A note on genetic isolation of Mediterranean sperm whales (Physeter macrocephalus) suggested by mitochondrial DNA

Abstract

Thirteen sperm whales were sampled, using sloughed skin, in the Mediterranean Sea during six distinct encounters. Individuals were discriminated using the results of molecular sexing, mitochondrial control region sequencing and microsatellite genotyping (3 loci). Samples from 57 specimens were available from sperm whale strandings on northern European coasts. The first ~ 200bp of the mitochondrial DNA (mtDNA) control region of each sample were sequenced and three different haplotypes were identified. The frequency of each haplotype was significantly different between the Mediterranean Sea and the eastern North Atlantic, suggesting that sperm whales in the two areas comprise different maternal entities.

Genomics reveals the role of admixture in the evolution of structure among sperm whale populations within the Mediterranean Sea

“…Our data support the differentiation between the North Atlantic and Mediterranean Sea described in previous genetic and acoustic studies (e.g., Drouot, Berube, et al, 2004;Engelhaupt et al, 2009; Mesnick et al, 2011;Morin et al, 2018;Rendell & Frantzis, 2016).…”

Acoustic estimates of sperm whale abundance in the Mediterranean Sea as part of the ACCOBAMS Survey Initiative

“…Although the Mediterranean Sea is connected to the neighbouring North Atlantic Ocean, the shallow Camarinal Sill to the west of the Strait of Gibraltar may act as a significant barrier to the passage of sperm whales, essentially containing the Mediterranean individuals as a discrete subpopulation. This is supported by genetic studies (Drouot et al, 2004a;Engelhaupt et al, 2009) that indicate little genetic flow between the Mediterranean Sea and Atlantic Ocean. Additional evidence of population segregation comes from acoustic studies investigating the variation of 'codas', stereotyped patterns of broadband clicks used in communicative contexts.…”

“…These straits are characterised by relatively shallow water sills that may restrict the movements of deeper water cetaceans. The Strait of Gibraltar provides the only natural connection between the Mediterranean Sea and the North Atlantic Ocean; however, the low densities encountered near the 290 m deep Camarinal Sill supports the theory that it acts as a migratory barrier to sperm whales (Drouot et al, 2004a;de Stephanis et al, 2008;Engelhaupt et al, 2009). The Strait of Sicily provides a 160 km wide interface between the western and eastern basins, and the maximum depth of the area is only 316 m; the nearby Strait of Messina is only 3 km wide with a maximum depth of 80 m. Despite the noted year-round presence of sperm whales in the Ionian Sea (Pavan et al, 2008;Caruso et al, 2015), it is likely that both straits may also act as a significant deterrent to the movement of sperm whale groups between east and west (Lewis et al, 2007;Boisseau et al, 2010), with inter-basin movements possibly restricted to adult males (Frantzis et al, 2011).…”

“…The total estimate also included 197 whales in the contiguous Atlantic region outside block 1. This block was surveyed during ASI in part due to its importance to smaller odontocete species (such as killer whales Orcinus orca and long-finned pilot whales Globicephala melas; Cañadas et al, 2023;Panigada et al, 2023); as sperm whales along Morocco's Atlantic seaboard are likely to belong to a separate sub-population, it is not appropriate to consider these animals as part of the core Mediterranean assemblage as there is little evidence of movement between the two populations (Drouot et al, 2004a;Engelhaupt et al, 2009). Therefore, the estimate for the surveyed regions alone (i.e.…”