SECONDARY SEXUAL DIMORPHISM AND PHYLOGENETIC CONSTRAINTS IN : A MULTIVARIATE APPROACH

Ecology Program-The Institute for Environmental Sciences and Department of Biological Sciences, Texas Tech University, Lubbock, TX 79409-3131 (MRW) Department of Biological Sciences, Central Connecticut State University, New Britain, CT 06050-4010 (RRH)

We develop a method to evaluate the degree to which particular morphological character- istics contribute to multivariate group differences in general and to secondary sexual di- morphism for size and shape in particular. In addition, we recommend a correlative ap- proach to assess the degree to which the contribution of characters to group differences is consistent in different taxa. We apply both methods to a suite of 12 cranial characters obtained from populations of 18 species of bats in five families (Emballonuridae, Nocti- lionidae, Phyllostomidae, Vespertilionidae, and Molossidae) from Caatinga and edaphic Cerrado biomes of northeastern Brazil. As expected, a correlation usually does not exist between profiles of the importance of characters to sexual dimorphism from the two biomes if the taxa are monomorphic with regard to sex (e.g., Vampyrops lineatus, lituratus, and Myotis riparia); any differences between the sexes within a biome are a result of chance. In contrast, significant correlations between profiles of importance of characters to intersexual variation in the two biomes usually exist when species are dimorphic (e.g., geoffroyi, perspicillata, soricina, discolor, Mo- lossus molossus, and Artibeus planirostris). Significant constraints on the expression of sexual dimorphism exist between populations of the same species; similar suites of char- acters are involved in intersexual variation if dimorphism exists. Such constraints appear inoperative at higher taxonomic levels. We hypothesize that once differentiation occurs at the specific level, coadapted gene complexes and genetic dynamics associated with epi- stasis, pleiomorphism, and linkage disequilibrium no longer constrain dimorphism in the same fashion as in the ancestral condition.

Key words: sexual dimorphism, phylogenetic constraints, morphometrics, Chiroptera, Phyllostomidae, Molossidae, Vespertilionidae, Emballonuridae, Neotropics, Brazil

From as early as the time of Darwin polygamous mating systems, unequal sex (1859), evolutionary biologists have been ratios, differential maturation rates, and dis- intrigued by secondary sexual dimorphism. similar resource utilization is critical to a Indeed, the mechanisms giving rise to sec- number of evolutionary theories (Daly and ondary sexual dimorphism, as well as its Wilson, 1978; Sealander, 1957). Nonethe- consequences, continue to be of interest to less, confusion exists as to what character- systematists (Mayr, 1942; Wade, 1976; Ya- istics are ultimate factors selecting for di- blokov, 1974), geneticists (Arnold, 1985; morphism and which are secondary effects Falconer, 1960; Lande, 1987; Leutenegger of the dimorphic condition (compare sexu- and Cheverud, 1985; Wright, 1968, 1977), al-selection hypothesis-Tri,vers, 1972; and ecologists (Bell, 1982; Shine, 1986; Wilson, 1975; resource-utilization hypoth- Shine and Crews, 1988) alike. The relation esis-Selander, 1966, 1972; and big-mother between secondary sexual dimorphism and hypothesis-Ralls, 1976, 1977). Moreover,

Journal of Mammalogy, 76(4):981-992, 1995 98 1 982 JOURNAL OF MAMMALOGY Vol. 76, No. 4 controversy surrounds the quantification of in part, is predicated on differential regu- dimorphism. Although secondary sexual di- lation of gene activity in males and females morphism historically has been considered and should be constrained by the bound- from a univariate perspective, Willig et al. aries established within species to the extent (1986) and Willig and Owen (1987), like that coadapted gene complexes are involved others before them (Cheverud et a]., 1985; and characters are pleiotropic (Lande, 1987; Jolicoeur, 1959, 1984), have argued that a Raff and Kaufman, 1983). Consistent with univariate approach is inadequate unless this view is the idea that phenotypic varia- single character hypotheses are of interest tion between sexes may be limited to par- rather than those concerning variation for ticular characters in one species, which dif- size and shape in general. In contrast, Cor- fer from those involved in dimorphism in ruccini (1987) suggested that the univariate another species. As a consequence, "close- approach, even in a multivariable setting, ly related species differ most in secondary can be more informative under certain cir- sexual characters of males, which are there- cumstances (i.e., when one or more uni- fore among the most rapidly evolving and variate test is significant, but the multivar- taxonomically important morphological iate test is not significant). traits," in higher (Lande, 1987:84). Systematists often implicitly or explicitly Following the same reasoning, populations consider dimorphism to be an attribute of a within a species more likely would express species when used in morphometric studies dimorphism via a consistent suite of mor- of geographic variation or secondary sexual phometric characters because the groups are variation. Two generally unacceptable ap- linked to the degree to which they share proaches are pervasive. The conservative gene pools. Hence, even if groups within a approach has been to analyze geographic population differ in the balance among se- variation separately for each sex if signifi- lective forces that result in dimorphism, cant dimorphism is expected, detected, or certain characteristics may be more predis- documented in the literature for populations posed toward lability whereas others may of the taxon of interest (Dowler and Gen- be more invariant. The objectives of this oways, 1979; Genoways, 1973; Hendrick- study are threefold: to present a general sen, 1973; Hollander, 1990; Humphrey and quantitative method whereby the impor- Setzer, 1989; Robertson et a]., 1992; Rus- tance of a particular character in the dis- sell, 1968). Conversely, when dimorphism crimination of groups can be ascertained; to is slight or undetected by statistical meth- suggest a quantitative approach that mea- ods, variation attributable to sex has been sures the degree to which the characters that ignored in subsequent analyses of geo- are indicative of group differences are con- graphic variation because data are com- sistent; to apply these techniques to the bined without regard to sex (Carleton and question of whether secondary sexual di- Eshelman, 1979; Cooper et al., 1993; Dra- morphism is constrained by phylogeny in goo et a]., 1990; Engstrom and Choate, bats from two different biomes from north- 1979; Moncrief, 1993; Riddle and Choate, eastern Brazil. 1986; Van Cura and Hoffmeister, 1966). In either approach, statistical power may be sacrificed and hypotheses of interest ig- The Caatinga of northeastern Brazil is a large nored because of reduced sample size or a (650,000 km2), heterogeneous, semiarid region failure to appropriately incorporate consid- with a characteristically unpredictable precipi- erations of secondary sexual variation and tation regime. In areas unaffected by post-Cre- its interaction with geographic variation taceous erosion, the original sandstone substrate into analyses. persists as isolated plateaus or chapadas domi- The maintenance of dimorphism, at least nated by woodland-savanna vegetation (edaphic November 1995 WILLIG AND HOLLANDER-SEXUAL DIMORPHISM IN BATS 983

TABLE1.-Description of the suite of cranial characters used to examine secondary sexual vari- ation in bats from Caatinga and edaphic Cerrado habitats of northeastern Brazil.

Morphometric character (acronymn) Description Greatest length of skull (GLS) Distance from most anterior part of rostrum (excluding teeth) to posteriormost point of skull Condylobasal length (CBL) Distance from anteriormost edge of' premaxillae to the pos- teriormost projection of the occipital condyles Postorbital constriction (POC) Least distance across top of skull posterior to postorbital process Mastoid breadth (MB) Greatest width of skull, including mastoids Breadth of braincase (BBC) Greatest width across braincase posterior to zygomatic arches Rostra1 breadth (RB) Width of rostrum at suture between premaxilla and maxilla Breadth across upper molars (BUM) Maximum width of outer alveolus of one molar to outer al- veolus of opposite molar Breadth across upper canines (BUC) Width from outer alveolus of canine to outer alveolus of other canine Length of maxillary toothrow (LMT) Length from anterior edge of alveolus of first tooth present in maxillae to posterior edge of alveolus of last molar Length of upper molariform toothrow (UMT) Maximum length from anterior edge of alveolus of first pre- molar to posterior edge of alveolus of last molar Greatest length of mandible (GLM) Length from anteriormost point on ramus (excluding teeth) to posteriormost point on coronoid process Length of mandibular toothrow (LLT) Length from anterior edge of alveolus of canine to posterior edge of alveolus of last molar in mandible

Cerrado). A Precambrian crystalline basement is on a multivariate phenetic evaluation of large exposed in extensive lowland areas where semi- from northeastern Brazil (Williams et deciduous thorn-scrub vegetation characterizes a]., 1995), specimens provisionally allocated to the landscape (Caatinga). Bats were obtained by Tonatia childreni, by Willig and Mares (1989) mist-netting in Caatinga habitats (Exu, Pernam- are assigned to Tonatia saurophila herein. buco, Brazil) as well as from edaphic Cerrado Significant microgeographic or intersexual habitats on the Chapada do Araripe (Crato, variation in morphology was assessed via mul- Ceara, Brazil). Caatinga and edaphic Cerrado tivariate analysis of variance on the suite of cra- sites were only 45 km apart, and all collection nial characters in Table 1;detailed results appear localities within each site were restricted to a in Willig et al. (1986), with descriptive statistics circular area of ca. 80 km2. Mares et al. (198 1, summarized in Willig (1983). Stepwise discrim- 1985) and Willig (1983, 1986) provide a more inant-function analysis (Program Discriminant; detailed account of the study area and collection SPSS Inc., 1986) was used to determine the lin- procedures. ear combination of variables that best distin- Mensural data were obtained from 20 adult guished between the morphologies of males and males and 20 adult females from each site for females. Separate analyses were conducted for each species whenever possible; otherwise, all each site (Caatinga versus edaphic Cerrado). collected specimens of a taxon (Willig, 1983; The loading of each variable on the discrimi- Willig et al., 1986) were included in samples. nant-function axis is a measure of the impor- Twelve cranial characters, each measured to the tance of each variable in discriminating between nearest 0.1 mm with dial calipers, constituted the sexes. However, some variables that are impor- variable suite (Table 1). We follow the nomen- tant in differentiating between sexes may have clatural recommendations of Willig and Mares low loadings on the discriminant axes if they (1989) in assigning bats from northeastern Bra- have high communality with other variables but zil to species, except in the case of Myotis, little unique discriminatory ability. As a conse- where we follow Woodman (1993) and correctly quence, variables that significantly differ be- use the feminine specific epithat, riparia, in tween sexes may not appear as important dis- place of riparius (the masculine gender). Based criminators based on factor loadings or may not 984 JOURNAL OF MAMMALOGY Vol. 76, No. 4 even appear in the final equation based on step- means of evaluating character-specific phyloge- wise, step-up, or step-down algorithms. To avoid netic constraints on the expression of secondary this problem, the importance of the original sexual dimorphism. The degree of concordance characters in discriminating between sexes was between character suites, in terms of the impor- ascertained by separately correlating each char- tance profile of variables as intergroup discrim- acter to the discriminant-function score for each inatory agents, can be evaluated by correlating individual. The magnitude of the square of the the importance values of each character between correlation coefficient quantifies the importance groups (Pearson's product moment correlation- of the variable in distinguishing between sexes Sokal and Rohlf, 1981). A high correlation can and provides a measure of the proportion of the exist between the importance values for sexual variation in the discriminant-function scores that dimorphism in two different localities, even if is accounted for by variation in the original mor- males are larger than females in one locality and phometric character. In all cases, we have stan- females are larger than males in the other local- dardized the polarity of discriminant-function ity. The direction of dimorphism is obscured axes so that males have higher loadings than do when the correlation coefficient is squared in the females. The sign of the correlation coefficient formula for importance. The correlation of im- thereby reveals the direction of dimorphism: portance values thereby measures the similar in- positive correlation between an original charac- volvement of characters in discriminating be- ter and the discriminant-function score indicates tween sexes regardless of the polarity of the con- that males are larger than females with respect tribution. to that character. This quantitative method is applicable to sit- uations involving more than two groups or more than one discriminant axis. In general, the im- Eighteen species of bats in five families portance (Ii) of a variable (i) in discriminating (Emballonuridae, 1 species; Noctilionidae, among a number of a priori groups (n) is given 1 species; Phyllostomidae, 12 species; Ves- by: pertilionidae, 2 species; Molossidae, 2 spe- cies) were obtained in adequate numbers for multivariate analyses of secondary sex- ual dimorphism. In a number of cases, a where X2 is the proportion of the variation species only occurred in a single site (Caa- among groups accounted for by discriminant- tinga or edaphic Cerrado), and, as a con- function j, and rij2is the square of the correlation sequence, an analysis of phylogenetic con- coefficient between original character i and dis- straints on the expression of dimorphism criminant-function j. The importance of a vari- was not possible at the specific level. None- able thereby varies from 0 to n - I, where 0 theless, it was possible to identify the cra- indicates no discriminatory value in a character and n - I represents maximal discriminatory nial characters that contributed most to ability. Dividing the importance value by n - 1 morphometric distinction between males scales the index to a range from 0 to I and fa- and females. cilitates comparisons between analyses involv- Secondary sexual dimorphism within a ing a different number of discriminant-function site.-Eight species of bats occurred in ad- axes. In the special case of sexual dimorphism, equate numbers for reliable statistical anal- n = 2 and a single discriminant axis exists, with yses of secondary sexual dimorphism with- Ii equaling rij2and varying from 0 to 1. in an area. Two of those species (Trachops Bar diagrams, in which the height of the bar cirrhosus and Eptesicus furinalis) were not for a particular character i is equal to Ii, then dimorphic based on multivariate analyses of provide convenient mechanisms for viewing the relative importance of particular characters in cranial characters (Willig et al., 1986). In discriminating among groups. A comparison of those cases, importance values were consis- bar diagrams for the same species in different tently low compared with most situations in areas, or for different species in the same higher which secondary sexual dimorphism was taxon (e.g., species within a genus) provides a significant (Fig. la and lb). Six of the spe- November 1995 WILLIG AND HOLLANDER-SEXUAL DIMORPHISM IN BATS

FIG.1.-Values for profiles of importance for 12 cranial characters that distinguish between sexes in species of bats from a single area (Caatinga or edaphic Cerrado) in northeastern Brazil (a, Trachops cirrhosus; b, Eptesicus furinalis; c, Noctilio leporinus; d, Peropteryx macrotis; e, Tonatia bidens; f, Phyllostomus hastatus; g, Lonchophylla mordax; h, Neoplatymops mattogrossensis). Acronyms and descriptions of cranial characters are in Table 1. The height of a bar for a particular character equals its importance value (I) and estimates the proportion of variation between sexes that is accounted for by that character. The sign above each bar indicates direction of dimorphism for that character, with males larger than females indicated by a plus (+), and females larger than males indicated by a minus (-). 986 JOURNAL OF MAMMALOGY Vol. 76, No. 4 cies restricted to a single site (Noctilio le- rado where importance values for all char- porinus, Peropteryx macrotis, Tonatia bi- acters were low (Fig. 2d). dens, Phyllostomus hastatus, Lonchophylla Consistent secondary sexual dimorphism mordax, and Neoplatymops mattogrossen- in the Caatinga and edaphic Cerrado was sis; Fig. lc-h, respectively) were dimorphic exhibited by Anoura geoffroyi, Glossopha- based on multivariate analyses of cranial ga soricina, and Carollia perspicillata characters (Willig et al., 1986); the profiles (Willig et al., 1986) based on multivariate of importance values differed considerably analyses of cranial characters. The correla- among species. tion between profiles of importance values Phylogenetic constraints within spe- was highly significant (P < 0.001) for A. cies.-Ten species of bats occurred in ad- geoffroyi (r = 0.97) and C. perspicillata (r equate numbers in each area to provide an = 0.93), indicating phylogenetic or intra- evaluation of phylogenetic constraints on specific constraints on the characters that the expression of dimorphism in distinct may differ between sexes. Breadth across populations of a species. Four species were upper canines and rostra1 breadth greatly monomorphic in both Caatinga and edaphic contribute to the difference between males Cerrado, three species exhibited consistent and females in A. geoffroyi (Fig. 3a) and in dimorphism in both sites, and three species C. perspicillata (Fig. 3b). Those characters exhibited site-specific dimorphism. with high importance values are larger in Four species that occurred at both sites males than in females. Although intersexual (Vampyrops lineatus, Artibeus lituratus, variation in G. soricina consistently was rotundus, and Myotis riparia) significant in Caatinga and edaphic Cerra- were monomorphic for cranial characters do, the profiles of importance values were (Willig et al., 1986). All but D. rotundus not correlated. In particular, breadth of failed to exhibit a significant correlation be- braincase and greatest length of skull con- tween profiles of character importance in tributed the most to dimorphism in the Caa- Caatinga and edaphic Cerrado (compare tinga, whereas mastoid breadth and, to a Fig. 2a-c with Fig. 2d). This observed non- lesser extent, breadth across upper canines significance is expected; the characters and length of upper molariform toothrow, identified in the discriminant-function anal- contributed to dimorphism in the edaphic ysis somewhat separate the sexes in each Cerrado (Fig. 3c). sample, but the suite of characters chosen Three species (Phyllostomus discolor, to discriminate in each area would not be Artibeus planirostris, and Molossus molos- expected to be similar if the sexes are sta- sus) each exhibited secondary sexual di- tistically indistinguishable (i.e., any differ- morphism, which was habitat-specific, as ences are no greater than that attributable to indicated by significant two-way interac- chance alone). Although D. rotundus does tions in multivariate analyses of variance of not exhibit significant secondary sexual cranial characters (Willig et al., 1986). variation (Willig et al., 1986) at either site, Nonetheless, the highly significant correla- a significant correlation between profiles of tion (0.001 < P < 0.01) between profiles importance values occurred between popu- of importance in each area for P. discolor lations from the Caatinga and edaphic Cer- (r = 0.73) and for M. molossus (r = 0.77) rado (R = 0.82; P < 0.001). Breadth across suggests that the morphological characters the upper canines, condylobasal length, involved in dimorphism are similar within greatest length of mandible, and greatest each species, regardless of biome (Fig. 3d length of skull differed most between sexes and 3e, respectively). In the case of M. mo- at both sites, but the magnitude of differ- lossus, dimorphism is strong, with condy- ence was insufficient to affect significant lobasal length, greatest length of mandible, dimorphism, especially in the edaphic Cer- greatest length of skull, length of mandib- November 1995 WILLIG AND HOLLANDER-SEXUAL DIMORPHISM IN BATS

FIG.2.-Values for profiles of importance for 12 cranial characters that distinguish between sexes in species of bats from Caatinga (cross-hatching) and edaphic Cerrado (hatching) of northeastern Brazil (a, Vampyrops lineatus; b, Artibeus lituratus; c, Myotis riparia; d, Desmodus rotundus). None of these species exhibited significant secondary sexual dimorphism at either site. Acronyms and descriptions of cranial characters are in Table 1. The height of a bar for a particular character equals its importance value (I) and estimates the proportion of variation between sexes that is accounted for by that character. The sign above each bar indicates direction of dimorphism for that character, with males larger than females indicated by a plus (+), and females larger than males indicated by a minus (-). 988 JOURNAL OF MAMMALOGY

FIG.3.-Values for profiles of importance for 12 cranial characters that distinguish between sexes in species of bats from Caatinga (cross-hatching) and edaphic Cerrado (hatching) of northeastern Brazil (a, Anoura geofSroyi; b, Carollia perspicillata; c, Glossophaga soricina; d, Phyllostomus has- tutus: e, Molossus molossus: f, Artibeus planirostris). The first thee species (a-c) exhibited secondary sexual dimorphism in a consistent fashion in both sites, whereas the last thee species (d-f) exhibited dimorphism that was site-specific. Acronyms and descriptions of cranial characters are in Table 1. The height of a bar for a particular character equals its importance value (I) and estimates the proportion of variation between sexes that is accounted for by that character. The sign above each bar indicates direction of dimorphism for that character, with males larger than females indicated by a plus (+), and females larger than males indicated by a minus (-). ular toothrow, length of maxillary, and ga and females are larger than or indistin- mastoid breadth, each contributing appre- guishable from males in the edaphic Cer- ciably to the difference between sexes in rado. Similar profiles of characters are in- both sites. The significant two-way inter- volved in the dimorphism, as indicated by action in M. molossus is likely a result of the highly significant, positive correlation positive synergism; that is, males are con- (0.001 < P < 0.01), but the direction of the sistently larger than females, equivalent size differential between the sexes differs, character profiles are involved in the di- as indicated by the sign of the correlation morphism, but the size differential is ex- coefficients used to produce importance aggerated in one biome compared with the values. In particular, breadth across the up- other. In contrast, the significant two-way per canines, mastoid breadth, and rostra1 interaction in P. discolor involves negative breadth are larger in males than in females synergism. The sexes are dimorphic, but from the edaphic Cerrado, but larger in fe- males are larger than females in the Caatin- males than in males from Caatinga (Fig. November 1995 WILLIG AND HOLLANDER-SEXUAL DIMORPHISM IN BATS 989

3d). Dimorphism in A. planirostris is com- sensus is that morphological characters in plex. Intersexual variation is not indepen- males and females cannot evolve indepen- dent of biome (a significant sex-by-area in- dently within populations. teraction-Willig et al., 1986), and the pro- Migration between populations reduces files of importance values are uncorrelated interdemic variation in gene frequencies as well (Fig. 30. Males are larger than fe- and morphology. The existence of coadapt- males for all characters in the Cerrado, with ed gene complexes should further reduce breadth across upper canines, breadth the likelihood that different suites of char- across upper molars, length of maxillary acters (genes and their associated morpho- toothrow, and length of upper molariform logical consequences) would become in- toothrow contributing most to dimorphism. volved in dimorphism in two populations In contrast, mastoid breadth, rostra1 between which considerable movement of breadth, and length of upper molariform individuals occurs. Perhaps for these rea- toothrow contribute most to dimorphism in sons, systematists frequently have consid- the Caatinga, with males having larger mas- ered secondary sexual dimorphism as if it toid breadths and females having larger ros- were a species-specific attribute rather than tral breadths and lengths of upper molari- a population-level phenomenon. For the form toothrows. same reasons, closely related species, as a consequence of their shared genetic heri- tage, may involve similar characters in the Theoretical context.-Comparisons of expression of dimorphism, when it occurs. morphological features within and among Our results allow us to address two in- populations aid in understanding how and terrelated questions concerning the evolu- to what extent variation among individuals tion of secondary sexual dimorphism. First, is molded into differences that separate rac- do different populations of the same species es and species (Mayr, 1942; Simpson, 1944; exhibit similar patterns of secondary sexual Yablokov, 1974). Sexual reproduction re- variation; second, do closely related species duces genetic and, hence, morphological exhibit more similar character profiles than differences between sexes in an analogous do distantly related species? fashion to the manner by which migration IntraspeciJic phylogenetic constraints.- between populations reduces interdemic ge- Nine of the 12 species that occurred in both netic and morphological variation. Indeed, Caatinga and edaphic Cerrado exhibited the degree to which morphologies of males correlations between patterns of importance and females are affected by the same genes values that would be expected if phyloge- or segregating factors constrains the evo- netic constraints are in operation. One of lution of secondary sexual dimorphism. De- the four monomorphic species (D. rotun- spite factors favoring dimorphism in pop- dus) and four of the six dimorphic species ulations (e.g., intersexual selection, intra- (A. geoffroyi, C. perspicillata, P. discolor, sexual selection, competition for resources, and M. molossus) exhibited significantly reproductive demands in females), genetic correlated profiles of importance values. correlations between sexes are reinforced as The two dimorphic taxa that do not con- a consequence of a variety of dynamic ge- form to expectations each exhibit such low netic processes such as pleiotropism, epis- correlations between profiles of importance tasis, and linkage disequilibrium (Lande, values (G. soricina, r = 0.07; A. planiros- 1987; Raff and Kaufman, 1983). Arnold tris, r = 0.02, respectively) that the nonsig- (1985), Fisher (1930, 1958), and Lande nificance is unlikely to be an artifact of (1987) provide useful insight into the ge- sample size. Two phenomena could contrib- netic dynamics involved in the evolution of ute to this: reduced migration between Caa- secondary sexual characters. The clear con- tingas and edaphic Cerrado populations of 990 JOURNAL OF MAMMALOGY Vol. 76, No. 4 each species; elevated migration between Brasileira de Ciencias (project 85; Ecology, either of these populations and another pop- Evolution, and Zoogeography of , as ulation outside the domain of this study. part of a larger program, Ecological Studies of Constraints at higher taxonomic lev- the Semi-arid Region of Northeast Brazil). Ad- els.-If the legacy of shared gene pools in ditional funds were provided by the Carnegie Museum of Natural History. Support to M. R. the past limits the degree to which differ- Willig during early stages of the research was ences in sexes can be expressed in dimor- provided by a Mellon Fellowship from the Uni- phic taxa, the correlation of profiles of im- versity of Pittsburgh. M. A. Mares, A. F? Leao, portance values should decrease as one and F? E. Vanzolini contributed in countless makes comparisons within genera, subfam- ways to the success of the project; their support ilies, and families. Of the 28 populations is gratefully acknowledged. J. L. de Carvalho, examined (combinations of species and T. E. Lacher, Jr., and K. E. Streilein assisted with sites), the vast majority did not correspond various aspects of fieldwork. H. H. Genoways, to this expectation. Discounting conspecific S. L. Williams, and S. B. McLaren assisted with correlations, the highest correlations were museum-related aspects of this work. The manu- infrequently between members of the same script was improved because of critical com- ments from G. Baumgardner, J. K. Jones, Jr., T. genus (only for Phyllostomus) or subfamily E. Lacher, Jr., M. A. Mares, R. Pimentel, A. Pen- (none). In fact, most populations had pro- niman, R. D. Stevens, and especially R. D. files of importance that were uncorrelated Owen. Computer analyses were supported by with that of any other population (e.g., Ar- the Department of Biological Sciences, Texas tibeus planirostris, G. soricina, L. mordax, Tech University, through the aegis of J. M. and M. molossus from the Caatinga and G. Burns. soricina from edaphic Cerrado) or, at most, maximally correlated with a population from a different subfamily (e.g., Anoura ARNOLD,S. J. 1985. Quantitative genetic models of geoffroyi, C. perspicillata, G. soricina, sexual selection. Experientia, 4 1: 1296-1 3 10. BELL,H. L. 1982. Sexual differences in the foraging Noctilio leporinus, Neoplatymops matto- behaviour of the frill-necked flycatcher Arses teles- grossensis, Phyllostomus discolor, and Ton- copthalmus in New Guinea. Australian Journal of atia bidens from the Caatinga, as well as A. Ecology, 7: 137-147. CARLETON,M. D., AND R. E. ESHELMAN.1979. A syn- geoflroyi, A. planirostris, C. perspicillata, opsis of fossil grasshopper mice, genus Onychomys, and M. molossus from edaphic Cerrado). and their relationships to Recent species. Papers in Taken together, these data suggest that once Paleontology, University of Michigan, Museum of Paleontology, 2 1:1-63. differentiation occurs at the specific level, CHEVERUD,J. M., M. M. DOW,AND W. LEUTENEGGER. coadapted gene complexes and genetic dy- 1985. The quantitative assessment of phylogenetic namics associated with epistatis, pleiotroph- constraints in comparative analyses: sexual dimor- phism in body weight among primates. Evolution, ism, and linkage disequilibrium no longer 39:1335-1351. constrain the expression of dimorphism. COOPER,T. W., R. R. HOLLANDER,R. J. KINUCAN,AND For the most part, patterns in the exhibition J. K. JONES,JR. 1993. Systematic status of the deer mouse, Peromyscus maniculatus, on the Llano Es- of intersexual variation appear species-spe- tacado and in adjacent areas. The Texas Journal of cific and relatively unrelated to systematic Science, 45:3-18. arrangements at the generic level or higher. CORRUCCINI,R. S. 1987. Univariate versus multivar- iate morphometric variation: an alternate viewpoint. Systematic Zoology, 36:397-398. DALY,M., AND M. WILSON.1978. Sex, evolution, and behavior. Wadsworth Publishing Company, Bel- We dedicate this work to the memory of J mont, California, 387 pp. Knox Jones, Jr., his participation in and support DARWIN,C. 1859. On the origin of the species by of research in mammalogy continues to be an means of natural selection, or the preservation of inspiration to those endeavoring to study mam- favoured races in the struggle for life. John Murray, London, United Kingdom, 597 pp. malian biology. Field research was funded by a DOWLER,R. C., AND H. H. GENOWAYS.1979. 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