Common Bottlenose Dolphin Ecotypes or Separate Species?

Offshore and coastal dolphins have different feeding and environments which could mean that they are different species of bottlenose dolphin. Recent molecular studies in California have shown the two populations to be genetically differentiated (Perrin, 2011, p. 1). If they are different genetically, even if its not greatly, it would be accurate to say that they could be a different species. Differentiation between coastal samples from California and samples from the Gulf of California suggest that offshore and coastal bottlenose dolphins are not the same populations (Perrin, 2011, p. 4). This differentiation could be due to the separate types of ecosystems they live in.

Since they are living in two different ecosystems, they must have adapted to live differently to thrive in different conditions. Habitat type and prey distribution are expected to directly influence the isotopic signatures of the predator (Barros, 2010). Food availability and type is different in both areas and requires different strategies to gather and hunt for food. Prey of bottlenose dolphins inhabiting estuarine sea grass habitats and phytoplankton-dominated habitats are distinct (Barros, 2010). Sea grass and offshore phytoplankton can differ in carbon, nitrogen, and sulfur isotope values (Barros, 2010). The prey is different, making a more distinct ecosystem for both types of dolphins. The difference in food requires different food harvesting techniques. The diets of these dolphins will also be unique as they are, of course, consuming different prey. This also affects the physiology and biology of dolphins.

The type of prey these dolphins are consuming will have an impact of the physiology and biology of the dolphins as they become more adapted to their niche environment. Offshore dolphins were primarily identified by their hemoglobin profile as all inshore individuals have single- hemoglobin electrophoretic profiles opposed to the double banding profile in offshore dolphins (Barros, 2010). Further proving the genetic diversity between the two due to environmental differences. In US waters, a group of marine mammals that exhibits demographic independence from other such groups is considered a stock that should be managed independently (Vollmer & Rosel, 2017). If the dolphins are independent, then it may be safe to say that they are different species of dolphin that have evolved to different climates and feeding patterns. Stocks were delineated based on the hypothesis that dissimilar habitats, climatic, and oceanographic characteristics may limit dispersal (Vollmer & Rosel, 2017). There are no obvious barriers, but the fact that the habitats that these two main types of dolphins live in are different and have separate niches is a good way of determining if they are indeed two separate species.

The use of tissue and teeth samples give us a more accurate representation of diet and how it changes. Tissues that are rapidly replaced, such as skin, reveal the diet of an animal in the relatively recent past, whereas tissues that do not have turnover rates, such as teeth, reflect diet over longer spans of time (Knoff, 2007). If both are examined, we can see how much the diet and physiology of the dolphins has changed over time and how much of an impact being in a separate habitat affects them as well. We can see how long it has been since they have had similar diets to see if they are distantly related. This has a great effect on physiology and changes the need for longer or shorter dive times. Offshore species were observed taking longer dives, as they need to dive further for food, while coastal required shorter dives due to the shallower waters (Woodward, 2018). They need to be able to dive longer in the much deeper water to find food for longer periods, while the coastal require much shorter dive times as they are in shallower and potentially more food rich waters. Although it is not clear as to if they are indeed two separate species, it seems that the evidence shows that they are potentially separate species. The evidence is not yet clear, and the boundaries are not strict or obvious, but given the evidence shown it is safe to say tat they are more than likely different species as they adapted to different habitats.

Works Cited

Barros, Nélio B., et al. “Stable Isotopes Differentiate Bottlenose … – Wiley Online Library.” Wiley, 15 Apr. 2010, onlinelibrary.wiley.com/doi/full/10.1111/j.1748-7692.2009.00315.x.

Knoff, Amanda, et al. “Ontogenetic Diet Changes in Bottlenose Dolphins – Wiley Online Library.” Wiley, 7 Dec. 2007, onlinelibrary.wiley.com/doi/full/10.1111/j.1748-7692.2007.00174.x.

Perrin, William F., Janet L. Thieleking, William A. Walker, Frederick I. Archer, and Kelly M. Robertsonn(2011). Common bottlenose dolphins (Tursiops Truncatus) in California waters: Cranialndifferentiation of coastal and offshore ecotypes. Marine Mammal Science, 27:769–92.nhttps://doi.org/10.1111/j.1748-7692.2010.00442.x.

Woodward, Mike, and Edward P. Debold. “Acidosis and Phosphate Directly Reduce Myosin’s Force-Generating Capacity through Distinct Molecular Mechanisms.” Frontiers, Frontiers, 18 June 2018, www.frontiersin.org/articles/10.3389/fphys.2018.00862/full.

Vollmer, Nicole L., & Patricia E. Rosel (2017). Fine-scale population structure of common bottlenosendolphins (Tursiops truncatus) in offshore and coastal waters of the US Gulf of Mexico. MarinenBiology, 164:160 https://doi.org/10.1007/s00227-017-3186-x.