1 00:00:04,620 --> 00:00:06,120 Hey there! For this video we're going to 2 00:00:06,120 --> 00:00:09,180 be talking about phenotypic plasticity; 3 00:00:09,180 --> 00:00:11,700 which is how individual phenotypes can 4 00:00:11,700 --> 00:00:13,280 vary in response to the environment. 5 00:00:13,280 --> 00:00:15,090 We're gonna go through a number of terms 6 00:00:15,090 --> 00:00:17,391 associated with plasticity. Some of the 7 00:00:17,391 --> 00:00:19,430 key ones among those, are reaction norms 8 00:00:19,430 --> 00:00:21,329 and polyphenisms. And we're also going to 9 00:00:21,329 --> 00:00:22,710 be talking about a special form of 10 00:00:22,710 --> 00:00:27,579 plasticity known as performance curves. 11 00:00:27,579 --> 00:00:28,890 So, if you'll remember back to some of 12 00:00:28,890 --> 00:00:31,430 our earlier videos, there are three main 13 00:00:31,430 --> 00:00:33,989 sources of phenotypic variation among 14 00:00:33,989 --> 00:00:36,510 individuals. The first are genetic 15 00:00:36,510 --> 00:00:38,440 differences which we talked about quite 16 00:00:38,440 --> 00:00:40,390 a bit in our last couple of videos. But the 17 00:00:40,390 --> 00:00:42,570 second which is just as important, 18 00:00:42,570 --> 00:00:44,260 sometimes more important, are 19 00:00:44,260 --> 00:00:46,649 environmental effects and this includes 20 00:00:46,649 --> 00:00:48,859 things like phenotypic plasticity. This 21 00:00:48,859 --> 00:00:51,149 is any situation in which the 22 00:00:51,149 --> 00:00:53,239 environment is inducing differences in 23 00:00:53,239 --> 00:00:56,059 phenotype rather than the genes. You can 24 00:00:56,059 --> 00:00:58,839 kind of think of this as twins or clones 25 00:00:58,839 --> 00:01:00,890 having the exact same genetic background 26 00:01:00,890 --> 00:01:03,670 but showing different phenotypes. And 27 00:01:03,670 --> 00:01:05,990 this may be adaptive meaning it has a 28 00:01:05,990 --> 00:01:07,460 positive effect on fitness or 29 00:01:07,460 --> 00:01:10,190 maladaptive. And the final of these is 30 00:01:10,190 --> 00:01:12,300 random chance. Today, because we're 31 00:01:12,300 --> 00:01:13,800 talking about plasticity, we're really 32 00:01:13,800 --> 00:01:15,750 going be focusing on number two: The 33 00:01:15,750 --> 00:01:18,000 effects of the environment on the 34 00:01:18,000 --> 00:01:21,500 phenotype. And so let's take a moment to 35 00:01:21,500 --> 00:01:22,510 talk about what I like to call the 36 00:01:22,510 --> 00:01:24,750 beastie area of plasticity jargon there 37 00:01:24,750 --> 00:01:26,520 are a lot of words that gets thrown 38 00:01:26,520 --> 00:01:29,650 around and they all mean almost the same 39 00:01:29,650 --> 00:01:31,600 thing. They're highly synonymous but not 40 00:01:31,600 --> 00:01:34,300 perfectly synonymous. So, the first of 41 00:01:34,300 --> 00:01:36,480 these is the more overarching umbrella 42 00:01:36,480 --> 00:01:39,640 term and that is phenotypic plasticity. 43 00:01:39,640 --> 00:01:41,420 And we use the word plasticity in a 44 00:01:41,420 --> 00:01:43,440 sort of older sense. What plastic was 45 00:01:43,440 --> 00:01:46,150 mean it was named for. And it's the idea 46 00:01:46,150 --> 00:01:47,710 of something be able to being able to 47 00:01:47,710 --> 00:01:51,300 take any form. And so plastics we call 48 00:01:51,300 --> 00:01:53,960 plastic because you can melt them down 49 00:01:53,960 --> 00:01:55,720 and mold them and make them into any 50 00:01:55,720 --> 00:01:57,670 form you want. That's why we call them 51 00:01:57,670 --> 00:01:59,490 plastic. And so when we talk about a 52 00:01:59,490 --> 00:02:01,730 phenotype being able to take multiple 53 00:02:01,730 --> 00:02:03,570 forms even though an individual has the 54 00:02:03,570 --> 00:02:06,340 same genotype, we call this phenotypic 55 00:02:06,340 --> 00:02:08,590 plasticity. So that's sort of the 56 00:02:08,590 --> 00:02:10,780 broadest overarching term for any time 57 00:02:10,780 --> 00:02:12,370 the environment can be affecting 58 00:02:12,370 --> 00:02:15,159 organisms. Again it can be adaptive or 59 00:02:15,159 --> 00:02:16,810 maladaptive. We 60 00:02:16,810 --> 00:02:18,420 usually think of plasticity though as 61 00:02:18,420 --> 00:02:20,480 being active responses to the 62 00:02:20,480 --> 00:02:23,000 environment. So if an organism you know 63 00:02:23,000 --> 00:02:26,379 freezes to death it being so cold has 64 00:02:26,379 --> 00:02:28,469 caused its body to turn into a solid 65 00:02:28,469 --> 00:02:29,760 which you could say is a change in its 66 00:02:29,760 --> 00:02:31,769 phenotype but that's not in any way an 67 00:02:31,769 --> 00:02:33,420 active response. That's just the wreck 68 00:02:33,420 --> 00:02:35,730 damage induced by the environment. That's 69 00:02:35,730 --> 00:02:37,381 not really what we're talking about when 70 00:02:37,381 --> 00:02:39,760 we talk about plasticity. We're instead 71 00:02:39,760 --> 00:02:42,909 talking about the kind of things that 72 00:02:42,909 --> 00:02:44,400 have been actively in response to the 73 00:02:44,400 --> 00:02:46,780 environment. A nice example that most of 74 00:02:46,780 --> 00:02:49,079 you have probably experienced is if you 75 00:02:49,079 --> 00:02:53,200 go outside and put your skin in the Sun 76 00:02:53,200 --> 00:02:56,180 it's likely to change color. For me, I'm 77 00:02:56,180 --> 00:02:59,499 quite pale, I have the the the problem if 78 00:02:59,499 --> 00:03:01,989 I do this too long my skin turns bright 79 00:03:01,989 --> 00:03:04,290 red and hurts. That would not be 80 00:03:04,290 --> 00:03:05,409 plasticity. 81 00:03:05,409 --> 00:03:07,799 That's just damage. But if I go out in 82 00:03:07,799 --> 00:03:10,359 the Sun and in response to being in the 83 00:03:10,359 --> 00:03:12,989 Sun my skin produces more melanin, 84 00:03:12,989 --> 00:03:17,299 becomes more brown, that actually helps 85 00:03:17,299 --> 00:03:21,279 protect my skin and my DNA and my cells 86 00:03:21,279 --> 00:03:24,389 from the damage caused by ultraviolet 87 00:03:24,389 --> 00:03:26,680 radiation. That would be an example of 88 00:03:26,680 --> 00:03:32,590 adaptive plasticity. Really anytime the 89 00:03:32,590 --> 00:03:35,450 organisms are having an active response 90 00:03:35,450 --> 00:03:37,750 to environmental variation, we can turn 91 00:03:37,750 --> 00:03:40,670 phenotypic plasticity. Now another word 92 00:03:40,670 --> 00:03:42,900 that's often used very synonymously with 93 00:03:42,900 --> 00:03:46,510 phenotypic plasticity is acclamation. 94 00:03:46,510 --> 00:03:47,739 Acclamations a little different than 95 00:03:47,739 --> 00:03:49,430 just plasticity writ large. 96 00:03:49,430 --> 00:03:51,120 Because plasticity writ large can 97 00:03:51,120 --> 00:03:54,400 include variation that is reversible or 98 00:03:54,400 --> 00:03:56,650 irreversible. An example of an 99 00:03:56,650 --> 00:03:58,120 irreversible form of phenotypic 100 00:03:58,120 --> 00:04:00,430 plasticity is temperature dependence sex 101 00:04:00,430 --> 00:04:03,169 determination in many reptiles. These 102 00:04:03,169 --> 00:04:06,340 animals, their genes do not determine 103 00:04:06,340 --> 00:04:08,209 whether they're male or female instead, 104 00:04:08,209 --> 00:04:09,529 it's the temperatures they experience 105 00:04:09,529 --> 00:04:11,450 when they're in the egg. But once they 106 00:04:11,450 --> 00:04:14,139 develop into a male or a female, that 107 00:04:14,139 --> 00:04:16,169 can't go backwards. So, that still 108 00:04:16,169 --> 00:04:18,900 phenotypic plasticity but it is not a 109 00:04:18,900 --> 00:04:22,199 form of acclamation. Acclamation is 110 00:04:22,199 --> 00:04:24,889 something that is reversible and tends 111 00:04:24,889 --> 00:04:26,389 to be in response to extend it or 112 00:04:26,389 --> 00:04:28,919 chronic exposure. Tanning is actually a 113 00:04:28,919 --> 00:04:31,410 pretty good example of acclimation. 114 00:04:31,410 --> 00:04:33,550 Another term that gets thrown 115 00:04:33,550 --> 00:04:37,389 around is phenotypic flexibility. This is 116 00:04:37,389 --> 00:04:39,509 somewhat similar to acclimation, but in a 117 00:04:39,509 --> 00:04:43,460 way is an even broader term. This really 118 00:04:43,460 --> 00:04:46,650 is talking about any form of response to 119 00:04:46,650 --> 00:04:49,610 the environment that can reverse itself. 120 00:04:49,610 --> 00:04:51,580 This is just having a generally flexible 121 00:04:51,580 --> 00:04:54,930 phenotype. Tanning would be an example of 122 00:04:54,930 --> 00:04:57,310 having a generally flexible phenotype as 123 00:04:57,310 --> 00:04:59,330 would bodybuilders. The fact that you can 124 00:04:59,330 --> 00:05:02,120 put stresses on your muscles cause them 125 00:05:02,120 --> 00:05:04,050 to grow and get bigger. If that can 126 00:05:04,050 --> 00:05:06,680 rapidly reverse, if you stop working out 127 00:05:06,680 --> 00:05:08,229 but then if you start working out you 128 00:05:08,229 --> 00:05:10,009 can build up your muscles again would be 129 00:05:10,009 --> 00:05:13,729 a good example of phenotypic flexibility. 130 00:05:13,729 --> 00:05:16,819 And finally, developmental plasticity are 131 00:05:16,819 --> 00:05:18,221 consequences of the environment that 132 00:05:18,221 --> 00:05:19,970 tend to be irreversible because they 133 00:05:19,970 --> 00:05:23,520 influence how the organism develops from 134 00:05:23,520 --> 00:05:27,430 a zygote to a full adult organism. So, 135 00:05:27,430 --> 00:05:29,159 temperature dependent sex determination 136 00:05:29,159 --> 00:05:30,990 is an example of developmental 137 00:05:30,990 --> 00:05:33,259 plasticity. Other examples have to do 138 00:05:33,259 --> 00:05:34,750 with things like I'm sure you've heard 139 00:05:34,750 --> 00:05:38,629 that parents/when pregnant women 140 00:05:38,629 --> 00:05:40,300 can't adjust their diets and things in a 141 00:05:40,300 --> 00:05:41,590 way that might be beneficial to their 142 00:05:41,590 --> 00:05:43,509 baby's development, brain development, 143 00:05:43,509 --> 00:05:45,580 learning. Those would all be examples of 144 00:05:45,580 --> 00:05:47,990 developmental plasticity, the kind of 145 00:05:47,990 --> 00:05:50,009 influence of the maternal environment on 146 00:05:50,009 --> 00:05:53,030 the developmental trajectory of the 147 00:05:53,030 --> 00:05:55,560 babies. So these are sort of four big 148 00:05:55,560 --> 00:05:57,400 terms we're going to use to describe. 149 00:05:57,400 --> 00:05:59,229 Very similar things, this is all the 150 00:05:59,229 --> 00:06:02,419 environment affecting the phenotype of 151 00:06:02,419 --> 00:06:06,409 individuals, but with slightly different 152 00:06:06,409 --> 00:06:10,060 meanings as I've just explained. Another 153 00:06:10,060 --> 00:06:13,230 set of important plasticity jargon, are 154 00:06:13,230 --> 00:06:15,080 the difference between a reaction norm 155 00:06:15,080 --> 00:06:18,580 or a polyphenism. This totally depends 156 00:06:18,580 --> 00:06:20,790 on whether the phenotype changes 157 00:06:20,790 --> 00:06:22,800 continuously in response to the 158 00:06:22,800 --> 00:06:25,020 environment or if there's a threshold 159 00:06:25,020 --> 00:06:26,689 response so the phenotype is in one 160 00:06:26,689 --> 00:06:28,880 state in one environment and a different 161 00:06:28,880 --> 00:06:31,530 state in a different environment. So, 162 00:06:31,530 --> 00:06:33,550 a reaction norm, sometimes also called a 163 00:06:33,550 --> 00:06:35,439 norm of reaction sort of flipping the 164 00:06:35,439 --> 00:06:37,280 word around, is any time we have a 165 00:06:37,280 --> 00:06:40,409 continuous response to the environment, 166 00:06:40,409 --> 00:06:42,849 An example is shown by the growth 167 00:06:42,849 --> 00:06:43,849 heights 168 00:06:43,849 --> 00:06:45,830 these plants and responds to temperature 169 00:06:45,830 --> 00:06:47,040 and this shows that when it's really 170 00:06:47,040 --> 00:06:49,610 really cold the plants don't grow it all, 171 00:06:49,610 --> 00:06:51,370 when it's moderately cold the plants are 172 00:06:51,370 --> 00:06:53,729 kind of short, when it as it warms up the 173 00:06:53,729 --> 00:06:55,560 plants get bigger and bigger and bigger 174 00:06:55,560 --> 00:06:57,819 until it gets too hot and the plants 175 00:06:57,819 --> 00:06:59,560 start to get shorter again. This is a 176 00:06:59,560 --> 00:07:02,300 continuous response of these plants to 177 00:07:02,300 --> 00:07:04,830 the environment. Totally driven by the 178 00:07:04,830 --> 00:07:06,750 environment you could have totally 179 00:07:06,750 --> 00:07:09,460 clonal plants with the exact same genes 180 00:07:09,460 --> 00:07:10,849 and their phenotype would vary in this 181 00:07:10,849 --> 00:07:14,189 way. Polyphenism, an example of a 182 00:07:14,189 --> 00:07:15,819 polyphenism includes temperature 183 00:07:15,819 --> 00:07:17,479 dependent sex determination, as I 184 00:07:17,479 --> 00:07:19,169 mentioned before. If you have one set of 185 00:07:19,169 --> 00:07:20,990 temperatures, the baby develops into a 186 00:07:20,990 --> 00:07:22,219 male. If you have another set of 187 00:07:22,219 --> 00:07:24,330 temperatures it develops into a female. 188 00:07:24,330 --> 00:07:25,860 Another really good example is in 189 00:07:25,860 --> 00:07:28,819 honeybees, whether or not the individuals 190 00:07:28,819 --> 00:07:31,069 develop into a regular worker bee or a 191 00:07:31,069 --> 00:07:33,360 queen bee. And this is totally dependent 192 00:07:33,360 --> 00:07:36,889 on the diet that the larvae are fed by 193 00:07:36,889 --> 00:07:38,699 the other worker bees. If they're fed a 194 00:07:38,699 --> 00:07:40,449 standard diet they grow up and develop 195 00:07:40,449 --> 00:07:42,939 into a worker bee. However, if they're fed 196 00:07:42,939 --> 00:07:44,530 something called royal jelly, which is a 197 00:07:44,530 --> 00:07:48,830 really nutrient-rich form of the diet, 198 00:07:48,830 --> 00:07:52,630 that diet induces the larvae to develop 199 00:07:52,630 --> 00:07:55,669 into a much larger, very fertile honeybee. 200 00:07:55,669 --> 00:07:58,080 Very different phenotype. That's the 201 00:07:58,080 --> 00:07:59,760 queen bee, but the queen bee is 202 00:07:59,760 --> 00:08:02,569 genetically identical to her worker bees. 203 00:08:02,569 --> 00:08:04,560 This difference, this polyphenism is 204 00:08:04,560 --> 00:08:09,389 completely driven by the environment. 205 00:08:09,389 --> 00:08:10,580 We're generally going to be thinking 206 00:08:10,580 --> 00:08:14,259 more about reaction norms than polyphenism. So I want to dive into it just a 207 00:08:14,259 --> 00:08:17,740 little bit more. This graph shows sort of 208 00:08:17,740 --> 00:08:20,490 the stylized version of a reaction norm. 209 00:08:20,490 --> 00:08:23,060 Our x-axis is the environment, with two 210 00:08:23,060 --> 00:08:25,259 extremes on the left and the right, and 211 00:08:25,259 --> 00:08:28,449 the y-axis is the value for our trait. 212 00:08:28,449 --> 00:08:30,439 And in this case, what we see is we have 213 00:08:30,439 --> 00:08:33,500 two genotype. So, these two individuals 214 00:08:33,500 --> 00:08:36,130 with different genes or these could be 215 00:08:36,130 --> 00:08:38,010 two populations of clonal individuals 216 00:08:38,010 --> 00:08:40,050 where they all have the exact same 217 00:08:40,050 --> 00:08:43,080 genetic makeup. Either the red group 218 00:08:43,080 --> 00:08:44,529 all has the exact same genetic makeup 219 00:08:44,529 --> 00:08:45,810 and the blue group all has the exact 220 00:08:45,810 --> 00:08:49,550 same genetic makeup. And the idea is that, 221 00:08:49,550 --> 00:08:51,820 what phenotype they show is largely 222 00:08:51,820 --> 00:08:53,780 driven by their environment. So in one 223 00:08:53,780 --> 00:08:56,440 extreme, we see that genotype A 224 00:08:56,440 --> 00:08:58,829 has a smaller value for its phenotype 225 00:08:58,829 --> 00:09:01,680 than genotype B. But at the other extreme 226 00:09:01,680 --> 00:09:03,110 maybe this is a hot environment, this 227 00:09:03,110 --> 00:09:05,860 flips and so we can see market 228 00:09:05,860 --> 00:09:08,320 phenotypic variation on the landscape 229 00:09:08,320 --> 00:09:11,690 that's driven more by the the phenotype 230 00:09:11,690 --> 00:09:13,630 than just the pure genotype. In this case 231 00:09:13,630 --> 00:09:15,240 you actually have both sort of driving 232 00:09:15,240 --> 00:09:17,270 things because the genotypes differ and 233 00:09:17,270 --> 00:09:18,600 how they plastically respond to the 234 00:09:18,600 --> 00:09:20,280 environment. Which we'll be talking about 235 00:09:20,280 --> 00:09:23,450 a bit more in our next video. And it also 236 00:09:23,450 --> 00:09:26,370 highlights that patterns of phenotypic 237 00:09:26,370 --> 00:09:29,930 plasticity can vary among genotypes. 238 00:09:29,930 --> 00:09:34,240 Sometimes, you have them all responding 239 00:09:34,240 --> 00:09:36,500 to the environment in the exact same way, 240 00:09:36,500 --> 00:09:38,370 sometimes you have the molix responding 241 00:09:38,370 --> 00:09:39,682 in about the same way, but sort of with 242 00:09:39,682 --> 00:09:41,029 different intercepts so it's like they 243 00:09:41,029 --> 00:09:42,550 have different starting points. And 244 00:09:42,550 --> 00:09:45,360 sometimes you have 245 00:09:45,360 --> 00:09:48,630 genotypes whose reaction norms cross 246 00:09:48,630 --> 00:09:51,250 that's when you have both plasticity and 247 00:09:51,250 --> 00:09:57,190 genetic effects. And this suite of 248 00:09:57,190 --> 00:09:59,899 options is really interesting and in his 249 00:09:59,899 --> 00:10:03,970 important mode for evolution, but we're 250 00:10:03,970 --> 00:10:05,690 going to talk about this again more in 251 00:10:05,690 --> 00:10:08,160 our next video. For today and for this 252 00:10:08,160 --> 00:10:09,260 video I really just want you to 253 00:10:09,260 --> 00:10:13,529 understand that phenotypic plasticity is 254 00:10:13,529 --> 00:10:16,800 variation and phenotype caused by the 255 00:10:16,800 --> 00:10:20,220 environment. And different genotypes can 256 00:10:20,220 --> 00:10:25,449 have different reaction norms. Another 257 00:10:25,449 --> 00:10:27,750 example of a reaction norm that we are 258 00:10:27,750 --> 00:10:29,150 going to talk about a lot in this class 259 00:10:29,150 --> 00:10:32,889 and you should have already seen SimUText is the performance curve. An 260 00:10:32,889 --> 00:10:35,270 idealized version is shown here in this 261 00:10:35,270 --> 00:10:39,310 case we have the pressure or difficulty 262 00:10:39,310 --> 00:10:42,610 of your class and the y-axis is how well 263 00:10:42,610 --> 00:10:45,670 you perform. And the curve is just sort 264 00:10:45,670 --> 00:10:47,310 of this hump shaped curve and the idea 265 00:10:47,310 --> 00:10:49,459 is that if your class is too easy, 266 00:10:49,459 --> 00:10:50,459 you're not going to perform all that 267 00:10:50,459 --> 00:10:52,500 well because you're just switched off. If 268 00:10:52,500 --> 00:10:55,110 the class is just challenging enough, 269 00:10:55,110 --> 00:10:57,050 your performance will be optimized it's 270 00:10:57,050 --> 00:10:59,410 gonna be the highest. And if the class is 271 00:10:59,410 --> 00:11:01,570 way too hard ,you're gonna stress out and 272 00:11:01,570 --> 00:11:04,430 your performance is going to drop. So, 273 00:11:04,430 --> 00:11:05,980 that's totally dependent on how hard 274 00:11:05,980 --> 00:11:07,970 your class is and has nothing to do with 275 00:11:07,970 --> 00:11:09,860 your genetic propensity for class. 276 00:11:09,860 --> 00:11:11,470 This would be an example of a 277 00:11:11,470 --> 00:11:13,860 performance curve and thus an example of 278 00:11:13,860 --> 00:11:18,690 phenotypic plasticity of a sort. We touched 279 00:11:18,690 --> 00:11:20,610 on thermal performance a little bit 280 00:11:20,610 --> 00:11:22,130 earlier in our very first example of a 281 00:11:22,130 --> 00:11:24,120 reaction norm. But it's a nice sort of 282 00:11:24,120 --> 00:11:26,510 classic example of a performance curve 283 00:11:26,510 --> 00:11:27,760 so we're gonna dive into it just a 284 00:11:27,760 --> 00:11:30,269 little bit more. So in this case, we see a 285 00:11:30,269 --> 00:11:32,070 thermal performance curve which again is 286 00:11:32,070 --> 00:11:34,970 an example of a reaction norm. Our x-axis 287 00:11:34,970 --> 00:11:37,490 is body temperature and our y-axis is 288 00:11:37,490 --> 00:11:39,709 relative performance. This could be how 289 00:11:39,709 --> 00:11:42,140 many babies and individual makes, it 290 00:11:42,140 --> 00:11:43,910 could also be something like how fast 291 00:11:43,910 --> 00:11:47,160 they can run. And thermal performance 292 00:11:47,160 --> 00:11:49,300 curves tend to be this hump shaped curve. 293 00:11:49,300 --> 00:11:51,520 They're left skewed. The skew is the 294 00:11:51,520 --> 00:11:53,720 direction the tail of the distribution 295 00:11:53,720 --> 00:11:55,570 points. So, that means the humps more to 296 00:11:55,570 --> 00:11:58,060 the right, a little confusing but is the 297 00:11:58,060 --> 00:12:01,730 left skewed curve. And this curve like 298 00:12:01,730 --> 00:12:03,089 all performance curves can be 299 00:12:03,089 --> 00:12:05,990 characterized by a handful of parameters 300 00:12:05,990 --> 00:12:08,370 including an optimum. So, in this case 301 00:12:08,370 --> 00:12:09,970 it's the body temperature at which 302 00:12:09,970 --> 00:12:13,860 performance is its highest. Two critical 303 00:12:13,860 --> 00:12:16,519 limits, in this case the body 304 00:12:16,519 --> 00:12:17,800 temperatures were performance is the 305 00:12:17,800 --> 00:12:22,940 very lowest for ectothermic animals when 306 00:12:22,940 --> 00:12:24,399 we measure these critical thermal limits 307 00:12:24,399 --> 00:12:26,421 is often is when they really when they can 308 00:12:26,421 --> 00:12:29,339 stand up. If you get some too hot or too 309 00:12:29,339 --> 00:12:31,910 cold a bit before they could die, you 310 00:12:31,910 --> 00:12:33,899 actually have them sort of slip into a 311 00:12:33,899 --> 00:12:35,899 coma-type state and they can't work 312 00:12:35,899 --> 00:12:37,360 their muscles anymore. So those are the 313 00:12:37,360 --> 00:12:39,850 critical thermal limits and then some 314 00:12:39,850 --> 00:12:42,420 parameter that describes how wide the 315 00:12:42,420 --> 00:12:44,089 performance breath is because you could 316 00:12:44,089 --> 00:12:47,089 have a situation where you have your 317 00:12:47,089 --> 00:12:49,040 critical limits and basically a plateau 318 00:12:49,040 --> 00:12:50,459 where everything in between you have 319 00:12:50,459 --> 00:12:51,959 high temperatures or this could be 320 00:12:51,959 --> 00:12:54,029 extremely narrow where basically they 321 00:12:54,029 --> 00:12:57,000 have high performance at the optimum and 322 00:12:57,000 --> 00:12:59,709 then it rapidly drops off on both sides. 323 00:12:59,709 --> 00:13:01,150 So, this parameter is telling you sort of 324 00:13:01,150 --> 00:13:04,889 how wide that high performance area is. 325 00:13:04,889 --> 00:13:07,980 In this case it's a "B", which means 326 00:13:07,980 --> 00:13:10,029 that it's the range of temperatures at 327 00:13:10,029 --> 00:13:13,540 which the organism is able to have at 328 00:13:13,540 --> 00:13:17,980 least 80% of its peak performance. So, 329 00:13:17,980 --> 00:13:19,300 that's a performance curve, in this case 330 00:13:19,300 --> 00:13:21,690 a temperature or a thermal performance 331 00:13:21,690 --> 00:13:23,470 curve. 332 00:13:23,470 --> 00:13:27,290 And we think a major reason for these 333 00:13:27,290 --> 00:13:28,519 performance curves, particularly in 334 00:13:28,519 --> 00:13:30,019 response to temperature has to do with 335 00:13:30,019 --> 00:13:32,660 how biochemical reactions work. 336 00:13:32,660 --> 00:13:34,300 Biochemical reactions are quite 337 00:13:34,300 --> 00:13:37,350 temperature sensitive. As temperature 338 00:13:37,350 --> 00:13:40,740 goes up, proteins become a bit more 339 00:13:40,740 --> 00:13:43,510 flexible. Enzymes and other proteins are 340 00:13:43,510 --> 00:13:44,829 pretty much always sort of wiggling 341 00:13:44,829 --> 00:13:46,769 around and changing shapes. And that's 342 00:13:46,769 --> 00:13:48,790 sort of how an enzyme works, is it'll 343 00:13:48,790 --> 00:13:50,660 wiggle into one shape that allows it to 344 00:13:50,660 --> 00:13:52,690 grab a substrate it'll then wiggle into 345 00:13:52,690 --> 00:13:54,550 another shape with that substrate and 346 00:13:54,550 --> 00:13:55,860 that's what it does to catalyze a 347 00:13:55,860 --> 00:13:58,880 reaction. So it sort of snapping between 348 00:13:58,880 --> 00:14:01,990 states between shapes. As you heat them 349 00:14:01,990 --> 00:14:03,690 up, they're able to wiggle a bit, 350 00:14:03,690 --> 00:14:08,529 a bit more rapidly. All compounds, 351 00:14:08,529 --> 00:14:10,350 all molecules move around a little more 352 00:14:10,350 --> 00:14:12,339 when they're at a higher temperature. And 353 00:14:12,339 --> 00:14:13,780 so then they're able to have the 354 00:14:13,780 --> 00:14:16,100 reactions go much more quickly. But at 355 00:14:16,100 --> 00:14:17,800 some point they get so hot, that they're 356 00:14:17,800 --> 00:14:19,519 wiggling around so rapidly that they 357 00:14:19,519 --> 00:14:21,279 stop doing a very good job of catalyzing 358 00:14:21,279 --> 00:14:23,530 reactions. And that is then when your 359 00:14:23,530 --> 00:14:25,680 performance would drop back off. So, this 360 00:14:25,680 --> 00:14:29,120 is just showing how the phenotype of the 361 00:14:29,120 --> 00:14:30,980 organisms can vary in response to the 362 00:14:30,980 --> 00:14:34,120 environment just because of how 363 00:14:34,120 --> 00:14:35,899 biochemical reactions are sensitive to 364 00:14:35,899 --> 00:14:37,639 the environment. In this case, sensitive 365 00:14:37,639 --> 00:14:41,560 to the temperature environment. However, 366 00:14:41,560 --> 00:14:43,190 lots of other factors can influence 367 00:14:43,190 --> 00:14:45,949 enzymes too. And this is only one route 368 00:14:45,949 --> 00:14:48,090 that can cause phenotypic plasticity but 369 00:14:48,090 --> 00:14:50,180 it is one of the important routes, 370 00:14:50,180 --> 00:14:51,870 especially for flexible phenotypic 371 00:14:51,870 --> 00:14:53,630 plasticity, the kind of thing that can be 372 00:14:53,630 --> 00:14:56,509 reversible. So in this case we see an 373 00:14:56,509 --> 00:14:58,699 environmental variable on the x-axis and 374 00:14:58,699 --> 00:15:00,980 we have enzymatic activity on the y-axis 375 00:15:00,980 --> 00:15:03,100 This is really how fast it can catalyze 376 00:15:03,100 --> 00:15:05,069 a reaction. We already talked about the 377 00:15:05,069 --> 00:15:06,560 thermal performance curve which is just shown 378 00:15:06,560 --> 00:15:08,480 in the far left. The middle one shows you 379 00:15:08,480 --> 00:15:10,769 an example for pH. But this basically is 380 00:15:10,769 --> 00:15:11,889 showing you is that when you have 381 00:15:11,889 --> 00:15:14,730 relatively neutral pH's around 7, 382 00:15:14,730 --> 00:15:16,870 the enzymes function well but if pH gets 383 00:15:16,870 --> 00:15:19,569 either too acidic or too alkaline, you 384 00:15:19,569 --> 00:15:23,750 get a very reduced enzymatic activity. 385 00:15:23,750 --> 00:15:25,680 Showing how a phenotype can respond to a 386 00:15:25,680 --> 00:15:29,620 pH environment. Finally, on the right is 387 00:15:29,620 --> 00:15:31,370 just showing the response of enzymes to 388 00:15:31,370 --> 00:15:34,149 substrate concentration. As the amount of 389 00:15:34,149 --> 00:15:36,089 stuff for them to work on goes up, 390 00:15:36,089 --> 00:15:37,709 their activity goes up. And it goes up 391 00:15:37,709 --> 00:15:39,970 quite rapidly, but at some point there's 392 00:15:39,970 --> 00:15:41,970 enough substrate in the environment that 393 00:15:41,970 --> 00:15:45,380 the enzymes are are being able to use 394 00:15:45,380 --> 00:15:46,810 substrate as fast they can, they can't 395 00:15:46,810 --> 00:15:48,350 use it any faster, so you have this 396 00:15:48,350 --> 00:15:53,540 asymptote. And this and it stops changing 397 00:15:53,540 --> 00:15:54,540 in response to the environment at that 398 00:15:54,540 --> 00:15:56,400 point. In this case, it's almost more like 399 00:15:56,400 --> 00:15:59,310 a threshold response. But these are three 400 00:15:59,310 --> 00:16:02,029 different forms of reaction norm. Again, 401 00:16:02,029 --> 00:16:04,910 continuous phenotype variation in 402 00:16:04,910 --> 00:16:09,310 response to an environmental variant. So, 403 00:16:09,310 --> 00:16:13,089 quick wrap-up. The environment can pretty 404 00:16:13,089 --> 00:16:15,970 dramatically influence the phenotype of 405 00:16:15,970 --> 00:16:20,129 individuals. This is a really important 406 00:16:20,129 --> 00:16:21,690 and it's something we often skip over in 407 00:16:21,690 --> 00:16:23,660 biology classes. Although, it's something 408 00:16:23,660 --> 00:16:25,399 that I'm sure you intuit, many of you 409 00:16:25,399 --> 00:16:27,170 know about you all know about tanning, 410 00:16:27,170 --> 00:16:29,010 you all know about working out, so you 411 00:16:29,010 --> 00:16:31,480 have some notion that phenotypes 412 00:16:31,480 --> 00:16:33,569 can vary in response to an environment. 413 00:16:33,569 --> 00:16:36,370 But we tend to talk about how genes are 414 00:16:36,370 --> 00:16:38,920 everything and a gene will code for a 415 00:16:38,920 --> 00:16:40,769 trait, then that individual has that 416 00:16:40,769 --> 00:16:42,680 trait as like a fixed thing. However, it 417 00:16:42,680 --> 00:16:44,920 turns out there's a very large fraction 418 00:16:44,920 --> 00:16:46,790 of the variation among individuals that 419 00:16:46,790 --> 00:16:49,379 can be explained by the environment. As a 420 00:16:49,379 --> 00:16:51,840 whole, we call this phenotypic plasticity, 421 00:16:51,840 --> 00:16:53,230 although there's a number of sort of 422 00:16:53,230 --> 00:16:55,230 other terms with similar meanings, 423 00:16:55,230 --> 00:16:57,230 such as acclimation phenotypic 424 00:16:57,230 --> 00:17:01,920 flexibility, developmental plasticity, so 425 00:17:01,920 --> 00:17:04,790 on. An important thing about phenotypic 426 00:17:04,790 --> 00:17:06,589 plasticity that's quite different from 427 00:17:06,589 --> 00:17:09,790 evolutionary change, is plastic changes 428 00:17:09,790 --> 00:17:11,589 can occur within the lifespan of an 429 00:17:11,589 --> 00:17:13,360 individual, I mean they can respond to 430 00:17:13,360 --> 00:17:16,059 the environment very rapidly and more 431 00:17:16,059 --> 00:17:19,440 rapidly than evolutionary change can. But 432 00:17:19,440 --> 00:17:20,740 there is a bit of a trade-off 433 00:17:20,740 --> 00:17:23,839 in this, because if a phenotype can be 434 00:17:23,839 --> 00:17:26,900 fully changed just by the environment, 435 00:17:26,900 --> 00:17:28,459 that means natural selection cannot 436 00:17:28,459 --> 00:17:30,880 effectively act on it because there's no 437 00:17:30,880 --> 00:17:33,320 heritable trait variation. In this case, 438 00:17:33,320 --> 00:17:34,740 if we think of our breeder's 439 00:17:34,740 --> 00:17:37,770 equation, we would have 'h' squared a 440 00:17:37,770 --> 00:17:40,090 heritability of zero, if it's a fully 441 00:17:40,090 --> 00:17:41,700 plastic trait. Meaning it could not 442 00:17:41,700 --> 00:17:44,480 evolve generation after generation. Now 443 00:17:44,480 --> 00:17:45,780 that's not to say that phenotypic 444 00:17:45,780 --> 00:17:47,150 plasticity is completely 445 00:17:47,150 --> 00:17:48,720 removed from evolution by natural 446 00:17:48,720 --> 00:17:51,440 selection. Because although a specific 447 00:17:51,440 --> 00:17:55,309 phenotype cannot evolve, reaction norms 448 00:17:55,309 --> 00:17:57,700 can evolve. So, how each individual 449 00:17:57,700 --> 00:18:00,340 genotype responds to the environment is 450 00:18:00,340 --> 00:18:01,780 something that natural selection can act 451 00:18:01,780 --> 00:18:04,039 on. And we're talking about that as well 452 00:18:04,039 --> 00:18:06,230 as how we can distinguish the fraction 453 00:18:06,230 --> 00:18:07,809 of variation caused by the environment, 454 00:18:07,809 --> 00:18:09,450 and the fraction of variation that's 455 00:18:09,450 --> 00:18:12,290 caused by genes in our next video. Thank you!