Lecture 13 IB - Exam 3

describe endosymbiosis of bacteria

• organism that lives within the body or cells of another organism and plays a key role in development of multicellular organisms

• mutualistic relationships allowed them to take on new abilities

• process of symbiont transmission allows insect to acquire its symbiont

• This happens when one organism lives inside another organism or its cells.

• These inside-living bacteria were important for the evolution of multicellular life.

• When both benefit (mutualism), they can gain new abilities.

• Insects can get these helpful bacteria through a process called symbiont transmission.

describe insect microbes interaction

• heritable bacterial endosymbionts are common in insects

• past decades has seen explosion of studies characterizing biology of symbionts

• divided into 2 groups: obligate or primary symbionts and facultative or secondary symbionts

• Many insects have bacteria that live inside them and are passed down to their offspring.

• In recent years, scientists have studied these bacteria a lot to learn how they work.

• These bacteria are grouped into two types:

  • Obligate (primary) symbionts: insects need them to survive.

  • Facultative (secondary) symbionts: insects don’t need them, but they can still be helpful.

describe facultative bacterial symbionts

• horizontal transfer where host acquires symbiont from the environment or another host 

• pathogen transmission occurs with a bite of another organism that transfers a microbe

• have much broader array of effects, ranging from mutualism to manipulation of reproduction

• wolbachia: most common arthropod intracellular bacteria, common reproductive parasite

• These are bacteria that insects can pick up from the environment or other insects (horizontal transfer).

• They can also spread like diseases, through a bite that passes the bacteria.

• They can have many different effects — some are helpful (mutualism), while others change how insects reproduce.

• Wolbachia is the most common example — it lives inside many arthropods and often acts like a reproductive parasite.

describe wolbachia

• wolbachia: obligate intracellular insect parasite

• perhaps the most common reproductive parasite on planet

• explored in population replacement programs 

how does wolbachia affect insects

• highly varied across insects

• some require wolbachia to mate, can help host evade pathogens

• shown to prevent acquisition of plasmodium in anopheles mosquitoes

• Its effects are different for different insects.

• Some insects need Wolbachia to reproduce, and it can also protect them from diseases.

• In Anopheles mosquitoes, Wolbachia can stop them from getting the malaria parasite (Plasmodium).

describe wolbachia in control programs

• wolbachia’s effect on reproduction: interest for insect control

• causes 4 important phenotypes

1. male killing: males killed during larval development

2. feminization: males develop as females or infertile pseudo-females

3. parthenogenesis: females can reproduce without males

4. cytoplasmic incompatability

• populations surveyed for presence of wolbachia

• insects grown with wolbachia, and released into population

• spreads rapidly → causes population crash

• Scientists study Wolbachia because it changes how insects reproduce, which can help control their populations.

• It can cause four main effects:

  1. Male killing: male insects die before becoming adults.

  2. Feminization: males turn into females or infertile “fake” females.

  3. Parthenogenesis: females can have babies without males.

  4. Cytoplasmic incompatibility: certain males and females can’t produce offspring together.

describe cytoplasmic incompatability

• males with one Wolbachia strain cannot mate successfully with females with no Wolbachia or a different strain

• interferes with chromosome division in embryotic cells, causing dividing out of sync

describe obligate bacterial symbionts

• pea aphid and buchnera: bacteria produces essential amino acids that aphid cannot gain from diet

• plant sap is low in amino acids and high in sugar and nitrogen 

• insect provides food and shelter to bacteria and reduced exposure to predators

• necessary for the survival of the insect 

• acquisition of bacteria through vertical transmission (parent to offspring)

• symbionts do not need to survive independently of host 

• mutualists with nutritional function that occur in insects that feed on imbalanced diets such as plants saps or cellulose

• Some insects need certain bacteria to survive.

• Example: Pea aphids have Buchnera bacteria that make essential amino acids the aphid can’t get from plant sap.

• Plant sap has lots of sugar but not enough amino acids, so the bacteria help.

• The insect feeds and protects the bacteria, keeping them safe from predators.

• These bacteria are passed from parent to offspring (vertical transmission).

• They can’t live on their own and mainly help insects with nutritional needs when their diet is unbalanced, like plant sap or cellulose.

describe blattodea

• includes cockroaches and termites

• until recently, termites were treated as a separate order: isoptera

• recent molecular evidence suggests that termites and roaches are closely related

cockroaches as pests

• suspected that humans have evolutionary aversion to cockroaches that makes them more feared than mosquitoes

• blattodea have 30 species that are associated with humans

• only 4 are considered pests

• do not vector disease but linked to allergic reactions that cause asthma

• can passively transport pathogens on body surfaces

• aversion to light, so present even when not visible (up to 48% infestations not detected)

cockroaches

• extremely resilient, difficult to control

• can survive w/out feeding for up to a month

• some can survive below freezing temperatuers

• pest species tend to prefer dark and damp spaces

• majority of species are inoffensive (not likely to upset, hurt, or anger anyone)

• live in range of habitats, abundant in tropics and sub tropics

• roaches that live outdoors can be found in leaf litter, under bark, and in wood

• few species are of conservation concern

• omnivorous: feed on almost anything

• symbiotic bacteria in the gut can digest cellulose in some species of roach

• in many species, symbionts might be essential for their survival

• presence of symbionts suggests termites and cockroaches were closely related

social behavior of blattodea

• social insects: gregarious or inclined to aggregate

• small number exhibit some level of parental care

• pheromones influence behavior with ability to distinguish through odors

• german cockroaches leave fecal trails to guide others to food sources

termites

• belong to order blattodea

• termites are exclusively eusocial

• eusociality is highest order of social organization

• likely evolved with sub social route of cockroaches

• the step to eusocial may have been aided by genetic relatedness

social behavior of cockroaches

Cockroaches form aggregations and display level of parental care, termites are eusocial

social behavior of cryptocercus

wood-dwelling roach genus, exhibits parental care and has symbiotic relationship with wood digesting bacteria

how are cockoraches and termites similar

• Share closer phylogenetic relation to termites

than other cockroaches

• All termites are eusocial and represent a

monophyletic lineage

• Close relation to roaches, reliance on gut

microbiota to digest nutritionally poor food

• Parental care suggests food source primary

evolutionary pressure for termite eusociality

termite ecology

• Feeding ecology determined by internal gut fauna

• “Lower termites” feed predominantly on wood

and rely on symbionts to digest cellulose

• “Higher termites” have lost the characteristic

symbionts, developed a compartmentalized gut

containing a variety of different bacteria

• Allows for feeding on lichen, soil, decaying plant

material and wood

• Adaptation has led to higher diversity of termites

what is cryptocercus

Cryptocercus: a genus of cockroaches

• Feeds on wood

• Subsocial (take care of their eggs or nymphs but don’t live in large, highly organized colonies)

• Houses similar gut bacteria to termites

termites thought to have evolved from roaches like these (evolutionary step)

insects and fungus

• involve both beneficial and harmful interactions

fungiculture

occurs when insects have evolved to farm fungus

growing or farming fungi, often by insects for food

leaf cutting ants

• taking leaves back to feed fungus colonies they farm that make up the primary source of food

• in different species, fungi can be facultative or obligate

• leaf-cutter practice higher culture which means fungi are fully domesticated by the ants

termites and mushroom

• termites also act as farmers where fungus termites are dependent on each other for survival

• termitomyces (known as termite mushroom)

• termites house and culture mushroom and the mushrooms provide food for termines

describe parasitic fungi

• infection of fungal spores enter body cavity and propagate

• eventually kill the insect (which releases spores back into environment)

• complex interaction where a manipulation of behavior causes insect to behave in a way that facilitates success of fungus

• Fungal spores infect the insect’s body and grow inside it.

• Eventually, the fungus kills the insect, and the insect’s body releases new spores into the environment.

• Some fungi can change the insect’s behavior to help the fungus spread more effectively.

Entomopathogenic Fungus

• Do not require ingestion but attack cuticle directly

through penetration of exoskeleton

• Certain entomopathogenic fungi (Metarhozium and

Beauveria) have been of interest in insect control

• Potential for this serves as an eco-friendly alternative

to chemical insecticides

• These fungi don’t need to be eaten; they attack insects by penetrating their outer shell (cuticle).

• Examples like Metarhizium and Beauveria are studied for controlling insect populations.

• They are a more eco-friendly alternative to chemical insecticides.

Zombie Ants

• A parasitic Cordyceps fungus

(Ophiocordyceps unilateralis) is

commonly known as zombie-ant fungus

• Primarily targets carpenter ants in

tropical, humid environments

• Identifiable at the end of the life cycle

when reproductive structure (fruit) is

seen on dead host

• Leads to dramatic changes in the

behavior of ant, causing them to

leave nests and rainforest floor

• Controls brain and ant will climb to

higher areas of canopy and lock

mandibles onto leaf above ground

• This is optimal height for fungal

spore growth and dispersion

• A fungus called Cordyceps (Ophiocordyceps unilateralis) is known as the zombie-ant fungus.

• It mainly infects carpenter ants in tropical, humid areas.

• You can see it at the end of its life cycle when the fungus grows a fruiting structure on the dead ant.

• The fungus changes the ant’s behavior, making it leave its nest and the forest floor.

• It takes control of the ant’s brain, causing it to climb higher in the canopy and lock its jaws onto a leaf.

• This position is ideal for the fungus to grow and spread its spores.

cordyceps

Thousands of Cordyceps species that specialize on one species of insect