Levels Of Morphological Variation Research Articles

Taxonomy-testing and the ‘Goldilocks Hypothesis’: morphometric analysis of species diversity in living and extinct Hispaniolan hutias

Understanding the dynamics of the Late Quaternary Caribbean mammal extinction event is complicated by continuing uncertainty over the taxonomic status of many species. Hispaniola is one of the few Caribbean islands to retain native non-volant mammals; however, there has been little consensus over past or present levels of diversity in Hispaniolan hutias (Capromyidae: Plagiodontinae). Craniodental measurement data from modern hutia specimens, previously classified as both Plagiodontia aedium and P. hylaeum, display morphological differences between Hispaniola's northern and southern palaeo-islands using MANOVA and PCA. Although attempts to amplify mitochondrial DNA from the holotype of P. aedium were unsuccessful, this specimen is morphometrically associated with southern palaeo-island specimens. The mandibular size distribution of recent Plagiodontia specimens is unimodal, but the Late Quaternary mandibular size distribution is multimodal and displays much broader measurement spread, representing multiple extinct species. Finite Mixture Analysis was used to assess the best fit of different taxonomic hypotheses to the fossil mandibular size distribution. All retained FMA models include living hutias and P. spelaeum as distinct taxa; PCA further demonstrates that levels of morphological variation between modern hutia populations are lower than levels between living hutias and P. spelaeum, so that living hutias are interpreted as the single species P. aedium. Taxonomic differentiation for larger-bodied hutias is less well defined, but most retained models show only one larger species, for which the only available name is P. velozi. ‘Plagiodontia’ araeum is morphologically distinct from other species and is reassigned to Hyperplagiodontia. Hispaniola's plagiodontine fauna has lost its largest and smallest representatives; similar trends of body size selectivity in extinction risk are shown more widely across the Caribbean mammal fauna, possibly due to different regional anthropogenic threats (invasive mammals, hunting) affecting small-bodied and large-bodied mammals during the recent past. This apparent pattern of extinction selectivity is named the ‘Goldilocks Hypothesis’.

Comparison of Jaw Muscle Morphology in Two Sympatic Callosciurine Squirrels (Callosciurus ErythraeusandDremomys Rufigenis) in Vietnam

Laboratory of Anatomy, Department of Basic Veterinary Sciences, Obihiro University of Agriculture and Veterinary Medicine, Obihiro 080-8555, JapanIn this study, we focus on the jaw muscle morphol-ogy of two callosciurine squirrel species, Callosciuruserythraeus and Dremomys rufigenis. Callosciuruserythraeus (Callosciurini: Sciuridae: Callosciurinae) isan arboreal squirrel that inhabits Southeast Asia fromeastern India to the Malayan archipelago, Indochina,southern China, and Taiwan (Nowak 1999; Can et al.2008; Francis 2008; Smith and Xie 2008). D. rufigenis,another member of the tribe Callosciurini, is found sym-patrically with C. erythraeus throughout Southeast Asia(Nowak 1999; Can et al. 2008; Francis 2008; Smith andXie 2008). Koyabu et al. (2009) previously reported thatthe sympatric C. erythraeus and D. rufigenis displaynotable difference in craniodental mechanics. Both C.erythraeus and D. rufigenis are known to prefer fruitsand insects, as generally seen in other tree squirrels.However, C. erythraeus also feeds extensively on hardseeds and tough tree bark, which are rarely included inthe diet of D. rufigenis. For example, C. erythraeus isreported to frequently forage on the hard seeds ofPinus, Camellia, and Castanopsis tree (Chou et al.1985; Sonoda et al. 2001; Lu 2003; Men et al. 2007).Callosciurus erythraeus is also known to often strip toughbark to obtain sugar from sweet tree saps (Tamura andOhara 2005), whereas this dietary behavior seems to berare or not reported in D. rufigenis (Medway 1969;Nowak 1999; Smith and Xie 2008). Koyabu et al.(2009) demonstrated that C. erythraeus possesses agreater mechanical advantage of the masseter and tem-poralis muscles for chewing compared to D. rufigenis.Callosciurus erythraeus was also found to display greaterleverage of the masseter and temporalis for incision.Given these findings, it was suggested that C. erythraeusshould be capable of generating greater bite force for agiven muscle force at the cheek teeth and that the cranio-dental divergence between C. erythraeus and D. rufigenismay facilitate their trophic separation under sympatry.In their study, however, only the analysis of mechani-cal leverages was conducted, and comparisons of jawmuscle morphology were not incorporated. Althoughthe craniodental arrangements and mechanical advantageof the masticatory muscles are critical parameters thataffect the amount of force production, muscle mass isalso another essential contributor to the bite forces ananimal can generate (Raadsheer 1999). Since the biteforces an organism can generate should constrain therange of food items it can eat (Lucas 2004), variation inmasticatory muscle mass has undoubtedly been funda-mental for the dietary diversification of rodents. Giventhe great range of diet and phenomenal level of morpho-logical diversity found across rodents, studies on rodentmuscle mass variation should provide promising avenuesto study the ecomorphological patterns of mammals ingeneral. To date, reports on muscle mass are availablefor some muroids (e.g., Hiiemae and Houston 1971;Weijs and Dantuma 1975; Satoh 1997; Satoh and Iwaku2004) and New World squirrels (Ball and Roth 1995).Although Thorington and Darrow (1996) provideddetailed anatomical descriptions of jaw muscles for someOld World squirrel species, still very little is describedquantitatively for them. Here, to bridge the gaps in ourknowledge of Old World squirrel muscle morphology

The relationship between molecular variation and variation in the wing shape of three aphid parasitoid species: Aphidius uzbekistanicus Luzhetzki, Aphidius rhopalosiphi De Stefani Perez and Aphidius avenaphis (Fitch) (Hymenoptera: Braconidae: Aphidiinae)

This paper examines the relationship between molecular and phenotypic variability among three closely related cereal aphid parasitoids: Aphidius rhopalosiphi and Aphidius uzbekistanicus from Euro-Asia and Aphidius avenaphis from North America. A. rhopalosiphi has the same distribution and shares the same aphid hosts as A. uzbekistanicus. The genetic variation of these parasitoids was explored using a barcoding area of the mitochondrial COI gene. Phenotypic variability based on the wing shape and stigma shape was explored using geometric morphometrics. Molecular analyses revealed the existence of two distinct clades: the A. rhopalosiphi clade, which is characterized by a high level of within-clade genetic variation, and the A. uzbekistanicus/A. avenaphis clade, which has almost no variation at the barcoding area of the mitochondrial COI gene. Generally, a high level of variation in wing shape has been shown within populations of both clades. Our results indicate that there is no relationship between the level of the variation at the barcoding area of the mitochondrial COI gene and the level of morphological variation. The genetically uniform A. uzbekistanicus/A. avenaphis clade had even greater variation in stigma shape than A. rhopalosiphi clade, which is characterized by a high level of genetic variation.

Morphological diversity of some introduced tree peony cultivars

Tree peonies, native to China, are widely cultivated in many countries, but the threat of genetic degradation in new varieties is serious due to the selection of local cultivars as parents in breeding. Hence, it is important to use introduced cultivars from different origins when breeding new varieties. To assist in en- larging the genetic basis of tree peonies, we examined 41 morphological traits of 68 introduced tree peony cultivars from the USA, France and Japan, and compared them to 21 local varieties. We found high levels of morphological diversity among cultivars; coefficients of variation based on morphological traits ranged from 14.3% to 159%, with an average of 44.5%. A principal component analysis (PCA) integrated these 41 traits into 10 principal components. Among these components, 7 were most strongly associated with the first fac- tor, representing flower characters; the other 3 were associated with the second factor, representing leaf cha- racters. Results of a cluster analysis concurred with those of the PCA analysis. All cultivars clustered into two groups: the first was characterized by those that exhibited non-leaf-chromatic, larger flower diameter, non-petal-blotch, late flower time and erect flowers, and most of them were foreign cultivars; the second in- cluded foreign and Chinese cultivars and can be further classified, and was characterized by non-leaf-chro- matic and small flower diameter. Moreover, the cluster analysis showed that most foreign cultivars were

Biosystematic studies on Adenophora potaninii Korsh. complex (Campanulaceae) V. A taxonomic treatment

Abstract Adenophora is an extremely variable genus, and its taxonomy is very controversial. Of the genus, Adenophora potaninii complex, including A. potaninii, A. bockiana, A. wawreana, A. lobophylla, A. biformifolia, A. polydentata, and A. wawreana var. lanceifolia, is a typical group with different taxonomical treatments due to high level of morphological diversity. We carried out extensive biosystematic studies based on population sampling, transplantation experiments and offspring tests, cluster analysis, and a crossing experiment. The results reveal four main findings. (i) Leaf forms of the A. potaninii complex were extremely polymorphic; the leaf form of A. potaninii and A. bockiana, and that of A. wawreana and A. biformifolia could be found, respectively, on a single population or among the offsprings of a single plant. (ii) Cluster analysis and a crossing experiment indicated that A. bockiana and A. polydentata could not be separated from A. potaninii, nor A. biformifolia from A. wawreana. (iii) Adenophora potaninii and A. wawreana were gradational in morphology and their compatibility value was slightly reduced compared to that within each entity. (iv) Adenophora lobophylla was distinct from the other members of the complex in shape and size of corolla, relative length of style, and shape of capsule. This species was incompatible reproductively with the other members of the complex, but partly compatible with A. stenanthina, a species in another section. Therefore, we recognized only one species with two subspecies in the complex, A. potaninii subsp. potaninii and subsp. wawreana, moved A. lobophylla out of the complex, and reduced all the other names as new synonyms.

How Humans Differ from Other Animals in Their Levels of Morphological Variation

Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations.

New Taxa and a New Combination in the North American Species of Froelichia (Amaranthaceae)

Two new species, one new variety, and a new combination of Froelichia are described from North America. Froelichia xantusii from Baja California Sur is being recognized as a species endemic to southern Baja California and separate from F. interrupta in which it had been previously included. Within F. interrupta two varieties are here recognized, the newly described Froelichia interrupta var. colimensis from southern Nayarit to Oaxaca and the new combination Froelichia in- terrupta var. alata from the Sonoran Desert. Froelichia latifolia is described from eastern Texas and has been segregated from the widespread F. floridana. A key to the genus in North America is also included. The genus Froelichia Moench is a group of 16 spe- cies, two varieties, and five subspecies native to the Western Hemisphere. It is classified in the subfamily Gomphrenoideae of the Amaranthaceae, a likely monophyletic group consisting of 20 genera centered in the tropical and subtropical regions of North and South America and characterized by having bispo- rangiate anthers and pollen with a reticulate exine and deeply recessed pores (Schinz 1893; Townsend 1993; Borsch 1998). The genus Froelichia consists mostly of herbaceous annuals and perennials, with two shrubby species and associated subspecies occurring in the Ga- lapagos Islands. While the genus is widespread, ex- tending from the southern extreme of Canada to north- ern Argentina and Uruguay, it is most abundant and species-rich in the desert and semi-desert range lands of the southwestern and south-central United States and Mexico and the scrublands of central South Amer- ica in Brazil, Paraguay, and northern Argentina. In all these regions, Froelichia is most common on sandy sub- strates where it can sometimes be the dominant ele- ment in the vegetation, though more commonly it is a minor component of the flora. Froelichias are recognized mostly by their spikes of small, densely wooly flowers, a characteristic that has inspired its common names Cottonweed and Snake- cotton. At a more technical level, Froelichia is distin- guished by the unique feature among the Amarantha- ceae of a fully indurate perianth that surrounds and is dispersed with the fruit. This perianth (often implicitly included as part of the ''fruit'' in many flora treat- ments) is characteristically winged on its lateral mar- gins, though the size and dissection of these wings will vary among species and to a lesser extent among in- dividuals. During the course of a full taxonomic revision of Froelichia in North America (McCauley 2002) it became evident that the current circumscription of the species did not adequately represent the diversity of taxa across the study area. Multivariate morphological and molecular phylogenetic analyses in conjunction with extensive field observations indicated a series of dis- crete entities deemed significantly unique morpholog- ically and phylogenetically from more widespread taxa and restricted to limited geographical ranges to warrant taxonomic recognition. Thus, two new species and two varieties are here being recognized. The two new species are being segregated from common wide-ranging taxa that have been recognized as possessing high levels of morphological variability, F. latifolia R.A. McCauley from F. floridana (Nutt.) Moq. and F. xantusii R.A. McCauley from F. interrupta (L.) Moq. Two varieties, both of F. interrupta, represent dis- crete morphological forms that are geographically seg- regated though phylogenetically they show little dif- ferentiation from the typical form of the species.

Evolution in the Arctic: a phylogeographic analysis of the circumarctic plant,Saxifraga oppositifolia(Purple saxifrage)

Summary • A survey of chloroplast DNA variation in the circumarctic-alpine plant, Saxifraga oppositifolia, has resolved two highly divergent cpDNA lineages with geographically widespread and mainly allopatric distributions that are largely concordant with those of two subspecies, that is, subspp. oppositifolia and glandulisepala. These subspecies differ for a single morphological trait and hence level of morphological divergence does not equate to molecular divergence within the species. • The two cpDNA lineages were estimated to have diverged from their most recent common ancestor 5.37–3.76 Ma, that is, during the early to mid-Pliocene. • A nested clade analysis was conducted in an attempt to determine how past episodes of range fragmentation, range expansion and long distance dispersal may have influenced the geographical distribution of cpDNA haplotypes. • In Alaska – a known refugium for the species during the last ice-age – high levels of cpDNA diversity may be partly explained by divergence between populations that were isolated in different ice-free regions. It remains to be established whether the two subspecies of S. oppositifolia exhibit some form of reproductive isolation from each other under conditions of sympatry.

Morphological variability and concealed deleterious effects inDrosophila melanogaster populations

The effects of brother-sister mating on viability of offspring were analyzed in relation to morphological variation of the individuals constituting the sib pairs.Drosophila melanogaster populations can be subdivided into 2 distinct groups of individuals that differ in the level of morphological variation and in their response to inbreeding. Genomes free of major deleterious factors appear to be favored by natural selection. A reduction in effective population size due to an environmental shift with consequent selection is thus not expected to be followed by inbreeding depression.

MORPHOLOGICAL VARIATION IN THE HORSESHOE CRAB LIMULUS POLYPHEMUS.

Limulus polyphemus (L.) is one of the four species of horseshoe crabs alive today. These animals are well-known for their marked resemblance to fossils from the Mesozoic, and L. polyphemus has frequently been cited as an organism which has evolved very slowly over the last 200 million years (Mayr, 1963, p. 304; Selander et al., 1970; Williams, 1975, p. 147; Sekiguchi and Sugita, 1980). Such cases of apparent stasis have led to questions about the relative levels of variability in lineages evolving at different rates (discussed by Selander et al., 1970). Data about levels of morphological variability in Limulus are rarely cited, although Schuster (1955, 1957) has documented interlocality size variation with some suggestion of shape differences as well. Selander et al. (1970) found that levels of polymorphism and heterozygosity for allozyme loci in Limulus were comparable to those found in more rapidly evolving organisms, but the relation between these electrophoretic characters and morphological data, such as can be evaluated from fossil specimens, is not clear (Wilson et al., 1973; Turner, 1974; Turner et al., 1979). Sekiguchi and Sugita (1980) have suggested that the slow rates of morphological change may be partly explained by the persistence of a conservative systemfor regulation of gene expression during development. This may imply that variability in such a regulatory system does not match that found at electrophoretic loci. The purpose of the present study is to report the results of an analysis of morphological variability within and among populations of Limulus polyphemus.

Genetics and Morphometrics of Cerion at Pongo Carpet: A New Systematic Approach to this Enigmatic Land Snail

Gould, S. J., D. S. Woodruff, and J. P. Martin (Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138; and Department of Zoology, Duke University, Durham, North Carolina 27708) 1975. Genetics and morphometrics of Cerion at Pongo Carpet: a new systematic approach to this enigmatic land snail. Syst. Zool. 23:518-535.Cerion displays an extraordinary range of phenetic diversity. This has led to the naming of several hundred species, though only a mere fraction of these are valid if, as we believe, morphological diversity does not reflect reproductive isolation in this genus. The taxonomic morass has precluded fruitful evolutionary study of these extremely plastic animals. We apply techniques of multivariate morphometrics and biochemical genetics to a local situation on the northeastern coast of Great Abaco, Bahamas. Here, a local population is semi-isolated along a strip of coastline near the settlement of Pongo Carpet; it is in contact with other populations only to the north. Its morphology is highly distinct and, on all previous criteria, it merits recognition as a separate species. We find, however, that its patterns of covariation (as revealed by factor analysis) cannot be distinguished from those of the only recognized taxon of northern Abaco, C. bendalli (while patterns in the southern Abaconian species, C. abacoense, are entirely different). Canonical analysis displays a cline towards standard morphology from the region of maximum isolation at Pongo Carpet to the northern area of potential contact with standard C. bendalli. Levels of morphological variation do not differ among samples; those of intermediate morphology show no increase in variability or other signs of hybridization. Starch-gel electrophoresis showed the pongo carpet samples to be genetically indistinguishable from standard bendalli at the 18 structural gene loci surveyed. No evidence for selfing or inbreeding was detected. The proportion of polymorphic loci in each population ranged between 16.6-22.2%; genic heterozygosity per individual was 5.25-6.79%. The only genetic anomaly within the area contrasts some standard and pongo carpet samples with C. bendalli from elsewhere on Abaco and Grand Bahama Island. We conclude that the pongo carpet population is a well-marked geographic variant within Cerion bendalli. The coordinated application of biochemical genetics and multivariate morphometrics can resolve many issues in the systematics of highly variable organisms. [Geographic variation; Cerion; morphometrics.] Cerion is a classic among evolutionary classics for its supposed protean speciation. Clench (1957) lists 302 recorded from the Bahama islands alone. Whether the plethora of specific names be justified or not, we may safely state that phenetic diversity within the genus can only be described as fantastic (Fig. 1). Moreover, variation within any local population is strictly average in extent; thus, local popu1 This is the third in a series of papers on The Natural History of Cerion. Previous items are Gould (1969a and 1971). 2 Department of Zoology, Duke University, Durham, North Carolina 27708. lations are strongly marked, and demes in close geographic proximity can be very different in mean morphologies. How can we deal with such a genus in a modern way? The old practice of erecting a name for each local variant does not, in all likelihood, reflect the biology of reproductive isolation. Yet this procedure has colored all previous approaches to Cerion. For example, the standard hypothesis (Clench, 1957; Mayr and Rosen, 1956) that of Cerion are haphazardly distributed by vagaries of hurricane transport depends upon the general validity of current specific nomenclature. If the species