Tropical Diversity (2019) 1(2): 48-56.

ISSN: 2596-2388

DOI: 10.5281/zenodo.11068861

RESEARCH ARTICLE

48

Geographic variation in Prionotus punctatus (Bloch) (Teleostei,

Scorpaeniformes, Triglidae): a geometric morphometric analysis

Variação geográfica em Prionotus punctatus (Bloch) (Teleostei, Scorpaeniformes, Triglidae):

uma análise morfométrico-geométrica

Mauro J. Cavalcanti1* https://orcid.org/0000-0003-2389-1902, Paulo Roberto Duarte Lopes2

https://orcid.org/0000-0001-5781-5284

1Ecoinformatics Studio, Caixa Postal 46521, CEP 20551-940 Rio de Janeiro, RJ, Brazil, E-mail: maurobio@gmail.com

2Departamento de Ciências Biológicas (Museu de Zoologia - Divisão de Peixes), Universidade Estadual de Avenida

Transnordestina, s/no (km 03 – BR-116), CEP 44036-900, Feira de Santana, BA, Brazil.

*Email: maurobio@gmail.com

Received: August 14, 2019 / Accepted: September 30, 2019 / Published: October 2, 2019

Resumo Padrões de variação geográfica na forma

do corpo foram analisadas em nove amostras de

populações da cabrinha Prionotus punctatus

(Bloch) da costa nordeste, sudeste e sul do Brasil,

usando técnicas de morfometria geométrica. As

nove amostras foram ordenadas pela análise de

variáveis canônicas em três grupos

correspondendo às regiões norte e sul da isoterma

de 23C. As diferenças de forma representam um

contraste entre um aumento da altura do corpo nos

exemplares do litoral nordeste e um alongamento

do corpo nos exemplares das outras amostras.

Estes resultados sugerem que existe extensa

variação geográfica em P. punctatus no litoral

brasileiro. Os padrões de variação geográfica na

forma do corpo são aparentemente relacionados

ao decréscimo na temperatura da água na direção

sul ao longo da costa.

Palavras-Chave: Prionotus, América do Sul,

morfometria geométrica, variação geográfica.

Abstract Patterns of geographic variation in body

shape were analyzed in nine population samples

of the searobin Prionotus punctatus (Bloch) from

the northeastern, southeastern, and south Brazilian

coast, using geometric morphometrics techniques.

The nine samples were ordinated by canonical

variate analysis into three groups corresponding to

regions north and south of the 23C isotherm. The

shape differences represent a contrast between an

increase in body depth in the specimens of the

northeastern coast and an elongation of the body

in the remaining samples. These results suggest

that there is extensive geographic variation in P.

punctatus along the Brazilian coast. The patterns

of geographic variation in body shape are

apparently related to decreasing water temperature

southward along the coast.

Keywords: Prionotus, South America, geometric

morphometrics, geographic variation.

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

49

Introduction

The searobin, Prionotus punctatus

(Bloch) is a medium-sized benthic fish found in

shallow to moderate depths feeding mainly on

crustaceans and molluscs. It ranges from the coast

of Central America (Belize) to Argentina

(Ginsburg 1950). In Brazil, P. punctatus has been

recorded from Pernambuco to Rio Grande do Sul

(Figueiredo & Menezes 1980). Although not

considered to be a species of commercial

importance, P. punctatus is a large component of

demersal fisheries in the southeastern Brazilian

coast, and provides local fishermen with a source

of income when catches of other species are

reduced (Andrade 2004). Therefore, detailed

knowledge of its distribution is important for the

management of this species as a potential

economic resource. However, despite its wide

distribution, little is known about the patterns of

geographic variation in this species. Ginsburg

(1950) pointed out the existence of differences in

meristic and morphometric characters among

local population of P. punctatus from the

Caribbean and the South American coast, but

because of the small size of the samples available

to him, this author could not draw definite

conclusions regarding the taxonomic significance

of these differences. He concluded, however, that

the differences seemed to be in the range of those

usually detected among the local populations of

species with a wide geographic range. Over the

last two decades, several studies have documented

the widespread occurrence of extensive

geographic variation in both benthic and demersal

marine fish species along the coasts of South

America and Africa in the South Atlantic Ocean

(see Cavalcanti & Lopes 1998 for a short review).

These studies offer abundant support to the

emerging paradigm of populations of marine

species as closed systems, only very loosely, if at

all, by the gene flow promoted by ocean currents

(Cowen et al. 2000, Hellberg et al. 2002).

Despite its potential to detect patterns of

size and shape changes at both the inter- and

intraspecific levels, geometric morphometrics

(Bookstein 1991) methods have been infrequently

applied to the study of geographic variation in

local populations of marine fishes. Corti &

Crosetti (1996) were the first to report the

application of geometric morphometrics to the

analysis of patterns of geographic variation in size

and shape of a marine fish. More recently,

Valentin et al. (2002), Medina et al. (2008),

Oliveira et al. (2009), Luceño et al. (2013, 2014)

and Cabasan et al. (2017)also applied similar

techniques to analyze geographic variation in

marine fish species.

The objective of this work was to analyze

geographic variation in body shape in P.

punctatus along the Brazilian coast, applying

geometric morphometrics and multivariate

statistical methods.

Materials and Methods

The specimens of P. punctatus examined

in this study are housed in the collections of

Universidade Estadual de Feira de Santana, Bahia

(UEFS), Universidade do Estado do Rio de

Janeiro (UERJ), and Pontifícia Universidade

Católica do Rio Grande do Sul (PUCRS). A total

of 56 individuals from 9 localities were measured.

Localities, geographic coordinates and sample

sizes are listed in Table 1.

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

50

Table 1. Locality, geographic coordinates, location relative to the 23°C isotherm, region, and sample size of the nine

populations of Prionotus punctatus examined in the present study.

Number

Locality

Latitude

Longitude

Location

relative to

23°C

isotherm

Region

Sample

size

1

Baía de Todos os Santos

12° 48' S

38° 36' W

North

NE

28

2

Baía de Guanabara

22° 48' S

43° 08' W

South

SE

7

3

Baía da Ilha Grande

23° 09' S

44° 30' W

South

SE

5

4

Caraguatatuba

23° 40' S

45° 20' W

South

SE

5

Porto Belo

27° 07' S

48° 34' W

South

S

3

6

Florianópolis

27° 35' S

48° 34' W

South

S

3

7

Garopaba

28° 04' S

48° 40' W

South

S

1

8

Torres

29° 21' S

49° 44' W

South

S

2

9

Mostardas

31° 05' S

50° 57' W

South

S

2

Because the number of specimens from

some samples was inadequate for statistical

analyses, the localities were pooled into three

non-contiguous regions, located respectively to

the north and to the south of the 23° C isotherm:

(1) the sample from the northeastern coast of

Brazil (NE); (2) the samples from the southeastern

coast (SE); and (2) the samples from the southern

coast (S) (Fig. 1). This division was done on the

basis of the proposal by Palacio (1982) that the

23° C isotherm (the line of constant mean annual

temperature, located approximately at the 21° S

latitude) defines the limit between two distinct

biogeographic regions in the Brazilian coast. A

previous study by Cavalcanti & Lopes (1998)

provided evidence of geographic variation in

quantitative characters in the batfish

Ogcocephalus vespertilio corresponding to the

regions north and south of the 23° C isotherm.

Measurements were made using a truss

network protocol (Strauss & Bookstein 1982;

McGlade & Boulding 1986), anchored at 10

homologous anatomical landmarks (Fig. 2).

Landmarks refer to: (1) anterior tip of the snout on

the upper jaw; (2) most posterior aspect of the

neurocranium (beginning of scaled nape); (3)

origin of pelvic fin; (4) origin of spinous dorsal

fin; (5) origin of anal fin; (6) origin of soft dorsal

fin; (7) insertion of anal fin; (8) insertion of

second dorsal fin; (9) insertion of first ventral

caudal fin ray; (10) insertion of first dorsal caudal

fin ray. All measurements were taken with an

electronic caliper to the nearest 0.05 mm.

The 21 interlandmark distances obtained

from the truss network were converted to

Cartesian coordinates by means of a simplified

multidimensional scaling algorithm (Carpenter et

al. 1996), using the UNFOLD program written by

H. J. S. Sommer.

The raw coordinates of all specimens

were aligned (i.e. translated, rotated, and scaled to

match one another) using the Procrustes

generalized orthogonal least-squares (GLS)

superimposition method, which fits one

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

51

configuration over another by minimizing the

squared distances between homologous landmarks

(Rohlf & Slice 1990). The average configuration

of landmarks resulting from this procedure served

as the "reference" or tangent configuration

(defining the point of tangency between the non-

linear shape space and the approximating tangent

space, see Rohlf, 1996) in the subsequent

computations.

Canonical variate analysis and

multivariate analysis of variance were used to

evaluate the patterns of variation and

discrimination among the population samples of

P. punctatus. Canonical analysis provided

weighted combinations of characters, termed

canonical variates, maximizing among-sample

variation with respect to the within-sample

variation. Each canonical variate represented an

identifiable fraction of the total variation in the

data. This has been one of the most widely used

ordination technique for studying geographic

variation (Gould & Johnston 1972; Thorpe, 1976).

Shape changes associated with the canonical

variate axes were depicted as deformation grids

generated by regressing the partial-warp scores

onto each canonical axis (Rohlf et al., 1996). All

computations were performed using the software

MorphoJ v.1.0.6d (Klingenberg 2011).

Figure 1. Distribution map of the nine population samples of P. punctatus analyzed in this study

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

52

Figure 2. Locations of the 10 anatomical landmarks (numbered points) and morphometric distance measurements

recorded on each specimen of Prionotus punctatus.

Results

The canonical analysis of body shape

variation showed that the Mahalanobis distances

among the nine populations of P. punctatus

differed significantly between the Northeastern

and Southeastern or Southern populations (Wilks’

lambda, P < 0.0001), but not between the

Southeastern and Southern populations (P =

0.2005). Two canonical vectors accounted for

100% of the total among-group variation, with the

first and second canonical vectors explaining,

respectively, 81.8% and 18.2% of the total

variation. The space defined by these two

canonical vectors disclosed three groups of

populations, one formed by the Northeastern

Brazil population, a second representing the

Southeastern Brazil population and a third

composed of the Southern Brazil populations (Fig.

3). The Baía de Todos os Santos (Northeastern

Brazil) population is discriminated from the other

populations along the first canonical vector,

whereas the group formed by the populations of

Baía de Guanabara, Ilha Grande, and

Caraguatatuba (Southeastern Brazil) is separated

from the Southern Brazil (Porto Belo,

Florianópolis, Garopaba, Torres, Mostardas)

populations along the second canonical vector. A

few individuals from the Southeastern and

Southern populations overlap partially in the

space of the second canonical vectors, indicating

that these individuals are morphometrically

similar.

The shape changes depicted along the

canonical variates (Fig. 4) indicate a relative

increase in body depth in the specimens from Baía

de Todos os Santos, as well as an elongation of

the caudal region in the specimens of the

remaining populations, leading to a more bulky

shape in the populations of Northwestern Brazil

and a more slender shape in the populations of

Southeastern and Southern Brazil.

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

53

Figure 3. Outlines of scatterplots of individual scores from the canonical variates analysis of the population samples of

P. punctatus, with 95% confidence interval around group means (NE = Northeastern; SE = Southeastern; S = Southern).

Figure 4. Shape changes in P. punctatus in relation to the reference specimen (in light blue) along the first (top) and

second (bottom) canonical variates (in black).

Discussion

The results presented in this paper point to

extensive variation in shape in the populations of

P. punctatus studied. Geographic variation in

marine fishes has been regarded as the

consequence of different environmental

conditions, such as water temperature, salinity,

and dissolved oxygen (Barlow, 1961; Gunther,

1961), acting on groups of geographically

isolated populations and leading to adaptive

genetic changes (Palumbi, 1994).

The waters of the coast of Cabo Frio, near

Arraial do Cabo, are influenced by an important

Cavalcanti & Lopes (2019)

Geographic variation in Prionotus punctatus

54

coastal upwelling phenomenon, characterized by

lower salinity and temperature and richness of

nutrients. To the north, coastal waters are under

the influence of the tropical waters of the Brazil

Current, of higher salinity and temperature, and

with a reduced nutrient content (Valentin 2001).

This may act as an important factor in the

differentiation of marine populations and has

already been shown to influence patterns of

geographic differentiation in several species of

demersal fishes occurring along that stretch of the

Brazilian coast (Vazzoler, 1971; Vargas, 1976;

Yamaguti, 1979; Paiva Filho & Cergole, 1988;

Cavalcanti & Lopes, 1998; Oliveira et al., 2009).

In a study of age and growth of P. punctatus in

the southern coast of Brazil, on the basis of

increments in the sagittal otolith, Andrade (2004)

suggested that water temperature may in fact be

one of the most important environmental factors

affecting the growth patterns in this species.

A major potential limitation of the present

study are the small sample sizes available for

some localities, that while not being atypical of

most systematic studies, could disturb the results

of statistical analyses. Nonetheless, in the present

study these small sample sizes might be expected

to obscure patterns of differentiation rather than

create them. Further studies, including the

collection of specimens from the intervening

areas, will be necessary in order to provide a more

complete understanding of the underlying causes

of geographic variation in P. punctatus along the

Brazilian coast.

Acknowledgments

We thank Drs. Ulisses L. Gomes (UERJ)

and Carlos T. Lucena (PUCRS) for kindly

allowing us to examine specimens under their

care. We also thank H. J. S. Sommer III

(Pennsylvania State University) for the software

to reconstruct landmark coordinates from truss

distance data, and Jailza Tavares de Oliveira-Silva

(UEFS) for the photo of a specimen of P.

punctatus. Joey P. Cabasan (University of the

Philippines Mindanao) provided constructive

criticism and valuable suggestions which

contributed to the improvement of an earlier

version of the manuscript. This paper is dedicated

to the memory of Dr. Dennis E. Slice (1958-

2019), for his everlasting contributions to

morphometrics.

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