Parasites: Crash Course Zoology #11 - Free Educational videos for Students in K-12

Parasites: Crash Course Zoology #11 - By CrashCourse

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00:0-1	allow me to introduce the best animal out there .
00:03	Well at least if you ask me , the american
00:06	black bear Rome's most of north America from Alaska to
00:10	Mexico . As we watch her bear friend go about
00:13	her day , we're actually looking at two ecosystems ,
00:17	the forest and the bear herself . Let's live a
00:21	day in the life of an american black bear and
00:24	her parasites . An ecosystem is a community of organisms
00:29	interacting with their physical environment . Like most wild animals
00:34	, this bear is home to parasites which are animals
00:38	that evolved to live on or in other animals causing
00:43	their hosts harm on her body . She has ecto
00:47	parasites which spend their lives outside the bear . A
00:52	whole bunch of lice fleas and ticks crawl around in
00:56	the forest of the bears for sipping from the streams
01:00	of blood that flow just below the surface . Occasionally
01:05	a mosquito or even a vampire bat may visit when
01:08	it gets dark out and maybe spread a disease if
01:11	she's really unlucky in her body are endo parasites who
01:16	have evolved to spend their lives inside another living thing
01:21	. Our bear might host some plati helm in these
01:24	like tapeworms she got from eating infected fish or rabbits
01:29	. These worms find their way to the nutrient packed
01:32	intestine and the muscles where they latch on and suck
01:36	up nutritious bear juices . She might also have another
01:40	wormy fila nematodes in her intestines or in rare cases
01:45	, other nematodes called lung worms . These are just
01:49	some of the at least 31 parasite species that live
01:54	in and on black bears . And we haven't even
01:58	touched on non animal parasites like protozoa or viruses .
02:03	But as she goes about her day , the effects
02:06	of her parasites are probably pretty mild and she can
02:10	live a normal life . Most bears infected with parasites
02:14	look and act perfectly fine even when they have several
02:19	uninvited guests . As long as there aren't too many
02:24	have a nice day . MS , bear and friends
02:27	, parasites are an essential part of their ecosystem .
02:31	Whether that ecosystem is a forest , a stream or
02:34	the inside of a bear and studying them teaches us
02:38	not just about the parasite but also its host and
02:42	even their shared evolution and ecology . So stick with
02:46	me . It's probably going to get pretty weird .
02:48	I'm Ray Wynne Grant and this is crash course zoology
02:59	. Yeah . Nearly every environment on earth and that
03:04	includes animals is home to some kind of parasite .
03:09	Some individual animals have a lot of parasites and some
03:13	carry very few . We call this parasite load or
03:17	the amount of parasites and individual carries in or on
03:20	its body , which varies a lot between animals formally
03:24	, parasitism is a symbiotic relationship between species where one
03:29	organism the parasite lives on or inside another organism ,
03:34	the host causing it some harm the host provides the
03:38	parasite with food or safety or way to have offspring
03:42	, or sometimes all three . And in return ,
03:46	the parasite does nice things like steal nutrients or wreck
03:51	their hosts reproductive system , like they literally bite the
03:55	hand that feeds them . So the host isn't really
03:58	getting anything out of the deal , which is why
04:00	parasites are sometimes described as predators that eat in units
04:04	of less than one . But parasites aren't quite the
04:07	same as predators who kill and eat other animals .
04:11	For one , they're usually much much smaller than their
04:14	hosts and they usually try to keep their hosts alive
04:18	. They also interact with their hosts a lot more
04:21	than a predator interacts with its prey sometimes for years
04:24	at a time , parasites are super specialist and structurally
04:29	adapted for their exploitative lifestyle . While a lot of
04:33	parasites have lost traits because they've adapted to rely on
04:36	their host to fulfill some of their needs . There's
04:39	so much more than that parasites are a super diverse
04:42	group of animals and there are lots of ways we
04:44	can split them into categories . One way is by
04:48	where they live . So whether they're endo parasites inside
04:52	the body or ecto parasites outside the body like we
04:56	saw with our bare we can also categorize parasites by
04:59	how they find their host . Though some animals fall
05:03	into more than one category or change their strategy over
05:06	their life cycle . Those ticks and lights that we're
05:09	on our black bear are directly transmitted parasites . They
05:13	find their hosts on their own , like by waiting
05:15	and tall grass and hopping on as the bear walked
05:18	by . And directly transmitted parasites usually have a lot
05:22	of the features we see in non parasitic animals like
05:25	being able to move around on their own . There
05:27	are also trophic lee transmitted parasites like roundworms that spread
05:31	by getting eaten . A lot of these parasites use
05:35	being eaten by one animal called an intermediate host to
05:39	travel to its primary host , where it reproduces .
05:42	Like the larvae could burrow into the muscles of a
05:44	fish or rabbit and begin growing when they sense the
05:48	proteins and acid in the gut of their primary host
05:51	. The bear after being eaten . And lots of
05:54	bacteria and viruses as well as parasitic worms called helmets
05:59	, are vector transmitted parasites . They get into their
06:02	proper hosts with the help of another organism called a
06:06	vector that transfers the disease causing agent from one organism
06:10	to another . A lot of the blood feeding animals
06:13	fall here too , like the mosquitoes hovering around our
06:17	bear could be vectors for the West . Nile virus
06:20	ticks can transfer the bacteria that causes Lyme disease and
06:23	so on , which brings us to another way .
06:26	We can categorize parasites how they get energy . All
06:30	the mosquitoes , ticks and leeches that nibble at their
06:33	host without killing it outright are showcasing micro predation .
06:38	Usually they don't do too much damage by themselves .
06:41	But sometimes numbers or mismatched ecologies can make micro predators
06:47	become capital P predators . Like we saw with sea
06:50	lamprey back in episode four invertebrates who you've probably noticed
06:55	by now are way more hardcore than us , coordinates
06:59	might use parasitic castration . This is when a parasite
07:03	rex , it's hosts ability to reproduce so that the
07:06	parasite can suck up all that energy that would have
07:09	gone to making eggs are finding a mate . Animals
07:12	normally use a lot of their resources to reproduce .
07:16	So that's an even bigger free lunch buffet for the
07:18	parasite . But I guess at least the host gets
07:22	to go on living , which isn't always the case
07:26	paris , a toy is just end the actual life
07:29	of their host , which is pretty bold move for
07:32	a parasite . Most paris a toys r insects like
07:35	many wasps but lay their eggs on host larvae .
07:39	Sometimes the larvae develop inside the host , sometimes outside
07:43	. Sometimes the host is immobilized once it's infected and
07:47	sometimes it keeps going along its business until the larvae
07:51	kill it . Either way , the parasite oid sucks
07:54	energy from its host until there's nothing left and don't
07:58	think parasites are safe from other parasites . There are
08:01	parasites that attack the larvae of other parasites , which
08:04	is called hyper parasitism . One example is the cabbage
08:09	white butterfly , which is attacked by two species of
08:12	parasite Oid wasps . The larvae of those wasps are
08:16	attacked by another wasp . So you get a moth
08:19	infected with a parasite that's itself infected with another parasite
08:23	. It's basically like a parasite turducken situation . Since
08:28	parasites and their hosts share such a close relationship ,
08:32	we might wonder how evolutionarily related they are . Let's
08:36	say we wanted to make a taxonomic sandwich where the
08:38	host is one piece of bread and the parasite is
08:41	the other and the evolutionary time between them is the
08:44	filling . Like take E . Perplex of the parasite
08:47	and E perplex of the host . Their sandwiches ,
08:50	just two pieces of bread in Karsiyaka . Perplexing are
08:53	parasite . Oid wasps who are like self parasites .
08:57	E perplexity usually parasite ties is the eggs of citrus
09:01	black flies . But when there's no male wasps around
09:05	unaided , females will lay unfertilized eggs inside larvae of
09:10	their own species . True to form the new baby
09:14	. E perplexing cannibalizes its cousin to grow up .
09:18	Since these wasps have a half load deployed sex determination
09:21	system where sex depends on the number of chromosome sets
09:25	and offspring has unfertilized eggs always become males . So
09:31	now there's males to solve that fertilization problem turns out
09:35	you can't even trust your evolutionary relatives . These wasps
09:39	are adelphia parasites which target animals that are very closely
09:44	related to themselves , often belonging to the same family
09:47	or even genus . Talk about terrible in laws In
09:51	general though hosts and their parasites are usually not closely
09:55	related . For one , there are just so many
09:58	parasites out there . It's a lifestyle that's evolved literally
10:02	over 100 times , which is because there are so
10:05	many niches or ecological places that they can take .
10:10	Each species of animal is its own ecosystem and each
10:14	tissue or cell type a unique habitat . Parasitism is
10:18	smart Evolutionarily speaking because you freeload off someone else's hard
10:23	work to get food , have babies move around or
10:25	find a home . And with natural selection being as
10:29	selective as it is , animals can use every little
10:32	advantage they can get though . Freeloading might be kind
10:36	of harsh parasites get a bad reputation , but they're
10:40	really important parts of their ecosystems . For example ,
10:44	parasites are a fundamental part of the food web .
10:47	And for some animals , parasites are even part of
10:49	their regular diet . Like al possums love to eat
10:52	ticks , But parasites depend on their hosts for survival
10:56	, which sometimes put them on the wrong side of
10:58	conservation efforts . Like the California Condor might went extinct
11:03	in the late 1980s when the 22 remain in California
11:06	, condors were brought into captivity and deloused for a
11:10	breeding program . In saving condors , we doomed the
11:14	mites an example of what's called conservation induced extinction .
11:18	With the benefit of hindsight , we've realized we lost
11:22	a lot of information about not only the mites but
11:25	the condors as well . The might bio hackers probably
11:29	knew some things about the condor immune system . We
11:31	don't , for example , and having parasites in a
11:34	population isn't bad . It at least means that the
11:38	hosts are also present . And since a lot of
11:41	parasites use multiple hosts , there are a good indicator
11:44	of how the whole ecosystem is doing so , scientists
11:48	are starting to use parasite abundance to track the effects
11:51	of pollution or other forms of environmental degradation and are
11:55	pushing for more parasite conservation . And lastly , parasites
11:59	are also really important in the context of evolution .
12:03	There an agent of natural selection , Since parasite infected
12:06	animals have a harder time passing down their genes and
12:10	studying how parasites interact with their hosts . Might give
12:13	us some hints about how things happened millions of years
12:16	ago , like how complex social relationships between animals may
12:20	have evolved from animals , picking parasites off each other's
12:24	skin or for so , studying parasites could change everything
12:28	we know about animals , parasites are mysterious , but
12:32	next episode will dive deep into some of the most
12:35	enduring zoological mysteries and how sometimes more information means more
12:42	complicated questions . Thanks for watching this episode of Crash
12:46	course ideology , which was produced by complexity in partnership
12:49	with PBS and Nature . It's shot on the team
12:52	Sandoval Pierre stage and made with the help of all
12:55	of these nice people . If you'd like to help
12:57	keep Crash Course free for everyone forever , you can
13:00	join our community on Patreon .

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