LECTURE #4
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why is blood an advantageous food source?
blood is a relatively nutritious food source compared to other common food sources and therefore can provide a distinct fitness advantage
what two conditions in particular facilitate the switch to blood feeding?
1. a close association with vertebrates may predispose arthropods to switch to a blood feeding life style
2. some insects have mouthparts that are pre-adapted to blood feeding
how can arthropods be considered "closely associated" with vertebrates?
many arthropods live in the nests and burrows of vertebrates (ie. birds and rodents)
what are specific advantages associated with living in close proximity to vertebrates?
1. it provides a warm and humid environment
2. steady source of food: hair, feathers, feces, food left overs and blood from one wounds
provide an example of "a close association with vertebrates
LICE: all species of lice live in close proximity to vertebrates
what are Mallophaga?
biting lice", the ancestral group of lice that feed on hair and feathers
what is thought to be the reason "sucking lice" started making wounds?
to obtain a blood meal
what are sucking lice also known as?
anoplura
where did anoplura arise from?
within the mallophaga
what is the difference between mallophaga and anoplura?
anoplura have a much higher fecundity
how has blood feeding evolved within the mallophaga? what is the evidence?
the proboscis is lengthened to facilitate blood feeding although it retains biting mouthparts; through this we can see that blood feeding has evolved multiple times independently
what is an ectoparasite on elephants and warthogs?
haematomyzus hopkinsi
what is unique about insect groups with piercing mouthparts?
these insects tend to have a high proportion of subgroups that are blood feeders
what are kissing bugs?
a subfamily of reduviidae, part of the "true bugs" the heteroptera (piercing mouth parts are a characteristic of this order) : PRE ADAPTED MOUTH PARTS!!
what two factors likely facilitated the switch to blood feeding in the group reduviidae?
reduviids are predacious on other insects and have the following characteristics that make the transition to blood feeding likely...
1. piercing mouth parts
2. adaptation to a high protein diet
what kind of moth takes a blood meal?
vampire moths
what are the THREE distinct phases host seeking in blood feeding arthropods can be divided into?
1. appetitive searching
2. activation and orientation
3. attraction
what is APPETITIVE SEARCHING?
during this phase the arthropod has not yet detected any host cues
what is ACTIVATION AND ORIENTATION?
this phase starts when an arthropod has detected host cues and starts moving towards it
what is ATTRACTION?
during this phase, the arthropod has approached the host and is deciding whether to commence blood feeding
APPETITIVE SEARCHING:
what kind of process is this in most arthropods?
an active process; arthropod moves around looking for host cues
APPETITIVE SEARCHING:
what is a common characteristic of blood feeders that do this? examples?
ones that fly; black flies, mosquitoes, sandflies...
APPETITIVE SEARCHING:
for which kinds of arthropods is this a PASSIVE process?
the ones that live in close approx. with their hosts; lice, fleas...
APPETITIVE SEARCHING:
provide another example of PASSIVE APPETITIVE SEARCHING.
ticks; These arthropods wait in the vegetation for a host to
pass by closely, at which point they extend their front
legs, hoping to latch on to host
APPETITIVE SEARCHING:
what is host seeking tightly controlled by?
circadian rythmes; each species will generally only host seek during a certain time of day
APPETITIVE SEARCHING:
provide 2 examples of the previous card
1. anopheles gambia's host seeks at night; adds aegypti feeds during the day
2. Tsetse fly host seeking is tightly linked to various physiological processes
APPETITIVE SEARCHING:
Most blood feeding endopterygote insects will do what for several days after becoming an adult?
postpone host seek; their mouth parts and digestive systems may not be ready, in this case they will have another nutrient source (nectar, honeydew...)
APPETITIVE SEARCHING:
in which kind of insects do juveniles, females and males typically blood feed as their only source of food so all stages will search for hosts. give an example.
In exopterygote blood feeding insects; kissing bugs
APPETITIVE SEARCHING:
which insects it is common for only the females to blood feed as requirement for producing eggs. give an example.
In endopterygotes; black flies
ACTIVATION AND ORIENTATION:
when does this phase start?
when a host cue is detected and the arthropod starts moving towards it
ACTIVATION AND ORIENTATION:
what is one of the most important host cues for blood feeding?
insect odor
ACTIVATION AND ORIENTATION:
a variety of odors are used to identify a host, provide examples.
1. CO2: plays a role in virtually all species, but relative importance varies between species
2. breath or sweat: molecules in our sweat that are attractive are often produced by the bacteria fauna on our skin
ACTIVATION AND ORIENTATION:
elaborate on the significance of CO2 in this process with an example
PROXIMITY: in specialist species, e.g. Anopheles gambiae, CO2 seems to be mostly important in long range attraction. Other molecules become important when the insects gets close
ACTIVATION AND ORIENTATION:
what happens when a host odor is detected?
a flying insect will respond by flying UPWIND and
orienting themselves by making sure the odor concentration continues to increase as they get close to host
ACTIVATION AND ORIENTATION:
what has been estimated about mosquito/calve detection?
It has been estimated that a mosquito can detect a calve from 30-80 meters away
ACTIVATION AND ORIENTATION:
what are diurnal species?
species that are active during the day
ACTIVATION AND ORIENTATION:
give an example of a diurnal species
tsetse flies are very attracted to large moving targets which they can detect from 50 m away
ACTIVATION AND ORIENTATION:
which works at a closer distance (typically) when comparing vision and olfaction?
vision
ACTIVATION AND ORIENTATION:
species living in what kind of habitat rely more heavily on vision?
open habitats v. those in more forested areas
ACTIVATION AND ORIENTATION:
how does heat play a role in this phase?
blood feeding arthropods are attracted to heat; bed bugs get really excited when they feel a heat source nearby (close range)
ACTIVATION AND ORIENTATION:
give an example of how you can "test" this attraction to heat
offering mosquitoes blood in a membrane that has been heated to 37 degrees celsius will elicit a strong feeding response
ACTIVATION AND ORIENTATION:
how can a blood feeder tell when blood feeding is no longer viable? (give an example; think body lice!)
body lice can sense a drop in temperature of a few degrees, usually indicating the death of a host
ATTRACTION:
what happens when a host has been approached?
information from all three senses is integrated to decide if a suitable host has been found
ATTRACTION:
many flying blood feeders are "generalists", what does that mean?
they can and will feed on a variety of animals, although they prefer large herbivores
ATTRACTION:
why do flying blood feeders prefer large herbivores?
these are abundant and they tend to defend less against bites because they loose little blood with each bite
ATTRACTION:
what kind of animal vigorously defends themselves against mosquitoes?
birds
ATTRACTION:
what kind of hosts do NON-flying blood feeders tend to desire?
non-flying blood feeders = lice, fleas; hosts with nests and burrows (ie. rodents and birds)
how do blood feeders feed?
in some blood feeders, the mouthparts have become modified to form a piercing "proboscis
describe the mosquitoes blood feeding structure
1. labium houses stylet
2. stylet = mandible, maxillae and hypopharynx; this all enters the skin when taking blood meal
what is a stylet?
portion of piercing proboscis that is inserted into the skin; made up of mandible, maxillae and hypopharynx
describe the structure of the hypopharynx
two channels...
1. a large one for sucking up the blood meal
2. a small one to inject saliva
in various species of blood feeders, what is main the difference between mouthparts?
function is similar; put together differently
in what other species do the mouth parts cut to make small wounds from which blood is then sucked up?
black flies and stable flies
describe the design of the stable flies mouth parts
designed for cutting and tearing a wound
what species has "scissor like" mouth parts?
the black fly
what is a complication blood feeders have to deal with? define it.
vertebrate haemostasis (blood clotting)
list the three vertebrate defenses against blood loss...
1. vasoconstriction
2. platelet aggregation
3. coagulation
what process would severely reduce blood feeding efficiency and potentially block the proboscis?
??
what is the response of vertebrate tissue upon contact with the proboscis?
inflammation, pain and discomfort
Almost all blood feeding arthropods inject the following compounds during blood feeding, what are they?
1. Vasodilator
2. Anti-platelet aggregator
3. Anti-coagulant
4. Anti-inflammatory compound
blood feeders do NOT have what? however, they do what to prevent IMMEDIATE pain?
an anesthetic (works directly on pain receptors); feed carefully
why do arthropods inject the previously mentioned compounds?
to increase feeding efficiency
how can you differentiate between groups and their compounds?
each group has independently evolved proteins that perform the same functions
what is the effect of apyrase?
The effect of apyrase for example, which inhibits platelet aggregation, on blood feeding efficiency is quite large
what does apyrase do?
1. it inhibits plate aggregation
2. it is correlated with feeding time
Most temporary ectoparasites (e.g. mosquitoes) take what size blood meal?
as large as they can manage
why do most temporary ectoparasites take large blood meals?
EXAMPLE?
1. hosts may be hard to find
2. blood feeding is risky
3. day time feeders may need multiple hosts; minimizes risk
EXAMPLE: female mosquito
what size meal do species that reside on host permanently take up? why?
EXAMPLE?
smaller meals...
1. host is always available
2. risk of feeding is not much more than of living on hosts
EXAMPLE: tick
define endosymbionts
Endosymbionts are bacteria that live inside an other organisms in a mutually beneficial relationship
what are obligate blood feeders?
those that only feed on blood
what is unique about obligate blood feeders?
they always have endosymbionts that produce a series of vitamins that are absent from the blood meal
what is the result of killing off symbionts with antibiotics?
a great reduction in fecundity, unless vitamins are supplemented
give an example of an arthropod that needs symbionts
Tsetse flies have symbionts they need for egg production
what (typically) is required of blood feeders before producing an egg batch?
taking up a blood meal
what are cases where an exception exists?
in species who are autogenous
ie. mosquitoes, black flies, sandflies and deer flies
what is autogeny?
means the ability to produce an egg batch prior to first blood meal
a few species always lay an egg batch before blood feeding; what are they?
obligatory autogeny (this we see most when hosts are RARE)
other species can choose to either feed or to lay eggs; what are they?
facultative autogeny (will only lay eggs before blood feeding if it has sufficient nutritional reserves)
what does the choice between facultative and obligatory depend on?
1. availability of hosts
* if hosts are easy to find, insect may blood feed first
2. larval nutrition
* (i.e. nutrient reserves) -> if an insect has lots of reserves it may lay eggs first
LECTURE #5
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who provided the beginning quote?
andrew spielman
MOSQUITO SEXING:
which (M/F) mosquito blood feeds and transmits disease?
females ONLY
MOSQUITO SEXING:
how can you identify a male mosquito?
feathery" looking antennae
MOSQUITO SEXING:
how can you identify a female mosquito?
antennae that looks like a "twig with a few hairs
MOSQUITO SEXING:
which type of mosquito mates AWAY from the host thus explaining why male encounters are rare?
anopheles
MOSQUITO SEXING:
which type of mosquito mates CLOSE to the host thus explaining why males are more abundant?
aedes aegypti
MOSQUITO CLASSIFICATION:
superorder
endopterygota
MOSQUITO CLASSIFICATION:
order
diptera
MOSQUITO CLASSIFICATION:
family
culicidae (all mosquitoes belong here)
MOSQUITO CLASSIFICATION:
how many subfamilies are mosquitoes divided into?
3...
1. Toxorhynchitinae (has been used as pest control)
2. Anophelinae
3. Culicinae
MOSQUITO CLASSIFICATION:
of these subfamilies, how many total genera exist?
42
MOSQUITO CLASSIFICATION:
how many mosquito species have been described?
3,400
SUBFAMILY 1/TOXORHYNCHITINAE:
what genus is contained by this subfamily?
Toxorhynchites
SUBFAMILY 1/TOXORHYNCHITINAE:
how many species exist in this subfamily?
94
SUBFAMILY 1/TOXORHYNCHITINAE:
where do most species of this subfamily inhabit?
tropical areas, although several are in the US
SUBFAMILY 1/TOXORHYNCHITINAE:
how are these mosquitoes unusual?
neither the male or female blood feeds or transmits diseases; both sexes do feed on plant nectar, honey dew...
SUBFAMILY 1/TOXORHYNCHITINAE:
why do these mosquitoes NOT blood feed?
The mosquitoes acquire a lot of protein reserves as larvae, because the larvae prey on other mosquito larvae; May kill/eat as many of 400 larvae
SUBFAMILY 1/TOXORHYNCHITINAE:
what is the significance of these mosquitoes in the realm of biological control?
1. attempted use a pest control
2. hard to rear lg. enough # of them
3. very susceptible to insecticide
SUBFAMILY 1/TOXORHYNCHITINAE:
how can you recognize a toxorynchites mosquito?
1. 90 degree bend in proboscis
2. long palps of the males (also bend)
3. considerably larger than other mosquitoes with iridescent scales along their body
SUBFAMILY 2/ANOPHELINAE:
what are the three genre in this subfamily?
1. anopheles
2. chagasi
3. bironella
SUBFAMILY 2/ANOPHELINAE:
how many species have been described?
473
SUBFAMILY 2/ANOPHELINAE:
do they blood feed?
yes, only females
SUBFAMILY 2/ANOPHELINAE:
what diseases do this species act as a vector for?
1. human malaria
2. lymphatic filariasis
3. several arboviruses (yellow fever, zika...)
what is an arbovirus?
arthropod borne virus
SUBFAMILY 2/ANOPHELINAE:
are the anopheline considered a major nuisance?
no! they do not occur in the very large numbers that some other species of mosquitoes do
GENUS ANOPHELES:
when are anopheles mosquitoes active?
adults are crepuscular/nocturnal; this means that they blood feed and mate from dusk to dawn
GENUS ANOPHELES:
why do insecticide impregnated bed nets work well in malaria control?
anopheles mosquitoes are NOCTURNAL
GENUS ANOPHELES:
how many eggs do females lay per batch?
50-200 eggs
GENUS ANOPHELES:
what is the ease of consistent population suppression? why?
not easy; few left over females can produce many offspring
GENUS ANOPHELES:
where must eggs be laid? why?
Eggs cannot resist desiccation and have to be laid on water surface
RECOGNIZING AN ANOPHELES:
what is the most identifiable physical trait of an anopheles mosquito?
dark and pale scales on wings
RECOGNIZING AN ANOPHELES:
how do anopheles mosquitoes rest?
at a 45 degree angle, abdomen pointing upwards
RECOGNIZING AN ANOPHELES:
how are anopheles larvae "stored"?
floating horizontally at the water surface position
GENUS ANOPHELES:
where are the larvae of the anopheles found?
in clean, unpolluted water of various habitats
1. Temporary pools
2. Open sunlit pools
3. Rice Fields
4. Edges of stream
5. Salt water marshes
6. Grassy ditches
GENUS ANOPHELES:
as is the case with most mosquito larvae, what kind of feeders are the anopheles larvae?
filter feeders; on microorganisms in the water
(HOWEVER; larvae can chew, cannibalism has been reported)
SUBFAMILY 3/CULICINAE:
how many genera are in this subfamily?
38
SUBFAMILY 3/CULICINAE:
how many species are in this subfamily?
2750
SUBFAMILY 3/CULICINAE:
what are the two MOST important genera in this subfamily?
aedes and culex
SUBFAMILY 3/CULICINAE:
why are aedes and culex so important?
they transmit the following:
AEDES
- yellow fever virus
- dengue virus
- zika virus
CULEX
- west nile
- other encephalitic viruses
SUBFAMILY 3/CULICINAE:
are these considered major pest species?
YES! they can be very abundant and cause a LOT of annoyance
SUBFAMILY 3/CULICINAE:
in adult culicinae, where does the abdomen point?
downwards when resting
SUBFAMILY 3/CULICINAE:
where do culicinae larvae float? how do they breathe as a result?
with their body at angle to water surface; using siphons
SUBFAMILY 3/CULICINAE:
what are siphons?
breathing tubes
SUBFAMILY 3/CULICINAE:
do the eggs float?
no
GENUS CULEX:
how many species does this genus contain?
well over 1,000
GENUS CULEX:
where do larvae of this genus live?
a wide variety of habitats; pools, puddles, ditches, borrow pits, rice fields
GENUS CULEX:
where do culex lay eggs?
in rafts
GENUS CULEX:
what is the most important culex mosquito? why?
culex quinquefasciatus (southern house mosquito); vector of WEST NILE, LYMPHATIC FILARIASIS AND ZIKA
GENUS CULEX:
where are these mosquitoes located?
worldwide distribution, favors sub-tropics
GENUS CULEX:
where do culex breed?
in water with HIGH organic content (ie. pit latrines, blocked drains, ditches...)
GENUS ADES:
where are aedes located?
wide distribution
GENUS ADES:
what can be said about the quality of aedes eggs?
they can withstand desiccation (up to several months); this promotes man-facilitated dispersal
GENUS ADES:
what are the 2 main types of habitats larvae commonly breed in?
1. container habitats
2. flood water
GENUS ADES:
give an example of container habitats/flood habitats
1. CONTAINER
* tree holes
* plant axils
* man made containers
2. FLOOD WATER
* flood plains
* irrigated fields
* woodlands
* coastal areas
GENUS ADES:
what happens after significant flooding or rain?
large numbers of this species will emerge
GENUS ADES:
what is the most important mosquito of the aedes species?
ades aegypti; the yellow fever mosquito
GENUS ADES:
describe ades aegypti and their relationship to humans
highly adapted to humans; both in their ecology and feeding preference
GENUS ADES:
describe ades aegypti and their breeding habits
breeds in storage pots, jars or inside/outside homes; in general they breed in close proximity to human habitation
GENUS ADES:
describe ades aegypti and their origin --> current location
origin = africa; brought to the new world in 15th and 16th century and is currently distributed across the tropical and semi-tropical areas of the world (including US)
GENUS ADES:
what is unique about the "snow pool" mosquito, ades communis?
can be so abundant that it is impossible to be outdoors and can kill large animals through exanguination (blood loss); 9,000 bites/min (human can lose 1/2 blood in 2 hrs)
GENUS ADES:
why do these "snow pool" mosquitoes become so numerous?
1. lots of larval habitat (permafrost preserves melt water pools)
2. few predators (no fish!)
3. little larval competition and each female produces A LOT of offspring
GENUS ADES:
how can mosquito population numbers be tied to the weather?
the emergence of larvae/eggs upon the arrival of rains (mosquito favorable environment)
ie. paper out of TX A&M reports on live stock loss through mosquito abundance after a hurricane
anophelines vs culicnes
ANOPHELINES
1. 45 degree resting angle
2. feathery male/stick female
3. spotted wings
4. parallel sub-water eggs
CULICINES
1. downward resting angle
2. feathery male/stick female
3. no spots on wings
4. some floating eggs, some not, use siphon for breathi
texas is home to how many species of mosquitoes?
87
how many mosquitoes are in the US?
170
list a few of the most important mosquitoes in Texas
ADES
1. aegypti
2. alibopictus
ANOPHELES
1. albimanus
2. quadrimaculatus
(both american malaria mosquitoes)
CULEX
1. quinquefasciatus
what has happened to ades aegypti in the US in the past 20 years?
its distribution has decreased dramatically from its once well established presence in the south of the US
what has the population of ades aegypti dramatically decreased in the US in the past 20 years?
the recent introduction of ades albopictus (asian tiger mosquito); their larvae inhabit the same areas and often outcompete the aegypti species
when was aides albopictus first introduced to the US?
early 1980's through tire trade with japan and taiwan through houston (the tire recapping capital of the world); their presence was set. in 1985
what does the diet of aides albopictus look like?
it is diverse, they feed on many mammals, birds and humans
in lab, what arboviruses can albopictus be infected with?
at least 22 different arboviruses; including dengue, west nile, yellow fever and zika
how are aegypti and albopictus different in terms of human interaction?
aegypti bites more often and is considered a more dangerous vector of "human" viruses
what does albopictus have potential to be in terms of vectors?
a bridge vector; a vector that can transmit viruses from other vertebrate animals to humans
when do aides albopictus feed on humans?
in the day time; this makes them a big nuisance mosquito
THE EVOLUTION OF VECTOR-BORNE DISEASE
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what are the two main branches of "strategists"?
r/k
what is an r-strategist?
ie. TICKS: a species that produces lots of tiny offspring and gives little parental care
* little competition within species
* survival via luck
* high fecundity
* small body size
* early maturity
* short generation time
* ability to disperse offspring wi
What is a K-strategist?
ie. HUMANS: a species that produces fewer large offspring with some to lots of parental care
* lots of competition within species (crowded environments)
* survival via nurture
* low fecundity
* large body size
* maturity with parental care/investment
* lo
what does "r" represent in terms of population growth?
growth rate
what does "k" represent in terms of population growth?
carrying capacity
who came up with the idea of natural selection, the first explanatory mechanism for evolution?
charles darwin with his evolutionary theory written in "the origin of species
who was herbert spencer?
He pioneered the field of social darwinism by applying Darwin's ideas to human behavior; coined the term "survival of the fittest
what is natural selection truly about?
successful reproduction from generation to generation
define "fitness" in the evolutionary sense
the proportion of the individual's genes in the next generation
describe the passage of a gene/how to determine its "fitness
1. If population size is stable, 1 copy of a gene on average contributes one
copy to the next generation.
2. If all individuals contribute equally, all have fitness = 1
(no change in frequency, unless by chance; "genetic drift")
3. If a gene has two allel
is natural selection slow or rapid?
rapid and effective
ie. an allele with 5% selective advantage (selection coefficient s=0.05) will go from 5% to 60% in 100 generations
why is natural selection such a common process?
organisms "strive" to maximize their reproduction, because they are made up of genes that have maximized reproduction in the past
how can a species maintain a general fitness of "1"?
As long as each of these strategies produce on average two offspring that survive they are equally successful and their fitness is 1
define virulence
the degree of pathogenicity of an infectious disease
what is considered HIGH virulence?
high mortality, severe illness (malaria, yellow fever)
what is considered LOW virulence?
low/no mortality, minor symptoms
(common cold)
describe the relationship between reproduction and virulence
Higher reproduction -> higher virulence (upward linear)
*Generally, if a pathogen has a higher virulence (than a similar type of other pathogen), it also has a higher number of individual pathogens inside the host
Given enough time a state of peaceful coexistence
eventually becomes established between any host and parasite"
Rene Dubos (1965)
what does the above quote convey?
1. pathogens should evolve to MINIMIZE damage to the host, as this would result in longevity for both parties
2. Disease with high virulence were thought to have recently switched to a new host and did not have the time to adapt and minimize virulence.