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Morphometric variation in populations of Calomys musculinus a

María C. Provensal & Jaime J. Polop

a

a

Department of Natural Sciences , Universidad Nacional de Rio Cuarto , Estafeta Postal No. 9, Rio Cuarto, 5800, Cordoba, Argentina Published online: 19 Nov 2008.

To cite this article: María C. Provensal & Jaime J. Polop (1993) Morphometric variation in populations of Calomys musculinus , Studies on Neotropical Fauna and Environment, 28:2, 95-103, DOI: 10.1080/01650529309360892 To link to this article: http://dx.doi.org/10.1080/01650529309360892

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Studies on Neotropical Fauna and Environment Vol. 28 (1993), No. 2, pp. 95-103

0165-0521/93/2802-0095$25.00 © Swets & Zeitlinger


Morphometric Variation in Populations of Calomys musculinus* María C. PROVENSAL and Jaime J. POLOP

PROVENSAL, M.C. and J.J. POLOP (1993): Morphometric Variation in Populations of Calomys musculinus. Studies on Neotropical Fauna and Environment 28, pp. 95-103. Adult specimens of Calomys musculinus were selected by using discriminant functions. Variation in seven selected cranial mensural variables of these specimens from different localities, different habitats, and different years was examined using multivariate statistical analysis. In males, analysis of geographic trends indicated a relative character homogeneity between localities and a general correspondence between the samples of the same years. Significant inter-annual variation within localities was revealed. In females there was no significant variation between localities and between yearly samples. It is suggested that the differences in the character states reflect differences in the course of development of the males in different years, possibly as the result of a demographically driven social selection pressure. María C. Provensal and Jaime J. Polop, Department of Natural Sciences, Universidad Nacional de Rio Cuarto, Estafeta Postal No. 9, 5800 Rio Cuarto, Cordoba, Argentina.

Introduction The field mouse Calomys musculinus (Thomas, 1916) is one of the most widely distributed small rodents in Argentina. It ranges from the provinces of Formosa and Salta in the north to the province of Rio Negro in the south, approximately from 22° to 38° south latitude. It is found in a broad range of biogeographical provinces and habitats including deciduous xerophilic woodland, matorral, or even grassy steppe. It lives in regions where the mean minimum temperature may be only 5°C and in regions where it is 17°C. Precipitation in some of these areas may occur in almost any month, varying between 80 and 1200 mm per year, or in other regions where it varies between 80 and 250 mm and is concentrated in the summer months. The species is obviously extremely adaptable to a wide range of habitats (Kravetz and Polop, 1983) with great écologie tolerance. One would expect to find great genetic, morphological, and behavioral heterogeneity among its various populations. * This study was supported by the Consejo de Investigaciones Cientificas y Tecnicas de La Provincia de Cordoba (CONICOR), by the Consejo de Investigaciones Cientificas y Tecnicas de la Nacion (CONICET), and by Program 477 of the Universidad Nacional de Rio Cuarto.


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MARiAC.PROVENSAL AND JAIME J.POLOP

Evolutionary theory recognizes ecological factors to be one of the components of intra- and inter-population variation. Contributing to this variation one can recognize habitat factors, temporal-climatic factors, and factors dependant on population density. The first two of these relate to geographic variation. Gardenal et al. (1980), analysing electrophoretic results from C. musculinus from different localitites, demonstrated a high degree of polymorphism and heterozygosity but did not detect differences between populations (Gardenal et al., 1986). One must realize, however, that interpopulation heterogeneity in numerous other species manifests itself in morphological variation. Therefore, the objective of our study is to make a morphological comparison of populations of C. musculinus and seek causal factors for variation in a region that offers an exceptional mosaic of environments and in which the species under study is the principle reservoir of Junin virus, the causal agent of the widespread Argentine Hemorrhagic Fever. Material and Methods The specimens of C. musculinus came from five localities in the province of Cordoba and one in the province of San Luis (Fig. 1). Three of these localities (Chucul, Gigena, and Laguna Larga) lie in the phytogeographic province "Espinal" (Luti et al., 1979). It is a plain at low elevation (600-900 m) with vegetation dominated by algarrobo (Prosopis alba, P. nigra), accompanied by quebracho bianco (Aspidosperma quebracho bianco), mistol (Zizyphus mistol) and itin (Porlulaca kuntzie). The locality Donovan, which corresponds to the "Caldenal" district of the phytogeographic province "Espinal" (Anderson et al., 1970), is characterized as an open woodland with trees 8 to 12 m tall. The dominant species is calden (Prosopis caldenia), followed in order of abundance by chanar (Geoffroea decorticans), with an abundant herbaceous layer of Stipa tenuis, Stipa tenuissima, and Setaria eliantha. Actually, forestry and agricultural practices have led to the disappearance of much of this woody plant formation so that it is now restricted to a few small, relictual patches. The localities Rio Tercero and Cruz del Eje have considerable areas of scattered trees and brush in the phytogeographic province of "Bosque Serrano" (Luti et al., 1979), which is found between 500 and 1300 m elevation. The arboreal layer is dominated by molle (Lithraea ternifolia). Also present are cocos (Fagara coco) and manzanos del campo (Ruprechtia apelata). The bushy layer is represented by a mixed romerillal in which Eupatorium buncifolium is most abundant. Species of Stipa and Festuca are found in the herbaceous layer. The "Bosque Serrano" is receding and being replaced in many areas by brushy vegetation of species mentioned above. In each locality animals were collected with Sherman live traps set in lines 50 m long, with two traps set at each station. The stations were 5 m apart. The trapping periods varied between four and seven days, and were toward the end of autumn. Since all of the specimens from the different localities were not caught in the same year, collections were made in the autumn at Chucul in the years 1983 through 1988 in order to determine the amount of annual variation in the characters being studied. In each specimen seven cranial characters were measured: condylo-zygomatic length, length of molar toothrow, length of mandible, height of mandible, zygomatic breadth, distance between the jugal processes, and width of rostrum. These measurements were taken with calipers to a precision of 0.02 mm. These characters were chosen because in C. musculinus their variance conforms to the requirements of normality and homogeneity (Provensal and Polop, submitted). Later, the individuals were assigned to appropriate age groups defined by discriminant functions for this species (Provensal and Polop, submitted). Sexes were analysed separately because of the sexual differences in cranial measurements in this species (Provensal and Polop, submitted). Consequently, in the following analyses it was possible to minimize variation due to seasonality, age, and sex. The existence of phenetic variation was estimated by the generalized D2 statistic, having determined previously the multivariate normal distribution and the homogeneity of matrices of variance and covariance. The phenetic similarity between populations was established using the D2 of Mahalanobis and cluster analysis (UPGMA). For this last analysis, a phenogram was constructed based on the D2 statistic. In

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MORPHOMETRIC VARIATION IN CALOMYS MUSCULINUS


each analysis the collections in different years at Chucul were treated separately. Individuals from each population were assigned to age groups on the basis of discriminant function analysis (Table 1). Individuals assigned to the adult group within each population showed little variation and no significant morphologic differences, so they were used as representatives of each geographic sample in the subsequent analyses. Juveniles were not used in these analyses. Because of the small number of specimens (3), the samples of adult females from Cruz del Eje and Donovan could not be used in the analyses.

Results When the variation in different populations of males is analysed (Table 2), significant differences can be detected. The values of D2 of Mahalanobis document significant differences in the cranial measurements of samples from different localities within the same phytogeographic region (Chucul-Laguna Larga; ChuculGigena), between different phytogeographic regions (Chucul-Donovan; Rio Tercero-Gigena; Chucul-Rio Tercero), and variation between different years at the same locality (Chucul 1983-Chucul 1987; Chucul 1984-Chucul 1987; Chucul 1986-Chucul 1987; Chucul 1987-Chucul 1988). The distances between these pairs of samples are summarized in a cluster analysis (Fig. 2). This phenogram illustrates the geographic associations of the samples from the different localities and years, based on values of the D 2 of Mahalanobis. Both analyses (Table 2 and Fig. 2) suggest only a slight relationship between the various mouse samples and the phytogeographic regions from which they came, but a general correspondence between the" samples and the years of capture. Note the degree of similarity between the pairs Laguna Larga 1981-Rio Tercero 1981; Chucul 1985-Donovan 1985; and Chucul 1987-Gigena 1987. These last two localities belong to the same phytogeographic region and are situated quite close together, and their

Table 1. Number of males and females of Calomys musculinus from each locality, listed in their respective age groups.

Young Specimens Age Classes Localities

Chucul 1983 Chucul 1984 Chucul 1985 Chucul 1986 Chucul 1987 Chucul 1988 Cruz del Eje Donovan Laguna Larga Rio Tercero Gigena

I

Adults II

male

female

0 1 1 12 22 17 1 1 28 4 11

2 2 0 7 15 14 3 0 14 4 7

male

III-IV-V-VI female

male

female

4 13 7 23 39 15 6

5 8

7 16 9 22

5 11 19 16 3 3 9 7 12

98

MARIA C. PROVENSAL AND JAIME J. POLOP

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