Quantifying variation in killer whale (Orcinus orca) morphology using elliptical Fourier analysis

Abstract

In the northeastern Pacific Ocean, there are three “ecotypes” of killer whales that differ in diet, ecology, behavior, acoustics, genetics, and morphology. Previous attempts to describe the morphological differences among populations of killer whales (Orcinus orca) have been limited to descriptive accounts or categorical studies. We used elliptical Fourier analysis (EFA) to quantify shape differences of dorsal fins and pigmentation patterns among the ecotypes from photo‐identification data of more than 500 individuals. Variation in shapes of the dorsal fin, saddle patch, and eye patch were successfully quantified using EFA, and there were highly significant (P < 0.01) differences among the ecotypes in all three morphological traits. The ability of EFA to discriminate ecotypes based on dorsal fin and eye patch shapes was substantial, while it did not perform as well for saddle patches. Visualization of the shape variation along principal component axes mirrored previous descriptions of the differences among ecotypes. Although the degree of inheritance of morphology in killer whales has not been determined, these results are consistent with previous inference of reduced gene flow between the ecotypes, and introduces elliptical Fourier analysis to the study of cetacean morphometrics.

Morphometrics of mammal‐eating killer whales from drone photogrammetry, with comparison to sympatric fish‐eating killer whales in the eastern North Pacific

“…Greater agility and smaller body sizes may be advantageous in fish‐eating SRKWs, while BKWs may benefit from larger body sizes as they hunt larger and more formidable marine mammals. Phenotypic differences in the pigmentation of the saddle patch and eye patch regions and the shape of the dorsal fin (Baird & Stacey, 1988, Emmons et al, 2019) have previously been reported for these ecotypes. Similarly, genomic signatures of diet adaptation have been revealed between Resident and BKWs, notably relating to differences in digestive requirements for diets of different protein content (Foote et al, 2016).…”

“…The HW/BHDF index was designed to quantify tissue loss in this region, and significant declines have been detected in emaciated SRKW individuals prior to death (Fearnbach et al, 2018). This measure is not as sensitive for detecting changes within individuals as the “eye patch ratio,” which measures the divergence of the white eyepatches of killer whales (Fearnbach et al, 2020), but Residents and BKWs are known to have small phenotypic variations in eye patch pigmentation that could impact the eye patch ratio (Emmons et al, 2019). The HW measure does not depend on pigmentation and has previously been used to compare killer whale ecotypes with known eye patch differences (Durban et al, 2021).…”

Assessing the patterns and drivers of shape complexity in the amblypygid pedipalp

“…A Procrustes fit was also required to align shapes. This method of alignment is often employed in studies that use elliptical Fourier analysis to quantify shapes with few major protrusions such as orca fins, human crania, and posterior lobes of Drosophila (Emmons et al, 2019;Friess & Baylac, 2003;Takahara & Takahashi, 2015).…”

Using pictographs as traits to explore morphological diversity in sharks

“…Additionally, advancements in open-access software have facilitated a broader application of geometric morphometrics to photogrammetric, tomographic, and, even, standard photographs datasets (Baken et al, 2021;Emmons et al, 2019).…”

“…Reconstructive techniques, such as Fourier analysis (Lestrel, 1982; Rohlf, 1986), can be used in lieu of defining specific loci to approximate the entire pictograph as a series of sine and cosine waves. Additionally, advancements in open‐access software have facilitated a broader application of geometric morphometrics to photogrammetric, tomographic, and, even, standard photographs datasets (Baken et al, 2021; Emmons et al, 2019).…”