Phenotypic variation in dorsal fin morphology of coastal bottlenose dolphins (Tursiops truncatus) off Mexico

Abstract

Geographic variation in external morphology is thought to reflect an interplay between genotype and the environment. Morphological variation has been well-described for a number of cetacean species, including the bottlenose dolphin (Tursiops truncatus). In this study we analyzed dorsal fin morphometric variation in coastal bottlenose dolphins to search for geographic patterns at different spatial scales. A total of 533 dorsal fin images from 19 available photo-identification catalogs across the three Mexican oceanic regions (Pacific Ocean n=6, Gulf of California n=6 and, Gulf of Mexico n=7) were used in the analysis. Eleven fin shape measurements were analyzed to evaluate fin polymorphism through multivariate tests. Principal Component Analysis on log-transformed standardized ratios explained 94% of the variance. Canonical Discriminant Function Analysis on factor scores showed separation among most study areas (p<0.05) with exception of the Gulf of Mexico where a strong morphometric cline was found. Possible explanations for the observed differences are related to environmental, biological and evolutionary processes.Shape distinction between dorsal fins from the Pacific and those from the Gulf of California were consistent with previously reported differences in skull morphometrics and genetics.Although the functional advantages of dorsal fin shape remains to be assessed, it is not unlikely that over a wide range of environments, fin shape may represent a trade-off among thermoregulatory capacity, hydrodynamic performance and the swimming/hunting behavior of the species. (Aleyev, 1977; Pauly and 48 Palomares, 1989;Fish, 1998;Wright, 2000), and this is also widely accepted in 49 cetaceans (Fish and Hui, 1991; Berta and Sumich, 1999;Fish and Rohr, 1999; Reynolds et al., 50 2000;Morteo, 2003). Morphological variation of the dorsal fin, to some extent, has been used for 51 population and/or species identification (Lang and Pryor, 1966;Aleyev, 1977;Fish, 1998; 52 Weller, 1998;Morteo et al., 2005;Felix et al., 2017). 5354 The dorsal fin of delphinids is important at two functional levels: thermoregulatory and 55 hydrodynamic. Little empirical evidence exists, however, regarding the integrated performance 56 of dorsal fins for most cetacean species (Lang, 1966;Fish and Rohr, 1999; 57 Meagher et al., 2002; Pavlov Westgate et al., 2007;Barbieri et al., 2010;and Rashad, 2012; van 58 der Hoop et al., 2014). Estimating integrated performance is challenging since plasticity may be 59 in part regulated by the energetic cost of different swimming behaviors related to locating, 60 chasing, handling, and ingesting prey, thus maneuvering abilities may be important in feeding 61 success, and the dorsal fin may play an important role for swimming stabilization 62 Fish and Rohr, 1999). Also, the dorsal fin is the only appendage that is constantly exposed to 63 ambient air, and thus is subject to different thermoregulatory conditions from the rest of the body 64 Westgate et al., 2007;Barbieri et al., 2010). (Walker, 1...

How to tell them apart? Discriminating tropical blackfish species using fin and body measurements from photographs taken at sea

“…This was done using relative measurements rather than absolute measurements, which is an established method of analysis in morphometry ( e.g ., Rone and Pace , Morteo et al . , Félix et al . ).…”

“…Existing fin terminology was used when available, including the fin base (distance from anterior to posterior fin insertion) and foil (curvature of the fin's leading edge) (Weller 1998, Morteo et al 2017. Fin depth (horizontal distance from anterior fin insertion to trailing edge) YAHN ET AL.…”

“…Fin and flipper features are adapted to meet habitat or foraging demands, as observed in off-shore and coastal bottlenose dolphin populations (Hersh and Duffield 1990, Morteo et al 2017, Félix et al 2018).…”

“…This study demonstrated the efficacy of using fine scale morphometrics to discriminate between four similar cetacean species in Hawaiian waters. This was done using relative measurements rather than absolute measurements, which is an established method of analysis in morphometry (e.g., Rone and Pace 2011, Morteo et al 2017, Félix et al 2018. One benefit to analyzing relative measurements is that data can be collected remotely and noninvasively, without requiring animals to be stranded, captured, landed, or otherwise in-hand.…”

High similarities in dorsal fin ratios of common bottlenose dolphins (Tursiops truncatus) in the Caribbean Sea

“…As we recognized that dorsal fin variation in common bottlenose dolphins could result from selective environmental pressures (Costa et al, 20;Wiszniewski et al, 2010), we tested the hypothesis that common bottlenose dolphin's dorsal fin varies with geographical location as has been previously reported by Morteo (2004) and Morteo et al (2017) for this species from the Gulf of Mexico. To test this, we gathered a large data set of common bottlenose dolphin dorsal fins from eight discrete populations in four countries within the Caribbean Sea, and we used previously established methods for comparing the shape of dolphin dorsal fins by measuring different standardized ratios (Morteo, 2004;Morteo et al, 2017). This enabled direct comparisons of our results with previously generated dorsal fin ratios in the literature and in a population at Holbox, Mexico (Morteo et al, 2017), at the confluence of the Caribbean Sea and the Gulf of Mexico.…”