Can Genetic Differences Explain Vocal Dialect Variation in Sperm Whales, Physeter macrocephalus?

Abstract

Sperm whale social groups can be assigned to vocal clans based on their production of codas, short stereotyped patterns of clicks. It is currently unclear whether genetic variation could account for these behavioural differences. We studied mitochondrial DNA (mtDNA) variation among sympatric vocal clans in the Pacific Ocean, using sequences extracted from sloughed skin samples. We sampled 194 individuals from 30 social groups belonging to one of three vocal clans. As in previous studies of sperm whales, mtDNA control region diversity was low (π = 0.003), with just 14 haplotypes present in our sample. Both hierarchical AMOVAs and partial Mantel tests showed that vocal clan was a more important factor in matrilineal population genetic structure than geography, even though our sampling spanned thousands of kilometres. The variance component attributed to vocal dialects (7.7%) was an order of magnitude higher than those previously reported in birds, while the variance component attributed to geographic area was negligible. Despite this, the two most common haplotypes were present in significant quantities in each clan, meaning that variation in the control region cannot account for behavioural variation between clans, and instead parallels the situation in humans where parent-offspring transmission of language variation has resulted in correlations with neutral genes. Our results also raise questions for the management of sperm whale populations, which has traditionally been based on dividing populations into geographic 'stocks', suggesting that culturally-defined vocal clans may be more appropriate management units.

Quantifying humpback whale song sequences to understand the dynamics of song exchange at the ocean basin scale

“…The songs of the Panamanian yellow-rumped cacique (Cacicus cela) and the village indigobird (Vidua chalybeate) appear to continually evolve or change with time (Payne, 1985;Trainer, 1989). Within cetaceans, sperm whales (Physeter macrocephalus) form acoustic clans over large geographic areas that are composed of multiple, matrilineal groups that share distinct dialects of patterned clicking sounds (see Whitehead, 2009;Rendell et al, 2012). Killer whales (Orcinus orca) are also organized into matrilineal pods, each with a distinct vocal dialect that overlaps to varying degrees with the dialects of other pods in the area to again form acoustic clans (Deecke et al, 2000;Riesch and Deecke, 2011).…”

Depredating sperm whales in the Gulf of Alaska: local habitat use and long distance movements across putative population boundaries

“…Low genetic diversity worldwide provided little basis for differentiating groups of whales using mtDNA or nuclear markers (Lyrholm et al 1999). Whitehead (2003) and Rendell et al (2012) have proposed a population structure based upon groups of whales using the same communication or vocal dialect unbound from geography and genetics. Thus, a species with low genetic diversity and wide ranging movements, perhaps including males foraging in ocean basins apart from the females and immature whales, is culturally connected acoustically rather than geographically.…”

Acoustic differentiation of Shiho- and Naisa-type short-finned pilot whales in the Pacific Ocean

“…Evidence suggests that, for other social cetaceans, variability in the vocal repertoire can be both socially driven [e.g., killer whales (Yurk et al, 2002;Riesch et al, 2006;Deecke et al, 2010;Filatova et al, 2012;Crance et al, 2014;Musser et al, 2014) and sperm whales (e.g., Rendell et al, 2012;Cantor et al, 2015)] and behaviorally driven [e.g., killer whales (Filatova et al, 2013;Holt et al, 2013)]. Shortfinned pilot whales are a highly social cetacean, known to form stable social groups for a decade or more (HeimlichBoran and Hall, 1993;Mahaffy et al, 2015).…”

“…This type of divergence has been identified in bats [e.g., horseshoe bats (Yoshino et al, 2008)], birds [e.g., rufous-collared sparrow (Tubaro et al, 1993)] and cetaceans [e.g., blue whales (McDonald et al, 2006), humpback whales (Winn et al, 1981), and striped dolphins (Papale et al, 2013)]. This variation can be caused by a variety of factors, including isolation and subsequent adaptation to a local environment (e.g., Graycar, 1976;Ding et al, 1995), morphological or genetic differences between populations (Janik and Slater, 2000;Slabbekoorn and Smith, 2002), socially maintained differences between sympatric or parapatric populations, called dialects [e.g., sperm whales (Rendell and Whitehead, 2003;Rendell et al, 2012;Gero et al, 2016), killer whales (Ford, 1989(Ford, , 1991Filatova et al, 2012)], or acoustic drift between geographically separated populations (Conner, 1982).…”