Page ‹#› at Lower Elevation Sites, the Beeflies Are Present and the Plant Sets More Seed When Greya Is Excluded

B. Mutualism in one environment may be parasitism in a different environment End of mutualism lecture…

Cheaters in mutualisms highlight the An example with a yucca moth relative, Greya close evolutionary relationship and a wildflower in the Northwest, between mutualism and parasitism Lithophragma For example lycaenid butterfly mutualists may evolve into parasites But also, mutualism in one environment may be parasitism in another

B. Mutualism in one environment may be B. Mutualism in one environment may be parasitism in a different environment parasitism in a different environment

Greya, like yucca moths, lay eggs in some Unlike yucca, however, Lithophragma may be ovules and pollinate others pollinated by other pollinators, such as beeflies

Bee-flies are efficient pollinators and do not lay eggs in any flowers

Mutualism in one environment may be parasitism in a different environment Lithophragma occurs in several mountain At high elevation sites, Greya is the only valleys and at different elevations in Oregon pollinator, and here it serves as a mutualist - the plant benefits by its presence

Page ‹#› At lower elevation sites, the beeflies are present and the plant sets more seed when Greya is excluded. So whether the interaction between Greya and Lithophragma should be termed a mutualism Here Greya is or parasitism of the plant by Greya depends a parasite, on the presence of a third species! reducing plant fitness.

IV. Mutualism/parasitism - closely related IV. Mutualism/parasitism - closely related interactions interactions Mutualism may evolve into parasitism C. A story of parasitism leading to mutual Parasitism may evolve into mutualism dependency

And some relationships may be difficult to classify

1. Parasitic wasps may be infected with a bacterium called Wolbachia 1. Parasitic wasps may be infected with a bacteria called Wolbachia The bacteria are transmitted only in the eggs It is not in the evolutionary interests of the bacteria to end up in a male wasp. Why Infected egg Uninfected egg not?

Page ‹#› The bacteria ‘do not want’ to end up in a Haplodiploidy male. n So.… they make all male eggs female! n n How do they do that?

They manipulate the haplodiploid sex determination of their wasp hosts 2n

Female Male

How does it do that? When Wolbachia invades a population of parasitic wasps, eventually the males disappear So in haplodiploid systems Females develop from fertilized, diploid eggs Males develop from haploid, unfertilized eggs In this species, the only way to In Wolbachia infected wasps, the see a male is to chromosomes in the male eggs treat the females double and the egg develops as a with antibiotics! female that can transmit the bacteria...

So the wasp is completely dependent on And because there’s no natural selection the bacterium for reproduction and the on male function, mutations accumulate strain of bacteria is completely dependent and the males produced when bacteria is on the wasp for a home. removed are sterile Is this a mutualism? When you treat these females with antibiotics, It may be difficult to categorize an you get males interaction if you cannot compare with no mature species with and without the interacting sperm species

Page ‹#› Pop quiz Today: Parasitism and disease

Grading: 5 points for name (being present in I. Introduction to parasites and lecture), and 5 points for correct answer to disease the question (10 total pts.) On one side of card, write your 4-digit code a worm’s eye view (you will use this for picking up your quiz) On the other side write your name, and answer this question: Define competitive displacement

A. Parasitism - the most common A. Parasitism - the most common lifestyle? animal lifestyle? Why so many parasites? Estimates suggest that as many as half of all species are parasites Because most free-living species have parasites associated with them

Parasite load (worms only) of North American mammals (76 mammal spp. sampled) Why so many parasites? Mean no. of No. of parasites per species of individual parasite per Because most free-living species host host population have parasites associated with Platyhelminthes Trematodes 108 1.8 them Cestodes 140 2.8 Nematodes 117 5.3 AND, most parasites are specialists Acanthocephalans 1 0.3 (they attack few or maybe just one Mean no. of species) parasite species 3 10

Page ‹#› Remember how two species obligate mutualisms Why are most parasites specialists? can lead to co-speciation? The same is true for specialist parasites and their hosts... Parasites must Coevolution of primates and parasitic 1) establish on/in host - may need to cross skin, nematodes gut wall 2) evade host immune system, or if ectoparasite, behavioral defense (grooming, swatting) 3) grow and reproduce in host 4) disperse from and find new host

Adaptations for one species unlikely to be Nematodes Primates effective on another

B. Types of parasites Simply grouped by size... B. Types of parasites Simply grouped by size... Microparasites - viruses or single cells includes viruses, bacteria, protists, and Microparasites - viruses or single cells simple fungi includes viruses, bacteria, protists, and simple (unicellular) fungi Macroparasites - multicellular includes multicellular fungi, arthropods, and parasitic worms (e.g. nematodes and flatworms)

B. Types of parasites B. Types of parasites Human diseases caused by microparasites Size influences the way the host is used... Viruses - influenza, HIV Microparasites generally infect cells, while macroparasites are usually external or in Bacteria- tuberculosis, plague the gut Protists - malaria (trypanosome), amoebic dysentery (amoeba)

Page ‹#› III. Parasite transmission B. Types of parasites Human macroparasites How are parasites transmitted?

Arthropods - lice, mosquitoes, ticks Direct or indirect transmission Nematodes - Onchocerca (River blindness), intestinal roundworms

Platyhelminthes - Schistosoma, tapeworms

III. Parasite transmission III. Parasite transmission

How are parasites transmitted? How are parasites transmitted?

Direct or indirect transmission Direct or indirect transmission

1. Direct transmission - from one host to 1. Direct transmission - from one host to another without vectors or intermediate another without vectors or intermediate hosts hosts 2. Indirect transmission - transmission via another species

1. Direct transmission may be vertical or horizontal or both 1. Direct transmission may be vertical or horizontal or both Vertical transmission - from parent to offspring in early development. Generally Examples of vertically-transmitted human mother-offspring. Why? diseases -

•through infected gametes (most often rubella, syphilis, hepatitis B, HIV eggs) •through birth process: mother-offspring - these are also horizontally transmitted

Page ‹#› 1. Direct transmission may be vertical or horizontal or both 2. Indirect transmission (horizontal only) b. Horizontal transmission - transfer via When parasite is transmitted from one host contact with infected individuals or to the other host via another species. contaminated products The other species may be vectors or intermediate hosts.

Vectors - ectoparasites of the host, serve as a hypodermic of pathogen Intermediate hosts house the parasite for part of its life cycle, Definitive host where reproduction occurs

Intermediate hosts may live in proximity to Mosquito definitive hosts (e.g. Schistosoma), or may biting human be prey of the final hosts

Mosquitoes Video clip: trematodes, snails and birds vector …?

The snail-trematode example IV. Selection on parasites to maximize transmission Which was the intermediate host? Which was the definitive host? The problem - how to get you or your progeny off the host ‘island?’ Example also illustrates host behavior modification, whereby the parasite increases its transmission by changing the behavior of its host

Page ‹#› IV. Selection on parasites to maximize transmission IV. Selection on parasites to maximize A. For direct, horizontally-transmitted transmission parasites, exit routes may be feces, body fluids, lesions A. For direct, horizontally-transmitted parasites transmission dependent on:

density of hosts and

frequency of encounters between infected and uninfected individuals

IV. Selection on parasites to maximize transmission IV. Selection on parasites to maximize transmission D. Virulence and transmission - more

A. For indirect parasites transmission What’s virulence? dependent on:

a whole bunch of factors concerned with biology and ecology of both hosts

What’s virulence? What’s virulence? X X X X How sick the host gets... How sick the host gets...

Generally - virulence is related to the speed at which host is converted to parasites…

For example - 48 -72 h cycle of fever and chills of malaria

Page ‹#› IV. Selection on parasites to maximize transmission 1. The conventional (and not necessarily correct) wisdom: parasites become less D. Virulence and transmission virulent over evolutionary time 1. The conventional (and not necessarily Why is this sometimes true? correct) wisdom: parasites become less virulent over evolutionary time a. Hosts evolve resistance Why is this sometimes true?

1. The conventional (and NOT always So if more virulent parasites reproduce correct) wisdom: parasites become less more, why doesn’t selection always lead to virulent over evolutionary time greater virulence?

But if more virulent parasites reproduce Generally, dead hosts don’t transmit the more, why doesn’t selection on parasites parasite… lead to greater virulence? Natural selection acts to maximize transmission of the parasite

Rabbits from North Africa accidentally introduced to Australia in 1800s

Natural selection acts to maximize transmission of the parasite

An example of evolutionary change in virulence of a virus

Page ‹#› Example Rabbits from North Rabbits from North Africa Africa accidentally introduced accidentally introduced to to Australia in 1800s Australia in 1800s spread and spread and became became major pests, endangering native major pests, plants and animals endangering native Biological control plants and program started: animals myxoma virus from S. America released in 1950

Initially, virus was highly virulent High virulence, low transmission Myxoma virus is indirect, horizontally - 100 transmitted virus, spread by mosquito

numbers vectors 0 100 Why might high virulence lead to low

Proportion transmission?

0 Highly Intermed. Low Virulent virulence Then, variation in virulence appeared Initially, virus was highly virulent

Eventually, the dominant form had intermediate virulence Low virulence, Moderate virulence, low transmission high transmission 100 Infective forms of virus causes lesions - 0 areas where mosquitoes can bite 100

Why might low virulence lead to low 0 100 transmission? Proportion

0 Highly Intermed. Low Virulent virulence virulence

Page ‹#› What does the rabbit-myxoma virus example illustrate?

What does the rabbit/myxoma virus example illustrate? Natural selection acts to maximize transmission of the parasite - not necessarily to reduce its virulence!

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