Convergent evolution of skim feeding in baleen whales

Abstract

The origin of pygmy right whales (Caperea marginata), the smallest and most enigmatic of the living baleen whales, remains contentious. Morphological analyses largely continue to ally Caperea with right whales (balaenids) based on shared cranial features like a tall braincase and a narrow, highly arched rostrum. By contrast, molecular data and some anatomical evidence suggest a closer relationship with rorquals (balaenopterids), but fail to explain "the substantial issue of convergence posed by the many balaenid features of Caperea" (Berta & Demere, 2017). To resolve this question, we sequenced the nuclear genome of C. marginata (812,269,251 paired reads; 47X average depth of coverage, with 89.33% of the genome covered at ≥10X) and subjected it to a multispecies coalescent analysis including representatives of all baleen whale families. Our results confirm Caperea as sister to rorquals and, thus, the convergent origin of its right whale-like anatomy. Considering this overwhelming molecular evidence, we propose that the traditional taxonomic grouping of Caperea with right whales be abandoned.

The tympanoperiotic complex of the blue whale, Balaenoptera musculus

“…Ekdale et al's (2011) and our own works show that tympanoperiotic morphology is compatible with the mysticete taxonomic subdivisions adopted by a number of students (Bisconti et al, 2023; Boessenecker & Fordyce, 2016; El Adli et al, 2014; Churchill et al, 2011; Deméré et al, 2005). This taxonomic interpretation contrasts with most molecular results and some morphological and total evidence studies that support a close relationship of Caperea marginata and Balaenopteroidea, as well as a paraphyletic status for Eschrichtiidae, Balaenopteridae, and Balaenoptera (Árnason et al, 2018; Dutoit et al, 2023; Lammers et al, 2019).…”

“…Such a result finds corroboration in several morphology‐based studies like those of Bisconti et al (2023, 2017); Bisconti, Damarco, Mao, et al (2021), Boessenecker and Fordyce (2016), and El Adli et al (2014). However, this result, again, contrasts with molecular phylogenies in which Caperea is not related to Balaenidae (Dutoit et al, 2023; Wolf et al, 2023). Moreover, earbone morphology supports the monophyly of Balaenomorpha (including Balaenoidea and Balaenopteroidea).…”

“…This clade is basal in the Balaenoptera lineage as it represents the sister group of a larger clade including Balaenoptera omurai and two nested monophyletic groups including, respectively, Balaenoptera edeni and Balaenoptera borealis , and Balaenoptera bonaerensis and Balaenoptera acutorostrata . The inclusion of IRSNB 1540 does not impact the monophyly of Balaenoptera to the exclusion of Megaptera novaeangliae and Eschrichtius robustus , suggesting therefore that the earbone morphology does not support the paraphyly of Balaenoptera (Árnason et al, 2018; Dutoit et al, 2023; Lammers et al, 2019; Wolf et al, 2023). Megaptera novaeangliae is the sister group of Balaenoptera thus confirming the monophyly of Balaenopteridae as including Balaenoptera and Megaptera and excluding Eschrichtius robustus .…”

A High-quality Oxford Nanopore Assembly of the Hourglass Dolphin (Lagenorhynchus cruciger) Genome

“…In addition, considerable uncertainty remains around the evolutionary relationships between Lissodelphininae -the subfamily of true dolphins to which the hourglass dolphin belongs (Goodall et al 1997;Vollmer et al 2019;Harlin-Cognato and Honeycutt 2006;Cope 1866;McGowen 2011;Banguera-Hinestroza et al 2014;Leduc, Perrin, and Dizon 1999). Genomic data could be particularly useful in resolving such taxonomic confusion, as demonstrated recently in resolving the taxonomic placement of the pygmy right whale (Caperea marginata) (Dutoit et al 2022).…”