bodies that were either repeated (appendages) or segmented, or both, and called them "______ transformations" Bateson was interested in what such developmental transformations revealed about evolutionary change E. Lewis, C. Nüsslein-Volhard, and E. Wieschaus were awarded the the Nobel Prize in Physiology or Medicine in 1995 for their discovery of homeotic and segmentation genes
segmentation
Henry Bateson (1861-1926) Naturalist, evolutionary and developmental biologist, and geneticist Translated Mendel's work into English, and named the science of genetics Noted a number of developmental 'abnormalities' in animals in parts of bodies that were either repeated (appendages) or segmented, or both, and called them "homeotic transformations" Bateson was interested in what such developmental transformations revealed about evolutionary change E. Lewis, C. Nüsslein-Volhard, and E. Wieschaus were awarded the the Nobel Prize in Physiology or Medicine in 1995 for their discovery of homeotic and ______ genes
neoteny
Heterochrony Paedomorphosis - ontogenetic changes occur as larval features of an ancestor become morphological features of a descendant, i.e., juvenile character stage of ancestor is retained An example - ______ (somatic traits) in Mexican axolotl salamander, Ambystoma mexicanum Most extant salamanders live in water as juveniles, and on land as adults But the axolotl lives in water for entire life cycle and never loses traits associated with life in water - gills and flattened tail
Paedomorphosis
Heterochrony _____ - ontogenetic changes occur as larval features of an ancestor become morphological features of a descendant, i.e., juvenile character stage of ancestor is retained An example - neoteny (somatic traits) in Mexican axolotl salamander, Ambystoma mexicanum Most extant salamanders live in water as juveniles, and on land as adults But the axolotl lives in water for entire life cycle and never loses traits associated with life in water - gills and flattened tail
posterior
Homeotic genes and diversification in animal body plans In Drosophila melanogaster Hox genes occur in 2 clusters on chromosome 3, the Antennapedia and the Bithorax clusters, these control anterior-______identity of segments corresponding to their order on the chromosome Position of Hox gene expression shown for the blastoderm stage of the embryo and for regions that they form in adult fly
Bithorax
Homeotic genes and diversification in animal body plans In Drosophila melanogaster Hox genes occur in 2 clusters on chromosome 3, the Antennapedia and the _______ clusters, these control anterior-posterior identity of segments corresponding to their order on the chromosome Position of Hox gene expression shown for the blastoderm stage of the embryo and for regions that they form in adult fly
Antennapedia
Homeotic genes and diversification in animal body plans In Drosophila melanogaster Hox genes occur in 2 clusters on chromosome 3, the _____ and the Bithorax clusters, these control anterior-posterior identity of segments corresponding to their order on the chromosome Position of Hox gene expression shown for the blastoderm stage of the embryo and for regions that they form in adult fly
transcription
How do Hox genes function? Do major structural differences result from simply turning expression of a Hox gene 'on' or 'off'? Hox genes encode ______ factors that regulate transcription of "downstream" target genes by binding to DNA control regions (promoters, enhancers, cis-regulatory elements) of those genes Studies of the Ubx gene show that morphological divergence can be due to differences in expression but also timing of gene expression controlled by Hox gene(s) Evolutionary changes in spatial patterns of Hox gene expression also underlie body plan adaptations within animals
morphological
How do Hox genes function? Do major structural differences result from simply turning expression of a Hox gene 'on' or 'off'? Hox genes encode transcription factors that regulate transcription of "downstream" target genes by binding to DNA control regions (promoters, enhancers, cis-regulatory elements) of those genes Studies of the Ubx gene show that _____ divergence can be due to differences in expression but also timing of gene expression controlled by Hox gene(s) Evolutionary changes in spatial patterns of Hox gene expression also underlie body plan adaptations within animals
mouse
Hox gene expression patterns in vertebrates e.g., segment-specific anterior-posterior patterning in the _____; horizontal bars indicate segmental patterns of Hox gene expression in hindbrain and spinal cord Darker bars correspond to areas of relatively high gene expression, arrows connect genes in the HoxB cluster with homologous genes in Drosophila. Note mouse has 5 more genes in this cluster.
ultrabithorax
Hox genes in Drosophila E.g., a well characterized Hox mutation - mutation in the ______ gene (Ubx) transforms a 3rd thoracic segment (T3), which produces halteres*, into a 2nd thoracic segment which produces wings (*halteres - the Drosophila homologue of the hind-wing of 4-winged insects)
phyla
Hox genes in animals Studies have shown that all animal _____ have Hox genes genes have homeobox sequences similar to those of their homologues in Drosophila (where first found) genes often have same gene order and orientation as in Drosophila, although some copies may be missing most animals have a single Hox cluster or complex mammals have four Hox gene clusters (Hoxa, Hoxb, Hoxc & Hoxd) that arose by gene duplication in different parts of the genome, and a total of 13 different genes (compare to 1 cluster of 8 genes in Drosophila) within some animals, structural evolution of Hox genes has occurred
four
Hox genes in animals Studies have shown that all animal phyla have Hox genes genes have homeobox sequences similar to those of their homologues in Drosophila (where first found) genes often have same gene order and orientation as in Drosophila, although some copies may be missing most animals have a single Hox cluster or complex mammals have ______ Hox gene clusters (Hoxa, Hoxb, Hoxc & Hoxd) that arose by gene duplication in different parts of the genome, and a total of 13 different genes (compare to 1 cluster of 8 genes in Drosophila) within some animals, structural evolution of Hox genes has occurred
duplication
Hox genes in animals Studies have shown that all animal phyla have Hox genes genes have homeobox sequences similar to those of their homologues in Drosophila (where first found) genes often have same gene order and orientation as in Drosophila, although some copies may be missing most animals have a single Hox cluster or complex mammals have four Hox gene clusters (Hoxa, Hoxb, Hoxc & Hoxd) that arose by gene ______ in different parts of the genome, and a total of 13 different genes (compare to 1 cluster of 8 genes in Drosophila) within some animals, structural evolution of Hox genes has occurred
Ubx
Hox genes in closely related taxa Genetic differences at Hox loci may also result in developmental differences between closely related species e.g., pattern of epidermal cell hairs on legs of Drosophila species (A) Differences in T3 segment map to the Ubx locus; _____ gene expression correlates precisely with hair patterns Amino acid sequence of Ubx protein is identical in both species, so regulatory changes (expression) must be responsible (B) Similar example in Drosophila spp., size of sex comb bristles on T1 segment correlates with expression of sex-combs reduced (Scr) locus
coevolution
It wasn't until 1903, 20 years after Darwin's death that a hawkmoth - Xanthopan morganii subsp. praedicta - with an exceptionally long proboscis was discovered in Madagascar. What is the benefit here? An association that has resulted in the highly specific, intimate ______ of these two organisms (pollination, nectar as rewards)
obligate
Lichens Lichens are composite organisms that result from a symbiotic association between a fungus ("mycobiont") and a photosynthetic microbe ("photobiont"), either a green algae or cyanobacterium Lichens are considered an example of an _____ symbiosis - the two symbionts cannot live on their own individually
multicellular
Mutualisms and adaptation Mutualistic symbiosis often provides one or both symbionts with new capabilities or opportunities bacteria & other microbes have formed many intimate mutualisms with ______ organisms, especially animals, many of which have lost the ability to synthesize essential metabolites such as amino acids & vitamins e.g., sap-feeding homopteran insects (aphids, leafhoppers, cicadas) harbor symbiotic bacteria which provide essential compounds which plant sap lacks: - bacteria are vertically transmitted in host insects - bacterial phylogeny closely matches the phylogeny of their insect hosts, indicating associations are ancient and stable 'sharpshooters' such as Cuerna sayi are nutritionally dependent on 2 endosymbiotic bacteria, Sulcia & Baumannia*
extreme
Mutualisms are interactions between species in which individuals of both species benefit (to varying degrees) - no set path by which mutualisms evolve, i.e., may begin from initially neutral or one-sidedly beneficial interactions - often the individuals of the participating species are associated for much of their lives and may exist over long periods of time (up to many millions of years) - such associations may result in ______ adaptations
exploitation
Some mutualisms have evolved as the result of reciprocal ______, in which each species obtains something from the other but with associated "costs" i.e., some mutualisms have arisen from parasitic or otherwise exploitative relationships
Rhizobia
Symbiotic nitrogen fixation What is the basis of this symbiosis? Nitrogen is often the limiting element for plant growth ______ infect root cells to induce formation of nodules where they fix atmospheric N2, an energy requiring process*, via nitrogenase enzyme complex Bacteria supplied with carbohydrates (carbon source) and oxygen for their growth from plant photosynthesis Host plant supplied with source of fixed nitrogen (NH3+ for proteins) from bacterial fixation *Overall reaction, catalyzed by rhizobial nitrogenase 6 e- + 6 H+ + N2 2NH3 amino acids
rate
The "Holy Grail" - connecting an understanding of genes and development* With the advent of the Modern Synthesis (1930s-1940s) research revealed genes code for the developmental traits themselves and genes control the ______ of their development Developmental systems began to be studied by geneticists: e.g., - developmental mutants in Drosophila, T. Dobzhansky, W. Gehring - developmental mutants in guinea pigs, S. Wright - development & speciation in plants, L. Dunn, G. L. Stebbins - development in sea urchins, R. Britten and E. Davidson
rearrangements
The Hox gene complex has experienced a high number of structural changes during their evolution in the genus Drosophila. Three major ______ (squares: A, Antp-Ubx; B, Ubx-abdA; and C, lab-pb), seven micro-inversions (circles) and three gene transpositions (inverted triangles) have been identified and mapped to the phylogenetic tree by comparative analysis.
inversions
The Hox gene complex has experienced a high number of structural changes during their evolution in the genus Drosophila. Three major rearrangements (squares: A, Antp-Ubx; B, Ubx-abdA; and C, lab-pb), seven micro-______ (circles) and three gene transpositions (inverted triangles) have been identified and mapped to the phylogenetic tree by comparative analysis.
transpositions
The Hox gene complex has experienced a high number of structural changes during their evolution in the genus Drosophila. Three major rearrangements (squares: A, Antp-Ubx; B, Ubx-abdA; and C, lab-pb), seven micro-inversions (circles) and three gene _______ (inverted triangles) have been identified and mapped to the phylogenetic tree by comparative analysis.
paedomorphosis
Timing of development Heterochrony - refers to changes in the rate and timing of development Heterochrony focuses on the time in the process at which a developmental trait is first expressed in a species relative to when that same trait is first expressed in the ancestor of that species There are 4 types of heterochrony, the most commonly encountered is ______
Heterochrony
Timing of development ______ - refers to changes in the rate and timing of development Heterochrony focuses on the time in the process at which a developmental trait is first expressed in a species relative to when that same trait is first expressed in the ancestor of that species There are 4 types of heterochrony, the most commonly encountered is paedomorphosis
phenotype
Types of interspecific interactions Reciprocal (______) selection - evolution in one species in response to selection imposed by a second species, followed by evolution in the second species in response to reciprocal selection imposed by the first species considered a prerequisite for coevolution to occur some evidence for it in host-parasite interactions phenomenon seldom documented in natural populations
mutualistic
Types of interspecific interactions _____ interactions - evolutionary association where each species benefits, by changes that cause increases in their relative fitness e.g., lichens, root symbioses (rhizobia, mycorrhizae), gut symbioses, marine coral reefs
antagonistic
Types of interspecific interactions ______ coevolution interactions - in which one species decreases the fitness of the other, or both - e.g., predator-prey, host-parasite, plant-herbivore interactions - such interactions may produce an "evolutionary arms race" which may go on indefinitely
arms
Types of interspecific interactions antagonistic coevolution interactions - in which one species decreases the fitness of the other, or both - e.g., predator-prey, host-parasite, plant-herbivore interactions - such interactions may produce an "evolutionary ______ race" which may go on indefinitely
cheaters
Yuccas and yucca moth mutualism Mutualisms are NOT always stable over evolutionary time e.g., 2 lineages of yucca moths have evolved from mutualistic ancestors no longer pollinate - they have become _____ - lay so many eggs that the larvae consume most/all of the yucca seeds in a fruit
mutualism
Yuccas and yucca moth mutualism This example provides the basis for understanding the evolution of a ______ between species As in any association, there exists the potential for conflict because a partner that cheats by exploiting its partner without paying the cost of providing a benefit in exchange is likely to gain a selective advantage But selection tends to favor protective mechanisms, including punishing "cheaters" to prevent over-exploitation There are factors which should favor evolutionary stability, including . . . - lifelong association with the same host or partner - restricted opportunities to switch to other partners or resources
conflict
Yuccas and yucca moth mutualism This example provides the basis for understanding the evolution of a mutualism between species As in any association, there exists the potential for ______ because a partner that cheats by exploiting its partner without paying the cost of providing a benefit in exchange is likely to gain a selective advantage But selection tends to favor protective mechanisms, including punishing "cheaters" to prevent over-exploitation There are factors which should favor evolutionary stability, including . . . - lifelong association with the same host or partner - restricted opportunities to switch to other partners or resources
protective
Yuccas and yucca moth mutualism This example provides the basis for understanding the evolution of a mutualism between species As in any association, there exists the potential for conflict because a partner that cheats by exploiting its partner without paying the cost of providing a benefit in exchange is likely to gain a selective advantage But selection tends to favor _____ mechanisms, including punishing "cheaters" to prevent over-exploitation There are factors which should favor evolutionary stability, including . . . - lifelong association with the same host or partner - restricted opportunities to switch to other partners or resources
stability
Yuccas and yucca moth mutualism This example provides the basis for understanding the evolution of a mutualism between species Interaction between yucca species and their pollinating moths provides an example of how evolutionary ______ can be achieved - moth lays only a few eggs in each flower, distributed to many flowers - only a few of the many developing seeds are consumed by moth larvae - plant aborts fruits with too many eggs laid in them, limits loss of resources - fruit abortion imposes strong selection on moths that lay too many eggs in a flower because eggs/larvae in aborted fruits perish
Coevolution
_____- evolving interactions among species
Mutualisms
______ are interactions between species in which individuals of both species benefit (to varying degrees) - no set path by which mutualisms evolve, i.e., may begin from initially neutral or one-sidedly beneficial interactions - often the individuals of the participating species are associated for much of their lives and may exist over long periods of time (up to many millions of years) - such associations may result in extreme adaptations
