• Species Interactions

Chapter 17: Coevolution and Mutualism

Interacting species may coevolve

Biotic selective agents evolve

Species act as selective agents on each other

+/- consumer-resource

predator-prey, parasite-host, plant-herbivore

- /- competition

+/+ mutualism

trophic, seed dispersal, pollination, defense

Heliconius butterflies have big eyes

The caterpillars feed on Passiflora leaves,,,

Passiflora leaf shapes and egg mimics are defensive against a

visual herbivore

Two other vine genera in the rainforest are pollinated by it

• Anguria and Gurania in squash family

• They are high canopy vines

• They have bright, red tubular flowers with a bright yellow marking the center

• Heliconius get pollen from them..they use the amino acids in egg production

• Very specialized

• What about Florida firebush?

Mimicry complex M. marsaeus M. menophilus

M. ludovica

Northern Peru

throughout South America

“Coevolution” in the strict sense is the process whereby

• populations of

• two or more species interact,

• traits of each may evolve in response to traits of the other

• reciprocal selective effects on traits

Coevolution is mediated by biological agents.

• evolutionary effects of biological agents are unlike those of physical factors

– biological factors stimulate mutual evolutionary responses

– adaptations of organisms in response to changes in the physical environment have no effect on that environment

– biological agents foster diversity of adaptations

– physical agents foster convergence

Antagonists evolve in response to each other.

• Charles Mode coined the term coevolution in a 1958 article in Evolution:

– host and pathogen: cycling of virulent/avirulent pathogens and susceptible/resistant hosts

• In a 1964 article in Evolution, Paul Ehrlich and Peter Raven placed coevolution in an ecological context

– closely related groups of butterflies tend to feed on closely related species of plants

– specialization is associated with host plant chemistry

The carrot family includes Queen Anne’s Lace, celery, cilantro, parsley, dill….

Berenbaum found: The evolutionary history of the chemistry shows increasing complexity and increasing toxicity and increasingly specialized occurrence ONLY highly specialized insects feed on the most toxic ones These are descended from close relatives that feed on less toxic ones Insect families such as Swallowtail butterflies, that feed on carrot family also feed on distantly related Citrus family… Which also has furanocoumarins!

Many plants…subset of these…subset of these

Papilio thoas from Peru

Some other examples of coevolution

in antagonistic interactions …

• European rabbits and South American myxoma virus in Australia

• Houseflies and Nasonia wasps in Pimentel’s lab

• Wheat and wheat rust in agricultural systems: gene for gene interaction

• specialization of scales on individual genotypes of ponderosa pine trees

Identifying Coevolutionary Responses

• the evolution of strong jaws and associated muscles by hyenas to crack the bones of their prey is not coevolutionary, because the bones of the prey have not evolved to resist being eaten

• the evolution of the ability of an herbivore to detoxify substances produced by a plant specifically to deter that herbivore is coevolutionary

Competition and Character Displacement

• character traits of two closely related species differ more in sympatric regions than in allopatric regions

• this pattern may have arisen from strong selective pressure for divergence in sympatry, a process called character displacement

Mutualism (+/+): Interactions between species that benefit both participants

• Trophic

– lichen: partnership between algae and fungi

– Rhizobium-plants

– Mycorhizzae-plants

– wood digesters in rumens…bacteria within ciliates

• Defensive

– cleaner shrimp-eels

– ants-plants

• Dispersive

– pollinators-plants

– seed dispersers-plants

Trophic Mutualism

• Trophic mutualisms usually involve partners specialized for obtaining energy and nutrients

Defensive Mutualism

• Defensive mutualisms involve species that receive food or shelter from their partners in return for a defensive function

Dispersive Mutualism

• Dispersive mutualisms involve animals that:

– transport pollen in return for rewards such as nectar

– transport and disperse seeds in return for the nutritional value of fruits or other structures associated with seeds

Coevolution?

• The term coevolution has sometimes been used broadly to describe the close association of certain species and groups of species in biological communities.

• Are these examples of coevolution?

Are close associations coevolutionary?

• Do pairs of species undergo reciprocal evolution or

• do “coevolved” traits arise as responses of populations to selective pressures exerted by a variety of species, followed by ecological sorting?

• Are species organized into interacting sets based on their adaptations, coevolved or not?

Figure 17.19.The Yucca Moth and the Yucca

The Yucca Moth and the Yucca

• Yuccas (genus Yucca) and yucca moths (genus Tegeticula)

• mutually beneficial

• obligatory

• carefully studied

Moth larvae have no other food source and yucca plants have no

other pollinator... • adult female yucca moths carry balls of pollen

between yucca flowers by means of specialized mouthparts

• during pollination, the female moth deposits eggs in the ovary of the yucca flower

• after the eggs hatch, the developing larvae feed on some of the developing yucca seeds, not exceeding 30% of the seed crop

• the yucca exerts selective pressure on the moths (through abortion of heavily infested fruits) to limit moth genotypes predisposed to lay large numbers of eggs (cheaters)

Is the Yucca/Yucca Moth Mutualism Coevolutionary?

• Many aspects of the mutualism are present in the phylogenetic lineage of nonmutualistic moths within which Tegeticula evolved

– host specialization and mating on the host plant

– traits present in the moth lineage before the establishment of the mutualism itself,

– evidence for preadaptation

– what appear to be coevolved traits may have been preadaptations that were critical to establishment of the mutualism in the first place

Figure 17.20: phylogenetic analysis

Summary…idea of coevolution

• Interactions among species are major sources of selection

• Coevolution is the interdependent evolution of species that interact ecologically

• Consumer-resource systems give abundant examples: host-pathogen, host-parasitoid, plant-herbivore..

• Competition can lead to character displacement.

Summary: mutualisms

• Mutualisms are relationships between species that benefit both.

• Mutualisms may be trophic, defensive, or dispersive.

• Phylogenetic analysis allows us to infer the evolutionary history of interspecies interactions

• Identification of coevolved relationships is difficult, and preadaptations may complicate evolutionary interpretation