CURRENT CONCEPTS IN BIOLOGY
CURRENT CONCEPTS IN BIOLOGY BIO 380T
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This 5 page Class Notes was uploaded by Ezequiel Orn on Sunday September 6, 2015. The Class Notes belongs to BIO 380T at University of Texas at Austin taught by Staff in Fall. Since its upload, it has received 201 views. For similar materials see /class/181738/bio-380t-university-of-texas-at-austin in Biology at University of Texas at Austin.
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Date Created: 09/06/15
Investigation 93 A Step in Speciation The small salamanders of the genus Ensalina are strictly terrestrial They even Lay their eggs on land Nevertheless these salamanders need a moist environment and do not thrive in arid regions In California Ensalina eschschollzii has been studied by R C Stebbins at the University of California Berkeley This investigation is based on his work Materials per team of l outline map of California 8 different colored pencils Figure 924 rw u w i ll JJV uwlu L wwa tug Part A Collection Areas Procedure 3 Imagine that you are working with Stebbins s salamander specimens some of which are pictured in Figure 924 In the following list salamanders are identi ed by subspecies A subspecies is a geographically restricted population that differs consistently from other populations of the same species The parentheses after each subspecies contain a number and a color The number is the total of individuals Stebbins had available for his study The color is for you to use in designating the subspecies Following this is a list of collection areas They are indicated by a code that ts the map of California in Figure 925 For example 32 R means that one or more E e croceutor specimens were collected near the intersection of Line 32 and Line R This investigation demonstrates how speciation occurs and should emphasize for students that a scientist s real work begins when she or he starts to organize and analyze data Dr Stebbins s research was published in University of California Publications in Zoology 48 1949 317 526 Students should plot data individually but use small groups to consider the discussion question Time One class period Discussion Part A 1 No In those areas where salam anders do not occur there probably are specific limiting factors such as arid or semiarid conditions Historical factors such as human habitation also can affect the distribution 2 Salamanders occur in the mountainous regions except in mountainous desert ranges 3 The fact that subspecies are geographical variations within a species suggests there is an order to the distribution of these subspecies Because of ancestral relationships adjacent species should be more like each other than widely separated subspecies a E e croceutor 15 brown 32R 32S 30T 3lT b E e eschscholtzz39i 203 red 30M 320 348 35V 36W 35Z 38Y 40Z E e klauberz39 48 blue 36Z 38a 40a 39a 0 d E e oregonensis 373 purple 9B 7E 6E l3C lOC 7D lSD e E e picta 230 yellow 2B 2C 3C 4C f E eplatensis 120 green 8 10 l lM l3M lSM 1500 l7M lSP 20Q 24S 2lR 25T 26U g E e xanthoptica 271 orange 1 7G l 7F l9H 190 201 20 211 4 Plot each collection area by making a small X mark on an outline m that has a grid like the one in Figure 925 Use the colors indicated for each subspecies population to make a distribution map of Ensatz39na eschscholtzz39i in California gt V Exceptions can be explained Stebbins postulated that subspecies 5 E e picla is closest to the ancestral form and that subspeciation has taken place southward along the coastal and the inland mountains This would explain the difference in pattern between coastal and inland mountain forms and the similarity among coastal forms and among island forms At the end of the investigation you may want to discuss with your students the most likely center of origin of the species including a consideration of gene flow isolation mechanisms The spotted forms tend to be in the inland Sierra Nevada and the unspotted forms along the coast except in southern California where spotted and unspotted forms occur together Populations of E e eschschallzii and E e klauberi occur in same area in southwestern California 451 Figure 925 Map of California with the grid to be used in plotting distributional data Discussion Part B 1 They represent genetic intergrades hybrids between subspecies 2 The drawing should be an inter grade between E e eschrcl roltzii and E e xanthopica Making such a drawing is a dif cult but challenging assignment requiring 39 imagination There are dines from north to south between the two adjacent subspecies E e xanthopica in and E e eschrcl roltzii in the south In general from north to south the eyelids tend to become lighter and ark p39 tation of body tends to disappear or become restricted to dots To be more speci c toward the south a Lemonyellow eye patch disapp ears b Orange coloration of Ventral surface becomes restricted to underside oflimbs and tail or is lost sketches will not show this ofcourse c Yellow dos on sides ofback appear d Small black dots on sides of b ack app ear e Tip oftail becomes lighter This Discussion question should encourage 1 Is the species unifome distributed Use your knowledge ofthe species studenm to look Very carefully eco logical requiremenm to offer an explanation of its distribution Are a wings there any other ctors that might affect distribution This question should encourage 2 Consider the physiography of California in Figure 925 Does the species students to look Very carefully at the seem more characteristic of mountain areas or of Valley areas drawings 3 Do you expect any panern in distribution of subspecies Why or why 3 These two are geographically not isolated by several hundred miles 4 v 39 L I 4 39 Figure 924 Y L with another subspecies occurring yellow u quot 39 39 39 39 39 quot 39 39 39 between them plain brownorange bodies One has small orange spom on a black 4 To see if here were an background There are other differences as well For example some of ih ergrade SPeCh hehS ahd 0 see if them have white feet Now refer to your distribution map Does there the W0 Shhspeeies Populahehs appear to e any or er to ay these color patterns occur in occupied the same region Califomia For example do the spotted forms occur only along the The two Shhspeeies are coast Do spotted forms occur in the north and unsponed ones in the imen ixed Wi h 0 intergrades south See the references listed in For 5 Subspecies E e eschrcl roltzii and E e klauberi are different from each Further Investigation other What relationship is there between their distributions Part B Additional Collections Procedure 5 You may wonder if there are salamanders in some areas for which you ha no records You also may wonder if there might be additional subspecies F which you have no specimens A biologist faced with these questions would leave the laboratory and go into the field to collect more specimens Imagine that you have done so and returned with the following data b E e eschschaltzz39i I 6 red 36Z 41 Z 33M 34W 34U c E e klauben39 23 blue 40b 40Z 36a h Unidentified population 8 44 black and green 41 511 711 7F 61 9F i Unidentified population 9 13 black and red 28T 27T 26T 28S 29T k Unidentified population 11 131 black and blue 231 241 241 29M 25 251 1 Unidentified population 12 31 black and yellow 6C 7C 613 6 Mark with a 0 the following places that were searched for Ensarz39na without success 111 141 17K 19K 22N 26Q 5M 32U 32A 35F Specimens of populations 8 and 9 are shown in Figure 924 There are no illustrations for populations 11 and 12 Discussion 1 According to Stebbins the unidentified populations are not additional sub species What then is the probable genetic relationship of populations 8 9 and 11 to the subspecies plotted on the map 2 On this basis describe or make a colored drawing of the appearance you would expect specimens of population 11 to have 3 Why is it unlikely that you would ever find individuals combining characteristics of E e picta and E ex0nthaptca 4 Look at the distribution of the original collections of E e eschschaltzii and E e klauben What reasons were there for trying to collect additional specimens from extreme southwestern California 5 How do the results of the additional collections differ from the results in other places where two different populations approach each other 6 Bear in mind the biological definition of a species and also the appearance and distribution of the named populations of Ensa na Which one of these populations could be considered a species separate from E e eschschaltzii This population was indeed once considered by biologists to be a separate species 7 Now imagine that while examining salamanders in another collection you find specimen j from population 10 shown in Figure 924 Compare its characteristics especially the spotting pattern with those of the named populations Also consider the distribution of these populations Between which two is this specimen most likely a hybrid On your map draw a line along which you might expect to collect other specimens like this one 8 In a brief paragraph explain why Stebbins concluded that there is only one species of Ensa na in California 9 Suppose volcanic activity in northern California should become violent and completely destroy all the salamanders in that region How would this event affect the species Ensuring 0 gt1 00 0 Population E e klauberi This is the only form without intergrades with other forms Students may wonder if further collecting would turn up intergrades A provocative discussion might involve what the intergrades would be between and why Incidentally many biologists formerly concluded that E e klauberi was a separate species Between E e klauberi and craceatar Note that the intergrade specimen has spots that tend to form bands Individuals of E e craceatar have definite spots those of E e klauberi are banded Note also that the two spots on the head almost form a band The line is a clockwise are from roughly 32U to 35Z from the most southerly E e craceatar around the east side of E e eschschaltzii to the most northerly E e klauben39 These intergrades were collected at 33Y and 35Y The map shows intergrades between all the subspecies except the two that exist together in southern Califomia It would seem likely that subspeciation has taken place from a common ancestor in the north closely related to E e picta down the two separated mountain chains The two subspecies that exist together without intergrading must have become so different from each other that they are reproductively isolated You can see why these two were thought to be separate species before all the information on the intergrades was available These species rings and loops may be a nuisance to a biologist who merely wants to classify objects but they are exciting to a student of evolution It would break the chain of inter breeding subspecies because E e eschschaltzii and E e klauberi at the southern end of the range do not interbreed This would produce two reproductively isolated populationsi two species For Further Investigation What accounts for the one record of E e xanthoptica in the Sierras with the rest of the subspecies subspecies occurring along the coast For Further Investigation There are several possible explanations The specimen may have been introduced accidentally by humans or irrigation in this region may have allowed the specimen to move across the broad valley More intensive collecting in the valley might show more specimens in the inland mountains with perhaps a connection between the coastal and inland populations in the not too distant past In actuality more than just this one individual were located in the inland mountains in this same general region Consult D B Wake and K P Yanev Geographic Variation in Allozymes in a Ring Species the Plethodontid Salamander Ensa na eschschallzz39i of Western North America Evolution 40 1986 702715 and 0 B Wake et al lntraspecific Sympatry in a Ring Species the Plethodontid Salamander Ensa na eschschallzii in Southern California Evolution 401986 866
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