Head adaptation for sound production and feeding strategy in dolphins (Odontoceti: Delphinida).

Head morphology in toothed whales evolved under selective pressures on feeding strategy and sound production. The postnatal development of the skull (n = 207) and mandible (n = 219) of six Delphinida species which differ in feeding strategy but exhibit similar sound emission patterns, including two narrow-band high-frequency species, were investigated through 3D morphometrics. Morphological changes throughout ontogeny were demonstrated based on the main source of variation (i.e., prediction lines) and the common allometric component. Multivariate trajectory analysis with pairwise comparisons between all species was performed to evaluate specific differences on the postnatal development of skulls and mandibles. Changes in the rostrum formation contributed to the variation (skull: 49%; mandible: 90%) of the entire data set and might not only reflect the feeding strategy adopted by each lineage but also represents an adaptation for sound production and reception. As an important structure for directionality of sound emissions, this may increase directionality in raptorial feeders. Phylogenetic generalized least squares analyses indicated that shape of the anterior portion of the skull is strongly dependent on phylogeny and might not only reflect feeding mode, but also morphological adaptations for sound production, particularly in raptorial species. Thus, postnatal development seems to represent a crucial stage for biosonar maturation in some raptorial species such as Pontoporia blainvillei and Sousa plumbea. The ontogeny of their main tool for navigation and hunting might reflect their natural history peculiarities and thus potentially define their main vulnerabilities to anthropogenic changes in the environment.

Coronary anatomy of Commerson's dolphin (Cephalorhynchus commersonii) / Anatomia coronaria de la tonina overa (Cephalorhynchus commersonii)

The Commerson's dolphin (Cephalorhynchus commersonii) is an odontocete cetacean specie that lies in the waters of the southern hemisphere. With the aim of studying the course and distribution of Cephalorhynchus commersonii's coronary arteries, an exhaustive heart dissection was performed on one specimen. To the extent of our knowledge, and basing upon an extensive bibliographic research on the commersonii species, this is the first reported description of a Commerson's dolphin heart anatomy. Despite the fact that the analysis of a unique specimen does not allow to establish final conclusions, comparisons reveal broad similarities between Cephalorhynchus commersonii's coronary distribution and previous anatomical studies describing the heart of various marine diving mammals and the human fetus circulation. Diving mammals have developed an anastomotic system along evolution, in order to adjust their bodies to diving imposed conditions, and minimize the oxygen demand of the heart muscle. The present work begins with the identification of the patterns and similarities between Commerson's dolphin heart anatomy when compared to other odontecete species, to continue with an exhaustive description of the Commerson's dolphin coronary anatomy.

La tonina overa (Cephalorhynchus commersonii) es una especie de cetáceo odontoceto que se encuentra en las aguas del hemisferio sur. Con el objetivo de estudiar el curso y la distribución de las arterias coronarias de Cephalorhynchus commersonii, se realizó una disección exhaustiva del corazón de un ejemplar. Hasta donde sabemos, y basándonos en una extensa investigación bibliográfica sobre la especie, esta es la primera descripción informada de la anatomía de un corazón de este ejemplar. A pesar de que el análisis de una sola muestra no permite establecer conclusiones finales, las comparaciones revelan amplias similitudes entre la distribución coronaria de Cephalorhynchus commersonii, los estudios anatómicos previos que describen el corazón de varios mamíferos marinos buceadores, y la circulación del feto humano. Los mamíferos buceadores han desarrollado un sistema anastomótico a lo largo de la evolución para ajustar sus cuerpos a las condiciones impuestas por el buceo y minimizar la demanda de oxígeno del músculo cardíaco. El presente trabajo comienza con la identificación de los patrones y similitudes entre la anatomía del corazón de tonina overa en comparación con otras especies odontecetas, continuando con una descripción exhaustiva de la anatomía coronaria.

Ontogeny of the skull of Sotalia guianensis (Cetartiodactyla: Delphinidae) on the Northern coast of Brazil

This study aimed to investigate the ontogenetic development of the skull in the Guiana dolphin (Sotalia guianensis Van Bénéden, 1864 ) through the comparison of 29 morphological non-metrical characters together with the estimated age of 54 specimens derived from four areas on the northern coast of Brazil. The state of each character was associated with the age of each specimen to assess the formation of bone structures, and the degree of fusion of the sutures in each state of the character studied. Nineteen qualitative morphological characters presenting state ontogenetic variations have been analyzed statistically. The analysis depicted that the characters associated with the parietal-frontal suture, parietosupraoccipital, parietoexoccipital, supraoccipital-exoccipital and basioccipital-pterygoid varied according with the age. The results suggest that the physical maturity of the cranium was more premature in the specimens from the Northern Coast, suggesting a geographical adjustment of the species, or a biological response to an intense pressure of by-catch in fisheries over decades on the populations.(AU)

O objetivo do estudo foi investigar o desenvolvimento ontogenético craniano do boto-cinza (Sotalia guianensis Van Bénéden, 1864), comparando 29 caracteres morfológicos não métricos aliados às estimativas de idade de 54 espécimes provenientes de quatro áreas da Costa Norte do Brasil. Cada estado de caráter foi associado à idade de cada espécime para avaliar a formação de estruturas ósseas e o grau de fusionamento das suturas em cada estado de caráter analisado. Foram analisados estatisticamente 19 caracteres morfológicos qualitativos que apresentaram variação nos estados de caráter. A análise revelou que os caracteres que diferiram de acordo com a idade foram aqueles ligados à sutura parietal-frontal, parietal-supraoccipital, parietal-exoccipital, supraoccipital-exoccipital e basioccipital-pterigóide. Os resultados indicaram que a maturidade física do crânio foi mais precoce nos espécimes da Costa Norte, sugerindo uma estruturação geográfica da espécie ou uma resposta biológica a uma intensa pressão de captura acidental em redes de pesca sobre as populações.(AU)

Lectin spatial immunolocalization during in vitro capacitation in Tursiops truncatus spermatozoa

Spermatozoa interactions with the female reproductive tract and oocyte are regulated by surface molecules such as glycocalyx. The capacitation process comprises molecular and structural modifications which increase zona pellucida binding affinity. Lectins allowed us to describe glycocalyx changes during maturation, capacitation and acrosome reaction. This study had as its aim to identify lectin binding patterns using four lectins with different carbohydrate affinity in bottlenose dolphin (Tursiops truncatus) spermatozoa both before and after in vitro capacitation. Two semen samples from the same dolphin obtained on consecutive days were used, with four different lectin binding patterns becoming visible in both samples before and after capacitation. A highly stained equatorial segment with prolongations at the edges appeared as the most frequent pattern with Wheat germ agglutinin (WGA) in uncapacitated spermatozoa. However, it was homogeneously distributed over the acrosomal region after capacitation. Instead, the use of Peanut agglutinin (PNA) resulted in most spermatozoa showing high labelling in the acrosomal periphery region before capacitation and a homogeneous staining in the acrosomal region within the population of capacitated spermatozoa. Nevertheless, the most representative patterns with Concavalin A (ConA) and Aleuria aurantia agglutinin (AAA) lectins did not change before and after capacitation, labelling the acrosomal region periphery. These findings could contribute to the understanding of the reproductive biology of cetaceans and the improvement of sperm selection techniques.(AU)

Lectin spatial immunolocalization during in vitro capacitation in Tursiops truncatus spermatozoa

Spermatozoa interactions with the female reproductive tract and oocyte are regulated by surface molecules such as glycocalyx. The capacitation process comprises molecular and structural modifications which increase zona pellucida binding affinity. Lectins allowed us to describe glycocalyx changes during maturation, capacitation and acrosome reaction. This study had as its aim to identify lectin binding patterns using four lectins with different carbohydrate affinity in bottlenose dolphin (Tursiops truncatus) spermatozoa both before and after in vitro capacitation. Two semen samples from the same dolphin obtained on consecutive days were used, with four different lectin binding patterns becoming visible in both samples before and after capacitation. A highly stained equatorial segment with prolongations at the edges appeared as the most frequent pattern with Wheat germ agglutinin (WGA) in uncapacitated spermatozoa. However, it was homogeneously distributed over the acrosomal region after capacitation. Instead, the use of Peanut agglutinin (PNA) resulted in most spermatozoa showing high labelling in the acrosomal periphery region before capacitation and a homogeneous staining in the acrosomal region within the population of capacitated spermatozoa. Nevertheless, the most representative patterns with Concavalin A (ConA) and Aleuria aurantia agglutinin (AAA) lectins did not change before and after capacitation, labelling the acrosomal region periphery. These findings could contribute to the understanding of the reproductive biology of cetaceans and the improvement of sperm selection techniques.

Ontogeny of the skull of Sotalia guianensis (Cetartiodactyla: Delphinidae) on the Northern coast of Brazil

This study aimed to investigate the ontogenetic development of the skull in the Guiana dolphin (Sotalia guianensis Van Bénéden, 1864 ) through the comparison of 29 morphological non-metrical characters together with the estimated age of 54 specimens derived from four areas on the northern coast of Brazil. The state of each character was associated with the age of each specimen to assess the formation of bone structures, and the degree of fusion of the sutures in each state of the character studied. Nineteen qualitative morphological characters presenting state ontogenetic variations have been analyzed statistically. The analysis depicted that the characters associated with the parietal-frontal suture, parietosupraoccipital, parietoexoccipital, supraoccipital-exoccipital and basioccipital-pterygoid varied according with the age. The results suggest that the physical maturity of the cranium was more premature in the specimens from the Northern Coast, suggesting a geographical adjustment of the species, or a biological response to an intense pressure of by-catch in fisheries over decades on the populations.

O objetivo do estudo foi investigar o desenvolvimento ontogenético craniano do boto-cinza (Sotalia guianensis Van Bénéden, 1864), comparando 29 caracteres morfológicos não métricos aliados às estimativas de idade de 54 espécimes provenientes de quatro áreas da Costa Norte do Brasil. Cada estado de caráter foi associado à idade de cada espécime para avaliar a formação de estruturas ósseas e o grau de fusionamento das suturas em cada estado de caráter analisado. Foram analisados estatisticamente 19 caracteres morfológicos qualitativos que apresentaram variação nos estados de caráter. A análise revelou que os caracteres que diferiram de acordo com a idade foram aqueles ligados à sutura parietal-frontal, parietal-supraoccipital, parietal-exoccipital, supraoccipital-exoccipital e basioccipital-pterigóide. Os resultados indicaram que a maturidade física do crânio foi mais precoce nos espécimes da Costa Norte, sugerindo uma estruturação geográfica da espécie ou uma resposta biológica a uma intensa pressão de captura acidental em redes de pesca sobre as populações.

Sound Generating Structures of the Humpback Dolphin Sousa plumbea (Cuvier, 1829) and the Directionality in Dolphin Sounds.

The macroscopic morphology of structures involved in sound generation in the Indian Ocean humpback dolphin (Sousa plumbea) were described for the first time using computed tomography imaging and standard gross dissection techniques. The Indian Ocean humpback dolphin may represent a useful comparative model to the bottlenose dolphin (Tursiops sp.) to provide insights into the functional anatomy of the sound production in dolphins, since these coastal dolphins exhibit similar body size and share similarities on acoustic behavior. The general arrangement of sound generating structures, that is, air sacs and muscles, was similar in both the bottlenose dolphin and the Indian Ocean humpback dolphin. The main difference between the two species existed in a small left posterior branch of the melon in the Indian Ocean humpback dolphin, which was not found in the bottlenose dolphin and might reflect an adaptation of directionality for high frequency communication sounds as seen in some other delphinids (e.g., Lagenorhynchus sp., Grampus griseus). Thus, this may be the main reason for the asymmetry of the sound production structures in dolphins. Additionally, the longer rostrum in Indian Ocean humpback dolphins might suggest a more directional echolocation beam compared to the Lahille's bottlenose dolphin. Anat Rec, 302:849-860, 2019. © 2018 Wiley Periodicals, Inc.

A new tropical Oligocene dolphin from Montañita/Olón, Santa Elena, Ecuador.

A new small probable Oligocene dolphin from Ecuador represents a new genus and species, Urkudelphis chawpipacha. The new taxon is known from a single juvenile skull and earbones; it differs from other archaic dolphins in features including widely exposed frontals at the vertex, a dorsally wide open vomer at the mesorostral groove, and a strongly projected and pointed lateral tuberosity of the periotic. Phylogenetic analysis places it toward the base of the largely-extinct clade Platanistoidea. The fossil is one of a few records of tropical fossil dolphins.

Posterior respiratory apparatus of inia geoffrensis and Sotalia fluviatilis: structure and ultrastructure / Aparato respiratorio posterior de inia geoffrensis y Sotalia fluviatilis: estructura y ultraestructura

SUMMARY: This study aimed to characterize the structures of the posterior respiratory system of two species of river dolphins: Inia geoffrensis and Sotalia fluviatilis. The respiratory tract of both species was evaluated using macro and microscopic techniques. Four macroscopic anatomical structures were identified: Trachea, main bronchus, tracheal bronchus and lung. The presence of the exuberant tracheal bronchus suggested ease of gas exchanges. Histological analysis revealed the presence of alveolar ducts and myoelastic sphincter in these Amazonian cetaceans. The posterior respiratory portion of the Amazonian dolphins presents similarity with other odontocetes and the knowledge of this structure can also help contribute to the understanding of the physiology of diving and how these species are adapted to their habitat.

RESUMEN: Este estudio tuvo como objetivo caracterizar las estructuras del flujo respiratorio de dos especies de delfines de agua dulce: Inia geoffrensis y Sotalia fluviatilis. Los tractos respiratorios fueron estudiados con las técnicas de evaluación macroscópica y microscópica. En ambas especies se identificaron cuatro estructuras anatómicas macroscópicas: tráquea, bronquios principales, bronquio traqueal y los pulmones. La presencia de un bronquio traqueal exuberante sugiere un aumento en el intercambio de gases y el aumento de tiempo de inmersión de las especies. El análisis histológico reveló la presencia de los conductos alveolares, y del esfínter mioelástico en los cetáceos amazónicos. La porción respiratoria posterior de los delfines del Amazonas tiene similitud con otras ballenas dentadas y su conocimiento puede contribuir a la comprensión de la fisiología del buceo y a como estas especies están adaptadas a su hábitat.

Morphology and Ultrastructure of the Amazon River Dolphin (Inia geoffrensis) Spermatozoa.

The spermatozoa from seven adult Amazon river dolphins (Inia geoffrensis, CETACEA: INIIDAE) were analyzed by light and electron microscopy. The spermatozoa showed an elongated ellipsoid shaped head and a long tail with a well distinguishable midpiece. The head spermatozoa have a smooth surface like other odontocetes examined, with the exception of the Delphinidae family. The mean dimensions of the spermatozoa were within the range already reported for other cetaceans. The spermatozoa midpiece, as in other cetaceans, showed a random pattern of mitochondria, different from that described for other mammals. Further studies of sperm morphology of a wider spectrum of cetacean families could help to better understand the reproductive biology of these animals and the intergeneric and intrageneric relationships among them, as well as, among other mammals. Anat Rec, 300:1519-1523, 2017. © 2017 Wiley Periodicals, Inc.

Comparative anatomical description of brain hemisphere surfaces in toninha dolphin and humans

Pontoporia blainvillei (cetacean order and odontoceti suborder), popularly known in Brazil as Toninha, is a small dolphin with a long, thin beak found on the southern shore waters of the western Atlantic. The brain development of dolphins (expressed by the encephalization coefficient) in relation to body size is quite high, and is second only to humans. This high correlation in brain development between dolphins and humans was targeted in this research to describe and compare the morphology of cerebral hemisphere surfaces of these two species. Five brains of Pontoporia blainvillei donated by the BioPesca Project (a non-governmental organization) were analyzed. The brains were fixed in 20% formaldehyde solution for further description and comparison to human brains described in books of neuroanatomy. The telencephalon of Pontoporia blainvillei is rostrally tapered and expanded at the caudal end and it has a greater number of folds/gyrus when compared to human species. Some encephalic grooves/sulcus are similar to grooves found in the human species, such as the cruciate sulcus (central sulcus), lateral fissure (Sylvian cleft), cingulate sulcus and calcarine sulcus. The same encephalic lobes are seen in both species; however the parietal and temporal lobes are highly developed in the Pontoporia blainvillei. These differences are associated with specific function of the species, as the presence of the an efficient auditive system in dolphins.

Comparative anatomical description of brain hemisphere surfaces in toninha dolphin and humans

Pontoporia blainvillei (cetacean order and odontoceti suborder), popularly known in Brazil as Toninha, is a small dolphin with a long, thin beak found on the southern shore waters of the western Atlantic. The brain development of dolphins (expressed by the encephalization coefficient) in relation to body size is quite high, and is second only to humans. This high correlation in brain development between dolphins and humans was targeted in this research to describe and compare the morphology of cerebral hemisphere surfaces of these two species. Five brains of Pontoporia blainvillei donated by the BioPesca Project (a non-governmental organization) were analyzed. The brains were fixed in 20% formaldehyde solution for further description and comparison to human brains described in books of neuroanatomy. The telencephalon of Pontoporia blainvillei is rostrally tapered and expanded at the caudal end and it has a greater number of folds/gyrus when compared to human species. Some encephalic grooves/sulcus are similar to grooves found in the human species, such as the cruciate sulcus (central sulcus), lateral fissure (Sylvian cleft), cingulate sulcus and calcarine sulcus. The same encephalic lobes are seen in both species; however the parietal and temporal lobes are highly developed in the Pontoporia blainvillei. These differences are associated with specific function of the species, as the presence of the an efficient auditive system in dolphins.(AU)

Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications.

Comparisons of skull shape between closely related species can provide information on the role that phylogeny and function play in cranial evolution. We used 3D-anatomical landmarks in order to study the skull ontogeny of two closely related species, Lagenorhynchus obscurus and Lagenorhynchus australis, with a total sample of 52 skulls. We found shared trends between species, such as the relative compression of the neurocranium and the enlargement of the rostrum during ontogeny. However, these are common mammalian features, associated with prenatal brain development and sensory capsules. Moreover, we found a posterior displacement of the external nares and infraorbital foramina, and a strong development of the rostrum in an anteroposterior direction. Such trends are associated with the process of telescoping and have been observed in postnatal ontogeny of other odontocetes, suggesting a constraint in the pattern. Interspecific differences related to the deepness of facial region, robustness of the feeding apparatus and rostrum orientation may be related with the specific lifestyles of L. obscurus and L. australis. We also tested the presence of three different modules in the skull (basicranium, neurocranium, rostrum), all of which presented strong integration. Only the rostrum showed a different ontogenetic trajectory between species. Even though we detected directional asymmetry, changes in this feature along ontogeny were not detectable. Because asymmetry may be related to echolocation, our results suggest a functional importance of directional asymmetry from the beginning of postnatal life. J. Morphol. 278:203-214, 2017. © 2016 Wiley Periodicals,Inc.

Assessing Disease and Mortality among Small Cetaceans Stranded at a World Heritage Site in Southern Brazil.

Cetaceans are considered environmental sentinels and their health often reflects either anthropogenic or natural spatio-temporal disturbances. This study investigated the pathological findings and mortality of small cetaceans with the aim of detecting hazards and monitoring health trends in a high-biodiversity area. Between 2007 and 2012, 218 stranded cetaceans were recorded on the Paraná coast, southern Brazil. Fifty-seven (26.1%) of these animals, including 50 Sotalia guianensis, 2 Pontoporia blainvillei, 2 Stenella frontalis, 1 Stenella longirostris, 1 Tursiops truncatus and 1 Globicephala melas were necropsied and samples were collected for histopathology. Causes of death were determined in 46 of the 57 (80.7%) animals and most (30 or 65.2%) were ascribed to anthropogenic activities, including fisheries bycatch (28/30) and trauma (2/30). The remaining 16 fatalities were considered natural, and attributed to pneumonia (10/16), emaciation (3/16), septicemia (1/16), neonatal pathology (1/16) and choking via food obstruction (1/16). Irrespective of the cause, bronchointerstitial pneumonia, associated with parasitism, lymphadenitis and membranous glomerulonephritis were common findings among all fatalities. These results suggest, that while anthropogenic activities are a leading cause of cetacean strandings in Paraná, underlying pre-existing diseases may contribute towards deaths. Although the studied area is considered a biosphere reserve by UNESCO, complex anthropogenic and natural interactions might be occurring, increasing cetacean susceptibility to hazards. This study may help facilitate developing an effective conservation plan for coastal cetaceans focusing on reducing fisheries interactions, habitat degradation and pollution as mechanisms for ultimately increasing species resilience.

Acoustic characteristics of biosonar sounds of free-ranging botos (Inia geoffrensis) and tucuxis (Sotalia fluviatilis) in the Negro River, Amazon, Brazil.

Odontoceti emit broadband high-frequency clicks on echolocation for orientation or prey detection. In the Amazon Basin, two odontoceti species, boto (Amazon River dolphin, Inia geoffrensis) and tucuxi (Sotalia fluviatilis), live sympatrically. The acoustic characteristics of the echolocation clicks of free-ranging botos and tucuxis were measured with a hydrophone array consisting of a full-band and an acoustic event recorder (A-tag). The clicks of the two species were short-duration broadband signals. The apparent source level was 201 dB 1 µPa peak-to-peak at 1 m in the botos and 181 dB 1 µPa peak-to-peak at 1 m in the tucuxis, and the centroid frequency was 82.3 kHz in the botos and 93.1 kHz in the tucuxis. The high apparent source level and low centroid frequency are possibly due to the difference in body size or sound production organs, especially the nasal structure, the sound source of clicks in odontoceti.

Reproductive morphology of female Guiana dolphins (Sotalia guianensis).

The reproductive morphology of cetaceans is poorly studied and, despite the large number of strandings, reports on this subject are scarce due to access to carcasses mostly in an advanced state of decomposition. The present study aimed to describe histological characteristics of the female genital tract of Sotalia guianensis, in order to assist in future studies on the reproductive biology of these animals. Females of different ages, from stranding events on beaches in northeastern Brazil, were used. Fragments of all organs were collected and processed for light and scanning electron microscopy. Histological analyses showed that these structures were similar to those found in terrestrial mammals, with some peculiarities, such as the presence of differentiated cells in the vulvar subepidermal layer, not described in the literature on cetaceans. Reproductive studies with a morphological description of the female genital organs are extremely important, since they would enable a better understanding of the species reproductive physiology and assist in the development of new strategies for the species conservation.

Ontogenetic development and sexual dimorphism of franciscana dolphin skull: A 3D geometric morphometric approach.

The aim of this work was to study the postnatal ontogenetic development of Pontoporia blainvillei skull, identifying major changes on shape, and relating them to relevant factors in the life history of the species. We analyzed a complete ontogenetic series (73♂, 83♀) with three-dimensional geometric morphometric techniques. Immature dolphins showed a very well-developed braincase and a poorly developed rostrum, and the principal postnatal changes affected the rostrum and the temporal fossa, both structures implied functionally to the feeding apparatus, thus suggesting a specialized mode for catch fast prey in P. blainvillei. Osseous elements associated with sound production were already well developed on immature dolphins, suggesting the importance of this apparatus since the beginning of postnatal life. Sexual dimorphism was detected on both shape and size variables. Females were bigger than males, in accordance with previous studies. Shape differences between sexes were found on the posterior part of premaxillaries and external bony nares (P < 0.01), suggesting that this sexual dimorphism is related to differences on vocalization capabilities.

Morphological analysis of the flippers in the Franciscana dolphin, Pontoporia blainvillei, applying X-ray technique.

Pectoral flippers of cetaceans function to provide stability and maneuverability during locomotion. Directional asymmetry (DA) is a common feature among odontocete cetaceans, as well as sexual dimorphism (SD). For the first time DA, allometry, physical maturity, and SD of the flipper skeleton--by X-ray technique--of Pontoporia blainvillei were analyzed. The number of carpals, metacarpals, phalanges, and morphometric characters from the humerus, radius, ulna, and digit two were studied in franciscana dolphins from Buenos Aires, Argentina. The number of visible epiphyses and their degree of fusion at the proximal and distal ends of the humerus, radius, and ulna were also analyzed. The flipper skeleton was symmetrical, showing a negative allometric trend, with similar growth patterns in both sexes with the exception of the width of the radius (P ≤ 0.01). SD was found on the number of phalanges of digit two (P ≤ 0.01), ulna and digit two lengths. Females showed a higher relative ulna length and shorter relative digit two length, and the opposite occurred in males (P ≤ 0.01). Epiphyseal fusion pattern proved to be a tool to determine dolphin's age; franciscana dolphins with a mature flipper were, at least, four years old. This study indicates that the flippers of franciscana dolphins are symmetrical; both sexes show a negative allometric trend; SD is observed in radius, ulna, and digit two; and flipper skeleton allows determine the age class of the dolphins.

Reproductive aspects of male franciscana dolphins (Pontoporia blainvillei) off Argentina.

As the first study to investigate reproductive aspects of male franciscana dolphin -Pontoporia blainvillei - in Argentine waters, the aim of this paper was to assess sexual maturity by using histological and morphometric methods. P. blainvillei was labeled as "Vulnerable" by the IUCN in 2008. The specimens analyzed were either incidentally caught in artisanal fishing nets (n=47) or found stranded on the beach (n=3). Testis weight and testicular index of maturity were reliable indicators of sexual maturity, being their values: MTW: 1.14 ± 0.60-4.49 ± 1.94; IM: 0.03 ± 0.01-0.09 ± 0.03, for immature and mature specimens' respectively. It was found that the hierarchical cluster analysis (HCA) might be appropriate for establishing sexual maturity stage, based on both the body morphometric measurements and age. The values for age, standard length and total weight at attainment sexual maturity were 2.92-3.54 years, 126.19-126.27 cm and 23.47-23.75 kg. Considering the extremely low relative testis weight, the reversed sexual length dimorphism, the absence of secondary sexual characteristics, and the lack of scars from intrasexual combats in males, the hypothesis that sperm competition does not occur in the species, and male combats for accessing female reproductive may be rare for P. blainvillei is reinforced. All these features fit the species within a serial monogamous mating system.