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8 Sep
2019

Lay Summary – NO PLAGIARISM

Category:ACADEMICIANTag: , :

main points to be covered:-the compelling question this paper tried to address,-how does (do) the researcher(s) go about answering it-what evidence is found-what conclusions are made.Homework 1: Lay Summary InstructionsIn one page, write a Lay Summary for the journal article that your Lab Instructor assigned to your section. Inconcise paragraphs that your aunt or uncle might understand, explain the compelling question this paper tried toaddress, how does (do) the researcher(s) go about answering it, what evidence is found, and what conclusions aremade.A lay summary is like the USA Today version of the article. You want to engage the reader using creative writingskills, but you also must be careful that your summary neither misleads nor foster misconceptions about science.For example, you should avoid words like, ”prove”, “correlate”, “hypothesize”, and “theorize” that are useddifferently in science than in everyday language.Summaries will be evaluated on how well they engage a lay reader, summarize the main finding(s), show languageskills, and follow the format instructions.Assignment Details:• Audience—Layperson such as an aunt or uncle.• Format—Single-spaced, 10-pt font, and fits on a single page. The document should include your name, sectionnumber, and 1-inch margins.• Submitting the assignment— Bring a hardcopy to lab and upload a .pdf document to the specified dropbox onD2L (unless instructed otherwise by your Lab Instructor).• Due date—Hardcopy is due by the beginning of lab during the 2nd week of class. [Note: You will read yoursummary aloud to other members of your group during lab.]• Grading—Please look over the associated grading rubric before you write and submit this assignment.
ORIGINAL INVESTIGATIONEncephalization of Bathyergidae and comparison of brain structurevolumes between the Zambian mole-rat Fukomys anselli and the giantmole-rat Fukomys mechowiiDieter C.T. Kruska, Katja SteffenZoological Institute, Haustierkunde, Christian-Albrechts-University, Universita¨t Kiel, Olshausenstr. 40 – 60, D 24118 Kiel, GermanyReceived 8 February 2008; accepted 10 April 2008AbstractEncephalization indices were calculated for Fukomys anselli and Fukomys mechowii by using interspecific allometriclines of Tenrecinae (recent Eutheria with the smallest brains) and average Rodentia to compare brain sizes independentof body size influence. These were contrasted with corresponding indices of other Bathyergidae and additionally withother rodents. The Bathyergidae species had indices within the variation of some Cricetidae and Muridae and thus donot differ in encephalization. F. anselli, however, had a clearly higher encephalization index than the sister species F.mechowii. The sizes of diverse structures were measured in the brains of these two species by help of the serial sectionmethod. No differences were found in relative composition. The lower encephalization of F. mechowii is discussed as aspecial phenomenon of gigantism during phylogenetic radiation which similarly was documented for other forms.r 2008 Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Published by Elsevier GmbH. All rights reserved.Keywords: Fukomys anselli; Fukomys mechowii; Encephalization; Brain composition; GigantismIntroductionAbsolute and relative size of the brain as well asproportions of brain parts are highly diverse inmammals (De Winter and Oxnard 2001; but see alsoFinlay et al. 2001). Interspecific allometric studies of thebrain to body size relation revealed different encephalization plateaus for several orders (Baron et al. 1996;Kruska 2005; Ro¨hrs 1966; Stephan et al. 1991). Thus,more highly evolved species of mammalian orders havelarger brains, and in general these can be contrastedwith those less progressive and minor encephalized.In addition, very often adaptive radiation to specialecology and life styles within different orders isconnected with enlargement or regression of total brainsize or certain brain structures. Evidently this happenedconvergently during evolution and can be shown fordifferent encephalization plateaus when contrasting,e.g., semiaquatic, aquatic or arboreal species withground dwelling relatives (Kruska 1988, 2005).In this connection adaptive radiation of species to astrictly subterranean life style is of interest. This occurredseveral times during phylogeny within very differentmammalian radiations. Thus, such convergence is knownfrom the Marsupialia (Notoryctes) and eutherian ordersas the Zalambdodonta (Chrysochloridae), Insectivora(Talpidae) and especially within several families of theRodentia (Cricetidae, Geomyidae, Ctenomyidae, Octodontidae, Rhizomyidae, Spalacidae, Bathyergidae).Adapted to fossorial activities and underground life, allthese forms share some corresponding morphological aswell as physiological characteristics.ARTICLE IN PRESSwww.elsevier.de/mambio1616-5047/$ – see front matter r 2008 Deutsche Gesellschaft fu¨r Sa¨ugetierkunde. Published by Elsevier GmbH. All rights reserved.doi:10.1016/j.mambio.2008.04.002 Mamm. biol. 74 (2009) 298–307Corresponding author. Tel.: +49 431 880 4513;fax: +49 431 880 1389.E-mail address: dkruska@zoologie.uni-kiel.de (D.C.T. Kruska).Concerning brain size and brain composition it couldbe assumed that this form of a rather protected lifeunderground would be connected with smaller brains,reduced sense organs and smaller sensory brain parts,which would result in lower encephalization comparedwith relatives adapted to non-fossorial life styles.However, this was not the case in Chrysochloridae andTalpidae since independent of body size these formsclearly had larger brains than the non-fossorial Tenrecinae, which have the smallest brains of all recentEutheria (Stephan et al. 1991). Likewise brains of theblind Spalax also were larger compared with those oflaboratory rats within the order Rodentia (Frahm et al.1997).Mole-rats of the family Bathyergidae are anotherstrictly fossorial group. They are endemic to Africasouth of the Sahara and evolved within the hystricognath rodents in a special and separated radiation fromearly miocene ancestors. No sister-group relationship ofthese forms to any other rodent radiation could beestablished (Thenius 1969; Honeycutt et al. 1991). Thetaxonomy and systematics of the Bathyergidae are stillunder question but in general two subfamilies arerecognized today. The Bathyerginae includes two speciesof Bathyergus which are slightly larger in body size, digwith their enlarged forefeet and claws and live solitary.The other subfamily, the Georychinae, comprisesGeorychus capensis, Heliophobius argenteocinereus, Heterocephalus glaber and an uncertain number ofCryptomys species (Scharff et al. 2001). Recently a newgenus Fukomys was recognized valid for some formerCryptomys species although both genera are not clearlyseparated from each other by morphological traits ormorphometric differences. The new genus was characterized by allozyme, nuclear and mitochondrial DNAmarkers and high karyotypic diversity with diploidnumbers from 48 to 70 versus the rather stable 2n ¼ 54for Cryptomys (Ingram et al. 2004). Altogether 14species of Fukomys are described until now (Kocket al. 2006) and about five of Cryptomys. However,except for F. mechowii the other Georychinae aresmaller sized and all use enlarged chissel-like incisorsfor fossorial activities. Heterocephalus and someFukomys species are the only mammals that areknown for their eusocial organization in family clans(Bennett and Jarvis 1988; Burda 1990; Burda andKawalika 1993; Jarvis 1981, 2001; Lacey and Sherman1981).Since there only is little information on brains of theBathyergidae (Pirlot 1990) the aim of this study is firstlyto get insight in the general encephalization of somebathyergid species compared to Tenrecinae and nonfossorial rodents. Secondly the relatively small Fukomysanselli will be compared with the larger sister speciesFukomys mechowii concerning relative proportioning ofthe brain.Material and methodsTen (five males, five females) F. anselli and 11 (five males, sixfemales) F. mechowii were obtained alive from Prof. H. Burda,University of Duisburg-Essen. The F. anselli were in the first orsecond generation bred under human care. The founderindividuals of this breeding colony originated from the regionof Lusaka, Zambia. They were of the 2n ¼ 68 karyotypepopulation which led to the description of this new species(Burda et al. 1999). The F. mechowii individuals were caught inthe wild from the population near Ndola, Zambia and keptunder human care for several months. The individuals wereadult and between 1.5 and 5 years old.All the animals were sacrificed under deep anaesthesia.Total body weights were recorded immediately after death andthe brains were dissected from the skulls and freshly weighed.Visceral organs were additionally dissected, weighed andstored in formalin (10%). Net cadaver weights were calculatedas total body weight minus viscera weight (Table 1).To get an impression on the encephalization of Bathyergidsin general, data on brain and body weights for some specieswere used from the literature and geometric means of theindividual values of both Fukomys species (Table 2). Theinterspecific allometric line for Tenrecinae according toBauchot and Stephan (1966) served as one reference line andthe interspecific allometric line for average Rodentia asanother. The latter has previously been calculated using brainbody size data of 64 species from 20 families of Protrogomorpha, Myomorpha, Glirimorpha, Sciuromorpha, Caviomorpha, and Hystricomorpha (Kruska 1980, 1988; for slope andposition of several mammalian interspecific allometric lines seeARTICLE IN PRESSTable 1. Individual brain and body size data of the twoFukomys species F. anselli and F. mechowiiNo. Species Sex TBW NCW BW18142 Fukomys anselli Female 58 30 1.1818181 Fukomys anselli Female 80 44 1.2318406 Fukomys anselli Female 54 31 1.2218410 Fukomys anselli Female 66 38 1.2118411 Fukomys anselli Female 50 29 1.1118164 Fukomys anselli Male 83 46 1.3518180 Fukomys anselli Male 100 53 1.3318407 Fukomys anselli Male 50 29 1.2118408 Fukomys anselli Male 80 46 1.2418409 Fukomys anselli Male 81 46 1.21— Fukomys mechowii Female 270 — 2.1118162 Fukomys mechowii Female 255 142 2.2118975 Fukomys mechowii Female 166 104 2.2118976 Fukomys mechowii Female 225 129 2.4518987 Fukomys mechowii Female 194 106 2.3218988 Fukomys mechowii Female 177 102 2.2518137 Fukomys mechowii Male 309 189 2.8318977 Fukomys mechowii Male 256 147 2.4019111 Fukomys mechowii Male 442 255 2.0919112 Fukomys mechowii Male 352 187 2.3619113 Fukomys mechowii Male 330 179 1.98TBW ¼ total body weight (in g); NCW ¼ net cadaver weight (in g);BW ¼ brain weight (in g).D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307 299also Kruska 2005). Encephalization indices for the Bathyergidae species were then estimated in relation to theinterspecific allometric line for Tenrecinae (EI te). Calculationswere also done in relation to the line for average Rodentia (EIro) (Table 2). The indices characterize the encephalization levelof a species above the plateau of Tenrecinae (EI te ¼ 100) orabove as well as below that of average Rodentia (EI ro ¼ 100).Average Rodentia have body size independently about 2.5times larger brains than Tenrecinae (EI te ¼ 244). Theencepalization indices of Bathyergidae are then comparedwith those of some other rodents.The brains of the two Fukomys species were fixed in AGFfluid (being a mixture of 80 ml alcohol 80%, 10 ml glacialacetic acid and 10 ml formalin 40%), after 3 days stored in80% alcohol and later photographed from dorsal, lateral andventral view. They were then embedded in paraffin. Six (3f,3m) brains of F. anselli and the same number of F. mechowiiwere used for serial sectioning. Accordingly they were cuttotally at 10 mm or at 20 mm in the frontal plane. About 250equidistant sections per brain were mounted on slices andNissl-stained with cresyl violett. The 80–90 of these, againequidistant and covering the whole brain, were photographedand projected on photographic paper at a known enlargement.On these the structures listed in Tables 3–6 were at firstdelineated in the same way as shown for rats in Kruska(1975a, b), then cut out and finally weighed. By use of thepaper weight, enlargement of photographs, section thicknessand the distance between sections the serial section volume foreach structure was determined (Stephan 1960; Kruska andStephan 1973). Due to tissue shrinkage during fixation andhistological processing the brain volume resulting from thesum of the major brain regions of the serial sections isconsiderably smaller than the fresh brain volume (fresh brainweight divided by 1.036 ¼ specific gravity of brain substance).The extent of shrinkage is different for each brain. Here, thebrains of F. anselli shrank by 44.1%, 50.0%, 44.8%, 45.2%,47.1%, 48.1% and those of F. mechowii by 46.1%, 33.7%,36.8%, 37.0%, 38.0% and 37.3%. Consequently a conversionfactor was calculated for each brain (being volume of freshbrain/sum of serial section volumes) and the serial sectionvolumes of all structures were converted into fresh tissuevalues. These are documented in Tables 3 and 4.ARTICLE IN PRESSTable 2. Brain and body weight data of several species ofBathyergidae and calculated encephalization indices in relationto the allometric line for Tenrecinae (EI te) and for averageRodentia (EI ro)Species TBW BW EI te EI ro SourceFukomys anselli 68.3 1.23 200 82 This studyFukomys mechowii 265.0 2.28 158 65 This studyCryptomys hottentotus 130.2 1.36 148 60 Pirlot (1990)Georychus capensis 132.3 1.79 192 79 Pirlot (1990)Bathyergus janetta 268.0 2.06 142 58 Pirlot (1990)Heterocephalus glaber 33.3 0.43 111 45 Pirlot (1990)The values for F. anselli and F. mechowii are geometrical means fromTable 1. TBW ¼ total body weight in g; BW ¼ brain weight in g.Table 3. Absolute volumes (in mm3) of diverse brain structures in 6 (3 females, 3 males) Fukomys anselli individualsFukomys anselli 18411 18142 18181 18409 18180 18164Pure brain tissue 1027.260 1116.848 1160.705 1129.175 1246.159 1279.176Medulla oblongata 117.236 126.244 128.375 143.119 152.528 132.775Cerebellum 177.231 169.333 193.753 204.897 213.982 225.052Mesencephalon 60.321 73.122 60.374 47.654 66.950 77.806Diencephalon 86.394 97.947 100.529 100.199 110.440 109.612Telencephalon 586.078 650.202 677.674 633.306 702.259 733.931Neocortex 272.478 303.577 332.056 302.412 322.284 366.566Corpus striatum 66.871 75.610 74.620 67.220 76.393 77.571Allocortex 246.729 271.015 270.998 263.674 303.582 289.794Neocortex (grey matter) 246.371 275.544 297.551 271.209 289.860 328.745Neocortex (white matter) 26.107 28.033 34.505 31.203 32.424 37.821Olfactory allocortex 131.148 144.054 144.801 146.078 161.529 147.998Bulbus olfactorius 43.359 45.842 47.218 47.614 54.851 29.506Regio retrobulbaris 3.600 5.358 6.739 6.234 6.603 6.906Tuberculum olfactorium 10.182 13.093 12.106 11.597 11.546 13.860Regio praepiriformis 43.618 43.464 46.048 45.207 53.597 53.844Nucleus amygdala 19.621 22.526 20.864 22.250 22.317 29.271Basal nuclei 10.768 13.771 11.826 13.176 12.615 14.611Non-olfactory allocortex 115.581 126.961 126.197 117.596 142.053 141.796Septum 16.960 16.111 16.062 16.923 19.291 19.263Hippocampus 60.612 65.009 70.947 64.538 77.316 76.819Schizocortex 38.009 45.841 39.188 36.135 45.446 45.714300 D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307In order to compare the composition of the brains of bothspecies and to get an idea about individual variability, all thediverse structures were calculated as percentages of pure braintissue (Tables 4 and 5). This pure brain tissue value resultedfrom calculations of fresh brain volume minus volumes ofventricles, nerves, hypophysis, epiphysis and parts of the spinalcord which had remained with the brains. Additionally meanpercentage values were calculated for any given structure ofboth species and then compared with corresponding values ofbrains from wild caught Norwegian rats Rattus norvegicus(Kruska 1975a, b; Kruska and Schott 1977).Results and discussionIndividual data on brain and body size of Fukomysanselli and F. mechowii are summarized in Table 1. In adouble log plot of these data the values for F. anselli areadjusted to an intraspecific allometric line with a slopearound a ¼ 0.20 (not shown) as is typical for othermammals (Kruska 1980, 1988, 2005) but this was notthe case for the data of F. mechowii.Concerning the encephalization degree of Bathyergidae limited data for brain and body sizes of other specieswere found in literature (Pirlot 1990) only of singleindividuals per species. These were compared with thegeometrical means of the data of the two Fukomysspecies (Table 2). As can be seen in Fig. 1 the values ofthe Bathyergidae species are placed between the interspecific allometric lines of the Tenrecinae and averageRodentia. This means, after adjusting for body size thespecies have larger brains compared with Tenrecinae,but they have smaller brains compared with rodents onaverage. This is also documented by the encephalizationindices (Table 2). These are greater than 100 in case ofEI te and smaller than 100 for EI ro. However, theBathyergidae species have reached different encephalization levels, e.g., Fukomys anselli and Georychuscapensis have the largest brains followed by Fukomysmechowii, Cryptomys hottentotus and Bathyergus janetta. Very clearly H. glaber has the smallest brain which isonly slightly larger than that of Tenrecinae. Althoughfor most of the Bathyergidae these values are ratheruncertain because of limited data, the values for the twoFukomys species are valid.In this respect it is of interest to know someencephalization indices of other rodents with fossorialbut additionally non-fossorial activities. These werecalculated as EI ro from geometrical means of a greaternumber of literature data and are as follows:Cricetidae: Cricetus cricetus (n ¼ 57 Frahm 1973;Adam 1973 unpubl.) EI ro ¼ 59; Mesocricetus auratusARTICLE IN PRESSTable 4. Absolute volumes (in mm3) of diverse brain structures in 6 (3 females, 3 males) Fukomys mechowii individualsFukomys mechowii 18162 18987 18976 19113 19112 18977Pure brain tissue 2062.711 2134.879 2287.866 1843.912 2170.674 2249.974Medulla oblongata 254.809 235.223 218.970 190.588 211.816 256.126Cerebellum 383.397 345.007 341.344 374.681 380.318 373.804Mesencephalon 102.467 91.793 119.419 102.179 99.066 106.012Diencephalon 155.824 170.201 192.432 130.657 168.228 182.148Telencephalon 1166.214 1292.655 1415.701 1045.807 1311.246 1331.884Neocortex 584.429 648.692 696.370 527.950 657.719 696.155Corpus striatum 127.337 137.229 165.825 98.893 138.804 143.977Allocortex 454.448 506.734 553.506 418.964 514.723 491.752Neocortex (grey matter) 508.503 557.820 617.031 472.088 591.445 616.241Neocortex (white matter) 75.926 90.872 79.339 55.862 66.274 79.914Olfactory allocortex 246.519 265.371 302.362 240.112 278.296 262.735Bulbus olfactorius 69.727 78.961 86.625 79.568 86.280 77.958Regio retrobulbaris 6.827 9.272 8.938 8.684 8.663 7.687Tuberculum olfactorium 25.774 28.244 31.212 21.281 27.774 23.805Regio praepiriformis 86.724 84.241 104.019 77.769 90.473 84.094Nucleus amygdala 36.431 40.462 48.193 34.425 40.425 39.788Basal nuclei 21.036 24.191 23.375 18.385 24.681 29.403Non-olfactory allocortex 207.929 241.363 251.144 178.852 236.427 229.017Septum 31.138 31.559 30.938 21.672 29.082 28.323Hippocampus 112.357 128.695 142.656 106.873 131.310 121.994Schizocortex 64.434 81.109 77.550 50.307 76.035 78.700D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307 301(n ¼ 61 Frahm 1973) EI ro ¼ 61; Phodopus sungorus(n ¼ 60 Frahm 1973) EI ro ¼ 58; Clethrionomys glareolus (n ¼ 228 Lo¨bmann 1968; Adam 1973 unpubl.) EIro ¼ 82; Microtus agrestis (n ¼ 16 Adam 1973 unpubl.)EI ro ¼ 71; Ondatra zibethica (n ¼ 27 Adam 1973unpubl.) EI ro ¼ 71.Muridae: Mus musculus (n ¼ 71 Rohn 1971 unpubl.)EI ro ¼ 66; R. norvegicus (n ¼ 78 Kruska 1975a) EIro ¼ 62; Apodemus sylvaticus (n ¼ 267 Klemmt 1960;Adam 1973 unpubl.) EI ro ¼ 91; Apodemus flavicollis(n ¼ 37 Adam 1973 unpubl.) EI ro ¼ 90.Spalacidae: Spalax ehrenbergi (n ¼ 8 Frahm et al.1997) EI ro ¼ 99.From this it can be concluded that Fukomys mechowiihas approximately the same encephalization level as thethree hamster species as well as mouse and rat. Anevidently higher encephalization is documented forFukomys anselli with an index comparable to Ctethrionomys glareolus. Very surprising, however, is the factthat the strictly fossorial blind mole-rat Spalax ehrenbergi in a distinct radiation shows the highest encephalization of these rodents mentioned. The evidentdifference between the two Fukomys sister speciesremains surprising especially in the light of theircommon ancestry and rather similar life styles.However, concerning the outer appearance and exceptfor differences in size the brains of Fukomys anselli andFukomys mechowii are very much alike and remind of arodent brain (Fig. 2). They show relatively small andlissencephalic hemispheres and a prominent cerebellum. Indorsal view the contour of the hemispheres appears morerectangular and less elongated as in some other rodents,e.g. rats or mice. An occipital pol is not very prominent,possibly greater parts of a visual area are lacking in thesemicroptic mammals. Viewed from lateral the olfactorybulbs seem of normal size but the hemispheres are not veryhigh. They do not exceed the height of the cerebellum.Tiny optic nerves and a small chiasma opticum are hardlyto recognize in ventral view of both brains.The measured fresh tissue sizes of diverse brain partsare summarized in Table 3 for Fukomys anselli and inTable 4 for Fukomys mechowii. They, of course, differ insize from brain to brain and species to species because ofdifferences in total brain size and individual variability.The relative values (Tables 5 and 6) are more reliable fora comparative approach. Also here a certain individualvariability can be seen in both species which in similardimensions also is known from other mammals andcomparable studies. Min.–max. and mean values ofrelative structures sizes of the brains of both Fukomysspecies are given in Table 7 and contrasted with comparable data of wild Norvegian rats (Kruska 1975a, b;Kruska and Schott 1977). These three species showcorresponding results concerning brain proportioning.ARTICLE IN PRESSTable 5. Relative values of the brain structures in Fukomys anselliFukomys anselli 18411 18142 18181 18409 18180 18164Pure brain tissue 100.00 100.00 100.00 100.00 100.00 100.00Medulla oblongata 11.41 11.30 11.06 12.67 12.24 10.38Cerebellum 17.25 15.16 16.69 18.25 17.17 17.59Mesencephalon 5.87 6.55 5.20 4.22 5.37 6.08Diencephalon 8.41 8.77 8.66 8.87 8.86 8.57Telencephalon 57.06 58.22 58.39 56.09 56.36 57.38Neocortex 26.52 27.18 28.61 26.78 25.87 28.66Corpus striatum 6.52 6.77 6.43 5.96 6.13 6.07Allocortex 24.02 24.27 23.35 23.35 24.36 22.65Neocortex (grey matter) 23.98 24.67 25.64 24.02 23.26 25.70Neocortex (white matter) 2.54 2.51 2.97 2.76 2.61 2.96Olfactory allocortex 12.77 12.90 12.48 12.94 12.96 11.57Bulbus olfactorius 4.22 4.11 4.07 4.22 4.40 2.31Regio retrobulbaris 0.35 0.48 0.58 0.55 0.53 0.54Tuberculum olfactorium 0.99 1.17 1.04 1.03 0.93 1.08Regio praepiriformis 4.25 3.89 3.97 4.00 4.30 4.21Nucleus amygdala 1.91 2.02 1.80 1.97 1.79 2.29Basal nuclei 1.05 1.23 1.02 1.17 1.01 1.14Non-olfactory allocortex 11.25 11.37 10.87 10.41 11.40 11.08Septum 1.65 1.44 1.38 1.49 1.55 1.51Hippocampus 5.90 5.82 6.11 5.72 6.20 6.00Schizocortex 3.70 4.11 3.38 3.20 3.65 3.57302 D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307The telencephalon is the greatest part of the fundamental brain regions followed by the cerebellum, themedulla oblongata and then the diencephalon andmesencephalon which clearly are smaller. Within theforebrain the neocortex with a prominent portion ofgrey matter is only slightly greater than the allocortex.The latter structure consists of olfactory and nonolfactory (limbic) parts to nearly similar extent althoughin the Fukomys species the olfactory structures seemslightly larger in relative size. When comparing the meanARTICLE IN PRESSTable 6. Relative values of the brain structures in Fukomys mechowiiFukomys mechowii 18162 18987 18976 19113 19112 18977Pure brain tissue 100.00 100.00 100.00 100.00 100.00 100.00Medulla oblongata 12.35 11.02 9.57 10.34 9.76 11.38Cerebellum 18.59 16.16 14.92 20.32 17.52 16.61Mesencephalon 4.97 4.30 5.22 5.54 4.56 4.71Diencephalon 7.55 7.97 8.41 7.08 7.75 8.10Telencephalon 56.54 60.55 61.88 56.72 60.41 59.20Neocortex 28.33 30.38 30.44 28.63 30.30 30.94Corpus striatum 6.18 6.43 7.25 5.37 6.40 6.40Allocortex 22.03 23.74 24.19 22.72 23.71 21.86Neocortex (grey matter) 24.65 26.13 26.97 25.60 27.25 27.39Neocortex (white matter) 3.68 4.25 3.47 3.03 3.05 3.55Olfactory allocortex 11.95 12.43 13.22 13.02 12.82 11.68Bulbus olfactorius 3.38 3.70 3.79 4.31 3.97 3.46Regio retrobulbaris 0.33 0.43 0.39 0.47 0.40 0.34Tuberculum olfactorium 1.25 1.32 1.36 1.15 1.28 1.06Regio praepiriformis 4.20 3.95 4.55 4.22 4.17 3.74Nucleus amygdala 1.77 1.90 2.11 1.87 1.86 1.77Basal nuclei 1.02 1.13 1.02 1.00 1.14 1.31Non-olfactory allocortex 10.08 11.31 10.97 9.70 10.89 10.18Septum 1.51 1.48 1.35 1.18 1.34 1.26Hippocampus 5.45 6.03 6.23 5.79 6.05 5.42Schizocortex 3.12 3.80 3.39 2.73 3.50 3.50Average RodentiaTenrecinaelogTotal Body Weight (g)Fukomys anselliFukomys mechowiiCryptomys hottentotusBathyergus janettaGeorychus capensisHeterocephalus glabera = 0.63b = -0.9800a = 0.63b = -1.36800.40.20.0-0.2-0.4-0.6-0.81.0000 1.5000 2.0000 2.5000Brain Weight (g)log3.0000Fig. 1. Interspecific allometric lines of Tenrecinae and average Rodentia and specific data plots of Bathyergidae.D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307 303relative values for the diverse structures of F. anselli withF. mechowii differences obviously occur for the telencephalon, the total neocortex and its grey matter.However, such differences could not be assured statistically and consequently as a main result both specieshave brains of identical relative composition althoughvery clearly at different encephalization levels.Compared with the rat brain composition on theother hand some differences are obvious. Here the meanrelative values of cerebellum and telencephalon aresmaller and those of medulla oblongata, mesencephalonand diencephalon larger. Within the smaller telencephalon of rats again the total neocortex and its grey matterare larger as in mole-rats, while the allocortex, especiallyits olfactory parts, are smaller. Maybe in comparisonwith Rattus norvegicus the larger olfactory structures inthe brains of the two Fukomys species compensate to acertain degree the lack of extensive visual structures intheir smaller diencephalon and neocortex.In conclusion both Fukomys species have reachedencephalization levels comparable with those of someCricetidae and Muridae with above ground life styles. Inthis example there is no convincing evidence for theassumption that ecological niche adaptation duringphylogenetic radiation is dependent of or connectedwith evolutionary brain size increase or decrease.Moreover, F. anselli and F. mechowii have similar lifestyles although the former consumes plant materialsexclusively whereas the latter is omnivorous (Burda andKawalika 1993). Therefore, the most striking result isthe similar relative composition of brains in these twospecies which have clearly different encephalizationindices.In this connection the following must be recognized.Concerning the relationship of brain to body size thefollowing resulted from the fossil record of the Equidaeas well as of the Tylopoda: with the origin of new speciesduring phylogeny an increase of body size was notARTICLE IN PRESSFig. 2. Brains of Fukomys anselli (18181 – left) and Fukomys mechowii (18976 – right) in dorsal, lateral and ventral view.304 D.C.T. Kruska, K. Steffen / Mamm. biol. 74 (2009) 298–307always or necessarily connected with a brain sizeincrease similarly as the interspecific allometric relationof recent forms (see Kruska 1982a, 1987). Very oftenduring evolutionary processes a certain ‘‘persistence’’ ofbrain size is characteristic during phylogenetic body sizeincrease (Edinger 1960). On the other hand a brain sizeincrease is also documented for the radiation of Equidaeand Tylopoda which happened in an ‘‘erratic’’ wayrather independently of body size. For recent mammalian species Ro¨hrs (1958) mentioned several examplesfor such ‘‘erratic’’ breakthroughs of interspecific allometries upward, i.e. closely related species with similarlife style and behaviour which have greater brains at thesame body size of sister species. Thus, progressiveencephalization during phylogeny was documented forseveral clades, e.g., for carnivores (Kruska 1988, 2005;Finarelli and Flynn 2007). As already was mentionedduring phylogenetic radiation of mammals interspecificallometries also were broken through downward,namely in cases where an extensive retardation of brainsize is opposed to a phylogenetic acceleration of bodysize. As an example from the recent fauna the giantforest hog Hylochoerus meinertzhageni can be mentionedcompared with the other species of Suidae andHippopotamus amphibius contrasted with the pigmyhippo Choeropsis liberiensis (Kruska 1970, 1982b). Bothgiant forms derived phylogenetically from smaller formsclosely resembling the other recent species of the familyin size (Thenius 1969). The brain size did not follow thebodily gigantism in an interspecific mode. Consequentlyboth giant species clearly are less encephalized.Just the same, within the group of tree-squirrels giantspecies of the genus Ratufa likewise evolved from smallersized forms. Calculations on brain and body size datafrom literature (Kruska unpubl.) resulted as follows: fourspecies of the smaller sized Sciurus had greater and rathersimilar EI ro values, S. carolinensis 150, S. niger 155,S. rufiventer 155, S. vulgaris 159. The value for the northAmerican semiarboricol Tamias striatus was 150, forTamiasciurus hudsonicus 169 and the African Funisciuruscarruthersi 162. In contrast the Asiatic giant squirrelsclearly had smaller values: Ratufa indica 93 and Ratufabicolor 119. Furthermore within the Petauristinae thesmaller Pteromys volans had an index of 142 whereas thegiant Petaurista petaurista only had 108.In the light of these results we may conclude that thegiant mole-rat F. mechowii in contrast to F. anselli is justanother example of downward breakthroughs of interspecific allometries in the brain to body size relation.Consequently the encephalization index is not alwaysARTICLE IN PRESSTable 7. Comparison of relative sizes of brain structures (pure brain tissue ¼ 100) in Fukomys anselli (n ¼ 6) and Fukomysmechowii (n ¼ 6) with wild Rattus norvegicus (n ¼ 8, Kruska 1975a, b, Kruska and Schott 1977)F. anselli F. mechowii R. norvegicusMin.–max. Mean Min.–max. Mean Min.–max. MeanMedulla oblongata 10.4–12.7 11.5 9.6–12.4 10.7 12.2–13.2 12.6Cerebellum 15.2–18.3 17.0 14.9–20.3 17.4 13.7–16.5 14.9Mesencephalon 4.2–6.6 5.5 4.3–5.5 4.9 6.3–7.3 6.8Diencephalon 8.4–8.9 8.7 7.1–8.4 7.8 8.9–9.8 9.3Telencephalon 56.1–58.4 57.3 56.5–61.9 59.2 55.1–58.3 56.4Neocortex 25.9–28.7 27.3 28.3–30.9 29.8 29.3–33.0 31.1Corpus striatum 6.0–6.8 6.3 5.4–7.3 6.4 4.6–5.4 5.1Allocortex 22.7–24.4 23.7 21.9–24.2 23.0 18.9–21.2 20.2Neocortex (grey matter) 24.6–25.7 24.6 24.7–27.4 26.3 25.0–28.8 27.1Neocortex (white matter) 2.5–3.0 2.7 3.0–4.3 3.5 3.5–4.3 4.0Olfactory allocortex 11.6–13.0 12.6 11.7–13.2 12.5 9.2–11.1 10.4Bulbus olfactorius 2.3–4.4 3.9 3.4–4.3 3.8 2.1–3.6 3.1Regio retrobulbaris 0.4–0.6 0.5 0.3–0.5 0.4 0.7–0.9 0.8Tuberculum olfactorium 0.9–1.2 1.0 1.0–1.4 1.2 0.4–0.5 0.4Regio praepiriformis 3.9–4.3 4.1 3.7–4.6 4.1 2.7–3.6 3.2Nucleus amygdala 1.8–2.3 2.0 1.8–2.1 1.9 1.8–1.9 1.8Basal nuclei 1.0–1.2 1.1 1.0–1.3 1.1 1.0–1.2 1.1Non-olfactory allocortex 10.4–11.4 11.1 9.7–11.3 10.5 9.4–10.1 9.8Septum 1.4–1.7 1.5 1.2–1.5 1.4 1.1–1.4 1.3Hippocampus 5.7–6.2 6.0 5.4–6.2 5.8 5.6–6.5 6.0Schizocortex 3.2–4.1 3.6 2.7–3.8 3.3 2.4–2.8 2.5Min.–max. and mean values of individual variability are given.D.C.T. 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