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Dolphins are highly social animals usually reported in large groups comprised of individuals of a single species, although they are often reported associating with other species as well. The drivers for the formation of these mixed-species associations (MSAs) are poorly understood, and records in Brazilian waters are scarce. To better understand their occurrence in the region, we assessed seasonal and spatial distribution of MSAs in waters over the outer continental shelf and slope off Brazil (22° to 33° S). Data were collected during spring and autumn between 2009 and 2014. From a total of 187 Delphinidae sightings, 28 consisted of MSAs. Tursiops truncatus was the most frequently sighted species in an MSA (n = 22 sightings) and was mostly found in lower numbers than its associated counterparts: Globicephala melas, Stenella frontalis, Grampus griseus, and Pseudorca crassidens. MSAs between Stenella attenuata and Stenella longirostris or Delphinus delphis and S. frontalis were also reported. Our data did not show any seasonal or spatial trends in overall MSA frequency; nevertheless, the widely distributed T. truncatus appears to shift its associates according to their local abundance (e.g., associating with G. melas in the southern region of the study area and with S. frontalis in the southeastern region). Although a lot remains to be investigated regarding the ecological drivers for such associations between sympatric dolphins in Brazilian waters, this was the first effort to describe their occurrence and distribution patterns using cetacean dedicated surveys. [ABSTRACT FROM AUTHOR]

Coastal and offshore ecotypes of common bottlenose dolphins have been recognized in the western South Atlantic, and it is possible that trophic niche divergence associated with social interactions is leading them to genetic and phenotypic differentiation. The significant morphological differentiation observed between these ecotypes suggests they represent two different subspecies. However, there is still a need to investigate whether there is congruence between morphological and genetic data to rule out the possibility of ecophenotypic variation accompanied by gene flow. Mitochondrial DNA (mtDNA) control region sequence data and 10 microsatellite loci collected from stranded and biopsied dolphins sampled in coastal and offshore waters of Brazil as well as 106 skulls for morphological analyses were used to determine whether the morphological differentiation was supported by genetic differentiation. There was congruence among the data sets, reinforcing the presence of two distinct ecotypes. The divergence may be relatively recent, however, given the moderate values of mtDNA nucleotide divergence (dA = 0.008), presence of one shared mtDNA haplotype and possibly low levels of gene flow (around 1% of migrants per generation). Results suggest the ecotypes may be in the process of speciation and reinforce they are best described as two different subspecies until the degree of nuclear genetic divergence is thoroughly evaluated: Tursiops truncatus gephyreus (coastal ecotype) and T. t. truncatus (offshore ecotype). The endemic distribution of T. t. gephyreus in the western South Atlantic and number of anthropogenic threats in the area reinforces the importance of protecting this ecotype and its habitat. [ABSTRACT FROM AUTHOR]

Sperm whales live in culture-based multilevel societies in which the fundamental social level is the nearly permanent social unit of females and immature individuals, and the largest level is the clan constituted by social units that share a common coda repertoire. This study describes the coda repertoire and vocal clans of sperm whales in Brazilian waters recorded between 2011 and 2016. Inter-click intervals of codas were used to quantify similarity between repertoires. The analysis showed two evident clans, in the north and the south, distinct in their repertoires. The clan of the north, termed the "5R" clan, presented a predominant production of codas containing five regularly spaced clicks, not found in the clan of the south, termed "D" clan, which repertoire was dominated by long codas with 10–13 clicks with descending inter-click intervals. Codas with five regularly spaced clicks with the same rhythm and tempo as those found in the "5R" clan of Brazil are also predominant in sperm whales recorded in the Island of Dominica, at a distance of approximately 2700 km from the north of Brazil, which corresponds to the extension of the areas of sympatric clans. The sharing of 5R type by the both distinct clans is likely the result of cultural transmission in which conformism through social learning homogenizes coda repertoire. The results of this study corroborated the hypothesis that social boundaries, here the clan level, are maintained by cultural identities. • Sperm whales from western Atlantic Ocean off Brazil have distinct coda repertoires. • North of the equator, vocalisations of the "5R" clan contained predominantly 5R codas. • A southern "D" clan at 29°-34°S emitted longer codas with descending patterns. • The northern 5R codas showed affinities to whale populations of the Caribbean. • Vocalisation data provide evidence of at least two different cultural identities. [ABSTRACT FROM AUTHOR]