Ontogeny and Allometry of Body Shape in the Blacktail Shiner, Cyprinella Venusta

Copeia, 2000(1), pp. 270–275

Ontogeny and Allometry of Body Shape in the Blacktail Shiner, Cyprinella venusta

CRAIG S. HOOD AND DAVID C. HEINS

Ontogenetic changes in body shape and its associated allometry were studied in the Blacktail Shiner, Cyprinella venusta, using geometric morphometric methods. We males, 215 females), collected in Catahoula 182 ;397 ؍ used a single, large sample (n Creek, Jourdan River drainage, Hancock County, Mississippi. Ten body landmarks were digitized from each specimen, which yielded partial warp scores that were used as shape variables to describe body shape change during ontogeny, assess sexual dimorphism, and investigate the relationship between reproductive status and ontogenetic body shape change. We also assessed the effect of sexual dimorphism on size and body shape. The null hypothesis of isometry during ontogeny was strongly rejected by multivariate regression of shape on size for both sexes (males, P Ͻ We found large, highly .(16.238 ؍ females, P Ͻ 0.0001, F ;21.970 ؍ F ,0.0001 significant sexually dimorphic differences in the body shapes of males and females Wilks’ lambda, 0.758), which ,7.535 ؍ MANOVA for overall shape, P Ͻ 0.0001, F) remained significant using MANCOVA with size as a covariate (log SL, P Ͻ 0.0001, ,Wilks’ lambda ,34.829 ؍ Wilks’ lambda, 0.438; log CS, P Ͻ 0.0001, F ,34.872 ؍ F 0.439). Moreover, the ontogeny of body shape differs between males and females. There were highly significant shape differences among reproductive classes within males and females. These findings suggest that change in reproductive status may occur in concert with body shape change.

HE study of body shape in fishes has been (Loos and Fuiman, 1978; Loos et al., 1979). The T a subject of research investigations for over present paper analyzes ontogeny of body shape a century. Only recently have geometric mor- in the Blacktail Shiner, Cyprinella venusta, a com- phometric methods been used to understand mon freshwater cyprinid inhabiting medium to body shape change and its associated allometry large river tributaries of the southeastern and during ontogeny (Bookstein, 1991; Rohlf, 1998; central United States. The objectives of the Zelditch et al., 1998). As a result, the ontogeny study were to describe ontogenetic body shape of body shape change has been studied for only change and its concomitant allometries in a a small number of fishes, including the Piranha, common North American minnow, to assess sex- Pygocentrus (Fink and Zelditch, 1995a, 1995b; ual dimorphism in the ontogeny of shape Zelditch and Fink, 1995), Threespine Stickle- change, and to investigate the relationship be- back, Gasterosteus (Walker, 1993, 1997); Sea Bass, tween reproductive status and ontogenetic Dicentrarchus (Loy et al., 1996); Sea Bream, Di- changes in body shape. plodus (Loy et al., 1998); and Callichthyid Cat- fish, Callichthyes (Reis et al., 1998). These studies have shown that body shape changes during on- MATERIALS AND METHODS togeny are not simply the result of uniform large-scale events (e.g., dorsoventral elonga- We chose a single, large sample (n ϭ 397 tion) but that localized small-scale shape chang- specimens, Table 1) for our analyses to avoid es unique to each species contribute to its on- any potential confounding effects associated togeny. Interestingly, none of these studies de- with multiple collections from different times or tected sexual dimorphism in body shape within localities. The sample (Mississippi State Univer- the study species, although small sample sizes in sity, MSU 933) was taken by minnow seine on several studies did not allow a rigorous evalua- 26 May 1970 from Catahoula Creek below the tion. mouth of Dead Tiger Creek, Jourdan River Even less is known about body shape ontog- drainage, Hancock County, Mississippi. Speci- eny in cyprinid fishes. Studies of development mens were fixed in 10% formalin and preserved in cyprinids include an overview of larval devel- in 50% isopropyl alcohol. The study site has opment within ostariophysian fishes by Fuiman been described by Heins and Clemmer (1975), (1984) and qualitative descriptions of larvae and various aspects of the reproductive biology and posttransformational fishes in Notropis of C. venusta at Catahoula Creek have been de-

᭧ 2000 by the American Society of Ichthyologists and Herpetologists HOOD AND HEINS—BODY SHAPE IN CYPRINELLA VENUSTA 271

TABLE 1. SIZE DISTRIBUTION (SL, mm) OF SPECIMENS. Size classes were not used in statistical analyses but illustrate the size distribution of the sample [(n ϭ 182 males (range 22–87 mm, mean 43 mm), 215 females (range 22–72 mm mean 43 mm)].

SL size class mm 20 25 30 35 40 45 50 55 60 65 70 75 Ն80 Males 5 12 25 37 32 16 17 24 5 2 3 1 2 Females 4 9 46 29 35 33 18 18 9 12 2 0 0

scribed by Heins and Dorsett (1986) and Heins unpubl.). The landmarks were analyzed using and Baker (1987). morphometric (tpsREGR vers. 1.18, F. J. Rohlf, We tested the effect of alcohol preservation 1998, unpubl.; tpsRELW vers. 1.14, F. J. Rohlf, on shape using another sample of fresh-caught 1997, unpubl.; MORPHEUS vers. 1-30-98, D. specimens. Our results showed that isopropyl al- Slice, 1998, unpubl.) and statistical (SAS vers. cohol does not significantly change shape data 6.12, SAS Institute Inc., 1996; NTSYS vers. 2.02c, after three months of storage when compared Applied Biostatistics Inc., 1998, unpubl.) pro- to initial observations of formalin-fixed fish grams. (pers. obs.). Following image capture, we determined the We collected data for 10 landmarks on each sex and reproductive condition of fish by go- individual (Fig. 1) using a two-dimensional vid- nadal examination. Males were classed into five eo-based data capture system that included a stages of reproductive condition using a scheme BW CCD video camera and PCVISIONϩ frame- modified from Heins and Machado (1993). Sex- grabber. Landmarks were obtained using the ually immature (latent, LA) males had very digitizing software program MORPHOSYS small, threadlike testes that were transparent to (vers. 1.29, C. Meacham and T. Duncan, 1990, cloudy white or translucent. The enlarged, opaque white testes of sexually mature males were categorized into four classes of enlarge- ment, including small (MA1, threadlike), mod- erate (MA2, cordlike), large (MA3, rope-like), and very large (MA4, bulging-convoluted). We determined the reproductive condition of females, using with some modification, the ovarian classification of Heins and Rabito (1986), which should be consulted for further details. Sexually immature (latent, LA) females had ova- Fig. 1. Landmarks used to capture body shape var- ries without developing eggs (translucent to iation in Cyprinella venusta; all landmarks were located white oocytes). Sexually mature females in all on midline of the body in each specimen: (1) origin other stages of ovarian condition had, in their of dorsal fin, basal junction of first dorsal fin ray; (2) follicles, one or two groups of gametic cells un- nape of neck, posterior boundary of supraoccipital dergoing ovum formation. Early maturing (EM) bone; (3) tip of snout, upper margin of mouth; (4) females had ovaries containing one group of posterior margin of opercular series; (5) origin of pel- translucent to white oocytes. Ovaries of late ma- vic fin, basal junction of first pelvic fin ray; (6) origin of anal fin, basal junction of first anal fin ray; (7) turing (LM) females contained a single, bimod- origin of anal fin, basal junction of the last anal fin al group of oocytes that were white to cream ray; (8) origin of caudal fin, basal junction of ventral- colored. Mature (MA) females had ovaries con- most caudal fin ray; (9) origin of caudal fin, basal taining two distinct groups of oocytes in the fol- junction of dorsal-most caudal fin ray; (10) origin of licles, the larger ones being cream to yellow. dorsal fin, basal junction of the last dorsal fin ray. A Ovaries of ripening (MR) females also had two series of 103 specimens were digitized twice (three separate groups of follicular oocytes, the larger months between capture sessions) to evaluate mea- oocytes being translucent with elevated vitelline surement error associated with these landmarks. Paired t-tests of centroid size (CS) on these repeated membranes. Ovaries of ripe (RE) females had digitizing sessions were nonsignificant (P ϭ 0.954, t ϭ one group of white to cream oocytes in the fol- 0.058), root mean square error (RMS) was 0.034 mm licles with ovulated, ripe eggs (transparent with and percent incongruence (PI) 0.055% (Hildebolt elevated vitelline membranes) in the ovarian lu- and Vannier, 1988). mina. 272 COPEIA, 2000, NO. 1

A preliminary study of adult C. venusta dem- different stages of reproductive condition: onstrated highly significant sexual dimorphism males, LA, MA1-MA3, MA4; females, LA, EM- in both size and shape variables; therefore, sex- LM, and MA-RE. The number of MA4 males was es were treated separately throughout the statis- too small to include in statistical analyses. tical analyses. We used standard length (SL in mm) and centroid size (CS) as measures of size. RESULTS Centroid size is a geometrically based measure that is the square root of the sum of the squared ANOVAs testing sexual size dimorphism distances of landmarks to their centroid (Book- showed there were significant differences in size stein, 1989, 1991). Both SL and CS were log between the sexes (log SL, P ϭ 0.004, F ϭ 8.389; transformed prior to statistical analysis. log CS, P ϭ 0.006, F ϭ 7.760), with adult males We described shape changes during ontogeny being larger (mean, 53.5 mm in SL) than adult using geometric morphometric methods (Book- females (mean, 49.1 mm in SL). Analysis of sex- stein, 1991, 1996; Rohlf and Marcus, 1993). ual dimorphism in shape (partial warp scores Shape variables were extracted from the land- and uniform components appended for overall mark data using tpsREGR. Landmark configu- shape variability) showed highly significant and rations for each specimen were aligned, trans- large differences in shapes of males and females lated, rotated, and scaled to a unit centroid size (Fig. 2; overall shape, P Ͻ 0.0001, F ϭ 7.535, by the generalized least squares fit criterion Wilks’ lambda, 0.758; uniform shape, P ϭ 0.038, (GLS) described by Rohlf and Slice (1990). Us- F ϭ 3.298, Wilks’ lambda, 0.984; nonuniform ing the consensus configuration of all speci- shape, P Ͻ 0.0001, F ϭ 8.315, Wilks’ lambda, mens as the starting form (i.e., tangent config- 0.766). MANCOVAs of shape by sex with size uration of Rohlf et al., 1996), partial warps rep- held constant (log SL and log CS treated as co- resenting the nonuniform shape variables and variates) also showed highly significant shape uniform components (Bookstein 1996) were differences between sexes (log SL, P Ͻ 0.0001, obtained from tpsREGR and used in subsequent F ϭ 34.872, Wilks’ lambda, 0.438; log CS, P Ͻ analyses. The thin plate spline interpolating 0.0001, F ϭ 34.829, Wilks’ lambda, 0.439). function (TPS) was used to visualize overall, uni- Shape sexual dimorphism is evident in over- form, and nonuniform shape changes. all, uniform, and nonuniform components of Sexual size dimorphism (SSD) was tested us- shape space (Fig. 2). Males have relatively lon- ing sexually mature adults (males scored MA1 ger heads (landmarks 2-3-4), especially dorsally to MA4, females scored EM to RE) because SSD (from the nape of neck to snout, landmarks 2, is often manifested only in sexually mature in- 3), whereas females have smaller and more sym- dividuals (Pryon, 1996; Stamps, 1993). Tests for metrical head shapes. The shape of the abdo- sexual dimorphism in size and shape were con- men from the attachment sites of the pelvic fin ducted using ANOVA and MANOVA, respective- (landmark 5) to those of the anal fin (land- ly. MANCOVA was used to evaluate sexual di- marks 6 and 7) is distinctly different, with fe- morphism in shape with size held as a covariate males exhibiting an abrupt shape change in- (log SL and log CS) as described by Adams and volving the insertion site of the anal fin. Finally, Funk (1997). Differences in the ontogenetic tra- tail shape (including the caudal peduncle) dif- jectory of shape changes of males compared fers between sexes. Males have relatively wider with females were evaluated by comparing the and longer tails than females (landmarks 7, 8, slopes of multivariate regressions using partial 9 and 10) and the tails of females are ventrally warp scores as variables. The overall hypothesis deflected slightly at the attachment of the cau- of ontogenetic allometry was tested by multivar- dal fin (landmarks 9 and 10). iate regression of shape variables (partial warp The null hypothesis of isometry during on- scores and uniform components) regressed on togeny in each sex is strongly rejected by the size (log SL and log CS) as described by Rohlf results of multivariate regression of shape on et al. (1996) and discussed by Rohlf (1998), size (males, P Ͻ 0.0001, F ϭ 21.970; females, P Zelditch et al. (1998), and Monteiro (1999). Ͻ 0.0001, F ϭ 16.238). Thus, there is allometric Monteiro (1999) discusses the use of Goodall’s body shape change during ontogeny within F as a test statistic for multivariate regression of both males and females of C. venusta (Fig. 3). shape variables. The heads of the smallest (youngest) females Evaluation of size and shape change among are relatively longer and more asymmetrical reproductive classes within sexes was examined (the dorsal aspect, landmarks 2 and 3, being using the same set of analyses described above. longer), than in large adults (Fig. 3). Thus, the Reproductive classes were determined by sepa- postcranial body grows faster than the head and rating fish of each sex into groups representing head shape changes to a more symmetrical HOOD AND HEINS—BODY SHAPE IN CYPRINELLA VENUSTA 273

Fig. 2. Ontogenetic shape changes in males and females decomposed into overall, uniform, and nonuniform components. These visualizations reflect shape change between the consensus of males and consensus of females with all specimens included in the shape space (n ϭ 397 specimens). form in adult females. Juvenile males begin with males a more symmetrical tail develops (land- similar, relatively long and asymmetrical heads marks 7, 8, and 9). but retain asymmetrical head shape as large A comparison of the smallest (youngest) adults. Ontogenetic shape change in the abdo- males with the smallest females shows them to men (landmarks 5, 6 and 7) is dramatic in fe- share many aspects of body shape. A notable males; adults exhibit an abrupt shape change at difference occurs in the abdomen (landmarks the anal fin. Tail shape and overall body depth 5, 6, and 7) where some local shape differences changes in both males and females involve en- that emerge in the adults already are evident. largement of the tail and midbody. Both juve- Tests of the differences in ontogenetic trajec- nile males and females have relatively narrow, tory between males and females, as represented ventrally deflected tails. In females, the ventral in the allometric relationship described in the deflection is retained in adults, whereas in multivariate regression of shape on size, showed

Fig. 3. Ontogenetic shape changes within males and females. Visualizations reflect shape changes within females (with only females included in the shape space, n ϭ 215) along a multivariate regression of small to large specimens, and a similar set of visualizations within males (with only males included in the shape space, n ϭ 182). 274 COPEIA, 2000, NO. 1 that differences in slopes were not significant (P eas in C. venusta that show localized shape ϭ 0.09, F ϭ 1.568, Wilks’ lambda, 0.945). change differ significantly in males versus fe- MANOVAs testing for shape differences males. Head shape, abdomen shape, and tail among reproductive classes within males and fe- shape take different forms in each sex. Thus, males were highly signficant (overall shape in our study demonstrates that significant sexual males, P Ͻ 0.0001, F ϭ 5.810, Wilks’ lambda, dimorphism in both size and body shape 0.632; females, P Ͻ 0.0001, F ϭ 6.098, Wilks’ emerge during ontogeny. lambda, 0.447). Similarly, MANCOVAs of shape The ontogeny of shape change in C. venusta among reproductive classes with size as a covar- differs in males as compared with females. The iate (log SL and log CS) were highly significant smallest males and females in our sample (SL within males and females. Tests of the differenc- Ͻ 30 mm) generally have similar body shapes; es in ontogenetic trajectory between reproduc- however, small differences in the three areas tive classes within males were marginally nonsig- (head, abdomen, tail) where differing localized nificant (P ϭ 0.062, F ϭ 1.648, Wilks’ lambda, shape change occurs during ontogeny are al- 0.857). Similar tests for ontogenetic trajectory by ready evident between them. Changes in head reproductive classes within females yielded slopes shape are accentuated as male ontogeny pro- that were significantly different (P Ͻ 0.0001, F ϭ gresses, whereas changes in abdomen shape are 2.440, Wilks’ lambda, 0.693). These results show pronounced in the ontogeny of females. that the trajectory of shape change among male For each sex, the reproductive groupings gen- reproductive classes (fish scored LA vs MA1-3) erally were expected to show progressive chang- are not different, even though there are signifi- es in shape concomitant with reproductive mat- cant shape differences among the classes. Within uration and subsequent involvement in sexual females, there are significant differences in the activities. We found a significant relationship be- trajectory of shape change among female repro- tween reproductive status and ontogenetic ductive classes (fish scored LA vs EM-LM vs MA- shape change. Within both males and females, RE) that accompanies significant differences in reproductive classes had significantly different shape among the groups. body shapes and in females the trajectories of shape change among reproductive classes were DISCUSSION significantly different. The finding that body shape varies with major differences in repro- Our study of ontogenetic shape change in C. ductive status within a sex may simply reflect venusta demonstrates both uniform and non- that reproductive status varies broadly with age. uniform (localized) shape transformations dur- Nonetheless, the demonstration of body shape ing growth and development. The postcranial change associated with reproductive status sug- body elongates antero-posteriorly, and the tail gests that changes in reproductive status and midbody regions deepen dorso-ventrally in throughout ontogeny may occur in concert with both males and females. These shape changes body shape change. are reflected in the uniform components of shape change as well as in the highest spatial ACKNOWLEDGMENTS scales of nonuniform shape change. Previous geometric morphometric studies of We thank C. Taylor for access to the collection ontogeny investigating species as different in of C. venusta housed at Mississippi State Univer- body shape as piranhas (Fink and Zelditch, sity Museum (MSM). G. Clemmer and F. Mc- 1995a, 1995b; Zelditch and Fink, 1995), three- Corkle made the original collections. All mor- spine stickleback (Walker, 1993), sea bass (Loy phometrics software is available from the SUNY et al., 1996) and catfish (Reis et al., 1998) have Stony Brook morphometrics Web site located at also demonstrated that shape change at the http://life.bio.sunysb.edu/morph. Funding sup- highest spatial scales (spanning the entire body) port was provided by a sabbatical leave and the involves postcranial elongation and midbody Mullahy Fund, Loyola University (CSH), and a deepening. These studies also have shown lo- Tulane University sabbatical leave (DCH). calized shape change in several body areas, usu- ally including the head. We found significant SSD between sexually LITERATURE CITED mature adults. A number of previous studies ADAMS,D.A,AND D. L. FUNK. 1997. Morphometric (Heins and Baker, 1987; Heins and Dorsett, inferences on sibling species and sexual dimor- 1986; Pryon, 1996) also have found significant phism in Neochlamisus bebbianae leaf beetles: multi- SSD in C. venusta, which may be the result of variate applications of the thin-plate spline. Syst. sexual selection (Heins, 1990). Three body ar- Biol. 46:180–194. HOOD AND HEINS—BODY SHAPE IN CYPRINELLA VENUSTA 275

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