Ecological divergence and speciation in common bottlenose dolphins in the western South Atlantic

Abstract

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. | 17 COSTA eT Al.

Movements and habitat use of bottlenose dolphins,Tursiops truncatus, in south-eastern Brazil

“…Although different tissues were analysed when comparing studies, the observed δ 13 C values showed divergence possibly induced by the habitat use of the species in different regions of the Brazilian coast. Therefore, our results reinforce previous studies, which have described the existence of two stocks of bottlenose dolphins showing differences in their distribution, that are individuals in estuarine-shallow coastal waters south of 28°S and individuals in coastal-oceanic waters north of 28°S (see Costa et al ., 2019). However, there are no available investigations regarding isotopic values from latitudes lower than Rio de Janeiro state along the Brazilian coast.…”

“…In recent years, morphological and genetic evidence has indicated that two distinct forms inhabit the South-western Atlantic Ocean (SAO): one in the south and the other in the north of 28°S. According to the authors, these forms appear to show differences in cranial morphology and a variation in their distribution (see Ott et al ., 2016; Fruet et al ., 2017; Costa et al ., 2019). The southern form is usually sighted in salt lagoons and estuaries of the southern coast of Brazil, Uruguay and Argentina (see Simões-Lopes & Fabian, 1999; Fruet et al ., 2011; Giacomo & Ott, 2016; Wickert et al ., 2016; Genoves et al ., 2018), and has been proposed as a new species for the genus, T. gephyreus (see Wickert et al ., 2016; Genoves et al ., 2018).…”

Speciation in marine environments: Diving under the surface

“…The genetic and phenotypic characterization of populations associated with different habitats (Costa et al, 2021) (Choo et al, 2021; van der Ven et al, 2020), similar to the role of wind for dispersing seeds of terrestrial plants. Thus, the comparison of patterns of dispersal predicted from biophysical models with those inferred from genetic data allows us to understand how currents influence speciation in the sea (Sjöqvist et al, 2015).…”

Selection on ancestral genetic variation fuels parallel ecotype formation in bottlenose dolphins

“…Here, we tested for parallel evolution driven by ecological niche specialization in a highly social marine mammal, the common bottlenose dolphin, which has a worldwide temperate and tropical distribution. Two ecotypes of common bottlenose dolphins (coastal and pelagic, also called offshore) have recurrently formed in multiple regions of the world (25)(26)(27)(28)(29). Coastal populations were suggested to have been founded from pelagic source populations (25)(26)(27)30).…”

“…Bottlenose dolphins (Tursiops sp.) also exhibit complex behaviors, such as habitat specialisation or social learning of foraging techniques, that strongly influence their patterns of genetic variability (28,31,38), and we hypothesize that these also facilitate their ability to adapt to novel conditions.…”